Sunday, November 7, 2010

Home Away From Home


The comment thread on my previous post about space patrols raised the issue of base stations for more prolonged missions, extending to years.

This has application far beyond military or quasi-military patrols. In fact it is fairly fundamental to any extensive, long term human presence in deep space. Whether or not we put permanent bases on the surface of Mars, Europa, or wherever, we will surely place permanent or semi-permanent stations in orbit around them. Particularly because the stations can be built in Earth space, where the industry is (at least initially), and flown out to where they will serve.

Hab structures intended for prolonged habitation should be fairly large, if only because if you are going to live for years in a can it should be at least be a roomy one. And they must be thoroughly shielded against radiation, much more than ships that you only spend a few months aboard every few years.


So let us play with some numbers. Make our spin hab a drum, 200 meters in diameter and 100 meters thick. Volume is thus about 3.14 million cubic meters. The ISS has about 1200 m3 of pressurized volume and a mass of some 300 tons, for an average density near 0.25, but the mass includes exterior structures such as keel and wings. Let average interior density be about 0.16, for a mass of 500,000 tons.

If we allow 100 cubic meters per person the onboard population (whether 'crew' or simply residents, or a mix) can be up to 30,000 people. This is about twice the density of a middle class American urban apartment complex. Given that much of the usable volume must be working areas, public spaces, and so forth, the actual crew or population might be more on the order of 10,000 people, equivalent to a decent sized small town or a fairly large university or military base. Thus the hab has 10 times the volume of an aircraft carrier and twice as many people.

Spin the hab at 3 rpm and you get almost exactly 1 g at the rim.

By my standard rule of thumb the cost of this hab is on order of $500 billion. That is a steep price tag, but on the other hand it is only five times the cost of the ISS, and you need very few of these unless you are engaged in outright colonization.

Now, shielding. The standard for indefinite habitation is about 5 tons per square meter of cross section. (Earth's atmosphere provides about 10 tons/m2.) Portions of the hab where people do not spend much time, and exterior to where they do spend time, can be counted toward the shielding allowance. So let us say that the outer 10 meters of the interior (about 35 percent of the volume) are used for storage, equipment rooms, and the like. This provides about 2 tons per square meter of shielding, 40 percent of the requirement.

The remaining 3 tons per square meter of exterior shielding must cover about 125,000 square meters of surface, so shielding mass is about 375,000 tons, adding 75 percent to the mass of the hab, now 875,000 tons. This shielding need not be 'armor.' As I recall, water provides pretty good shielding against GCRs, your biggest radiation problem, and water is so useful that having 375,000 tons of it on hand in a reservoir will never be amiss.

Moreover, to move the hab you can vent off the water (or pump it out) and not need to lug the mass, assuming you can replace it wherever you are going. The deep interior of the hab, more than 25 meters from the surface (about 28 percent of the volume) is still shielded by the rest of the hab structure, so the hab can carry a reduced population during the transfer.

You are still moving a half million ton payload, so don't expect to rush it unless you have a really badass drive bus handy. Habs being repositioned across the Solar System probably travel on Hohmann orbits, and have drive accelerations of a few dozen microgees, good for about 1 km/s per month of steady acceleration.


For a smaller hab structure, scale down the linear dimensions by half, to 100 meters diameter and 50 meters thick. Structural mass, volume, and capacity are all reduced by a factor of 8, to 400,000 cubic meters, 60,000 tons, and a crew / resident population of about 1500-4000. Our 'mini' hab is now broadly comparable in volume, mass, and crew to an aircraft carrier.

Surface area is only reduced, however, by a factor of four, to about 30,000 square meters. Moreover, the smaller hab provides less interior self-shielding. If we keep the same proportions our internal reserved zone is just 5 meters deep and provides only 20 percent of the needed protection, not 40 percent.

We now need about 120,000 tons of shielding - twice the unshielded mass of the hab. If we move the hab fully shielded our payload mass is 180,000 tons. Remove the shielding and payload mass is just 60,000 tons, but no part of the smaller interior is fully self-shielded, so any crew on board during a 'light' transfer must be relieved every few months. On the bright side, if you have a 100 gigawatt drive bus floating around, or about $100 billion to buy one, you can take a fast orbit and get there in a few months.


The image shows a drum-hab station ship with a spin hab of the full sized type described above, 200 meters in diameter by 100 meters thick, fitted with a heaviest class drive bus for transfer. I am delicately ignoring details of the connection between the spin drum and the hub structures.

The shuttles approximate the NASA Shuttle, as a visual size reference. The deep space ships docking up to it are large fast transports, 300 meters long, ten times heavier than the patrol ship discussed last post. The station ship itself is about 675 meters long by 450 meters across the outrigger docking bays.

In my image the station ship is no aesthetic triumph. Allowing for my limitations as an graphic artist (compare to commenter Elukka, from the last comment thread), the transport class ships don't look too bad, but the station ship merely looks tubby instead of grand. Some modest architectural improvements might yield a more impressive appearance with little change in overall configuration.

Of course the interior will matter immeasurably more to the people on board. Mostly, presumably, it will resemble the interior of a very large oceangoing ship, corridors and compartments, probably including some fairly imposing public spaces, comparable to the grand saloon of a 20th century ocean liner or even larger. It can be as elegant or as sterile as you like (or both, depending on deck and sector). The third popular choice, rundown industrial gothic, is constrained by how far you can go in that direction before the algae dies or the air starts leaking out.

So find yourself a cubby and make yourself at home. You might be here for quite a while.

232 comments:

1 – 200 of 232   Newer›   Newest»
Mr. Blue said...

Of course, if you're out far enough, you're going to want:

1) A hospital. Nothing too big, but able to handle pretty much anything that comes up.

2) A courtroom. Not primarily for criminal cases, but a lot of civil things. Mining claims, lawsuits, and the like. It may be more informal than our current system- more along the lines of a Judge Judy at first.

And the obligatory repair shops, mineral purchasing agents, and a good bar/restaurant.

Byron said...

Interesting. I see the habs as being slightly more modular, probably using discs that are stacked on a hub as needed. It still is pretty much the same. Also, if you can use the water as remass, you get shielding for part of the voyage.

Thucydides said...

Interestingly enough, this has at least three potential uses:

Permanent duty as a spacecraft, assuming a large enough drive bus, and a source of fuel and remass at each end of the trip.

Colony/space station once in place.

Cycler spacecraft, once the orbital parameters are tweaked. Accelerate once and you are in business.

Stacking disk shaped modules may have advantages in terms of both financing and scalability (no "housing bubble" if the market does not materialize), as well as a certain safety factor should something go wrong on one of the modules.

Most colonists/passengers will probably want open space, so perhaps most of the living quarters will be built along the outside wall leaving a huge central "atrium". The storm shelter might take the form of a "lake" suspended in the zero g zone in the center of the cavity (the mass of the object means that acceleration will be very slow, so a thin polymer membrane is probably all that is needed to keep it in place).

nqdp said...

I have to agree with Bryon that habs (or any large space structure, for that matter) will be a bit more modular. I suspect that nuclear reactors, frames, radiators, and other generic components will generally last longer than whatever political or economic forces decided to build the hab in the first place, and so re-purposing the parts or re-configuring the station in a decade or two will probably be extremely normal.

And yes, I know that Rick is "delicately ignoring" certain details of the construction... but as an architecture student, that's a bit harder for me to do. So when I see a monolithic design, I assume that the hab is one giant component that can't be taken apart.

Random Axis said...

Yay, something I finally feet smart enough to comment on!

I'm not so sure that there would be a permanent orbiting station around any of the Galilean moons. They all orbit within Jupiter's radiation belts, which makes me think the mass penalty for shielding may be too high. It would be much easier to just bury a hab underground.

I'm imagining a large station pretty far out and in orbit around Jupiter itself. It's the "last safe place" in the area before you descend into the radiation belts. It's where you stop off on the way up to replace electronics that were damaged and clean yourself of any potential cancers.

Milo said...

Byron:

"Also, if you can use the water as remass, you get shielding for part of the voyage."

Too bad you need shielding for the whole voyage.



Random Axis:

"I'm not so sure that there would be a permanent orbiting station around any of the Galilean moons. They all orbit within Jupiter's radiation belts, which makes me think the mass penalty for shielding may be too high."

We're not going to be in the Jupiter system at all unless we've already been able to shield against the radiation.

And stations can carry more shielding than ships (mass penalties aren't as big a deal if you're not planning to go anywhere), although of course there are still limits (you still need to lug it into orbit first).

Once you have a permanent base anywhere in the Jupiter system, though, space station or moon dome, that gives you a platform from which you can reach the rest of the system in days. That's pretty useful.

As for civilian space stations, those will probably exist to facilitate trade and shipbuilding, so they will appear near whatever settlement is actually doing the trading.

Jedidia said...

""I am delicately ignoring details of the connection between the spin drum and the hub structures.""

you know, you don't need to spin the drum mechanically. You can spin the whole station by thrusters, once you reached spin velocity it'll stay spinning (obviously). Then you can mechanically spin the DOCKING facility in reverse so ships can dock to it. This might sound like a bad Idea at first, with all those heavy ships docked to it, but the nice thing is when you are accelerating it, you won't have any ships docked there. Once it's spinning at the right speed, and your connection is sufficiently frictionless, the amount of power you have to put into it to keep it stable even with heavy ships docked to it should still be quite small.

If the connection is not sufficiently frictionless, you'll be in big trouble anyway when you have ships docked assymetrically, no matter which part spins which.

The best solution would probably be to simply have the traditional docking port in the center and have other ships parked around the station without any physical connection.

If such a station would become a major trading hub, you'll probably be best of Clarke-style with one rotating hab station and a completely disconnected docking and loading complex that wouldn't be much more than a giant truss with all sorts of RMS, container cages and a small zero-g hab with control room, a lounge and a few beds as well as an emergency sickbay for the crew on station. Once they complete their shift, they can transfer back to the Hab-station. Disadvantage is, you'll need a seperate power source for this one, so you'll have to fly in another reactor.

This way you'd also reduce the risk of someone running his ship right into your major hab when something goes terribly wrong on a docking aproach.

Anonymous said...

At least one of the open public spaces could be configured as a 'garden' room, with plants and perhaps artificial sunlight, to help stave off homesickness for earth. It could be a part of the station's life support system, and a source of fresh fruit and vegetables.

R.C.

Geoffrey S H said...

@Thucydides

"Interestingly enough, this has at least three potential uses:

Permanent duty as a spacecraft, assuming a large enough drive bus, and a source of fuel and remass at each end of the trip.

Colony/space station once in place.

Cycler spacecraft, once the orbital parameters are tweaked. Accelerate once and you are in business."

I have to nit-pick here.


I think it was established some months ago that they’d be completely useless as a method of transport.
To be useful in any way to people on planets or anyone not in their orbit, they would have to slow down at some points (or small craft catch up with them and transfer cargo/people). This would use up propellant and thus defeat the object of having a cycler in the first place. That’s just the commercial problems.
The military problems included the slow time getting anywhere, and the utter predictability of its arrival times.

I’m sorry, but as a concept, the cycler won’t work.

Jim Baerg said...

Random Axis said:
"I'm not so sure that there would be a permanent orbiting station around any of the Galilean moons. They all orbit within Jupiter's radiation belts"

Apparently Callisto is an exception to that. From this I get the information "The radiation level at the surface of Callisto is equivalent to a dose of about 0.01 rem (0.1 mSv) per day." which would equal 36.5 mSv per earth year.

From this I see that there are places on earth with considerably higher background radiation which give no evident ill effect to the human residents.

Tony said...

Well, we have to question the primary premises somewhat. For a long time, probably the next two or three hundred years, permanent human presence is going to be limited to the surfaces of Earth and Mars. During that time there's no real purpose for a human presence in space, except to do biomedical research on humans living in the space environment. Why, I don't know, since nobody actually lives there and any biomedical research you want to do could just as easily be done on the trip out to Mars. Maybe the real reason is to give the researchers and engineering crews porthole-gazing experience so that when they get home they can write navel-gazing magazine articles and books about how Earth-y the Earth is.

Which is not to say the the building of large habs in space will never happen. It's just to point out that we really don't know how or why people would build large habs in space.

We now return you to your regularly scheduled speculation.

Thucydides said...

The advantage of a cycler is the really heavy stuff like the radiation shielding and life support only has to be accelerated once. Small craft can do the taxi thing between the cycler and the destination, since they have much less mass to accelerate and need much less robust life support systems.

True, the cycler may end up like an abandoned railway line if the backers didn't estimate the demand properly (or the market dries up for whatever reason), but an enterprising group can salvage it and repurpose it as a spacecraft again, or settle it into a permanent orbit as a hab.

Tony said...

A cycler is a good solution for a certain set of circumstances. The problem is that it only has utility within those circumstances. In an environment of high Isp, constant acceleration -- or even just high delta-v short duration burns -- a cycler has no real utility. Who wants to take seven to eight months to get to Mars, when you only really need take a month out of your schedule for the trip?

Byron said...

Thucydides:
What is it with you and cyclers? I know that for certain uses they are a good idea, and this might even be one of them. However, when we get to fast spacecraft, they become a lot less practical to build.

Milo:
Yes, but not as much. But you have half the water on average, so it should provide some protection. It's not enough for indefinite habitation, but for a little while it should work. You would have more than a few months for sure.

Geoffrey:
I'm not positive cyclers won't work at all. They do work, but only when delta-V is very expensive, like today, and you have a high passenger volume. Once it becomes cheap enough that making a trip faster than hohmann orbits allow makes economic sense, cyclers will be relegated to steerage passengers and really cheap cargo service.

Thucydides again:
No, cyclers won't be abandoned. They won't be built after engines become better enough to allow non-hohmann transfers, but they will still be used. From the shipping company's point of view, the stuff is already there, so they should use it. What they will probably do is sell steerage-class tickets. If they used tethers to launch the cargo, the cycler has an even longer life. After it gets old enough that passengers don't pay, you use the tethers for supercheap cargo.

KraKon said...

I'm so far behind on the reading list :/

Tony said...

Byron:

"...after engines become better enough to allow non-hohmann transfers..."

We already use non-Hohmann orbits for interplanetary travel, because a Hohmann transfer is a mathematical curiosity, not a trajectory design. About the purest application of Hohmann's work is the transfer orbit used to move geosynchronous satellites from their post-launch parking orbits to their final mission orbits, and even then only for launches at or near the equator, or for non-equatorial (i.e. "figure eight") orbits.

Interplanetary transfer orbits are more correctly classififed as eliptical, parabolic, or hyperbolic. Eliptical orbits can be practically defined as those below solar escape velocity. (That's why they form an elipse.) Parabolic and hyperbolic interplanetary orbits are above solar escape velocity.

A parabolic orbit is pretty narrowly defined. In practical terms it is the minimum energy escape trajectory.

So when you want to talk about fast transfer orbits, it's not so much taling about the difference between Hohmann orbits and non-Hohmann. It's the difference between eliptical and hyperbolic orbits. And really you're talking about the difference between (in ascending order of energy):

Low energy eliptical (an orbit that will just get you there; this is what we commonly use right now),

High energy eliptical (an orbit that gets you there as fast or nearly as fast as possible, without escaping the solar system),

Low energy hyperbolic (a not very fast hyperbolic orbit -- something a fairly pedestrian launch vehicle by today's standards can do for a spacecraft under a metric ton in mass, 15-20 years to get past the median orbital distance of Pluto), and

High energy hyperbolic (something that will get you there lickety-split, make your fuel supplier very happy, and give our heroic captain nightmares about being able to put on the brakes, rather than take an unscheduled interstellar tour).

Cambias said...

Thucydides:

Given that cheap high-boost drives which make cyclers obsolete may never exist, I think they're worth discussing.

Boarding my own hobbyhorse, I still can't think of a reason for doing anything around Jupiter. Getting anything out of that well is harder than launching directly from Earth! And the radiation is worse than anyplace else in the Solar System. Maybe the outer moons aren't too deep in the gravity well, but the same is true of the Jovian Trojan asteroids.

I expect Jupiter's importance in space travel will be as a convenient source of gravity-assist maneuvers. Eventually perhaps some posthuman godlike Kardashev II civilization may find a use for it, but in the Plausible Midfuture it'll be the Antarctica of the Solar System.

Rick said...

Welcome to another new commenter!

Yes, by the time the population gets to the 10,000 range a lot of tertiary functions will appear, including lawyers and judges, however informal they may be in the early stages.

If disk hab modules are placed side by side on one hub they might be outwardly indistinguishable from what I've shown. We tend to picture modules with a substantial gap between them (at least I usually do, for most purposes). But putting the disks flat up against each other, or nearly so, minimizes exterior surface area and therefore shielding mass.


Well, we have to question the primary premises somewhat. For a long time, probably the next two or three hundred years, permanent human presence is going to be limited to the surfaces of Earth and Mars.

This is quite possible, and you may even be generous about Mars.

By no means do I consider the familiar space future of extensive human habitation to be inevitable, or even particularly likely.

We can explore the Solar System very well with robotic craft, and we are doing so. We would like to send humans, to benefit from everything from the scientist's eye to the mechanic's tap with a wrench.

But that means sending human life support, which is immensely, staggeringly, irredeemably heavy. Atlas and those poor Caryotid gals buckle at the knees under the stupendous mass of human life support.

Oh, and did I mention the mass of human life support?

Soyuz, a basic short duration orbital minibus, weighs in at 7.2 tons for 3 seats, 2.4 tons/person. NASA Orion is 8.9 tons for 4 seats, 2.2 tons/person.

The ISS, a long duration spacecraft that more closely resembles the hab section of an interplanetary ship, is 300 tons for a crew of 6, 50 tons/person.

In estimating habs, I allow a minimum 5 tons/person for transport class ships with duration up to a few months, 50 tons/person (plus shielding) for permanant or semipermanent habitation. YMMV, but I think my figures are optimistic.

The reason I'm in rant mode about this is that in any case we are talking TONS of gross payload capacity for each human you send into deep space.

For comparison, Cassini-Huygens weighed in at 2.5 tons, and 5.6 tons including the drive bus. So the real tradeoff, in a practical sense, is that each human you send into space is as expensive in payload capacity as 1-20 major interplanetary robotic missions.

That is what human spaceflight is up against, the sheer weight penalty of sending people.

Milo said...

Tony:

"For a long time, probably the next two or three hundred years, permanent human presence is going to be limited to the surfaces of Earth and Mars."

Don't forget Luna.

Mars is useless unless you're either looking for native life forms or planning a massive terraforming project.

Of course, most places in the solar system are useless unless you're looking for some kind of research interest...



Byron:

"Once it becomes cheap enough that making a trip faster than hohmann orbits allow makes economic sense, cyclers will be relegated to steerage passengers and really cheap cargo service."

Cyclers are useless for cargo, unless it's highly perishable cargo that requires static preservation equipment of some sort.



Tony:

"We already use non-Hohmann orbits for interplanetary travel, because a Hohmann transfer is a mathematical curiosity, not a trajectory design."

Technically yes, but the transfers we use still tend to be minor tweaks on the Hohmann orbit, which are hardly any faster.

The exception is when we use planetary flybys, which is actually pretty common. Unfortunately, those operate on a kind of unreliable schedule since you need three or more planets to be aligned properly with respect to each other.


"And really you're talking about the difference between (in ascending order of energy):

[...]"


Exactly. And informally, it's pretty obvious that "non-Hohmann orbit" is supposed to mean "high-energy elliptical or low-or-high-energy hyperbolic orbit".

Milo said...

Cambias:

"Boarding my own hobbyhorse, I still can't think of a reason for doing anything around Jupiter."

It's much closer than any gas giant. (Saturn is twice as far away as Jupiter, Uranus is twice as far away as Saturn, and Neptune is half again as far away as Uranus.) Given that the difficulty of interplanetary travel is such a huge problem for space enterprises, it's quite possible that cutting down on the distance you have to go is worth some increase in the difficulty of working there when you arrive.

People are also kinda interested in Europa, although personally I'd rather be looking at Enceladus - if only because Saturn's system is where I'd prefer to go anyway (pretty rings, intriguing Titan).



Rick

"So the real tradeoff, in a practical sense, is that each human you send into space is as expensive in payload capacity as 1-20 major interplanetary robotic missions."

So...

Okay, when are we going to be able to send 20 major interplanetary robotic missions per year?

Luke said...

Regarding the Jovian radiation environment - although the radiation is very intense, a quick survey of the available data suggests it is not very penetration. Not like galactic cosmic rays, at any rate. Shielding that can reduce the dose from galactic cosmic rays to something tolerable for long term habitation should be able to completely shut out the Jovian radiation, at least from the quick survey I did.

Now, why you would actually want to live around Jupiter is another matter entirely. Just because you can doesn't mean you should.

Tony said...

Milo:

"Don't forget Luna.

Mars is useless."


In the opinion of many it is the Moon that is useless. Its gravity is too low, its proximity to the Sun has radiation safety implications, and its most useful resources -- for organic chemistry, at any rate -- is locked up in rocks, as far as we know for sure. (Yes, I know about the ice fields that supposedly exist in polar craters, but even the LCROSS results were inconclusive on that score.)

On Mars, you're significantly further out from the Sun (for radiation safety), the gravity may be enough for human health, and the water is...well, enough to create ground fog observable from orbit under certain circumstances.

About the only thing about the Moon that recommends it is proximity, and even that is not a big a deal as some would have you believe. Unless you keep a rescue rocket on the pad full time, people living on the Moon are at least months away from succor in case of an emergency. It's not the days/years dichotomy that some dishonest brokers want you to believe. It's more like months/years. That could be significant, but it's a less conclusive factor than has often been advertised by those who should know better.

"Technically yes, but the transfers we use still tend to be minor tweaks on the Hohmann orbit, which are hardly any faster."

Sorry, but that's incorrect. They're roughly in the same energy class, but they're not Hohmann orbits. They don't rely on perfectly matched elipses. They use gravitational capture, aerobraking, or aerobraking and landing for rendezvous, whereas Hohmann's work assumed a propulsive impulse to match the destination orbit.

Interplanetary transfer orbits are in fact often slightly less energetic that classical Hohmann orbits, because the trajectory design can rely on using the gravity (and sometimes atmosphere) of the target body to squeeze out a few hundred meters per second that wouldn't be there in the textbook case.

"Exactly. And informally, it's pretty obvious that "non-Hohmann orbit" is supposed to mean "high-energy elliptical or low-or-high-energy hyperbolic orbit"."

The reason I'm making a point of this is that there's no need to be informal. Worse, it perpetuates something that should never have gotten into the lexicon, particularly that of the interested laymen, who think they are being jargonically cool, but who really just label themselves as not up-to-speed when they use such terminology. IOW, I'm offering advice on how not to sound like a Space Cadet. Maybe that isn't important to some people. But maybe it is important to others. Just my $0.02.

Byron said...

OK, I guess that I should have been more clear. We, here, in doing theoretical calculations, often plan on hohmann orbits. Even if we don't, the results are often close. What I meant was that the transfers are significantly faster than hohmann orbits, most likely in the parabolic-hyperbolic range.

Cyclers can be used for cargo if you have tethers set up. The cargo serves as ballast, but it's practically free. And when the life support stops working, you just carve off chunks of the cycler, and use the mass to add more to the cargo. It's not going to be a prime way, just cheap.

