Tuesday, August 3, 2010

Space Warfare XI: La Zona Fronteriza

Terciera landing, 1583

The return of this ongoing series on space warfare is inspired by recent comments in the Running on Rails thread, and also on Part V of this series, regarding laser weapons. Commenters Byron and Turbo10k independently raised the question of the threshold between deep space and local space, in maritime analogy between 'blue water' and 'brown water.'

Thus the image of the Spanish landing on Terciera in the Azores in 1583, showing the advanced state of amphibious doctrine at that time. Though the remainder of this discussion considers mainly 'blue water' action, in deep space at a higher techlevel. And here is an arbitrary but always appropriate link to Atomic Rockets.


Suppose an expeditionary force is approaching from deep space. For our purpose it makes no matter whether the attackers are in transfer orbit from Mars, Europa, the rings of Saturn, or from a wormhole.

The defenders may choose to defend from low orbit, or even from the surface. I argued in the first of this series, Space Warfare I: The Gravity Well, that the disadvantage of 'low ground' may be countered, or more than countered, by the advantage of concealment ranging from submarines to missile-launching trucks. In particular, surface launched kinetics are convenient and deadly against ships in low orbit. For the wider defense of local space, kinetics launched from low orbit can take advantage of an efficient Oberth effect boot to kick them into the teeth of an incoming attacker.

A defense based on the ground, or orbital forces, can also dispense with costly deep space ships with their specialized propulsion and long duration life support. Ground troops need only plain old barracks, while orbital forces can obtain provisions and support from the civil orbital infrastructure.

On the other hand, a close in defense means fighting amid that same orbital infrastructure, implicitly leaving it vulnerable to the attacker. Urban warfare is hard and costly for an attacker, but it is also pretty damn hard and costly for the city. There is good reason to fight the wolf at the threshold and not by the hearth.

Fighting at the threshold instead of the hearth may make the battle less interesting, because if we are fighting away from the clutter we don't need to worry about hitting civilians, can pretty well distinguish good guys from bad guys, and therefore can give free play to automated systems firing at Stupendous Range.

This battle is likely to be boring, but shame on us for complaining. These people aren't fighting for our entertainment - well, on a meta level they are, but to them it is sheer bloody murder. (Even if the battle is robotic, fortunes in hardware are being thrown away.) The battle is also likely to be Lanchesterian, which is of more consequence.

What constitutes the threshold and not the hearth will be determined first and foremost by weapon ranges, as the range of smoothbores set the traditional three-mile limit.


Even under the modest, midfuture assumptions I typically use, these ranges qualify as Stupendous Range. Consider a 1 gigawatt UV laser, zapping at 100 nanometers through a 10 meter main mirror - a main armament worthy of a laser star, but nothing magical. It can concentrate its beam onto a 1 meter spot at 40,000 km range, and burn its way through Super Carbon Nano Stuff armor at about 1 centimeter per second, a meter in less than two minutes of steady zapping.

At 400,000 km - lunar distance - our battle star can burn through a millimeter in less than 15 seconds (spot size 10 meters), scorching surfaces and destroying any sensitive surface equipment, such as sensors.

Kinetics, if launched at more than escape velocity, have nominally unlimited range. Their practical range is determined by flight time and target performance. If the target can veer farther in the time before intercept than the kinetic's deflect motors can reach, then it is home free. Otherwise it is at risk of a hit and must engage the kinetic with point defenses.

Kinetic target seekers, we will assume, have chemfuel deflect motors, with high acceleration but limited delta v, perhaps 3 km/s. (This is distinct from the initial boot that sends the bus toward the target.) If the target is a deep space ship with a high ISP drive, its acceleration is limited to the milligee range. At 3.5 milligees the target can put on 3 km/s in about 87,500 seconds, just over a day.

So if flight time is more than a day the ship can 'outrun' the target seekers. Less than a day, and it will have to engage them. And at a closing rate of 10 km/s the target seekers' intercept envelope extends to 875,000 km - twice lunar distance.

These are nominal figures, and highly sensitive to input assumptions, but they give us a sense of the scale of things. Given no ambiguities about who the players are, a range of 100,000 km is knife fighting distance in space. Relatively unsophisticated kinetics can reach out and touch you at distances approaching a million kilometers, and plausible midfuture lasers can scorch you at a similar distance.

You can defend a zone this large from low orbit, but your orbital infrastructure is vulnerable to an attacker at a similar distance. Thus the frontier zone, on order of a million km, within which your close-in defenses are effective, but beyond which you must mount any forward defense.

For the attacker it is the same picture, viewed from the other side. Within the defender's frontier zone you are exposed to direct attack by home defenses; beyond it you can only be engaged by 'forward' defense forces.

And for some acts of war - notably deep space blockade - you as attacker need never enter the defender's frontier zone. You need only engage departing ships after they leave the defended zone, or arriving ships before they enter it. Which could involve some interesting deep space chases, especially if the requirement is to board targets, not simply blast them.

A deep space blockade is in some ways easier to sustain than a traditional sea blockade. No storms will drive you off station, and while on station you consume only stationkeeping propellant.

The blockade constellation might be headed by a base station, a jumbo tender with most of the support functions, kept well back, and supporting half a dozen 'cruiser' laser stars fitted to carry boarding crews, gunships, etc.

In response to this threat, a defender who does not wish to pay for a full deep space force might build 'monitor' laser stars, not configured for true deep space missions but with sufficient delta v to force a blockader to engage or fall back onto an escape abort orbit that lifts the blockade.


Now for a little opera. The Hegemony need not rule planets, nor even dominate their local space; it is enough to blockade them. You can be independent, but you will be isolated. When people can't get their Rigelian green fuming brandy, governments tend to bend. The Hegemony's loose grip can be broken only by someone willing to build deep space forces and force it to actively defend multiple blockades ....



Related posts: Here's the Space Warfare series, plus some closely related ones. Note that my views are also a moving target - the form of killer bus I proposed in Part VII turned out to be hugely inefficient given even present-day guidance technology.

I: The Gravity Well
II: Stealth Reconsidered
III: 'Warships' in Space
IV: Mobility
V: Laser Weapons
VI: Kinetics, Part 1
VII: Kinetics, Part 2 - The Killer Bus
VIII: Orbital Combat
IX: Could Everything We Know Be Wrong?
X: Moving Targets

Also ...

Battle of the Spherical War Cows: Purple v Green
Further Battles of the Spherical War Cows

And last but not least

Space Fighters, Not
Space Fighters, Reconsidered?

234 comments:

1 – 200 of 234   Newer›   Newest»
Thucydides said...

Throwing out a few assumptions here:

Combat spacecraft will have high thrust, low ISP drives or drive modes to help evade incoming projectiles. A ship with a nuclear reactor has a potential ready made NERVA drive with an ISP of 800+ and the potential for lots of thrust, even if for most of the flight the reactor is at "flight idle" and generating electrical power for the cruise drive and ship systems. Fusion drives have the option of dumping remass into the exhaust beam for the same purpose.

Interceptor weapons can have torch like accelerations right now using ORION drove technology. An asteroid interceptor project had the following characteristics: launch against a 100 meter chondritic asteroid coming at 25 km/sec. 1000 megatons if it hits. Launch when it is 15 million kilometers away and try to cause 10000km deflection.A minimal Orion weighing 3.3 tons with no warhead would do the job. 115 charges with a total of 288 kiloton yield. Launch to intercept in 5 hours. These are the weapons you really have to protect against, gigaton weapons can destroy any ship and colony structures as large as Island 3. Against planetary surfaces, they are totally devastating, and could devastate Earthly continents.

It may be far easier to track and intercept incoming or outgoing trade than carry the fight to the enemy. Most trade will be a series of individual pods coasting on minimum energy orbits (something like individual shipping containers today), so a powerful laserstar capable of burning targets at cis lunar distances will be able to pick off selected pods, disrupting trade and futures markets between the contestants. Armouring pods makes no sense, and the orbital parameters may have been input years or even decades before the start of hostilities, so pods will not have countermeasures or masking technology installed.

As you can see, there are lots of assumptions and options, the only real pressure will to be to take these starting assumptions and knit them into a coherent whole.

nqdp said...

I think that there's another disadvantage of defending from low in the gravity well that wasn't mentioned here: If you're in low orbit (say, 200km), then the horizon is pretty close to you. The planet will be blocking slightly less than half of your vision (this will decrease as your altitude increases). If your fleet is spread evenly across the entire planet, and the attacking fleet is clustered together, then only half of your fleet can aim at the enemy fleet at a time.

Assuming the fleets are more or less equal, the enemy can fire at you twice as fast as you can fire back. He'll get to fight your defenses bit by bit as they pop over the horizon. And that's not a good way for the low-orbit defender to win.

The conclusion of this logic is that if a defender thinks he might be caught unprepared, he should put his ships as far from his planet as possible. That way, the planet blocks less of his vision.

Hopefully, the defender can see the attacker coming from a long ways off, and adjust his ships' orbits accordingly, but the attacker might be able to pose as a civilian fleet or use some sort of FTL.

I guess you could also fire kinetics over the horizon, but only if you had any remaining forces there to direct the fire.

UmbralRaptor said...

It sounds like the ranges are large enough that "frontier" battles may well take place outside of any planet's moon system. OTOH, with assumptions for smaller range, and larger moon systems (say, Jupiter or Saturn), one may well get gaps in the low orbit/ground defenses. Would this define fleet placement?

@Thucydides: as a potentially silly question, how would nuclear saltwater rockets compare in performance and mass? We're also probably assuming that we want to capture planetary populations/infrastructure, semi-intact.

Milo said...

A deep space blockade is highly impractical given the three-dimensionality of space, the dynamic nature of orbits (so you can't stay "stationary" relative to Earth unless you're near the same distance from the sun as Earth), and the limited delta-vees of spaceships (making it hard to chase more than one target before returning to refuel). The only effective way to blockade a planet is to capture part of its orbital space (although a relatively high orbit might be sufficient, but you'd need to at least get into the Hill sphere).

Alternatively, you could keep your ships in parking orbits near home, then launch them on a single-target intercept whenever you detect your enemy launching a merchant ship (remember, no stealth, so you can see this from across the solar system). But that's not really a "blockade", more like privateering. And it would still be difficult - seems to me a privateer would need significantly more delta-vee than a blockade runner to reliably catch it, given that at any given time both enemy and the enemy's trading partner may be on the opposite side of the sun from you. Of course, having nearby allies (stopping Terra from trading with Mimas while you have allies on Tethys, who can simply intercept the ship with low-delta-vee missions as it approaches Saturnian space) helps, but that kind of leads back to the "you must control planetary orbits" thing.

Citizen Joe said...

I think that when you look at the tactics in hard numbers you'll miss out on the more important comparisons between attacker and defender. It really needs to be more of a comparison of forces. The distance to the laserstar is less important than the amount of material it can penetrate before impact. That is part of the defense of low orbit At stupendous range, you're going to have trouble targeting a fast moving object against a planetary background, which means you're going to be wasting your power shooting at it. This is especially true vs. ground based weapons that have an atmosphere to protect them. By the time you get close enough to target those low orbit ships, you may not have the maneuverability to get out of the way of any kinetics.

It seems a bit like trench warfare. If you pop your head out, it will likely get shot off. But you can't make any progress unless you do. That was only broken by the invention of the tank, that could roll right over the trenches and endure the sniper fire.

UmbralRaptor said...

I wonder if a fleet in a planet's L1 or L2 point could relatively cheaply blockade low energy transfer orbits to/from that planet. Staying on station would be cheap, but I'm not sure they would be too close to the planetary defenses, too far from incoming/outgoing ships, or both.

Milo said...

UmbralRaptor: Interplanetary low energy transfers - if by that you mean the Interplanetary Transport Network - take on the order of centuries, which is unreasonable even for unmanned cargo craft. The ITN is only really practical for cheap transport between moons, which is probably not even an issue anymore if rockets have become cheap enough to have interplanetary wars. Unmanned interplanetary cargo craft will more likely be sent along Hohmann transfers (which don't care about Lagrange points) during peacetime, and on somewhat more expensive courses when they're trying to avoid capture (so they're not limited to a signle predictable and easily-interceptable launch window). Chances are they'd still be unmanned, unless they're actually armed.

"Interplanetary superhighway" (as it's sometimes also been called) is really a misnomer. "Interplanetary sidewalk" is more accurate. Even its mechanism has been compared to walking (in that it takes advantage of instability to move around easily, similar to how you walk by shifting a little and then falling on your foot).

Milo said...

Oh, and another thought - if Helium-3 shipments are being sent on multi-year Hohmann orbits from the gas giants (or Rigellian brandy is sent on multi-year Hohmann orbits from a distant wormhole, or whatever), then you may well be able to intercept coasting cargo haulers that were sent on peacetime trajectories before the war broke out. That could disrupt supplies a little, or at least drive prices up, even if faster blockade runners are then sent out to make up for the loss.

Byron said...

The problem with chases is that they really favor the chaser, at least stern chases. This assumes the chasee has to stay ahead the whole time. Also, there will be predictable zones that most ships will go through to launch for certain destinations, which can then be blockaded. It won't be perfect, but most ships won't have the delta-V to get by without going through those zones.

Rick said...

If kinetics are a factor, combatants will have suitable deflect motors. Using a nuclear reactor designed primarily as electric supply to a plasma drive in a NERVA style mode will be a demanding design requirement! But evading kinetics is costly of propellant at ranges below a few hundred thousand km.

Moderate sized Orion interceptors wouldn't pack gigatons of impact energy - I think that figure is for an asteroid that the Orion deflects.

But any warfare at space techlevels faces the problem of annihilation, if only by old fashioned nukes. The bottom line is that blowing stuff up is cheap. So I assume 'limited' warfare as the only sort that can be fought more than once.

I would take 'low energy transfer' orbits to mean Hohmann. Cargo pods on slow orbits will be easy to wax. But disrupting outbound slow cargo will take years to have any direct effect, though the futures markets will go haywire at once.

Intercepting and boarding ships all over a planetary system is pretty much out, unless you have a really high techlevel. I see blockade as interdicting inbound and outbound traffic to a planet, or equivalent region of local space. Still pretty demanding!

Milo said...

Byron: Actually, come to think of it that could work. Although orbits steeper than Hohmann are likely to be practical (no-one is going to have colonized other planets at Hohmann speeds), they're still likely to try to go in a prograde direction, going with the flow of their source and destinations' orbits. So a cruiser in L4 - or, since that's rather far away, on an unstable solar orbit closer than L4 but still outside the Hill sphere - might have a decent shot at catching and outbound cargo, while a cruiser in L5 could do the same for inbound cargo. Will be more effective in the inner solar system - or more accurately, when the planet you're blockading has a smaller orbit than the planet it's trading with - but that's okay since in the outer solar system people would be colonizing moons instead of planets anyway.

Rick: Mutually Assured Destruction does seem like a reasonable projection if current trends persist, but most people want to read about superpowers clashing at full power - or at least about a superpower using its full power to oppress canny rebels - which is incompatible with a MAD scenario. So it's best to decide that somehow MAD remains limited to planetary warfare (encouraging planet-wide alliances, since you can't effectively attack each other but you want to be united when the Martians come knocking!), while interplanetary missiles are not effective despite their high destructive potential because you can see them coming from so far away that you have weeks to intercept them. To avoid this you need an attack fleet sufficiently well-armed to fight the defenders - and sufficiently versatile to react to their movements, so you're not a coasting duck for intercept missions - which needs to at least punch through into orbital bombardment range (which is also inside the range where planetary defenses can shoot back at you). Once you're in orbital bombardment range you can probably wipe out the planet pretty well (although it may still take long enough for the defenses to have a shot at shooting down your fleet), but first you need to get there. And capturing planets intact is usually more lucrative than scorched earth tactics - after all, you're potentially getting the economy of an entire PLANET. Is this a likely result of space war? Maybe, I don't know. But it's more interesting than another Cold War.

Why is "intercepting and boarding ships all over a planetary system" out? If you have a reasonable-sized fleet spread out in high Earth orbit, I would expect you'd be able to stop other ships from passing through high Earth orbit. I haven't done the math on how many you'd need, and it depends on how maneauverable you are (and whether you're willing to send "match our orbit for boarding or we shoot!" messages, making the merchant ship expend most of the delta-vee for maneauvering), but any spacecraft technology capable of interplanetary colonization is probably able to move around planetary orbits semi-comfortably. The lower an orbit you can reach without coming in range of planetary defenses, the more effective you can block traffic.

Anonymous said...

In a blockade, such as you've described, why don't you make use of staitite(sp?) mines...those stationary solar sails? Use them to 'guard the approches' while your manned ships sit at L-whatever and control them; If your laserstars are that effective, then just have them threaten any manned merchant ships into changing their orbit and Delta-V to dock with the approperate ship in the blockade's constallation. As far as unmanned cargo pods go, zap them, hit them with kinetics, or send a 'bus' with a high Delta-V rocket to either deflect them into an orbit useles to the defender (but still retrevable after the war), or turn them into kinetic missiles the defender has to destroy; expending weapons and/or revealing launcher locations.
Of course, this could also be used by the defender; the manned, control spacecraft could look like any OTV going about it business in orbit, the weapons platforms would just look like ordinary satillites; until they shoot at you. Mixed in with the various civilian spacecraft in orbit, you might not be able to determine which ones are military and which ones are civilian until you're within weapons range...
Oh, and even if one in a dozen cargo pods has a failsafe bursting charge that goes off when its being hijacked or docking with a tug, that might put a damper on the whole messing with cargo pods strategy...and one q-ship escorted into your constellation's inner boundry where your main weapons aren't able to swing around and target quickly enough to destroy the enemy before it wreaks havok isn't a very pleasent thought either.

Putting your blockade constellation at a Trojan point with your mines at the 'close approches', might also be a good way to go...until the defender builds a giant-laser-equiped spacestation that can reach out and burnout your sensors at a couple of light-seconds range and melt your communications antenna/optics...

Ferrell

Hugh said...

What would change if the blockader and blockadee share the same planet?

Suppose a near future equivalent to the 1493 Papal Bull gives Mars to China (they got there first), the United States claims the Jovian system, and the European Space Agency Ltd Gmbh gets 120 degrees of the asteroid belt. (The green fuming brandy is made from exotic carbonates mined on Titan.)

Would it be easier or harder for one such party to enforce a blockade on space products reaching earth?

Byron said...

The L4 and L5 are awefully far off to be blockade bases. I'd guess the L2 as the most likely location for headquarters. MAD can work on an orbital scale. In DOTB (I know I keep bringing it up, but I've done most of my thinking there) a war breaks out between India and the US on one side, and China on the other. Neither side uses surface to orbit weapons, as if they do, all the orbital infrastructure goes, which nobody wants.
I do think that warships will likely use NERVA/electric drives, as it gives the optimal balance of thrust and ISP for military missions. It's probably what will separate warships from merchant ships.
When we speak of deep-space blockade, I don't see why we assume outside the hill sphere. Luna is not even a quarter of the way to the edge. Actually, I'd expect that, if possible, an attacker would land on Luna to use as a base. Lunox would be a decent remass, and it would allow some sort of harbor. Even if it's not possible, I'd think that you'd want to station your ships close enough that you can catch merchies before they build up enough delta-V, so you don't have to make them waste all of it. If they spiral out, intercept them right before they reach escape velocity.
Rick, I have an idea for a future blog post: chase scenes in space. I've been working out pursuit logic for a torch universe, and it massively favors the pursuer. If they can burn remass faster in exchange for more thrust, then they can easily run the pursuee into the ground. The only problem is getting home. There are a coupe of other things that could be done though. I can imagine a crew throwing everything they can out the airlock, or a contest to see who can go into a lower orbit.
Of course, after the chase, you get into the problem of stopping...

