Wednesday, August 10, 2011

Destination: Mars

ESA Mars Lander
The first human interplanetary mission will, more likely than not, go to the Red Planet. Apart from the Moon it is the easiest major body in the Solar System for us to reach. Its surface bears evidence of rivers and seas, and liquid water may still occasionally flow there. The similarity of its landscapes to the American Southwest is an illusion, but it remains a candidate for life, and its chief rivals - Europa and Titan - are far more distant and hard to reach.

A single image (of an artifact, for example) could of course change all this. But for now at least, Mars is the likely first place to go.


I am not concerned with pure stunt missions, whether by some multi-billionaire or an emergent great power. For this discussion I presume that a human mission to Mars is intended to explore Mars. Yes, other motivations will surely be in the background, involving the usual suspects. But the more serious the exploratory intent, the more likely that going to Mars will lead to further developments rather than end up as a costly one-off.

This does not mean that every individual mission must 'do science.' The engineering demands of safe human interplanetary travel justify what amount to shakedown missions, say, a manned flyby that does nothing but demonstrate our ability to perform the transfer mission. But the program as a whole should be aimed at advancing our knowledge of Mars.


The model here is not Apollo but the robotic deep space program, which in spite of some embarrassing failures (feet/second != meters/second), has in all been a profound success.

A first implication is that a human mission will be undertaken only when robotic missions reach diminishing returns. It is no doubt true that a geologist with a hammer could learn more about Mars in a day than our rovers have learned over years. But the cost of sending that geologist would be very much greater than the next few rovers. And human missions are subject to some constraints, such as landing where it is safe to land.


My instinct in thinking about a Mars program is to proceed cautiously and incrementally - unmanned tests of the vehicle, then a human flyby, then orbit without landing, and only then a full-on landing. I am not sure that each of these stage is strictly necessary, and there are alternate possibilities, such as a visit to a NEO, that would similarly exercise spacecraft and procedures.

And some of these missions - notably, orbiting without landing - might be able to 'do science' on an important and relevant scale. In particular, a crew on Mars orbit can operate surface vehicles and manipulators remotely, but without significant light lag - like steering a minisub from the surface, not steering a rover from Pasadena.

This is as good a place as any to note that 'going to Mars' combines at least two very distinct space missions: the deep space journey to Mars orbit and back, lasting at least months and perhaps most of two years; and landing on Mars, working there for weeks, and lifting back off to Mars orbit. This in itself is reason to test the Mars orbital capability before the surface landing.

Mars Direct argues in effect for a very different functional division - in effect a one way trip to the surface of Mars, then use of a second pre-positioned (and pre-fueled) spacecraft for the trip back. This feels cut-rate and precarious to me, not least because Zubrin is so much like a real estate promoter, not quite trustworthy on principle.

To be sure, there's no reason this architecture couldn't be tested in an unmanned mission, but I also have doubts about packing the hab elements into form factors suited to Mars landing and liftoff. It seems like awfully cramped crew quarters for such a long mission, or else a much larger cabin than you need to carry the crew and some rock samples from the surface to Mars orbit.

In any case, as longtime readers know, I have bias in favor of fast human travel using high ISP propulsion - most likely solar electric, though perhaps nuclear electric - for getting to Mars orbit and back. Faster travel means less exposure to radiation and weightlessness, the main health hazards of prolonged spaceflight.

Solar electric has now been successfully flight tested by the Dawn mission. A fast (~3 month) trip to Mars requires a much higher drive power/mass ratio, which may not be attainable. But solar electric space propulsion is far from technical maturity, and it may well be able to approach the 1 kg/kW standard for fast travel. .

Electric drive pretty much precludes the Mars Direct approach anyway, since an electric spacecraft is ill-suited to aerobraking, and doesn't need it. The surface components of the mission can be sent separately - a Hohmann transfer is fine, since the crew isn't aboard until the Mars landing.




Discuss.


The image, from a European proposal for Mars exploration, is recycled from an earlier post on interplanetary exploration.

248 comments:

1 – 200 of 248   Newer›   Newest»
Gnaskar said...

"Faster travel means less exposure to radiation and weightlessness"

For anything larger than the very smallest craft, cable spin induced artificial gravity becomes a serious option. Assuming the use of a high thrust, short burn engine, and aerobraking to slow down on the other side. So I guess that takes me down the opposite extreme, ruling out nuclear/solar electric for the same reason you'd prefer it. High thrust engines also means slightly less mass restrictions than electric, canceling out longer time exposed to radiation with more shielding.

Of course, cable spin gravity is virtually untested, as is most forms of high speed aerobraking.

@Mars Direct
"It seems like awfully cramped crew quarters for such a long mission, or else a much larger cabin than you need to carry the crew and some rock samples from the surface to Mars orbit. "

The plan, from what I gather, is to use a big capsule to get there, and a small one to return. The semi-direct variant even goes so far as to have three craft. One hab (also a craft for the crew to go to the surface in), one Mars Ascent Vehicle (a small capsule for bring crew and rocks to Mars orbit) and a return vehicle. It's still a bit frail as plans go, having to have three perfectly functioning parts, two of which have been effectively abandoned for two years before the crew arrive.

-Gnaskar. (Long term reader, first time poster)

Monte Davis said...

I'd take the Zubrinistas a lot more seriously if the resources devoted to the Devon Island PR-fest had gone into a small-scale but full-length trial of the chemical engineering.

1) Build a small room within which temperature, insolation, and atmosphere all cycle as nearly as possible to what we now know of the Martian surface.

2) Let a bench-scale apparatus inside, with outside power but no supervision or maintenance, produce methane and water for a couple of years. Extra credit for electrolysis and storage of H2 and O2.

IMHO that would be both more useful and more persuasive than any number of fanclaves in the Canadian Arctic.

Monte Davis said...

Oh, almost forgot: the room should also incorporate Mars-like dust (complete with nifty peroxides and superoxides) and low-torr winds.

Gas- and liquid-phase chemE is much much easier than pushing lunar regolith around, but you do need to deal with regolith that insinuates itself into your pumps etc.

NB that I'm not asking for Mars-surface gravity; I'm feeling benign today.

Anonymous said...

I agree with Rick's general approach: best wait until a lot more has been done with robots and best wait until a better interplanetary transportation (such as a very efficient solar-electric system) is available.

But I don't think it would make any economic sense for people to stay only "weeks" on Mars, except perhaps in the case of an initial mission which would be tasked mainly to lay groundwork for the next one.
If your life support can handle a long voyage, why couldn't it handle a long stay? Once you've invested in making the surface expedition more than an improductive test and/or symbolic achievement (which implies, as Rick writes, that you wouldn't launch the hab element), prolonged planet-side life support becomes less expensive than life support on the return-trip even if you don't make use of Martian materials.

And I'm amazed the support for a crewed Mars flyby.
As to putting a crew in orbit, I don't believe remote-controlling robots from orbit would be economic except as part of a manned landing mission or perhaps if you had an implausibly expensive robotic armada (but at that point, you really want a manned station in Mars orbit). But it could make sense with some assumptions.
What really puzzles me is what benefit one would derive from putting a live crew on Earth-Mars test flights. There's so much stuff to transport to Mars besides the bodies, you can easily do an unmanned full-size (or rather full-mass) test.
Life support tests are of a different nature and are better done on Earth and near Earth, not on a Mars flight. Doing them on a Mars flight is not cautious! Nor is doing more Mars flights than necessary.
If you're comitting to landing people on Mars and getting them back, everything will have to be paid for and ready at some point to achieve the objective. Preliminary missions which do not advance the objective only add to the overall cost and should therefore be avoided... unless of yourse your plan is to sell a preliminary for its own sake, with no real propspect of achieving the stated objective.
If you want to fund preliminaries, there are many things that can be developed and tested right here on Earth, without any white elephant in LEO, much less a huge interplantary craft. That would be potentially interesting for other purposes than the Mars expedition and relatively cheap. Therefore it wouldn't be such a big loss if the Mars expedition never happened.

Something else suprised me on the other thread: who thinks a productive return trip to Mars lasting years should be done with a crew of three or four?

Finally, it seems some of you believe there would be a place for people in space after a near-future Mars mission. Unless something really amazing is dicovered on Mars, they may be a small number of successive missions but after the objective is achieved, it'll be a "one-off" as Rick says. Do you believe Apollo was a dead-end because it was not "serious" enough? Aside from a scientific expedition to Mars, what would you want people to do in space in the near-future?

Full disclosure for people who have not read the other threads: I do not believe it would be rational to bring back crews from Mars in the near-future nor do I believe something that expensive would be seriously undertaken.

-Horselover Fat

Tony said...

Monte Davis:

"NB that I'm not asking for Mars-surface gravity; I'm feeling benign today."

Just make sure the process design under consideration doesn't have any obvious or hidden gravity dependencies. It would be not so good if the thing got on Mars and started running at 33% efficiency, or 33% yield-over-time.

Anonymous said...

=Milo=



For those looking for some hard science fiction, I suggest The Martian (scroll down). The premise of the story: In the near future, NASA undertakes a series of Mars missions using solar-electric propulsion. During the third such mission, a freak sandstorm forces the crew to evacuate early - and one crew member gets stranded on the surface. The story is about his efforts to survive, contact Earth, and return home, often by jury-rigging the equipment available to him to do stuff it was never meant to.

MarylandBill said...

Just a thought, but I think the real purpose of doing human manned test flights to Mars orbit is that you want to test the full system in operation before you test landing a person on Mars and humans are part of the system. Indeed, having humans on the spacecraft during the long journey will add variables that are probably impossible to model properly without humans on board.

Tony said...

Re: Horselover Fat

Once again, the point of an incremental mission strategy is to do the minimum number fo hard things for the first time on any given mission. Long duration (as in multi-year) interplanetary spaceflight is a hard thing. Going into and launching out of a Mars orbit is a hard thing. Landing and staying on Mars is a hard thing. Taking one hard thing at a time is not crazy. It's simple prudence.

As for the rest of your scattershot points:

Staying only a few weeks on the surface of Mars is a requirement of some high-energy, relatively short duration mission plans. If you're concerened about life support duration, you might choose such a mission.

Other mission plans require long surface stays. A study of such a plan, based on minimal technological assumptions, was presented at a conference a couple of years ago:

http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/41431/1/09-3642.pdf

Note that long surface stays require a lot of resources, to the point that 1/2 of the mission mass is devoted to landers carrying surface stay resources, 1/4 to a crew lander, and 1/4 to the transit hab. This makes an incremental approach

WRT to crew numbers, well, if you're relying on the Multi-Purpose Crew Vehicle (MPCV, formerly Orion) for Earth return, then four is a hard limit imposed by that hardware selection. Note that the mission mentioned above is designed for a crew of four in part because the MPCV is the least risk Earth return vehicle.

WRT returning the crew to the Earth, it's not an option, it's a requirement. While astronauts have been known to willingly risk their lives to fly in space, they're not going to agree to die for sure, nor are they going to agree to spend the rest of their lives on Mars. We're talking about highly intelligent, accomplished people. They've got stuff to live for back on Earth. And it's not like the paying public would go along with marooning under the label "colonization" either.

Finally, you seem to have a funny idea about why and how Apollo was undertaken. At the level of national policy, it was always just a Cold War propaganda stunt. Even though NASA seriously studied a decade worth of continued exploration using Apollo hardware, the whole point of the program was to get a man to the Moon and back. It was mission accomplished on July 24, 1969, when Apollo 11 landed in the Pacific. Some more money was available to keep the program going through Apollo 17, but after that it was on to (supposedly) cheaper space shuttles and space stations.

A manned Mars program, on the other hand, would probably have to be undertaken as a budget-flat long term program with no overall policy objective.

Tony said...

MarylandBill:

"Just a thought, but I think the real purpose of doing human manned test flights to Mars orbit is that you want to test the full system in operation before you test landing a person on Mars and humans are part of the system. Indeed, having humans on the spacecraft during the long journey will add variables that are probably impossible to model properly without humans on board."

+10

Rick said...

Welcome to a couple of new commenters!

Spin would deal with the gravity issue (en route), but as Gnaskar noted, it's another technique to be developed.

I'm not clear on how high thrust eases mass restrictions; it seems like the longer the travel time the more shielding mass the transfer craft must carry.

The gravity issue also applies to the surface stay. We don't know what effect a third of a gee has - it might be nearly as good a full weight, or nearly as bad as microgravity.

Generally my preference is to do the first mission within ~6 months. As we learn more, follow up missions can stay longer until eventually you're rotating crews to a permanent base.

No surprise that I agree with the +10 regarding test flights.

Tony said...

Here's as good a place as any to mention this:

Encyclopedia Astronautica is back up at the same old place (www.astronautix.com). Somewhat different site design and a lot more ads, but otherwise as good as ever.

mithril said...

it seems to me that if we pick mars as the 'next step' in manned space travel*, we could test some concepts here at earth. spin gravity for example, could be tested using a testbed in earth orbit. whether the mars crew could safely live for however long the trip takes in the confines of the vehicle could be tested with copies of the vehicles living spaces orbited and manned in a simulation test for however long the mission is expected to last. and so on.

*personally i'm not convinced mars is a natural choice of destination. there is little at mars that couldn't be handled with remote probes..and any infrastrucutre that allows manned missions allows us to send larger, more capable probes to mars instead..and we could send ALOT more of them, since probes don't require food, air, or water.
i'd be more likely to assume the next major manned missions to be to jupiter or saturn. lots of stuff to learn there, and far enough away that unmanned probes can't really do much fine detail work. to explore europa or titan, we'd have to have alot better AI than is likely to be developed anytime soon, for example. and manned missions to the outer system have the advantage of developing the infrastrucutre needed to move stuff out that far..which means you can build craft that can move ALOT of stuff (reletively speaking) fairly easily to mars if we ever decide to send a manned mission there.

Damien Sullivan said...

I agree that expecting a lack of astronaut return is, to use the original word invoked, irrational. People aren't throwaways.

OTOH I'm not sure crewed flyby is rational either, given constraints on planning and project lifetimes. I suppose it depends greatly on how long the trip takes. If it's 3 months each way on some fast drive, not so bad, you can do a flyby then the next mission a year later. If you're spending 18 months each way in some low-energy trajectory, that's 3 years spent just doing another testing stage, and 3 years for the astronauts never leaving their cramped little modules, and not doing "real" things like landing. Segments of human lives aren't throwaway either.

Automation is such that you can test flyby (or rather, orbit and return) of the large vehicle without crew on board, and you can test long-term occupation of the module in Earth orbit. Admittedly that takes two vehicles, if you do them concurrently, which is its own cost. (Earth surface just for life support, but need orbit for gravity and radiation.)

But after that I suspect it'd be crewed mission with intent to land from Mars orbit and return, especially if travel time is long. Don't have to land if something goes wrong along the way, after all.

Zubrin's total plan might be half-baked but it seems to have sensible parts, perhaps not original to him. If you want a long surface mission, you don't have to send the supplies on the fast trip, but can send them ahead more cheaply. If we can land rovers, we can land pallets of MREs and other supplies. Landing the return launch vehicle ahead of time seems neat too, though you want to make sure sandstorms don't get at it while you come for it.

Anonymous said...

I, too, agree with an increamental approch; a Mars orbit mission without a manned landing makes sense; test the lander and have a long term observitory of the local enviornment of your manned landing site, plus you can put nonparishable items (like tools), in it for use by the later manned landings.
As far as testing the life support, spin options, and radiation shielding of the primary spacecraft, NRO and Trojan missions would be good candidates.

Ferrell

Rick said...

I elfed a duplicate comment.

The return of Encyclopedia Astronautica is very good news! And timely, given recent discussions here that touch on actual space practice and performance.

Europa and Titan are tough to reach! Chemfuel travel times are so excessively long as to be pretty much out of the question, and even early generation nuclear electric is a long haul.

Regarding robotic probes, I think the first second or two of light lag is the killer for joystick style remote piloting - this is why, whether you're dealing with Mars or Titan, I think humans in orbit around it can do a lot of remote stuff on the surface that just can't be done from Pasadena.

I agree that multi-year pure training missions get dicey! But I'm an advocate of fast travel anyway.

Travel time is a big advantage of robotic missions. All of our 'robotic' probes actually have human crews; they just live in Pasadena, easier on the human factors. And we have successfully done missions running into decades - awesome if you think about it.

Rick said...

I should add that a bench test of the chemical technology for brewing fuel on Mars would indeed be more persuasive than Arctic showboating!

mithril said...

@rick:
"Europa and Titan are tough to reach! Chemfuel travel times are so excessively long as to be pretty much out of the question, and even early generation nuclear electric is a long haul."

exactly. if we're willing to just throw money at the russians or private industy, we could orbit a manned mars mission pretty quick. we really don't need much in the way of new technology, just a willingness to spend alot of money and settle for less.

but that wouldn't really help space exploration much. we'd need no real development of cheaper heavy lift boosters. no development of a decent in system drive. no push to really develop the infrastructure needed to push beyond mars.

so i say, aim higher. aim for jupiter or saturn, where we can't explore by proxy. where we have to develop the ability to make space travel easier just to get there.

and if in doing so, we reach a point where we can use a mars trip as a test-bed for jupiter mission technology, great. do it then. but IMO there isn't much reason to go to mars ourselves if we can do it with probes via remote.

i think the fixation with mars stems from the "well, we went to the moon, and once your to the moon, your halfway to mars, right?" misunderstandings.
obviously Zubrin and others with the knowledge of how difficult space travel really is (and i'm not sure zubrin's kept up with the times, IMO) generally have their own agenda's for picking mars. zubrin's big on colonizing it, for example, and sees 'mars direct' as a way to "plant the flag" for such an effort early.

i don't mean to say people who hold those same beliefs are in any way wrong..i just try to be pragmatic. there is little economic reason to settle mars. you can make an economic tie between a space program and economic developments spin off tech for example)..so why spend money on sending people to study a planet that we don't really need people present to study? why not set a difficult goal, that will require some serious new tech (and thus, drop serious new spin-off tech into the economy), and which will explore somewhere we really haven't been able to explore remotely?