I very much disagree about Luna's uselessness. LCROSS detected hydrogen in large quantities, radiation shielding is easy to do (dump regolith atop the hab), and it's very accessible. That, more than anything else, will determine colonization. While it may not be days/years to get anything there, it's possible if you're ready for it. For vital equipment, what's to stop you from keeping a rocket on the pad? Say, a converted ICBM. The base calls and needs something soon. If you have the payload ready in three days, it's a week total. Plus, it's three days home if something really bad happens, and mission control is right there.

atomic kit kat said...

hey guys. new poster and what not. been reading this for awhile now and decided i'd finally chime in. just thought i'd make an observation since this was a spin off of the space patrol thread.

space stations die. anything that's in space when (not if, humans being humans)the shooting starts will turn into a debris field in fairly short order if it can't move. a static target is a dead target in modern war right now. in space doubly so since you have to defend yourself from multiple threat vectors, 360 of them, that can effectively launch attacks outside your ability to detect or intercept.

in terms of a good story you have to have a station, but in terms of survivability when very angry people start to toss around large pieces of metal, random trash and the obligatory rock or 476, then you start to run into one hell of a problem. namely how do i protect my trillion dollar investment and at what point do i stop dumping money into protecting it. red queens race with a vengeance.

i've came up with lots of good ways to protect a station but none of them are full proof and all you really need to kill a station is a couple of really pissed of people with a ship and 8-9 months to spare, to start pushing rocks. granted its a mite more complicated that that but the points still the same.

you need an orbital infrastructure to have any chance to make anything in space work but that same infrastructure can't move and so is devastatingly vulnerable to low tech space players or any colony with a grudge and a ship. so that means you would need these patrols to go and hang around in some big empty holes in space for the reason of asking "what you are doing here".

now granted i'm making an assumption that in the plausible mid-future space is going to be semi-crowded but if we are going there in the first place (and i REALLY think we need to get off this rock in the largest numbers possible before we kill ourselves off) there will be something that we will all want.

so a patrol ship/s do serve a very important role in space. the ship doesn't have to actually BE present in a given point in space to control or interdict said point, it just has to be able to project sufficient force at that point make anyone occupying it unhappy. these interdiction missions would probably be best carried out by one of two types of ships, a cruiser analog meant for long duration missions to well, cruise, for lack of a better word. the other ship type would be some kind of carrier analog with a combination of maned and unmanned ships to project its sphere of influence and provide targeting data for the "persuaders".

any way i could go on like that for awhile but its not really on point with the thread, but i thought it worth mentioning. as to the whole, "send a really big ship form one place to another as a station" i think it would be more economically feasible to send the station/s as a modular construction. essentially you have a fairly smart robot with a few humans in the loop, move a power plant and a life support module out to the point in space you want your hab and drop it off. as your hab grows you bring in more modules to expand it with the same ships. if at some point you wanna move it some place else or there is no longer the same level of demand and no need for all the extra modules you detach a few and move them to where they are needed. if the construction is standardized it would be a fairly simply concept of plug n' play.

atomic kit kat said...
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atomic kit kat said...
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atomic kit kat said...
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Tony said...

Byron:

"I very much disagree about Luna's uselessness. LCROSS detected hydrogen in large quantities, radiation shielding is easy to do (dump regolith atop the hab), and it's very accessible. That, more than anything else, will determine colonization. While it may not be days/years to get anything there, it's possible if you're ready for it. For vital equipment, what's to stop you from keeping a rocket on the pad? Say, a converted ICBM. The base calls and needs something soon. If you have the payload ready in three days, it's a week total. Plus, it's three days home if something really bad happens, and mission control is right there."

Diana sings a Siren's song. Be careful you don't listen.

Byron said...

Atomic Kit Kat:
The distinction between space station and spacecraft is not as clear as you seem to believe. Any station will have small thrusters for station-keeping and orbital adjustments. They won't be immobile the way a ground installation is. It's not really any harder to protect against plausible midfuture weapons than a ship is. (Maneuver is vastly overrated in that case. Ships aren't going to dodge around like something out of Star Wars.)

Tony:
You're talking to the wrong person on that. We may have to agree to disagree.

Anonymous said...

A reason for sending a space station to, say, Jupiter or Saturn, is to have a central location to stage expeditions and/or support temporary research bases on various moons. The space stations would provide logistic, medical, and other support to these teporary bases, at least until those bases became permanent. And, while physical will be needed, some form of magnetic or electrical shielding could replace (or augument)some of it; the overall mass savings might not be that great, but it could increase the efficency of the shielding.

Oh, and there is a fairly large human presence in Antarctica engaged in both research (long-term) and tourism (short-term). Humans, go figure...

Ferrell

Rick said...

An unusual spam comment on a new thread, hawking video services - duly elfed without trace.

I sometimes say 'Hohmann-like' or some such, but usually I simply say slow orbits and fast orbits, the latter being the sort you generally need a high ISP drive to use. So far as I know there's no elegant approximation for those orbits, the way Hohmann is an elegant approximation of typical slow, economical orbits.

But I'm not inclined to be rigorist on this blog about the common practice of using 'Hohmann' as shorthand for slow orbits in general.


Cyclers could be viable if you want to do regular interplanetary travel and you don't have a drive capable of fast orbits. If you are on the slow boat anyway it ought to be roomy and it needs to be shielded, and ends up very heavy.

I don't think cyclers will happen, though, because a decent nuclear electric drive is not all that far past current tech. If you can build a nuke electric generator with power density of 1 kW/kg, comparable to a gasoline engine, you are good to go.

Playing with my Travel Planner, even a third of that power density will get you to Mars in 120 days, about half the nominal Hohmann time.

So my guess is that if we are going to pony up for routine interplanetary travel, we will invest in a drive that can take fast orbits.

As to where is worth going to, that will depend a lot on what our robotic probes find. Life trumps all else, except archeology. (And ruins are evidence of life.)

But Mars is easier to reach than the outer system, it looks rather like Earth in pictures, and history gives it a special place in the popular culture.

Tony said...

Byron:

"You're talking to the wrong person on that. We may have to agree to disagree."

Be that as it may. But I am speaking from personal experience ;-) .

Jim Baerg said...

"Of course the interior will matter immeasurably more to the people on board... It can be as elegant or as sterile as you like (or both, depending on deck and sector)."

Sterile no. If it's going to provide most of the food & oxygen needed by the residents, most of the interior will be one big greenhouse. For some limited duration trips supplies that get used up will require less mass & volume than the plant life, but not if people are to live there for many years.

Maybe there will be some (bio)tech development that would allow food & O2 production without green plants, but I suspect that would be after 'plausible mid-future'.

Native Jovian said...

During that time there's no real purpose for a human presence in space, except to do biomedical research on humans living in the space environment.

I have to disagree with this. I think any large-scale exploitation (whether that means colonies, research stations, or whatever) of anything outside the Earth-Luna system is going to necessarily involve a large, permanent orbital presence around your object of choice. If a planet is your metaphorical gold mine, then the hab orbiting it is going to be your boom town. Why? There's a couple reasons:

1) Once you're in orbit, you're halfway to anywhere. This is equally true whether you're in orbit around Earth or around Saturn. Anything that can stay in orbit you're going to want to keep there, just to avoid the expense of hauling it up and down the gravity well. If living in space is cheap enough (relative to living on whatever you're orbiting), this will include everything not absolutely required to be on the surface, from the beancounters to the candlestickmakers, while relatively tiny teams of people doing the actual work you're there for rough it on the surface.

2) Space is space. Lessons learned about living in orbit around Earth can be applied to living in orbit around Mars much more readily than lessons learned about living on Mars can be applied to living on Titan. An orbital hab would be a relatively known quantity in an otherwise unknown environment. With fewer unknowns to deal with, the possibility of a catastrophic loss of an orbital hab is much lower than the possibility of a catastrophic loss of a surface installation -- especially if you already have some practice running orbital habs.

3) Since you have to travel through space in order to get to your destination, you're already fairly well equipped for living in space. As we've been discussing here, the difference between a space ship and an orbital hab is rather less than the difference between a house and a houseboat. You can get all your materials from Earth and do all your assembly in Earth orbit -- where it's relatively cheap -- and just sail it into orbit around where ever you want to live. Okay, so it's not quite that simple, but building a working orbital hab and then shipping it to another planet seems preferable to me to shipping a bunch of materials and laborers to another planet and then telling them to build a place to live. There's been discussion in this thread about how expensive people are in space -- so why not leave the construction crew at home, and only send the people that you actually want there in the first place?

Or maybe my Gundam roots are showing and I just want to see big ol' Island 3s spinning gracefully through the sky. Either way, I think learning to live in space itself is going to be the first step in learning to live anywhere off Earth except Luna and perhaps Mars.

Native Jovian said...
This comment has been removed by the author.
Rick said...

Belated welcome to a new commenter, who was already attacked by the Blogger gods to boot.

In this post I'm speaking of stations and habs in a broader sense, not just military, so their vulnerability to attack is not a major concern. (If everyone in space is under attack all the time, there won't be much space travel.)

Almost everything can be modular, but habs need to be as physically compact as practical to minimize shielding mass and cost.

The Moon has obvious logistical advantages as a place to reach. Its real problem is that its many glamorous connotations are all terrestrial. The Moon is hard to sell, because most of the arguments amount to using it as a staging base for eventual deep space missions. But in that case why not just do the interplanetary missions, i.e. Mars?

And the staging base arguments are more relevant to eventual regular traffic than initial exploration.

Rick said...

Regarding 'sterile,' I meant in the stylistic or cinematic sense, not literally. Gleaming white surfaces, harsh lighting, all that.

I don't know that a large human presence is necessary in space, except for colonization (obviously!). Even for the ever popular space mining trope, I suspect that automating the process, and accepting some failures, is cheaper than sending people.

But if we DO send a lot of people, I think orbital habs will be more the rule than surface settlements. If we turn out to need close to 1 g for health, habs are the only practical way to provide it. And the surfaces may be difficult working environments.

Thucydides said...

Setting up in free space is always easier since you are nicely insulated by vacuum, and can manipulate the environment for whatever parameters you want. The same template which works in cis lunar space will also work around Saturn or Mercury with some tweaks (mostly with the mirrors and radiators).

Building on a planet or moon means dealing with gravity, thermal loads, day night cycles and planetary events (think of Io for the most extreme version), each solution custom engineered to whatever place you are on. While I expect there will be plenty of contrarians who will have a want or need to set up shop on planets and moons, in the end the free space dwellers will be expanding geometrically and becoming the dominent force in the Solar system.

Of course, you first need reasons to get people out there in the first place.....

Cyclers will exist if the demand for mass transportation of large numbers of human passengers exists, along with the stipulation that efficient, high speed drive is not available or economical. High speed drives *may* exist but be uneconomical for general use (think of trans Atlantic air travel in the period between the late 1920's and the introduction of the 707). If economical high speed drives exist, then of course it makes sense to go to Mars in 39 days rather than 180 days. If you ae already constrained to taking 180 days, then you need correspondingly greater mass for radiation shields and life support, which drives you in the direction of the cycler to minimize the drive and remass demands.

As for Jupiter, the magnetosphere is the most energy rich region of space outside of the Solar photosphere, and that alone will probably interest people.

atomic kit kat said...

Byron:

yeah i know the difference in a ship and a station and that a station has to have station keeping properties but to be effective as a station it has to occupy a given area. if i know you have to be in that given area then i toss a lot of crap that way. even if you move, you can only move so far and so fast. if i crunch the numbers to figure out what those moves are and how fast you can do them then i can saturate the area in which you have to be. then you die.

now you can armor your station and give it some decent defensive armaments but it doesn't change that you still have to be in a given area to be effective. if you did put sufficient means of propulsion on the station to allow it to make some fairly large movements in rapid order then you have a ship. a very large, very expensive ship that sits there being a target. and since you are stationary the same rules for killing a station apply. granted having the ability to MOVE if you have to means that any effective attack would have to be more complicated in both planing and tech level and would cut down on the number of players who could execute said attack but doesn't change that you are going to die.

well to be fair you may not be destroyed but you will most likely not be able to perform you primary mission which would be as a station and all the support for various other groups that, that entails. and while out right destruction would be the preferable goal denying you use of your station for months or a year+ while it was repaired would be just as effective for what ever purpose a hostile force/s has reason for being there. oh and don't forget random acts of terror, man being man.

Byron said...

What do you mean when you say "but to be effective as a station it has to occupy a given area"? That's true, but the area in question is so large that saturating it to the point of overwhelming defenses is flat-out impossible. I'll do the math on it.
Let's say that the station you are attacking can alter it's orbital period up to one minute, and has one orbit before it gets hit. During the two minute window, the station will travel 900 kilometers. Let's assume it can be 1 km on either side of the track. The total area that has to be covered is 1800 square kilometers. The average cross-section of Rick's station is 31415 m2. If it takes a 25 kg projectile to kill the station, and the defenses mean that it will take 5 projectiles to get a hit, the total mass required to kill the station will be 7,161,972 kg. This is a best-case scenario. With time or maneuver, the amount required for a kill goes up. The delta-V required for the sort of change outlined above is around 30 m/s. And if you come closer, the difference between station and ship largely disappears. A ship might make .1 G if it's really powerful. More under thrusters, but there's not really any difference between ship thrusters and station thrusters.
For more on defenses, see spherical war cows.

Geoffrey S H said...

This popped up unto my head, from the "Empire Strikes Back" scene between General Melver and Vader:

"What is it General?"

"My Lord, the cycler constellation has completed its deceleration burn and is approaching the 6th moon in the Javian system. Comm Scans have detected an em-field capable of resisting any ew-hacking attampt."

"Pilot-specialist Ozzel has decelerated us too close to the moon- he has used up valuable propellant."

"The Pilot-specialist thought unpredictability was neccessary-"

"-The Pilot-Specialist is as clumsy as he is stupid. Now prepare your troops for a surface attack."

Clay said...

I'm not familiar with the details regarding radiation shielding out in space.

Ignoring combat for the moment, what are some of the variables regarding radiation in space?

And what are some of the solutions?

Thanks in advance,
Clay

Jim Baerg said...

Rick: "Regarding 'sterile,' I meant in the stylistic or cinematic sense, not literally. Gleaming white surfaces, harsh lighting, all that."

I was thinking in both senses myself. Plants all over the place means it isn't sterile in the stylistic sense either I'll concede that the plants might do better under 'harsh' lighing.

Rick said...

Clay - follow the link about radiation in the original post. It goes to the Atomic Rockets page, with tons of stuff on both weapon radiation and natural space radiation.

Short form, there are two main hazards. One is solar storms, which let off a huge burst of energetic charged particles. Adequate protection is a compact 'storm cellar,' shielded on the side facing the Sun, that all personnel can crowd into for up to 48 hours or so.

The other hazard is random high energy cosmic rays, GCRs, that rack up a steady unshielded dose of about 0.6 sieverts/year. The lifetime exposure limit for astronauts, 4 Sv, is reached in about 7 years. An ordinary cabin structure will cut the dose by about a third.

The annual limit for nuclear industry workers is 0.05 Sv, which would only allow an annual maximum of 6 weeks travel aboard a small, unshielded ship. Adding 100 kg/m2 of shielding increases this to about 5 months.

The much heavier shielding I discuss in the post is to meet the standard for general populations, including pregnant women, etc. - the standard you need for permanent human communities in space.

Unguided kinetics are very unlikely to hit if launched from any distance. Even against a non-maneuvering target you need exceedingly precise aim if there is no midcourse correction. And even ships with low thrust, high ISP drives can put on an OMS burn of a few meters per second.

If unguided kinetics are launched from 1000 km away at a closing rate of 10 km/s, you have 100 seconds to evade, and at an average 10 meters per second you can deflect yourself up to 1 km. It takes an awful lot of shrapnel to fill up an evasion envelope 1 km in radius.

Hence the importance of target seekers, which have a good chance of hitting unless engaged and crippled.

Clay said...

Rick:

Thanks for the radiation info. I skimmed the radiation section, but not closely enough.

As for unguided kinetics, you make a good argument, but I wonder how long you can maneuver before you run out of Delta-v. It's a lot cheaper to accelerate a bunch of bird shot out your way than for you to move your entire ship.

I just don't see a good solution against this attack. For every ounce of armor piled on to brush off my shot, your mass penalty grows and you burn through Delta-v that much faster. For every burn you make to dodge, you lose Delta-v. For every burn you don't make, I play the shot gun odds.

The important point is that I don't expect to do much, if any, damage for a long time. My goal is to make you dodge. Missing is almost as effective as hitting, because eventually you won't be able to maneuver.

I guess the critical point is can you carry more Delta-v for your giant ship than I carry bird shot in my relatively little one. Or fleet of little ships.

It still seems to me that patient sniping by little ships can take out the big guys. There are just so many critical parts to hit--sensors, radiators, drive, mirrors. You have to maneuver, but if you do, you burn up Delta-v. If you don't, I wear away critical systems until you can't defend. And then I lob a guided nuke straight down.

Either way, it's the death by a thousand cuts.

Has anyone gamed out these scenarios for real as opposed to just talking about them?

Byron said...

Clay:
Did you even read my analysis? Unguided kinetics are simply useless against any sort of maneuvering target. It took 7 kilotons to get one 25 kg hit on a target when the target used 30 m/s of delta-V. That's nothing. Even if you reduce the mass required for a hit, it's still a lot more than just a guided projectile. My basic point is that a station has the same chance as a ship. It's like trying to hunt tanks with cruise missiles. A tank is a lot slower than an airplane, and thus more vulnerable to cruise missiles (without midcourse updates), right? Well, yes, but it's still not practical. (I know it's not a perfect analogy, but I have yet to find one.)
Also, you act like delta-V is completely non-renewable. Stations will by definition be on the defensive, making resupply likely.
The above ignores various errors in my analysis. Such as not allowing the station to change it's inclination much, which probably adds an order of magnitude, and the fact that I grossly lowballed point defenses.
And I'm working on setting up a game (Rocketverse).

Tony said...

Native Jovian:

"1) Once you're in orbit, you're halfway to anywhere..."

What an overused, yet misunderstood, cliche that is. Yes, achieving LEO is half or more of your delta-v requirement for anywhere inside the orbit of Ceres. But that only works if you accept minimum energy trajectories and months or years of travel. If you're talking about high energy interplanetary transfers, getting off of a planetary surface is a small part of the exercise.

And, speaking of minimum energy orbits, there's no technical or economic reason build a station in orbit at either end of the journey. It's not like you have an orbital Baker, halfway between L.A. and Vegas, where you can get breakfast and answer nature's call. Because of the non-coplanar relationship of planetary orbits, the parking orbit you launch into to go from one or the other is unique to each surface launch site and interplanetary transfer opportunity. A station in any conceivable orbit is likely in the wrong orbit for initiating a transfer.

"2) Space is space..."

It is? Space around Mars is like space around Earth, either inside or outside of the Van Allen Belt? Space around Ceres is like...what? How are any circum-planetary spaceenvironments like interplanetary space?

The rest of this item sounds disturbingly like the "space is a place" mantra you hear from time to time at sci-fi cons. The reason to be in space is to get someplace, not be in space. I'll leave it at that.

Milo said...

Luke:

"Now, why you would actually want to live around Jupiter is another matter entirely. Just because you can doesn't mean you should."

That applies to anywhere in space.

Unfortunately.



Tony:

"Its gravity is too low,"

We have no idea what values are desirable. Mars's gravity is still far lighter than Earth's, so I doubt it'll somehow be completely fine while Luna's gravity is impossible to adapt to. Settling either one would require some way of dealing with low gravity conditions - even if just by accepting the effects it has on your muscles and bones (you're not using them until you return to a higher-gravity location, so who cares?).


"Unless you keep a rescue rocket on the pad full time,"

If we had a serious moonbase, we probably would. Of course, outside of emergency situations launches will be somewhat more leisurely - at least, once the rocket is used, replacing it for another launch gets costly.

Another advantage of proximity: communication. Luna is close enough to be able to access the Tellurian internet with only a couple seconds lag, which would be a serious advantage for the comfort of the inhabitants. Plus that whole bit about the trip only taking days, regardless of how long it took to set up (which even in your estimate is still an order of magnitude faster than Mars).



Rick:

"the sort you generally need a high ISP drive to use. So far as I know there's no elegant approximation for those orbits, the way Hohmann is an elegant approximation of typical slow, economical orbits."

Sure there is. It's called the one-tangent transfer. Draw an ellipse/parabola/hyperbola which is tangent to the inner planet's orbit and crosses through the outer planet's orbit (as opposed to the Hohmann transfer, which is tangent to both), and then proceed with calculations in the same manner as with Hohmann.

Milo said...

Native Jovian:

"Once you're in orbit, you're halfway to anywhere."

That sounds catchy, but it isn't really accurate. You're only halfway to anywhere if you don't mind spending years getting there. If you want reasonable travel times, then distant objects become increasingly difficult to reach, much harder than getting into orbit (especially for the outer solar system).

Also, if you do insist you're halfway to anywhere, then remember the converse: once you're in orbit, the world under you is as difficult to reach as an entirely different planet.


"Anything that can stay in orbit you're going to want to keep there,

Unless there was no reason to put it in orbit at all in the first place.


"so why not leave the construction crew at home, and only send the people that you actually want there in the first place?"

If you're planning to colonize the destination, then the settlers will need to raise their own construction crews.

If you're merely going there for research, then the vast majority of the crew on your ship will be scientists who will want to go somewhere dictated by the needs of their research, and that's probably the surface of the world they're researching.

Either way, ground facilities are necessary. And once you've landed, you might as well stay down until you have a reason to go back up.



Rick:

"Short form, there are two main hazards. One is solar storms, which let off a huge burst of energetic charged particles. Adequate protection is a compact 'storm cellar,' shielded on the side facing the Sun, that all personnel can crowd into for up to 48 hours or so."

Speaking of which, when you have a space station colony of, say, several thousand people, cramming all personnel into a storm cellar is no longer so practical. Even if you could do it, many of those people are going to be unhappy about doing that kind of thing regularly once they're living in space permanently, and you just know that sooner or later someone is going to get caught outside.

Storm cellars may work for ships, but a permanent station really needs to have enough normal shielding to resist solar storms directly.

For that matter, are you also bringing your crops into the storm cellar?

Clay said...

Hey Byron:

Yes. I read your analysis. Here's my thinking. These ships are vulnerable. They are covered in vital points. And they have to haul their propellant with them. So what are the limitations?

Setting) You are maneuvering your big ship and--as you point out--dodging my buckshot. But for how long? Given the vulnerability of ships, this isn't like hunting tanks with a cruise missile; it's like hunting helium balloons with an air gun. The trick here is that you have to move because I keep sniping. And I don't stop shooting to chivalrously allow you to refuel.

So now what?

Scenario 1) You keep maneuvering until I run out of bird shot. That will take a while. I never hit you, but it takes a while and a lot of maneuvering. Then I go home. Here's the question: having successfully dodged my shots for who knows how long, do you still have enough Delta-v to hang around? Do you still have enough fuel to get back home? And what do you do if I've brought another little drone up in the meantime; after all, I can buy many of my little drones for the price of your big ship.

Scenario 2) You run out of Delta-v before I run out of buckshot. Now how good is your maneuvering? Instead of sniping at you with a few shots, I begin firing broadsides in your direction. Sure, I still miss, but there's a big difference between hitting a dodging target, and hitting a stationary one. If I can knock out either (a) your point-defense/laser/etc or (b) your radiators that allow you to run your point-defense, then it's fast ball time with the nuke missile.

Scenario 3) You reach a fuel resupply area. Now how do you refuel? Do you stop? If so, it's fast ball time. Or is this area heavily patrolled by other ships, in which case, my little drone is not just tying down this ship, but also other ships needed to guard the fuel depot.

Bottom line: your strategy isn't cost effective at all compared to mine, and that's where I see the war is space being won. If my strategy allows me to neutralize--even if I don't actually destroy--your ships, while I still have free drones to harass your shipping, terrorize launch vessels, hunt down your satellites, impede your fuel production/transfer facilities, attack energy production facilities, wear your down, etc... then I can win a war even if I don't win the battles.

I don't think decisive, Trafalgar type contests are going to occur, which is why I disagree with your tank analogy, and really all discussions of warships in space. They don't make sense anymore given three key factors:

1) humans just don't seem cut out to live in space except in EXTREMELY expensive and heavy structures, which makes human habitable ships strategically too costly because of mass penalties because

2) you have to haul your fuel a long way from its processing plant. Fuel is thus an Achilles heel which means

3) long shots that force them to burn up their fuel are just as good as actually hitting them, since they can't afford to actually run out.