Geoffrey S H said...

Perhaps kinteics craft would be on the edge of the blockade, to engage any serious craft that get through, with laser stars to "poke" into the habited LEO areas- unless bomb-pumped laser missiles on kinetics craft could do the job better?...

I do think the problem of heat radiators on lasercraft being bigger than those on kinetics craft would also be an issue though.

Winchell said...

Obligatory links about Lanchesterian battles:

Lanchester's Laws and Attrition Modeling, Part I

Lanchester's Laws and Attrition Modeling, Part II

Byron said...

There are really two ways to make a blockade, and several different strengths, depending on intent and forces available. You can either be nice, intercepting and boarding ships, or just kinetic them. The second is much cheaper, but it's probably frowned upon.
The strength of the blockade will depend on the number of vessels present. A punitive blockade would just stop passage through the most common routes, increasing the delta-V required to reach the world. This actually gives people a "soft" option for blockades, allowing a power to send a few ships and cause pain, but not stop it altogether. This isn't really an option with naval blockades.
Stronger blockades will catch more ships on more courses, strangling the world instead of just restricting trade. It's possible to combine boarding and kinetic blockades, boarding ships in the normal zones, and shooting up blockade runners outside them.

Turbo10k said...

W00t new Space Warfare post.
Will give proper reply once I read through.

Milo said...

Hugh: In your scenario, you could simply use ICBMs to nuke all the enemy's spaceports, which should "blockade" them pretty nicely. Of course your own nation would probably not survive the global thermonuclear holocaust that ensued, but you could do it and they'd be helpless to stop you. This is what I mean about superpowers not fighting at full power. (Ballistic missile defense? Not effective enough even under normal conditions, completely hopeless when the enemy is concentrating fire on a small number of targets.)

Other than that you could use surface-to-orbit weapons to zap incoming cargo craft as they approach. If you want to actually capture/dock with the craft then you need warships in orbit, which would be fragile unless your nation has space superiority around Earth's orbit.

Byron/"When we speak of deep-space blockade, I don't see why we assume outside the hill sphere. Luna is not even a quarter of the way to the edge.": That depends on your definition of deep space. I consider it to refer to either interplanetary or interstellar space - orbital space, no matter how high, doesn't count. I think a high orbit blockade is plausible (depending on available technologies, etc.), but a beyond-orbit blockade would be difficult, and you'd need to be at most slightly outside the Hill sphere. You can't just put your blockade halfway between Terra and Uranus, or wherever it is they're trading with.

It could be interesting, though, if Terra and Luna end up at war with each other. If weapon ranges are large enough to directly attack across Terra-Luna distances (and remember, surface-to-orbit weapons are better than stuff you can mount on a ship, and on Luna don't have to worry about shooting through an atmosphere either), then they would they able to intercept a fair number of shipments without even launching a single warship... although you would probably want some warships on the opposite side (L3 for a Lunar blockade of Terra, L2 for a Terran blockade of Luna), to intercept shipments launched in the direction away from your planet/moon.

Milo said...

Byron/"Rick, I have an idea for a future blog post: chase scenes in space.": My thought is that whichever side has more delta-vee wins, unless their delta-vees are fairly close, in which case whichever side has more acceleration wins. If both are fairly close, then the escaper wins as long as it's at all possible to reach a friendly base with the available delta-vee. I think the pursuing craft will often have more delta-vee than the pursued craft, since the pursuer may have launched specifically to catch its quarry, while the pursuee will often have been attempting to perform some other mission before the annoying attacker decided to chase it. Also, remember that "available delta-vee" does not count stuff you have in the tanks but have already budgeted for other purposes, such as returning home. Sometimes you might be able to defeat a ship by chasing it to the point that it "gets away" from you, but doesn't have the delta-vee to return home - call it a "ring-out". Though a ship knowing it's at risk of a ring-out would normally choose to fight or surrender rather than keep running. The ship needn't be permanently lost, though - in due time a rescue mission may be mounted, if it has enough life support to last that long and wasn't going fast enough to reach solar escape velocity.

The one odd case is if your ships have more delta-vee than they know what to do with, which will only happen with very powerful torches. In this case the pursued craft wins except in one special case: namely, when the pursued craft is trying to safely reach a friendly base, while the pursuing craft is willing to shoot past on a drive-by shooting. In this case the pursuer would continue accelerating while the pursuee needs to start decelerating to reach the friendly base, so the pursuer would be near-guaranteed to reach the pursuee in time... but may or may not be able to disable it in the brief amount of time they encounter each other. After that the pursuer will hurtle past the pursuee's "friendly base" (which is not friendly to the pursuer, so you'll be making a minor course adjustment so you don't pass too close), and will have to laboriously have to start reversing its direction and go home, eating huge amounts of delta-vee.

The question, though, is who's chasing who and why. Unless it's a race, two ships are not likely to suddenly start chasing each other starting from parallel trajectories in deep space.

Byron/"There are really two ways to make a blockade, and several different strengths, depending on intent and forces available. You can either be nice, intercepting and boarding ships, or just kinetic them. The second is much cheaper, but it's probably frowned upon.": That depends. If they're unmanned barges, it's probably not too big a deal if you blow them up, as far as war crimes are concerned. (Although it does raise the issue that the barge may belong not to the planet you're blockading but to the planet it's trading with, in which case attacking it may bring more factions into the war. Especially if the trading partner wasn't even actively trying to skirt your blockade, as in the case of intercepting barges launched on a peacetime Hohmann transfer before the war broke out.) However, ships are valuable and their cargo is also valuable (otherwise why are you intercepting them?), so capturing them would be useful if you felt you could afford to do so safely. (You'd need a prize crew to pilot the captured ships to somewhere you can offload their cargo, though. Or at least obtain the control codes that let you access the barge's remote-control...)

Milo said...

Here's a simple example of how to think of chase scenes in space. It is, of course, highly simplified and approximate. Say Mars wishes to invade Terra. The Martian fleet then keys in the following mission plan:

A1. At Mars, burn 25% of their delta-vee to set course for Terra.
A2. At Terra, burn 25% of their delta-vee to stop, while proceeding to shoot/bomb any defenders waiting for them there. Maybe land troops. Whatever.
A3. At Terra, burn 25% of their delta-vee to return home.
A4. At Mars, burn 25% of their delta-vee to stop.

(In fact, they would be saving a few percent for minor course corrections and in-combat maneauvers, but I'm assuming those are small enough that they don't matter much. In any case, Mars and Terra would probably save similar amounts, so it balances out.)

As soon as burn A1 is performed, and long before burn A2, the Terrans know Mars is hostile. They now have the choice of either heading out to meet the Martians in deep space, or waiting to engage the Martians in Terran orbit. I think the latter would usually be better, but for the sake of argument, we'll say they have reason to do the former.

Thus the Terran fleet keys in the following mission plan:

B1. At Terra, burn 25% of their delta-vee to head along the same trajectory the Martians are following, in the opposite direction.
B2. When they meet the Martian fleet about halfway between Terra and Mars, burn 50% of their delta-vee to match speeds with the Martians, which means sending them on a course back home to Terra (which is convenient since that's where they were planning to go after the battle anyway).
B3. Fight the Martians. (This is too complicated to preprogram, but it'll be on the planning table.) Coast back home while you're at it.
B4. At Terra, burn 25% of their delta-vee to stop.

As soon as burn B1 is performed - and the Martians have still only performed burn A1 of their mission plan - the Martians know the Terrans are intercepting them. They now need to choose whether they wish to continue on their original mission plan (requiring them to fight the Terran defense fleet, hopefully winning and allowing them to continue on their course to Terra itself), or to use their 75% remaining delta-vee to abort to Mars as follows:

A1. At Mars, burn 25% of their delta-vee to set course for Terra. (Completed.)
C2. Wherever they are now, near Mars, burn 50% of their delta-vee to fully reverse course and head back home. (Actually, they wouldn't reverse course exactly because Mars has moved in the meantime, but close enough for government work.) Possibly somewhat less if they're slow-thrusting and haven't built up to full speed yet.
C3. At Mars, burn 25% of their delta-vee to stop. Their propellant tanks are now just as empty as in their original mission plan, even though they've covered much less distance, since that's the cost of trying to get your space-train off the space-rails.
C4. Explain to their tyrannical Martian overlord why they returned from their "invasion" empty-handed.

But let's say they don't abort and choose to allow a fight to happen. Note that they have no choices except for fight or abort, since they cannot reach Terra without sticking to their original mission plan, unless they don't mind being unable to return home afterwards.

So the Terran and Martian fleets meet. The Martians still have 75% of their delta-vee, while the Terrans still have 25% of their delta-vee, which means the Terrans actually have a bit better acceleration if that matters (since they have less propellant mass). Both fleets are coasting on a path to Terra, but they are stationary relative to each other, thanks to the Terrans' efforts to match speeds with the Martians.

They now blast each other out, Midway in SPAAAAACE! style, or whatever. Their delta-vee and acceleration are too limited to do much combat maneauvering, so this will be a bunch of "stationary" ships shooting at each other.

[To be continued...]

Milo said...

Now, if the Terrans lose, they cannot retreat. They are already on a course home and will need all their delta-vee just to stop, but the Martians are heading in the same direction and will keep shooting at them until they surrender or are destroyed.

However, if the Martians lose, then they still have the option to change their mission to the above-described abort. The Terrans do not have the delta-vee to attempt to match their thrust, so the surviving Martians would get away (although that would still count as a victory for the Terrans, who succesfully stopped their home from being invaded).

An additional complication is that the Terrans didn't necessatily have to put on enough velocity to meet the Martians halfway. A third of the way or less would be enough to get far enough from Terra to engage the Martians at a safe distance. Even with that it'd be hard to get enough delta-vee to make chasing the Martians practical, but I haven't done the math.

So what happens if the Terrans chose to fight in orbit instead? In this case, the situation is the opposite - the Terrans can retreat if they have an allied planet that's willing to take them in, since they have plenty of uncommitted delta-vee due to having never keyed in mission B, but the Martians cannot guarantee retreat because the Terrans have enough delta-vee to chase them if they want to. (Alternatively the Terrans may use their delta-vee to give them an edge in orbital combat maneauvers, sacrificing some of their retreating/chasing advantage for increased chances of victory.) In addition to the advantage of being in range of their planetary defenses, this shows that fighting in orbit is clearly superior to heading off the enemy in deep space... provided you think you can keep your civillians from being blasted in the crossfire.

[Wow. I'm wordy, eh?]

Anonymous said...

Milo:
The thing about fighting in orbit is that the defenders now need to intercept orbit-to-surface weapons, as well as ship-to-ship weapons; the attackers, on the other hand, now need to contend with both ship-to-ship weapons and surface-to-orbit weapons. hen both groups are in deep space, they only have to worry about ship-to-ship weapons; however, both Mars and Terra can launch refueling missions, if they achieve space superiority.

Something that was said elsewhere in the blog was about nations on different worlds waring against each other, with other nations being neutral or aiding one or another nation covertly. Say France gets tired of the Southern Martian Confederation of City-States (SMCCS) raiding its research outposts and refueling station on Phobos, so it declares war; Italy (who is the major trading partner of the SMCCS on Earth) sells weapons to SMCCS; France is unwilling to board or intercept ships or cargo pods from a fellow EU member so shipments get through, until France pursuades the Grand Lunar Republic to intercept Italian ships and cargo pods for "custom inspections"...Things get interesting after that.

Ferrell

Citizen Joe said...

Interplanetary warfare seems to be a suicide battle.

Option 1: Steep orbit. High burn in. High burn to slow down. Pros: Rapid transit and avoids prolonged exposure to long range weapons (lasers). Cons: Uses up 90% of remass, leaving little for defensive maneuvering. This is the equivalent of a forced march leaving soldiers tired and ill suited for combat.

Option 2: Flyby. High burn in. Strafe. Return home. Pros: remass requirements controllable allowing for return trip on aborts. High flyby speed minimizes time exposed to long range weaponry. Cons: Long way to go for minimal attack window. Minimal opportunity for capturing territory.

Option 3: Shallow orbit. Minimal thrust in. Match orbit. Engage targets. Pros: Significant control over remass. Abort to home more available. Remass available for defensive maneuvering. Cons: Slow approach maximizes exposure to long range weapons.

It seems to me that a capture scenario would involve multiple layers of tactics. First send your invasion fleet. As they are taking up siege positions, send your orbital destroyers. About the time that the destroyers flip, you send your flyby's to target long range weapon platforms. Ideally, the flybys take out the main guns allowing the destroyers to cross the no-man's land and engage orbital vessels. Failure then allows abort to the siege armada and return home (abandoning the destroyer vessels). Assuming orbital superiority is achieved with the destroyers, the siege group comes in for the planetary invasion, or provides support for the destroyers. It is very much a time on target scenario but the defender will see it coming months (or years) ahead of time.

Byron said...

I was referring more towards classical chases, such as the one at the end of "On Basilisk Station" I know that the one with higher delta-V or acceleration will win, but the problem is, from a story point of view, making it suspenseful. If we assume that the pursuer catching up ends the chase, then either superior delta-V or superior acceleration will end it. The chances of having ships that are closely enough balanced in performance to make a suspenseful chase are nonexistent. The stuff about Mars fleets is not quite what I meant.
The whole topic came to mind as part of an RPG adventure I'm writing. BTW, thanks to whoever suggested GURPS. I'm hooked now.
Personally, I don't really see anyone in the plausible midfuture actually invading a planet. Destroying the defenses is enough to make it impossible to resist. I'll try to be more specific in the morning.

Citizen Joe said...

I think that intercepting and boarding anything but a non-maneuverable or willing vessel would be next to impossible. There is a point of no return on all ships at which point you are committed to your destination (or years in orbit before the next re-entry window opens). That point is likely very close to either the source or destination. In order to capture another ship, you have to not only intercept it (which is very heavy in remass usage) but you have to match the velocity (which is even more costly). An intercept would therefore need to start fairly close to the original launch. That would be pretty obvious that you're trying to intercept and thus you'd be interdicted by defense boats. Outside of the defensible sphere it would simply be too costly in terms of delta-V's to pull off.

Milo said...

Citizen Joe: The main advatnage of arriving quickly is that it gives the enemy less time to prepare. If Terra has allies on Mercury, and Mars wants to launch a surprise attack on Terra, then they'll want their fleet to arrive at Terra faster than Mercury is able to send reinforcements. (Possibly this will involve waiting until a time when Mercury has a poor launch window.) Even if reinforcements arrive later, you'll get the benefit of fighting them seperately, which is a big deal in Lanchesterian combat.

If you take a really long trip, then the defender's fleet can zip over, bomb your home planet while most of your fleet is away, and zip back in time to defend against your attack. So "slow" attacks should take no longer than twice the duration of "fast" attacks, to prevent that.

Also, it's kinda hard to get your soldiers to put up with a war where a single mission takes longer than all of World War II.


Byron/"I know that the one with higher delta-V or acceleration will win, but the problem is, from a story point of view, making it suspenseful. If we assume that the pursuer catching up ends the chase, then either superior delta-V or superior acceleration will end it.": The most interesting chases happen in orbital space. First, the increased clutter in the environment plus the complex orbital mechanics add more complications compared to the relatively straightforward physics in deep space. Second, the shorter scales and time ranges involved gives you less time to figure out an optimal course, leading to the possibility of someone making a mistake. There is also the possibility that you might not know the exact specifications of the enemy ship. If the pursuee is equipped for atmospheric operations while the pursuer is not, then that gives you an option to get away by making an emergency landing on the planet.

Another kind of plot point you could use is if the pursuee has good delta-vee but poor acceleration, so you need to gruadually draw away. The challenge is then not in the chase itself, but rather in surviving the pursuer's fire long enough to build up to escape speed. This might encourage the pursuer to find ways to get their weapons to fire faster, possibly risking overheating...

But barring those things, in most situations, the pattern of my Terra-Mars example holds: both sides will know whether or not any given side can effectively run away, and they might know it days before the encounter even happens. The challenge is finding maneuvers that edge you into an advantageous trajectory at affordable cost - by the time the sides meet, most of the interesting piloting choices will already have been made. That's when the gunners take over.


Byron/"Personally, I don't really see anyone in the plausible midfuture actually invading a planet. Destroying the defenses is enough to make it impossible to resist. I'll try to be more specific in the morning.": If you're willing to go scorched earth on the planet, then yes, destroying the defenses all you need to accomplish. If however you want to conquer it mostly intact, then you need to be able to send someone in to surpress guerilla resistances. See also Iraq, where the US still has trouble despite having massive military superiority including bomber aircraft against an enemy with poor anti-air capability.

I do agree that conventional surface-to-surface warfare with field battles between armies is probably not going to get done much. Massed armies and fortifications are too vulnerable to orbital bombardment.

In gaming terms, guerilla warfare is probably better suited for RPGs, while wargames will be set in space.

Milo said...

Citizen Joe/"I think that intercepting and boarding anything but a non-maneuverable or willing vessel would be next to impossible.": Mind you, you can make a vessel non-maneuverable by shooting out its engines, if you can get close enough for a sniper shot.

And you can make any vessel willing by threatening to blow it up if it doesn't comply.


Citizen Joe/"An intercept would therefore need to start fairly close to the original launch.": Rather, close to either the original launch, or its destination, or some point along its route (this last one being unlikely). Do note that since interception missions are so propellant-intensive, the interceptor will typically start fresh, and return home to refuel after each intercept. Which means that if your blockade is in high orbit around an enemy planet (which is the best place to put them), then you need good logistics to keep them supplied...

Also, if you're intercepting unarmed merchant craft, then you can afford to strip down most of your weapons and armor, and chase it down with a ship that's mostly engine and propellant. (Basically a militarized tugboat.) While the quarry is still loaded down with cargo. Ideally the tugboat then gets close, uses its single gun to shoot out your engine, drains your propellant tank into its own, and then pushes you where it wants you to go. Of course, this might backfire on you if it turns out to not be as unarmed as you thought...


Citizen Joe/"That would be pretty obvious that you're trying to intercept and thus you'd be interdicted by defense boats.": Assuming that the defense boats can intercept you. Or that the defenders have armed escorts for all their cargo barges, which is expensive.

I agree with Byron's "soft blockade" concept. It does seem easier to simply limit trade and drive up prices - blocking the cheap and slow Hohmann barges, forcing armed escorts, etc. - than to fully block all traffic. Bonus: this allows stories about daring blockade runners.

Citizen Joe said...

RE: Threatening a ship to make it compliant. Much of the time, the primary thrust characteristics are limited by orbital mechanics. The course, setting, burns, etc. have already been set. Threatening to blow someone up in that case just leaves them with the option of a long lingering death when they miss their destination and fly off into the void.

Actually shooting a target in the engines usually means shooting them in the most protected area since the thruster is probably doing more damage than your puny lasers. It also means potentially destroying your target and creating a lot of debris that you may end up flying through. Opening fire on another ship is also going to tag you as a hostile for the whole system, which means you'll like be fired upon by any other ships. Even if you do survive the encounter and recover something, then what? You'll be declared a pirate and tracked throughout the system and then destroyed/seized by customs as you approach a planet. If you're state sponsored then that state will accrue sanctions. Space is a hard mistress and everything needs to line up just right for a rendezvous.

I suspect a more likely scenario involves some accident on board which some how interferes with a vessel's mission. The salvagers then race to file their flight plans and intercepts. Or, orbital defense disables a vessel and salvagers go in to clean up the mess.

Thucydides said...

Orion asteroid interceptors can have arbitrarily high acceleration (the one cited accelerates at 100 G), which makes evasion difficult and generates an incredible amount of kinetic energy on impact.