Longbeast said...

Off on a slight tangent from how the thread has been progressing so far...

Does anybody know if there is a small asteroid in a suitable orbit such that a mars ship could use it as a radiation shield for part of the trip?

I do realise that you still have to use the same amount of fuel in matching orbit with a rock as you would do in just flying out in open space, but if you can have your manned section of the craft held up against the side of an asteroid, that shields you from half the sky, and halves your radiation dose. It might mean that you could get away with using much less powerful/efficient engines, since you can tolerate longer journey times.

The problem comes in having to find an asteroid that passes close by both earth and mars at vaguely the right velocity. Spending extra fuel to take an indirect route is only worth it if you can save delta-v overall for the missio,

Another problem is that you could only do it once, unless by some miracle there is a naturally occurring cycler craft up there that we haven't spotted yet. You might still need to go fast on the way back.

Coolbeans said...

Once proper lightweight equipment/reactors are developed for electric propulsion, it'll probably be the most effective and economic transportation for a very long while, considering how fast and how much you can move about when you have an alpha of 1, or less. It seems much simpler and "down to earth" than fusion or other more exotic systems, on another note.

However, I doubt holding off missions until we have these systems is a good idea, considering how far away these systems actually are, technology wise. In electric propulsion, the engine does not matter as much as the power system that keeps it running. You need incredibly good reactors to travel fast. "Todays" reactors have a mass/power ratio of 100kg/1kw, and to use electric propulsion in the way people promote it you need 1kg/1kw, or less. These power systems are very, very far away. NASAs goal to create a reactor with 65kg/1kw failed (Mostly budgetary reasons, but it hints that it's not an easy task.). And even settling for something like 15kg/1kw, which is incredibly good, provides very litte advantage over chemical, and NTR is probably superior for Mars/Moon if you want to develop propulsion specifically for manned missions.

Space reactors are not a mature technology, and we might have to wait incredibly long (Perhaps 50 years or more) until these lightweight power systems are fully developed, considering the long way from the reactors of today to the reactors of fast travel, the lower budget and overall political landscape.

There's been a lot of buzz about Solar electric, however, but i suspect it's also based on wayyyyyy too optimistic equipment assumptions, like almost all manned electric propulsion these days. I'd be happy to be proved wrong, however.

Citizen Joe said...

Longbeast has brought up a crude version of the cycler system I brought up so long ago. You put a 'large' cycler object going between Earth and Mars and then traffic just hitches a ride. You still have the same amount of delta-V, but because the cycler has all the shielding and residential support for the year long journey, you don't have to accelerate that part (more than once).

Anonymous said...

Mithril:

"I'd be more likely to assume the next major manned missions to be to Jupiter or Saturn."

Yeah. I favor focussing on our nearby moon until we develop the capability to reach Saturn comfortably.

Not easy, though.



Rick:

"But I'm an advocate of fast travel anyway."

Who isn't? I don't think any space agency would use slow travel for crewed missions if fast travel isn't available. The problem is when it isn't...

Anonymous said...

(SA Phil)

If you had a Interplanetary Nuke/ Electric Space Craft capable of making the round trip -- it would be a lot easier to test the other requirements.

Tony said...

SA Phil:

"If you had a Interplanetary Nuke/ Electric Space Craft capable of making the round trip -- it would be a lot easier to test the other requirements."

Nuclear and solar electric are worthwhile evolutionary steps that we should work towards. But they are not technologies worth waiting on.

Anonymous said...

(SA Phil)

We could make either now.

So the idea that they aren't worth "waiting on" is interesting.

Tony said...

SA Phil:

"We could make either now.

So the idea that they aren't worth "waiting on" is interesting."


There are no space-qualified solar or nuclear systems that even approach the 1 kg/kw threshold of usefulness, and no ongoing programs to develop them. We couldn't "make either now" and maybe not for decades.

Anonymous said...

(SA Phil)

What is the 1kw/kg requirement?

Where is the math that says its some hard number?

The only Power/Mass requirement is where you do not gain a mass advantage over chemical rockets for the same mission.

Besides which you could come close to that number for solar now, not decades from now. Use a non silicon thin film on a polymer superstrate.

No one is making those panels because there is no money in it - not because the technology doesn't exist. Solar is a commidity that sells far too low to justify exotic semiconductor materials without a need.

And the nuclear problem is one of lack of R&D budgets. Political realities "no more nukes" and assorted garbage.

Its the same "market realities" vs technical realities confusion that exists in the other thread.

Coolbeans said...

Reply to Anonymous:

1kw/kg is an absolute necessity. It's just as simple as that. Look up the papers that Adastra puplished, for instance. They already make silly high assumptions on their equipment, and with an alpha of 20kg/kw they only managed to make a Mars plan unwieldier (With ship switcharoos, big ships requiring orbital assembly, etc.) only to end up with the same, or longer, travel time compared to chemical. If you insist on travelling fast, no matter the mission complexity, you can probably build one with todays reactors, but it would almost entirely consist of thousands of radiators, propellant tanks, etc. Like 30 ISS made into one ship, or more. And to what end?

Other, more mature, electric propulsion systems will fare better, like normal ion thrusters, but unless you approach 1kg/kw you always end up with an impossibly (Tens of thousands of tonnes, usually) huge spaceships composed of propellant tanks, radiators and a bulging, metallic monster that is the reactor. And a tiny payload.

And solar power isn't getting close to 1kw/kg. No power system is, since there's no real R&D dedicated to it. Partly because there's no interest, and partly because it's unrealistically optimistic to expect such a system from a short, simple R&D program, and not from gradual technology improvement over many, many decades.

There are a few papers published out there on lightweight power systems, but i doubt their credibility for many reasons.

Electric propulsion is wonderful, but saying that, in the near term, it's some sort of fast transport, then you're not truthful.

Anonymous said...

And solar power isn't getting close to 1kw/kg.
============================

We can already exceed that with thin film deposited on a polyimid. You just approach that for an Earth based system due to water concerns.

In fact I beleive its been ~20 years since they proved you could exceed that.

Unfortunately the 1990's paper by ECD/Ovonics isnt online that mentions their best power/weight achieved for thin film on kapton.

There is this link though:
http://www.sti.nasa.gov/tto/Spinoff2006/er_4.html

If you look at those panels remember 90% of the weight is the package encapsualting the solar panel to keep the water away from the film.

There is a 4kg 330 watt panel within 100 feet of where I am sitting. That one has the packaging you wouldn't need in space.

(SA Phil)

Rick said...

Bear in mind that my original post assumes that we won't be sending people to Mars (let alone beyond) for quite a while - perhaps the second half of the century. More broadly, at the end of near future and beginning of the midfuture.

This is the context of my preference for electric drive: substantial evolutionary development, not a crash program built around essentially off- the-shelf technology.


The power density figure of 1 kW/kg is a figure of merit. It isn't precisely 'the Law of Science.' It an engine performance threshold, and an order of magnitude value that corresponds to a typical acceleration around 1 milligee.

You might be able to get to Mars in three months with 1 kW per 3 kg, but at 1 kW per 10 kg you just won't have enough oomph to use the engine's delta v potential within that time.


The Dawn probe shows the current all-round state of the art, and its power plant gives it an acceleration of about 8 microgees, a factor of 125 less than the benchmark one milligee. But it is the first spacecraft to use solar electric as a 'main drive,' so we are still very early in this technology.

Thucydides said...

Mars is an interesting issue since the problem has been examined on paper since the early 1950's (at least). There are generally two main approaches to the problem; some versioojn of Das Marsprojekt, where you build a really large and capable ship or fleet in Earth orbit and send it to Mars, or Mars Direct. (ORION nuclear pulse drive is a third stream, but implausible for many reasons).

For better or worse, no one has moved much beyond the paper project in the 60 or so years it has been seriously studied, and even flight hardware that *could* have been used has either died in early development or been cancelled. Trips to Mars have been technically possible since the 1960's; Saturn V boosters could have lofted NERVA stages capable of providing enough thrust to do the job (with ISP's of 800 seconds, potentially upgradable to 1000 seconds), but since the Russians were not challenging anyone to a Mars race, it was seen as prudent to reduce the budget for space and put money into projects with larger political constituencies.

As far as I know, the Mars Direct plumbing schemes have been bench tested, although I am not clear if they were actually tested in a Mars box or not. Most of the chemical reactions are pretty straight forward, indeed they are "Gaslight Era" or high school level chemistry, which means that "Mars Proofing" the chemical reactors should be relatively simple to do.

Monte Davis said...

..."Mars Proofing" the chemical reactors should be relatively simple to do...

Sorry, but that's the kind of handwaving that makes me cringe.

Yes, the chemistry is straightforward -- and I salute Zubrin for the broad-brush insight that led to a neat scheme for in situ production of oxygen, water, and fuel for surface exploration and return launch. Given the ugly logarithm in the rocket equation, that dramatically reduces what has to be landed on Mars, and accelerated for TMI, and lifted from Earth.

..And it all depends on that nifty package you send ahead to suck up Martian atmosphere by the tonne, react it with hydrogen in "gaslight-era chemistry," and store the products.

Unattended. For many months. In environmental conditions and cycles very different from those experienced by any such equipment operating on Earth or in space. If there's a glitch, any glitch, the follow-up manned mission goes nowhere.

That is a serious design, development and testing challenge, Thucydides... even before you get to little matters like making it ultra-light/strong for the initial launch and Mars landing, 100% proof against vacuum and radiation for the transit, etc.

So is it unreasonable to ask the Mars Direct crowd to take one comparatively small step on the critical path? To stop exulting in the power of Zubrin's broad-brush insight and start getting into the costly, time-consuming, frustrating details -- where the devil is?

As I hinted before, all this applies tenfold or a hundredfold to anything like mining lunar water, silicates, or He3. I've watched mining and ore-processing startups on Earth; even for something as plain-vanilla as iron ore, technicians and engineers spend thousands of hours installing and fine-tuning before they get close to design throughput. (Some never do, and Vale or BHP or Billiton smiles at the bankruptcy auction.) And that's with beefy steel components unconstrained by weight or power, working in shirtsleeve conditions. So -- tell me again about how a few Falcon Heavy Mark XII launches will be enough to kick off Luna's industrial revolution..?

Geoffrey S H said...

I would like to see fiction that has a Martian landing in the 23rd century or later- why do they always assume its in this century or the next?

Monte Davis said...

Ummm... because since the sprint of 1957-1969, space enthusiasts have grossly, systematically underestimated how hard, expensive, and slow progress would be?

There are lots of reasons, but one big one is embedded in the word "aerospace." People looked at the two generations between the Wright Flyer and big commercial intercontinental turbojets -- and assumed that another two generations would take us from Gagarin to 2001: A Space Odyssey.

That so many people still subscribe to that bogus analogy explains, IMHO, the decades of pointless bickering over "what went wrong." We'd have our Mars landing by now, you see, if it weren't for lack of Vision, or NASA / BoLockMart stodginess, or Green hippie anti-scienceism, or failure to heed my Aneutronic Quantum Fusion Theory, or...

Rick said...

... or $200 billion or thereabouts. Read this post from last year: First Stage.


Robinson's Second Law: For every gram of science handwavium aboard a future spacecraft, there is a ton of plumbing handwavium.

The quote at Atomic Rockets is a bit different, but to the same effect. All cool technologies - such as brewing fuel on Mars - involve lots of plumbing: lines, valves, pumps, filters, and so on.

Plumbing is failure prone, which is why plumbers make good money, which makes it expensive. Plumbing is where the devils in the details mostly hang out. Test it thoroughly before depending on it.

Monte Davis said...

Yup. You've attracted a crowd here with a comparatively high degree of realism along those lines -- as well as exemplifying it in your posts, of course.

Which is why this has quickly become my favorite space blog. Thank you very much for its existence, and for your deft maitre-d'-ing.

Anonymous said...

Sorry, but that's the kind of handwaving that makes me cringe.

=============

Hmm but perhaps this particular handwave isn't as far out of reach as many others.

What are the conditions on Mars that we need to get a chemical reactor to survive?

One of the biggest challenges for internal combustion engines for example is getting them to survive in the Earth's environment.

Two of your biggest challenges .. water in the fuel and dirty air - likely wouldn't be there on mars.

(SA Phil)

Anonymous said...

Spending a couple of decades, and billions of dollars, developing a 'space crusier'(reusable interplanetary) type spacecraft would seem like a serious step toward manned exploration of the Solar System; it may be too serious for some politicians.

Ferrell

Gnaskar said...

"Two of your biggest challenges .. water in the fuel and dirty air - likely wouldn't be there on mars. "

Depending on the amount of dust in the atmosphere, which is currently unknown. The thin atmosphere would suggest little, the high wind speed and low gravity would suggest more. In the end it comes down the size of the grains, and local conditions where you land.

There's a huge difference between a car designed for the Russian winter and one designed for a Sahara trek. finding a site on Mars with good conditions for a fuel production plant could make all the difference.

It's still damn flimsy to base your mission an unmanned new tech reactor on an alien world.

...

A backup plan could be considered. Say you have an Orion type vehicle ready to launch, so if the chemical reactor breaks down after making enough propellant to reach orbit, but not enough to reach Transfer orbit, you can still do the mission.

Having a refueling rover [a basic rover with a big tank of methane/LOX] launchable with enough propellant take the ERV into Mars orbit in case it doesn't even do that would be even better. It would allow the mission to continue without the chem plant, though at very increased cost.

Anonymous said...

Depending on the amount of dust in the atmosphere, which is currently unknown. The thin atmosphere would suggest little, the high wind speed and low gravity would suggest more. In the end it comes down the size of the grains, and local conditions where you land.

=======
But you aren't going to directly intake air for the chemical reactor. You are going to use processed oxygen.

Is that not the system that they are using in the example?

Maybe that makes the oxygen processing portion more challenging though.

(SA Phil)

Anonymous said...

(SA Phil)

On the Orion idea -- why cant we just use a NTR for a Mars lander?

Powered landing and Powered Lift Off.

We have a less gravity .. and no environmentalists to worry about.

You could also use the light weight Nuclear Reactor you use for the lander propulsion as your Electric Drive power source for the interplanetary space craft.

Thucydides said...

The reason no one has tested a Zubrin type chemical reactor is no one is willing to pay for it. In the Case for Mars book, Zubrin quotes an improbably small cost for the bench test proof of principle device, so yes it is a very small handwave to suggest that it is relatively simple and cheap in real terms to Marsproof such a device. We have devices of similar complexity operating in pretty harsh environments from the high arctic to deep under the ocean, so there is a useful knowledge base to start from.

NTR's have been proposed for Mars landers, so there is nothing outlandish about the idea except for the additional nuclear reactor(s) and shielding needed to accomplish this. Using NERVA type reactors offline to provide the "hotel" power for the ship in transit has been proposed, but NERVAs run in this mode would not approach the 1Kg/Kw weight needed for effective high speed transport.

Oddly, splitting humans from cargo could work in either direction. Contemporary solar sail technology is capable of achieving a 1m/sec^2 acceleration, quite enough to get the payload to Mars in 120 days on a flyby trajectory; the cargo can be dropped off for an aerobraking and the sail will return to Earth in about two years. Nuclear powered electric drives could probably match this sort of acceleration for fairly small (read unmanned) ships, providing most of the same benefits for delivering cargo and probes to Mars in advance of a manned expedition, which because of its size and mass, comes via slowboat..

Damien Sullivan said...

1 meter/s2 for solar sails?

Anonymous said...

(SA Phil)

(On Nerva ...)

Nerva was a Nuclear Thermal Rocket design from the late 60's/early 70's

It was not the absolute limits of the technology.

The technology does have limits -- Nerva just isn't it.

For example, there was a higher thrust/weight competitor even at the time NERVA was tested.

Tony said...

SA Phil:

"(On Nerva ...)

Nerva was a Nuclear Thermal Rocket design from the late 60's/early 70's

It was not the absolute limits of the technology.

The technology does have limits -- Nerva just isn't it.

For example, there was a higher thrust/weight competitor even at the time NERVA was tested."


It really doesn't matter whether NERVA was a mature technology or not. We're not going to use nuclear for launch vehicles. And nuclear thermal propulsion for interplanetary transfer or planetary landing probably doesn't make all that much sense in terms of ROI. The billions spent on development (or redevelopment, depending how far past NERVA you aim for) could just as easily be psent on building, fueling, and orbiting more (better understood and likely more reliable) chemical stages for exploration.

Tony said...

Monte Davis:

"As I hinted before, all this applies tenfold or a hundredfold to anything like mining lunar water, silicates, or He3. I've watched mining and ore-processing startups on Earth; even for something as plain-vanilla as iron ore, technicians and engineers spend thousands of hours installing and fine-tuning before they get close to design throughput. (Some never do, and Vale or BHP or Billiton smiles at the bankruptcy auction.) And that's with beefy steel components unconstrained by weight or power, working in shirtsleeve conditions. So -- tell me again about how a few Falcon Heavy Mark XII launches will be enough to kick off Luna's industrial revolution..?"

This is going to sound harsh, but the facts often are -- the vast majority of space enthusiasts haven't ever been in the machine shop, on the factory floor, or out on the job site. They simply don't comprehend how ideas get turned into reality. They don't even understand relatively simple examples like "I, Pencil", much less grok it. How can they be expected to think and speak in an informed manner on something as complicated as industrializing space?

Anonymous said...

Tony,

It really doesn't matter whether NERVA was a mature technology or not. We're not going to use nuclear for launch vehicles.

==============
Why not?

This is the Mars based lander/launcher I am discussing.

(SA Phil)

Tony said...

SA Phil:

"Why not?

This is the Mars based lander/launcher I am discussing."