Clay said...

Of course, this is all moot since I'm planning on using nanotechnology to solve all these problems.

:)

Clay said...

One final thought on what I'm gonna call "the dodge"

How does dodging work in orbit? I see lots of talk about how battles will likely only occur near planets. So how do you dodge then?

What about all those people and ships you're supposed to be protecting? Politically, can you afford to dodge while I blast your stuff? How long before you get removed from command?

And what happens to all that theoretical running room when much of it is already occupied by the planet itself? What does the gravity well do to your fuel consumption?

Finally, what about having to track all the other crap that orbits planets, including satellites and other technology? Will this make you more predictable? Can you plot maneuvers that take into account shots from me and all that stuff fast enough?

Byron said...

Milo:
Both of you are somewhat right. The station would have shielding for normal flares. However, there would also be a cellar for really big flares.

Clay:
We are both talking about the long-range use of unguided kinetics, right?

Given the vulnerability of ships, this isn't like hunting tanks with a cruise missile; it's like hunting helium balloons with an air gun.
You missed the entire point of the analogy. It was that unguided kinetics are incredibly impractical. And I don't need you to allow me to refuel. To force the use of 30 m/s of delta-V, you would have to use somewhere in the neighborhood of 100 kilotons with 25 kg projectiles (the difference from my calculations is due to not adding inclination and lowballing defenses). And if you shoot at a smaller ship, the mass required rises. You can drop it by dropping projectile mass, but the problem remains.

Scenario 1 pretty much states I'm in orbit around my home planet. That reduces leftover fuel considerations to 0.
Scenario 2 is somewhat strange. Why not kill me with your kinetics? Why use the nuke?
Scenario 3 is also strange. Why do I need a depot? Just send a small shuttle with the remass, and dock while I'm out of danger. If you're at range, then response time will be fairly long. My analysis was on a 90-ish minute response.

I laughed when you called my strategy not cost effective. You're tossing around truly huge amounts of stuff, and calling my plan uneconomical.

Your factors depend on me being the attacker, which might be true in some circumstances. It does prove this sort of thing is better for defenders. It's still not practical.

The better solution is to guide the kinetics, as you don't need anywhere near as many. They can't really be dodged, but they're more likely to be useful for the kill. And in my opinion, birdshot is best for forcing people to keep their mirrors shuttered while my killer kinetics sneak up on them.

(continued)

Byron said...

Of course, this is all moot since I'm planning on using magic to solve all these problems.

I'll let Tony deal with this one.

My analysis was based on dodging in orbit. In many ways, over long timeframes, it's easier than dodging in open space. You make a small burn, and that changes your orbital period or inclination. That puts you somewhere else quickly. Over a week, you can be anywhere in your orbital region with minimal delta-V expenditure.
The stuff to be protected is sort of moot in this case. Shooting at habs is a war crime almost by definition, and you can't close enough to board before they get back. The planet is actually a good thing, as outlined above.
And yes, cluttered orbital space won't be a problem. It's actually not that crowded in an absolute sense, and CBDR is your friend.

Clay said...

Byron:

First, the nanotech reference was a joke to prior conversations. Humor man.

Second, the flaw in your thinking is that I don't have to shoot much at all. My kinetics are small. They are designed to pick at you, not be death blows. I'm not trying to destroy you. All I have to do is pick at you so that you have to keep moving. You burn fuel; you lose position; and you get to enjoy a court-martial when you go back home for dereliction of duty.

As for laughter, I laughed at your war crime answer to my attacking your habitats. Like bombing doesn't happen. Guess what. I'm doing it. Now what?

In any case, I'll just issue a "bail out in 24 hours before we blow away your habitat" notice and then blow it away. Now what are you gonna do? You can't just yell no fair. You gotta defend that stuff.

Maybe I'll toss a few nukes down on your planet while I'm at it. Turn it into slag.

How's "the dodge" looking now?

Clay said...

One more point. Cost effective is definitely not your strategy.

Consider, a manned mission to mars was estimated to cost 500 billion in the early 90's. Around the same time, they actually did an unmanned mission for 250 million.

That's a ratio of what: 1 to 2000

Assuming manned tech gets a whole lot better, do we really think it will ever exceed a ratio of 1 to 100.

So, if I can tie up your manned ships (which are effectively like battleships) with just some of my vessels, where does that leave you. Again, even assuming 1 to 100, you can't run "the dodge" and expect to win.

Assuming any parity at all, I can avoid your ship(s) and use my remaining drones to slag your resources and planet.

Clay said...

I'd like to address two assumptions that others seem to have.

First, in an earlier comment, Rick assumed a launch speed of 10 km/s for my projectiles. I imagine that's because he was thinking big shells designed to be ship killers. But what happens if we drive that speed up to 100 km/s and drop the projectile size to very small? Now instead of 100 seconds to evade, you only have 10. Your hiding space goes down. Remember, I'm not looking for knock-out blows. These are the lightest of jabs I'm throwing.

At the same time, the mass of my projectile can go down quite a bit, but because of the speed gain, it can still pack a punch, even if it's tiny it will probably still penetrate. Thus, forcing you to move and perhaps damaging something that matters.

Third, and this is important if I really want to destroy you, at ratio's of 100 to 1 up to 1000+ to 1, I can field a lot of ships for every ship you put into space. I think it helps to challenge the 1 on 1 assumption. My drone fleet of 500 times your numbers can fire a lot of little kinetics in coordination--enough that I wonder if a bigger ship can find itself boxed in.

Fourth, I understand using guided projectiles would help a lot if I'm really trying to hit you, but I'm not. Guided projectiles cost more, have more to break down from heavy acceleration, and have a lot more mass.

I'm patient, and I'm playing the strategic bombing game with my reserves against your civilians and space infrastructure while we fight our battle.

Even if I never kill your ships. Even if you're much smaller than 1 km radius hiding space does actually keep you safe and all that 1 gee maneuvering (Rick assumed 10 m/s) somehow doesn't exhaust your Delta-v. Even if it's a Jutland and nobody wins. If I can blast your infrastructure and keep you moving, how do I lose?

Rick said...

Halfway to anywhere

This is true in one limited but important respect. Low orbit is where you transfer between entirely different kinds of spacecraft, interplanetary ships and landing shuttles.

As Milo noted, 'halfway' applies both ways - low orbit is not particularly close to the surface below it. They are separated by a shuttle ride, a non trivial mission for Mars, larger moons, or even Ceres.

That said, even though the objective is presumably to explore the surface, I am inclined to keep as much of the logistic support as possible in orbit, to avoid the extra effort/cost of landing it.

Also my personal guess is that for prolonged habitation we need 0.5 g or more - the problem isn't just bones and muscles, it is the heart. IF this turns out to be the case, surface stays are limited to ~6 months unless you mount the whole base on a turntable.


The level of shielding I specify for permanent habs, 5 tons/m2, should protect against solar storms as well as GCRs. It provides the same level of protection as Earth's atmosphere at high elevations.


In the unguided kinetics "make 'em dance" scenario scenario, where is the attacker getting their unlimited supply of gravel, and at what rate are they expending it?

Suppose that the target has an OMS engine capable of 20 milligees, enough to put on 20 m/s in 100 seconds, deflecting yourself by 1 km. Suppose also that 5 percent of the target ship's mass is OMS propellant available for evasive burns.

The target thus has about 150-225 m/s of evasion delta v, depending on your OMS propellant, enough for 7 minutes of continual 'dancing.' The attacker is going to have to throw an awful lot of unguided rubble to require that much evasion.


If ships engage each other at very close range, the whole assumption set becomes different, and unguided kinetics become dangerous. But very close range fights are likely only in scenarios such as a boarding inspection going pear shaped, etc.

Milo said...

Clay:

"Scenario 1) You keep maneuvering until I run out of bird shot. That will take a while. I never hit you, but it takes a while and a lot of maneuvering."

I don't need to dodge you forever. I just need to dodge you long enough to shoot back. The best defense is a good offense.


"You reach a fuel resupply area. Now how do you refuel? Do you stop?"

There is no such thing as "stopping" in space. Two ships/stations docked to each other are still in orbit, and both retain the use of their thrusters. They just move together.

Depending on how long it takes to refuel and how far away your attacking craft is, I might even have time to stop without exposing myself to undue risk.


"Of course, this is all moot since I'm planning on using nanotechnology to solve all these problems."

In other words, a wizard did it?

Realistic nanotechnology doesn't just conveniently solve your biggest problems while otherwise preserving a familiar setting.


"What about all those people and ships you're supposed to be protecting? Politically, can you afford to dodge while I blast your stuff?"

If I dodge, your shot will not hit some valuable thing behind me. With high probability, it will careen off into space, never to be seen again. Space is empty.

Also, I can still shoot at you while I'm dodging.

Milo said...

Byron:

"Both of you are somewhat right. The station would have shielding for normal flares. However, there would also be a cellar for really big flares."

That may work as long as "really big flares" are something that happens only as often as earthquakes or hurricanes.

Keep in mind that due to the need for shielding on all sides, you can't efficiently give every household their own storm shelter in their basement.



Rick:

"That said, even though the objective is presumably to explore the surface, I am inclined to keep as much of the logistic support as possible in orbit, to avoid the extra effort/cost of landing it."

The question is, how much can your logistic support do when it's disconnected from the things it's supporting?

There are some things that make sense to keep in orbit, like communication relays and the (parked) ride you'll use to return home, but major things like life support have to go where the people are.

Jedidia said...

>>What an overused, yet >>misunderstood, cliche that is.

Not if you are already in a stage where you have completely seperated the tasks of Surface-to-Orbit vessels and interplanetary vessels.

Because, interplanetary vessels would use high efficiency drives, which simply don't have enough thrust to get their own behind off of earth. Ergo, they have a LOT more Delta-V per ton of propellant. A VASIMR is the most plausible mid-future drive, and if they can make fusion work (**keeps on praying**) a fusion drive would also come into the plausible range. Such engines can reach Mars in two months with quite reasonable amounts of propellant.
While for STO, we are more or less facing a limit. We have Aero-spikes, hybrid engines that can breathe oxygen from the atmosphere and similiar stuff up our sleeves which might give us some improvement in payload lift, but we won't be able to improve our current technology that much. An SSTO that can lift significant payloads is not on the plausible mid-future horizon.

So for all we know, interplanetary trips will not be such a headache once the tech is sufficiently tested (no one has doubts that a VASIMR can do the job, and we could design a vessel with more or less current tech), the headache is getting all this stuff into orbit.

So I think it is still fair to say that, once you have a specialized interplanetary vessel assembled in orbit, you ARE halfway to anywhere, or at least halfway to Mars...

As for the actual topic of spacestations and that they would be vulnerable to attack, well... Someone had to be pretty insane to blow up a several thousand tons station in his OWN orbit. He'll be cutting his own flesh. Indeed, it might even be feasible to threaten the rebellious martian governement that you'll abandon and blow up your own station in their orbit. If you do it right, they will have one hell of a time getting into space in the next few centuries...

The stations would probably have to be more protected against boarding and intrusion than against mad dictators making one gigantic mess in their own orbit. Even in Saturn orbit, a few thousand tons blowing apart with enough strength will provide quite a hazard for future trafic between the moons.

Tony said...

Rick:

"This is true in one limited but important respect. Low orbit is where you transfer between entirely different kinds of spacecraft, interplanetary ships and landing shuttles."

Which presumes that such a dichotomy will exist. In a world of cyclers, the only human occupied habitats would be the cyclers themselves. Your pause in orbit, after launching, will only be an hour or so, until you're at the point to take off for the cycler. Once you get to the other end of the line, you undock and go for a aerobraking maneuver down to the surface. Stopping at a station in low orbit -- as mentioned earlier, the wrong orbit, almost all of the time -- has no value.

In a world of much faster interplanetary craft, once again, what is the purpose of a station? Ships that have to anchor out in a roadstead aren't serviced from a subsidiary platform anchored out their with them. Supplies, cargo, repair equipment/personnel, and passengers come and go in lighter craft, directly to and from the port. Low orbital space is likewise a roadstead for interplanetary craft, and operations between Spaceport X, Y, Z and the roadstead orbits (there will be more than one, probably as many as there are (spaceports * destinations)) will likely be handled with lighter craft, not by putting a station in one specific orbit.

"That said, even though the objective is presumably to explore the surface, I am inclined to keep as much of the logistic support as possible in orbit, to avoid the extra effort/cost of landing it."

My understanding of logistic support must be significantly different from your's, Rick. If it's logistic support for surface operations, it has to be on the surface at some point. If it's logistic support for space operations, well, I just covered what I think would likely be the case: there's no one preferred orbit, therefore there's no better place to base logistics support than on the ground, sending up only what you expect to be used anyway, and whose launch cost you can't avoid.

If you're thinking about the case at the Mars or large asteroid end of the journey, well ,just how far into the future is it going to be before the industray at any of those destinations is going to support spacecraft construction or repairs? There won't be any logistics support for space travel anyplace other than the Earth for at least that long.

Clay said...

I'm envisioning really small projectiles. Sub-penny sized: 1 gram projectiles.

I have no idea if I'm using Eric Rozier's on-line calculator for kinetic kill weapons correctly, but a 1 gram 1cm radius projectile (about half the mass of a penny) at 100 km/s looks like it generates a little more than the force of a land mine according to the atomic rocket's boom table.

Is that right? That's more than I was thinking.

The nice thing about using 1 gram projectiles is that talking about kilograms gives us both a mass estimate and ammo count.

If that's right, then let's say I go in with 100 kg worth of ammo. That's 100,000 rounds. Assuming I fire 1 per second, I can fire these things at you for a loooong time.

@Milo:

Dude. I was joking about the nanotech. Didn't you see the smiley face. Did you really not know? And I know stopping is relative, but so what. How do you hook up with a fuel barge if you're dodging? And how do you keep me from blowing it to kingdom come first. Or is it another giant ship just like your first one?

More practically, if you dodge drone-1's shot you're correct--it won't hit civilians. The problem is that while drones 1-50 are tying you up, drones 51-100 are slagging your civilization. And I've got the surplus drones since my drones cost pennies to the dollar against your ships.

So I guess that's my scenario. I've got a swarm of cheap ass drones. You can't catch one without really burning your reserve of Delta-v, and then how will you dodge the rest of my swarm's shots. Id you play "the dodge" then they may or may not hit you unless I tell 'em to drive in on you hard. To keep mass down, they probably aren't armored except on the nose for just that kamikazi eventuality, but I don't care because I'm not doing the frontal charge. I'm more interested in the attrition game: keep you dancing with super fast 1 gram shots with part of my drone swarm, while the rest of my fleet turns your civilization into a warm memory.

Like fusion warm.

Even if you're right and I can't beat you, at the end, you've got these really expensive, big gun ships with no home to go back to.

Clay said...

@ Jedidia:

Blowing up space stations and/or planets can be seen in two ways depending on if we're still all in system, or we have some FTL abilities and this is war between independent star systems.

If FTL, then you simply slag your enemy and go home.

If not FTL, and this is a war with one side being non-Earth peoples and the other Earth, then this is deterrence where the disenfranchised get to insist on being taken seriously and not being cut off from food stuffs or whatever, or else they slag everybody.

It sounds crazy, but then deterrence always sounds that way.

Tony said...

Re: Jedidia

And? If you have to switch horses, getting into orbit is all of the way to orbit and none of the way to your ultimate planetary destination.

Or, looking at it from the arrivals, rather than the departures, perspective, getting into orbit is all of the way into orbit and none of the way down to the surface.

Or, looking at it from the shipper's business perspective, it's all of the way to more expensive shipping, because instead of handling everything at the dock in port, you have to pay for cargo lighterage, passenger lighterage, fuel barges, and all of their operating costs, on top of the actual bill for cargo/passenger/fuel delivery to the pier. It may be the only way you can do business under the circumstances, but that doesn't mean it's a cheap way.

Byron said...

Clay:
One more point. Cost effective is definitely not your strategy.

Consider, a manned mission to mars was estimated to cost 500 billion in the early 90's. Around the same time, they actually did an unmanned mission for 250 million.

That's a ratio of what: 1 to 2000

This is a massive, massive, false comparison. Actually, it's two.
1. You assume that the aims of the two alternatives are the same. They are not. You assume that the human mission would do the same as the unmanned mission did. At a guess, based on Apollo, it would have around 100 times the science output the probe did (I know you can't measure science, but it's a rough guess). That brings it down to 20 to 1.
Even if they did have the same objectives, you can't generalize that to warfare.
2. They did not have the same conditions. It would take 500 billion to put the first crew on Mars, including research and development, testing, and all the other investments. Once it's done, I'll guess that successive flights would be about 1/4 the cost, which brings the ratio for drones to 5 to 1. That's close enough that it's not legitimate to claim superiority for drones. The weapons will be the same no matter the crew status, and will likely make up most of the cost. Performance is likely to suffer more than cost.
And to top it off, you can't claim superiority for a method because you use drones and I don't. If I did, would your plan still work? That determines cost-effectiveness.

You're going to want to capture my orbital infrastructure, not destroy it.

The efficiency of a projectile launcher will likely be negatively influenced by speed. You still have to deal with all of that waste heat.
And close force ratios are perfectly reasonable. Guided projectiles would help no matter what. Consider:
In my previous example, it took 7 kilotons to blanket the area. If I instead use projectiles that will home for the 60 seconds before impact at 1 m/s2 I need 27 tons. Which is more effective?

Milo:
That was pretty much my point. Maybe some flares would limit the areas people could be in some as well. (You can't go into the outer sections, and don't spend much time away from the core.)

Byron said...

(continued)
Clay, a landmine won't be enough to disable a ship in most conditions. And I'm fairly certain that it won't be terribly practical to boost stuff to that velocity any time soon. And 1 per second? I laugh at you. How is that supposed to stop me? My analysis requires a total of 268,000 projectiles. Yes, you can cut that by a factor of up to 5 if we disregard point defenses, but it still doesn't allow you to force me to do that much. IE, you can't force me to use 30 m/s of delta-V with your ammo load. This plan won't work. If we can shoot as fast as you want, the ammo required is still a lot. Your logistics problem is far worse than mine. After all, you need a bunch of rocks every day, and all I need is remass. Plus, what's to stop me from shooting at your drones with guided rounds, and killing them.

Clay said...

Bryon:

I don't know how else to say it. I'm not trying to stop you with these projectiles. I'm not trying to stop you with these projectiles. I'm not trying to stop you with these projectiles.

These projectiles are not designed to kill you. They are designed to make you move around and burn fuel and not defend your space stations and home planet. At best, they may knock out some piece of this laser you have on your ship either by shaking it out of alignment, damaging it marginally, or--and this is the big one, damaging your radiators. It's the radiators I want.

If I do even try to kill you, it's a guided nuke.

But I won't. I'm not trying to stop you with these projectiles. I'm not trying to stop you with these projectiles. These projectiles are not designed to kill your ship.

On the other hand, if you don't dodge, I will knock out your radiators which will take out your point defense. And then I will nuke your ship.

But don't worry. Just do "the dodge" and watch as I incinerate your civilization.

Which reminds me. You keep telling me what I'm going to do with your orbitals. I don't mind you giving me your prediction of future tech, but I still get to decide my actions. So let me tell you, once and for all, what I'm going to do to your orbitals and probably your planet. I'm going to nuke them. Take that as a given. Dodge that.

I can't honestly believe that you think this giant manned ship, with all its life support, is only going to cost 5 times my drone. How many backups does your ship have in case the life support goes down. How much mass for the different areas of the ship for them to live on, exercise in, sleep in, control the ship from, store consumables, go to the bathroom, etc...

And your assumption about the science stuff driving up the mars mission is ridiculous. Come on. Be fair.

At least my numbers are based on something. You totally invented yours. It costs over a billion just to launch the space shuttle.

I have to ask, honestly, do you honestly think a drone is going to cost just 1/5th of a fully manned space ship.

I think I'll stop arguing now. I've made my case. Whether it convinces you is something else.

Byron said...

I did not claim that a "giant ship" is going to cost 5 times what a drone does. I'm saying that there is no overwhelming cost advantage to using drones. When have I ever specified what I'm going to build? And you seem to be disregarding rule 1 of warfare: no plan survives contact with the enemy. I think lasers are a good countermeasure here.
According to the laser weapons calculator, at 1000 km, you would have a spot size of 4.8 cm with a 10 m mirror and 500 nm beam. That's going to zap your drones before they can do anything. All I have to do is force them far enough back they can't be any threat. And you can't stop me from doing so. Pull back too far, and you simply can't fire enough shots. And if you can, the logistics burden would be too much.

Byron said...

And your assumption about the science stuff driving up the mars mission is ridiculous. Come on. Be fair.
What do you mean by that? Let your unwarranted assumption go unchallenged? My point is simple. You were comparing a probe with a manned mission. The manned mission will accomplish far more than the probe. Let's say the probe produced 1 unit of science. I estimate a manned mission would produce 100. Thus, we have to assume that 100 probes would have to have equaled one manned mission. My ratio, though a guess, is likely far closer than yours.
And no, I'm not saying a drone would be a fifth the cost of a manned ship. What I'm saying is that for mars science (which is the only thing we can really discuss here) I can accomplish 5 times as much per dollar with probes. As for space warfare, I don't know. Nor do you. However, I'll give an example. In Rocketverse, a ship I built for about $1 billion and that massed 300 tons dry, had a total crew system (life support, habitat, etc) of 54 tons and $21 million for a crew of 18. Performance would be better without the crew, but cost would be only slightly less. So no, drones aren't all that great.

Milo said...

Clay:

"How do you hook up with a fuel barge if you're dodging? And how do you keep me from blowing it to kingdom come first."

It's moving in synchronization with me (in order to be able to dock), meaning it's dodging too.


"More practically, if you dodge drone-1's shot you're correct--it won't hit civilians. The problem is that while drones 1-50 are tying you up, drones 51-100 are slagging your civilization."

Then I have to make a choice of which 50 drones to spend my time shooting at, a choice I would have to make independantly of whether I'm using ships or stations. This is a decision I will be making entirely independantly of how I'm using my thrusters, which are different systems that don't interfere with my weapons.

Also, you just committed a war crime by attacking civilians.


"They are designed to make you move around and burn fuel and not defend your space stations and home planet."

I don't know how else to say it. Defending does not hamper my ability to also attack. Defending does not hamper my ability to also attack. Defending does not hamper my ability to also attack.

The purpose of defense is to buy me enough time to hit back. If I kept dodging and doing nothing else for long enough, then yeah, of course you'd eventually kill me. But this takes you enough time that your drones would not actually last that long in real combat.


"I can't honestly believe that you think this giant manned ship, with all its life support, is only going to cost 5 times my drone."

A giant manned ship does not cost only 5 times a small drone. It might, however, cost 5 times a giant drone of comparable combat quality.

Your drone is cheap because it's worthless.

Clay said...

Your drone is cheap because it's worthless.

It's weird you keep arguing this point because I don't really disagree. They are worthless, or at least mostly so. Their appeal is that I don't have to win the battle to win the war.

I'm honestly laughing about this now.

I agree to disagree about how effective my drones will be against this wonderful ship you have that can jink in every direction, never breaks, has plenty of fuel, and all while still always targeting this giant mirror instantly, also in every direction, (it's a gunstar right? -- like in the last starfighter) to put your laser on target perfectly without any delay or heat problems. I don't know of any military gun that has this ability. But fine. Yours will. It'll even have a death blossom feature. COOL!!!!

And your reward for having these gunstars is watching my Ko-Dan Armada slag your planet. Hooray!!!

So what are your ships worth if you can't ever go home?

You keep pointing out the war crimes charge, but in our hypothetical future, this is no defense of your planet. It's just a legal point.