NextBigFuture ran a series of calculations which included sending a missile from Earth to Mars in 24hr or less:

Another aspect of the fast acceleration that is possible is that an unmanned Orion go from Earth or Earth orbit to Mars (decelerate at halfway) and get to Mars in under one day going at 100Gs if Mars and Earth are in the close approach. If the unmanned version was going at 1000Gs (which was a design that is possible), then Earth to Mars could be done in a few hours. At about 300Gs and you would be looking at a Mars Overnight package delivery.

Mars comes to about 50 million kilometers (36 million miles) of Earth on close orbital approach. This is just over three times the asteroid intercept scenario.


Given the various factors being discussed here, I would think Laserstars would be posted as far forward as practical in order to provide maximum coverage. In the sort of midfuture we are talking about, a station might be tethered to the Moon using a Pearson elevator to L2 in order to ensure the station (or at least the mirror) can provide coverage of cic-lunar space. A huge SPS at the Earth-Sun L1 point could power a massive series of laserstars and provide coverage over the in er solar system. Mercury could launch platoons of mirrors into the solar photosphere and tap the power of the sun to drive a laser capable of shooting across the Solar System...

Byron said...

I'm not so sure that interception is this impossible. It should be possible to divert from LEO to higher orbit if you're far enough out. Possibly interceptors would be prepositioned out to board, then the enforcer ships would be closer in. Superhigh velocity kinetic missiles would seem easy to block. All you need is a bag of sand to throw in the way, destroying the guidance system. It then misses, and heads out of the solar system.

Citizen Joe said...

Orbital intercepts and seizures are possible and even likely. In order to stay in orbit at a certain altitude, you have to be at a certain velocity. Change that velocity and your orbit changes. Additionally, when you run out of propellant, you remain in orbit rather than floating off into the void. Aborts simply result in re-entry to the planet.

It is the interplanetary intercepts and seizures that I don't believe to be feasible.

Thucydides said...

High energy KE Torches would have a series of Penetration aids, including a bag of sand cast forward once the acceleration phase ends. Even a cloud of debris impacting at these sorts of velocities would cause incredible damage to any space structure, and you can imagine the "shotgun" effect on the surface of a moon or asteroid when the debris cloud hits.

Even the Earth would not be safe. If we grant the Torch missile was reduced to a fine powder by the interceptor, this powder is still moving at the same velocity as the Torch was and would scrub through any and all orbital structures, satellites and debris before dumping the considerable kinetic energy in heating the upper atmosphere (as all the particles burn up).

Milo said...

Citizen Joe/"Threatening to blow someone up in that case just leaves them with the option of a long lingering death when they miss their destination and fly off into the void.": Even if they didn't save delta-vee for some sort of emergency abort... that's why you take them into the brig. You can then blow up what's left of their ship, or nudge it into a relatively safe solar orbit for later retrieval.

If you're performing a blockade in orbit, you'll be able to get access to a lot of outgoing ships while they haven't yet built up to full speed (assuming electric engines with high delta-vee and low acceleration, which is likely for anyone and doubly so for civillian ships). Although this agrees with your "you need to be near the launch point" assessment.


Citizen Joe/"Opening fire on another ship is also going to tag you as a hostile for the whole system, which means you'll like be fired upon by any other ships.": Performing a blockade and forcibly boarding other people's ships is a hostile act in general. Even if you do it quietly, all the victim needs to do is send a single message home. You're not going to be doing this if the enemy has enough ships within firing range to vaporize you. A blockade is something you do once you have space superiority over high orbit.

Piracy doesn't pay in space, not unless you at least have some sort of home port that's willing and able to protect you from retaliation. As long as you board ships in accordance with the lawful customs of war (whatever those are in the future), though, no-one will care except the nation you're already at war with.


Citizen Joe/"I suspect a more likely scenario involves some accident on board which some how interferes with a vessel's mission. The salvagers then race to file their flight plans and intercepts.": This is definitely a good plot hook for some stories. It doesn't have much to do with war tactics though, at least at first glance.

Milo said...

Thucydides/"Orion asteroid interceptors can have arbitrarily high acceleration (the one cited accelerates at 100 G), which makes evasion difficult and generates an incredible amount of kinetic energy on impact.": Orion engines are also ridiculously expensive for a one-use missile. Are they useful for deflecting anything smaller than an asteroid?

As for anti-planet use, that sounds frustratingly reasonable...


Byron/"Superhigh velocity kinetic missiles would seem easy to block. All you need is a bag of sand to throw in the way, destroying the guidance system. It then misses, and heads out of the solar system.": That only works if you can then thrust even a little to dodge the now-unguided projectile (assuming it was guided properly to begin with). A ship can. A planet can't.


Citizen Joe/"Additionally, when you run out of propellant, you remain in orbit rather than floating off into the void. Aborts simply result in re-entry to the planet.": Only if the planet is friendly. Which it won't be if you're blockading it.

Fortunately, losing your propellant doesn't automatically make you crash. You simply stay in orbit and can even keep shooting at stuff that comes close, until you find some source of propellant (like when your fleet finally forces the enemy's surrender, or when supply ships arrive... although propellant is pretty hard to supply across planets due to mass ratio problems).


Citizen Joe/"It is the interplanetary intercepts and seizures that I don't believe to be feasible.": Hmm, so we're actually in agreement?

I posted an example of a scenario where a Mars fleet can be succesfully intercepted in deep space, and discussed who would and wouldn't then be able to flee if necessary, although that was a special case since the interceptors were starting from (and ending at) a convenient position. Working out a three-planet situation could get pretty complicated depending on the orbital mechanics. Of course, actual warships would have navigation computers that can easily tell them whether any given intercept is possible...

But yeah, in the general case, interplanetary intercepts are something you try to avoid unless it's over something really valuable, or a slow (and unmanned so it's not such a big deal if you blow it up) Hohmann barge.

Citizen Joe said...

A classic example of the deep space intercept would be hitching a ride on one of those massive cyclers we discussed a while back. That works because a) the cycler is a willing dock and b) the cycler is, by and large, not maneuvering. However, in my interpretation, one doesn't intercept and return home, instead one intercepts and rides to the next destination.

While someone could theoretically hijack a cycler, it would be akin to a pirate seizing an entire town. Likewise, ordering a cycler to divert is much like the tale of the aircraft carrier ordering a light house to divert course.
http://www.snopes.com/military/lighthouse.asp
Cyclers would also be too valuable to simply destroy.

Milo said...

Actually, Thucydides, what kind of delta-vee is your Orion missile putting out? The closest approach of Mars to Earth is 78.33875 Gm. To get there in, say, 12 hours, you would need to go at 1813.4 km/s (assuming instananeous acceleration, and no deceleration since you're a missile). That's 0.6% c, or 393 kiloRicks. I recall that typical nukes were described as carrying 4 kiloRicks, and an Orion "engine" is made of nukes, so how exactly is it carrying that much energy? And 12 hours is still a pretty long time. (For every halving of the desired strike time, double the speed and quadruple the Rickage.)


Regarding space piracy, the most effective way to steal an express spaceship's cargo (as opposed to a Hohmann barge) is to sneak onboard when it's launched (probably disguised as a legitimate passenger), then hijack it in transit from onboard the same ship. Which is fitting, since that's how most train robberies were done. But you still need some method to ensure your safety once the hijacked ship arrives at its destination (either its intended destination, or some other port if it somehow still has enough delta-vee to divert). If the port allows you to safely disembark, you can then lay low planetside with your ill-gotten riches. Also note that even if you can't divert a spaceship to a different planet, it shouldn't be too much trouble to force it to land on the same planet but a different port than it had originally planned, which is useful if the planet is Balkanized (at least sufficiently so to have at least one pirate-friendly spaceport).

Hohmann barges cannot be hijacked in this manner, on account of taking years to reach their destination and not having any food or air on board. But they are slow enough to chase down.

All of this discussion has, of course, been assuming that delta-vee is seriously limited. If you have torchships with so much delta-vee that the most important limitation on their mobility is the amount of acceleration the human crew is able to endure, things work very differently. However since such ships can continuously accelerate, they're still nigh-impossible to chase down, for entirely different reasons.

Byron said...

I'm assuming the orion missile is sent against a ship. Nobody rational is going to shoot them at planets during the plausable midfuture (we're still in the solar system) for two reasons:
1. It's a bad idea for both MAD and ally reasons. Unless we assume that the planets are squaring off, then both sides will be on both planets. That makes doing damage to your ally's world stupid. Plus, if the enemy has these missiles, they might do the same to you.
2. It's a very inefficient way to deliver energy. You could get a lot more bang by launching nukes, along with the fact that you can actually directly affect surface targets.
I can see them being used against spacecraft, at least small versions. However, they likely won't be big enough to really damage a planet.
Ordering a ship coming from deep space to "heave to" shouldn't be that difficult. They can pretty easily burn to alter their final orbit, and you can shoot them if they don't.

Milo said...

...An Orion missile against a ship? Isn't that kind of like using a stealth bomber loaded with napalm to root out a rodent infestation? Okay, that's not quite fair. Ships are expensive too. Still, that's a lot of money you're throwing on a one-shot missile that can only kill one ship at best.

...Actually, I was about to start analyzing the effectiveness of point defenses against a target you see coming hours or days in advance, when I realized that at those distances, the ship you're shooting at has the time to simply change orbit to hide on the far side of the planet. No, interplanetary anti-shipping missiles do not work.

Rick said...

Let me think a bit about blockade runners and interceptors.

One thing to note - if the frontier zone is about 1 million km, that is less than 0.01 AU, so the distance scale of blockade is much smaller than the interplanetary distance scale.

The burn duration in tactical mode will be limited (given my framework assumptions) - a day or two max, if tactical acceleration is on order of 10 milligees. A ship will put on about 10 km/s, and flat space travel distance is, by convenient coincidence, about 1 million km.

The blockade runner does not need to take a fast trip, just make a fast getaway, so a substantial fraction of their propellant allowance can be given over to this (relatively) high thrust departure burn.

Likewise a blockading interceptor needs to hustle out after a blockade runner, but once it has made the intercept it can shift to cruise mode and make a more gradual deceleration and return, at higher Isp for reduced propellant consumption.

Other things equal the interceptor has the advantage. The blockade runner presumably has to carry a substantial payload; the interceptor only needs moderate armament, plus a couple of gunships and a boarding crew. And it's after-mission, getting back, probably requires less delta v than even a 'slow' orbit to another planetary zone.

But there are complications. The blockade runner's payload may be very light - like Lenin in a sealed railroad car. And an interceptor that leaves only fuel margin for a slow return risks getting drawn off station for a prolonged time.

So blockade intercepts involve strategic as well as tactical judgments, and the outcome may not be known in advance. Though it will become pretty clear hours or even days before the actual intercept, or failure to intercept.

Byron said...

I have several things. First, I would imagine that shooting an Orion missile at a planet is going to make everyone on that planet irritable. Particularly if that planet is Earth. In any plausible scenario, this is to be avoided at all costs. Second, the missile could be made a bus, or use small nukes. It would likely be a planetary-defense weapon, as firing through orbital space would be nasty for the attacker when he got there.
Lastly, manned intercepts of blockade runners aren't necessary. To illustrate:
During my blockade of Mars, my laserstar is sitting in the approach path for shipments from Earth. When a ship comes, it order it to change course, and dock with the boarding ship in high orbit. If it refuses, I blast it. If it agrees, I stay where I am, and launch a special missile. The missile matches velocities, and latches on to the side of the ship, carrying a nuclear warhead. If the crew behave themselves, they arrive in good shape, and the boarding party has the codes to remove the missile. If not, then they die. It's economical, easy to do, and safe. The missile would have to be carefully designed, but that's just engineering.

Milo said...

Although sacrificing delta-vee for thrust can be useful for combat maneuvers, it isn't very useful for interplanetary chases. The blockade runner will pull ahead in the beginning, but the interceptor will be able to gradually put on more speed and eventually catch up while the blockade runner is coasting.

It depends on how far from the blockade zone (and more importantly, for how long) the interceptor is willing to chase. Also, the interceptor will presumably want to save delta-vee for returning to the blockade zone or another friendly base after the chase, and possibly further maneuvers, while the blockade runner can devote its entire propellant allowance to reaching the trading partner.


Byron: I was replying to Thucydides, who was suggesting the Orion bus as an interplanetary missile (explicitly talking about how it could travel from Earth to Mars quickly). I do think kinetic missiles of various sizes are effective for defending your own orbital space, shooting at incoming enemy ships when they're reasonably close. This is one of the ways in which planets have a "coastal battery" advantage. Though I would rather not use nuclear propulsion to launch missiles from my own planet, if it can be helped...

Albert said...

All this talk about blockading, intercepting shipments, orbital maneuvers...

But why exactly shipments are a threat for your forces?

To bring useful help (i.e. weapons from allies) the cargo pods must be launched well in advance of any hostility.
Years. And being pods on an obvious route, they can be killed by simple kinetics.

Also, the quantity of material an actual cargo ship (hybrid liner-cargo) can deliver is not exactly game-changing in most situations.
Unless it is Unobtanium needed for some gimmick.

Imho the only scenario where a blockade may be useful is when the enemy is a young colony, or a relatively small space station. In that case their life-support will hopefully be self-sufficient enough that the only shipments are "interesting stuff", luxury, news, high tech, quality products, and also Sex, Drugs, Rock'n Roll as usual.

That way a blockade will make them live worse. While I have doubts a planetary population will actually notice it.

But if the colony is big enough, it will be more or less self-sufficient on these matters too, just like a (much bigger) planet.

So either you blockade a planet or a mature colony that doesn't really care or you blockade a small colony/station that probably you could conquer right away.

I'm exaggerating it a little, but I hope you get my point. :)

-Albert

Milo said...

The usual point of blockades, sieges, etc. is to strangle your enemy's economy, making them unable to afford continued warfare - or possibly inducing their citizens to rise up out of dissatisfaction with their condition. ("Because of your stupid war, I haven't been able to get any green-fuming Rigellian brandy in months! I've had enough!") Even merely wrecking the futures market can be useful in this regard.

The problem with this is that planets are generally large enough, with sufficiently well-developed economies, that they tend to not be very reliant on outside trade. (Earth currently does just fine without.) You can't just starve an entire planet to death the way you can do to a walled city, unless it's a very recent colony (but those aren't going to have much weapons). Of course, if the economy of The Future(TM) is entirely dependent on Helium-3 which gives vastly more energy than any other available/feasible technology, then stopping supplies may seriously hamper the enemy's ability to keep all those big, powerful warships running. Not to mention all those energy-intensive irrigation systems in Future Africa, etc. Once you've gotten used to having lots of energy, it's hard to go back. As for the gas giant moons (where the Helium-3 comes from), if multiple moons around the same planet have been settled, the close proximity of multiple worlds encourages trade, giving you more stuff to stop (although the tactics may be very different). And maybe they are still dependent on terraforming supplies from Terra... without them, they can keep their hydroponics running for a while, but they'll have trouble with long-term maintainance or colony expansion.

Really the question is why are you having interplanetary trade in the first place, given the vast cost of such shipments and that our one current case study of a planet is doing just fine on its own. If you can justify why trade is worth doing, you can probably also justify why it's sometimes worth intercepting or fighting wars over.

Blockades are also useful for keeping the enemy's warships pinned down at a convenient chokepoint, keeping them from interfering with whatever else you're up to. Though that wouldn't lead to blockade runners of the sort we're now discussing.

Rick said...

What Milo said - blockade doesn't need to starve a population out, or even totally disrupt its economy - merely cut off foreign trade that has become important enough that its loss is painful.

While it is a very good question whether a whole planet would be very dependent on external trade, any scenario of extensive interplanetary (or interstellar) trade pretty much implies that this trade is important. Certainly it is important to 'trade interests.'

Thucydides said...

"The primary mission of EarthForce is to protect the planet from impacts by natural or artificial bodies."

You can build lots of different space navies from that one starting point, simply by varying your assumptions. If the political and economic climate does not support long term space missions, EarthForce might consist of interceptor squadrons of a few ORION pulse drive missiles bunkered in distant deserts backed by powerful radar and optical tracking systems. A fully realized space civilization will have massive solar power stations and lasers of stupendous power at the Earth Sun L1 point to cover a large portion of the inner solar system.

Since artillery battles aren't that much fun, perhaps EarthForce uses a fleet of gravity tractors to deal with rogue NEO's, trusting that most of the new deep space colonies growing in the Asteroid belt and the moons of the Gas Giants are not going to declare hostilities and fire chunks of rock from their mass drivers at the home planet.

Each of these assumptions derives a different force structure, and each in turn generates a different outer perimeter that can be monitored and defended. Lots of variations are possible.

Even more fun is to see what happens when the initial assumptions become obsolete. How well is a 3 mile exclusion zone (defined or backed by heavy smooth bore cannons) really going to work in the air age? (One answer was the Boeing "Flying Fortress", named not for the heavy gun armament carried, but because it was initially designed to act as a platform to destroy enemy battleships far out at sea).

Milo said...

I'm rather dubious about solar-power, even on Mercury or in a permanently-lit Lagrange point. The advantage of solar power is in keeping you supplied for free for long periods. When you really need big amounts of energy, though, like for a zappy death ray, nuclear probably still works better. If your world has working fusion energy, then that totally seals the deal. (Of course, the sun technically is fusion energy, but it's a horribly inefficient way to tap the process unless you're a Type II civilization.)

As for exclusion zones... well, somewhere between 100 km and 1500000 km would be a good guess. The latter is Earth's Hill sphere.

Although space law would probably acknowledge that planets can have a legitimate concern about any object that's heading on a potential collision course with them, regardless of how distant it currently is. (This isn't a concern at sea due to friction, so stuff won't get any closer to you unless it makes an active effort. In space, the moment something burns in your direction, it has in a sense already entered your exclusion zone.)

Citizen Joe said...

I think that when it comes to distances and speeds involved in space, the demarcation point may instead involve time. But that zone must also be enforceable. We could claim authority over the entire solar system, but unless we an actually get 'police' out there then there are no teeth in that authority.

Anonymous said...

Space forces might be varied due to different requirements of different nations/colonies. Most Earth nations might simply want an Orbital Guard to protect against impacts; others may want/need to escort convoys or guard/intemidate colonies with deep-space light warships; others may need armed merchantmen to deal with pirates interfearing with their intermoon trade; still others may have dreams of empire and build a warfleet more typical of a bad sci fi movie than any realistic design; others might feel the need to act as an interplanetary cop and have examples of various types of spacewarcraft in its inventory. While invading a world might be impractical, invading a colony/nation (on another world) by a nation, or another colony, might be fesible in extreme situations, but probably rare. Also, blockading the off-world trade of a single nation might be do-able, where blockading an entire world probably isn't.
Just some things to think about.

Ferrell

Milo said...

Yes, space forces will be varied. In fact, this is something worth considering - the Solar System is a diverse place. For example, we only have 4 "Earth-like" rocky planets, and I doubt we're going to colonize Venus anytime soon. It's a little misleading to discuss (in the general sense) what kind of tactics you should use to attack "a planet", when there are only so many planets you might be interested in attacking - and each of those has its own quirks (Earth has a higher gravity and an atmosphere, as well as oceans for submarines to hide in, and a moon that fortifications can be installed on, which totally changes the character of surface-to-orbit and orbit-to-surface warfare). It's not like besieging a medieval castle in that you can always find on more castle to fight over (unless you have FTL, which is really beyond the plausible midfuture). There's more space around the gas giants, of course, but war there will look very different from a Terra-Mars war due to closer ranges and shorter times, more immediate relevance of orbital mechanics, smaller individual worlds, etc. Even then, Saturn has its dense ring system complicating things, and Neptune has only one hydrostatically-rounded moon. The powerful radiation and magnetic field of Jupiter may be tapped by spacecraft with magsail-type propulsion to allow continued maneuvering without propellant (I'm curious how plausible this is, I haven't done the math...).