There's no point. As much mass as there would have to be in a reactor and shielding, there would likely be no advantage over bipropellant chemicals, given the shallow gravity well of Mars (only 1/9 as deep as Earth's).

Anonymous said...

(SA Phil)

Ahh the phantom mass of the yet to be designed system again.

I thought we needed a nuclear reactor that was low mass for the 1 kw/kg target with electric propulsion.

Why not use the same reactor?

--------

I agree with you if for example you were using chem fuel to get to mars .. since then you wouldn't "need" the lightweight Nuclear reactor.

It still would be pretty nice to have if you are designing a year long mission.

Tony said...

SA Phil:

"Ahh the phantom mass of the yet to be designed system again.

I thought we needed a nuclear reactor that was low mass for the 1 kw/kg target with electric propulsion.

Why not use the same reactor?"


Because nuclear thermal rocket motors are not the same type of machine as a power reactor. A light power reactor/generator/cooler set is inherently designed for the microgravity environment, (probably) to use some kind of gaseous working fluid, and operate at a relatively low temperature and pressure. A nuclear thermal reactor for a rocket is deigned for high pressures, temperatures, and dynamic stresses.

"I agree with you if for example you were using chem fuel to get to mars .. since then you wouldn't "need" the lightweight Nuclear reactor.

It still would be pretty nice to have if you are designing a year long mission."


Most "long stay" Mars mission plans presume a small, relatively lightweight power reactor for the surface stay. But it's not a 1 kg/kw reactor and it's not designed to be part of a thermal propulsion system.

Elukka said...

Huh. I'm not specifically advocating NTRs for launch vehicles here, but if Astronautix is correct they're a damn sight better for that than I thought they were. It says the Timberwind engines had an isp of 1000 sec (up from Nerva's 800) and, more notably, a thrust to weight ratio of 30!

Aerojet has performed experiments of LOX injection with a simulated NTR propellant stream, and they say the technology would increase thrust by 50-100%, if memory serves. If the high estimate could be managed, the t/w ratio would be almost in the same class as a LH2/LOX chemical rocket.

Elukka said...

An important thing I forgot to note is that LOX injection would of course be at the cost of isp, though it wouldn't hurt it too much. Unfortunately I seem to have misplaced the document and can't find exact numbers...

Anonymous said...

Tony,

Because nuclear thermal rocket motors are not the same type of machine as a power reactor. A light power reactor/generator/cooler set is inherently designed for the microgravity environment, (probably) to use some kind of gaseous working fluid, and operate at a relatively low temperature and pressure. A nuclear thermal reactor for a rocket is deigned for high pressures, temperatures, and dynamic stresses.

===============

Hmmmm. I don't think I agree here. Especially since as you pointed out --> the gravity is a lot lower, and thus the thrust requirement for the NTR is much lower.

There is no real "Motor" in an NTR, instead it is a controlled coolant rocket.

The coolant/working fluid for the electrical reactor is recycled.

For the NTR its channeled out the back of the rocket at (probably) a higher operating temperature.

Both systems have the same desired nominal feature - low weight.

I am not sure the microgravity necessarily matters since the system will have to survive some level of pressure regardless, due to the need of coolant flow.

Although I am sure it increases the complexity of the system ..

There are a few upsides. No oxidizer for lander. You could also use the NTR as a Direct First Stage Propulsion with a detachable propellant tank.

(SA Phil)

Tony said...

Elukka:

"Huh. I'm not specifically advocating NTRs for launch vehicles here, but if Astronautix is correct they're a damn sight better for that than I thought they were. It says the Timberwind engines had an isp of 1000 sec (up from Nerva's 800) and, more notably, a thrust to weight ratio of 30!"

If you do the math, it turns out the t/w ratios on astronautix.com are based on engine weights, not vehicle weights. Most launch vehicle first stage engines have t/w ratios of 70 or above, in astronautix.com terms.

Tony said...

SA Phil:

"Hmmmm. I don't think I agree here. Especially since as you pointed out --> the gravity is a lot lower, and thus the thrust requirement for the NTR is much lower."

The thrust -- and total impulse -- required in any gravity field is the same for all launch vehicles. If it's lower for nuclear thermal, it's lower for chemical rockets too. If you want to substitute one engine type for another, you have to recognize that the lower the gravity field, the smaller the engine is going to have to be. Nuclear technology places a pretty high lower limit on how small an engine can get.

"There is no real "Motor" in an NTR, instead it is a controlled coolant rocket."

"Motor" and "engine" are nearly synonymous when talking about rockets. In fact, the simpler a rocket is, the more likely it is to be called a motor. Solid fueled rockets, for example, are almost invariable referred to as "motors".

Now, if you want to make the case that liquid fueled rockets, chemical or nuclear, should be called "engines", because of their mechanical complexity, I'll agree you have a point. Just let me know, I'll be happy to accomodate.

"The coolant/working fluid for the electrical reactor is recycled.

For the NTR its channeled out the back of the rocket at (probably) a higher operating temperature.

Both systems have the same desired nominal feature - low weight."


A power supply is a relatively low pressure, low temperature system. A rocket is high pressure, high temperature. One is made to run reliably over a long time, the other is made to run reliably for maybe a half hour at most. They are simply two different technologies. One cannot be substituted for the other.

"I am not sure the microgravity necessarily matters since the system will have to survive some level of pressure regardless, due to the need of coolant flow."

The acceleration environment affects all sorts of system parameters, like support structure design and mass, flow dynamics inside the machinery, and the design of auxiliary systems.

"There are a few upsides. No oxidizer for lander. You could also use the NTR as a Direct First Stage Propulsion with a detachable propellant tank."

Oxidizer provides reaction mass too.

And detachable propellant tanks? Really? You're going to manage reaction mass, structural, electrical, and data hookups all the way out at Mars?

Thucydides said...

1. Typo. Current solar sail technology can deliver 1mm/sec^2 acceleration. This was designed for the Haley's comet mission (cancelled in favour of an electric drive, which was also cancelled).

2. Nuclear reactors are quite versatile to be sure, but one size does not fit all, as noted. Comparison of NTR reactors, electric power reactors in the 1Kg/Kw range, NTR powered Mars landers and power reactors for Mars Direct type energy sources for the chemical reactors is somewhat like comparing a container ship engine, a Formula One racecar engine, a pickup truck engine and a 5 Kw generator engine.

Notionally these are all IC engines and you probably could kludge some sort of transmission that would allow you to power a ship from any one of these engines (or a power take off to get 5 Kw of electrical energy), but this would be quite inefficient at best, and probably kill any engine not running in its design environment.

Injecting LOX into an NTR exhaust stream may indeed increase thrust, but would also neuter two of the advantages of NTR: the essential simplicity (only one fuel tank, pump etc.) and the high ISP that would double the payload for a given mass of remass. With current technology, the simplification of the engine system and the ability to carry much more mass for shielding, consumables and a more robust spacecraft would seem to be major advantages for anyone contemplating a trip to Mars (or anywhere else, for that matter. NASA had pretty detailed plans for using NTR for space tugs and second generation trips to the Moon, for example).

Elukka said...

Tony:

"If you do the math, it turns out the t/w ratios on astronautix.com are based on engine weights, not vehicle weights. Most launch vehicle first stage engines have t/w ratios of 70 or above, in astronautix.com terms."

Yeah, I know, and 50% thrust increase through LOX injection puts it at a t/w ratio of 45 while 100% gets it to 60, which is what I meant by being almost in the same class as LOX/LH2 chemical rockets.

Rick said...

Does the figure for thrust/mass ratio allow for shielding? It had better, if the NTR is for the Mars ascent burn.

Really I don't see the need. The Mars ascent stage is basically a ferry vehicle, or can be. If you can't do a Mars orbital rendezvous, you have no business going to Mars.

Tony said...

Elukka:

"Yeah, I know, and 50% thrust increase through LOX injection puts it at a t/w ratio of 45 while 100% gets it to 60, which is what I meant by being almost in the same class as LOX/LH2 chemical rockets."

And you're also killing Isp by doing that, poisoning your rationale for using a nuclear thermal engine to begin with. Barring magitech, the relationship between thrust and efficiency is an inverse one.

Rick:

"Really I don't see the need. The Mars ascent stage is basically a ferry vehicle, or can be. If you can't do a Mars orbital rendezvous, you have no business going to Mars."

And that is so tricky that it represents a major capability in itself. Speaking of reasons to do an orbital insertion and return before a landing mission, one could see a rendezvous and docking in Mars orbit with a previously dispatched target vehicle to be a major mission objective, on the same order as rendezvous and docking were during the Gemini program.

Elukka said...

The isp is still way higher than any chemical rocket, and later in the ascent, when less thrust is required, you can go to pure NTR mode.

Anthony said...

Nuclear and solar electric are worthwhile evolutionary steps that we should work towards. But they are not technologies worth waiting on.
Why not? Mars isn't going anywhere.

Tony said...

Anthony:

"Why not? Mars isn't going anywhere."

Perfect is the enemy of good enough.

francisdrake said...

Ricks topics and the comments of the fellow posters provide a contiuous source of inspiration :-) After reading it, I thought "How would I do a manned Mars mission with current technology?" Below I sketched a split mission with solar-electric propulsion:

1. Cargo mission
The lander, a hab-rover and several smaller remote controlled rovers go first on a low energy trajectory. The lander (which is both lander and ascent vehicle) will wait in Mars orbit. It is fully fueled, so the astronauts can abort the landing in case something goes wrong on the way down.
(Note: This is different from Zurbrins plan where the crew is condemned to land after the retro burn.)

The rovers lands autonomosly on the surface. After the astronauts land, the rovers will drive remotely controlled to the landing site. There will be no fixed surface hab, nobody has to walk for miles through the desert after the landing. The hab-rover is sized like a mini-van. The crew can drive and live in it. The EVA-suits are outside on the back of the rover. They can be entered and sealed from inside, so no need to bring them inside, don-doff them in the cramped interior, clean out the peroxide dust, etc.

2. Manned mission
The crew is launched with the MPCV (Orion) which docks to the Mars ship and remains there. The MPCV will be used for direct atmospheric reentry on the return flight and provides a sealable pressurized room in case of an emergency during flight.

The Mars ship would be solar-electric, because I doubt that any spacegoing reactor development will get funding in the near future. The departure from Earth orbit would be on chemical fuel. This speeds up the whole journey considerably! You would not like to start a 9 month journey to Mars by adding another 4 months spinning up in Earth orbit.

The journey itself would be pretty much on an 'augumented' Hohmann trajectory, as the solar-electric drive will not allow for much engine power. The ships design will be dominated by the large solar panels of both sides of the 'spine'. The crews transfer hab will be on one end of the spine. Surrounding water tanks shall minimize radiation exposure to the astronauts. The vessel rotates to produce some artificial gravity. This requires the solar panels to be desgined to withstand the centrifugal force. They may be pointing outward radially from the ships mass center, so the ships design may look like a spinning array of many fragile solar arrays. The engines would be near the mass center, thrusting perpendicularly to the disks plane.

Capture to and spinning down in Mars orbit will take some time. As the crew is already close to their destination they can utilize this time to explore the landing site with the remote controlled rovers.

The ship will de-spin, rendezvous and dock with the lander in Mars orbit. After checking it out the crew will undock the lander, enter the Martian atmosphere and land close to the rovers.

The surface mission will be short-time, the time on the surface limited to a few weeks. Then the crew returns to the lander, transfers samples to the ascent part of the lander and launches back to the Mars ship.

The Mars ship then spins up its orbit and into a return trajectory to Earth. Before Earth arrival the crew and the Martian samples are transfered to the MPCV, which will enter Earths atmosphere directly. The Mars ship is either discarded or continous on an unmanned extended mission.
_____

I tried to make a sketch of a solar-electric Mars ship with radial solar panels:
http://www.flickr.com/photos/23161448@N02/6044776842/

Anonymous said...

2. Nuclear reactors are quite versatile to be sure, but one size does not fit all, as noted. Comparison of NTR reactors, electric power reactors in the 1Kg/Kw range, NTR powered Mars landers and power reactors for Mars Direct type energy sources for the chemical reactors is somewhat like comparing a container ship engine, a Formula One racecar engine, a pickup truck engine and a 5 Kw generator engine.

Notionally these are all IC engines and you probably could kludge some sort of transmission that would allow you to power a ship from any one of these engines (or a power take off to get 5 Kw of electrical energy), but this would be quite inefficient at best, and probably kill any engine not running in its design environment.

---------------

With all due respect - I disagree.

A Nuclear reactor is a Nuclear Reactor is a Nuclear reactor.

In other words the reactor itself could very well be exatly the same reactor for an NTR and a 1kg/kw electrical generator.

A nuclear reactor is critical mass of fissionables.

It is very possible you chose the same fissionables of the same quantities for both.

So the REAL differences come in when planning for the coolant / electrical generation / Thermal rocket / etc / realities.

Many here are saying its "impossible" they could live in the same platform.

All I am saying is maybe it is possible.

We again are at the "undefined" technological widget stage. Without even seeing a design it is being shot down as impossible. Or having too much mass, etc.

Based on what? Page 4 of the non- existant plans?

Instead of just difficult or "unlikely to happen in the next X years."

Keep in mind that pickup truck engines are used as electrical generators all the time. PTO is on the feature list of any truck program. (Usually near the bottom of the spreadsheet)

(SA Phil)

Anonymous said...

Tony,


And detachable propellant tanks? Really? You're going to manage reaction mass, structural, electrical, and data hookups all the way out at Mars?

=============

No the detachable part would be during the initial acceleration to get to Mars.

So fairly close to Earth actually.

(SA Phil)

Anonymous said...

(SA Phil)

The NTR/Electrical generator combo wouldnt exactly have to be 1kg/kw to produce the performance you want.

It would have to be 1kg (plus whatever other mass you can save on the mission) / kw.

Including any mass you could add because you have an NTR availible. (such as the detachable tanks)

Tony said...

SA Phil:

"A Nuclear reactor is a Nuclear Reactor is a Nuclear reactor.

In other words the reactor itself could very well be exatly the same reactor for an NTR and a 1kg/kw electrical generator."


Don't think so. An NTR would have to have a much more robust pressure vessel and a higher concentration of fissionables in order to generate the pressures and temperatures for rocket propulsion. Also, and NTR tosses expendable coolant -- and waste heat -- overboard as reaction mass. A power reactor has to have a closed coolant circuit and (in space at least) a radiative heat rejection system.

Could you use the same reactor? Yes. But the entire contraption would not be anywhere close to 1 kg/kw.

"We again are at the "undefined" technological widget stage. Without even seeing a design it is being shot down as impossible. Or having too much mass, etc."

Some things can be ruled out on basic engineering principles. If somebody came to you and told you that you could have a 500 hp IC power plant that fit into the same form factor as a two stroke that powers a kid's mini 50 dirt bike, what would you say?

"Keep in mind that pickup truck engines are used as electrical generators all the time. PTO is on the feature list of any truck program. (Usually near the bottom of the spreadsheet)"

Any IC engine in an automotive configuration is used as an electrical power generator for the vehicle electrical system. But if you were just interested in a couple of kilowatts of electrical power over an entended period of time, you wouldn't run a Cummins or a Duramax -- you'd get yourself a Honda generator.

Tony said...

SA Phil:

"No the detachable part would be during the initial acceleration to get to Mars.

So fairly close to Earth actually."


Ohhh...you mean expendable. And? All manned Mars spacecraft configurations involve expendable tankage or stages.

Tony said...

SA Phil:

"The NTR/Electrical generator combo wouldnt exactly have to be 1kg/kw to produce the performance you want.

It would have to be 1kg (plus whatever other mass you can save on the mission) / kw.

Including any mass you could add because you have an NTR availible. (such as the detachable tanks)"


You're talking about cost-benefit trades. I'll tell you what -- when you can produce a hybrid NTR/power-supply that can compete on mass and reliability with other solutions, you can be in the trade study. Until then, you're just playing "what if" with speculative technology.

Anonymous said...

Tony,

Some things can be ruled out on basic engineering principles. If somebody came to you and told you that you could have a 500 hp IC power plant that fit into the same form factor as a two stroke that powers a kid's mini 50 dirt bike, what would you say?

============
First you would do the math and calculate what is the maximum power yield you can get in that particular form factor.

Since you didnt give me a maximum RPM - the problem steers itself. I would use an extremely high RPM, since horsepower varies with rate.

Then I would ask other questions:
How much time do we have? What resources am I going to get? What is the budget? What are the other assumptions?

I assure you it is probably possible to get a 500 hp motor into the form factor approximately the size of a 50cc dirtbike. If you had said 500 ft/lb torque though -- Probably not doable.

================
I don't know the design contraints on lightweight Nuclear Reactors - nor what their probable maximums are.

Nor do I know the design contraints on NTR and the probable maximums (as far as lowest mass for effective use)

And neither do you.


(SA Phil)

Anonymous said...

Tony,

You're talking about cost-benefit trades. I'll tell you what -- when you can produce a hybrid NTR/power-supply that can compete on mass and reliability with other solutions, you can be in the trade study. Until then, you're just playing "what if" with speculative technology.

=============

What I am basically saying is when you get the 1kg/kw reactor you could look at modifying that technology to be a NTR hybrid.

And then make the mass tradeoff considerations.

Of course you wont develop either if you have planners so closeminded to not even consider doing the math first.

(SA Phil)

Tony said...

SA Phil:

"First you would do the math and calculate...

I assure you it is probably possible to get a 500 hp motor into the form factor approximately the size of a 50cc dirtbike. If you had said 500 ft/lb torque though -- Probably not doable.

================
I don't know the design contraints on lightweight Nuclear Reactors - nor what their probable maximums are.

Nor do I know the design contraints on NTR and the probable maximums (as far as lowest mass for effective use)

And neither do you."