Geoffrey S H said...

@Clay:

If you want to force Byron to dodge, you will need a craft capable of carry in all those kinetics.

Now, I can see the advantages of carrying masses of the things- they have no guidance system that can be knocked out, and by their nature, they are hard to zap; small and numerous.

So, in a combined offensive sytem with torch missiles taking up his pds, lasers poking at his heat radiators and unguided kinetics swamping the battlefield and making life... difficult navigationally, I can see a use for them.

There one tiny problem though, and Byron's stated it time and time again.

PAYLOAD

Your craft would need kinetics in the MILLIONS or even billions of tons to make it effective. Now sure, if you do what I do and give your craft an antimatter drive and place the setting at the very, very end of the plausible midfuture scale, you might, just, make it seem believable, emphasising the way in which kinetics are supporting weapons to missiles and lasers.

Oh, and it would be like 2 modern day frigates slugging it out with their 5 inch main gun. Again, not implausible (if their pds can take missiles, then move closer to engage them with one more thing that might get through on top of all the other stuff you're throwing) but trying to state that it is PREFERABLE to torch missiles prior to him losing pds functions is...somewhat stretching belief.

Sigh... arguments seem to happen more and more here. I'm probably responsible for that.

Thucydides said...

Clay, I don't understand why you would shoot at an oncoming ship with anything unless you are planing to kill it. Several of the space warfare threads earlier on in this blog talk about using kinetics to overmatch a target, and the possible countermeasures.

Now if I were in charge of the invading constellation, I would be using my laser of stupendous range to to destroy the launcher and sweep these things out of the sky. Given these weapons can engage targets several light seconds out, we are looking at opening engagements beyond the distance between the Earth and the Moon. At that range I don't even have to think too much about the kinetics, because I can scorch your launcher. Inside of the lunar orbital distance, I am now close enough to start burning through metals, and by the time I am about 1.3 the distance from the Earth to the Moon, I am burning through super nano carbon(tm) stuff.

As for the pesky oncoming KKV's, an unmanned wake shield of rock, slag or ice flying well ahead of the ship will soak up the really small ones, and force your guided ones to expend their (much more) limited delta V to get around and target the main target. I can make you dance too, sir! Finally, small projectiles will meet the Whipple shield protecting vital portions of the ship, or the armoured citadel structure surrounding the crew and electronics.

If you really want to kill the ship, you wil need to launch thousands of KKV's, and probably similar numbers of penetration aids, launch them very quickly so they come in waves rather than lined up like the obliging Kung-Fu fighters menacing the hero, and if you can, launch them from a wide range of bearings and distance to occupy the laser of stupendous range and minimize the effectiveness of the wake shield.

WRT the cost of going to Mars and minimizing logistical considerations, Robert Zubrin laid it out a long time ago with "The Case for Mars". The overall cost was estimated to be @ $30 billion, and all the logistics lands planetside with the crew; nothing is wasted in orbit (although you might have a few relay satellites if you wanted to.

Geoffrey S H said...

@ Thucydides.

...Meaning that the only kinetic counter for such a laser weapon would be relativistic kkv's.

Thus:

Will we get lasers of stupendous range first or rkv's? (Hopefully neither, but man will probably find a way unfortunetly).

I'm genuinely curious as to your thoughts here. History is my passion, and technological progressions have been an idle little hobby of mine lately.

Geoffrey S H said...

Oh, and Clay, if you want kinetics, you can only pretty much have it with antimatter drives. Fusion, while powerful, won't cut it.

Byron said...

Um, you seem to misunderstand our position. It's simple. If you happen to be close enough to really constrain our actions, we can zap you with the laser. If you're not, we can zap your incoming projectiles. Where do you get the stuff to throw at us, anyway? It's going to have to be refined.

Byron said...

For fun, I decided to work out some of the math for Clay's drone. These are all guesses, but the seem plausible. I'm using Rocketverse as a base, because it has the only compiled numbers I know of. If anyone wants me to, I'll send them the sheet with the finished ship.
First, how much power does it need? Rocketverse doesn't allow 100 km/s coilguns. The efficiency is -420%. 35 is about as high as it can go. This seems more reasonable. However, I'll set it at 10%. Clay's 100 km/s 1 g projectiles have 5 MJ of energy each. Firing at 1 shot/sec will require 50 MW, and generate 45 MW of waste heat. At 1600 K, that's close to 70 m2 of radiators. The reactor to power this thing is 25 tons, and produces 200 MW of waste heat, which requires another 300-ish m2 of radiators. The coilgun itself masses close to 100 tons. Total cost is on the order of 538 million. All of the above ignores things like armor and engines. So how is this drone cheaper than the competing ship?

Clay said...

Alright, I concede. I guess it won't work.

But I do have questions. My reading on lasers is that they have big practical limitations. The biggest being

1) Heat
2) You have to keep your beam focussed on the same spot on my skin for a given period of time to burn a whole through my armor. (This depends a lot on my armor of course and the power of your laser)
3) This gets harder if I spin. It also gets tough if I'm flying right at you and I have a big head of armor right at the front.
4) Finally, range diffusion means these long shots are less effective the further out you go, which means you burn longer and generate more heat.

There are big assumptions going on with dumping that heat that nobody seems concerned about. Everybody also seems to take it for granted that microshots moving super fast aren't going to be a problem.

Byron said...

1. The heat is either dealt with by radiators or heat sinks. If you keep pointed towards the enemy, you can armor the front edges of the radiators. It's not perfect, but we really can't deal with it.
2. That's what pulsed lasers are for. The problem is that cb lasers are easier to model.
3. See above. The second part is just a fact of life.
4. Yes, but you're less vulnerable if you are farther away.
I don't think that targeting fast-moving objects is that big of a deal. Put the beam in front of it, and blast it as it goes by. If it's coming straight at you, then it's not a problem at all. CBDR is your friend.

Clay said...
This comment has been removed by the author.
Clay said...

The heat is either dealt with by radiators or heat sinks. If you keep pointed towards the enemy, you can armor the front edges of the radiators. It's not perfect, but we really can't deal with it.

What do you mean you can't deal with it?

Also, what happens if bad guys are closing from multiple sides?

Byron said...

Physical impossibly. It's more practical, but I still don't see it as working well. You have to haul a bunch of stuff, and shoot it off with the intent of missing. I know that the same thing happens with kinetics in AVT, but those are guided, making it a lot more efficient. It actually might be useful, if the kinetics are low delta-V guided ones.

Byron said...

There is really no way to solve the problem. You either keep the edge of the radiator pointed towards the enemy, or store the heat in heat sinks and hope you don't run out. It's not perfect, but there's no alternative. And if you're under attack from multiple sides...that's a problem. I suppose two radiators would make it so there had to be at least three attackers to get the radiators.

Geoffrey S H said...

Maybe I should change my proposal to Clay and state that if he wants unguided kinetics to throw at missile and laser ranges- he'll need ALOT.7 kilotons for a predictable orbit. Thus How many tons for an unpredictable orbit. If your craft can carry millions of tons, then can it stop a similar craft that is UNLADEN.


Is a turret that fires unguided, unexplosive kinetics better protected than a mirror when the eyeball frying starts?

I take back the "point-blank" comment. It was stupid and laughable.

I think we need to establish what kind of lasers and missiles we are using here as well. Have I missed that?

As for the nature of the kinetics, of course it has to be refined, you've confused me there. If there is a use for unguideds, then they will be man-made. If there isn't then they won't be. I'm sorry, but I don't entirely know how that relates to the debate.

This was meant to provide some sort of compromise, but I've just been a complete ignoramous. Sorry about this.

Geoffrey S H said...

DRAT, I took too long to reply

Unless you want to armor the entire craft, closing from mnultiple sides will simply get you killed. No way to square it.

If you can predict where they are going anyway, it shouldn't happen to you.

Rick said...

First, a gentle reminder to everyone to be easy with each other, and not take offense when people word things clumsily.

On the dodging game. One gram hitting at 100 km/s releases about as much energy as 1 kg of TNT, roughly 4 MJ.

One effective defense is indeed armor, specifically a Whipple shield. The shield can have a much slower cross sectional density than the pellet, because it does need to stop the pellet, just vaporize it, or merely pulverize it.

A round 1 g pellet of Super Carbon Nano Stuff is about 9 mm in diameter. If it hits a 0.1 mm shield, it loses about 1 percent of its kinetic energy, enough to vaporize it. So my Whipple shield has mass of about 300 gram/m2, and a few tons will protect a 200 meter diameter hab.

I can also zap the pellets. I only need to engage the ones on collision course, and as noted, CBDR is my friend. A low power laser with a wide beam is plenty enough to illuminate the incomings, and then a 50 kJ zap vaporizes it. Probably a zap of as little as 1 kJ is enough to deflect it by impulsive shock from flash vaporizing the surface.

Or I can follow the US Navy's advice and shoot the archer, not the arrows. How are these kinetics being thrown? If they are being fired from a coilgun, the gun has to impart 4 MJ to each pellet.

If the pellets are being tossed from a bus, the bus needs a high specific impulse drive, and will take weeks to get up to speed. (Except with Orion, but 100 km/s is awfully fast for Orion.) And a bus produces a one time wave, not a steady stream.

I don't see this as effective. If I get tired of replacing Whipple shields when they're shredded, I'll just zap you or whack you with some guided kinetics. This seems like a weapon that doesn't hurt me, it only gets me mad. :-)

Byron said...

By "refined" I meant that you can't throw rocks. At least not 1 g ones. Bigger ones might work, with a "sabot" of sorts.

If you're interested in actual mathematical comparisons, join us at Rocketverse.

Rick, it's exactly 5 MJ.

Rick said...

Tony serves up some fascinating heresy:

what is the purpose of a station?

That question is probably worth a front pager, and I'm not going to try to engage the whole issue here. First the (very important) narrower question of expeditions.

Much of the logistics support I see keeping upstairs is human support. Onboard Mission Control. Main sick bay and most of the medical staff. Equipment and supplies that may or may not be needed.

Anything or anyone you avoid landing on the surface saves on the considerable effort of getting payloads down, and in the case of people getting them back up.

My thinking is colored by a couple of assumptions. One is that if we are sending a lot of people to the planets, we probably have a high ISP drive, and therefore a logistics system to support deep space ships that never land.

I grant that this need not imply the rocketpunk era vision of stations as orbital spaceports where ships are serviced and repaired while the crews take R&R in the station bar.

But a much bigger factor is my suspicion that prolonged low gravity will be nearly as unhealthy as prolonged microgravity, making spin habs the only option for prolonged human presence. The surface would then be a place people go on a 6 month rotation.

Clay said...

Bryon:

Looking at your figures for one of these drones. (I know I know but still)

You calculate 10% efficiency--meaning 90% inefficient. Is this the same efficiency you use for lasers?

What would the radiator size and energy consumption look like for .5 gram shooting at 100 k/s at 50% efficiency?

Jim Baerg said...

Tony: "Because of the non-coplanar relationship of planetary orbits, the parking orbit you launch into to go from one or the other is unique to each surface launch site and interplanetary transfer opportunity. A station in any conceivable orbit is likely in the wrong orbit for initiating a transfer."

What non-coplanar relationship? All the planets orbits are inclined only a few degrees from each other. If you are going from earth to anywhere in the solar system you launch into an orbit in the plane of the ecliptic & then from that orbit get into an interplanetary trajectory. If you have low thrust high ISP interplanetary spacecraft they will rendezvous with the surface to orbit shuttles in low orbit in the plane of the ecliptic. Whether there is any reason for there to be a permanent space station in that orbit for them both to rendezvous with is another matter.

Surface to orbit shuttles should be launched from somewhere between the tropics of Capricorn & Cancer to allow easy access to the ecliptic plane orbits

If some sort of momentum exchange tether system turns out to be practical you will want one in ecliptic plane orbit for transfer between surface to tether shuttles & transfer orbits to the moon & planets.

Luke said...

Clay (and Byron):

Coilguns are linear electric motors. Good brushless electric motors these days (and at those speeds the coilguns better be brushless) can get efficiencies of around 90% to 95%. They tend to be nearly constant power machines, with pretty flat efficiency curves regardless of speed.

The main limit will likely be the length of the coilgun needed to get your projectile to high speeds. The analysis depends on whether you have a synchronous (using ferromagnets) or asynchronous (using induction) motor, but just for example, suppose your coilgun can generate 1 tesla fields (a good number that will not saturate the ferromagnet). If the entire magnetic energy gets transferred to the projectile, the projectile will gain about 400 kJ per cubic meter swept out. Our presumed ferromagnet is probably mostly iron, with about 8000 kg/m^3. To reach 100 km/s, you will need 40 TJ per cubic meter. Since this is 100 million times the energy density of the field, you will need the projectile to sweep out 100 million times its volume in order to accelerate up to the desired speed. This means you need an accelerating track 100 million times the length of your projectile. with the proposed dime-sized projectiles, with maybe 1 mm thickness, you are looking at a track 100 km long.

Luke said...

Other thoughts on high speed coilguns:

Much of the inefficiencies of a coilgun will occur in the projectile, either as a result of the high fields jostling the magnetic domains around or due to ohmic heating from the inductive currents (depending on whether the coilgun uses synchronous or asynchronous principles). If we assume that half of the inefficiencies is due to what goes on in the projectile, we are looking at heat between 2.5% and 5% of the kinetic energy of the projectile. At 100 km/s, this translates to 100 GJ to 200 GJ per cubic meter of projectile, or 12 MJ/kg to 25 MJ/kg. This is three to six times the specific energy liberated by detonating high explosives, so you can expect your projectile to explode like a bomb inside your coilgun barrel.

Clearly, efficiency will be at a premium to prevent your projectile from disintegrating before it even leaves the barrel. One possibility is to use induction in a superconductive projectile (also known as the Meissner effect, a sort of perfect diamagnetism coming from perfect induction. Although this design would rely on induction, it would actually be synchronous so it is unclear if it would be called an asynchronous linear motor or not). This limits you to very cold temperatures, and to fields less than the superconductor's critical field (the latter of which limits how short you can make the coilgun).

Thucydides said...

Geoffrey S H,

Based on current knowledge and open source documents, it seems the lasers of stupendous range are not just plausible midfuture items, they are practically in service now.

Solid state lasers have reached the military critical power range of 100kW, and various chemical lasers have been demonstrated on ground and airborne platforms with sufficient energy and tracking to engage incoming mortar rounds and missiles.

Key areas for development are improving the efficiency and minimizing waste heat, cycle speed (to prevent the laser emitter from being overwhelmed) and refining the adaptive optics and optical train. Ruggedizing the entire assembly and miniaturizing the weapon system to fit vehicles smaller than Boeing 747 cargo jets or surface cruisers. I predict the perfection of "Surfatrons" (Plasma wake-field accelerators) will provide compact beam sources for military FEL's, now we can have megawatt beam power on a 747 or a 100kW beam on a F-35.

Boosting the parts into space and assembling them in orbit provides the basis of space weapons which have fewer optical limitations, and thus greater range. If this analysis is close to correct, than a first generation military space platform with a megawatt laser will be at least the size of a 747. It might also have a vague resemblance in terms of shape, with large wing shaped radiators, a thimble turret in the "nose" to house the mirror and so on.

Relativistic KKVs are still magitech, since there is no practical way with near or midfuture technology to accelerate to those speeds in any practical manner. Jumbo ORION boosters might get you close, but present a massive target during the boost phase (and practically scream "come get me" with the massive energy release). A "Skydiver" on a hyperbolic orbit deploying a solar sail at the closest approach to the sun can theoretically reach .13c, not bad but not relativistic speeds either.

Byron said...

Maybe my mass figures were off somewhat. 100 km of track is still a lot, though. Thanks for the info.
Luke, do you have penetration equations I can borrow? I'm working on a space battle spreadsheet, and I need data on what happens when a ship gets hit.

Milo said...

Clay:

"It's weird you keep arguing this point because I don't really disagree. They are worthless, or at least mostly so."

What this means is that you shouldn't be comparing the cost of a station or a battleship against the cost of a drone. You should be comparing the cost of a station or a battleship against the cost of an entire swarm of drones.


"And your reward for having these gunstars is watching my Ko-Dan Armada slag your planet. Hooray!!!"

Clay, look at it this way. What kind of space force would you like to have defending your planet against slagging by drone swarms? What kind of force can (cost-effectively) wipe out the entire swarm fast enough to keep your planet from getting slagged, without getting blown up itself first?

If nothing can, then you have MAD. This isn't a failing of any particular defense, it's just that your swarms themselves are absurdly powerful.

If something can, then you have to explain what your force can do - defensively, not offensively - that an orbital fort or two can't.

On a side note, my planet isn't defenseless. It has its own surface-to-orbit area defenses. Those mean you need a somewhat concentrated effort to do serious damage, not just a few harrassing drones. (In addition to the general difficulty of, you know, destroying a city, through an atmosphere.)



Geoffrey S H:

"Sigh... arguments seem to happen more and more here. I'm probably responsible for that."

What? Why?

Milo said...

Clay:

"1) Heat"

And your mass drivers aren't generating any?


"2) You have to keep your beam focussed on the same spot on my skin for a given period of time to burn a whole through my armor. (This depends a lot on my armor of course and the power of your laser)
3) This gets harder if I spin."


This is part of why I favor pulsed lasers. Continuous-beam lasers aren't really as useful as people make them out to be.

If your armor is thick enough to fully resist my strongest pulse, then yeah, I'm in trouble unless I can aim for a weak spot. But that armor also works against kinetics. Your drones won't have more armor than my battlestation. In fact, since armor mass for a given thickness scales with surface area rather than volume, it's one of the better reasons for justifying larger vehicles.


"4) Finally, range diffusion means these long shots are less effective the further out you go, which means you burn longer and generate more heat."

Lasers are, however, likely longer range than kinetics, which while theoretically retaining their full shot energy at any distance, become much easier to dodge at larger distances.



Byron:

"2. That's what pulsed lasers are for. The problem is that cb lasers are easier to model."

Are they now? Luke's continuous beam calculator has far more variables than his pulsed beam calculator.



Clay:

"Also, what happens if bad guys are closing from multiple sides?"

Either I have multiple guns (it's not unreasonable for a huge fort to house more than one weapon), or if I only have one, then it must be a really big one that can kill your ships quite quickly, allowing me to pick them off one by one without taking too long. Granted, the latter requires a good turret, which is difficult for a gun this size. But I only need to move the mirror, not the entire laser device.

Milo said...

Rick:

"Probably a zap of as little as 1 kJ is enough to deflect it by impulsive shock from flash vaporizing the surface."

1 kJ? Really? That's in handgun bullet territory.


"Much of the logistics support I see keeping upstairs is human support. Onboard Mission Control. Main sick bay and most of the medical staff."

Oh wow. Let's make it so that in case of a medical emergency, the nearest treatment facilities will be hundreds of kilometers overhead - if you're lucky! A rocket launch expensive, way too slow, and the gee-forces could be hard on someone who's already injured.

As for mission control... you could, I guess, but in any properly functioning organization the number of managers is going to be less than the number of people doing actual work. So your scientists' base will have room for a few commanders, even if they're not scientists themselves (which they might be - when people are so expensive to send, you try to send useful ones). Human morale alone may make it a good idea to keep the entire crew in one piece.


"Equipment and supplies that may or may not be needed."

That's some questionable mission planning if a significant portion of your payload mass is of dubious necessity.

Anyway that can almost be read as "unimportant stuff". So the only things left in orbit will be unimportant stuff? Good to know.

Byron said...

Milo:
Yes, but the same isn't true of the other laser calculator. For back of the envelope, cb is easier.
And 1 kJ might be enough for a 1 g projectile. Standard 9mm pistol bullets are 7-9 grams.

Milo said...

Rick:

"My thinking is colored by a couple of assumptions. One is that if we are sending a lot of people to the planets, we probably have a high ISP drive, and therefore a logistics system to support deep space ships that never land."

Yes, but this logistics involves launching supplies from the surface of a planet the vacuum-only ship is orbiting. Not the other way around.

The only stuff kept permanently in space is the stuff that needs to be used in space (like spaceships).


"I grant that this need not imply the rocketpunk era vision of stations as orbital spaceports where ships are serviced and repaired while the crews take R&R in the station bar."

I think that's actually one good reason for justifying space stations, if only small ones. Since your deep space ships never land, you're going to want some degree of ship maintainance equipment in orbit to service them. This assumes that the equipment is sufficiently long-lasting that avoiding repeated launches is actually worth it. Your station still needs supply shipments from below to refill raw materials and replace worn down equipment.

I don't know how much of a port city can be built around this premise of a maintainance station, but in any case I'm pretty sure those won't represent the majority of your civilization.


"But a much bigger factor is my suspicion that prolonged low gravity will be nearly as unhealthy as prolonged microgravity, making spin habs the only option for prolonged human presence."

Well, I can't argue with that. Not until we've had some actual experiments in the subject.

I have a more optimistic view on our ability to adapt to aberrant gravity, either naturally through acclimation or artificially through medicine or genetic engineering. But I haven't tested it. (People can already survive in zero gravity for months at a time, with some health deterioration but not so much that people refuse to do it. How long could we last with fully one-sixth of Earth's gravity? Besides, the first bit of gravity - that provides enough of a sense of "down" to have a floor to stand on - probably counts the most.)

Remember, altitude sickness can induce headache, vomiting, coma, and death within hours in the strongest of us. Looking at that, you'd think Tibet would be completely uninhabited. Wrong!

Luke said...

Thucydides:

While I generally agree with what you say, this one point:

I predict the perfection of "Surfatrons" (Plasma wake-field accelerators) will provide compact beam sources for military FEL's

seems unlikely. Mostly because plasma wakefield accelerators are inherently low efficiency. In the acceleration step of the electron beam alone, you are likely to recover less than 10% of your input laser energy, which will itself have inefficiencies. This is acceptable for a research institution. It is not so good for a weapons platform operating with a strict heat and power budget, especially when superconducting linacs can get acceleration efficiencies much higher than this (perhaps 30% to 60% of wall-plug power going in to your RF cavities could be expected to come out in the beam).

Rick said...

Medevacing to orbit is expensive, but not that slow (depending on launch procedures). Launch acceleration from the bodies we're discussing is less than 1 g. The alternative is paying to land the entire sick bay facility, then haul it back to orbit for the trip back home (or else have a second sick bay aboard the ship).

Agree that there's no real argument about the medical effects of fractional gravity - we won't have a clue until we experiment. So this is a pure 'author's choice' question.

Luke said...

Byron:

A formula for penetration that works over a wide range of impact velocities was developed by A. Tate
(J. Me&. Phys. Solids, 1967, Vol. 15, pp. 387 to 399 and J. Me&. Phys. Solids, 1969, Vol. 17, pp. 141 to 150). Unfortunately, it involves numerical integration. If you assume that the pressure to deform the impactor is equal to the energy per volume to excavate a crater in the target, however, you can put it in an analytic form
d = L (1 - exp{-B V^2)/mu
B = mu rho_p / (2 (1 + mu) Y_p)
mu = sqrt(rho_t/rho_p)
where d is the depth of penetration, L is the length of the projectile, V is the initial velocity of the projectile, rho_p is the density of the projectile, rho_t is the density of the target, and Y_p is the compressive yield strength of the projectile. This result isn't too bad at moderate velocities and approaches the correct hydrodynamic limit at high velocities.

This analysis does not take into account additional penetration which might come from the kinetic explosion of the projectile. The size of the resulting crater can be estimated if you know a value R_t, which is the energy per volume to excavate a crater in the target (note that this has units of pressure). This value is approximately three times the compressive yield of the target. So if you know the kinetic energy of the impactor you can determine the volume of the crater, and the depth of the crater will be somewhere close to the cube root of the volume. If this is larger than the penetration depth, use the crater penetration. Otherwise, use the penetration depth.

Note that the most effective kinetic impactors will be long rods, since the depth of penetration is linearly proportional to the length of the projectile.