And the idea of a "cruiser" spaceship is dubious, not only because of the train-tracks effect with rockets constantly having to land at a friendly base to refuel, but because a ship that can go lots of places has little point when there are only so many places you may be interested in going to. In sea warfare, there are numerous nations with coastlines, and each of those coastlines is itself long, and there is useful stuff on small islands and even swimming in the sea itself. In space, you don't have "castles" or "coastlines" or "planets" - you have Mercury, Venus, Terra, and Mars.


On an unrelated note, it occurred to me that in my Terra/Mars invasion example, I overlooked another important advantage the Terrans have that justify heading out to meet the Martians in deep space rather than in orbit - kinetics. The Terrans can release a salvo of kinetic weapons immediately before they start their deceleration burn (either as guided missiles or a shrapnel cloud, since a single slug is too easy to dodge at this range), which would head toward the Martians with the full combined speeds of both fleets, while the coasting Martians cannot launch kinetics at the Terrans (who will be near-stationary by the time they meet) with nearly the same effectiveness. The Terrans would then match speeds with the Martians to finish off the survivors, Midway in SPAAAACE! style, with lasers or whatever. (Drama dictates that armor and/or point defenses should be good enough against this kinetic salvo that the entire Martian fleet isn't wiped out before they even meet each other.)

Geoffrey S H said...

Empty space= less to worry about kinetics-wise. Far less civvie stuff to accidently hit and plenty tof time to laser it up/chart it, after a battle.
One thought I had inviolved constellations keeping just out of each others' laser-ranges through good manourves (while still of course gliding on their previous orbits and vectors). Empty soace means more room to do this without hitting orbiting habs and the like- orbital space is where you try and avoid lasers by zooming around (at slower speeds and closer ranges of course) faster than a laser turret/spinal mount can track you.

Milo said...

Note, though, that kinetics, at least unguided kinetics, are usually shorter-range weapons than lasers, due to their easy dodgeability (they take longer to reach you, and you see them coming). Thus the shorter ranges of orbital combat actually encourage kinetics, at least beyond the opening salvo.

Byron said...

Why would you bother with unguided kenetics, though? Guidance should be pretty cheap, and it vastly increases the hit probability.
If I was basing Orion missiles, they wouldn't be in a desert, they'd be in orbit.
The lack of locations is something I've run into in mental simulations as well. Orbital warfare is much more interesting among, say, Jupiter's moons. You can actually have enough players to be interesting. Also, the low delta-V requirements and transit times make a more appealing scenario for "warships". The kinetic intercept idea is interesting, but why send laser-armed ships out? Just launch kinetic busses repeatedly, bleeding the fleet until it gets in range. When that's done, send in your fleet. The big problem of attacking a planet is that weapons can be launched by the attackers without real reply. (I'm assuming you don't wish to launch kinetics into the planet's orbital space from far away, as it might be hazardous to your relationship with anyone on that planet.)

Geoffrey S H said...

Noted-Unless one finds a way to massively reduce the mass of the kenetics- at least the smaller fragments anyway...

Large coverage- paint(?), combined with harder metal shards (the latter with less area covered but harder to zap), with larger armoured shells among all this. Torch missiles (with lighter payloads of shards than the massive cloud but an almost 99% chance of a hit) on the flanks of the cloud to force the enemy constellation to choose between squeezing past the cloud, and breaking off and no doubt exposing aft drives while burning, no too mention running into the m,issiles which, if they prove unable to destroy the enmy craft, will at least slow them down (acceleration-wise of course) or damage them in some way for the next cloud of shrapnel and shells to finish them off. Essentially corridors of fire are laid down (with some laser bomb-pumped shells- laser-shells- and missiles providing laser support without the need for massive radiators) with manourves made based on how to best avoid the fire without exposing oneself to the next volley.

The cloud would be dense enough to prevent laser easily blasting through (though small holes woulded easily present the constellation coming through the cloud as a bottle-necked target. If there is enough laser craftto eliminate the cloud, theirt large heat radiators would be used against them by blasting them off with the use oflaser missiles (and shells) from the somewhat less vulnerable (in this respect) kinetics craft.



Dumb idea or no? Mass is a key factor obviosuly, if the cost came down enough, even if it was massively more expensive, would it be better to use expensive kinetics in the open to out-"range" lasers?

Please note, that the kinetics craft would have turrets for aall-firing arc coverage and magazines filled with paint, shards, various loadouts of shells and chem/torch missiles- commanders can select the loadout for a shell-heavy cloud or shards, though a mix would be the best IMO.

Sorry if that's convaluted, but it is getting rather late :(

Thucydides said...

The use of solar energy for large military installations in free space should not be discounted. First off, Fort Apache will not have the logistical issues of maintaining a constant supply of 3He or Boron for the fusion reactors (and the associated risks of anything from explosives to commandos to malware being carried into the complex.

The second consideration is the SPS can be used to supply baseline power to paying customers, which makes this one of the few paying propositions for military infrastructure. Lee Corey had the most interesting suggestion of separating the weapon from the power supply in the novel "Manna".

The people on Earth had the benefit of cheap electricity, blissfully unaware that multi gigawatt laser weapons were also orbiting overhead (carefully collapsed in hard stealth containers until needed).

Thinking more about energy, I think the future solar system may be demarcated into three major zones:

The Solar Economy, roughly reaching out to Mars. The abundant cheap solar energy provides the base power and laser and microwave beams send power to cooperative targets. by the 23rd century, Mercury may well be the "capital" due to the ability to tap massive amounts of energy.

Jupiter, which has a powerful magnetosphere, is self contained. Energy can be tapped using electrodynamic tethers, and ships and industry can be quickly and cheaply powered throughout the Jovian system.

In deep space, 3He will be needed for the reasons given earlier (high energy density) and the lack of alternatives; Uranus will probably be the "capital" of deep space due to the abundant supplies of 3He.

The demarcation lines of the Solar, Magnetosphere and 3He economies will probably be the conflict zones are located.

Milo said...

Byron/"Guidance should be pretty cheap": Yes, but inert slugs are very very cheap. So you can launch more of them. Also individual slugs can be smaller than you can fit an effective guidance system on (while still packing a nice punch due to using futuristic mass driver technology to go really fast). And long-distance guided missiles are more vulnerable to point defense, since you just need to disable the sensors or engine while it's still outside of slug-range, not vaporize the projectile.

People still use unguided projectiles today and I do not expect this practice will fall out of favor anytime soon.


Geoffrey S H/"Torch missiles (with lighter payloads of shards than the massive cloud but an almost 99% chance of a hit)": Not quite. Missiles can be zapped with point defense, while clouds cannot (for the same reason you cannot kill a low-hanging fog by shooting it with a gun). So missiles do colossal damage (good chance of single-hit kill on any ship struck) but can fail to cheap point defenses, while clouds do much less damage but are guaranteed to do at least some.

If in your universe point defenses are ineffective, then of course everyone will use missiles and not much else.

Milo said...

Thucydides: I doubt the gas giants will be shipping Helium-3 to each other. It's likely even Jupiter can mine their own Helium-3 more easily than they can import it all the way from Uranus. Interplanetary Helium-3 trade would be to places that can't make their own, such as the inner solar system. (And possibly places like the Kuiper belt, although I'm not sure why anyone would want to colonize there in the first place.)

Solar power at Mercury is about 9.13 kW/m^2. (This assumes you're permanently illuminated, as a satellite at L1, and have solar panels at 100% efficiency. Practical values will be less.) So let's say you need 140 megawatts, which Wikipedia tells me is just over the power consumption of a Boeing 747 (i.e., a spaceship is going to need much, much more, nevermind an armed one). Your solar panel then needs to be a square 128 meters to a side. Ouch.

Geoffrey S H said...

Apologies- I meant 99% (or whatever) in terms of zeroing in on a target- they can be shot out of the void just like in reality for aerial targets. My apologies for not making that clearer.

Thucydides said...

Milo, what I am talking about is the primary sources of energy in each of the three regions of the Solar System.

Mercury and installations that close to the sun will be receiving close to 10X the energy of a similar sized solar panel in Earth Orbit, so they are still getting highly concentrated energy (and there is no real limit to the size of a solar collector in free space). Sending that energy to cooperative receivers across the inner solar system via laser of microwave beam drives the economy. Beamed energy will still be viable to the asteroid belt, but now customers there might also be getting offers of energy from Jupiter (beamed in via electrodynamic tethers) or 3He from Uranus.

Deep space will need concentrated energy, which may be cheaper via fusion reactors running on Uranian 3He rather than beamed power from the inner solar system. Deep spacers might also be wary of disruptions caused for any reason of power beams coming from the inner system. Still, beamed power to deep space installations might be attractive in some situations, and a potential irritant between the various Powers as they vie for customers and influence.

Byron said...

I doubt that people will want to rely on something as vulnerable as solar panels for most military power. They can't be armored, and are prime targets for sand or paint warheads. Those are the sort of weapons that spaceships will be armored against, as it's otherwise to easy to disable a laserstar.
Beamed solar is going to be viewed with suspicion because of the laser issue, while fusion is far more under the user's control.
While unguided weapons are cheaper, we have to take two things into account: range and mass. The mass that hits the target is the only thing that matters. However, you have to lug around everything you fire, and it makes sense to try to get as much as possible to hit the target, particularly if the weapons are made on a planet. It's far cheaper to make 10 guided warheads on Earth and lift them into space than it is to make 100 unguided warheads on Earth and lift them into space. Range will also be severely limited for unguided projectiles. If we assume each projectile has a negligible cross-section, then ships will have about one projectile for each surface area they can be in. The problem is that the area increases with the square of the time of flight, not counting 3D maneuvers. Pretty soon, you have to shoot a lot of shells, when each guided one might cover an area 10 or more times that size. I'll have to do the math later, but I don't think that at most ranges it will be worth it to use lots of dumb bullets. Plus, if PD is powerful, then the number of dumb bullets goes up just as fast as guided ones, because they get vaporized. If it's just blinding guidance, then it's probably still cheaper to go guided, as you can overwhelm them with fewer rounds then would have to be fired to be dodge-proof.

Anonymous said...

I'm leery about the prospect of beamed power. It might seem like a convenient way to make space travel and colonization much easier, but it seems to me that any technology that can efficiently beam a planet's power supply across multiple light-minutes, isn't that far off from being made into a ridiculously powerful directed-energy weapon. If you assume ridiculously powerful antiplanet weapons do not exist, neither will beamed power. Plus, actual cargo ships give people something to fight over (which is bad for actual space planners, but good for authors).


Byron: Exactly. Mercury will probably use solar power for many civilian applications, but their military will prefer fission or fusion, except mayble for expendable long-term peacetime sensor satellites.


I see unguided kinetics as a sort of space carronade - cheap and devastating but shorter-ranged than other weapons. (Of course, they would still have better range than any historic naval gun, but they would be short-ranged relative to lasers.) They would be used when you can manage to maneuver close to the enemy, are fighting in confined orbits, etc.

Guided kinetics are entirely different, and don't function that differently from guided missiles with non-kinetic warheads, as far as deployment tactics and counter-tactics go.

The details are going to depend a lot on how well laser technology pans out, given that currently we don't have much of it (as far as weapons go) yet are assuming everyone in the future will.

Milo said...

Oh, and that was me. Sorry.

Turbo10k said...

I think that space warships will probably use shotgun-cruise missiles while planetary defences would use clouds of shrapnel for high orbit warfare. Here's why:

Space warships, as bryon said, have strict mass-ratio limitations, so each pound counts. This is why Laserstars are so effective in space, they are reusable, lightweight and have little in the way of expendables. Kinetics are far heavier, can only be used once per shot, and don't go at lightspeed. Shotgun-warhead guided missiles are probably the most effective ship-to-ship kinetics as they combine the advantages of Never Missing with the point-defence overwhelming shrapnel that is needed for a Kill Shot.

OTOH, plants have no mass-ratio limits, unlimited resources and city-wide industries for weapons and launchers. Planetary defences would then favour a system that covers a maximal area as attacks can come from all directions, and something that does not need to be activated to work due to lightspeed lag. On the atomic rockets site, a single Orion can haul into orbit 2 million metric tons; if we consider it to be all iron (dumb, cheap spherical shells), we would have around 3.6 million spheres 30cm in diameter. That's a lot. Whatever the concentration of spheres/m3, you can create a huge cloud. And its still a single Orion load. If we have a space elevator and a few years' warning, I believe a determined planet can defend itself quite well from attacks in a given direction. You could say that if detected early enough, this cloud, however huge, could be dodged quite easily, but just how early can you detect cold metal balls against a solar or planetary background?

Ok, that's done. As for the original subject, I'll put a word in:
Orbits don't have to be fixed. Low earth orbits are fast. Add them together and you've got a situation where fleets can split up to cover 3-4 orbits, only boosting to rapidly change orbit left/right and dodge the odd ASAT missile. I see warships being able to keep this up until they run out of propellant, so they burn back to a 'safer' high orbit, restock, then dive back in for round 2. Keeping this going, we could have a support group composed of laserstars and command ships in 'Outer space' and an attack group of warships and orbital bombardiers in LEO dropping in to attack and retreating to resupply.

Also:

Defend against Martians all while allowing commerce? Making a GIANT shrapnel cloud with a large hole in it. Cloud has several explosives and 'dead' missiles in it. Commercial ships go in out of hole. If you spot Martian warships burning towards you, let hell break lose, close all gaps with the explosives and shoot away with the missiles already in place. Depending on where you put the cloud (compromise between far away to avoid interference with you own warships, close enough for maintenance or creation of new holes) you could have your 'dead' missiles go 'live' with only half the distance to cover. You know, defences don't have to be close to home, OR solid targets.

Turbo10k said...

Space warships, as bryon said, have strict mass-ratio limitations, so each pound counts. This is why Laserstars are so effective in space, they are reusable, lightweight and have little in the way of expendables. Kinetics are far heavier, can only be used once per shot, and don't go at lightspeed. Shotgun-warhead guided missiles are probably the most effective ship-to-ship kinetics as they combine the advantages of Never Missing with the point-defence overwhelming shrapnel that is needed for a Kill Shot.

OTOH, plants have no mass-ratio limits, unlimited resources and city-wide industries for weapons and launchers. Planetary defences would then favour a system that covers a maximal area as attacks can come from all directions, and something that does not need to be activated to work due to lightspeed lag. On the atomic rockets site, a single Orion can haul into orbit 2 million metric tons; if we consider it to be all iron (dumb, cheap spherical shells), we would have around 3.6 million spheres 30cm in diameter. That's a lot. Whatever the concentration of spheres/m3, you can create a huge cloud. And its still a single Orion load. If we have a space elevator and a few years' warning, I believe a determined planet can defend itself quite well from attacks in a given direction. You could say that if detected early enough, this cloud, however huge, could be dodged quite easily, but just how early can you detect cold metal balls against a solar or planetary background?

Turbo10k said...

Ok, that's done. As for the original subject, I'll put a word in:
Orbits don't have to be fixed. Low earth orbits are fast. Add them together and you've got a situation where fleets can split up to cover 3-4 orbits, only boosting to rapidly change orbit left/right and dodge the odd ASAT missile. I see warships being able to keep this up until they run out of propellant, so they burn back to a 'safer' high orbit, restock, then dive back in for round 2. Keeping this going, we could have a support group composed of laserstars and command ships in 'Outer space' and an attack group of warships and orbital bombardiers in LEO dropping in to attack and retreating to resupply.

Also:

Defend against Martians all while allowing commerce? Making a GIANT shrapnel cloud with a large hole in it. Cloud has several explosives and 'dead' missiles in it. Commercial ships go in out of hole. If you spot Martian warships burning towards you, let hell break lose, close all gaps with the explosives and shoot away with the missiles already in place. Depending on where you put the cloud (compromise between far away to avoid interference with you own warships, close enough for maintenance or creation of new holes) you could have your 'dead' missiles go 'live' with only half the distance to cover. You know, defences don't have to be close to home, OR solid targets.

Milo said...

Unfortunately, your shrapnel sphere is three-dimensional and has lots of intersecting orbits going at different angles. It's going to be difficult to keep a consistent hole in that. Then again, if it's near or beyond lunar orbit, then the orbital period may be slow enough that you don't have to worry about orbital mechanics in the short term. In the longer term, though, that's going to be a huge mess to maintain and clean up.

It's also going to take quite a bit of shrapnel to fill high orbit.

Rick said...

I used to be a big fan of shrapnel, but playing with some numbers last fall changed my mind.

The problem is that unguided shrapnel can be sidestepped rather easily. A ship can easily have a chemfuel OMS system capable of 0.1 g. A 30 second burn (requiring a modest 1 percent of mass as fuel) gives the ship a deflect velocity of 30 m/s, and carries it 450 meters, nearly half a km. A one minute burn will carry it 1.8 km.

Even if the ship has a target cross section equal to a 100 meter circle, its jink envelope for a 30 second burn is 81 times larger, and for a 60 second burn it is 324 times larger.

In other words the chance of unguided shrapnel is slim to insignificant if unguided flight time approaches one minute. On the other hand, if you get within 10 seconds of the target its jink radius is only 50 meters, and you have a good chance of a hit.

So for maximum effectiveness you want to deliver GUIDED kinetics to within about 10 seconds flight time of the target - call it 100 km, at a 10 km/s closing rate. At that point, even if point defense burns out the guidance the inert slug will probably still hit.

And terminal guidance packages should be relatively cheap, making a swarm of relatively small, guided target seekers the most effective option. Individually they carry less armor than bigger slugs, so they are burned out more quickly, but the defense has to take out almost the entire swarm.

I picture killer buses carrying swarms of up to thousands of target seekers, each about the size of a 100 mm shell, with a mass of a few dozen kg. At 10 km/s each will pack the punch of a few hundred kg of TNT, and even if your defense takes out 90 percent you still take 100 plus hits. Major hurtsies.

A jumbo killer bus might cost $1 billion equivalent, but if it takes out a $5 billion laser star - or keeps it at bay - it has done its job.

Citizen Joe said...

Rick: "I picture killer buses carrying swarms of up to thousands of target seekers, each about the size of a 100 mm shell, with a mass of a few dozen kg. At 10 km/s each will pack the punch of a few hundred kg of TNT, and even if your defense takes out 90 percent you still take 100 plus hits. Major hurtsies."

Do I need to point you to the Mass Effect video on Newton? Assuming 10% hit, that still means that you've polluted your battle space with 90% of of the penetrators. If you're being a responsible aggressor, as opposed to a terrorist, you'll be fighting for a reason, probably territory, then you'll need to track all of those rounds. Another thing to note is that, due to the nature of how the kinetic kills work, the rounds and the target need to be heading towards each other. That means that, once past the wave of kinetics, they are home free. That's getting into a purple/green debate but my point is that the kinetics leave a destructive legacy in their wake unless there is some sort of natural phenomenon that will clear the space of the debris (like Jupiter).

Turbo10k said...

Humm....
So instead of a massive, expensive cloud of kinetics, we have cold KKV-busses in cis-Mars space, ready to fire at command?
Nice.

Plus, a question: What happens if we explode several large nuclear charges at the edges of a kinetic cloud? Does it fly wildly in all directions or can the pefectly spherical/directed explosion be used to throw the cloud away from an orbit/into the enemy constellation?

Geoffrey S H said...

Ah, nukes against a cloud.

Didn't thik of that...neat.

Byron said...