Nobody has to know the specific constraints for a given power output. One just has to know that there are competing and incompatible requirements. Could you get 500 hp out of a 10 pound motor? You think so, but I doubt it. To get the horsepower, you have to run the engine at a gajillion RPM. But as soon as you hook it up to the load of a 370 kw generator or a vehicle power train, the mechanical drag alone is going to cut your RPMs down to a very low fraction of your unloaded rate. In fact if you tried to add load at speed, you'd rip the motor off its mounts. If you tried to run up to speed under load, you'd probably not even get the thing to spin. The problem? Competing and incompatible requirements. You can't drive something that needs 500 hp of input power with a motor that weighs less than Aunt Minnie's overfed pomeranian.

The same principles apply to the question of NTRs and lightweight nuclear generator sets. The requirements of rocket motors are not compatible with the requirements of lightweight power supplies. To suggest that they could be seems just a bit fantastic.

Tony said...

SA Phil:

"What I am basically saying is when you get the 1kg/kw reactor you could look at modifying that technology to be a NTR hybrid.

And then make the mass tradeoff considerations.

Of course you wont develop either if you have planners so closeminded to not even consider doing the math first."


+10 on pathos, +0 on logos.

If you develop a 1 kg/kw power supply, you will have optimized mass to the point that rocket pressures and temperatures are out of the question. Working the other way, withstanding rocket temperatures and pressures requires so much hardware that low weight to power ratios are out of the question. By making smart trades and accepting greater risks, you may be able to converge a bit, but not as much as you suggest.

Anonymous said...

Tony,

By making smart trades and accepting greater risks, you may be able to converge a bit, but not as much as you suggest.

=============

Thats where the mass tradeoff comes in.

For example we could not now do 1kg/kw and NTR in an acceptable mass tradeoff.

So the question is how close can they be?


And what are the actual design tradeoffs envisioned for 1kg/kw? You seem to imagine that it is making a fragile system.

(SA Phil)

Tony said...

SA Phil:

"Thats where the mass tradeoff comes in.

For example we could not now do 1kg/kw and NTR in an acceptable mass tradeoff.

So the question is how close can they be?


And what are the actual design tradeoffs envisioned for 1kg/kw? You seem to imagine that it is making a fragile system."


Not fragile, just not robust enough to withstand rocket propulsion levels of dynamic stress. To go back to automotive examples, a scooter motor is perfectly adequate for its intended application, but you wouldn't try to use one to drive an F-350.

To the general question, could you use an NTR reactor as a power supply? Yes, but only at the cost of accepting the hardware mass of a high pressure reactor chamber, propellant turbopumps and heavy shielding, while at the same time accepting a completely parallel system of power system hardware. Also, the reactor control system would have to be pretty sophisticated to enable reaction across such a wide power range. Doable? Probably. Practical and useful? I'm highly skeptical.

Anonymous said...

Tony,

Could you get 500 hp out of a 10 pound motor? You think so, but I doubt it. To get the horsepower, you have to run the engine at a gajillion RPM. But as soon as you hook it up to the load of a 370 kw generator or a vehicle power train, the mechanical drag alone is going to cut your RPMs down to a very low fraction of your unloaded rate.

==================
full load is full load.

The crankshaft doesn't care what you hook the engine up to.

How much power could you get to the wheels?

That is a transmission problem, not an engine problem. I mentioned other assumptions.

You would need a pretty high N/V to be sure.

But you wouldn't need a gajillion rpm. 25,000 perhaps as a guesstimate.

The probblem wouldn't be so much "mechanical drag" as lost mechanical advantage.

You woudln't have any power at low rpm, so if it were a dirtbike you would have to spool it way up before it did much.

It would feel something like turbolag.


(SA Phil)

Monte Davis said...

...not robust enough to withstand rocket propulsion levels of dynamic stress.

This bears a bit of unpacking. In a chemical rocket engine, once the fuel and oxidizer come out of the pintle[s] into the combustion chamber, they react->heat->expand out through the nozzle: while the combustion chamber wall, throat and nozzle experience high T and P, they form one relatively simple enclosing envelope.

A high-thrust NTR means streaming tons of hydrogen [or whatever] per second through channels in a structure that is both a matrix for fuel elements (holding them in a precise spacing and geometry) and a very good heat exchanger, with lots of complex surface area as intimate as possible with a very fast flow.

On general principles of fluid dynamics and thermodynamics, you can expect that to be a fertile breeding ground for all kinds of wild transients and resonances, fiercely vibrating a structure that absolutely must be dimensionally stable and must not shed bits & pieces into the exhaust stream.

Can I solve that? Sure -- just beef up the structure until it'll withstand all that stress with plenty of safety margin.

(Oh... you wanted it to FLY??!!??)

Anonymous said...

(SA Phil)

I will mention you snuck an additional assumption in there by saying the motor had to be "10 pounds".

The original conditions were "form factor".

Form factor in automoive engineering is a 3 dimensional space allowance.

Anonymous said...

(SA Phil)

Does your 1kg/kw reactor not have similar cooling rquirements as the NTR?

After all the core melts at X temperature. You do need to avoid that.

So you also have to cool the 1kg/kw reactor. To an even lower temperature it has been suggested. So does it not also have flow problems, etc.

Since an NTR essentially is just taking your engine coolant and dumping it into space as reaction mass.

Anonymous said...

(SA Phil)

Also - since a NTR is acually more efficient than a chemical rocket -- even if you couldn't use it to run an electric drive due to mass problems-- it STILL could be better than using a Chem fuel ship for the mission.

Even if the NTR was only the interplanetary drive.

Anthony said...

Tony: Perfect is the enemy of good enough.
True. Now, convince me of 'good enough'. The fact is, there's little reason to get to Mars beyond curiosity, and it's tough to get there.

Tony said...

Anthony:

"True. Now, convince me of 'good enough'. The fact is, there's little reason to get to Mars beyond curiosity, and it's tough to get there."

Beyond scientific curiosity, it represents a major national prestige project. In fact, it is probably true to say that the national prestige factor will loosen up more money than any amount of scientific return. So if a government is going to spend the money at all, one would probably expect funding for sooner rather than later. Also, NTR or nuclear/solar electric involve considerable commitment of resources that could be used to fund going to Mars (or wherever) with more developed technologies.

Anonymous said...

(SA Phil)

Of course if you develop a better propulsion technology you open up a lot more than Mars.

Just like our missile/rocket development opened up a lot more than sticking a flag on the moon.

Tony said...

SA Phil:

full load is full load.

The crankshaft doesn't care what you hook the engine up to.

How much power could you get to the wheels?

That is a transmission problem, not an engine problem. I mentioned other assumptions."


Wow...

The crankshaft definitely does care what you hook the engine up to. Simplistically, a 500 hp motor should be able to drive a 370 kw generator. But there would be transmission losses, so let's a say 300 kw generator. That's a generator the size of an oil drum, supposedly driven by a motor that fits in less than a cubic foot. If the motor stayed together, it would come off it's mountings and spin around the drive shaft. It wouldn't spin the generator.

"You would need a pretty high N/V to be sure."

Adding the mass of a ridiculously high ratio gear train, rendering the task even more impossible.

"You woudln't have any power at low rpm, so if it were a dirtbike you would have to spool it way up before it did much.

It would feel something like turbolag."


You're missing the point. A miniscule motor is not going to be able to deliver hundreds of horsepower for the simple reason that it can't generate enough mechanical force over time. swerving back on subject, a reactor and cooling system degined for electrial power generation can't generate enough force over time to be an NTR.

"I will mention you snuck an additional assumption in there by saying the motor had to be "10 pounds".

The original conditions were "form factor".

Form factor in automoive engineering is a 3 dimensional space allowance."


I didn't sneak anything in. We're talking about using real materials in the real universe. A 50cc motor, as previously mentioned, fits in less than a cubic foot. Making our supermotor out of steel, you'de be trying to drive hundreds or thousands of pounds of machinery with something that massed less than 50.

"Does your 1kg/kw reactor not have similar cooling rquirements as the NTR?

After all the core melts at X temperature. You do need to avoid that.

So you also have to cool the 1kg/kw reactor. To an even lower temperature it has been suggested. So does it not also have flow problems, etc.

Since an NTR essentially is just taking your engine coolant and dumping it into space as reaction mass."


An NTR runs at a lot higher neutron flux than a nuclear electrical generator. It generates much more heat per unit of reactor volume. IOW, a power reactor is designed to never get as hot as a rocket engine in the first place. Therefore it doesn't need to be constructed to the same standards.

"Also - since a NTR is acually more efficient than a chemical rocket -- even if you couldn't use it to run an electric drive due to mass problems-- it STILL could be better than using a Chem fuel ship for the mission.

Even if the NTR was only the interplanetary drive."


Well, there's technical efficiency and then there's cost efficiency. If a nuclear rocket costs $10 billion to develop, while a complete Mars mission costs the same no matter what hardware you use, I can see someone buying the Mars mission before the NTR.

Anonymous said...

Tony,

Wow...

The crankshaft definitely does care what you hook the engine up to. Simplistically, a 500 hp motor should be able to drive a 370 kw generator. But there would be transmission losses, so let's a say 300 kw generator. That's a generator the size of an oil drum, supposedly driven by a motor that fits in less than a cubic foot. If the motor stayed together, it would come off it's mountings and spin around the drive shaft. It wouldn't spin the generator.

Adding the mass of a ridiculously high ratio gear train, rendering the task even more impossible.

You're missing the point. A miniscule motor is not going to be able to deliver hundreds of horsepower for the simple reason that it can't generate enough mechanical force over time. swerving back on subject, a reactor and cooling system degined for electrial power generation can't generate enough force over time to be an NTR.

I didn't sneak anything in. We're talking about using real materials in the real universe. A 50cc motor, as previously mentioned, fits in less than a cubic foot. Making our supermotor out of steel, you'de be trying to drive hundreds or thousands of pounds of machinery with something that massed less than 50.

===========================
========================

“Give me a place to stand and a lever long enough and I will move the world.”
--Archimedes, a very long time ago.

Again the transmission was not part of your original assumption.

Neither was your application.

The original assumptions are reprinted below.

=============
=================
Tony,

Some things can be ruled out on basic engineering principles. If somebody came to you and told you that you could have a 500 hp IC power plant that fit into the same form factor as a two stroke that powers a kid's mini 50 dirt bike, what would you say?

================
===========

You asked me if you can get 500 hp in the form factor of a 50 cc motor. I said "probably"

You then moved the goal posts around in a dancing game worthy of ABC television.

Also full load is full load. It always is full load. That is how speed/load works.

There is never more crankshaft pressure than full load. You could hook the engine direct drive up to a generator the size of the planet earth - the crankshaft wouldnt care.

Sure it wouldnt move the earth around hooked up like that.

But if you had a lever long enough it would.


(SA Phil)

Tony said...

SA Phil:

"You asked me if you can get 500 hp in the form factor of a 50 cc motor. I said "probably"

You then moved the goal posts around in a dancing game worthy of ABC television.

Also full load is full load. It always is full load. That is how speed/load works."


Sorry, Phil, but when somebody says "500 horsepower", they mean 500 measured horsepower under load, not anything else. I was personally thinking of brake horsepower, which is the most ideal measurement, because it excludes parasitic loads and transmission loss.

Nobody moved the goalposts on you. You simply dodged the question.

"There is never more crankshaft pressure than full load. You could hook the engine direct drive up to a generator the size of the planet earth - the crankshaft wouldnt care.

Sure it wouldnt move the earth around hooked up like that.

But if you had a lever long enough it would."


If you had a lever long enough, it would mass more than the object you were trying to move.

Anthony said...

Beyond scientific curiosity, it represents a major national prestige project.
This is true. It is, however, an unreasonably expensive prestige project at this time. Let's say we've decided a Hohmann transfer orbit is acceptable, and we're using modern rocket engines. We'll basically be assuming UDMH/N2O4.

Putting a payload on a course for Mars (Hohmann) takes about the same delta-V as putting a payload into GSO, at least with chemical rocket engines (with low thrust drives, it takes considerably more); a Proton rocket can put about 3.5 tons on that course. It will need another 2.1 km/sec at Mars to enter low orbit, if you aren't aerobraking that will require about a 50% fuel fraction, plus some structure, so figure 1.5 tons into low Mars orbit. We'll also need the same delta-V to get on to a return path, so we have about 600 kilograms for the actual payload. We'll assume aerobraking on Earthfall.

That's obviously not sufficient for a human, so we either need to build a much larger rocket, or build a larger craft in low orbit (high orbit is inefficient because we need to take advantage of the Oberth effect). This is a slightly less efficient orbital path, but the main cost is that we have to build a large object in orbit; it's around forty tons in LEO per ton of actual payload. If we figure that our transport can be 1/4 of the size of the ISS (which is probably generous, the ISS doesn't have radiation shielding because it's inside the Earth's magnetic field and six people sounds like a reasonable crew), the total mass is ten times the ISS, and unlike the ISS, it actually needs to be able to withstand fairly high acceleration (if not, we need significantly delta-V; the Oberth effect is the friend of chemfuel rockets).

That's basically a trillion dollar project, which isn't happening, and it puts us on a slow transfer orbit. Thus, we're going to need to do new development, and it's just a question of what that development will be.

Anonymous said...

(SA Phil)

You are not using the same definition of load as I am.

"Max Load" is an engine characteristic. It is demand on the engine. You can get max load no matter what you hook up to the engine.

What you are talking about is work you want the engine to perform. Two entirely different things.

Anonymous said...

(SA Phil)

And yes you can have 500 hp with low torque and high RPM and do the same work a 500 hp high torque engine does with low RPM.

Its in the gearing. Mechanical Advantage. You left the transmission out of your original example. Maybe you were thinking direct drive. If so, you left it out of the question.

Its possible the transmission would end up being the size you imagined for your 500 hp motor when you thought the whole scenario up.

Tony said...

Re: Anthony

Since none of the mission concepts under consideration involve the use of hypergolic storables (except maybe for Mars-orbit-insertion/Earth-transfer-injection) you've just gone the long way 'round the barn to make an irrelevant argument.

Tony said...

SA Phil:

"You are not using the same definition of load as I am.

"Max Load" is an engine characteristic. It is demand on the engine. You can get max load no matter what you hook up to the engine.

What you are talking about is work you want the engine to perform. Two entirely different things."


Then I think you are using an irrelevant measure. If the engine spins around the crankshaft -- because you hooked it up to a generator rotor that weighs 20 times as much, or to the transmission of a vehicle that wieghs 100 times as much -- then it's not delivering measurable power. You're just giving a demonstration of inertia.

"And yes you can have 500 hp with low torque and high RPM and do the same work a 500 hp high torque engine does with low RPM.

Its in the gearing. Mechanical Advantage. You left the transmission out of your original example. Maybe you were thinking direct drive. If so, you left it out of the question.

Its possible the transmission would end up being the size you imagined for your 500 hp motor when you thought the whole scenario up."


No disrespect intended, but horsefeathers. The point was that an engine of a given size can generate only so much power over a given interval of time. A dinky miniengine, given the right hookup, could indeed move a large truck (across a frictionless surface -- it wouldn't be able to overcome friction on normal pavement) very, very slowly. But horsepower is a measure of force over time, so no matter what kind of technology you used, a ten pound engine is not going to generate 500 measured horsepower.

And that point was made to illustrate that a machine designed to produce say 50 kilowatts of electric current steadily over years of use ain't in the same mechanical class as one designed to produce hundreds or thousands of kilowatts for a fraction of an hour.

Anonymous said...

(SA Phil)

An NTR isnt really deisgned to produce thousands of killowhats for a fraction of an hour.

It is a reactor -- A mass of fissionables. It will produce heat at a given rate for months/years.

Unless you do something to slow the reaction that is. Flood it with Boron or something.

So it isn't really "designed" for a short burst. The rocket part might be, but the reactor itself is different.

Anonymous said...

(SA Phil)

RE: tiny Motors

With the right transmission the 500 hp tiny motor will move the truck the pretty much the same as the 500 hp big motor. (Minus friction)

When they are both at 500 hp that is.

The problem will come in with the lack of torque. So the light motor would need to spin up all the time. It would therefore have a horrible lug curve, its dynamic response would be terrible.

But
Work In= Work out

Dynamic response was undefined.

Tony said...

SA Phil:

"An NTR isnt really deisgned to produce thousands of killowhats for a fraction of an hour.

It is a reactor -- A mass of fissionables. It will produce heat at a given rate for months/years.

Unless you do something to slow the reaction that is. Flood it with Boron or something.

So it isn't really "designed" for a short burst. The rocket part might be, but the reactor itself is different."


The fissionables in an NTR are in the same functional space (and inside generally the same form factor) as in the combustion chamber of a liquid chemical rocket engine. The big difference is that neutron heating is used to generate sufficient reaction mass pressure, rather than a highly exothermic chemical reaction. An NTR's reactor vessel has to withstand all of the dynamic stresses of a chemical rocket engine, precisely because it is designed to produce hundreds or thousands of kilowatts over the duration of a propulsive event.

Anthony said...

Since none of the mission concepts under consideration involve the use of hypergolic storables (except maybe for Mars-orbit-insertion/Earth-transfer-injection) you've just gone the long way 'round the barn to make an irrelevant argument.
The only place I was specifying hypergolic storables was for the Mars orbit insertion and the Earth transfer insertion; other than that, I was just using the Proton because it's established technology. Using LOx/LH2 for LEO->MTO cuts the weight required in LEO by about a third but also requires handling LH2 fuel in orbit, which seems like a headache (though on reflection, you could probably deliver water up to your orbital assembly and use solar-electric to crack it there). This still doesn't cut the price down into the range that relevant to prestige projects.

Tony said...

SA Phil:

:RE: tiny Motors

With the right transmission the 500 hp tiny motor will move the truck the pretty much the same as the 500 hp big motor. (Minus friction)

When they are both at 500 hp that is.

The problem will come in with the lack of torque. So the light motor would need to spin up all the time. It would therefore have a horrible lug curve, its dynamic response would be terrible.