Byron said...

Thanks.
What about lasers? I've looked at your site, but what would be reasonable equations for cb and pulsed?

Milo said...

The formula here (crater_radius = constant * (shot_energy / armor_strength)^(1/3)) is probably a good guess for any weapon that works through cratering (relying on applying large amounts of energy to a small point), including not only pulsed lasers but also high-speed kinetics (but not slower ones where long-rod penetration is important).

The exact formula Luke gives is probably inaccurate since he says he's assuming cylindrical craters (useful to simplify the math but not really realistic), and he explains on the site some confusion about a mess of different ways to measure strength. Still, should be fine for simple calculations.

Luke said...

Byron:

In the most pared-down, simplified form, the penetration of pulsed lasers and CW lasers are about equally difficult to calculate.

For CW lasers at high enough intensity, the primary means of penetration is melt-erosion of the solid (the laser impinges on the solid, melts a thin layer of the surface, and evaporates enough of the melt to produce a hypersonic jet of escaping vapor), in which nearly all of the energy of the laser goes into melting the solid and only a small amount goes into evaporating and accelerating the jet. This doesn't work on carbon (like the sooper carbon nano-stuff armor) because carbon sublimates rather than melts, so you will need to input the heat of evaporation rather than the heat of fusion. This method starts to break down once you don't have enough intensity to develop a high pressure vapor jet, in which case you need to input enough energy to vaporize a hole rather than just melt it.

For pulsed lasers, the energy per volume to excavate a crater is about three times the compressive yield strength of the material (there's a formula involving not just the compressive yield strength but the shear modulus as well, but the result depends only logarithmically on the ratio of the shear modulus to the compressive yield, so it can mostly be ignored and replaced by three times the compressive yield). The diameter of a crater will thus be about the cube root of the pulse energy. Once you have figured the number of pulses and the energy per pulse, it becomes a simple matter to determine both the depth and radius of the hole that is excavated. This method breaks down when the spot size of the laser pulse is larger than the crater it would produce if focused to a spot. When this threshold is passed, it quickly reduces to the CW laser values.

Byron said...

Thanks again, Luke. I should have the final spreadsheet ready soon.

Byron said...

One more question:
What happens on the other side? Should I just assume whatever gets hit is destroyed, and that's it, or what?

Clay said...

Wow! Thanks Luke. I'd say that puts paid to coil guns forever.

Now, here is my next piece of food for thought: do you attack the ship or just the radiators.

I still like this idea of killing the radiators to knock them out of the fight.

So scrapping the projectiles, and moving on to pulsed lasers, is it possible to build small drones to blast away radiators.

Luke said...

Byron:

You know how big of a hole a laser makes, so you can decide if what is on the other side can survive with a hole that big in it.

For projectiles, the hole tapers from wide at the entrance to narrow at the end. You can estimate an average hole width by finding the volume of the crater that is excavated, dividing by the penetration depth, and taking the square root. Of course, the overpressure might cause additional casualties to anyone in a compartment penetrated by a kinetic.

Clay:

Coilguns may have some use, but 100 km/s boosts are unlikely. You would need to keep the velocity low enough that the projectile does not melt (which also helps with the barrel length, since the barren length goes as the square of the final velocity), and would probably use the induction variety since with ordinary conductors there is no upper limit to the field it could handle (allowing a much shorter barrel - barrel length goes down as one over the square of the magnetic field). A 3 km/s boost with a 30 T field would require a barrel 100 times the projectile length, for example, and would have 1000 times lower energy density.

Small lasers tend to lose out to big lasers. The reason is that big lasers have a longer range, and since it takes a long time for the small lasers to drift through the engagement range of the big laser until they can commence firing, this gives the big laser plenty of time to fry the small lasers. This argues against small laser-armed radiator killing drones.

Anonymous said...

"And? If you have to switch horses, getting into orbit is all of the way to orbit and none of the way to your ultimate planetary destination.

Or, looking at it from the arrivals, rather than the departures, perspective, getting into orbit is all of the way into orbit and none of the way down to the surface.

Or, looking at it from the shipper's business perspective, it's all of the way to more expensive shipping"

Yes, of course. And from a MISSION perspective, you're halfway to mars.

A ship that can launch from earth AND reach Mars in a matter of 2 months isn't anywhere on the mid-future horizon, discounting maybe Orion, if you happen to have a place on earth you can nuke to your lesure.

As for Orbits and Planes, you can change plane from any orbit to any orbit. But it does take quite a nice amount of delta-v, which is why plane alignement will also be done by high efficiency drives right AFTER orbit eject. On an interplanetary scale, the plane differences are not very significant, really.

Which all sums up that you pretty much NEED a station in a sensible plane (i.e. somewhere close to the ecliptic) to do the freight turnover etc.

Jedidia said...

Sorry, forgott to put my name up there...

Byron said...

Luke, one more question. How much energy, velocity, whatever, is lost when the projectile or laser penetrates a piece of armor?

Rick said...

Radiators may be less vulnerable than we imagine, precisely because they are so large that punching small holes in them may only degrade them slightly.

On the other hand, critical damage will take them out quickly, the equivalent of dismasting rather than simply shooting holes in the sails.

But as longtime readers know, I believe that a laser versus laser battle is an eyeball frying contest. The fastest way for me to both end the pain and put you out of action is to zap your laser optics.

If you are zapping back at me, your optics have to be unshuttered, exposed to my beam. And I don't need to burn through them, just scorch the surface enough to ruin their optical quality.


Which all sums up that you pretty much NEED a station in a sensible plane (i.e. somewhere close to the ecliptic) to do the freight turnover etc.

Well, you don't actually need a station simply to transfer cargo (or propellant, people, etc.); the ships can just rendezvous and dock. A station, if you have one, is to provide secondary or longer term services - maintenance, a layover point for crews, etc.

I have taken the importance of stations for granted, but this may be a rocketpunk-era trope that turns out not to fit the realities of space travel.

Jedidia said...

Well, you don't actually need a station simply to transfer cargo (or propellant, people, etc.); the ships can just rendezvous and dock.

That is of course true. But if you have significant turnover, it might be cheaper in the long run to have facilities up there that can handle the cargo faster than a shuttle could, and that spares your shuttle the effort of having to carry any equipement for the task.

On the other hand, I'm still wondering if it wouldn't be cheaper in the end to just deorbit the containers. This would demand a heatshield on every container, as well as a chute system and some cushions (or, in the case of earth, some floats). Might not be cheap in the weight budget, but I haven't done the math to see if it might not pay off after all.

But even if the weight penalty would proof managable, there's still some open questions, that also figure into the viability of a station: A shuttle going up to get cargo down can also carry cargo UP. It's more expensive than sending the shuttle up empty, but it's by far cheaper than sending another one up with cargo and having it return empty.

Such a bidirectional service would call for a designated gathering place. Of course you can time two ships to be in similiar orbits when the shuttle arrives, but if you have enough freight trafic that will quickly become a major logistic concern. A static meeting point would seem a logical solution, especially since you don't have to plan the timings so well. You can send up freight for a freighter that arrives in a week while getting the freight of a ship that just arrived, and leave it at the station for the freighter to pick up.
Also, any crew will probably need shoreleave. If you rendevous in a random orbit, you'll have to send TWO empty shuttles up, unless you have one big enough for crew AND cargo (and rated for both). When you have a station, you can make use of the normal ferry lines that will probably (maybe) exist. Or you have a big enough station that the crews can have two weeks of vacation without missing anything, but that would be somewhere about B5-size, not really what we're discussing here.

So I'd say: If you are in a backwater colony in which the most important date of the year is the arrival of the suply ship, you can comfortably do without a station. If you have any serious turnover going on, as should be expected on earth in a scenario we're talking about, and maybe at one of the older, more grown colonies with, say, a hundred thousand people (I kow, that's a lot. But the original topic was to have a station around jupiter as crises intervention, so I may assume that there are at least that many people that could make trouble), a station seems still a major logistical advantage.

(hey, I found out how the cursives work :D)

Jedidia said...

Sorry for the double post. I got an error "the URL you requested is too large" and thought my post wasn't submitted...

Thucydides said...

The main reason to favour a surfatron over a liniac in a weapons system has to do with size. A liiac needs metres to accelerate a beam to the same sort of energies a surfatron can accelerate the electron beam to in milimetres.

A very complicated calculus will be needed to work out the trade offs, but for places you need a very compact beam generator, such as a fighter jet, UACV, Armoured Fighting Vehicle etc. then a surfatron *might* prove the better choice, especially if the choice is a low efficiency beam generator or none at all....

Geoffrey S H said...

Rick:

"But as longtime readers know, I believe that a laser versus laser battle is an eyeball frying contest. The fastest way for me to both end the pain and put you out of action is to zap your laser optics."

...which is why I've always been pro-kinetic. An access port, with an inert warhead shielding the missile could be alittle more survivablein such a contest- even if its just a back-up to more powerful lasers.

Thucydides:

Do you think lasers are thus overwhelmingly superiror to kinetics?

Everyone:

Are chem missiles good enough as a counter?

Milo:

Long story. I've manged to make many points the last few months that have stretched believability. More than most. I keep preserving useless concepts. Nevermind.

ANYWAYS

"Well, you don't actually need a station simply to transfer cargo (or propellant, people, etc.) the ships can just rendezvous and dock. A station, if you have one, is to provide secondary or longer term services - maintenance, a layover point for crews, etc."

While we are talking of stations... why just habs? Cage works for the repairing of spacecraft- any use for them outside of earth orbit- might they be folded up and transported or might they be too rigid?

Any functions so large-scale that a station radically different from spin habs and quarters would be needed?

Tony said...

Re: planes and orbits

I'm not sure why it is that people think a plane change of any magnitude is trivial. In fact it's so non-trivial that we don't even do them if we can avoid them. If you're sending a spacecraft to Mars, for example, you launch into a parking orbit in the plane of a unique transfer orbit. The plane of the transfer orbit happens to contain the Mars orbit inserion point or Mars atmospheric interface point. For multiple voyage, orbit-to-orbit spacecraft, no matter how much delta-v is available, one would think that the common approach would be to feng shui, as it were, gravity capture at the destination, putting oneself in a good parking orbit for the next scheduled departure.

People seem to be thinking in terms of a Space Grand Central Station. At Grand Central Station, you get off the bus or local train, or unload cargo from a truck. There you wait in the lobby, or your cargo is stored in a baggage handling room, until the time comes to board and load a train on the interstate line. The reverse happens at the other end -- people debark and cargo is unloaded, people grab cabs/bussess/trains to their final destination, and cargo is either transshipped or put on a truck for the receiver.

But that's not going to happen in space in the plausible midfuture. No matter how many ships are departing through a window, they're all going to the same place, and have all been parked, unoccupied (unoccupied? really? stay tuned...) for months in individual orbits relevant to each ship's planned departure. Yes, that's true even with high delta-v propulsion. Taking Mars transfers as an example, the window is widened somewhat, but you still have to leave when the Earth and Mars are realtively close.

Also, the spaceship operators want to maximize pax and cargo per departure. They're not going to want to spend fuel/remass on orbit matching with a station that isn't in the right orbit at arrival and won't be in the right orbit at departure.

The supposed convenience of the orbital station for crews doesn't even hold up, when the departure windows are many months apart. The crews would mothball the ship at the end of a journey, go down to the surface to do whatever their business is there, then, many months later, come back up a few days before the pax and cargo start arriving for the next voyage. Any necessar maintenance activity would be undertaken by a maintenance crew prior to the flight crew's arrival, or be done by the flight crew itself, as part of voyage prep.

Nota bene:

All of the peri-voyage activity takes place within a few weeks before and after the departure and arrival windows, and during the windows themselves. If you have an orbital station for interplanetary transit support, most of the time the staff wouldn't be doing much of anything.

Also, given sufficient delta-v -- advanced nuclear-powered VASIMR, perhaps -- travel doesn't necessarily stretch out over time to fit a relaxed window. Returning to our Earth-Mars example, an opportunity arrises in which every 26 months a Mars round trip mania occurs. Everyone with a ship leaves for Mars at about the same time, does a short turnaround at Mars, and comes back, avoiding a "wintering over" situation at the Mars end. The high work rates in Earth orbit happen twice, about five months apart. At the Mars end, there's one high activity period scheduled during the time between the Earth arrival and departure windows.

Rick said...

Purple/green raises its head again!

In principle, a combination of lasers and kinetics should be superior to either by itself. Suppose you have the more powerful laser, so that if I unshutter inside laser range I'd lose the eyeball frying contest. But if I throw some kinetics at you, you have to engage them, and I can zap your laser while you're zapping my kinetics.

Generally I've come to see lasers and kinetics as not a purple/green but as complementary, tactically and strategically.


There's no reason cageworks and other facilities couldn't be transported. Milligee accelerations don't require a lot of structural bracing.

Geoffrey S H said...

"Purple/green raises its head again!"

Oops! ;)

One odd idea I had was to give a station under the control of a national power a little both filled with earth from that particular nation- symbollically, the station thus is soverign territory for that nation, and is essentially "part" of that country. Thus, all rules and laws of that nation apply there- home away from home. Thus, with modules, where would the box go if it was split up to make part of another station, (or two?). With the bigger modules? The most important? Perhaps two boxes or more would be needed.

Its abit late over here, and that is honestly all I can think of to add to the discussion on stations right now.

Rick said...

Well, a box of soil would just be a symbolic grace note - I would imagine that if a modular were 'hiving' into two stations, the soil would be divided, and some more soil from the homeland added (either quietly or ceremoniously) to both.


I believe that inclination changes for high ISP drive ships are 'cheaper' than you would think. This is a byproduct of one shortcoming of those drives, the fact that their acceleration is too low to take advantage of the Oberth effect.

A high ISP ship spirals out gradually from low parking orbit. By the time it transitions from the spiral to its interplanetary insertion its orbital speed around Earth is quite low, probably less than 1 km/s, and it can execute substantial inclination changes with burns of a few hundred meters per second, about 1 percent of mission delta v.

You still have to justify it, versus shaving a day off the trip or simply saving 1 percent on your fuel bill, but it makes the cost of reaching a station much easier to justify.

One justification is to make more efficient use of shuttle capacity. If ships are all on different parking orbits, shuttle missions all have to be dedicated to a particular ship. If a ship has 150 passenger berths it cannot be served efficiently by a 100 seat shuttle, but this is not an issue if the shuttles serve a station. Passengers just buy a ticket to the station, then board their ship. Likewise with cargo shipments.

Similarly, if you have a cageworks to service ships between missions, the ships need to rendezvous with it anyway, and the cageworks will be a de facto transfer point, whether or not there is a facility there specifically dedicated to transfer services.

The seasonality of interplanetary travel is an economic complication whether or not there is a station. For example, if passenger shuttles are used mainly to carry passengers to and from deep space ships, they sit idle on the ground for most of the cycle.

Of course one solution to the seasonality problem is to have multiple destinations in your setting. Every planet has its own travel cycle, which will on average help with 'load balancing.'

None of this is dispositive, but it strengthens the case for stations in settings where you have extensive interplanetary traffic, ships being maintained on orbit, and so forth.

But it is ALWAYS useful to remember that Clarke and Heinlein were writing 50 years ago, at the dawn of space travel. We don't need technicians on orbit to keep comsats operating, and we may end up not needing them to keep ships operating. And so on.

Raymond said...

This is what I get for being too busy to keep up: one hundred and twenty-one comments to read through all at once.

I think I'll stay out of the purple/green rehash, except to agree with Rick about the complementary nature of the two weapons.

Tony:

If we're talking about fission-electric propulsion in the vapor-core reactor and VASIMR mould and capable of a specific power in the 1 kW/kg range, then we're probably also talking tens of km/s delta-v budget for most missions. A handful of km/s to match orbital plane with a station is, while not nothing, still reasonable. And for the kind of refuel/refit/replace operations a fission reactor may require, I can see the infrastructure needed to be fairly massive. As you've pointed out before, mass on-orbit is terribly valuable. Regular traffic requiring regular maintenance on nuclear reactors and superconducting magnetoplasma rockets could justify orbital facilities. They may not be manned continuously, but it may be worth the extra propellant cost to avoid expensive craft-specific missions.

There's also propellant. Yes, I understand the problems with an orbital propellant depot given current engine tech and space traffic, so don't even start. Nuke-electric craft in the kiloton range, however, would require much more propellant for interplanetary missions than could be launched in a single heavy-lifter. If they use argon as propellant (which the current VASIMR design does), they'd sidestep some of the long-term containment and boil-off issues facing hydrogen storage. It could be useful to spread out the propellant launches over the slow season and stockpile it for the Mars Rush.

If water is used as propellant, it may even be economical to gather it from nearby objects (in delta-v terms) rather than sending it up from the surface. Water would also lack some of the storage problems of pure hydrogen. In which case an orbiting depot would be the only economical mechanism I could think of.

As far as crew is concerned, depending on the traffic level it may either be empty for a large portion of the time, or resemble one of those mountain towns which double in population when tourist season comes around.

Jim Baerg said...

Tony said : "Re: planes and orbits

I'm not sure why it is that people think a plane change of any magnitude is trivial."

Haven't you been reading the posts? nobody has been saying that. Eg: check my comment of November 9, 2010 6:03 PM.

To get from earth to *anywhere* in the solar system you launch into an orbit IN THE PLANE OF THE ECLIPTIC so you don't have to change the plane of your orbit.

You have a point that space stations as transfer points between surface to orbit shuttles & interplanetary craft have not been adequately justified.

However, if there is some reason to have such a transfer station you only need one in an orbit in the plane of the ecliptic to service ships going from earth to *any* other planet in the solar system.

Luke said...

Byron:

The calculations for laser penetration immediately give the amount of energy lost from the beam. For CW beams, it takes an amount of energy equal to the energy it takes to melt all the volume of material in the beam path. Any energy remaining is delivered to what's on the other side of the barrier.

For pulsed beams, you know how deep each pulse excavates. So once you have delivered enough pulses to chew through the entire thickness, the rest of the pulses get through.

For long rod impactors, it is a bit more complicated. For the depth penetrated when the velocity of the end of the rod is v, my previous formula (valid for v=0) becomes
d = L (1 - exp{-B [V^2 - v^2]})/mu
B = mu rho_p / (2 (1 + mu) Y_p)
mu = sqrt(rho_t/rho_p)
where d is the depth of penetration, L is the length of the projectile, V is the initial velocity of the projectile, rho_p is the density of the projectile, rho_t is the density of the target, and Y_p is the compressive yield strength of the projectile. This can be solved for v if you know d
v = sqrt(V^2 + ln(1 - mu d/L)/B).
However, it is also important to take into account that the front end of the rod has eroded as it passed through the barrier. The amount of rod remaining at velocity v is
l = L exp[ -(mu rho_p/(2 (1 - mu^2) Y_p)) (v^2(1 - mu) - V^2(1 - mu))].
With this, you can find how much bang the rod does to stuff behind the barrier using the original formula.

For impactors that penetrate the barrier simply by virtue of exploding to gouge a crater, there is no penetration of the impactor through the barrier. You will still get fragments of the barrier forming high velocity projectiles, a blast wave and overpressure, and possibly a jet of hypervelocity vapor and re-condensed grit.

Clay said...

On the subject of laser battles and radiators, what would be the effect of lightly lasing the radiators with wide coverage.

Would heating a really wide area across the radiators, but maybe not enough to destroy them, still effectively prevent them from shedding heat.

Rick likes to poke 'em in the eye. I'm not so sure you can really blind the other guy, but I like the elegance of this kind of thinking.

In any case, I prefer the strategy of inhibiting an enemy's radiators--like choking them unconscious.

Milo said...

Clay:

"On the subject of laser battles and radiators, what would be the effect of lightly lasing the radiators with wide coverage."

If you try this, you better have lasers with more than 50% efficiency, or you'll be outputting more waste heat to your own radiators than you are to the enemy's.

Even with high-efficiency lasers, I doubt it's a very productive use of your firepower. You're trying to destroy through overheating a structure that is designed to shed heat.


"Rick likes to poke 'em in the eye. I'm not so sure you can really blind the other guy, but I like the elegance of this kind of thinking."

I dislike this kind of thinking because the demands of space opera call for carving ships into debris with flashy explosions, not taking them out of the fight mostly intact with minor damage to a sensitive component. Staring contests are not very exciting, unless you use something like Rick's mixed weapons strategy to spruce them up.

Jedidia said...

Concerning plane changes: I know that they are non-trivial. As I said, the amount of D-V for a significant plane change is very large.

For any low ISP drive, a parking orbit and a precise launch window are a neccessity. However, as soon as we talk about a VASIMR or anything with even higher ISP, the point becomes mute if you are close enough to the ecliptic. There are several reasons for this:

1. to insert into a specific parking orbit when returning from your destination, you have to spend additional Delta-V to insert to your parking orbit that fits your planned departure date in the future. So you're not really gaining anything, unless you just come back from Mars, stay in that orbit and wait for the next launch window from that orbit, which might or might not come and which might or might not be when Mars is in opposition.

2. Plane changes while still being in earth orbit require you to engage your engines during a limited time at the nodes. It is therefore a very tedious and time intesive matter to change plane while in Orbit with a low-thrust drive. The plane change has to be performed before entering or after leaving orbit (I hope my point above shows that you have to change planes anyway you turn it).

3. when launching close to the ecliptic, the plane changes are small and need a trivial amount of D-V for such an engine (usually a few hundred meters per second). Yes, I'll keep insisting on that one, since I did it a hundred times over in Orbiter with low-thrust drives: Spiral out from your current orbit, leaving the earths SOI with just a bit above escape velocity, align planes with a pretty short burst, and then thrust prograde like hell. The plane change barely figures in the total DV-budget, at least if you perform it BEFORE you accelerate too much.

Then there's the topic of seasonal activity, which is a more valid point I overlooked. However, let's consider launch facilities on earth: Do they even have the capacities to bring up all that stuff in that narrow window? If they don't, you're in trouble.

If they do, there's a few things to consider:
1. Launch facilities are expensive, and they cost you even if you don't launch. Does it pay to have them lay bare most of the time of the year? I agree that for conventional drive, there's no way around it. For a VASIMR (or even a fusion drive) things look a bit different: For the outer planets, it doesn't really figure into the equation. Those two AUs more or less aren't going to hurt you that much when you have to get to saturn anyways.

For closer targets the difference is of course more significant, but let's not forgett: You don't need twice as long because the distance is twice as big. If Mars is right at your front door, you have a hard time even spending all your Delta-V to accelerate and decelerate. If it's double the distance, it means you'll have to coast in between, but you're doing so at your maximum velocity, which may be significant. If we assume that we can reach mars in 39 days when it's closest (as has been proposed in reality) I think we can savely assume that we can reach it in a maximum of 55-60 days when it's farthest. I'll do a flight this evening to see if the numbers check out in (simulated) reality. According to my gut-feeling it will be less, but let's not overdo things.

Do these twenty days really weight so much in exchange for the benefit to use your ship at all times and have your launch facilities busy all year?
Agreed, it does weight a lot for passenger flights, but cargo usually doesn't care.

Jedida said...

I was wrong of course, and if I thought about it a bit more I would have noticed without experimentation, but I suck at "visual imagineering".

Even with a VASIMR, it is silly to launch yourself retrograde at a planet with a higher Orbit, or vice versa. Ricks fast large transport is very close to be able to do almost anything at anytime, but not practically.

So, in order to have a sensible trajectory, Mars must be ahead of earth in its Orbit, and about in the same third of the Orbit. During this time both launches from Earth to Mars and launches from Mars to Earth make sense. However, alignement happens only every 2 and a quarter years, While the non-optimal, but doable window opens up almost a year before that. So there will probably be leisure activity rising slowly into one hell of a traffic climax during the course of a year, that concludes at the time of alignement, wherupon there's no traffic at all for at least 15 months.

At least if Mars is your only colony. If you have several, there still is activity for the others.