I was thinking of similar things regarding unguided kinetics. The deciding factor will likely be the target's dodge velocity, which equals target acceleration * flight time. If it's too high, then they just aren't efficient. The size of the ship shouldn't really matter, as a bigger ship takes heavier projectiles to kill.
I like the carronade comparison, but the problem is that I wouldn't fire unguided kinetics in orbital space I want to keep intact. There is likely to be too much extra debris compared with guided kinetics.
On debris, Earth escape velocity is about 10.9 km/s from orbit. Any high-speed kinetic is likely to exceed that, never to be seen again. Where it ends up, I have no idea, but it won't be sticking around. Even something with one rick should clear itself, as it will either reach escape velocity or enter the atmosphere. Also, what happens when firing kinetics in orbit? What corrections must be made? I suppose I could abuse the Orbiter rendezvous software to find out.
Even with all this, the primary factor of weapon effectiveness is going to be the amount of destructive energy delivered on target verses the amount wasted. Coilguns might have an edge over lasers at short range, being more efficient, while missiles might be the weapons of choice at long range, as they don't add much waste heat.

Byron said...

On nukes against a cloud:
According to the nuclear weapons calculator, a 100 kiloton spherical charge will have to be within 70 meters to vaporize one of Turbo's spheres. I'm not sure how far it'd have to be to push it around, but at a guess, even for smaller pieces, it'd be pretty ineffective, as it will only vaporize 1 mm at 1.2 km. I'm not sure about the velocity of the vaporized material, but I can't see it being a very effective engine. Plus, it's wasting a perfectly good nuke on shrapnel that could often be better cleared with a laser. A spherical cow standard laser (from the first one) could zap a 30 cm sphere from over 10,000 km, and would be able to, at that range, produce about 1 kN of thrust. (That's a rough guess, as I can't see the jet being well-shaped.) The above nuke at 1 km would give about .0032 Newton-seconds. Both are for 30 cm targets. The numbers can scale as you please.

Byron said...

Two things:
1. Typo in the above math. The nuke actually gives 32 Ns. (Unit conversion error)
2. You could use nukes to find the shrapnel. If they're really hard to find on passive sensors, then just detonate a nuke in the cloud. The resulting thermal energy should light them up, allowing laser sweeping.

Geoffrey S H said...

Nuclear depth charges as it were?

Citizen Joe said...

More like a nuclear sonar ping.

Blast effects are really only effective in confined spaces so that the pressure can build up. That's why it is so hard to blow up a suspension bridge. 90% of it isn't 'there' so the blast just goes right by all the cables. In order for the nuke launched KK cloud to be effective, the cloud would have to be packed around the nuke in the first place. This is the same idea as packing ball bearings around a brick of C4 to cause more damage.

Milo said...

Okay, hmm. In my scenario, I wanted to use the kinetics as an opening salvo for a fleet battle. Let's say the fleets are each travelling at v (for a total closing speed of 2v), and have accelerations of a. The salvo will be launched immediately before the deceleration burn, so 2v/a time before fleet encounter. But the kinetic salvo are going faster than the fleet since they don't decelerate. The above time means the salvo/deceleration-start happens at a fleet distance of 2v*v/a (if my intuition is correct), which - with a kinetic closing speed of 2v - gives the non-decelerating fleet v/a time to dodge. In that time, they can move up to v*v/2a distance, although probably less in practice if they want to stay on course. Still, even for low closing speeds and 1 gee accelerations, this gives them a dodging radius in the thousands of kilometers.

Yeah, gotta use missiles, then. No cloud is going to hit unless the targets are very constrained in their maneuvering.


As for nuclear sonar pings... wow. Just wow.

Turbo10k said...

Milo-I still see kinetic louds as having a use, but less as a weapon than an engineering feat that prepares the battlefield; I could send a volley of shrapnel at the opposing constellation which would then certainly dodge them, but in a predictable manner. Two, three successive volleys would have them dodging into more an more defined paths. This would ease the job for missiles who have to expend less D-v into hunting them down and lasers who aren't vulnerable so much to lightspeed lag anymore.

As for my original idea of using clouds as stationary, forward defences, like barbed wire, we could upgrade it to a cloud of killer busses.

PS: What about the Earth defences stationed at Mars high orbit? Doesn't any interplanetary war start with destroying/neutralizing the enemy's forward posts? Today even, its much easier and more effective to sink a fleet patrolling in nearby oceans than try and hit the enemy's holand directly...

Byron said...

But most people don't let the enemy start with ships in their waters, and keeping those ships out by Mars is going to be expensive. You'll have to supply them from Earth, and who knows where the "interplanetary space" boundaries will fall. Plus, they might do the same to you. I think it'd be easier and cheaper, not to mention safer, to just launch missiles when they come. You can launch stuff at 10 km/s with 50% payload and a reusable bus. I worked it out in the spherical cow discussions.

Rick said...

Kinetics are more effective at high speed (specifically closing rate), so they will typically be fired at well above planetary escape velocity, at least for Earthlike and smaller planets. They are probably still in solar orbit, but will disperse so much that the risk of hitting one is insignificant.

The danger of making orbital space impassable doesn't come from kinetics, but from the wreckage of orbiting targets they hit.


Milo asks: PS: What about the Earth defences stationed at Mars high orbit? Doesn't any interplanetary war start with destroying/neutralizing the enemy's forward posts?

If Earth has ships in high Mars orbit, or in the Mars Hill sphere, they are in blockade position (though only actually blockading if they are interdicting traffic).

This might not be an act of war, but certainly not a friendly one, and expensive to keep ships on distant station like that.

On the other hand, this could be characteristic of space empires (or 'trade federations,' etc.). It does not rule planets, but keeps them under permanent threat of blockade, controlling the right of passage to or from the planet's local space.

This need not be overtly oppressive - if the tolls are modest, and right of passage not narrowly restricted, both space merchants and planetary populations may well regard the imperial presence as worth more in law and order than its cost in tariffs.

I recommend this policy of restraint to space imperialists who don't want to be perpetually keeping the lid on boiling hostility, or who are auditioning to be good guys.


Turning to another point raised upthread, the motives of war, that sounds like a topic for a front page post!

Milo said...

Kinetics would be fired at the highest speeds your guns are capable of.

Advantages of carrying most of your shot's energy in velocity rather than mass:
- The enemy has less time to dodge, therefore the weapon has more range.
- The shot carries less momentum, and so causes less recoil.
- The ammunition costs less mass for a given damage output.

Disadvantages of carrying most of your shot's energy in velocity rather than mass:
- Less momentum means damage gets inflicted more or less spherically from the impact point, rather than thin and deep armor-penetrating wound channels.

The advantages are just too many and too useful to worry about that one disadvantage. For armor-penetrating weapons, you can use drill-pulsing lasers.

The question is how hard your gun technology can fire. The Atomic Rockets site places railguns at 6 km/s, which isn't enough for Earth escape velocity, at least in low orbit (I'm too lazy to check high orbit). But railguns are rather inefficient, so more likely you'll have something like a coilgun or a scram cannon. I dunno how far you can reasonably crank those up. There's also the possibility of shooting in a retrograde direction, meaning you have to impart the shot with your own orbital velocity plus escape velocity.

Anonymous said...

Looking at something from Atomic Rockets website, the Nuclear Shaped Charge (NSC), I was struck by the potential; using a thin, light element cover on the charge, you can shoot a projectile at a fairly high speed (10 or 20 percent lightspeed) and with a relitively narrow expantion rate. this means you could have effective ranges in the tens of thousands of kilometers. So, unless I've screwed up my math (always a possibility) we might already have a kinetic weapon that rivals a laser in range and response time...if it takes a second for the pulse to reach your ship and it takes ten seconds to get out of the way, you're toast.

Ferrell

Turbo10k said...

Ferrel- 10-20% c as being fairy high speed is an understatement, right?
Just a question. How much do these projectiles created by NSC weigh? And there is no such thing as a kinetic weapon having the response time of a laser :)

Milo-I'm rather skeptic about Atomic Rocket's figures for railguns. With frictionless sabots, no air resistance and by using superconductor rails, I'm sure speed would only be limited by rail size and length ie how much you gun want to put in orbit.

As for my previous question about forward defences, I can add some things.

Depending on the

Turbo10k said...

As for my previous question about forward defences, I can add some things.

Depending on the history of interplanetary colonization, we would have Mars as a small colony, completely dependent on Earth. As that small colony expands, it becomes less and less dependent on Earth, until Earth accords independence to some of the Martian habs. The discussions go more like:

-Gimme independence or I blow up all ur colonies.
-Okay, but I keep some.

From this point, Earth posts the defences I posted about, but resupplied by Earth colonies ON MARS. Martians manage to wrestle some armed ships into orbit for say, self-defence or anti-piracy control...things spiral out from there. Mars wouldn't have defences around Earth for obvious reasons (Russian missiles on Cuba didn't last) so Home/Colony war looks lopsided with Home trying to regain control in the most cost-effective manner, while Mars trying to stop the Terran constellation arriving for back-up long enough for their submission to become too expensive.

Geoffrey S H said...

While rail-guns etc are an effective possibility for future artilliary, I would point out that the super-gun (of Iraqi/Matrix-Churchill vintage) could lob payloads into orbit, while using only conventional modern propellant. Less power required, though many disadvantages of course.
For the moment I'm steering clear of rail-guns, coil-guns etc in my future settings ubntil they become standared equipment in modern militaries.

Anonymous said...

Turbo10K said:
"Ferrel- 10-20% c as being fairy high speed is an understatement, right?
Just a question. How much do these projectiles created by NSC weigh? And there is no such thing as a kinetic weapon having the response time of a laser :)"
Yeah, I know it doesn't have the exact responce time...which is why I said it 'Rivels' lasers in response time, due to the fact that most kinetic weapons only travel a .001c at most, and that I wrote this late at night after a very long and tireing day ;)

The size of this weapon is about twice to three times the size of a nuke of the same yeld, but for a "one-shot, one-kill" type stand-off weapon, I think this is acceptable.

Ferrell

Milo said...

The problem with normal firearms is that their muzzle velocity is limited by the speed of sound in the propellant. I haven't been able to find a good cite for exact numbers, but limits of 4 km/s for solid propellants and 7.5 km/s for high-tech lab stuff is the best I could find on short notice. To go faster, you need more exotic techniques. True, they haven't become "standared equipment in modern militaries" yet, but neither are lasers. (A few experimental platforms that barely fit in a Boeing 747 and dump more waste heat than they inflict on the target does not equal standard equipment.)

Also keep in mind that the muzzle velocity of your kinetic weapons is typically going to be less than the exhaust velocity of your rockets (= approximately your delta-vee). Otherwise, why not use your mass drivers for propulsion? (Of course, propulsion mass drivers would be designed to shoot light stuff that disperses shortly after leaving the barrel, to avoid accidentally shooting stuff behind you.)

On another note, I certainly don't want to be the guy who has to design a gun barrel that can stand up to nuclear explosions! Also, that strikes me as a little expensive for firing a single bullet (especially when you add in the mass costs of the nuke and the barrel). But in theory it could work. In theory.


Turbo10k, in your scenario, it would seem best for the Martian rebels to use land forces (or ballistic missiles) to attack the bases still loyal to Terra. If they're trashed, that will leave the Terran ships without their resupply base.

Byron said...

While kinetics will be fired fast, there are limits on that. Energy costs are high, and might a few low-velocity kinetics get through where a high-velocity one fails? There is also a limit on how much cranking up the velocity can do. Beyond a few dozen ricks, it becomes pointless. Plus, why not fire lots of low-velocity kinetics at an incoming attacker, who adds his velocity?
As for coilguns, I'm a huge fan, for two reasons:
1. They're underrated. Nobody really pays attention to them, as lasers and missiles are more photogenic and popular.
2. With work, they can put laser efficiency to shame. Unlike a railgun, they can be used without throwing away most of then energy. Plus, it's a logical outgrowth of mass drive technology. Also, it can be used for more missions than a laser. I can use proxy warheads, small nukes, EMPs, etc.

Milo said...

Byron/"While kinetics will be fired fast, there are limits on that. Energy costs are high, and might a few low-velocity kinetics get through where a high-velocity one fails?": You can reduce energy costs by lowering mass, as well as velocity. I explained why, for a given shot energy, you would like to fire your shots at the highest possible speed (and lowest mass) that your technology can afford without horrendous efficiency losses.

If technology allows me to do it efficiently, I would carry my kinetic energy by accelerating a tiny grain of sand to relativistic speeds. Most likely, technology won't allow this.

Low-speed kinetics would be useful in fast-moving flyby shootings, but unlike some people here, I do not think those will constitute the only space battles. There will be opportunities for naval-style battles where the opposing fleets are more or less stationary while shooting at each other.


Regarding photogenicness... the irony is that missiles and projectiles would actually be more to look at than lasers, in space. In space, there is nothing to scatter light, which is good for weapon efficiency but bad for getting to watch cool laser beams shooting around. On the other hand, unless you're fighting in interstellar space or behind the shadow of a planet, physical missiles would be visible (at least from one side).

Turbo10k said...

Milo-Missiles can be seen from any direction due to exhaust flare.

Byron-Multi-purpose ammunition is something I forgot about. My favorite medium-distance kinetics are rail-accelerated guided rocket KE rounds. High speed+course correction ability.
I think the difference between guided rockets and missiles in space should be the warhead. Guided missiles have similar speeds, "ranges", targeting systems and course correction ability as regular missiles, but only have a "dumb" warhead. Missiles on the other hand have a variety of warheads (shrapnel, shotgun, nuclear, pump laser...) and more Dv...

Attacking Earth bases on Mars imo is like dropping a nuclear bomb on NYC. Its an all-out war declaration as you kill civilians and make Earth lose several trillion's worth of investment over the course of decades. Who says those terran defences stationed on Mars high orbit, having witnessed the deaths of millions of their nation as well as the definitive severance from resupply don't just nuke Martian colonies indiscriminately merely minutes after the initial attack.

Colony revolt has many reasons to be, but in the way I see it, has very little chance to be implemented on a large scale. I once thought up of a scenario where Martian hackers disabled the Terran's first-response capability, then blasted the nuke-carrying stations through hidden ASATs. Without nukes and not knowing who to retaliate against, those same defences are stunned long enough for martian spacewarships to move into a face-off(talk about that later).

Milo said...

And now we're back to the issue of MAD again. If the Terrans are in a position to inflict MAD on the Martians, then violent rebellion simply isn't possible. All the Martians might be able to do is pressure the Terrans into letting them go in order to avoid open war.

Anyway, if civilian deaths are a concern, you can perform surgical strikes against their spacelaunch capabilities. Same effect.


Good point about the exhaust flare, I had overlooked that. Though unguided projectiles don't have an exhaust flare, and missiles might spend some of their time coasting. (Then again, that could be a pretty effective visual in itself. You see a bright burning streak, then it suddenly disappears only a fraction of the distance toward you, and all is quiet. Seconds later, your spaceship is torn apart. Sort of a "calm before the storm" effect.)

Missiles of all sorts, with or without warheads, will have similar tactics, in that they're usable from about the same ranges, and are defended against with the same techniques (point defense works, dodging doesn't), which are entirely different from the tactics associated with unguided projectiles. This will shape classification schemes.

Turbo10k said...

I see kinetics as having two branches.
If you want a shotgun warhead, why not just launch a ship-sized kkv with a few million metric tons of buck shot?
If you want targeting, strap on a rocket and targeting sensors on any metal mass and its a missile. Why stop there? Each ship that can carry 3-4 jumbo jet sized missiles can effectively take down equipment 3-4 times its price.

In the search for effectiveness, we sacrifice "intresting". Nuclear bombs on earth are the extreme examples of those 50ib things that WW2 bombers used. In the end? They stop a war from ever happening.

Rick said...

One problem with 'guns' in general - whether traditional chemfuel or coilguns - is that they fire sequentially, a stream of shells. From the point of view of laser defense this is like bad guy ninjas conveniently attacking one at a time.

In a full on engagement, if the enemy has a laser star, kinetics are wasted unless you fire them en masse to take it out. Otherwise the laser star will just plink them. So - for main force engagements - I think your choices are pretty much laser stars or swarms of kinetics sent on their way by killer buses.

That said, most actual combat might be in other situations, such as boarding confrontations involving blockade runners and interceptors. In these cases shooting may break out at MUCH closer range, involving gunships and relatively light weapons.

Byron said...

Not really. If I can shoot faster than the laserstar can take them out, I can get through, or if I can concentrate my fire so the laserstar is overwhelmed, that would work. Plus, I bet kinetic rounds are cheaper than missiles, as you don't need the booster.

Turbo10k said...

Kinetic rounds are in fact MORE expensive than laser shots. One is an expendable, which you have to pay for its construction, transport cost, as well as the cost of the gun and ITS transport. You carry the round and its support all the way to the battlefield then only use it once. Lasers on the other hand are perfectly reusable and their biggest cost is only paid once: you buy the laser, you carry it to the frontline, then you can use it as many times as you want.

Lasers are the perfect deep space weapon, and are only vulnerable to clouds of shrapnel. No-one engages another ship with kinetics unless lasers are already in action.

Going back to the original post, I think the challenge would be to define orbits according to how far your weapons can reach out; The lightsecond seems a good, stable starting point :-))

Turbo10k said...

Oh and...

Remember the martian-revolt scenario? I said something about a face-off. What I mean is MAD in orbit. All the elements of an interplanetary orbit are in the same place. You have your own constellation, armed to the teeth but not going anywhere because they are being blockaded by the enemy's forward defences. In low orbit, you have the civilians. Space hads, satellites and cargo ships coming and going. Even lower, you have anti-orbit batteries that can blast the most of the blockade out of the sky but are vulnerable to a retaliation by enemy ground forces. If anything "happens", everything is played out within a minute. Batteries fire off, your constellation starts burning into high orbit all while overheating their lasers and shooting off all their missiles. The enemy's ships use their point defences to fend off the kinetics and ASATs, and use THEIR lasers/missiles on your constellation. They are also trying to get to high orbit to escape ground-to-orbit munitions, but also to enforce the blockade, now in danger. In the next few minutes, I see the constellations who gained a last second advantage blasting the other one out of the sky, creating a new blockade on the civilian/neutral ships that huddled down to low orbit to escape collateral damage or just getting involved. After battle (1 hour), we have ground troops moving around, with the winner of the orbital battle having space support (precision orbital laser strikes, orbital anti-material bombardment) to attack each other then destroy opposing surface-to-orbit defences.

Byron said...

I wasn't talking about kinetic rounds vs. lasers. I said that coilgun ammo will be cheaper than missiles, because of the lack of booster. The economics of laser vs. coilgun can be debated, but until we have numbers, it's pointless, and I don't see those coming for a very long time. I understand what you mean, but I don't think we can make a blanket assumption that lasers will always be cheaper. Superconducting coils sound cheaper than optical-grade mirrors and particle accelerators to me. If lasers are expensive enough, the ammo savings might not make much difference.

Milo said...

Lasers cost energy and coolant. Lots of energy, and unless you have really efficient tech, lots of coolant.

Now, the thing is that your engines probably already cost lots of energy anyway, so you have some to spare. Still, present-day guns are vastly more efficient than present-day lasers.

The real advantage of lasers, economically, is that kinetics need a separate ammunition stock for each caliber you want to fire. Ships often want to be equipped to fire multiple types of round to avoid overspecializing - typically, heavy cannons against capital ships, and lighter but faster-firing machine guns to track fast-moving targets - but historically, logistical difficulties sometimes drove them to only mount one type of gun despite the tactical benefit of having more. For lasers, meanwhile, not only do your high-caliber lasers and your low-caliber lasers feed from the same ammunition supply, but they might even be the same gun, dialed to different settings. This simplification in logistics is often worth it even if it means a little more cost per shot compared to kinetics.

Turbo10k said...

Dam I messed up.
What about the second post?

Rick said...

Did Blogger eat another post?

On the Mars orbit scenario, I gotta go re-read the earlier comment, then step through it mentally - it is information-dense. :-)

Anonymous said...