But
Work In= Work out

Dynamic response was undefined."


Dynamic response is the whole point. You place a thousand pound load on a 10 pound motor, your dynamic response is going to be that the motor breaks or it just spins around the shaft.

Lurching back onto the topic, if you try to use a machine designed to output a little bit of power over a long period to deliver a lot of power in a short period, your choices are:

Watch the machine blow up, or

Redesign and rebuild the machine to to do the work required of it.

Tony said...

Anthony:

"This still doesn't cut the price down into the range that relevant to prestige projects."

I can only suggest you read up on your Space Shuttle and ISS economics, keeping in mind that both were/are fundamentally national prestige projects.

Anthony said...

I can only suggest you read up on your Space Shuttle and ISS economics, keeping in mind that both were/are fundamentally national prestige projects.
The ISS is at the edge of what's viable as a prestige program, and had perpetual funding issues. You basically can't assume something larger than the ISS and consider it viable. Even programs a tenth that cost (e.g. the James Webb Space Telescope) have funding issues.

Anonymous said...

Tony,

Dynamic response is the whole point.

===============
====================

Then you should have defined it.

Dynamic response is the main reason trucks have big motors now.

It isnt horsepower. You could easily get 300 hp with a 2.0 liter 4 cylinder engine.
=====================
=================


You place a thousand pound load on a 10 pound motor, your dynamic response is going to be that the motor breaks or it just spins around the shaft.

==================
Its not going to break. None of that will happen. Not with a transmission. Instead the motor will spin and spin really fast and turn the trasnmission, which will then turn your "load"

Just like a pulley. It will have to spin a lot more than the big engine would. That is the difference.

If its a generator - you'd be fine. You dont need dynamic response for that.

All of these principles are in use.

Here is a neat concept car that uses a small diesel to generate hydraulic pressure, which it then ues to drive the wheels.

http://www.valentintechnologies.com/general/flyer-english.asp

It stores hydraulic energy in a high pressure system instead of expecting the engine to manage the dynamic changes.


(SA Phil)

Tony said...

SA Phil:

"Its not going to break. None of that will happen. Not with a transmission. Instead the motor will spin and spin really fast and turn the trasnmission, which will then turn your 'load'

Just like a pulley. It will have to spin a lot more than the big engine would. That is the difference."


Jeepers, Phil. Really.

Assuming an output rpm of 1,000 for the sake of argument, you're talking about driving a gear ratio of 25:1. Made of materials sturdy enough to drive a real large machine that demands some significant fraction of 500 hp to operate, that's a transmission that in itself would probably weigh over a thousand pounds. Once again, our miniengine either self destructs or spins around the shaft -- even without the output load engaged.

Anonymous said...

(SA Phil)

The Transmission requirements were undefined.

So was the application BTW.

The transmission can be a million tons as far as I'm concerned. As long as it gives me the mechanical transfer I need to use the 500 hp of the tiny engine.

We are back to Arch's lever.

If we were 25:1 and we needed to move 1000 pounds, the engine would only see 40 pounds. It doesn't matter how large the transmission is.

If we were at 1000:1 it would see 1 pound.

Are you sure you don't work for management? It isn't my fault you didn't define the application.

I already said if it has to be direct drive with no gearing it wouldn't work.

Thucydides said...

Look at the "real world" NTRs designed in the 60's, and you will indeed see that every working example was designed to produce high temperatures in as small a space as possible and handle as large a mass flow as possible to generate thrust.

The Phoebus NTR produced 5000 MW in a package which seems to be about the size of a minivan http://www.daviddarling.info/encyclopedia/P/Phoebus.html, perhaps the highest power density of any nuclear reactor ever built. No commercial reactor approaching that power output is anywhere near that small. Devices which operate at that sort of power density are highly stressed, and I suspect the reactor would be highly tempermental if you tried to run it at low power outputs for extended periods of time. (Even large reactors are not immune to runaway responses to transient events; the Chernobyl reactor escaped operator control starting with isolated pockets of steam creating voids in the cooling system, which allowed neutron flux to increase, speeding up the reaction rate, creating more steam pockets...)

For those of you more comfortable with the car analogies, consider the engine modifications made to "rice rocket" street racers. The small Honda and Mitsubishi engines can be boosted to hundreds of horsepower, but are cranky, tempermental in normal street driving and break down quite quickly. Fans of American big block drag racing understand the concept, the V-8 engines on drag racers are stripped down after virtually every race for inspection and repair, while the stock engine can last for decades.

The only way around the conundrum are "magitech" aneutronic fusion devices which can produce beams of charged particles for thrust. Mass can be injected into the beam to deliver higher thrust while accepting ISP's of "only" 10,000 seconds or so, while the straight beam can deliver an ISP of 1,000,000 seconds. Of course we may have been to Mars and back many times before anything like that is perfected.

Anonymous said...

(SA Phil)

One aspect I think I should point out again.

The Mars lander NTR / Power Plant hybrid would only need about 12% of the thrust as the NTRs designed in the 60's and 70's.

That might make a difference.

Anonymous said...

Tony: you're arguing mechanical engineering with an automotive engineer! get a grip and drop it already, you aren't going to win this one.

SA Phil: at some point you just have to say "Stop" and accept that you've won.

We get it; small engine, very slow acceleration; big engine, quick acceleration. The details of a Mars mission will depend on the objectives of the mission, the state-of-the-art of the tech used, and what kind of engine is used to get us there. We have options; let's try and define which is best for a given timeframe.

Ferrell

Anonymous said...

(SA Phil)

*grumble*

I really was only trying to make a point that we don't necessarily know a design is unworkable until we run though all the assumptions.

It could very well be that the NTR/Nuke Electric Power Plant hybrid is a bad idea even with 400 years from now tech.

But I am intrigued by the concept.

==============
As to the other ...

The engine problem only didn't make sense because most of the original assumptions were undefined. I simply refused to change the original problem.

For instance the hydraulic hybrid link I used. You could use the 500 hp engine to charge up fluid pressure to serve as your transmission.

That could "cushion" the initial start up of the shaft. And it would allow the engine to maintain its high speed performance constantly. The hydraulic system could make up for the engine's shortcoming.

They had a couple of set ups like this at U Wisc about 10 years ago. Really cool stuff. Disappointing they cant get any funding for those sorts of projects.

You could use a low mass high speed motor/hydraulic fluid system to save mass on a space craft actually if you needed to move something large.

--------------
But Tony is right if you change the problem to being a dirtbike sized *powertrain* instead of *powerplant* ... at that point you cant move anything you would normally want 500 hp for.

Anonymous said...

=Milo=



Tony:

"If you had a lever long enough, it would mass more than the object you were trying to move."

Hmm. Since I'm tired of all the bitter arguments here, let me sidetrack with a completely silly calculation!

Earth's weight is 5.9736 zettatons (10^21 tons). Let's say the lever is made of tungsten, which has a density of 19.25 ton/m^3, just so it's really heavy. If the lever has a diameter of one meter, then to match Earth's weight it would have to be 395.1 exameters long, or 41763 lightyears. If the lever has a diameter of one kilometer, than it would be 395.1 terameters long, which is 15.254 lightdays. In order for the level to be no longer than the orbit of Eris (567.6 lightminutes, 10210 Gm), it would have to be 6.22 km thick.

Tony said...

SA Phil:

*grumble*

I really was only trying to make a point that we don't necessarily know a design is unworkable until we run though all the assumptions.

It could very well be that the NTR/Nuke Electric Power Plant hybrid is a bad idea even with 400 years from now tech.

But I am intrigued by the concept."


And I was simply pointing out that electrical power generators and rocket engines have incompatible requirements. You don't need to "run though all the assumptions" to know that. You just have to apply fundamental principles.

"As to the other ...

"The engine problem only didn't make sense because most of the original assumptions were undefined. I simply refused to change the original problem."


When somebody gives you a horsepower number, they mean instantaneously delivered power, measured at the shaft. That's not "undefined", it's a common understanding.

"But Tony is right if you change the problem to being a dirtbike sized *powertrain* instead of *powerplant* ... at that point you cant move anything you would normally want 500 hp for."

Uh, Phil, the idea that the motor would be hooked up to a load that you need the power to drive in real time is also a common understanding.

And the point remains that low power output over time requires different engineering than high power output over time.

Anonymous said...

(Sa Phil)

The motor woud have the 500 hp at the flywheel.

500 hp as discussed. It will provide 500hp under load. Just like you want.

500 hp hooked up and running your machine (generator w/e)

You just need the right transmission to transfer the power.

Archimedes' Transmission at this point.

The Transmission is serving as the lever.



-----------------
The engine pushes a much smaller "weight" very fast. The transmission changes that to pushing a much bigger "weight" proportionally less fast.

Tony said...

Sa Phil:

"The motor woud have the 500 hp at the flywheel."

A ten pound engine is going to generate 275,000 ft/lb-sec at the power output? What material are we making it out of, Phil?

Rick said...

The fine grain technical details of reactor design are way above my pay grade. But in general, producing direct thrust and producing electrical power seem like very different requirements to ask of a reactor. Which doesn't make a dual purpose reactor impossible, but does make it tricky to accomplish.

Put another way, I have no problem buying a dual purpose NTR/electric drive in a 23rd century space warcraft, but I'd be very skeptical of such demanding technology for an early Mars mission in this century.

Tony said...

Rick:

Actually, there have already been proposals for Mars missions using "Bimodal" NTR. Of course, it's totally speculative technology.

Anonymous said...

Tony,

A ten pound engine is going to generate 275,000 ft/lb-sec at the power output? What material are we making it out of, Phil?
========================

So you have moved beyond the the fact that If I can get the 500 hp at the flywheel, I can transfer it to what you want to drive?

Because until now in this exchange you haven't.

So lets say I can make 1 foot pound at 275,000 rpm - I meet your requirement.

Or maybe 10 foot pounds at 27,500 rpm. Now were talking something a little more plausible.

So I would make it out of whatever material I can spin 27,500 rpm while making 10 foot pounds.

That really wasn't where the "probably" came in. The if comes in in how you burn enough fuel to make the power.

I was imagining you could actually make the engine larger than 50cc and still get it in the same form factor. Especially if you changed from incidential air cooling.

But that might not be a hard requirement.

(SA Phil)

Tony said...

SA Phil:

"So lets say I can make 1 foot pound at 275,000 rpm - I meet your requirement."

No. You have to deliver 275,000 ft/lb of work every second. That's 500 hp, by definition. So, once again, what are we making this magickal motor out of that it can actually exert so much force in the defined package size? No more excursions into theory without consideration of application, please. Give us a materials schedule that you think will support the delivery of 500 brake horsepower from a motor that fits in less than a cubic foot.

Anonymous said...

(SA Phil)

Ahh I knew I must be missing a step there. As are you.

So here is the actual conversion
(Torque x Engine Speed RPM) / 5,252 = Horsepower

so
Horsepower*5252 = Torque*Engine speed

so (500 Horse Power*5252)/25000 (RPM)= Torque

Plugging in the numbers I get 105 foot pounds.

So I need 105 foot pounds at 25000 rpm

or 52.5 at 50,000 rpm
or 27 at 100,000 rpm

Since gas turbines are built that exceed 50K or 90K rpm .. this isn't necessarily impossible.

So the actual question is how high RPM I can get and how much torque I can get there.

I would prefer the 105 foot pounds at 25,000 rpm. But it might take 250cc for that. looking at what racing bikes can put out.

Can you squeeze the 250cc into 12"x12"x12"? That might be a trick. A 1 cylinder 250cc would be 5cm bore x10cm stroke for example. So maybe.

You dont need super exotic materials. You just need to spin really fast. Which I beleive was my original response.

Tony said...

SA Phil:

"So I need 105 foot pounds at 25000 rpm"

Torque is irrelevant without power. You still need 500 hp measured at the shaft. Where is that coming from, in a package that fits in less than a cubic foot?

Anonymous said...

Tony,

Torque is irrelevant without power. You still need 500 hp measured at the shaft. Where is that coming from, in a package that fits in less than a cubic foot?

---------

Huh?

I have the Horsepower there. Its all listed. I even showed my work.

You need 105 ft pounds of torque at 25000 rpm to make 500 horsepower.

Or 515 foot pounds of torque at 5000 rpm to make 500 horsepower. That one should be easy to check - you'd only need a mldly built small block for that.

At the shaft -- which is essentially the same thing as at the flywheel. They hook the shaft to the dyno. No Transmission , that's how you measure bhp. You measure rpm and torque.

Your statement is completely backwards -- I need torque to turn whatever it is you need to turn.

I'll get that with the transmission.

QED - sorry man - you are just wrong.

(SA Phil)

Anonymous said...

*515=525

Typo

Anonymous said...

Rick said...

The fine grain technical details of reactor design are way above my pay grade. But in general, producing direct thrust and producing electrical power seem like very different requirements to ask of a reactor. Which doesn't make a dual purpose reactor impossible, but does make it tricky to accomplish.

Put another way, I have no problem buying a dual purpose NTR/electric drive in a 23rd century space warcraft, but I'd be very skeptical of such demanding technology for an early Mars mission in this century.

===================

I guess I do tend to come at things from the far side of the Plausible Mid Future..

But maybe that is subconsciously to counteract all the 5-10 minutes in the future advocates.

That said - how far away is a liquid core NTR? By design it runs a lot hotter than solid core -- maybe it would be a better candidate for the hybrid.

(SA Phil)

Paul said...

One can generate electricity in a NTR in an interesting way, to boost the Isp a bit.

The idea would be to do something like this:

(1) Pump the LH2 up to very high pressure.
(2) Heat the LH2 to high pressure gas.
(3) Expand the gas down to a lower pressure, quasi-isothermally (with several reheats)
(4) Inject the hydrogen, now at somewhat lower pressure, into the reactor chamber itself
(5) After the hydrogen has passed through the reactor, use the electrical power generated in step (3) to arc heat it.
(6) Expand the hydrogen out the rocket's nozzle.

Step (5) lets you heat the hydrogen above the melting point of the fuel and get somewhat higher Isp.

This scheme exploits the fact that nuclear rockets are not limited by energy, but rather by entropy. Gradually warming the pressurized LH2 could reduce the unnecessary entropy production even more.

T/W for this would render it suitable only for in-space use, I imagine.

Jim Baerg said...

Hi: I'm back to checking Rocketpunk Manifesto after some time on the road.

Re: the notion of a preliminary mission that only goes to Mars orbit.

How much interesting science (or engineering) is there to do at Phobos & Deimos? Could volatiles be extracted for use near Mars or for return to cis-lunar space & use there? Only if there is useful stuff to do at Mars' moons would I think the preliminary mission to Mars orbit with no landing to be worthwhile.

Re: Nuclear Thermal Rocket & power production from same reactor design.

The discussion in this thread seemed to be about getting similar power levels in both modes, which I agree with Tony would be at best extremely difficult. However, elsewhere I've seen the proposal of using the NTR briefly at high power in rocket mode & then at low power in electricity generation mode for such things as life support. This would be relatively easy to do & have the advantage of keeping the reactor components consistently fairly hot rather than cycling in a short time from cold to hot & back, thus reducing stresses on the system.

BTW some reactor designs have a very highly negative 'temperature coefficient of reactivity' ie: a small drop in temperature results in a large increase in fission rate & a modest rise in temperature shuts the reaction off. I think this would be a needed feature for the bimodal nuclear rocket/electric generator system.

Anonymous said...

=Milo=



Rick:

"Put another way, I have no problem buying a dual purpose NTR/electric drive in a 23rd century space warcraft, but I'd be very skeptical of such demanding technology for an early Mars mission in this century."

One thing I can say confidently is that a bimodal reactor would be notably less efficient at both purposes than one designed solely for one use or the other.



Jim Baerg:

"Only if there is useful stuff to do at Mars' moons would I think the preliminary mission to Mars orbit with no landing to be worthwhile."

Landing is landing, whether you're landing on a planet or a moon.

The nonsphericalicity of Mars's moons only makes them harder to work with.

Jim Baerg said...

"Landing is landing, whether you're landing on a planet or a moon."

Landings vary greatly in difficulty. The smaller the body the easier it is to do a soft landing with rockets. A nice thick atmosphere is a big help for aerobraking & parachutes to land softly.

I've seen the claim that in many ways Mars is the hardest body for soft landing a craft large enough to hold a few humans. The thin atmosphere is marginal for using aerobraking & parachutes & the gravity is high enough to make a rocket powered landing as on the moon require too much propellant.

A landing (or docking) with the martian moons has got to be much easier.

Tony said...

SA Phil:

"QED - sorry man - you are just wrong."

No. I'm not. You're missing the very fundamental fact that measuring horsepower involves imposing a load on the system. 500 brake horsepower is not just a power output measurement. It's a load measurement. And the necessary load to generate that measurement is going to stop a miniengine in its tracks.

Schlepping the discussion back on topic, I think you should look into the engineering of liquid chemical rocket propellant turbo pumps. The SSME LH2 pump in fact generates 100 hp/kg. That makes a 500 hp motor in a very small space sound possible. The only problem is that pumps drive relatively compressible liquids. If you tried to drive a mechanical transmission with one you'd rip the splines right off the shaft.

Tony said...

SA Phil:

"
That said - how far away is a liquid core NTR? By design it runs a lot hotter than solid core -- maybe it would be a better candidate for the hybrid."


How far away? Decades, centuries, maybe never. One has to remember that a lot of so-called rocket "designs" are conceptual leaps of faith. They're based on "if you could do this, then you could do that" kind of thinking. In the case of liquid core NTR, if you could get a stable liquid fissionable core that didn't melt the machine, you could get high Isp...if you could figure out a way to keep the heated reaction mass from melting the machine. Everything with an "if" in front of it is handwavium.

WRT using such a device for power generation, there's no way. It's designed for high energy over a short time. You simply don't need all of that energy to generate electrical power.

Tony said...

Paul:

"One can generate electricity in a NTR in an interesting way, to boost the Isp a bit.