Rick said...

Yeah, retrograde solar orbits are ruled out for practical travel unless you have a drive approaching torch level, capable of reaching (more or less) 100+ km/s in a few weeks.

Is there some orbit modeling software you are using to test orbits?

Jedidia said...

You CAN'T possibly tell me that you have never heared of Orbiter, the free space flight simulator??

in case that is indeed the case, go here:

http://orbit.medphys.ucl.ac.uk/home.php

everyone's of course also warmly welcome on the forum:

www.orbiter-forum.com

Luke said...

Milo:

If you try this, you better have lasers with more than 50% efficiency, or you'll be outputting more waste heat to your own radiators than you are to the enemy's.

It is not just the laser itself, it is the whole chain from initial power generation to the laser. Your laser might be 99.99% efficient, but if your reactor operates at 25% efficiency, you will be generating three times as much heat as laser output.

Incidentally, where radiator mass dominates the power plant mass, 25% efficiency is pretty optimal for a power plant to run at, since this gets the outlet temperature high enough to minimize radiator mass.

Jedidia said...

little post script:

Yeah, retrograde solar orbits are ruled out for practical travel unless you have a drive approaching torch level, capable of reaching (more or less) 100+ km/s in a few weeks.

I wasn't actually talking about a retrograde orbit, merely that the burn is retrograde (that doesn't result in a retrograde solar orbit, it takes one hell of a delta-v to anihilate the earths orbital velocity). I thought I could do the burn retrograde and wait for Mars to catch up, but of course I forgott the little detail that my orbit would go inwards when I decelerate (it's the abc of orbital mechanics, but I still manage to forget about it every now and then...).

You'd have the same problem if you wanted to catch up from Mars to the Earth in a prograde burn: you'd raise your orbit and it'd be one crazy maneuver to counter that with orbit inwards thrust to get down to earth.

blogs.echofiveecho.com said...

Re: planes and orbits

Yes, I realize that it's all sensitive to available delta-v and performance characteristics of your propulsion technology. But that's the point -- its sensitive to your propulsion technology, not a black and white issue, depending on somethreshold magnitude of delta-v. So I'm still not convinced it's trivial in the plausible midfuture.

Some have said, well, your arrival orbit and departure orbit won't be in the same plane, so rendezvousing with a station is not a problem. The thing is, matching an orbital station's plane is only a negligible exercise if it's inclination is somewhere between that of the nominal arrival and departure orbits. If it's to the outside of this region, you're wasting delta-v to go there.

Re: the ecliptic plane

Tchnically the ecliptic is defined as the plane of Earth's orbit at time T. (The plane wobbles somewhat due to gravitational perturbations caused by all of the other mass in the solar system.) It's not the plane of any other planet's orbit, except by very ocassional (on the order of millions of years) coincidence. It's true that the planes of most solar system destinations lie somewhere close to the ecliptic, but launching to the precise ecliptic at lift off time guarantees nothing at the levels of precision we're talking about.

Re: major service in space

Why? Judging by current spacecraft technology, you design for a nominal mission duration. For reusable craft, it should be no different, except that the mission duration would be a go. Say you design for a service life of 20 years on the Mars run. Okay, that's 9 round trip voyages. You design your power supply, your propulsion system, your life support, and everything else to last that long, plus maybe a 50% contingency margin. Anything that can be economically replaced is built into modules that can be undocked. You should make your target nine voyages, plus or minus a voyage.

Tony said...

My previous post meant to say:Re: major service in space

Why? Judging by current spacecraft technology, you design for a nominal mission duration. For reusable orbit-to-orbit craft, it should be no different, except that the mission duration would cover multiple interplanetary voyages...

Byron said...

As much as anything, that's because we can't service stuff in space at all (except with really expensive manned missions) and it's a big part of why satellites are so expensive. There is nothing else of a similar role designed to go entirely without maintainence during its service life. This is not something that would be done if not for the unusual environment of space operations. If we are reusing manned vehicles, there is no reason not to use parts that are very significantly cheaper than current ones, as they don't have to last forever.

Tony said...

Byron:

"As much as anything, that's because we can't service stuff in space at all (except with really expensive manned missions) and it's a big part of why satellites are so expensive. There is nothing else of a similar role designed to go entirely without maintainence during its service life. This is not something that would be done if not for the unusual environment of space operations. If we are reusing manned vehicles, there is no reason not to use parts that are very significantly cheaper than current ones, as they don't have to last forever."

I know I keep harping on it, but some anvils have to be dropped -- we're talking about the plausible midfuture here, in which humanity's technological base is still on the surface of the Earth, and everything used in space more complex than fuel/remass has to be brought up from the Earth. That ain't gonna change for several hundred years, at least. In that time, all spacecraft and all spacecraft components are going to be ultimately expendable in a way we're just not used to in any transportation industry on Earth. The type, number, and schedule of voyages for the spacecraft's entire service life are going to be known at design time. So the spacecraft is going to be designed for that service history, with plenty of safety margin to spare. It has to be that way, because there are no life boats, no parachutes, no revised flight plans, no safe fields for emergency landings. Nobody is going to bet their life on cheap parts that aren't made to last, because the only safe place is all the way at the end of the voyage, after everything works as designed.

Byron said...

I suppose that the navy could build their ships to go their entire life without an overhaul, too, but they don't. In general, they build them to have a decent bit of maintenance done every few years. That's what I'm seeing spacecraft doing, too. There is such a thing as redundancy, you know. The chances of all the parts failing are about the same if I have four short-term widgets, or two long-term widgets. The costs are the same, or even cheaper. Maybe on short-term widget fails, but the others still work. Plus, what happens if you have a failure in your long-term ship? Would you replace the part, or toss it aside and get a new one. Any man-rated ship will have a lot of redundancy built in. Why not use it to increase service life?

Tony said...

Byron:

"I suppose that the navy could build their ships to go their entire life without an overhaul, too, but they don't. In general, they build them to have a decent bit of maintenance done every few years. That's what I'm seeing spacecraft doing, too. There is such a thing as redundancy, you know. The chances of all the parts failing are about the same if I have four short-term widgets, or two long-term widgets. The costs are the same, or even cheaper. Maybe on short-term widget fails, but the others still work. Plus, what happens if you have a failure in your long-term ship? Would you replace the part, or toss it aside and get a new one. Any man-rated ship will have a lot of redundancy built in. Why not use it to increase service life?"

Naval vessels are a very poor analogy for the plausible midfuture in space. A naval base is a complex industrial organization, employing thousands of people, hundreds of which will get involved on a maintenance availability. That's in addition to the crew, who are much more numerous than you might find in a merchant vessel. This organization is not and cannot be insular. It's workforce is based in a community of several hundred thousand that surrounds the base.

This workforce will not scale the way some apparently think it will. There are too many disciplines involved in any complex vehicle, like a warship or a space ship, for the necessary maintenance force to be scaled down on a stricly linear basis (i.e. so many maintainers per ton of vessels to be maintained). You're going to have a huge and irreducible overhead in technology-specific experts, in order to have the right guy available when you need him. Take for example the ship I was assigned to for two years in the late Eighties, the USS Long Beach. Whenever we went out to sea, we always seemed to be dragging along one or two civilian manufacturer's reps to keep their eye on something or the other. There must have been dozens of them on the ship every day in port, but, with so many people running around in civilian clothes, you couldn't tell the difference between them and the regular sand crabs that worked for the base. But they had to be there, because the Navy, both uniformed and civil service, didn't have the entire skillset needed to keep their ships and ship's equipment going, even with hundreds on each ship and thousands working at the major base activities.

Now, you're going to tell me that you want to reproduce the cost of all of that in orbit, rather than just build the ships with adequate reliability in the first place?

Also, the only reason that works for the USN and like navies is that ships on the surface of the ocean are never far from help. If worse comes to worse with propulsion, for example, somebody can always pass you a tow cable and get you into port. If the air conditioning fails, guys can hang out on the weather decks until it gets repaired. If you have fire, flooding, whatever, there are always other ships within radio distance and, in extremis, a life jacket with a locator strobe. Keep your spirits up and hope the capatin made contact with rescue forces before you went over the side.

None of that is possible in a space ship, even one designed for some number of multiple voyages, the redundancy is designed for survivng the voyage you are on right now, and it had better not have to be invoked, nine voyages out of ten, or the ship was not well enough deisgned for manned interplanetary flight. That's simply not going to change under and forseeable set of realistic circumstances.

Byron said...

I generally agree with you in principle, but there are two major issues here:
1. You will have to have some sort of redundancy. If something breaks, then I doubt the vessel will be allowed to make another trip unless it is repaired. Thus, there will have to be some sort of repair capability, unless you believe that nothing will break, which I know you don't.
2. The voyages in question are quite long. Having five redundant systems with one failure during a normal mission on an airplane is a problem. Having five systems and one failure over the course of a year is a lot less of a problem. The only difference is how far away you are from home most of the time. And increasing reliability jacks up cost. So if it takes four life support systems to be certified for interplanetary flight, and my design costs a quarter of what yours does, and has a failure every two years, while yours has a failure every 4 years, whose is better?

Tony said...

Byron:

"1. You will have to have some sort of redundancy...Thus, there will have to be some sort of repair capability..."

Incorrect. You will need to have some sort of replacement capability on return to Earth. (For the plausible midfuture, that's where the technology base is going to be, exclusively.) That suggest modular design, not on-orbit maintenance, in situ, by experts.

"2. The voyages in question are quite long... So if it takes four life support systems to be certified for interplanetary flight, and my design costs a quarter of what yours does, and has a failure every two years, while yours has a failure every 4 years, whose is better?"

I wouldn't certify either for interplanetary flight. On a vessel service life of 20 years, I would specify 10 years MTBF for critical systems, modularize, and buy three of every module up front. That should give you reasonable cost control. It would also encourage standardization of modules, further reducing costs.

Rick said...

I waver on this point. I started to argue for a sealed-part, modular approach, but it strikes me that the real (off-) world experience of the ISS points in the other direction.

It requires constant maintenance by its crew; in fact that is most of what they do. But, so far as I can recall, in 10 years it has suffered no emergency that would have kept an interplanetary mission from safely returning to Earth.

Mir, as I recall, did have one or two such crises, but that is the point of the learning curve. I regard both Mir and the ISS as, fundamentally, 'captive' interplanetary training flights, testing our ability to safely perform prolonged missions without hand holding from Earth.

And the quiet good news is that it seems as if we can do exactly that.

This experience seems to fit a relatively traditional picture. A ship returning from an interplanetary trip might have some entire modules that get downchecked and replaced, but also get an intensified phase of ordinary maintenance, replacing air filters, balky indicator lights, and whatever have you, to turn it around for the next mission.

Thucydides said...

Lots of comments, so little time ;)

Lasers and kinetics are complimentary systems as far as military employment is concerned. Lasers allow for uber long engagements, pin point accuracy and can deal with pretty impressive swarming attacks. As well, a fully developed laser will have lots of secondary uses, such as providing boost power to laser engined missiles or lighters associated with the ship, communications (suitably dialed down) and so on. The sensor and optical units that provide the high degree of accuracy to the laser will also be useful (contemplate what you will be a able to see with a 5 or 10 m mirror).

Kinetics are useful as a compliment to the laser. In a long range attack, they distract the enemy laser since he has to clear the kinetic threat before frying your laser. At closer range, it is probably the real ship killer, since you could either overwhelm the opponents emitter through sheer numbers, or perhaps your spread is beyond the ability of the primary mirror to cover in the time before impact.

Chemical fueled KKV's will be somewhat marginal in that regard, since they will have very limited delta V, which should probably be horded for terminal manoeuvres. Some sort of high acceleration boost will be necessary, and I leave that as an exercise for the reader.

An orbital station might resemble a garage or truck stop more than the traditional idea of a Hilton, and going by many of the comments I can see it being a cage which orbits unmanned most of the time. During shipping season, multiple payloads of new or refurbished hab modules, full fuel tanks and shipping containers full of spare light bulbs, kleenex and other expendables gets boosted up to the cage for quick turnaround while ships come into orbit, swapouts and refueling takes place and the ship is prepared for another boost. All this starts several weeks or months before shipping season, and there will be a period after shipping season while things get sorted, items are sent groundside or into the solar furnace and repairs and upgrades to the cage are made.

I do have to agree that if you have a capable high ISP drive, then changes in orbital inclination would be part of your flight profile

Tony said...

Rick:

"This experience seems to fit a relatively traditional picture. A ship returning from an interplanetary trip might have some entire modules that get downchecked and replaced, but also get an intensified phase of ordinary maintenance, replacing air filters, balky indicator lights, and whatever have you, to turn it around for the next mission."

I wouldn't disagree with you, but anything designed to be replaceable by a non-expert is a module, in the engineering sense. We have to remember that Mir and ISS were managed in that context. And the methods used in those programs are instructive.

I would think an interplanetary spacecraft would be managed in a similar fashion. Remember, the operator is mothballing it in orbit at the end of a transit season. Before the flight crew departs, they manifest all replacements needed for the next voyage and email it to the mission planning office. The replacement modules are collected, packaged, and scheduled for upshipment with the flight crew, fuel, whatever else is loaded before pax/cargo. When the flight crew reports back from a half year to a year of decompress/vacation/family time, they go into flight prep. Among other things, they get refresher maintenance training and training for non-routine module replacements. You keep all of the engineering and technical experts on the ground, where they and their tools are relatively cheap, and just send up stuff that's actually needed in space -- replacement hardware, fuel/remass, flight crew, pax, and cargo.

Tony said...

Thucydides:

"I do have to agree that if you have a capable high ISP drive, then changes in orbital inclination would be part of your flight profile"

Of course they are. But going on to assert that rendezvousing with a station is therefore a negligible maneuver misses the point. As I pointed out earlier, if the station's orbital plane is outside the region defined by the planes of the arrival and departure orbit, then it's a waste of delta-v to go to the station. There's nothing that could be done at the station that could justify it.

Byron said...

Tony:
I think we're somewhat arguing past each other. The way your original comment was phrased sounded like you believed in no maintainence at all.
The problem with modules is mass. You're shipping up replacements for a lot of good components with a single bad one. If there is sufficient orbital commerce, then it makes sense to try to repair only the piece that went bad, saving a lot of launch mass. It might be that a combination of the two is used. Modules are replaced at Mars, and the bad ones sent back to Earth. There, they are repaired and sent back, and any bad parts from the trip back are repaired.

Thucydides:
I'm not so sure chemfuel kinetics are useless. Any PMF high-ISP drives are going to be low-acceleration. There will be no need for high-speed terminal maneuvers. I think that any missile will boost to an intercept course, then burn out, letting its warhead behave like a coilgun (side-steering). This has the advantage, particularly if you detach the engine, of making the incoming projectile harder to see and shoot at. However, it's not that hard to get enough delta-V out of a chemfuel rocket to do some damage.

On station seasons:
I think that it's likely that launches will be continuous and low-level. The problem is that it requires more infastructure to launch a bunch of stuff in a short time than a long time, at least for certain amounts of stuff. I know that at the moment, we could probably launch more without more infastructure. However, once it gets to the point of requiring more infrastructure for this launch surge, I'd react by spreading out my launches.

Tony said...

Byron:

"I think we're somewhat arguing past each other. The way your original comment was phrased sounded like you believed in no maintainence at all."

Hmmm...

"The problem with modules is mass."

The problem with on-orbit repair is mass. Please go back and reread my comments on naval maintenance organization and operations.

Fernando said...

I'm more interested on the day to day life on a space station of such size. Would it be like those towns, where everybody knows everybody? Or a office building, where everyone knows their place and most relations are confined to work?
Also, there are other little details... What about pets? Could they be banned in an environment where food and air are so scarce, or perhaps limited to small animals like guinea pigs or lizards? And what about children? It's bound to happen, someone will get pregnant on space; how will the children fare both physically and psychologically on space? Will they have birth anomalies (underdeveloped muscles, weak bones)?
I'm thinking of a space station like a factory or a corporation in space, with tightly enforced rules, for necessity, after all, if something goes wrong there is quite a probability that everyone could die, or at least pay a few millions on reparations. I wonder if the space pioneers will not be like the cowboys of the far west or the first European explorers, but rather business and science men and women, focused on doing their job and not letting anybody die... It's quite dry fiction if you put it like that... but realistic
Also, will this space station support weapons at all? The facility is mostly populated by civilians, and installing weapons is only asking for trouble. Obviously that in war, civilities like not destroying a space yard full of innocent people may be forgotten, but in a peaceful environment, destroying a space station will mean losing millions of dollars and hundreds of lives, not to mention the loss of an important resupply and strategic point. Would not be easier to send some espatiers, cut some holes and invade the space station. Even more easy, put some unmanned platforms and blockade the station, destroying everything that tries to leave or enter...

Byron said...

Yes. However, for a sufficient volume of traffic, it makes sense to repair the modules instead of replacing them. It really depends on the traffic level. With enough traffic, it does make sense to repair the modules. If there isn't enough, then it doesn't. We don't know the value of enough.

Fernando:
Probably more like a town, though I'm fairly certain 10,000 is larger than the "everyone knows everyone" threshold.
The spin gravity should cause children to develop normally. You're pretty much right on the rigid rules. We've discussed that in the past, as I recall. If there are weapons, they'd likely be antimeteor lasers, built to zap anything they couldn't dodge, or at least break it up. In wartime, I wouldn't arm it, in the same manner you don't arm merchant ships or the like. Mount the weapons on defending ships. Probably dismount the antimeteor lasers. Everyone will probably agree that shooting up colony stations is a war crime, as they'd be relatively easy to destroy. I've got a train of though running. Let me get back to it in a moment.

Tony said...

Re: Fernando

It'll be like living in a submarine that never goes anywhere. That's one of the arguments against stations using reasonably forseeable technology -- people who had to live there would go batsh!t crazy if they had to last out a tour longer than six months every two years, with amybe a mximum of five tours in any one lifetime. And the type of people who have the skill needed for on-orbit spacecraft maintenance won't be in it for prestige or the adventure. They'd have to be paid millions per year to do it.

Byron said...

Tony:
The colony station is an order of magnitude larger than an aircraft carrier. The supposed transfer station might not be, though. That's a bit different. We could use teleoperation to do the repairs, though.

Colonies and war:
OK. Here's my analysis of how space colony stations would work during a war. There are a number of factors and assumptions involved:
1. Everyone involved has these type of stations, so there's a MAD check involved.
2. People are rational, and will recognize the unprovoked destruction of a station and it's occupants as a war crime.
3. The stations are valuable enough to want to capture and defend.

People will be reluctant to destroy stations because, while it's quite easy to shoot at someones station with a missile, it's also easy for them to do the same to you. Neither of you can really afford to lose your orbital presence, or the bad press, so you don't shoot. However, the law says nothing about taking over someone else's station, or destroying it after it's evacuated. So you keep a fleet of ships at your stations to protect them, and your enemies do the same. When you decide to attack one of theirs, you send a fleet. It reaches their station, and challenges their fleet. ("Evacuate the station now, or we blow it up in two hours.") The enemy fleet comes out, and you fight. When the battle's done, the fate of that station is settled.

Tony said...

Byron:

"Yes. However, for a sufficient volume of traffic, it makes sense to repair the modules instead of replacing them. It really depends on the traffic level. With enough traffic, it does make sense to repair the modules. If there isn't enough, then it doesn't. We don't know the value of enough."

But you can't repair the modules on-orbit. I went through the exercise of describing the size and complexity of modern technical support organizations, then asked you to read it a second time, to make precisely that point. This isn't pipe bending or wrench turning we're talking about here. Each of these modules is going to be a complex machine in its own right, having been put together through the combined efforts of dozens, hundreds, even thousands of highly skilled engineers and technicians. This is the kind of stuff you send back to the factory for reconditioning or replacement. That's not going to change.

And we're not even considering just how small a "big" interplanetary transport industry is going to be. Two hundred years in the future there may still only be 10,000 people on Mars and maybe a tenth as many in other places in the solar system. There may only be a total of a thousand people going to Mars during each season. That's only going to take ten to twenty ships.

So each ship is still going to be a rare, special purpose item. There won't be all that much standardization, considering the number of likely operators. The US, Russia, China, Europe, and, possibly, Japan are likley to be the only multi-ship operators. Maybe Brazil, India, Indonesia (big ? here) might have one apiece. All of the ships are likely to be national technological prestige items, meaning they will share very few common components. So just how big would an orbital support organization really have to be, and how practical could it be?

Tony said...

Byron:

"The colony station is an order of magnitude larger than an aircraft carrier."

What colony station? Where?

Ten times the size of an Aircraft carrier? A million tons? I thought we were dealing with plausible reality here.

"The supposed transfer station might not be, though. That's a bit different. We could use teleoperation to do the repairs, though."

We could?

Byron said...

I'm getting the feeling that we're somewhat talking past each other here. You seem to be viewing a "module" as an "atom", the fundamental building block of a machine. I'm looking at it slightly differently, in that a module is likely to be made up of smaller parts which might not be replaceable by the crew, but could be fixed by somebody with a little more skill.
Take your computer. A "normal" person will view it as a module. If it breaks, send it somewhere, and get it fixed. I have my A+ certification. I view it as a bunch of modules. If it breaks, open it up and look inside. If the power supply is bad, take it out and replace it. Someone with even more training might view the power supply as a set of smaller modules.
You seem to view the crew as capable of replacing to the smallest reasonable part. I'm not so sure about that. If it isn't true, then some sort of on-orbit repair capability makes sense. To continue the computer example:
On the way to Mars, the number four computer suffers a failure. The crew replaces it at Mars with a new computer from the Mars depot, and brings the old one home. When they get home, it's couriered over to the Earth Repair Center, where it's opened up, and it's discovered that the power supply is bad. They send for a new one, and when it arrives, ship the computer back to Mars.

You're probably correct about modularity for the given example, but what happens if we bump the given numbers, say, three orders of magnitude? I know it's not as plausible, but for the sake of argument, it makes on-orbit repair more likely.

I wasn't sure which station he was asking about. Rick began with a colony station. It's not terribly plausible, but we can dream.

And why wouldn't teleoperated robots in Earth orbit be able to do repair work. There's virtually no lightspeed lag, and it's a lot cheaper than a human in orbit.

Raymond said...

Tony:

I think you're limiting the "plausible midfuture" to merely the t+200 timeframe. The range many of us have been taking for granted is somewhere between two and seven hundred years from now. I'm fairly sure that if we wanted to, we could have millions or tens of millions living off-world by the 2700s. Maybe even more.

I also think you're skipping over the messy details of the nuclear reactors we're assuming. I don't know of any reactor we've produced that would go ten or twenty years without substantial maintenance. I also don't think that kind of reactor would be launched fueled or even fully assembled. That might argue for at least a station in Earth orbit, with the kind of specialized, shielded, and heavy equipment you need for nuclear maintenance. Given a time t at which we hit the critical offworld population n, we could probably justify such a station for Mars as well.

Tony said...

Byron:

"You seem to be viewing a "module" as an "atom"..."

Sort of -- an atom defined by circumstances. For example, a breathing gas recycler it atomic at at least two levels:

1. Filters and any other consumables are atomic for preventive maintenance purposes, and

2. The entire recycler is atomic for failure replacement purposes.

The common denominator is that the module can be replaced by non-expert flight crew, either during the mission or, with a little specific training, as part of mission prep. The guiding principle is that the large and expensive support organization is kept on the ground.

"On the way to Mars, the number four computer suffers a failure. The crew replaces it at Mars with a new computer from the Mars depot, and brings the old one home."

What Mars depot? In the context of a plausible midfuture technology base, a voyage is defined exclusively as a round trip. That's why you build redundancy into all mission critical systems -- so the ship lasts until you get back to Earth.

"When they get home, it's couriered over to the Earth Repair Center, where it's opened up, and it's discovered that the power supply is bad. They send for a new one, and when it arrives, ship the computer back to Mars."