Milo said...
"On another note, I certainly don't want to be the guy who has to design a gun barrel that can stand up to nuclear explosions! Also, that strikes me as a little expensive for firing a single bullet (especially when you add in the mass costs of the nuke and the barrel). But in theory it could work. In theory."

The weapon is actually a morter or missile; the casing of the NSC withstands the explosion for a fraction of a second, after the round shoots off toward its target, the casing (and what's left of the weapon), is vaporized by the residual heat pulse. The NSC is a one use weapon, like any other missile or morter shell...although, if you could design one that could be fired more than once, that would be awsome! :)

Ferrell

Citizen Joe said...

I did a 5 mile long laserstar that needed that length for the linear accelerator for the D-He3 fusion drive system. It had a tunable laser up into the xray range. This had a devastating destructive capability out to light minutes which would of course be easily dodged if you knew it was coming. The trick was to fire time on target at some spatial location and have sheepdog style fighters coax the enemy ships into that path. This was done with Kinetic clouds of fusion fuel pellets. If they impacted, it would be at a speed that would induce fusion. If they missed and entered an oxygen rich atmosphere (like Earth) the fusion pellets would simply burn (as they are highly flammable). Depleted fusion core casing material (Silicon Carbide) was ground up and used to abrade the surfaces of the alien ships which would otherwise largely reflect lasers.

Much of the warfare conducted by the humans was a re-tasking of existing equipment. While the massive laserstar was extremely deadly, it could also be tuned to lower frequencies to act as a system wide transmitter. The fusion pellets were already available as fuel. The silicon carbide was considered a waste product.

Geoffrey S H said...

Any chance for a design/picture of that laserstar?

As for sequncial shots, in part that could be the point- the waves of shells and clouds forvcing the lasstar to keep frying them and so attract attention from other stuff...

Of course, multiple gun turrets/ accelerators might put out enough for the lasstar constellation to be overwhelmed after some alvos, and precision firing solutions and different speeds assigned to each shell fired sequencially might mean that each salvo actually arrives at exaclty the same time- and ammunition corse would be deep inside the spacecraft and well-protected, unlike the radiators required for lasers.

Interesting martion/earth orbit senarios there...

Byron said...

I'm still extremely leery of forward-deployed fleets like you propose. Besides the supply issue, which you've solved, there's also the men and ships. With any reasonable drive, it will take a month or more, making it extremely time-consuming to deploy ships. The US Navy uses 6-month cruises, which leaves me with 4 months on station, or less. I can go longer, but it gets into human factors issues. If it's a patrol fleet, that slightly changes things, as you actually have something to do, and a permissive base. You seem to have a weird mix, something like "they have a supply base, but nothing else." How this would work will vary based on the exact scenario. Even then, pre-positioning a fleet seems an incredibly inefficient way to defend against an enemy. It'd be easier to just wait for them to attack, then hit them with kinetics en route. When they finally arrive, your fleet's full strength can engage them, while they don't have defenses to aid them, and they've been worn down by the kinetics. If you wait in Mars orbit, then you will need about four ships per one deployed (if they need to return to Earth regularly). Also, they're vulnerable to sabotage. What if, as a prelude to revolt, the Martians sneak a nuke on one of the supply shuttles?
The exception is if you have a truly friendly base, and you are trying to contain trouble, not just defend. Oh, and you have the deployable forces to deal with it. Right now, the US does, but nobody else really does, so they deploy as needed.

Turbo10k said...

In the Mars/Earth scenario, I think terran forward defenses are a logical thing to have. We would have terran colonies, terran civilians and trillions of dollar's worth of assets on Mars and in its orbit. Posting fully combat capable warships in HMO would not be a handicap in any way. You won't have any relays between different combat groups, as Terran forward defenses are perfectly autonomous (defenses would then include the whole group: warships, space stations, orbital and surface depots, launch facilities, military bases ad personnel...) in relation to earth. Heck, most of the people defending earth's assets on mars would have been born and grown up there, so they are defending their home! I also see orbital and interplanetary warships as quite different, so anything Earth sends in retaliation to a major attack (ie a booby trapped service shuttle) would be like sending in the cavalry, not more troops.
The united state don't use the 4-for-1 rotation between military bases as they don't have a large american population actually living there, and would be wiped out if hostilities broke out. In that case, we could say the forward defenses have cheap, NERVA ships with light missiles and small lasers (think paramilitary), while it holds the hard, armoured torch battleships, fully robotic and armed with gigalasers, back home (think M1A1 Abrahams).

George-Lasers, in combat, use heat sinks, which are even better protected than internal ammunition.

Citizen Joe- Just call it TSF Boomstick.

Ferrel-The NSC would be expensive for a single shot weapon that has the same advantages and disadvantages as regular kinetics, albeit at longer ranges (compare to coilguns). I do see it however as a rapid strike weapon at closer ranges, or as a warhead on a precision strike ship-to-ship missile (no frag).

PS: NSCs don't have kinetic cloud ability to high cost-per-shot, and create supplementary debris after launch, this time coming right at you.

Geoffrey S H said...

Its Geoffrey, but that's ok- many, many people get my name wrong the first few times. Ah, the perils of having a name of 1st milleneum Norman origin. :)

Your senarios of Earth having "friendly" Martians controlling their assets on Mars but loyal to Earth presents a quite civil-war type background to work with. In a way its similar to (Ferrel's ?) someone's idea of Earth nations pushing for and eventually getting nation states on Mars that they can work with- leading to French/US whatever frreindly assets being deployed there to crush whoever's being provocative and upsetting the solar system stockmarket/whatever."Ethnic" origin is the same/blurred, but loyalties are very clearly defined.

As to heat-sinks: of course! I forgot about those. Thus, could a kinetivc craft keep up enough fire to make the laser craft overheat the heatsink and then switch to radiators.

Methinks only massive miniturisation of ammo could come even close to making this possible, but I'm ready to be surprised if its otherwise.

Byron said...

My comments on rotation were probably unclear, and assume that all the ships were getting was basic supplies. What I was saying about truly friendly bases is pretty much what Turbo said about the ships being there long-term. I was thinking of it being a patrol, like the ones the US keeps in, say, the western Pacific. Turbo seems to think of it more like the USS George Washington, which is based in Japan. In those situations, I can see it being feasible.
What this solar system is shaping up to look like is similar to the Cold War, and the various proxy wars therein.

Turbo10k said...

Byron-At least someone agrees with what I wrote, but I didn't know there was a real-life example!

Geoffrey-Actually, you don't need miniaturization of ammo, actually less than today. You have to strike a balance between number of targets and projectile resistance to point defense countermeasures. The latter point doubles as how much damage per projectile as the best anti-PD projectiles are the higher mass ones, and composed of dense and high refractory materials. And that's only the dumb warheads. In a setting where targeting is cheap, even the smallest projectile will be a guided rocket in its own right, with warhead, propellant, rocket, guidance and thrusters giving it up to 100kg/2-3 meters length. Surprised? I was too.

Thucydides said...

Based on much of what I have read in this and other threads (and on other boards and blogs) it seems the only real way to project power is to have a constant stream of military cyclers plying the solar system.

I am thinking of the Neofuel site's design for a donut shaped bladder filled with thousands of tonnes of ice. The military spacecraft can be "parked" in the donut hole, and their engines used for thrust and course adjustment (lots of remass inside), while the ice donut provides shielding and thermal mass to protect the spaceships clustered inside. When you reach the target area, the spaceships can be launched from the cycler, which then continues unmanned into deep space, perhaps returning in several centuries. The fleet command sends lots of unmanned cyclers on different orbits so warships can latch onto these as mobile shelters whenever they finish a mission.

Smaller versions can act as "arsenal ships" carrying hundreds or thousands of missiles and torpedoes in the donut hole, ready to launch barrages whenever they come in range. (A laserstar of stupendous power is also possible, thousands of tonnes of ice make a great heat sink for the weapon). The knowledge that the great powers have these things scheduled to cruise past on a regular basis will certainly serve to keep the lesser powers in check, or devote most of their military spending on counter missiles and laserstar constellations to defend the homeworld.

Milo said...

So wait, are you postulating large, poorly mobile weapons platforms that fly past planets on predictable courses at high speeds?

What exactly is the tactical justification of a military installation that can't stay near the enemy long enough to finish a battle, while being practically designed to be as vulnerable to kinetic mines as any spaceship can possibly be?

Thucydides said...

A military cycler is more akin to a submarine pen or dock facility than the warship itself, the actual fighting ships or KKV's will deploy prior to getting inside the enemy hill sphere or whatever else is decreed their zone of influence.

Even if they nested warships don't deploy, the sight of military cyclers cruising past on a regular basis will be similar to the "Great White Fleet" cruising around the world as a symbol of American power and resolve (or modern day deployments of carrier battle groups), a visible warning to everyone that the Great Power has the means to enforce their will.

It also complicates strategic planing, since there will be certain "windows" when the Great Power's ships will be in range, so anything you need to do must be done either between windows or using extreme camoflage and stealth, while sensors on the cyclers can keep you under pretty constant observation.

Using cyclers solves some of the conundrums of having "light" military spaceships, since lots of housekeeping services can be done by the cycler. The Great Power fleet will probably also have some heavy units capable of torch like performance to apply power directly, so there will be some balance in the fleet.

Turbo10k said...

Oh and how do you catch up with them? You'll have to expend propellant to reach them, seperate with them, fight, catch up with them again, and finally twice more to detach, the get back to orbit.

I prefer getting much less, but on an on-demand basis from the planet.

MAYBE you could have them as big guns that arrive regularly, commanded by friendly forces on station if fights break out, if not, they just let them continue their cycle. But then again, why not just put them on ships onstation or keep them back home?

The only viable reason to design such massive donuts would be to use them as blockade ships. The enemy roughly knows where they are, far far away in orbit, so can hit them; The ability to shrug off heavy damage and have lots of endurance with onboard supplies will be helpful here, as will massive damage output.

Also, if the GPs have torch drives, it kind of defeats the purpose of those 'Submarine pens' coming round regularly. A torch ship would be able to reach the zone of conflict in mere months, a bit like Spain sending an Armada to England. Then again it depends on how much intimidation you want. Mars showing tension, terrorist attacks rampant? Set up a show of force and some bullying with your donuts. Titan mainly autonomous, but you want nominal presence? Get local mercenaries to paint the Terran flag on the side. I think the forward presence would be heavily dependent on the situation you're surveying.

PS: C-O-S-T. A high endurance, high power, very large ship with the ability to fight AND travel for centuries...is expensive. What's your solution for that?.

Geoffrey S H said...

Build 'em in bulk and drive down the cost- simples! ;)

Milo said...

Keep in mind, the delta-vee needed to catch up, dock with, and then detach from a cycler and arrive at your destination, is equal to the delta-vee you would have needed to spend to just go there on your own. The cycler isn't thrusting adding no delta-vee to you.

The advantage of civilian passenger cyclers - if there is any - is that most of the bulk of the life support system and food supplies for surviving a long trip is kept and recycled onboard the cycler, rather than needing to be accelerated and decelerated all the time. Even so, I don't think it's worth the complexity of the system and the large number of cyclers you need to keep in solar orbit to account for their slow orbital period (which also makes a cycler unpleasant to live on during its off-season period). If most of your ships' bulk is weapons and armor which needs to be accelerated with them, rather than life support that doesn't, then cyclers really become pointless.

Milo said...

Oh, and: another disadvantage of cyclers is that it's hard to upgrade them as technology improves. This is becoming more and more of a concern in our age!

Geoffrey S H said...

Here’s a prototype image of a cycler offloading one of three kinetics warthrusts during the campaign season. Note the large radiators to expel the waste heat of the craft inside, and the inflatable habs for (rare) extra troop compliments if and when they are needed. Propellant tanks, refuelling containers and other equipment are contained inside what is essentially a drifting shell, propelled into an orbit by tugs and then left there to drift. Even the shell itself is merely a semi-rigid structure constructed out of the most convenient materials to hand.

http://img64.imageshack.us/f/militarycyclerinconstel.jpg/

Rick said...

I must be missing something here, because cycler stations seem like very poor military bases to me as well.

The Great White Fleet was not something any great power would do on a normal basis, but a one-off way for an emergent great power to show the flag globally - the sort of mission an already-established great power assigns to individual cruisers.

On Earth keeping a force deployed near Mars, it makes worlds of difference - so to speak - if Earth has friends already in Mars space, thus local habs/domes where crews can go on R&R, and a local source of general supplies.

Geoffrey S H said...

I'll admit I'm not particualrily a fan of the idea, but I can somewhatsee the sense of having a base you can stock with supplies and then let drift to the theatre of operations providing some support to the people there. Then ready to drift back to Earth and be restocked again- even a marginal imrovement in drive technologies would make them obsolete. Such a craft would probably be strictly logistics support only though due to the predictable orbit.

Milo said...

No, a cycler doesn't make it any easier to restock after a trip. Your restocking shuttle needs to put out as much delta-vee as the trip itself would take.

Cyclers only make sense when you want to carry lots of stuff that doesn't need to be restocked often (sports and comfort supplies that aren't expended when used, computers that can be upgraded over the internet without physically installing anything, food that can be recycled with onboard equipment, etc.), and when said stuff is meant to be used while in transit, rather than while stopped at the source or destination. There's some logic to using it for passenger liners, which do in fact meet these criteria for much of their payload minus the passengers themselves (even though I still don't think it's worth the overhead), but military bases carry different payload distributions that largely don't seem to meet these criteria to me. (They do still have crew and therefore crew comfort supplies, but these constitute a much smaller fraction of the ship's total mass.)

Byron said...

Cyclers strike me as a spectacularly bad idea for a military base, for some of the same reasons I objected to them in "Running on Rails" along with new ones.
First, it has no on-station endurance. A civilian cycler might not view this as much of a problem, but with a military ship, having only a narrow window is bad. What if I need to keep the fleet there? What if they just wait until right after one goes by, knowing that I can launch ships, but can't retrieve or support them.
Second, I'm sending people out on multi-year missions with only a very narrow zone of active time. The rest of the time they are just sitting there, doing nothing. Also, any equipment I send is there for the duration of the cruise.
Third, it's very predictable. I can't change the time it arrives, and they know that. All they have to do is wait for one to go by, and they might have months until the next one.
Fourth, it's expensive. I have to have enough forces to do what I need on each cycler. It'd be far cheaper to build one high delta-V fleet and keep it at home or something.
I think the idea of a huge mothership has some merit, but not as a cycler. It's sort of like a carrier, but for full-size ships. You move it to the target planet, and run your blockade from it. The idea sort of reminds me of the Mobile Offshore base. It would be a resupply point for the entire fleet, as well as allowing low-endurance ships to participate.

Turbo10k said...

Civilian cycler are cycler for civilian use that you only need to accelerate once? Interesting as a concept for saving Dv but you forget that it would make docking a complicated-accident prone process. For a orbital spaceport 'bus' to catch up with it, it has to match speeds but also if anythign were to go wrong with the bus, it does not have a safe, higher orbit to fall back on, it would be engaged in intercepting the cycler....

In a military situation where redundancy and safety is even more important than in civilian cases (if only from an economical point of view), would adding several complicated steps to have a single evident advantage (shock and awe) be worth it?

Geoffrey S H said...

Any crew would live off the supplies within, wasting some, while an automated craft would very likely be like the crewed one-unarmed, but with no one to defend it- thus open it up to potential capture and a loss of supplies.

Anonymous said...

I think that having a huge, mobile base to provide logistics support to a constellation of various heavy spacewarships and light, fast gunships. The mobile base transports the warcraft to a high orbit around a target planet or moon, where they deploy and perform their mission...torch (or sub-torch)logistics ships resupply the mobile base, which in turn keeps the warcraft supplied, manned, and maintained...think of them as more of a flying airbase than a carrier.

Ferrell

Milo said...

Yeah, except that if you had a flying (or non-flying) airbase, you would try to keep it near the action for more than one short window every few years.

Thucydides said...

Cyclers are a response to a lot of the points raised about running on rails; it does not really matter if you are going in a massive ORION battleship or elegant fusion powered lightship, everyone knows you are coming and has a pretty good idea of when and where.

The 100m diameter iceship proposed by Anthony Zuppero has a mass of 8000 tones, a considerable amount of mass for shielding against cosmic radiation, erosion by small particles and thermal mass against laser fire. It should also soak up impact from incoming KKV fire so the carried space hardware can exit. A 215m diameter donut has 40,000 tons of ice shielding the hardware, offering more protection and more room to carry your military hardware.

As for how this works, as the cycler enters the hostile Hill sphere or estimated defensive envelope, the on board ships and KKV's exit out the "back" and decelerate, allowing the massive ice shield to clear the space ahead (some KKV's would be launched out of the "front" to close with defenders at interplanetary speeds). The ships can deploy in relative peace, while the defender has to either get around the cycler to get a flanking shot, or try to blast through, littering space with chunks of ice moving through the defender's space at interplanetary speed. The incoming fleet might cause the ice donut to self destruct for the same reasons.

The invasion fleet can either stay on station, move in for the kill or do whatever else the dispatching power requires. When it is time to return, there will be another cycler launched by fleet HQ (maybe even years ahead of time) the ships and hardware RV's with and returns home.

Most military ships and hardware will probably be automatic in nature because of the long duration of missions (perhaps the only comparison would be ships of the line during the age of sail, where ships might be at sea for months or almost a year at a time; a punitive mission dispatched to Titan might take anywhere from 2 months to several years to arrive).

Actually, re reading the Neofuel site, Zuppero supposes several NERVA type engines are housed in the center of the donut to provide thrust; this is a ship in itself. If the engines are the engines of the space warships hangered in the middle (and tapping some of the ice for remass) then we get a bit closer to an aircraft carrier rather than a cycler/sub pen sort of idea.

So the downside of running on rails is countered a bit by protection and hanger service, while the warships are free to move as independent units once they arrive in the conflict zone.

Geoffrey S H said...

Of course, if you can move it with engines, why not simply put engines permanently on it, install weapons and simply make it a warcraft in its own right?

To answer my own question: the warcraft within do not have the supplies within, and so if they are lost, less suppplies go with them)unless assuming the "cycler" has surplus supplies to deal with all mission requirements.

A group of warcraft with a logistic constellation lagging behind could probably do much of this better though- especially once torch drive proliferate throughout the solar system.

Byron said...

Thucydides- Why are we doing this circus with the cycler instead of just using it as a mobile base? It'd be far easier to just move the thing across the solar system when you need it. The basic point of the cycler, as has been stated before, is to allow you to accelerate once stuff like life support systems, and stuff you can recycle, like food. None of the above really applies to military equipment, which all has to be stopped at it's destination. Plus, how often are these cyclers supposed to come by? If a planet only get one a year, then any given troublemaker has eleven months (if they're smart) before you can respond.
The carrying supplies, remass, and armor advantage also goes away when the cyler speeds out, leaving the ships behind. I have no problems with the forward base idea, but an actual cycler seems the worst possible way to do it. You're carefully throwing away most of the advantages of the cycler concept, along with the object's advantage as a long-term base, and increasing your military requirements exponentially. In return, I don't know what you get. I'd far rather deploy my fleet as needed.

Byron said...

And, to clarify in response to your comments about when and where, there's a difference between knowing that your fleet will be at my door in two months right after it launches, and knowing the next cycler pass is in ten months. Without a cycler, you can launch when you need to, making response time a couple of months. Just because they can see you coming doesn't mean you need to give them a schedule of when you can be there.

Turbo10k said...

I think the whole cycler concept is an attempt at the old problem: Creating authority that you can't enforce.

You want them rebels to tremble when the hear your name, but all you do is a predictable visit the whole year. Or worse if you respect Hohmann orbits....