The idea would be to do something like this:"


It wouldn't work. You can't cheat thermodynamics. Whatever electrical power you generated during your expansion cycle, you can't generate enough to heat the hydrogen back up by the same amount, much less a higher one.

Anonymous said...

Tony

No. I'm not. You're missing the very fundamental fact that measuring horsepower involves imposing a load on the system. 500 brake horsepower is not just a power output measurement. It's a load measurement. And the necessary load to generate that measurement is going to stop a miniengine in its tracks.
---------

No it wont.

Period.

If you were right - no IC powertrain would work.

Do you think a Big Rig has 40X the power of a Honda Civic? It has 40X the "load" (by your definition).

The shaft they are talking about with bhp is the crankshaft not the drive shaft.

But that doesnt matter either, because I am are going to change the torque/rpm ratio with the trasnmission.

And thus I will have the right torque at the right rpm to get the 500 hp I need for your specific application.

Ill have 500 hp at the back of the engine and Ill have (roughly) 500 hp after the transmisison. And then Ill have 500 hp connected to whatever it is you want to connect to.

The transmission will just slip until the is enough torque to move the "load" (your definition) and then lock into place. And bam 500 hp!

Yee haw.


And that is how it works whether or not I get 500 hp by geting 10 ft pounds of torque at 260,0000 rpm or 260,000 ft lbs of torque at 10 rpm.



(SA Phil)

Anonymous said...

(SA Phil)

Horsepower doesnt measure load -- it measures power. (work over time)

The SI unit is Watts.

Load is only one of the components of the work portion.

Anonymous said...

Tony,

Schlepping the discussion back on topic, I think you should look into the engineering of liquid chemical rocket propellant turbo pumps. The SSME LH2 pump in fact generates 100 hp/kg. That makes a 500 hp motor in a very small space sound possible. The only problem is that pumps drive relatively compressible liquids. If you tried to drive a mechanical transmission with one you'd rip the splines right off the shaft.

---------------

I already posted a link on how to work around that.

Use your IC motor to increase pressure in a compressable liquid, use the pressure to drive a piston at the "load" (your definition)

The hydraulic system/piston is the transmission -- and the system works. As I mentioned working examples exist.

On one end you have low torque, on the other you have higher torque -- the power is the same (basically)

I doubt its the only way to get 500 hp in a 1 cubic foot engine - but that is besides the point.


(SA Phil)

Tony said...

SA Phil:

I've worked with powered machinery more than a few times. Power is meaningless without load. You can calculate that you can get so much power at so much RPM, but as soon as you apply the load for that power, you find out that you can't maintain the RPM, using a motor made of real world materials. I'm discussing practical application. You're lost in theory.

Thucydides said...

Moving in a different direction, any Mars mission is bound to be long duration, which makes carrying a massive liquid Hydrogen tank (or even lots of little ones) a difficult proposition. LH2 is a deep cryogen, and would require either massively insulated tanks, a refrigeration unit and radiators or both to remain liquid throughout the multi year voyage.

Now we know that higher density fuels offer lower ISP's, but there might be an advantage to trading the mass of fuel or remass (if using an NTR) against the mass of the LH2 tank complex, not to mention the engineering conveinience as well.

Assuming there was enough information to ensure there was a supply of water on Mars or the Martian moons (or you were willing to send a tanker ahead of time), a NTR steam rocket might make the most sense, water is pretty compact and can act as part of the radiation shield. Water is known to be fairly plentiful in the Solar System (if not always in easily accessable form), and the plumbing issues are fairly straight forward.

Anonymous said...

Tony,

I've worked with powered machinery more than a few times. Power is meaningless without load.

=======================

let me guess - electric motor with no transmission?



----------

I've spent 100's of hours working with engine dynos. I am telling you - you are wrong.

The "load" is being handled. This is simple machine level physics here.

The engine never "sees" your final load. The Transmission does. The Transmission is the lever in this problem.

The engine sits at the end of the really long lever with low force (High rpm) and then the transmission converts it to the force you need at the other end. The other side of the lever has high force but is short (Low rpm)

You gave me Archimedes' transmission by failing to define it - so of course I am "stuck in theory".

But I wouldnt need to use Archimedes' transmission to convert 50 or 100 ft lbs of torque into 500.

Heck you could probably build this for real. You just wouldn't want to.

This stuff is done every day. Every time you see a buzzy Honda motorcycle blast past a Harley.

(SA Phil)

Tony said...

Nuclear steam rockets (NSR) have an Isp of 190-200. Maybe they make some sense with abundant water ice supplies and sticking to space-to-space applications. But for hardware launched from Earth for a known duration mission? almost anything, even storable hypergolics, would be better.

Most plans that foresee the need for space-storable cryogenic propellants presume that any such stage would have a solar powered propellant recondenser to capture and rechill the propellant.

Anonymous said...

(SA Phil)

Remember as far as I am concerned is you are saying that I can't convert a 105 ft/torque , 25000 rpm motor into something you might use a big block for.

When acceleration penalties or engine braking are not even considerations.

And I can have as big a transmission as I want.

You are basically arguing I couldn't repower an old Chevy Impala with a 250 cc racing motorcycle engine.

Tony said...

SA Phil:

I didn't give you Archimedes Lever, you assumed it. I honestly expected you to stay in the real world, but I guess that was silly, wasn't it?

As for working with dynos -- or any other kind of applied load -- are you seriously going to maintain that a 10 lb motor could even begin to spin the rotor of a dyno capable of measuring 500 horsepower? See -- that's what you continuously and obstinately insit on ignoring: You can't just will your little supermotor to spin at 25,000 RPM when it's hooked up to a load, either directly or through a transmission. The load will either brake the motor to a much lower RPM or brake it (probably catastrophically).

Speaking of electrical machine tools, except for bench grinders, drill motors, etc., they all have power transmissions, either belt or gear. With belt drives, when you overload the motor, you get belt slip. With gear drives, you can have tools break, the work fly out of the vise or chuck, gears strip, or, if properly designed, safety linkages snap. What you can't do, in either type of machine -- or with any type of motor in existence -- is have the motor maintain speed and drive the transmission at loads above rated power.

Tony said...

SA Phil:

"Remember as far as I am concerned is you are saying that I can't convert a 105 ft/torque , 25000 rpm motor into something you might use a big block for.

When acceleration penalties or engine braking are not even considerations.

And I can have as big a transmission as I want."


You assumed those things in order to make an abstract theoretical argument. I was illustrating a point using automotive technology. Implicit in that is that we remain in the real world where that technology is applied, not take excursions into inapplicable theory. With all due respect, don't blame me for your inability to remain within commonsensical constraints.

Damien Sullivan said...

What about using the water -- or better yet, hydrocarbons -- as a hydrogen carrier? Electrolyze/crack/reform to generate the hydrogen, dump the oxygen or carbon out the side. Comes down to whether the aggregate mass of the heavier atoms + energy for cracking is less than the mass of tank+equipment for pure H2 storage.

Anonymous said...

(SA Phil)

RE: Tony and his apparent hatred of Basic Mechanical Physics.

My little tiny motor in this example is making 50 or 100 ft lbs of torque at high RPM. That means it is also making decent torque at lower RPMs.

It is not a little tiny motor anymore.

So of course it will spin a 500hp dyno.

You seem to think the little motor is still putting out 3 ft lbs of torque or something.

Again torque is everything. Lack of Torque is why your motors wouldn't move your "load".

The only thing the engine is going to do is spin a shaft around at a certain torque and a certain speed.

That is all any of them do.

Horsepower is simply Torque X Engine Speed. The rest is conversion factors.

Horsepower isnt a load. Its a Power Measurement. This would be like you telling me Watts is an electrical load.

-----------
So if I have a transmission which will convert the torque to handle the application's torque requirement -- the system works.

The generator spins, the car moves, w/e.

The Horsepower comes in when you need that application to spin at a certain speed as well.

Work In equals Work Out.

The generator makes X Watts, the car moves 150 mph, w/e.

----------

You would need a sophisticated transmission to handle the slip to prevent stalls. A lot more sophisticated than a belt drive. But transmissions like this exist.

You drive them .. every day.

Tony said...

Damien Sullivan:

"What about using the water -- or better yet, hydrocarbons -- as a hydrogen carrier? Electrolyze/crack/reform to generate the hydrogen, dump the oxygen or carbon out the side. Comes down to whether the aggregate mass of the heavier atoms + energy for cracking is less than the mass of tank+equipment for pure H2 storage."

This implies carrying mass that you have no use for. Also, the math just doesn't work out. Water is 1/9 hydrogen and 8/9 oxygen, by weight. For any given amount of hydrogen, you have to have 9 times as much water, by weight, than you do liquid hydrogen. Now, an equivalent amount of liquid hydrogen would require a tank about 1.6 times the volume, but since taht much hydrogen weighs 1/9 of what the water does, that's hardly an issue.

Anonymous said...

(SA Phil)

You could use the reactor to make the hydrogen from water with heat. This was part of the Gen IV Nuclear Reactor proposals.

You could use the same Nuke to make the power for the electric drive.

Tony said...

SA Phil:

"RE: Tony and his apparent hatred of Basic Mechanical Physics."

I don't hate mechanics. I just won't be taken in by misapplication of theory.

"My little tiny motor in this example is making 50 or 100 ft lbs of torque at high RPM. That means it is also making decent torque at lower RPMs.

It is not a little tiny motor anymore.

So of course it will spin a 500hp dyno."


It will spin the dynamo -- if it can overcome mechanical drag in the system -- at a very low speed. It won't maintain your nominal 25,000 rpm, meaning it won't generate 500 hp...not if it's made out of real world materials.

"Horsepower is simply Torque X Engine Speed. The rest is conversion factors."

A realistic motor, made of realistic materials, won't maintain anywhere near your nominal speed under a load equivalent to 500 hp. It's that simple.

"Horsepower isnt a load. Its a Power Measurement."

It's a power measurement measured by applying a load, Phil. Without the load, it's a meaningless number.

"This would be like you telling me Watts is an electrical load."

I would tell you that. The electrical load on a circuit is equivalent to the power being drawn by connected devices (plus line loss, if that's significant). Load is commonly measured in kilowatts or amp-volts (which is the same thing, because P = I * E).

Dragging you kicking and screaming back onto topic, the point is made: small engines don't generate the same amount of power over time that large ones do. And large ones downrated to low power generation levels are overkill (and most likely highly inefficient).

Anonymous said...

===========
Tony,
It will spin the dynamo---if it can overcome mechanical drag in the system -- at a very low speed.
==========
=====

Dyno not Dynamo.

http://en.wikipedia.org/wiki/Dynamometer

Not the same. The Dyno will let it spin - that is how it works.

=====================
Tony,
It will spin the dynamo -- if it can overcome mechanical drag in the system -- at a very low speed. It won't maintain your nominal 25,000 rpm, meaning it won't generate 500 hp...not if it's made out of real world materials.
==============================
==============

The torque moving the "dynamo" isnt necessarily moving anywhere near 25,000 rpm. You are confusng which side of the transmission you are on.

(side A fast)------(side B slow)
(side A Low T)-----(side B high T)

the "Dynamo" is on side B.

The dyno would be on side A ... but that is for measuring horsepower - not doing work.


===================
Tony,
A realistic motor, made of realistic materials, won't maintain anywhere near your nominal speed under a load equivalent to 500 hp. It's that simple.
=====================
===================

I haven't bothered to move onto engine ideas because you are still stuck on how transmissions work.

You wont accept that an Engine that could make 100ft of torque at 25,000 rpm could potentially be harnessed for static speeds.

So its meaningless to come up with ideas on how to get there.

In your world Semi-Trucks don't work, Small cars can't climb hills, and your starter can't spin your engine.

In other words, for you to be right - cars would not work.

(SA Phil)

Thucydides said...

Using an NTR at high enough power to split water into H2 and O will be an interesting proposition. The temperature required is over 2000 degrees C, which is pretty close to the melting point of a lot of structural materials. As well, if the products of decomposition should recombine in the reactor by accident, well the chief engineer will have an interesting problem on his hands. As an aside, how will the O2 stream be separated from the high speed H2 stream? Letting it stream out the nozzle probably won't add much to the ISP, you have just created a very dangerous steam engine for space travel. (Putting water into the reactor at low pressure isn't going to help, by definition any liquids/gasses heated to over 2000 degrees C will have a lot of pressure and be moving at considerable speeds).

The two main reasons to suggest a steam rocket for space to space transfers (I should have made that clear) are the ability to use local resources, so you can reduce the amount of mass needed to get there in the first place, and to further reduce the ship's mass if the mass difference between a water tank and an LH2 tank was great enough. The low ISP is another issue as well, you would have to run many trade offs to create an attractive mission using this option.

Anonymous said...

Tony,

Dragging you kicking and screaming back onto topic, the point is made: small engines don't generate the same amount of power over time that large ones do. And large ones downrated to low power generation levels are overkill (and most likely highly inefficient).

=====================

Wild Bovine Waste.

A 500 hp small engine will generate exactly the same power over time as a 500 hp large engine.

Exactly the same.

If due to poor torque matching it wont move your nebulous application - it might not work. But they generate exactly the same power when they both work.

(SA Phil)

Tony said...

SA Phil:

"Dyno not Dynamo."

Typo, Phil.

"You wont accept that an Engine that could make 100ft of torque at 25,000 rpm could potentially be harnessed for static speeds."

I would accept it in an engine that can withstand the mechanical stresses involved. In something the size of kid's dirtbike motor? It's simple not believeable, if the machine is made out of real world materials.

"In your world Semi-Trucks don't work, Small cars can't climb hills, and your starter can't spin your engine.

In other words, for you to be right - cars would not work."


Cars and trucks work because their power plants are big enough (given the materials they are made out of) to drive the required loads, including losses to parasitic loads and transmission losses. Our notional miniengine wouldn't be able to that because it's too small to drive the transmission, parasitic loads, and overcome mechanical drag. It would simply stall or rip off its mountings, no matter what kind of transmission you hooked it up to.

You're engaging in willfull ignorance, Phil -- maybe not in mechanical theory, but in recognizing and adhering to the real world context that the discussion -- and the topic overall -- demands. I'm perfectly happy to let the readers decide what you are and why you act this way.

Tony said...

SA Phil:

"A 500 hp small engine will generate exactly the same power over time as a 500 hp large engine."

AFAIK you can't make a 500 hp engine out of real world materials that would fit in less than a cubic foot, Phil. That's the whole point. You're invoking the engine a priori when the fundamental question I'm asking you is how you could make the thing to begin with.

Are you simply not getting that you're being transparently obtuse?

Anonymous said...

Tony


I would accept it in an engine that can withstand the mechanical stresses involved. In something the size of kid's dirtbike motor? It's simple not believeable, if the machine is made out of real world materials.

==========

But its not the size of a kid's dirbike motor. It an engine that fits in the SPACE of a kid's dirtbike motor.

Gigantic difference.

(SA Phil)

Anonymous said...

(SA Phil)

RE: supposed willful ignorance.

I cant get you to agree that you can use a low torque high RPM motor to do the job of a high torque low RPM motor yet.

Why should I bother with the rest?

From where I sit you wouldn't accept that I could use a 1 liter 4 cyl. race motor to replace a 5 liter V8.

Even though I am okay with the acceleration hit.

Tony said...

SA Phil:

"But its not the size of a kid's dirbike motor. It an engine that fits in the SPACE of a kid's dirtbike motor.

Gigantic difference."


Only if you're being relentlessy and irretrievable pedantic. The L, H, and W of the motor -- IOW the size -- defines the volume in which it fits.

"RE: supposed willful ignorance.

I cant get you to agree that you can use a low torque high RPM motor to do the job of a high torque low RPM motor yet.

Why should I bother with the rest?"


I never disagreed, Phil. I simply dismissed it as irrelevant. The point is that you can only get so much power out of a given size package over a given amount of time, using real world materials. How you apply the power is beside the point.

"From where I sit you wouldn't accept that I could use a 1 liter 4 cyl. race motor to replace a 5 liter V8.

Even though I am okay with the acceleration hit."


Limping back onto the topic, this whole sidebar started because you were trying to suggest that an NTR reactor and a lightweight electrical power supply reactor could be made interchangeable. My illustration using IC motors was intended to point out that high power machinery and low power machinery aren't fungible. A small dirtbike motor can't give you what you want in a high power application.

The entire point, Phil, was power delivery over time. An NTR or a large truck motor delivers a lot of power over a given time. A lightweight electrical power reactor delivers a little power over the same time. That has mechanical design and implementation consequences, because high power and low power applications have incompatible constraints, meaning that you can't use the same machine to do both things. That's it. Nothing else.

Anthony said...

There's very little reason to use a steam rocket. If you have a local source of water and a power plant, you'll get better rocket performance, while requiring a much smaller power plant, by simply using the power plant to electrolyze the water and liquefy the resulting hydrogen and oxygen. This requires more total energy than the steam rocket, but you can generate the energy over hundreds or thousands of hours, instead of being forced to do it over the course of minutes.

Anonymous said...

(SA Phil)

RE: Tony's Tap Dance on Ice

No you basically said that some Engineering Challenges are just obvious.

Even though you aren't a nuclear engineer, nor was anyone else in the discussion.


==============================
Tony,
"Some things can be ruled out on basic engineering principles. If somebody came to you and told you that you could have a 500 hp IC power plant that fit into the same form factor as a two stroke that powers a kid's mini 50 dirt bike, what would you say?"
================================

You then spent 30 posts ignoring or arguing with every basic engineering principle I mentioned.

The later you even find an example of a 1000 hp motor that's probably close to the size you want ... and I even showed a possible way to transfer the power.

And you still are playing Mr. Contrarian. I think I have your number now, Fred. Tell Ginger I said "hi"

========================

As to the engine - 1 cubic foot is more room than you think. Remember I am scrapping the whole incidental air cool nonsense. Which is more than 50% of the total volume of one of those things. Ill replace with a nice streamlined 1"x12x12" radiator and an electric cooling fan.