Why? On average the computer has been in service for ten years, because we specified a 10 year MTBF. Replace it with the latest flight-qualified model compatible with the hardware and software in use on the ship. That goes for any other replaceable hardware modules.

Remember space is manifestly not an environment for "use it up, wear it out; make it do, or do without" type thinking. Repair is heavily deprecated WRT replacement, both by economics and good engineering sense. In fact, if I were designing with human life safety in mind, I would relegate repair to patching up serious in-flight failures just long enough to get home, at which point the failed unit is replaced and discarded as too unsafe to trust in the future.

"You're probably correct about modularity for the given example, but what happens if we bump the given numbers, say, three orders of magnitude? I know it's not as plausible, but for the sake of argument, it makes on-orbit repair more likely."

Ten million people in space by 2200? The Europeans managed a small fraction of that in the Americas from 1500 - 1700, with a lot more friendly environment and a lot higher emmigration rate than likely in space.

"And why wouldn't teleoperated robots in Earth orbit be able to do repair work. There's virtually no lightspeed lag, and it's a lot cheaper than a human in orbit."

Once again, we have to keep in mind that we're talking about highly specialized repair activities. even if you could make a teleoperated bot capable of all of the manipulations and orientations that a human can adopt (I'm not holding my breath), there is such a wide variety of tools and instruments in use in moder technology (even if you just limit yourself to the aerospace-relevant ones) that you would have to orbit an inventory massing thousands of tons to cover all of the bases.

See, we've become so used to the local {whatever} repair guy, or just fedexing stuff back to the factory, that we just don't realize how complex the technological base that supports us is. To reproduce that in space would be prohibitively expensive.

Tony said...

Re: Byron

I think of "modular" as anything that can be diagnosed and replaced by a non-expert with a minimum of specialized tools. That could be anything from consumables like filters to major systems, packaged in modules with minimal mechanical/electrical interfaces. That's certainly within the capabilities of flight crew, who are mostly there for engineering maintenance anyway.

Likewise, I don't think there will be a supply depot at Mars. A voyage will be defined as a round trip. System redundancy will be implemented to make a safe voyage on that scale.

Teleoperation of repairs might eventually be technically possible, but it would be practically impossible, because the total inventory of tools and instruments for working on technologies that might be included in a space ship must mass tens of thousand of tons, at a minimum.

Re: Raymond

based on the internal evidence of the literaturs, the Rocketpunk future was the next two or three centuries, figuring from 1950 or so. I'm restricitng myself to that.

As for nuclear power systems, The impression I got from being stationed on a nuclear wessel for two years was that the reactor was pretty much left alone for the 10-12 years between fuelings. Maintenance was all preventative and, if we're being honest with ourselves, most of that maintenance could have been designed out of the system, except that Rickover trusted people over technology. I personally think that's the correct attitude in technology management, but sometimes you have to rely on technology, as in the case of space systems.

Also, I see no added danger in launching reactors with or without fuel loaded. The fuel has to come up from the Earth anyway. When a space reactor fail, or just reaches the end of its fuel lifetime, the proper response is to put a solid kicker motor on it and dump it in the Sun. Heck, I'd have the disposal package mounting interface built into the original hardware, by design.

Milo said...

Fernando:

"I'm more interested on the day to day life on a space station of such size. Would it be like those towns, where everybody knows everybody? Or a office building, where everyone knows their place and most relations are confined to work?"

Office buildings are like that because people are only there when they're paying attention to work, and commute home when they want to relax or socialize. Unless you're so far into the future that commuting into and out of orbit is trivially cheap, stations will not be like that. Even if they exist primarily as a venture of some corporation, the people who live there would come to develop a sense of comraderie by necessity. They might not all like each other but they'll know each other.

Compare oil rigs or military bases.


"Also, there are other little details... What about pets? Could they be banned in an environment where food and air are so scarce, or perhaps limited to small animals like guinea pigs or lizards?"

Well, keep in mind that if you're trying to have a closed life support system (as opposed to expensively importing food), then you'll be unable to feed carnivorous pets like cats or dogs without also having someone breeding food animals.

I think the main problem isn't so much resources - most pets are pretty small - but rather complexity. Supporting pets requires infrastructure for appropiate food, veterinary medical care, and so on, which a small community may be unable to provide.

There's also the question of gravity. If you have Earthlike spin gravity, no issue, but if the station is in freefall, then that makes life quite hard for pets - even ignoring the question of health effects (which are likely to be similar on other vertebrates as on humans, and who knows about invertebrates?), most land animals are going to freak out and not have any idea how to move around. They could perhaps be taught, but that would certainly not be a trivial affair. Aquatic animals are easier to adapt to zero-gravity conditions - in fact, fish have already been successfully bred in space. So those might make good pets if you can manage an aquarium.

Larger pets, like horses, of course require quite a bit of room and will only appear in reasonably mature colonies.


"And what about children? It's bound to happen, someone will get pregnant on space; how will the children fare both physically and psychologically on space? Will they have birth anomalies (underdeveloped muscles, weak bones)?"

If your station has spin gravity, you'll probably be fine. (Coriolis effect might cause trouble, but I doubt it.) If you have no or only weak spin gravity, then they will likely have health issues comparable to those of adults in the same conditions.

My hunch is that children might actually be able to adapt to exotic conditions than people who are suddenly introduced to them later in life. It's trying to land on Earth afterwards that would give them trouble - they wouldn't even know how to walk!

There could be psychological consequences from growing up in an isolated society, although keep in mind that people aren't likely to have children in space until the station is large enough to consider itself a "community" with permanent residents. Otherwise people who get pregnant would just commute out.

Rick said...

Getting a feeling for the human dimension of space is, at least in part, why we wrestle with all these technical considerations.

Put another way, whether or not there are space station bars inhabited by pretty people of no technical skills but outstanding interpersonal ones will depend, ultimately, on technical considerations like booster recovery/replacement and available orbits.

And some of these questions touch on the (deliberate) central tension of this blog, between realism and Romance in the space future. Which I will be saying more about in a front page post, along with what I mean by 'midfuture.'

On the nuts & bolts discussion, I tend to agree that from an engineering perspective everything will be pretty modular. For a long time to come, space crews and habs will be very expensive, so there will not be specialized techicians or workshops beyond the most rudimentary level.

Note that in a way this makes 'spacer' a skillset a bit analogous to the able bodied seaman of yore, someone who can do all the basic onboard tasks, including EVA. As human spaceflight advocates often point out, a significant fraction of our robotic missions have been lost to mishaps that someone with a wrench could have fixed. That is pretty much what the crews will do.

For exploratory missions they might also be trained as scientists or whatever, but that would be all the more reason for the 'spacer' skillset to remain generalized.

What is harder to get is an equivalent of the ship's carpenter.

Milo said...

Byron:

"Colonies and war:"

Small colonies would most likely be ignored as too insignificant to bother with, unless they're sited over a valuable MacGuffinite lode, in which case they'd be fought over by contending superpowers without actualy having much to say on their own fate.

More advanced colonies that have grown enough to field their own navy would be players in war, just like everyone else.

I don't think colonies would get much different treatment simply because they're colonies - maybe because they're civilians, or because they're in an orbital station/dome city/other wacky environment, or whatever, but not just for being colonies.



Raymond (+Tony):

"I think you're limiting the "plausible midfuture" to merely the t+200 timeframe. The range many of us have been taking for granted is somewhere between two and seven hundred years from now."

I can't tell you how many years this will be "realistically", but I am thinking in terms of a setting where extraterrestrial colonies exist that have grown large enough to be politically and economically important, while still interacting using spaceships that follow something close to currently known physics. It isn't rocketpunk otherwise.

This is as opposed to the near future, where we're still poking around with probes that are barely capable of doing their jobs and have perhaps expanded the ISS's population by an order of magnitude or two without really changing its fundamental nature, or the far future, where we have magitech that's barely worth speculating about, hopefully including FTL.

The purpose of this blog is not to discuss what policy NASA should adopt for their projects over the next decade. We're here to discuss what space travel will be like when space travel actually exists, for real, whenever that may be.


"I'm fairly sure that if we wanted to, we could have millions or tens of millions living off-world by the 2700s."

And there's the nagging caveat. Do we want to?

Rick said...

The mega station getting mentioned is more or less the one I outlined in the post. I was exploring what size a hab would need to be for robust shielding NOT to be something like 90 percent of its mass, so that it could be repositioned without grotesque inefficiency.

I didn't try to examine under what circumstances we might actually build a station that big.

Anonymous said...

On the issue of children on habitats, there are at least a few Antarctic bases (the nearest equivalent we have to orbital habitats at the moment), where children have been born, and that have children permanently resident, with their own schools. Of course, those bases are Argentine and Chilean, making transport between base and homeland somewhat easier than it would be for America or Russia. No country has much geographic advantage over others when it comes to reaching space, though I imagine that habitats in LEO will be the first to have children aboard.
The problem of the children being isolated is probably not a major issue as long as there are a reasonable number of children of similar ages aboard the habitat. After all, as well as the Argentine and Chilean bases I was talking about, isolated island communities such as Pitcairn, Tristan da Cunha and Saint Helena (all of which have populations far below the 10,000 that Rick gave as a low-end population for his larger habitat) are able to raise normal, socialized children. Modern telecommunications, which would suffer virtually no lightspeed lag in LEO, could reduce this isolation further. For 50 years, Australia's School of the Air has been educating Outback children even more isolated than those of the island communities I mentioned before.

R.C.

Jim Baerg said...

Tony: "Also, I see no added danger in launching reactors with or without fuel loaded. The fuel has to come up from the Earth anyway. When a space reactor fail, or just reaches the end of its fuel lifetime, the proper response is to put a solid kicker motor on it and dump it in the Sun. Heck, I'd have the disposal package mounting interface built into the original hardware, by design."

Correct about the launching of reactors. Wrong about disposal for 2 reasons.

1) The delta-V to dump something into the sun will be prohibatively large for a long time to come. 30 km/s is certainly not doable with chemical rockets, & even with a high specific impulse drive will be OK for doing something valuable but not for waste disposal.

2) Used nuclear fuel has lots of leftover energy. Storing it somewhere for later reprocessing is the way to go. I'd have a used nuclear fuel storage site for space reactors in some high earth orbit like the earth-moon L4 point.

Lots of people repeat the dumb idea of sending nuclear 'waste' into the sun & I though it needed shooting down.

Citizen Joe said...

I wanted to point out that the "idle time" for cyclers is only a problem if they are idle during that time. Business isn't going to tolerate more than two days off (a weekend) for travel without some sort of productivity. Beyond that, it is considered vacation time. So when you're comparing four weeks to eight months, it doesn't matter. You'd arrive on station at the cycler and get put to work doing something productive. That could mean some sort of telecommuting or it could mean manufacture of products. The point is that whether you're on the fast leg or the 'idle' leg of the cycler trip, you're going to be working.

Now you still have to accelerate your taxi and cargo into cycler orbit. But, you don't have to accelerate the hab module or life support, etc. If the cycler is set up right, you might not need to pack disembarking remass for your destination. That requires large cyclers with a low delta-v restocking of remass (probably at the asteroid belt).

Note also that complete docking isn't necessary. Once the taxi/tug/freighter has accelerated to 'dock' with the cycler, it is going to continue on the same orbit whether it docks or not. That means you can sync up with the cycler and then shuttle over your crew, leaving the ship on remote access for minor course corrections. There is no need to dock a huge ship to the cycler (unless that's what the cycler was designed for, i.e. drydock).

Raymond said...

Tony:

"The impression I got from being stationed on a nuclear wessel for two years was that the reactor was pretty much left alone for the 10-12 years between fuelings. Maintenance was all preventative..."

I was acquainted with a nuclear tech from the Carl Vinson, and he said roughly the same thing, but also that the preventative maintenance was what gave the confidence to use the reactor for so long. As you point out, maintenance more involved than the basic preventative sort would be infeasible in space.

The preventative type, though, will probably require at least a couple robot arms and some heavy shielding, given that space reactors won't have the sort of 4pi shielding terrestrial reactors do. Even tasks like replacing a reactor as a module are likely going to require more than just a couple EVA suits. The penalty for dragging all that mass around the solar system would be prohibitive - why not put it on a station, at least in Earth orbit?

"...and, if we're being honest with ourselves, most of that maintenance could have been designed out of the system, except that Rickover trusted people over technology. I personally think that's the correct attitude in technology management, but sometimes you have to rely on technology, as in the case of space systems."

I wouldn't bet much on designing all or even most of the maintenance out of a space reactor. Even conservative designs run 500 or 1000 Kelvin higher than their terrestrial counterparts, due mostly to the vagaries of heat expulsion. The temperature range where ~1600 K is your cold side means you run into the same sorts of material limitations that make it difficult to design a reusable rocket engine. It may be trickier than you suppose to design such a system for as low a level of operational maintenance as you're assuming.

And frankly, given the (unfounded IMO) widespread distrust of nuclear tech, Rickover's attitude will not only be present, but squared and cubed.

"Also, I see no added danger in launching reactors with or without fuel loaded. The fuel has to come up from the Earth anyway."

Depends entirely on the nature of the fuel. Solid-core designs using uranium oxide pellets embedded in a graphite matrix? Not so much of a problem, as the core will stay largely intact during reentry and the fuel won't burn into radioactive dust. Vapor-core designs using uranium tetrafluoride? If there was a launch failure, it would take a specialized (and heavy) containment device to keep the fuel from turning into a Giant Radioactive Cloud Of Gaseous Death. Said containment device would be a useless mass penalty on an interplanetary spacecraft.

Besides, these reactors could easily be too large or too massive to launch fully assembled.

Milo:

"And there's the nagging caveat. Do we want to?"

For any of this discussion to matter, we have to assume the answer will be "yes".

On the timeline:

I've been assuming that a large portion of our discussions on this blog rely on a solar system populated enough to support things like basic off-world industry, at least limited interplanetary travel outside the most efficient launch windows, and at least some people living off-Earth full-time. The particular values of time t, offworld population n, cost c and overall scenario probability p are perhaps unsolvable at present.

Tony said...

Jim Baerg:

"1) The delta-V to dump something into the sun will be prohibatively large for a long time to come..."

It will? All you have to do is get the object in question to within a few million miles of the photosphere. Atmospheric drag will do the rest. All you really want to do is ensure that the first pass through the sun's atmosphere slows the object down enough that its orbit's aphelion is below the Earths by good couple of million miles or so. After that, a few decades or even centuries in a constantly diminishing disposal orbit is acceptable. We have no major business in that direction. That's well within the capabilities of relatively small motors -- maybe not kicker class, but certainly manageable expendables.

"2) Used nuclear fuel has lots of leftover energy. Storing it somewhere for later reprocessing is the way to go..."

Only if you have the reprocessing infrastructure available. How many hundreds of thousands of tons does even a small reprocessing plant mass?

"Lots of people repeat the dumb idea of sending nuclear 'waste' into the sun & I though it needed shooting down."

Well, I know I'm not the smartest person I know.

Byron said...

Tony:
You seem to assume that there are no options between "swap out the module and get a new one" and "put up a facility capable of rebuilding the entire spacecraft." This is not true. Take your gas recycler. What happens if a fan fails (burns out, bearings seize, etc.)? Are you going to swap the entire unit for something that can be replaced by anyone who knows their way around a soldering iron and has the parts? I'm advocating a level of maintainence one step up from what can be done by the ship's crew, not a complete facility.

Tony said...

Re: Raymond

If we can't get the necessary reliability, then we can't use nukes in space. For as far as I can see, we won't be economically able to use technologies in space for which we can't leave the industrial infrastructure on the ground. That's the sole and total context in which I make my contributions.

Byron:

See above. For the reasonably forseeable future (which I take to be synonymous with the plausible midfuture), any industrial infrastructure remains on the gound. So what if it's only a fan that deadlines a module? Keep the 10 year MTBF (at the module level) requirement in mind at all times when analyzing what I have to say. Even if you have a fan failure at 5 years, everything in that module is that old too. Module replacement and disposal is the only responsible course for human life safety engineering.

Rick said...

Getting within a few million miles of the photosphere requires, alas, nearly as much delta v as dropping straight into the Sun.

What sort of preventive maintenance tasks are actually performed on nuclear ship power plants? Onboard maintenance of a nuclear plant in space strikes me as awfully problematic. It seems like most components would be very heavy, very radioactive, or both.

So I tend to agree with Raymond that drive maintenance would pretty much have to be between missions, where you can bring heavy shielding and equipment into play without lugging it around (apart from the initial lift to orbit).

For the inner system, out to Mars orbit, solar electric is IMHO far preferable to nuke electric - no radioactivity and basically no moving parts. Unfortunately it gasps for sunlight by the time you reach the main asteroid belt, let alone Jupiter.

Citizen Joe said...

I think that betavoltaics mass out at about the same per kilowatt yield as photovoltaics at around Mars orbit. I.e. for the same mass of solar panels, etc. you can get the same yield from tritium batteries, which can operate regardless of distance from the sun. Yes, they are radioactive, but they throw beta particles rather than gamma. Beta radiation is blocked by a little aluminum (much lighter than fission shielding). It is also a 'cold' energy source, i.e. room temperature operations. Betavoltaics run around 5% efficiency, but the waste heat should be usable for life support or possibly pumped into a Stirling drive/flywheel inertial storage device.

In situations where you need more energy the closer you get to the sun, it makes sense that you'd have solar axillary power. An example might be a solar sail used for station keeping.

A big drawback with betavoltaics is half life. The isotopes used to generate the power decay so that you're producing half as much power by the time of the half life of the fuel. Of course, solar panels get degraded too, so they have a half life as well.

I had posited the notion that the 'belters' would use tritium batteries to power their mining ships. The waste product, helium-3, would be traded in for more tritium. The Helium-3 would then get sent back to Earth for use as 'clean' fusion fuel.

Of course, the 'dirty fusion' reactors would use tritium (typically D-T reaction) which makes for 'relatively' inexpensive fusion drives. The Helium-3 reactors just needed too much confinement to be useful in space.

Still, the plausible mid future is talking about fission reactors which makes for an ugly shielding problem for anyone near the active drive.

Tony said...

Rick:

"Getting within a few million miles of the photosphere requires, alas, nearly as much delta v as dropping straight into the Sun."

I come up with something in the neighborhood of 23.5 km/s (including Earth escape), for a minimum energy transfer to coronal interface at 10 solar radii. Pretty steep, but the reactor core and hot loop shouldn't mass more than few tons. Remember, we're not dumping the shielding or any auxiliary machinery, which should have, at the worst, low-level induced radiation.

"What sort of preventive maintenance tasks are actually performed on nuclear ship power plants?"

I'm certainly no expert, but most of the complex stuff -- pumps, condensers, etc. -- is outside of the reactor containment. In principle, except for the hot loop pump(s), all of the moving machinery would be on the cold loop, outside of containment. So maintenance would be the standard steam engineering drill.

It was stressed to us by a nuc chief, as part of our shipboard orrientation, that a reactor is just a kettle. It's one that bears watching, and that can be very dangerous if let out of control, but it's ultimately one of the simplest machines in the world, for the amount of power it can generate.

"So I tend to agree with Raymond that drive maintenance would pretty much have to be between missions, where you can bring heavy shielding and equipment into play without lugging it around (apart from the initial lift to orbit)."

I'll reiterate what I said earlier. I don't think we can use reactors in space that aren't at least 98% reliable, on the hot loop side, for the entire planned service life. I realize that's a tall technical order, but to me it's just a cost of doing business professionally and safely.

"For the inner system, out to Mars orbit, solar electric is IMHO far preferable to nuke electric - no radioactivity and basically no moving parts. Unfortunately it gasps for sunlight by the time you reach the main asteroid belt, let alone Jupiter."

Solar power doesn't have the energy density for high delta-v electric propulsion.

Rick said...

23.5 km/s is beaucoup, way beyond the reach of chemfuel, tough even for nuke thermal. The whole drive bus would have to make the swan dive.

If it is politically acceptable to put the nuclear fuel into orbit in the first place, I suspect it will be politically acceptable to dump the waste into a Lagrange point.

On solar electric power, there is already technical discussion of solar wings capable of delivering 0.3 kW/kg at 1 AU. That is about as much as I'd expect of an early generation nuke electric plant.

This does not count the mass of the actual thruster, but with either solar or nuke electric drives the power supply will be the heavy part.

Thucydides said...

The issue with nuclear drives is probably more complex than a first pass indicates. In order to keep mass down to an acceptable limit, much of what we see as separate systems will have to be combined on a practical spacecraft.

For example, a vessel using a NERVA type NTR will probably have some sort of flight idle mode where the reactor is still running at low power and coolant is being circulated in a closed loop to generate electrical power. This provides lots of "hotel" power and reduces thermal stress on the reactor core, but separate hot and cold loops might be omitted to keep the weight and parts count to a minimum.

To really get going with electric drives, a very lightweight, high energy density power core is needed, which leads to exotic fission designs like vapour core reactors and probably using some form of MHD to extract the energy; hardly user friendly designs with or without a maintainence base in orbit. (Is it any wonder that a small IEC fusion drive sees so attractive)

Going back to the idea that the space industrial base will be radically simplified, some form of beamed power system will be favoured, since the heavy and expensive parts will be close to home and the service crew, while the ships will have the light and relatively simple stuff on board. Solar cell banks or thermal mirrors won't have to be scaled up to such extreme sizes if they are drawing power from a laser in cis lunar space.

This will also carry over in terms of designing modules qualified for spaceflight, they will be simplified and use a minimum number of standard "templates" and interfaces. Once again, the idea is to minimize the parts count, as well as to gain as much quality control (since the overall production runs will be greater). This will also make the use of 3D printing technology more feasible for emergency repairs on board, since the amount of raw materials, design templates etc. will also be minimized.

As a bit of an aside, I recently came across an english edition of Von Braun's "Das Marsproject", which is about as Rocketpunk as you can get. The contrast between a fleet of Saturn 5 sized space shuttles making about a thousand launches to build a fleet of ten interplanetary ships and Robert Zubrin's "Mars Direct" only 40 years later (One Saturn class launcher for the return vehicle/fuel processor module and one Saturn class launcher for the manned ship [with a crew of only 4]) is pretty illustrative of how our capabilities have progressed.

Tony said...

Rick:

"23.5 km/s is beaucoup, way beyond the reach of chemfuel, tough even for nuke thermal. The whole drive bus would have to make the swan dive."

I got to thinking about it, and I guess you're right. I think the solution would be to carry a decommissioned reactor core going uphill to Mars, and dump it right before starting deceleration for Mars orbit insertion. That should be safely above solar escape velocity.

"If it is politically acceptable to put the nuclear fuel into orbit in the first place, I suspect it will be politically acceptable to dump the waste into a Lagrange point."

Problem with the L points is that they're only relatively gravitationally stable. Anything you put there is likely to be perturbed out into a random orbit after a decaded or two. So you would have to keep an eye on things and mount a station-keeping bus on every disposed reactor. Just more things to go wrong.

Which leads me to my other objection -- in designing for safety, one may accept risks that are necessary to get something done, but that doesn't mean one should accept risks that aren't. Putting the reactors in orbit and disposing of them when used up are necessary risks. Hanging on to them, betting the come, isn't.

"On solar electric power, there is already technical discussion of solar wings capable of delivering 0.3 kW/kg at 1 AU. That is about as much as I'd expect of an early generation nuke electric plant."

If they're comparable at 1 AU, one would think the nuke would have superior performance further out -- like anywhere we're likley to send people in next couple of centuries. Of course, if you can get an all-up solar power supply with the energy density to match a nuclear reactor at minimum mission insolation, I'd be happy to include it in the design, for reasons that should be obvious. But...but, I don't think we'd be talking about nuclear electrics except for the fact that they have value in some regime(s).

Rick said...

Oh, definitely nuclear electric has a place - anywhere much beyond the orbit of Mars.