Geoffrey- I think that lifes upport and supplies, in a space environment, would be highly standardised. I see those two as grain in space. Anyone can take and process it, from any platform and for any use. The only difference would be the weapons outfitted for the specific purpose (once again, why can't the missiles designed for a destroyer not be used for the battleship who has an urgent need for them). Oh, and if so, it gives your cycler an acute problem to piracy and theft...your rebels just have to use your stolen warships or build ones to same specifications, then all they have to do is intercept your handy cycler and use all the ammo your fleet is now deprived of.

Back to the orginal subject, I was wondering. Until now, we've only used LEO, HEO, geostationary and Hill sphere. Is there any was to greatly increase the number of orbits used? One going around the equator would probably be prioritized for the richest merchants, those a few degrees/altutide away from it would be less expensive in tax terms but cost more in propellant/time. We could have a neutral orbit and orbits that are strictly military. If you find yourself in them, you'd better be in distress. We could have static positions on top of the pole reserved for planetary defences, while HEO becomes a sort of parkign orbit where unidentified ships are sorted for landing/lower orbits...How about it?

Milo said...

I've tended to use HEO in a relative sense of "higher than the defenders can shoot you", rather than its current distance-based meaning. Kind of like low ground in a mountain country might still be higher than high ground in a plains country.

But yes, orbital inclination can be of tactical importance. Polar orbits are useful for attacking militaries because over the course of several orbits they will eventually pass over every place on the planet, so nowhere is safe from your orbital bombardment. Retrograde orbits let you continuously zip past prograde orbiters in the opposite direction at high speed, promoting use of kinetic weapons in both directions, while preventing prolonged contact.

Prograde equatorial orbits are cheapest to land/take off from, though it's questionable how much of an issue this will be in a future where space travel isn't prohibitively difficult.

I'm not sure about HEO as parking orbits. From what I've read, it seems that the Oberth effect actually recommends picking your parking orbits as low as possible. Unfortunately, you need to pass through HEO to get to LEO, so that complicates traffic control.

Anonymous said...

My Mobile Base idea would have it stay in a very high orbit(at the target planet) and support the combat spacecraft for the duration of the mission; high speed logistics ships would resupply the Mobile Base, either from the homeworld or from a permanent forward base on a moon, asteroid, or giant orbital habitat. After the mission is over, the Mobile Base would collect the constellation and ferry them back to their home port...or another target. The logistics ships would not only carry cargo, but rotate personnel as well.

Ferrell

Milo said...

What would you do if your mobile base is blown up in combat?

A base can be useful, but you don't want to get too dependant on it, and it has to be capable of defending itself. The high weapon ranges in space with nothing to block them, and the difficulty of holding a line due to the three-dimensionality of space, make it difficult to keep any ship in a "safe" location while more combat-capable ships shield it.

Rick said...

I don't see a military role for true cyclers, but I'm more supportive of the idea of a mobile base to support the combat elements of an expeditionary constellation, especially for missions such as blockade that require sticking around in the vicinity of the target.

By the time you have regular deep space war expeditions, classical cyclers are probably obsolete anyway - the newer ones upgraded with improved drives, to serve as mobile stations for civil use (with military versions a further modification).

Turbo10k said...

With modular spacecraft, drive and weapon upgrades seem meaningless to me. Further, upgrading or retrofitting a shit is essentially making a new one...the only difficulty with keeping cyclers up to date would be to catch up with them :)

I can however see cyclers as having a military use. If you are establishing a blockade or having recently invaded a planet or outpost, you would large supplies of whatever you need for warfare at the time. Worse, these logistics supplies have to be secure, as enemy ships and rebels outside of the zona frontiera would still pose a threat. As you don't want a slow, vulnerable supply ship with large payloads coupled to weight of armour and weapons (imagine a supertanker with naval guns and 3 inch armour on it) we could have cyclers!

They would be cost-effective and wouldn't require lots of protection, and if it did, its escort would be dedicated combat ships...Their use would however be limited to situations where you can establish a long-term presence. No need to send cyclers if you are packing up the next week!

Turbo10k said...

Flash Idea: IPAOM
InterPlanetary Anti-Orbital Missiles. Use the aforementioned fast missile not to hit the enemy's home planet with megaricks on relativistic damage (with ensuing MAD issues) but to send a hail of shrapnel onto the enemy's orbits. Double of concept of differentiated orbits for military/civil/transit ect. and you could target most of the enemy's military and lock fleet action in place with hitting (most) of the civil ships.

Citizen Joe said...

Assuming the deepspace laserstar scenario, which nobody would want to partake, a cycler would remain out beyond the range ground/orbital forces. While you could chuck rocks at a cycler's predictable orbit, said rocks could be destroyed by lasers well before they become a threat. Given that the cycler would have to deal with natural debris threats, it would stand to reason that they maintain some sort of kinetic protection. It would take a full on attack against the cycler in order to stop it and it would also be a suicide mission since you probably wouldn't have the resources to get home. If you did, then the setting wouldn't have need for cyclers in the first place. Combine that difficulty with the mixture of economic and social factors involved with destroying a cycler and they just aren't justifiable targets. In the meanwhile, your fleet could have tagged along with the cycler and used it for life support during the long trek, leaving more space for weapons on your actual combat vehicles.

Turbo10k said...

Humm...
We have two assumptions:
-Ship mass has little impact on ship manoeuvrability over long term engagements
-A centralised life support resupply system is necessary, or at least more efficient than just installing larger on-board supplies.

Oh and another one:
-Lasers, given sufficient range, can zap anything.

Think about it. A cycler just becomes another large ship. I see it as the robotic battleships described before, stripped of their kinetic and crew bays. Add on a scheduled departure time and torus-shaped armor made of ice and you've got a cycler. In other words, a reconverted warship....why not just send it along with the rest of the fleet?!

Cit' Joe: Social and economic factors? I don't see many accountants and middle-aged bank workers worrying about warships millions of kms away that only come round another planet once every decade. Another thing. The cost aspect.
Destroying something that is coming along at interplanetary speeds, more or less incapable of jinking, is very cheap. It's coming around in a decade? I can get several million tons of kirklin mines, guided missiles, random asteroids and such on intercept course in half that time...

Milo said...

If it has maneuverability equal to everything else then, no matter how large it is, it isn't a cycler. It's just a really large ship.

Citizen Joe said...

Economic issues like: The cycler is also carrying all the trade goods your planet needs and would cost astronomical numbers to replace plus many years to get back on cycle.

Social issues like: The cycler has a bunch of civilians and a bunch of clients waiting for their goods to arrive. Not to mention the rest of the habitats on the cycler path (like the belter colonies).

Cyclers aren't completely unmaneuverable. In fact, they would likely have a massive reserve of delta-V (at the expense of their profitability). Likewise your attack against the cycler presupposes that it is known to have a military escort. At which point the military escort could either destroy the assault or depart... which means you blew your load destroying the cycler and the military vessels just swoop in without any resistance.

This is pretty much the U-boats in the Atlantic scenario. That doesn't win you many friends.

Turbo10k said...

Sorry about the economic and social issues...I was looking at cyclers as from a purely military point of view. Otherwise, we'd have only two cargo ships:
-Cyclers for maximum efficiency and cheapness with low-revenue bulk products
-Torch cargo ships for more valuable things or anything that needs quicker delivery.

The first follow brachistone and have massive loads of solid propellant, as well as high isp. This is because they need maximum autonomy and minimum maintenance. Hell, they can have ice fuelled NERVA, with ice doubling as the external ring. The second would have something like VASMIR, more complicated and fuel hungry but faster.

But still. I thing a few million metric tons of stuff aimed at YOU will destroy everything it is targeted at, escort or not. If fact, I think if the escort gets hint such pre-prepared defences, it would deccelerate and evaluate the situation. Punch through and risk total destruction? Head back? If the latter isn't an option, they would probably seperate from the cycler and brachistrone into another safer planet's orbit... So yeah, U-boats in the atlantic.

Citizen Joe said...

I wanted to address a question upthread about docking with a cycler. The aspects of a cycler can vary depending on what your needs are. If you're looking at rapid transit time, then the approach vectors are very steep. Might be good for aerobraking. As you slow down your approach vectors, the transit time tends to increase, as does your 'idle' time. In either case, a ship traveling with the cycler doesn't really save any dV by doing so. It has to accelerate to the same orbit as the cycler, then ride along with it, then accelerate to destination orbit. The savings comes from not having to have all the life support on your ship. Once you get close to the cycler, you just wait your turn and slowly drift in for docking. At that point, your crew can partake in fresh food, gravity and radiation protection afforded by the larger vessel.

Some of the cyclers I like involve 'idle' trips into the asteroid belt, at which point their entry vector is pretty shallow. That makes for minimal dV shift on the vary large things coming back from the belt, like asteroid metals. I could easily see trade of processed goods (like food) being exchanged for raw materials (water ice, CO2 ice) which would be processed on the way back, thus idle time becomes production time.

Milo said...

Actually, steeper orbits have a larger orbital period, therefore they would have more idle time. You can get fairly fast travel by shooting your cycler out at near-solar-escape-velocity, but then it'll be a long time before you see it again. The steepest transfers (parabolic and hyperbolic) are forever beyond the reach of a cycler.

Byron said...

I still don't understand everyone's obsession with cyclers. The problem is that I don't see what you can do with them that can't be done by our plausible midfuture ships cheaper in the long run. They only really work for cargo (including passengers) that requires a lot of support that can be left on the trajectory. Radiation shielding, consumables (with recycling), etc. Joe's proposals to make them better add mass and don't really contribute. Economies of scale make it seem like a better idea to just ship the stuff the normal way, as it'd probably get there faster, and you wouldn't have to pay people to babysit the processor. The only exception is if you use a tether to give the delta-V. You launch passengers on the way to Mars, and at Mars, the tether takes them off and puts aboard cargo, which your tether then unloads. Even then, that's only to balance the energy, not because it really makes economic sense (except for the fuel saving).

Citizen Joe said...

Well, my cycler concepts are more like mobile space stations... or colonies. And they aren't freighters, they are manufacturing colonies. All of that stuff that is hard to do in space can be much easier within the spin hab of the cycler. And they have plenty of time to do the processing. If you look at the colony and manufacturing as their primary objective, then the occasional fast transit between two planets is just gravy.

A technological analogy is air conditioning. A/C wasn't developed to cool places, it was actually developed to dehumidify the air in the New York Times (I think... it was some newspaper) when it was so humid that the ink wouldn't dry. It was later used in tobacco factories to preserve the quality of the tobacco. The comfortable cold air was just a bonus to the workers. The same sort of concept could apply to the cyclers. Mining and refining need gravity for some processes so the cycler gets designed with a spin hab... the medicinal value to humans was just secondary. Plants get used to process CO2 and water, etc. Fresh fruits and flowers is just a side effect.

Milo said...

Manufacturing requires continuous input of resources and output of product, something cyclers are not known to be good at.

If you need gravity for your manufacturing processes, it seems easier to just perform them on the surface of a planet or moon, which conveniently has both gravity and resources, while taking less delta-vee to enter and leave than a cycler.

If you do need to perform your manufacturing in space for some reason, then a "stationary" space station orbiting near a convenient planet (probably the one the resources are coming from or the one the product will be used on) would seem more useful than a cycler.

Citizen Joe said...

Down shipping and up shipping through a gravity well is extremely expensive. So what I'm saying is that space products can and should be made from space resources as much as possible. One of my premises is that Earth is a 'Heavy World' and getting stuff off Earth easily never gets solved (by human technology). Yes, with a big enough engine we can make a brick fly, but it is easier just to make the brick in space.

Maybe some of my presumptions are way off. I'm assuming a combination of rocky, metallic, water, ammonia and CO2 ice as asteroids. I'm also assuming that the 'belters' will be trading their stockpiled 'waste' for renewed stores, most likely freeze dried rations. So the cycler factory would spend the 'outbound idle' time preparing foodstuffs for the belters. The belters trade their mineral wealth in. Some/most of the cycler facilities switch to mineral extraction and processing, eventually moving to finished products. As the workforce shifts, agriculture picks up again to provide the next round of food products, particularly for the time that the cycler moves people around.

Of course, the real point of the cycler (as I described) is to have an interesting setting and set up interesting plot events (like trying to catch the outbound cycler or holding out until the next cycler arrives).

Byron said...

1. Why can't the belters simply grow their own food? It'd be cheaper and more efficient.
2. Repeat after me: The point of a cycler is to allow items that do not really have to be accelerated and decelerated repeatedly, such as life support and radiation shielding, to avoid be accelerated and decelerated repeatedly. It is not a generic term for orbital transport.
3. Using a cycler for manufacturing makes no economic sense. The accountants are going to balk at sending something out that requires a crew for two years or more at a time, has a limited capacity (limited by the resources it can take onboard), which destroys economies of scale, and is probably no faster than shipping the raw materials, and processing them in LEO. If you want gravity for something, by all means use spin gravity, but a cycler isn't required for that. Plus, the crew will get mighty board and demand lots of money, something else the accountants won't like. If I was building a manufacturing colony, I'd just put it in orbit. The delta-V from the belt might be high, but if I use a tether to throw things back and forth, it might be a better option. That way, the cycler can be skipped completely, and we don't really have transport costs.
Cyclers strike me as being a lot like space fighters. They might see a little use early on, but they aren't really practical in most scenarios. You can include them, but it takes a lot of stretching of plausibility.

Citizen Joe said...

1. Belters can and probably will need to grow their own food. However, that 'food' will be more of a 'food product' than actual food. We're talking algae and worms as your primary energy source. Anything that resembles actual food would need a more dedicated and larger area. You think bored people complain, go a year on gruel.

2. The cyclers I'm envisioning don't do much accelerating although there are minor adjustments to keep the cycle just right. All the accelerations need to occur on shuttles/transports/freighters which catch up to the cyclers.

3. The amount of resources isn't limited to the amount that can be stored inside the cycler, it is the amount that can follow close to the cycler. While I'm envisioning an impossibly large cycler, that would itself be dwarfed by the cargo drifting along nearby (mostly netted asteroids). That is a lot of material to sift through, not just for specific compounds/elements but also to refine to specific isotopes. That takes time and work, not to mention equipment. Bored isn't really an option on a ship. The only people that might be bored are any belters that have retired and are heading home after 40 years mining asteroids.

If you're guiding principle is "What is likely to happen with current economies?" Then forget about space travel because it just isn't profitable. If you want cyclers, these are some plausible ways to get them into the system. Not plausible in their own right, but as part of a greater space economy they do work.

Of course if you just introduce torchships/teleporters/warpdrive or any other magitech then old school cyclers make no sense.

Milo said...

"Down shipping and up shipping through a gravity well is extremely expensive. So what I'm saying is that space products can and should be made from space resources as much as possible. One of my premises is that Earth is a 'Heavy World' and getting stuff off Earth easily never gets solved (by human technology)."

I didn't say "Earth", I said "a planet or moon". Luna has an escape velocity of only 2.38 km/s. Even Mars only has an escape velocity of 5.02 km/s. Merely entering orbit will typically take less than these values. Many dwarf planets (like Ceres) and gas giant moons are even easier. These numbers compare pretty favorably to interplanetary delta-vees (which are, per definition, what you would need to pay to catch up with a cycler).

Liftoff and landing on Earth will remain difficult, although the atmosphere, normally seen as inconvenient due to drag, can actually be of help here with proper design. (This is what I meant about each planet's shuttles having their own idiosyncracies.) Landing shuttles can use it for aerobraking (as the Space Shuttle does today, or else with a parachute), while launching shuttles can use airbreathing engines and aerodynamic lift for the beginning of the flight to reduce propellant needed (as the Skylon project is planned to do, and the Pegasus rocket in a sense already does in a two-stage manner). Or for a really radical approach...


"Maybe some of my presumptions are way off. I'm assuming a combination of rocky, metallic, water, ammonia and CO2 ice as asteroids."

Water, ammonia, and CO2? Sounds like the ingeredients for a healthy closed life support system! (Remember, ammonia is the main ingredient of artificial fertilizer.)


"So the cycler factory would spend the 'outbound idle' time preparing foodstuffs for the belters. The belters trade their mineral wealth in. Some/most of the cycler facilities switch to mineral extraction and processing, eventually moving to finished products. As the workforce shifts, agriculture picks up again to provide the next round of food products, particularly for the time that the cycler moves people around."

If you have the technology to build working farmland on a space station, then why not use that technology to put a closed life support where people actually live, i.e. on an asteroid? I see no sensible reason to deliberately send your sole supply of food beyond your reach for extended periods, especially when it also takes a lot of delta-vee to then carry that food to where you need it.

Also, what is the other end of your cycler's trip? It makes no sense to go on a long trip when both the inputs (water, ammonia, and CO2) and the outputs (food) come from/go to the same place (namely the asteroids where people live). It's pointless to just do a flyby past Earth for show unless you're interested in loading/unloading something there (which you just said is difficult).

Milo said...

"The cyclers I'm envisioning don't do much accelerating although there are minor adjustments to keep the cycle just right. All the accelerations need to occur on shuttles/transports/freighters which catch up to the cyclers."

Exactly.

Compare:

1. You put 100 tons of water, ammonia, CO2, and assorted minerals on a shuttle. Said shuttle pays a delta-vee of (arbitrary example) 10 km/s to catch up with a cycler on a particular orbit, docks with the cycler, and unloads its cargo. The cycler then processes all these resources into food. At the destination, the cycler loads 100 tons of food products onto the (still docked) shuttle, then the shuttle pays (arbitrary example) 15 km/s to disembark and match speeds with the target.

2. You put 100 tons of water, ammonia, CO2, and assorted minerals on a transport. Said transport pays a delta-vee of (arbitrary example) 10 km/s to set a course for its destination. Along the way, the transport processes all these resources into food, using equipment that costs only a fraction of the 100 tons of resources moved through it. At the destination, transport (now carrying 100 tons of food) pays (arbitrary example) 15 km/s to disembark and match speeds with the target.

3. You put 100 tons of water, ammonia, CO2, and assorted minerals on a transport. Said transport pays a delta-vee of (arbitrary example) 10 km/s to set a course for its destination. At the destination, transport (still carrying 100 tons of raw materials) pays (arbitrary example) 15 km/s to disembark and match speeds with the target. Here an orbital or surface station does the processing and turns the materials into food.

4. You have 100 tons of water, ammonia, CO2, and assorted minerals on a surface or orbital station, and immediately process them into 100 tons of food, then load those 100 tons of food onto a transport. Said transport pays a delta-vee of (arbitrary example) 10 km/s to set a course for its destination. At the destination, transport (still carrying 100 tons of food) pays (arbitrary example) 15 km/s to disembark and match speeds with the target.

Which of these is most efficient?

Answer: 1, 3, and 4 all cost exactly the same amount of energy and propellant, and 2 only costs slightly more. In each case you're accelerating 100 tons to 10 km/s, then decelerating 100 tons from 15 km/s. However, 1 has far more complicated logistics due to the long off-seasons of the cycler (necessitating many cyclers, which are expensive to make and launch) and the need for precisely timed launch windows to catch the cycler as it's passing. (And if you happen to be grounded that moment due to a solar proton storm your shuttle isn't shielded to deal with...)


"While I'm envisioning an impossibly large cycler, that would itself be dwarfed by the cargo drifting along nearby (mostly netted asteroids)."

Exactly.

If the cycler is dwarfed by the cargo near it, then it's pointless to have one. Cyclers are only useful when their permanent structure is significantly heavier than the payload that's constantly loaded and unloaded onto them. (For our purposes, a shuttle matching speeds with the cycler but staying outside still counts as "loading", since that's by far the most expensive component of a docking maneuver.)

Milo said...