The engine itself will consist of 1 piston, with a Bore of 3 inches and a Stroke of 3 inches. The piston will ride in the "cradle" of the crankshaft to reduce total space. Ill be generous and allow 2" of cylinder head clearance. This gives me cylinder dimensions of 8"x3" And an engine displacement of *350cc*.

I'd probably have room to increase the bore if 350cc is insufficient. For example a 5 inch bore would give me 965CC. But I think 350 is within the realm of believability.

No cam shaft, No "valve train" - I'll use electronic spool valves. No point is giving up the space.

No Air intake -- I will instead supply compressed air and compressed natrual gas directly to the cylynder head. This will allow me to have a supercharged engine without any parasitic losses...

No flywheel, Ill attach the crankshaft to the transmission and put a starter on it instead.

Since I have room for over 2" thick walls on this engine (well over in some places) .. Ill run some hellacious "boost". Maybe 40psi.

Exceeding 100 foot pounds of torque should not be any problem.

Racing bikes exist that hit 25,000 rpm already. So a piston engine at that speed is no biggie.

I have plenty of reserve space on the sides, and along the crank, I could probably even switch to a V and add a cylinder - but that wold be overkill.

The size of the 50cc dirtbike is 50cc, the size of its poweplant - The space, its form factor - is pretty large. 1 Cubic foot is gigantic with a big enough budget.

(SA Phil)

Anonymous said...

(SA Phil)

I remember the nuclear steam rocket idea being tossed around in conjunction with basically space icebergs --- probably 30 years ago.

The Idea would be to use a piece of a comet and melt it, using the steam as reaction mass.

Thrust was high, ISP low. Unfortunately Mass was also high.

The Mass Ratio would be crazy - maybe 99% of the total Mass at the start of the trip would be Ice.

Still it would probably "work" assuming you could get the Iceberg.

Anthony said...

On the '1 kW/kg' standard, let's say that we're starting by putting mass in low orbit. Now, one problem with a low thrust drive is that it takes an awfully long time to break orbit (and a lot more delta-V than with a high thrust drive). With a 10m/s drive, going from low orbit to mars transfer takes 3.6 km/sec delta-V (thank you Oberth effect) and a couple of minutes. With a 0.01m/s drive it takes 8.3 km/sec and a bit under ten days. We probably don't want thrust much under 0.01m/s. Also, if we want to out-perform a cryogenic fuel rocket, we need an exhaust velocity of upwards of 11 km/sec, and since the electric drive is substantially heavier, we probably actually want at least 20 km/sec (an optimal electric drive vehicle, trading off power for fuel, seems to be ~25% power plant and drivetrain). 0.01m/s at 20 km/sec is a power output of 100W/kg (of vehicle mass), and (with the 25% above), 400W/kg of drive (including reactor) mass. Deciding that you want 1,000W/kg (of drive/reactor mass) seems like a fair baseline for being worth the trouble.

Jim Baerg said...

"What about using the water -- or better yet, hydrocarbons -- as a hydrogen carrier?"

Or maybe ammonia. At a few hundred °C it breaks up into N2 & H2.

Paul said...

It wouldn't work. You can't cheat thermodynamics. Whatever electrical power you generated during your expansion cycle, you can't generate enough to heat the hydrogen back up by the same amount, much less a higher one.

You completely misunderstood what I wrote. No, it doesn't violate any laws of thermodynamics.

Remember, a nuclear engine, unlike a chemical engine, is not energy limited. If we cool the hydrogen by running it through the expander, we have an essentially infinite heat source available to reheat it.

What limits the nuclear engine is two things: (1) the temperature limit of the fuel elements, and (2) the entropy of the fully expanded exhaust gas. The latter places an upper bound on how much entropy can be produced by the engine. Ideally, all this entropy production will be in the fuel elements themselves, and all other processes in the engine will be as close to isentropic as we can practically make them.

Anonymous said...

Paul,


Remember, a nuclear engine, unlike a chemical engine, is not energy limited. If we cool the hydrogen by running it through the expander, we have an essentially infinite heat source available to reheat it.

----------


Interesting - basically taking advantage of the fact that you can never use up all of the heat from the reactor.

I hear Jay Leno "heat all you want, we'll make more"


(SA Phil)

Anonymous said...

(SA Phil)

That sounds approximately similar to the Hybrid Electro-Thermal MITEE listed on Atomic rockets.

If that information is roughly accurate that system has twice the ISP of a normal Solid NTR.

Or about 4 times a Chemical Rocket.

Not too shabby.

Paul said...

(SA Phil): I haven't looked at Atomic Rockets, but I wouldn't be surprised if the idea was the same.

The idea of using an arc to superheat the gas is also not optimal, since that produces entropy. It would be better to seed the hydrogen with some alkali element for ionization (lithium?) and accelerate the gas electrodynamically, assuming resistive losses weren't too high, before expanding it in the latter part of the nozzle.

Also, for in space use, the operating pressure would probably be kept low so the hydrogen is highly dissociated. This would maximize the entropy at the exhaust plane.

Tony said...

SA Phil:

"No you basically said that some Engineering Challenges are just obvious.

Even though you aren't a nuclear engineer, nor was anyone else in the discussion.

You then spent 30 posts ignoring or arguing with every basic engineering principle I mentioned."


No, Phil, I didn't argue with the principles. I dismissed your application of them as being irrelevant, if not outgright incorrect. If anybody ignored principles, it was you, by denying the equivalence of load and power, and totally ignoring things like inertia and mechanical drag.

Tony said...

Jim Baerg said...

"Or maybe ammonia. At a few hundred °C it breaks up into N2 & H2."

Are you sure that's not N2 + 3 H2?

In any case, you have a similar problem as water. Liquid ammonia is ten times as dense as liquid hydrogen, but it's only 3/17 hydrogen by weight. So you need 5 2/3 as much liquid ammonia by weight as you do liquid hydrogen, but the liquid hydrogen tank only has to have about twice the volume for the same ammount of hydrogen.

Tony said...

Paul:

"You completely misunderstood what I wrote. No, it doesn't violate any laws of thermodynamics.

Remember, a nuclear engine, unlike a chemical engine, is not energy limited. If we cool the hydrogen by running it through the expander, we have an essentially infinite heat source available to reheat it.

What limits the nuclear engine is two things: (1) the temperature limit of the fuel elements, and (2) the entropy of the fully expanded exhaust gas. The latter places an upper bound on how much entropy can be produced by the engine. Ideally, all this entropy production will be in the fuel elements themselves, and all other processes in the engine will be as close to isentropic as we can practically make them."


A nuclear reactor is not an infinite heat source. It can only produce so much heat per second of operation without melting. If you use some of that heat to preheat the reaction mass, then use that reaction mass to generate electricity through exapnsion mechanics, you have waste heat losses all along the way. Then you reintroduce the reaction mass into the reactor as a coolant, which heats it up again, but not to the point that it could have been without the parasitic cooling of the preheated reaction mass. So then you try to raise the temperature of the reaction mass by using the electricity that it produced during the previous expansion phase. But obviously you can't heat it up by as much as it was preheated, because you lost a lot of energy in producing the electricity in the expansion stage. And I haven't even mentioned the real fun part -- where does the energy come from to recompress the hydrogen for it's second trip through the reactor, so that it can be delivered at a rate to generate an efficient thrust level?

Tony said...

SA Phil:

"That sounds approximately similar to the Hybrid Electro-Thermal MITEE listed on Atomic rockets.

If that information is roughly accurate that system has twice the ISP of a normal Solid NTR.

Or about 4 times a Chemical Rocket.

Not too shabby."


It's more efficient but lower thrust. Also, it works on two different sets of reaction mass -- the mass used to generate eclectricity, and the mass that is broken down from H2 into H. That way it doesn't break any of the rules. (Though it still sufferes from the need to recompress the H2 before running it through the high pressure circuit.)

What Paul is suggesting is somehow getting more power out of reheating a working fluid than just running through once at maximum temperature and pressure for the reactor. That does break the rules, because there are waste heat losses along the way, and you can't get more than you have in the first place.

Anonymous said...

Tony,


No, Phil, I didn't argue with the principles. I dismissed your application of them as being irrelevant, if not outgright incorrect. If anybody ignored principles, it was you, by denying the equivalence of load and power, and totally ignoring things like inertia and mechanical drag.

==========

bla bla bla

I wasn't ignoring anything. My Engine was never 10 pounds, nor did it not have enough torque to move your mostly nebulous "load".

You gave me a cubic foot. You can have a hundred pound engine in that space.

The problem was in your head you were still picturing the tiny dirtbike engine. And you tend to think inside the absolute very center of the box.

Anyone who has read more than a handful of your posts would pick up on that.

(SA Phil)

Anonymous said...

Tony,

What Paul is suggesting is somehow getting more power out of reheating a working fluid than just running through once at maximum temperature and pressure for the reactor. That does break the rules, because there are waste heat losses along the way, and you can't get more than you have in the first place.

=============

I dont see whre he said more power. He said higher specific impulse.

(SA Phil)

Jim Baerg said...

Tony:
"Are you sure that's not N2 + 3 H2?"

Strictly speaking
2 NH3 -> N2 + 3 H2
I left out the proportions.

"In any case, you have a similar problem as water."

Not as bad though.
If you used water as the propellant in a Nuclear Thermal Rocket or laser/microwave beamed power launch system, you wouldn't get even as high a Ve (exhaust speed) as H2/O2 chemical rocket.

The Ve in a thermal rocket is roughly proportional to sqrt(T/m) where T is the absolute temperature & m is the average molecular weight of the exhaust.

T is limited by the material properties of the rocket structure. For a steam rocket m is 18. An H2/O2 rocket does a bit better by running with a bit more than 2 H2 for every O2. H2 has m=2.
NH3 has m=17, but after
2NH3 -> N2 + 3H2
m=8.5.

So in a nuclear or beamed power thermal rocket, ammonia gives a higher Ve than H2/O2 chemical, though less than H2 propellant, but without the hassle of supercold temperatures.

Which one is best in what circumstances given the tradeoffs, I don't know.

Tony said...

SA Phil:

"I dont see whre he said more power. He said higher specific impulse."

He did say specific impulse, but AFAICT, he's trying to get it by somehow extracting more work out of the reactor and reaction mass over a given time. That means he's trying to extract more power. The assertion "infinite heat source" gives that away.

Tony said...

Jim Baerg:

"So in a nuclear or beamed power thermal rocket, ammonia gives a higher Ve than H2/O2 chemical, though less than H2 propellant, but without the hassle of supercold temperatures.

Which one is best in what circumstances given the tradeoffs, I don't know."


According to Encyclopedia Astronautica, you can get an Isp of 550 in an ammonia NTR running at 3,500 K (Soviet YaRD OKB-456 engine). Running an LH2 NERVA type engine at that temperature would get you 900+ sec Isp. That leaves a lot of room for the mass of an LH2 chiller system to keep your propellant from boiling off.

Tony said...

SA Phil:

"I wasn't ignoring anything. My Engine was never 10 pounds, nor did it not have enough torque to move your mostly nebulous "load".

You gave me a cubic foot. You can have a hundred pound engine in that space."


I've always said "less than a cubic foot". (You can do a search on this page on "cubic foot" if you want -- in fact I invite you to.) Personally, I think a quarter of a cubic foot sounds about right for a 50cc engine, carburetor included. If you fill up 10% of that volume with steel, you get a motor weighing about 12 lbs. Being really generous, and saying you could fill up 20% of that volume with working machinery, you get at most a 60 lb engine.

"The problem was in your head you were still picturing the tiny dirtbike engine. And you tend to think inside the absolute very center of the box.

Anyone who has read more than a handful of your posts would pick up on that."


I offered you as an example engine a rocket turbo pump. Yeah, that's inside the dirtbike motor box...almost dead center. [rolleyes]

The box I'm thinking in, Phil, is real world applications and material strengths. You're playing with pure theory and not thinking about what a piece of machinery has to do to be useful. But of course, to borrow a turn of phrase, anyone who has read more than a handful of your posts...

Tony said...

Where I said "fill up 20%" in my previous post, I of course meant "fill up 50%".

Anonymous said...

Guy's, I don't want to read anymore comments about 1 cubic foot engines...unles it helps us get to Mars or helps us get around once we are there.

That being said, what do you think about the bifilm fuel, pulse-laser ignited fusion drive proposed by John J. Chapman? (sorry, no link, but the article is listed on Atomic Rockets blog June 28, 2011).
Mr. Chapman does state that at least a decade of work needs to be done on it to get from the drawing board to a working flight article. Does this sound plausible?

Ferrell

Anonymous said...

(SA Phil)

Sounds like a pretty decent system to me.

Its one of those things about any kind of fusion though it is always supposedly right around the corner.

Nothing I saw in that blurb says the fusion is self sustaining though.

I see he says you can make electric power but he only says "for onboard control systems" Not "to keep firing the laser".

So would the reaction just continue after it was started? Or would you need power the laser? With a fission reactor perhaps?

Or perhaps fire a laser from another location.

Anonymous said...

Farrell

Guy's, I don't want to read anymore comments about 1 cubic foot engines...unless it helps us get to Mars or helps us get around once we are there.

==========

I do apologize for allowing myself to get sucked into what felt to me like another serial strawman run around.

Sorry Rick and everyone else.

I even apologize to Tony, it is clear we don't communicate very well in these threads.

(SA Phil)

Paul said...

Does this sound plausible?

No rocket that assumes you have a fusion reactor (of any kind) is plausible, and certainly not in ten years.

Fission rockets are difficult enough, and fission was easy enough to build the first reactor in a squash court within about a year of starting the effort.

Paul said...

I dont see whre he said more power. He said higher specific impulse.

Yes, that's what I'm talking about. The scheme was not intended for high power density or high thrust applications (although it would have higher thrust than conventional nuclear-electric systems). I guess I needed to say that explicitly.

I have to say, having long experience on Usenet in years past, I find Tony's style of "debate" comfortably nostalgic. Who needs to actually understand what the other guy is trying to say when you can misinterpret it to your own advantage?

Tony said...

SA Phil:

"I even apologize to Tony, it is clear we don't communicate very well in these threads."

No apologies necessary. I'm sure you're right, the way you were looking at the problem. Gotta figure out how to get you to see the problem from a different angle...

Tony said...

Paul:

"Yes, that's what I'm talking about. The scheme was not intended for high power density or high thrust applications (although it would have higher thrust than conventional nuclear-electric systems). I guess I needed to say that explicitly."

I'm not going to argue with you on what you originally meant. You know and I don't. But your description really did sound like you were trying to get more energy out of a working fluid than the nuclear reactor could put into it. The way you should have described it was using some working fluid to generate electricity to more efficiently use another portion of working fluid. If that's not what you meant, then I would still argue that you're trying to cheat thermodynamics.

"I have to say, having long experience on Usenet in years past, I find Tony's style of "debate" comfortably nostalgic. Who needs to actually understand what the other guy is trying to say when you can misinterpret it to your own advantage?"

Inherrent in that dynamic is the totally and irremediably subjective nature of determining who is misinterpreting whom. Which is why any virtual group tends to become an insular old boys' network, just like any face-to-face one. I'm not complaining, mind you -- it's an artifact of human social norms.

Anonymous said...

=Milo=



Tony:

"it's an artifact of human social norms"

So... do you think aliens would be different?

Anonymous said...

The impression I got from the article was that the drive used an external power source to power the laser; turn off the laser and the reaction dies. Any power you get from the fusion reaction would (presumably) be from siphoning off a bit from the thrust via something like a MHD. I don't think that the engine could be discribed as a reactor; more like a fusion generator, basicly just a very powerful ion rocket motor. I'm not sure how big and heavy this engine would be, but I don't think it would be more complex than a high end theater movie projector. I'm also a bit more skeptical about the 10 year milestone, but am more comfortable with a 20-30 year paper-to-flight-article timeframe; if it can be made to work. Big if. Still, I'm hopeful.

Ferrell

Anonymous said...

(SA Phil)

I always get the impression from the things I've read that sustainable fusion is the really hard one.

Unsustainable if far simpler.

So since you are describing unsustained fusion... Maybe its far more practical.

Basically using a laser to make tiny fusion explosions.

I suspect Luke would know -- he seems really strong on the fusion reaction end of things.

Anonymous said...

(SA Phil)

Along those lines what about a fission fragment rocket?

Not for the first stage obviously you'd need to get well clear of the anti-nuke crowd first.

But it has excellent specific impulse. And it doesn't require very much electrical power.

Not sure about the thrust, "low" is always relative. I believe Rick was suggesting he needs around 10 milligees to make this work?


Would a hybrid NTR Fission fragment be possible? Basically a low thrust NTR (thus lower pressures, less rocket-like) where the reactor doesn't stay quite so intact.

It would be fun even if it just barely worked, if only to see the anti-nuke crowd howl.

Monte Davis said...

Phil: would you care to parse "anti-nuke crowd" further?

I have a pretty good quantitative grasp, and no superstitious fear, of nuclear power and radioactivity. I would have no problem living close to a competently managed power reactor.
I'm fine with launches of RTGs such as Cassini's. And if you come up with a way to magic a big honking NTR direct to orbit for use in space, I'll be happy.

But is it permissible to harbor some misgivings about the awkward intermediate cases? Those which feature a large inventory of nuclear material, presumably in a configuration as light as possible, accelerated from ground to orbit either under its own power or as passive payload for a chemical rocket? Because I do.

Anonymous said...

Phil: would you care to parse "anti-nuke crowd" further?

===============

It was mainly just a joke --

However there is a set that protested even the use of RTD's in space.

I do not mean those who would not want NTR's as Earth liftoff craft. I completely understand the objection to that.

I do however mean the people who suggest we should completely end nuclear electric power generation because of what happened in Japan.