But for travel inside the orbit of Mars, which we'll presumably undertake first, solar electric has enormous advantages, not just in operation but development. The entire needed technology can be developed first for robotic probes and simply scaled up.

In contrast there must be a fairly large minimum size for a reactor-powered nuclear drive bus. I'd guess on the order of tens of tons, larger than you need or want for robotic missions.

Raymond said...

Tony:

For some number of interplanetary craft in operation, placing a small portion of the industrial infrastructure into space would make economic sense. If the MTBF of a nuclear module is, say, five years, but it could be extended to ten with a mid-life service, then at five, or ten, or maybe twenty craft (pick a number, since until we actually build them we won't have detailed knowledge of the common failure modes) the cost of the servicing station would be less than the value gained by extending the powerplant lifetimes. At which point, put a station up. Until then, you're right, dump the reactor and swap in a new one. Just don't make the assumption that it will always be so. Repair will not always be deprecated in favor of replacement for all levels of space activity.

And the reactor will resemble a jet engine far more than a kettle. Terrestrial reactors are generally pressurized water reactors with separate coolant loops for the core and the generator. Most space designs are gas-cooled solid-core, with a single coolant loop (usually helium) and a Brayton cycle instead of a Rankine one. (There are also the vapor-core designs with magnetohydrodynamic generators, which are the most likely type to breach the 1 kW/kg level, but we haven't yet even built test reactors.) These will have a lot more hardware behind the shielding, and I suspect the most common failures will be in turbopumps and turbine blades, not the core itself. That's the sort of failure which lends itself to component-level replacement instead of module-level.

As for reprocessing, bear in mind that much of the mass of reprocessing on Earth is due to environmental concerns and waste containment, both in terms of plant size and the materials used to dilute the waste. Both can be substantially lessened by reduced containment (you're in space, after all) and by using fast-spectrum reactors to burn the long-lived actinides. In fact, certain types of "spent" fuel would be quite well-suited to use in reactors on the Moon or Mars. I say stash it somewhere - and if you're prepared to spend over 20 km/s to shoot it into the sun, you could also bury it on the Moon or strap it to an asteroid just as easily.

Rick:

Even the 0.3 kW/kg solar panels are still at 1-2 m^2/kg, which means a 300 MW solar array will be oh, roughly a square kilometer or two. Not plausible at all with present structural tech. Not a problem, I suspect, if we can build space elevators, but pretty unlikely for the next couple centuries.

That's the real problem with solar - not the mass, but the sheer bloody size. Gossamer wings are a nice image, but at that size, we might as well be talking solar sails instead of solar panels.

Nuke-electric, on the other hand, is far more compact (even with the radiators) and scales down much better than you think. SAFE-400 is 1200 kg including generator, and gets 100 kWe. No "tens of tons" required.

Nick P. said...

On the topic of space nuclear reactors I've often wondered if a sodium cooled fast reactor might fit the bill.

They've got fantastic power density somewhere in the range of a megawatt thermal per liter of core volume. Molten sodium can be pumped electromagnetically so coolant circulation pump would have no moving parts and be virtually maintenance free. The "control rod" could be a ring shaped neutron reflector that when moved somewhere along the core will reflect enough neutrons back to allow a chain reaction but otherwise too many neutrons will leak out halting the reaction. Perhaps the reflector ring itself could be electromagnetically actuated so that on the 'hot' side of things there is all of one (!) moving part.

On the 'cold' secondary coolant loop you could use a eutectic with a low melting point (Al-Mg?) so as not to have to worry about the loop freezing when the reactor shuts down (or at least requiring only minimal heat input to keep it fluid).

Lets say the secondary loop uses centrifugal pumps with fluid bearings lubricated by the coolant itself, a hand full of valves and refill connections and we come out to what, maybe a dozen or so moving components?

I Am Not An Expert and there might be some major show stopping detail I'm missing (Please! Tell me! I'd like to learn more.), but that strikes me at first glance as being a fairly reliable setup.

Rick said...

Solar electric wings are indeed humongous, but I don't see why sheer unfurled size would be a deal breaker. No doubt we'll make a couple of unwelcome discoveries about flexing, but in the end we're only subjecting it to a milligee of acceleration.

I wince at 'turbopumps and turbine blades,' because I hear the scream of money being sucked into the vortex.

On the other hand, I googled SAFE-400 and was duly impressed. That is indeed a scale suited to robotic missions, comparable to the Cassini bus.

I tend to agree that once you have, say, a fleet of half a dozen interplanetary ships operating on a regular schedule, some kind of on-orbit maintenance between missions becomes viable.


Note that there are some operational challenges we brush past. When a nuke electric ship is under power, its danger zone extends hundreds of km in all directions unless you are heavily shielded. These ships do not fly in formation!

Even when reactors are shut down I imagine that ferry operations will be pretty delicate. Basically approaching the ship from the forward end so that you are protected by its shadow shield.

Tony said...

Raymond & Rick:

"For some number of interplanetary craft in operation, placing a small portion of the industrial infrastructure into space would make economic sense."

"I tend to agree that once you have, say, a fleet of half a dozen interplanetary ships operating on a regular schedule, some kind of on-orbit maintenance between missions becomes viable."


For some number of vessels in regular service, yes. I think that number has to be in the high dozens, at least. Keep this number in mind when you read the following comments.

I think in the next couple of hundred years, the human interplanetary fleet is going to be under fifty vessels at any one time. Every vessel will be effectively in its own class, since even the largets operators will only have maybe a half dozen to a dozen vessels, bringing a new one online every two to three years.

And remember what I said earlier about every vessel being a point of national technical pride. Very few modules are going to be standardized, and then only across a few ships. Even the components that go into the modules will be largely non-standard across the whole fleet. And what nation interested in maintaining national technical pride is going to give the specialized knowledge and tools for their spacecraft systems to whoever is running this notional on-orbit maintenance station?

Rick said...

Thucydides' aside is really important. Space geeks are huge whiners, because we basically all compare reality to 2001: A Space Odyssey, and reality comes up the loser.

But the real reality is that we've made remarkable progress. When we do go to Mars the mission will be much smaller but much more sophisticated than von Braun imagined.

It will also be a lot more expensive, but von Braun's cost figures needed to be viewed through enough green eyeshades to block gamma rays.

Raymond said...

Nick P:

You're not missing any showstoppers. Reactors similar to what you describe have actually been built. The Soviets had a lead-bismuth eutectic reactor for their Alfa class subs, and the Americans initially had the Seawolf running a sodium-cooled reactor. Both sodium- and lead-cooled fast reactors are part of the Gen IV blueprint. There are some hiccups: the Alfas had to be kept warm, even in port, which was something of a challenge, and the Seawolf's sodium coolant leaked, which was a Big Problem considering sodium burns in air and explodes on contact with water. These wouldn't really be problems in space, though.

What would be a problem is the operating temperature. For a space reactor you want to have your operating temperature as high as your fuel and core materials will allow, so that you can increase your heat rejection efficiency (which scales to the fourth power of the temperature). Liquid-metal reactors can't get into the ~2000 K regime that helium-cooled solid-cores can, much less the ~3500-4000 K a vapor-core design could theoretically reach.

See here, here, and here for the Wiki Intro.

Rick:

I consider anything with a surface area measured in square kilometers to be a mega-engineering project. Even at milligee accelerations, you'd be looking at some serious torsion. In the 2-3 century timeframe, I wouldn't bet on it, simply because you'd require a lot more industry in space than even I'm proposing at that point in time.

And really, isn't that size regime the purview of solar sails (which would be lighter and require less structural reinforcement over their total area)?

Tony:

We don't seem to have that much of a problem sharing specs with the Russians WRT the ISS. We've already established international standards on docking collars and experiment bays, not to mention electrical interfaces.

Plus, I'm not thinking a mega-station like the one in the OP. I"m thinking a docking truss, some shielding, a couple robotic arms and maybe one of those fabs we were arguing about earlier. Five hundred tons, max - probably the same size and mass range as the crafts it services. It'd be there to facilitate module changes on the hot side as much as "repair" things. I don't think you'd need dozens of craft to make it pay off.

Note originally that I mentioned refit among the station's uses, too. Our experience with the ISS shows that docking and module additions/replacements were made easier with robotic arms instead of relying solely on RMS thrusters. I think outfitting a craft for its next mission would be streamlined by doing it with the aid of such a station, at a nominal delta-v cost to the mission when at the edge of Earth's gravity.

Thucydides (+ Rick):

The one problem with comparing current Mars mission profiles to Das Marsprojekt is that we've scaled down the goals, as well, or at least dragged them out over multiple missions.

I would love to see those thousand launches, though.

Tony said...

Raymond:

"We don't seem to have that much of a problem sharing specs with the Russians WRT the ISS."

Only because we've gone joint venture with them for cost control and uphaul/downhaul redundancy (and, it turns out, reliability).

There's no fundamental reason why future operators in an actively interplanetary future would be more than minimally interoperable -- probably at a level conceptually comparable to a RESTful web service that returns XML to the client. What goes on inside the ship is totally up to the operator, just as long as he can meet some basic interface conventions on the exterior.

"Plus, I'm not thinking a mega-station like the one in the OP. I"m thinking a docking truss, some shielding, a couple robotic arms and maybe one of those fabs we were arguing about earlier."

I think what we're missing here -- and I'm just as guilty as everyone else -- is that aside from a high delta-v propulsion unit and maybe a nuclear power supply, there are few technical difference between an orbital station and an interplanetary spacecraft. There's no reason an interplanetary craft wouldn't carry its own robtic arm(s). It's not like those things are particularly massive or bulky. That goes for most things an orbital station could offer.

Rick said...

Tony - Yes, the early period of interplanetary travel (whatever that means in chronological terms) will be characterized by granularity. There will only be a small number of ships, built by different agencies or consortia, and representing successive design generations.

But because a 'fleet of prototypes' is so staggeringly expensive, there will be efforts within each agency to standardize what can be standardized. On the large scale, pods configured to your biggest booster, but also fittings like hatches.

So. Suppose a major consortium has half a dozen ships. Built over a few decades, each one has new features and upgrades over its predecessors, while older ships are also upgraded with new pods sent up from Earth.

Obsolete pods are disposed of, outward if hazardous, downward otherwise. There is no reason to save them, because any serious refurbishing on orbit is impractical.

But all the ships and many of the individual pods share many standard fittings, When the Mark II hatch replaces the Mark I, you are not going to ditch every billion-dollar pod with Mark I hatches. You'll send up Mark II hatch kits, and an on orbit crew will install them.

This need not call for a 'station,' but about this time you get one more or less for free. Your oldest ship is downchecked for deep space service, but the hab is still safe for Earth orbit operation.

So just leave it in parking orbit and bring other ships into formation for on orbit servicing, giving you hotel space, onboard power, and so forth. This is a lot more convenient than having to keep ship's systems operating while you're buffing everything up.

Just to be clear, I am NOT talking about anything remotely like 'overhaul.' More like a thorough housekeeping. Gaskets, filter screens, lights, possibly a complete flush of the life support system - requiring alongside life support, if any human crew is going to stick around through the recycle.

So I think this scale, half a dozen or so operational ships in a constellation, is just about the point at which requirements and resources converge on an incipient orbital interface and support base.

Rick said...

I think what we're missing here -- and I'm just as guilty as everyone else -- is that aside from a high delta-v propulsion unit and maybe a nuclear power supply, there are few technical difference between an orbital station and an interplanetary spacecraft.

I plead not guilty, and don't even need to abuse my position as supreme judge of this blog. :-)

Tony said...

Re: Rick

I think you have a misconception here. I know that in modern maritime/naval practice, and even in aviation, that when the next generation of whatever is voyage/flight qualified, it's backfit into existing vessels/aircraft. But that requires the kinds of dockside/ground support personnel that just aren't going to be available in space.

You mentioned hatches as an example. Well, watertight/airtight doors come in sets with their mating surfaces, and are installed as a unit. That involves a structural modification, which in turn requires specialized technicians and yard/hangar support. It's not a simple component replacement. Most of what seems to be perceived here as routine maintenance really isn't. It requires the direct, immediate support of large industrial organizations.

As for downcertified ships being used for stations, okay, that's certainly possible, but one has to have a reason for it. I'm just not convinced there is one.

Raymond said...

One other use for a station we seem to have ignored (especially a downrated interplanetary craft) is training. I suspect certification for interplanetary flight will be over and above that for orbital. What better place to conduct it than a downrated craft parked in Earth orbit? Same goes for test flights for new equipment and modules, I suspect.

Tony:

All the uses we've mentioned - hab and nuclear maintenance, vehicle assembly, cargo and propellant staging, mission-specific refit, basic fabrication, advanced training - can be done without a station (or skipped). A station, I think, makes them easier and lowers the marginal cost, especially the downrated-interplanetary variety. As the constellation grows, the marginal utility of these activities increases. At some point those two curves intersect. I think it'll happen at closer to five craft, you suspect fifty. We may both be off. The intersection is somewhere, though.

As for the current joint-venture nature of the ISS, well, it's true we wouldn't necessarily require such a thing for interplanetary manned missions, but it might also be useful for the same reasons it was for the ISS.

Rick said...

I was picturing either a hatch that fits current mating surfaces, or mating surface and hatch as a modular kit, more or less bolted into place.

That might be impractical, but we're not mainly concerned with hatch technology. Surely a pod will be filled with what amount to plug & play modules; in fact I think you made that point in the first place.

The kind of on orbit servicing I'm picturing is not fundamentally different from what we have already done with the Hubble servicing missions, and presumably do aboard the ISS on an ongoing basis. Out with the old, or worn, and in with the new.

I would call the station a 'tender,' but without the connotation of machine shops and all that. You mentioned robot arms. They aren't that heavy, but a ship on semi-permanent parking orbit can be fitted with more than you need or want to haul to Mars or Ceres and back.

But the biggest utility, so long as you have people at the front end of this loop, is the hotel/barracks function. If you are going to steam clean a hab, or whatever is the equivalent, it is just a whole lot more convenient to have another hab to eat and sleep in.

In the earliest days you'll just work around it, port and starboard or some such, but once an older ship becomes available, why not press it into service?

The ship might not be downchecked, just have an obsolescent drive bus, and not justify the cost of clamping on a new one. The cost of retaining it in orbital service is the ongoing preventive maintenance cycle of the hab.

So the question is whether the cost of maintaining the hab in service is justified by the convenience of using it as a tender for servicing other ships.

Put that way I can see the argument going either way, depending on fairly fine points of cost accounting and engineering practice, and for that matter historical accident.

Robbie said...

Wow! This reminds me so much of the USG Ishimura from the game Dead Space! Except, this is what a realistic USG Ishimura would look like. Awesome work!

Milo said...

Rick:

"When a nuke electric ship is under power, its danger zone extends hundreds of km in all directions unless you are heavily shielded."

Which it should be. You need to be able to dock with other ships, and you can't do so with your engine off because you wouldn't be able to move into position to dock in the first place!

The whole concept of a shadow shield is a horrible lie perpetuated by writers who think that deliberately hazardous equipment is exciting.



Raymond:

"I'm thinking a docking truss, some shielding, a couple robotic arms and maybe one of those fabs we were arguing about earlier."

Robotic arms don't seem worth having a space station for. You can reasonably put a couple of those on the ships themselves, and even if you don't, you still have human arms.

You need some reasonably advanced tools on the station to justify its presence.



Tony:

"What goes on inside the ship is totally up to the operator, just as long as he can meet some basic interface conventions on the exterior."

Sounds sensible to me. You need international agreement on docking interfaces, communication protocols, and such, but anything that doesn't interact with the outside is your own business.

However, there could still be financial advantages to cooperating on other things. And when you have significant civilian space usage, people are going to be paying more attention to financial benefits than to national rivalries.


"You mentioned hatches as an example. [...] It's not a simple component replacement."

Well, actually, all you really need is a "plug" that has a Mark I hatch on one side and a Mark II hatch on the other side. That's how jury-rigged interface mismatch fixes are usually done.

Raymond said...

Ah, Milo, you and your utter hatred of both radiators and shadow shields. You realize shadow shields are a creation of NASA designers, not writers, right? And that if you do the numbers for full 4pi shielding of a reactor it will destroy your payload fraction?

You can still dock just fine - approaching from the front. And a thousand kilometers is close formation for interplanetary travel.

As for the robot arms, I was talking about the heavily-shielded type used for remote handling of nuclear reactor components, which are more massive than their more pedestrian brethren, and would best be left in Earth orbit rather than packing them all the way to Mars and back.

Rick said...

Belated welcome to a new commenter!

Also, ships do not use their main drives in rendezvous and docking. They'll use some kind of OMS. Nuke electric ships probably don't use any drive, but let ferries sidle up to them.

How much radiation is put out by shut-down reactors? Is there any prospect of putting a cold cap shield around reactors when in parking orbit? Or would that still be too heavy?


Solar electric. First a note that solar sails produce far less thrust per square meter of sail area.

Looking at my sim for a ship carrying 20-odd people to Mars (200 tons gross payload), it has specified drive power of 90 MW, so at 300 W/m2 it would need 270,000 m2 of wing area.

So the wings might have a span of 1 km and chord of 270 meters. Wing mass is 270 tons. This is beaucoup big and very lightly built - but it would be pretty much held together like a box kite; the actual loads will be a fractional ton.

For that matter there's really no need for a single wing - your hab pod can be towed by a flock of butterflies, like birds pulling Cyrano de Bergerac's moonship. Rather elegant, really, and you can assign butterflies according to payload and mission, from one to dozens.

Beyond Mars the elegance doesn't matter. But in the inner system - including, importantly, Earth orbital space - solar is competitive with at least early generation nuclear, and just stupendously more headache free.

Milo said...

Rick:

"For that matter there's really no need for a single wing - your hab pod can be towed by a flock of butterflies,"

Wings need to be next to each other, though, not in front of each other, otherwise they'll be in each other's shadow. So they'd need to be in formation with each other to ensure they don't get in each other's way, and the end effect on structural stresses would be similar to if you just had one big wing.

Of course, "towed" isn't accurate, since these "wings" are just generating energy - the thrust is provided by an electric engine on the main body, pulling the wings with it.

Tony said...

Well, I think I've said enough to make my point. I'm perfectly sanguine to leave it up the reader.

Jedidia said...

And a thousand kilometers is close formation for interplanetary travel.

Not for an orbital docking aproach, though. I have often wondered if actually the concept of a shadow-shield makes an orbital transfer station improbable all by itself.

The problem is, you have to synch orbit, which is usually done by taking on a slightly different orbit that intersects with the target orbit. Once you get close enough, you have to anihilate your relative velocity. While you usually don't have to thrust exactly in the direction of your target, you still have to maneuver pretty heavily. And you usually have to do it within a frame of 100 kilometers. If you match velocity at 500 to 1000 kilometers out, you'll have a hard time reaching the station (no, you can't just leisurely drift towards it from that distance, that's not how an orbit works).

While I'm not saying that it is impossible to dock to a station with a ship that has a shadow shield, it is at least DANGEROUS. you mess up one maneuver so close to the station, and everyone on there will have to get his ration of RadX at the sickbay. It simply seems not practical for mass commerce.

The situation improves the higher the orbit, because you have longer periods, i.e. a longer time window until your orbit takes you too far away again from the station. I'd have to see if docking to a GEO station is possible when matching velocities at a thousand kilometers, I know that it's practically impossible in LEO. And it will need a pretty strong RCS system, because on the final aproach use of the main engine is effectivly prohibited. The only way out of the dilemma I can see is a tug, but that again needs a whole lot of even more infrastructure.

So, gradually I start to think that indeed, for the plausible mid-future, an orbital transfer station might not be as practical as it seems at first glance.

Once you have a real MASS of traffic, it might make sense to have an Orbital station in an easy to reach orbit from the surface, and have atmospheric transfer vehicles up there that collect and distribute cargo in orbit, so the heavy lifters from earth only have to get to the station.

Anonymous said...

I would have thought that 'atmospheric transfer vehicle' would be a better term for the heavy lifters and shuttles moving between Earth and the station, while the craft moving between the station and the interplanetary craft would be 'orbital transfer vehicles', maybe colloquially called ferries or tugs.

R.C.

Jedidia said...

ah sorry, that was actually supposed to say "orbital"...

Rick said...

A flock of butterflies might provide an actual tow, because there is no reason not to mount thrusters on the butterflies, in addition to (or instead of) the payload.

The butterflies do have to fly in formation, so they don't shadow each other, but the formation doesn't need to be rigid because they are connected only to the payload, not each other.


Jedidia - yes, orbital rendezvous with nuke electric ships is a ... challenge.

Once commissioned they may never come closer to Earth than high orbit, perhaps even higher than GEO, with ferries connecting to low orbit. This means more infrastructure, but nuke electrics are so awkward to approach that there may be no choice.

This arrangement, I agree, does not leave much role for a station.


RC - There is no well established nomenclature for these various types of transfer vehicles. Here are my biases, YMMV:

Shuttle - surface to orbit. (Though in this century they may have little similarity to the classic spaceplane image.)

Ferry - inter-orbit transfer.

Taxi - short range transfer. (For getting between ships on rendezvous but not docked without going EVA.)

Tug - a drive bus that temporarily clamps onto other ships/pods to change their orbit.

Tony said...

Jedidia:

"Once you have a real MASS of traffic, it might make sense to have an Orbital station in an easy to reach orbit from the surface, and have atmospheric transfer vehicles up there that collect and distribute cargo in orbit, so the heavy lifters from earth only have to get to the station."

Sorry, but orbital mechanics says that's not a good idea. It's fundamentally easier to get to a given orbit from the ground than to go to another orbit before transfering to the target orbit. This is because velocity is a factor in the plane change energy equation. And you're moving a lot slower on the ground than you would be in orbit.

Here's a real world example that demonstrates the principle:

The ISS orbital inclination is 51.6 degrees, moving at 7700 m/sec (on the average). Launching due East from Cape Canaveral, you achieve an orbital inclination of 28.5 degrees.

Now the energy equation for simple plane changes is (from Bate; eq. 3.4-1):

delta-v = 2v * sin(theta/2)

Where:

v = orbital velocity = 7700

theta = angle between orbital inclinations = 23.1

sin(23.1/2) = sin(11.55) = .2002

2 * 7700 = 15400

15400 * .2002 = 3083 m/sec

Now, obviously, the Shuttle doesn't have that kind of delta-v in its OMS engines. But if you launch NE out of Canaveral you can get to the ISS, losing only a few percent of payload. (Yes, the useful payload, in the case of the Shuttle, is significantly reduced, but you have to remember that, for the Shuttle, the payload includes the Shuttle.)

One might argue that this is an extreme example, and it is. But the principle remains the same. If you're bringing something uphill to orbit, it's always cheaper just to go to the orbit you want to ultimately be in.

Tony said...

Rick:

"Once commissioned they may never come closer to Earth than high orbit, perhaps even higher than GEO, with ferries connecting to low orbit. This means more infrastructure, but nuke electrics are so awkward to approach that there may be no choice."

Now here's where intermodal operations make sense. It would cost a lot of energy to take an Earth-orbit shuttle, up to a high orbit. It's more efficient -- presuming you can make the necessary technologies cheap and reliable enough -- to bring the pax/cargo/fuel and transfer fuel up to a minimal mass ferry that takes them the rest of the way up to the parking orbit.

Rick said...

How does it work for apogee/perigee changes, rather than plane changes? Is there a delta v cost difference between going into LEO and then a transfer orbit (to geosynch or wherever) versus boosting straight into the transfer orbit.

But in any case the real concern is propellant, not energy or even delta v. A payload bound for high orbit might go into low parking orbit either to refuel or to switch to a high ISP drive. The latter will use much more energy and delta v for the climb, but much less propellant, reducing the total lift from Earth.

This is justified IF the cost of the ferry is less than the savings on lift mass. Which will only happen when you have a lot of inter-orbit traffic.

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