Especially when they don't similarly balk at the amount of radioactivity released by the coal industry every year.

Not to mention the other health related effects which cause much more damage annually than nuclear power ever did.

A great visualization is this graph.

http://www.geekosystem.com/wp-content/uploads/2011/03/death-rate-watts-550x373.jpg

If that information is accurate we would save huge numbers of lives by switching from coal to nuclear.

Which also happens to agree with information from other sources.


From s terrestrial standpoint - Nuclear Power would solve a lot of the problems we are now grappling with as far as the coming Energy Shortfalls. But political pressures and anti-nuke attitudes are going to continue to hold it back.

From a space development standpoint- the idea that we would ignore such a useful energy source because nukes are unpopular seems crazy.

So spraying fission materials in deep space sounds fine with me.

Spraying them over the panhandle of Florida -- I can see the objection.

(SA Phil)

Anonymous said...

Monte Davis,

But is it permissible to harbor some misgivings about the awkward intermediate cases? Those which feature a large inventory of nuclear material, presumably in a configuration as light as possible, accelerated from ground to orbit either under its own power or as passive payload for a chemical rocket?
====================

To paraphrase Sam K.

Unfortunately you have to get the car home somehow.

That one is the trickier part of the problem. If that were what people were the most concerned with - the objections would make a lot more sense.

Maybe there is the Macguffin for the a moon base after all.

http://www.space.com/6904-uranium-moon.html

(SA Phil)

Anonymous said...

If we could build a nuke-fuel production plant on Luna, probably Thorium, then nuclear powered interplanetary craft becomes easier to build, politically at least.

A Mars mission launched from Luna orbit would involve more logistics (crew transfer to Lunar orbit, maintenance of a large Lunar base, ect), and would change the dynamics of the mission; Lunar orbit to Mars orbit and return. I'm not sure what the total Delta V would be, or what the specific breakdowns would be. The infrastructure to support this mission would be very large and it would be utterly foolish not to use it to support many other missions. There's your expansion into space; building a launch facility on Luna to support the exploration of the Solar System. It'd probably cost as much as the whole of the Apollo Project and face much more opposition, but I think it's worth it in the long run.

Ferrell

Anonymous said...

(SA Phil)

I like the Luna base idea as well ala 2001.

You get to learn a lot of the habitation requirements for bases elsewhere.

You get to learn/overcome the challenges of fledgling space industry in a location that we have good enough propulsion to "easily" reach.

And since Luna has such a small gravity if you do get any space industry capacity there - you can launch quite a bit more into orbit.

Tony said...

Milo:

"'it's an artifact of human social norms'

So... do you think aliens would be different?"


I don't have a clue. One could reasonably make the argument that intelligence implies certain reaction to certain stimuli, even if you don't go the full Skinner. Or one could make the argument that there are more things in Heaven and Earth than are dreamt of in our philosophy. Given the present lack of dfinitive evidence, who knows?

Rick said...

Unfortunately, building a nuclear fuel production plant on the Moon is an enormous project in its own right - probably bigger and more expensive than the Mars mission.

Which is one more reason for my bias toward solar electric, at least for getting to Mars. We won't really need large scale nuclear energy in space until we are going to Jupiter and beyond.

This is kicking the can down the road, but the political considerations might be different in 2100. (Though I don't think nuclear powered launches are ever likely to be acceptable.)

Anonymous said...

Rick said:"(Though I don't think nuclear powered launches are ever likely to be acceptable.)"

Yeah, but I'd rather that nuclear launches be from Lunar surface than from Earth surface...

Ferrell

Tony said...

Seriously, can we once and for all sh!tcan the G. Harry Stine/Gerard K. O'Neill space industrialization dogma? Industrial bases, even for a single resource type, are just way too complex for transplantation off of the Earth anytime in the next several centuries (at least).

Anonymous said...

Tony,

Seriously, can we once and for all sh!tcan the G. Harry Stine/Gerard K. O'Neill space industrialization dogma? Industrial bases, even for a single resource type, are just way too complex for transplantation off of the Earth anytime in the next several centuries (at least).
=============

Centuries? Really?

300 years ago was basically before the Industrial Revolution.

How do you make that prediction? That's completely out of left field.

If you had said decades I would have been inclined to agree. We know what Industry looks like today and we roughly know how the pattern has come about since modern manufacturing has come about (basically WW2 on).

I just don't see how you can trace back a history of ~100 Years and project several hundreds more.

It is like the people who said going to the moon was impossible in the 1900's.

One thing that occurs to me. If we were to as you say once and for all Sh!tcan the idea of industrializing space for the next few centuries (at least), why have this blog?

(SA Phil)

Tony said...

SA Phil:

"Centuries? Really?..."

Centuries. Really.

The reason the last century in industry happened is because there was a population base and preexisting industrial base to build on. Neither of those exist in space. It would have to be entirely recreated there. I figure on that realistically taking centuries -- at least.

Modern high technology -- even seemingly mundane things like cars, steam turbines, and PCs -- exists very near the top of a pyramid of effort and resources that has a very broad base. It's just going to take a lot of time to move that broad base into space, if it can ever be done. (I refuse to rule out the possibility that it's just too har to do. It could be.)

"One thing that occurs to me. If we were to as you say once and for all Sh!tcan the idea of industrializing space for the next few centuries (at least), why have this blog?"

Because even if the industrial base remains on Earth for a long time, that doesn't mean there won't be humans in space while it is being established there. That's kind of the whole point. And that's essentially what this blog is about, AFAICT.

Also, as much as it pains people who don't want to think about these things, I think there needs to be a voice of caution. I didn't set out to set myself up as that voice, but it seems that I have become such an influence. That's okay -- I have broad shoulders.

Anonymous said...

Tony,

Also, as much as it pains people who don't want to think about these things, I think there needs to be a voice of caution. I didn't set out to set myself up as that voice, but it seems that I have become such an influence. That's okay -- I have broad shoulders.

-------------

I dont think caution is the right word.

More like the voice of technological pessimism.

-----
Sometimes your objections might be realistic. Other times less so.


In this instance. I think the actual determiners on whether there will be any industry on the moon would be 75% political will (since its a money thing) and 25% Technical.

As a rough guess.

As our technology improves it will increasingly be a political/money thing.

Of course I think that in the next 300 years humans will either solve many of our impending problems ... Or else there will be no humans in space at all.

But if we solve a lot of these resource based problems- It is possible our decendants will be able to fund some sort of Space Industry off Earth at some point.

As a civilization I think we spend more money on snack foods than Space Development. So I don't think it is a stretch.

(SA Phil)

Tony said...

SA Phil:

"I dont think caution is the right word.

More like the voice of technological pessimism."


If you want to say so. But that kind of thinking is more than a little bit self-serving, since that allows people who do say so to style themselves as "optimists". Very convenient, don't you think?

But if what is labeled "pessimism" is in fact mere realism...

"Sometimes your objections might be realistic. Other times less so."

Except that I'm not making objections. I'm just offering alternate opinions. Others style it as "objections" for their own rhetorical reasons.

"In this instance. I think the actual determiners on whether there will be any industry on the moon would be 75% political will (since its a money thing) and 25% Technical.

As a rough guess.

As our technology improves it will increasingly be a political/money thing.

Of course I think that in the next 300 years humans will either solve many of our impending problems ... Or else there will be no humans in space at all.

But if we solve a lot of these resource based problems- It is possible our decendants will be able to fund some sort of Space Industry off Earth at some point.

As a civilization I think we spend more money on snack foods than Space Development. So I don't think it is a stretch."


Capitalization of concepts is a dead givaway of religious feeling towards an issue.

Aside from that, I think I'll stick with the simple and obvious observation that it takes a society of millions -- perhaps tens of millions -- to maintain a high technology industrial base. When we have millions of people in space, then we'll see. But that will be several centuries, under any assumptions remotely in touch with reality.

Anonymous said...

Tony,

Capitalization of concepts is a dead givaway of religious feeling towards an issue.

===========
*eye roll*

========================
Tony,


Aside from that, I think I'll stick with the simple and obvious observation that it takes a society of millions -- perhaps tens of millions -- to maintain a high technology industrial base. When we have millions of people in space, then we'll see. But that will be several centuries, under any assumptions remotely in touch with reality.

================
Except that if the space industry is close enough to Earth it is not an industry in isolation.

Close to Earth being determined by the effectiveness of your propulsion system.

We concievably are 4 days from the Moon by Chemical Rocket. Repeatable to some extent based on your launch capability.

I support an Industrial effort in Asia where most of my ship times are in the months.

So an Industrial Effort on the Moon wouldn't take Millions of people in Space to support it.

But by all means... Set up a test case. Make a similair Industrial effort in Antartica.

(SA Phil)

Anonymous said...

Tony,

Except that I'm not making objections. I'm just offering alternate opinions. Others style it as "objections" for their own rhetorical reasons.

===============

If you say so ...

(SA Phil)

Tony said...

SA Phil:

"Capitalization of concepts is a dead givaway of religious feeling towards an issue.

===========
*eye roll*"


It's the same thing as all-caps or too many exclamation points, just not quite as offensive. But it's still uncalled for exhortative rhetoric. You should, sometime, compare your use of capitalized terms with how Thomas Paine had The American Crisis typeset. I think you might find it informative.

"Except that if the space industry is close enough to Earth it is not an industry in isolation.

Close to Earth being determined by the effectiveness of your propulsion system.

We concievably are 4 days from the Moon by Chemical Rocket. Repeatable to some extent based on your launch capability.

I support an Industrial effort in Asia where most of my ship times are in the months.

So an Industrial Effort on the Moon wouldn't take Millions of people in Space to support it.

But by all means... Set up a test case. Make a similair Industrial effort in Antartica."


Then you're not talking about space industry. You're talking about appendages of Earth industry in space. Okay...on those grounds, I really don't think you comprehend how complex industrial establishments are. Maybe at the factory you see raw materials and/or subcontracted parts come in one door and go out the other in completed automotive assemblies. But even at that point you're talking about thousands of tons of machinery and shelter to get anything done on an industrial scale. But beyond he materials and machinery, you have to have power, water, sewage, heating, lighting, maintenance, etc.

And we still haven't left the factory. When you extend the integrated enterprises that go together to make just one type of machine, just one or a few ways, you find out that you're dealing with a supply chain of thousands or hundreds of thousands, using millions of tons of machinery, shelter, and transport.

So, okay, put your factory in space. By the time you get around to supplying it and servicing it, you're going to wind up iether busting the piggy bank bringing it all up from Earth. Or you're going to bust it establishing all of the feeder industries necessary to make whatever it is you think you're going to make.

Jim Baerg said...

Rick: "(Though I don't think nuclear powered launches are ever likely to be acceptable.)"

However, launching an unstarted nuclear reactor into space for use there is another matter.

The uranium or plutonium in such a reactor is rather minimally radioactive. The fission products made during operation are much shorter lived & so much more dangerous. Space nuclear reactors would be less radioactive on launch than RTGs.

If the reactor powers a spacecraft that never after comes close enough for a chance of entry into earth's atmosphere, there is no *rational* reason to oppose its launch.

Anonymous said...

Tony, we're not talking about recreating GM on the moon...more like a modest complex of interfeeding workshops and small factories; we'd be talking about thousands of people and a small town, not Chicargo and the state of Illinois. Yes it will take decades and a barge-load of money, but if (always the if) we want to do it, it could be done before the end of this century. Most of the things needed could be manufactured locally, and the things that can't could be shipped, just like they are everywhere else (just at much cheaper rates), but shipping a rocket from the fatory in Colorado to the launch site in Florida is difficult but now routine; shipping parts from Earth to the moon is extremely difficult but can be made routine...at a cost. The cost is always the thing; not necessarily just money, but also time, effort, intrest, and dedication. When all of those come together, we'll do it; whether it come about in a few decades or a couple of centuries.

Ferrell

Monte Davis said...

Jim Baerg: Space nuclear reactors would be less radioactive on launch than RTGs.

Less radioactive, but a much greater mass. And while space RTG material these days is typically in tough little pellets (sintered/ceramic?), would the fuel elements for a space-only NTR be as tough in the event of a Rapid Unscheduled Disassembly Event during the ground-to-orbit leg?

..there is no *rational* reason to oppose its launch.

My guess is that it certainly won't happen unless and until chemical boosters attain a considerably lower RUDE rate -- and very likely won't happen unless and until we accumulate several more decades of routine, quiet success from many, many more terrestrial power reactors.

Are there plenty of "irrational" [your word] attitudes about nuclear energy out there? Of course. That doesn't change the fact that most of your fellow citizens do not care nearly as much about rapid progress in space as we do. As a consequence, even those with a realistic view of nuclear risks may well not consider NTRs for space a good trade-off.

FWIW, I've talked about Orion with Freeman Dyson quite a few times over the last 30 years. When he says that what might have been acceptable in a 1946-1963 world of routine atmospheric bomb testing became unacceptable after 1963, there's neither rancor nor wistfulness in it. Seems to work pretty well for him.

Monte Davis said...

SA Phil: One thing that occurs to me. If we were to as you say once and for all Sh!tcan the idea of industrializing space for the next few centuries (at least), why have this blog?

I balk a bit at "centuries" myself, because sometime in there -- given a continued technical civilization -- I'd expect entirely new physics and new technologies therefrom.
That said, your exchange reminds me of one I've repeatedly asked myself:

How many space enthusiasts would remain space enthusiasts if they knew [insert your milestone here: permanent Moon presence, Mars colony, Pallas becomes Pittsburgh, whatever] were 50 years away? 100? 200?

The question interests me because so much of the space blogosphere -- those who lived through Mercury -> Apollo (my teens) and those who are younger -- spends so much time and rhetorical energy gnawing the bone of "Why so slow since then? What went wrong?"

Or alternatively, "What development now [race with China + new JFK, Skylon, Orion redux, planet-killer asteroid, the lean mean free-enterprise mojo of Musk/Rutan/Bezos, whatever] will restore that fine galloping pace?"

I don't think anything will. I don't think anything "went wrong." 1957-1969 was anomalous, and 1969-2011 is a more realistic baseline for pacing ourselves and our expectations. That doesn't make me turn my back on space blogs.

Tony said...

Ferrell:

"Tony, we're not talking about recreating GM on the moon...more like a modest complex of interfeeding workshops and small factories; we'd be talking about thousands of people and a small town, not Chicargo and the state of Illinois. Yes it will take decades and a barge-load of money, but if (always the if) we want to do it, it could be done before the end of this century. Most of the things needed could be manufactured locally, and the things that can't could be shipped, just like they are everywhere else (just at much cheaper rates), but shipping a rocket from the fatory in Colorado to the launch site in Florida is difficult but now routine; shipping parts from Earth to the moon is extremely difficult but can be made routine...at a cost. The cost is always the thing; not necessarily just money, but also time, effort, intrest, and dedication. When all of those come together, we'll do it; whether it come about in a few decades or a couple of centuries."

Thousands of people in a small town, huh? Okay...I live in a samll town in a desert with a few thousand people. It couldn't survive if it wasn't on a major interstate route to bring it everything it needs from all throughout the 21st Century Western industrial base. Please forgive me if I think you're not thinking this through.

Tony said...

Monte Davis:

"I balk a bit at "centuries" myself, because sometime in there -- given a continued technical civilization -- I'd expect entirely new physics and new technologies therefrom."

With all due respect, Monte, I just don't see any justification for believing in new physics. People are going balk at this, but if they know their history of science and technology, they shouldn't -- the Space Age was built on 17th-19th Century science highly refined into 20th Century technology. We forget that much of the original thinking about spaceflight was done by essentially 19th Century men like Goddard, Tsiolkovsky, Hohmann, and Oberth. (Oberth was very much the Young Turk of this bunch, being born in 1894.) Our knowledge of orbital mechanics comes from Isaac Newton. Their work was very highly refined by the time men landed on the Moon, but it was still very much the foundation.

All of which is to say that if we don't see at least inklings of the new physics by now it's entirely possible that it just doesn't exist to be discovered. And I don't think it can be rationally argued that we do see any fundamentally new physics on the horizon. Even string theorists still have to kowtow to classical gravity and relativity where they are relevant.

"That said, your exchange reminds me of one I've repeatedly asked myself:

How many space enthusiasts would remain space enthusiasts if they knew [insert your milestone here: permanent Moon presence, Mars colony, Pallas becomes Pittsburgh, whatever] were 50 years away? 100? 200?

The question interests me because so much of the space blogosphere -- those who lived through Mercury -> Apollo (my teens) and those who are younger -- spends so much time and rhetorical energy gnawing the bone of "Why so slow since then? What went wrong?"

Or alternatively, "What development now [race with China + new JFK, Skylon, Orion redux, planet-killer asteroid, the lean mean free-enterprise mojo of Musk/Rutan/Bezos, whatever] will restore that fine galloping pace?"

I don't think anything will. I don't think anything "went wrong." 1957-1969 was anomalous, and 1969-2011 is a more realistic baseline for pacing ourselves and our expectations. That doesn't make me turn my back on space blogs."


Well, some things did go wrong in US spaceflight after Apollo, like the abandonment of working technologies for the Space Shuttle, but that would only have changed the schedule of what we have done in LEO, not necessarily the volume -- or not much. But sometimes I wonder if we could have kept going with Apollo technology. It wasn't exactly democratic, regardless of the popular (and populist) nature of the US political system. That did lead to negative perceptions among a lot of space enthusiasts, which I'm sure you remember better than I do. Maybe we had to take the Shuttle diversion to prove to ourselves that space couldn't be democratized and free-enterprised. So maybe it wasn't wrong at all, in the overall scheme of things.

But in general, I think you're right -- the average space enthusiast just can't admit to himself or herself that space isn't for him or her, that space is for the whole nation, or the whole of humanity (if you think that expansively) and that our part as laymen is to learn how space technology really works and educate those around us why it's important, even if it doesn't impact the average person in obvious ways.

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