"If your guiding principle is "What is likely to happen with current economies?" then forget about space travel because it just isn't profitable. If you want cyclers, these are some plausible ways to get them into the system. Not plausible in their own right, but as part of a greater space economy they do work."

All space travel might be a dubious proposition, but some forms are more dubious than others. I can reasonably deduce that task A will always be easier than task B under any future technology assumptions that obey presently known physics, even if both task A and task B are currently impossible.

It's like how giant mecha are an unlikely form of military vehicle, but if someone did develop them, I can be reasonably confident that they would be made of strong structural materials and not rice paper.

Byron said...

You completely missed the point of number 2. I said that the point of a cycler was to avoid having stuff accelerated repeatedly. The cycler is accelerated once, but stuff has to be moved to and from it. Thus, it only makes sense when that stuff can be supported by the cycler.
Here's the earthbound version of your cycler:
I'm founding a company to build a ship. This ship will be built for the following purpose:
1. It takes on wheat. It then sails to a country that needs bread, turning the wheat into bread in it's onboard bakery.
2. It reaches the destination, and trades it's bread for crude oil.
3. As it returns, it refines the crude oil onboard.
4. It trades the oil for wheat.
5. Repeat 1-4.
Would you invest in this company? I know the analogy isn't perfect, but your idea only might make a profit if everything works perfectly. If there's a solar storm or something, then the entire multi-year run is wasted. Plus, the duty cycle for both the food and processing factories is bad. I could build a factory half the size in Earth orbit or at the asteroid, and have it work all the time, and get the same amount of stuff.
Also, the belters likely won't like having to get all the food, or even just the good stuff, from you. It seems that you could just withhold it if you wanted more metal.
The limited launch windows also argue against the cycler concept. The belt station has to have a big enough mass driver or whatever to launch everything all at once. It then sits unused until the next cycle, two years or whatever later.
To sum up, let's say that Milo and I decide to set up an belt-mining business together (I'm presuming, but we're arguing the same side). Joe decides to set up his own. We each are going to set up a colony of miners, and deliver our product to LEO in finished goods. Let's compare costs:
We have the same miner labor costs, as neither method has an advantage there. We both have to ship our people out and back. Incidentally, I think that there won't be any permanent belter colonies. Belters will be on long-term contracts. Spend twenty or thirty years as a belter, then come back to earth and retire as upper middle class. It's because it's too hard to ship stuff out that far to allow a reasonable standard of living, at least in this scenario.
Mining equipment costs will also be the same. We're producing the same amount of resources.
Transport costs will favor us. We have one ship that makes occasional runs to move people. It is small, and has a small crew. The cycler is much larger, and has to be launched. That will be a huge startup cost. Also, it requires a larger crew to run the stuff. Ours only takes a crew to keep the ship running. Our mass driver can be smaller, as it can be used pretty much constantly.
Factory costs also favor us. We have to launch our farm out, but it's half the size of Joe's. Also, we don't have to accelerate stuff to it. Our factory can also be half the size, and it stays in low orbit, where personnel costs are lower.
Also, our model is more tolerant of failure and of economic swings. Joe is likely sunk if his cycler's Earth pass happens during a depression. Also, he looses out on booms, and only gets revenue once per pass. We have a constant stream of goods and revenue.
The question is, who would you invest in?

Thucydides said...

If the cycler does the processing/growing stuff as a secondary duty during the "down" periods, then it might make a bit of sense. The primary revenue source is transporting passengers, but since you are already out there, you can take on extra mass in the form of metals or volatiles on the leg inbound (passing the Asteroids on your way to Earth) and grow and sell food on the outbound leg (Earth to the Asteroids). The crew stays busy, there is the possibility of extra cash for the company and the owners and the asteroid miners have a somewhat predictable market. Large fluctuations can be evened out if multiple cyclers ply the route. Each individual cycler might take 2+ years to make a pass, but if multiple cyclers are timed to pass a planet every 6 months, then a fairly constant market begins to evolve.

Citizen Joe said...

Let me run these numbers:
At apogee, one MILLION tons of raw materials are loaded into cycler orbit at a cost of 1 km/s. During the long return trip, that million tons is processed into 100 tons of useful product in space and 10 tons of re-entry grade product (arbitrarily He3). As the cycler passes Mars, the shuttles pay 10 km/s using up maybe a third of the waste materials as remass to debark maybe half the finished space products. The cycler continues to Earth where the rest of the waste material is used as remass for a 15 km/s orbital burn. The balance of the 100 tons of space product and 10 tons of premium goods are dropped off for mega profit.

Processing on the way means you only accelerate the waste ONCE. As things get refined, waste shifts from 'cargo' to 'propellant'. By the time you reach your destination, your cargo is value added, reduced in mass and increased your propellant.

Now you could simply gather all your materials on site and refine everything to finished product and then send the finished product to Earth directly. But the problem there is why are you shipping stuff back to Earth when you can use it locally?

Milo said...

Or you could process directly at the mining station, and then you could accelerate the waste ZERO TIMES. Meaning you just saved the effort of accelerating 999890 tons to 1 km/s.

In addition to not having to build multiple factories (for your multiple cyclers to make up for their long orbital periods) and accelerate them to cycler speeds.


"But the problem there is why are you shipping stuff back to Earth when you can use it locally?"

Umm... yeah. Good question. Why are you?

Why load stuff on a cycler to Earth if you aren't even interested in shipping it to Earth?

Byron said...

I'm fairly certain if you go to both Earth and Mars, your apohelion will wander in the asteroid belt. That might make it a bit difficult to set up long-term bases. Milo made the point about the waste already, but the whole thing strikes me as a rather Rube Goldberg way to do things.
Actually, the root of the problem seems to me to be that you're thinking like a writer, not an engineer. A writer says "What can I do with cyclers? Oh, I know, I'll use them to help mine the asteroids." An engineer would say "I'm going to mine the asteroids. What's the best way to do it? A cycler with processing on it? No, because we only get to process for half the time. And there's the waste acceleration issue. (Sidenote: What do you do with the rest of the waste? You're going to have a giant cloud of rock dust flying around your ship. If you did launch any, it'd be just enough for the shuttle's mass driver.)
How about we send the asteroids back to Earth and process them in LEO? No, because that takes a lot of energy, and we also have giant asteroids headed for earth. We can refine the metal there, then send it back here. That sounds like a good idea."
Another problem. Where is this He3 coming from? I don't think asteroids have that much. They'll have less than Luna, actually. (Inverse square law.)
I would think that only processed stuff is allowed to be shipped to Earth. If your processing ratio is anywhere close to correct, then the full asteroid would make a tremendous weapon if anyone got crazy.
I can only see cyclers being used for cargo if tether transfer is being used. There is no reason to put more capacity on board then is needed for the primary job, passenger transport. After the pass, the crew shuts most stuff off, and the life support recycles. Anything else is just pleading. Why add extra life support when it costs money and delta-V, and doesn't really benefit the main mission. Even then, I don't know how long cyclers will be a good choice. You have the issue of limited launch windows, which you can't alter.

Anonymous said...

Cyclers are not spaceships; they are space stations that aren't in planetary orbit, but in solar orbit. This is a serpintine or eccentric orbit that as it loops around the sun, passes close to Earth at some point in the orbit, and (for example), Mars at another point of its orbit. The whole point of carrying shuttles on the cycler is to solve the problem of having propulsion systems avalable that take months or years to reach planets; the cycler provides the massive volume needed for life support, spin habs, and passive sheilding space planners thought was needed during the 80's and even the early 90's...Even now, with plasma engines and active radiation sheilding making the concept obsolite before it even gets beyond the blueprint stage.
Using a cycler as a military vehicle would be like taking a supertanker along as part of a carrier battle group.
So, how do you destroy an airbase? Not just damage it, or even make it unusable for an extended amount of time, but to blow it to bits? The same way you would destroy one of these Mobile Bases that are the size of a large space hab or small asteroid; you nuke it. And then the combat ships assigned to its battle constellation will nuke you. That seems like a bad choice all round.
Interplanetary warfare would seem to integrate elements from both naval and air warfare, along with elements unique to space travel. It also occures to me that we really don't need to work too hard to come up with motives for future wars in space; the people who live there (or have vital interests there), will come up with "reasons" all on their own! Just as people have done since before writting was invented.

Ferrell

Milo said...

I don't see how tether transfer would help. Every time your cycler snags a load of heavy cargo on a tether, Newton's third law means that your cycler gets deflected from its course a little, so you have to thrust to get back on course. In fact, getting back on course will cost just as much thrust as a shuttle would have had to pay to dock with you the normal way. (Possibly you'll need to spend less delta-vee, but you'll need to accelerate a heavier load, so the amount of thrust needed balances out.)

Byron said...

That's not exactly how it'd work. The inbound shuttle is released, and snags the tether, which slows it down. On the other end is the outbound shuttle, which gets launched close to the cycler. You basically swap velocities. It's not perfect, but it's better than each shuttle starting and stopping on it's own.

Milo said...

Oh, I get it now. What you're basically doing is trying to set up a perfectly elastic collision between the inbound and outbound shuttles, swapping their velocities without ever bringing the cycler into the equation (in which case why do you have a cycler?).

I'd like to see some schematics for how you plan to have the shuttles use each other as reaction mass...

Byron said...

Pretty much. The cycler is there because the losses will be less if all the shuttles have is passengers. There's a fairly extensive article on Wikipedia. It might make cargo on the long side practical, just to keep it balanced.

Milo said...

If you're willing to put up with the extremely large durations of the "long leg" of a cycler's trip for your return cargo transport, then you should also be willing to put up with the comparatively shorter trip times of a cheapish Hohmann transit.

Cyclers are all about optimizing their short leg at the expense of long downtimes. Possibly useful for people, not so much for cargo.

Oh... I see. You're carrying people on the short leg, and cargo of equal mass on the long leg (since you need to be carrying equal mass in both directions for this to work). Okay, but then your cargo would only mass as much as your people do (without long-term life support). Which means you won't be carrying very much cargo, only a few premium packages. Except that premium packages normally want fast travel. What you're doing is carrying small amounts of cargo that take a long time to arrive - not a very lucrative business proposition. You might do it anyway since you need ballast for your tether system to work, so you might as well try to carry somewhat valuable ballast if you can, but I can't see that being the main form of cargo transport in the solar system. Especially when compared to Hohmann barges.

Byron said...

I never said it was. It's just the only way I can see a cycler carrying cargo on a regular basis. Joe keeps pushing for cargo cyclers, and I just thought that tethers might allow some cargo as ballast. It wouldn't be a primary transport method, but it's a possibility, and it might make cyclers the really cheap passenger option after they are succeed by faster ships. The infrastructure's there, and it's practically free, so why not? Sort of interplanetary steerage.

Citizen Joe said...

Tether exchange won't work on the shuttles (at least not directly). Let's say the cycler is two days out from closest pass by the target planet. The lander craft would take off and start decelerating and the incoming shuttle would launch from the planet and start accelerating to where the cycler will be. Two days pass and the cycler is 'at the planet' but the lander craft is still decelerating and now dragging behind the cycler. Two more days pass and the lander has achieved orbit while the incoming shuttle has accelerated to the cycler's orbit and is now coasting along beside it. The two vehicles never get anywhere near each other.

Milo said...

Obviously tether exchange would require the shuttles to put up with fairly high forces, as they need to accelerate and decelerate quickly while within reach of the tether. Also, the tether needs to be strong enough to stand said forces. It's definitely not gonna be easy, but the amount of acceleration the shuttles can put out with their own engines isn't really relevant, since they aren't using their own engines for this maneuver.

Citizen Joe said...

The visual analogy would be a train driving by a low hill with tracks up and down the hill running parallel to the tracks that the train is running. One of the train cars detaches (probably at the end) and goes up the small hill with just enough momentum that the hill brings it to a stop at the top of the hill. At the same time, another car gets pushed off the hill and accelerates down in order to hitch on just as the train passes the junction.

The tether in this analogy would be the drop off car impacting the departure car at the top of the hill which pushes it down the hill on the other side. The problem with this is that the train would have been long gone by then.

For the tether to work, the drop off car would have to roll down hill, impact the other car with enough force that it throws the departure car up the hill on the other side just in time to catch the train as it is passing. Translating that scenario to the cycler/shuttle system, it means accelerating to the destination, maintaining all of the orbital differential momentum, then suddenly (in a few seconds likely) slowing down/accelerating to the appropriate orbital velocities of multiple km/s. If we assume a 100km tether and a modest 5 km/s orbital differential that's a deceleration time of 40 seconds with an acceleration of about 13G. I'm not sure how well a tether could take that strain, never mind the people (now chunky salsa).

By contrast, the same 100 km tether out at the asteroid belt where the orbital differential might be 1 km/s would result in a modest 2.5 G acceleration over a few minutes.

Byron said...

You might have to use a spinning tether, and launch the outbound shuttle, then use the inbound shuttle to make up the difference. It'd work over the long term. I'm just hypothesizing. I haven't worked out the engineering, just throwing out an option.

Turbo10k said...

Cargo cyclers?
I thought that cargo would be sent around the solar sytem like this:
Asteroids and cargo pods roped together around a steel pylon, then with a small drive, accelerated to a few km/s inbound. the tug then detaches and returns to base a hundred times faster or something. Masses involved are in millions of tons, with the whole cargo ship being shared between several companies/space habs. On destination, same man,eouvers, but in inverse. Fluctuation isn't really a problem with the space mineral market as huge volumes only arriving once a few years don't allow room for fluctuation...or at least slow fluctuations. As a rule (well, I think), fluctuation only happens as fast as transports carry goods. If we take 18th century economy, tea only changed prices (I'm talking about sevral percent range, not the whole economic depression/inflation cycle) as fast as the skippers could carry them back and forth. Okay, it might all be total bubb but i'ts what I think happens. I was really thinking that interplanetary economy was parallel to the terran economy in a solar colonisation scenario, slower, with exchanges predictable and cyclic.

Passenger ships are totally different, and akin to those premium value cargoes; they need to get THERE in a few weeks, not years. They would be d-V expensive cargo ships, equipped with the fastest drives, maneouverable and with huge tanks. They are only equipped with enough hab to stay in space for a single trip. If modular in design, it would only LAST a single trip, one way. It's reassembled for the return leg.

Now I really don't see why you would include industries on cyclers to cover their costs. Industrial capacity is severely limited by size and available energy, and products produced as such would be very expensive. Anything could be done cheaper at both destinations. Also, you all seem to forget that cyclers don't have crews. How much crew do you need to program something that happens only once a few years, and can be downloaded at destination? Maybe processors need watching over in the future....large life support is wash too. No-one on it, no need it. You could carry oxygen in liquid tanks for destination habs much more efficiently than recyling it constantly on board.

Just my view. Cargo doesn't need ships to be transported, and passengers need brachistone.

Turbo10k said...

Oshii please someone correct the wacky posts :/

Byron said...

I pretty much agree, though I think that cargo will be moved in as small of chunks as is possible. That way, it can be launched by mass driver, removing the tug, and it is less of a danger to the destination. People won't ship full asteroids unless it's pretty much all metal, and likely not even then. It wouldn't take too much of a nudge to send it into Earth.

Citizen Joe said...

There is a very large difference in orbital velocities from the asteroid belt to Earth. For example Ceres is about 18 km/s while Earth is about 30. That's a lot of acceleration if you're going to try turning back afterward. If you do your calculations just right and there are no problems along the way, you can get your cargo to slide right into capture orbit of Earth. If you don't you just committed a war crime against the whole population of Earth.

That being said, I've hypothesized chucking ammonia ice from Titan at Mars with the intent of it burning up and building the atmosphere. But that is quite a different thing that hucking a rock at Earth and hoping to catch it at the other end.

Thucydides said...

Since cargo will be sized to the cheapest method of transport, it will make sense to imagine single 20' ISO containers moving on minimum energy trajectories to their destinations. No ships are needed at all for cargo, only a mass driver or tether at either end.

The futures market is very important, since you are launching cargo with the expectation of fulfilling a contract months to decades in the future. If the actual demand isn't correctly anticipated, then there will be a boom or bust in the market. Only Earth, at the end of multiple "pipelines" from the asteroid belt to deep space, will have a fairly constant flow of goods coming in.

The delta V to go from the Earth to the Moon and back is also 4 X that of going just to the Moon; since the delta V "costs" will always be higher (and the Moon is pretty depleted in most items a space civilization needs like water, carbon, and nitrogen), I still see NEO's as being favoured over the Moon.

One suggestion that does make sense is to make the Moon a fortress with the sensors, weapons and base facilities to protect the Earth from impacts from natural or man made objects.

Turbo10k said...

In other words, use Luna as a sort of gateway to earth orbit...

I see cargo shipping, at such scales and with such potential for destruction as being reserved for national interplanetary transport systems. Much like today, where you pay NASA to get your satellite into space, you'd have several large asteroid mining companies renting cargo space onboard these large cargo ships, with leftovers for smaller enterprises. Responsibility for accidents would befall the whole nation though, prompting military action or something, instead of a trial for a single company... On the time-scale of decades, I'd be worried if the enterprise assuring the transport of several million tons of rock and ice, heading my way, becomes bankrupt due to separate investments and finds itself incapable of assuring my end, and I'd have to go dispatch some rescue ships to divert/catch it.

I don't think however, at 1-2km/s the cargo ships would pose much of a hazard, since you have ample time to intercept and erase errors in trajectory, years ahead of destination. Drone work ensues.

Flash idea! We have a nuclear electric/thermal/fusion/whatever drive accelerate the cargo net separately from the outer planets on the inward leg, using a tug. On the other end of the cargo net (I'm using net as it's so denuded of structure, a net is all that's left) we'd have a solar electric ion drive, providing fantastic Isp, but cheap nonetheless. As it approaches inner solar system, we can use the increased sunlight as energy for the ion drive, something we can't do all the way from Jupiter or Saturn.

PS: The 100 Megaton figure was based on the potential cargo capacity of a single Orion surface-to-orbit launcher, time a hundred for a looong trip. It was meant to be the Earth-to-Other ship, carrying rare processed chemicals, expensive electronics, mining equipment and bulk mechanical stuffs needed to make a space hab in one load. Coming back, loaded with gases such as He3 and space industry products, an inbound Other-to-Earth ship would be Much less massive, up to the kiloton range maximum. This leads to a situation where you have E-t-O ships being big, heavy and slow, then returning much less loaded and proportionately faster, zipping back for a second load.

Turbo10k said...

PS: The 100 Megaton figure was based on the potential cargo capacity of a single Orion surface-to-orbit launcher, time a hundred for a looong trip. It was meant to be the Earth-to-Other ship, carrying rare processed chemicals, expensive electronics, mining equipment and bulk mechanical stuffs needed to make a space hab in one load. Coming back, loaded with gases such as He3 and space industry products, an inbound Other-to-Earth ship would be Much less massive, up to the kiloton range maximum. This leads to a situation where you have E-t-O ships being big, heavy and slow, then returning much less loaded and proportionately faster, zipping back for a second load.

Turbo10k said...

Okay now please tell me what's the problem. I've got the full post that I've been notified as too long. By the time I break it up into two, I find the original post attempt strangely successful. Completely OT but will save me lots of trouble...

Milo said...

Turbo10k:

"I thought that cargo would be sent around the solar sytem like this:
Asteroids and cargo pods roped together around a steel pylon, then with a small drive, accelerated to a few km/s inbound. The tug then detaches and returns to base a hundred times faster or something."


This could be a good option if spaceships are expensive. If cargo tugs are cheap enough that you can afford to have several in operation at a time, then it's cheaper and less failure-prone to send them along with the cargo, rather than having the source and destination planets each use their own tugs.

Remember that during the coasting phase, you can power down the tug's machinery, so it's effectively costing you nothing except for the opportunity cost of having the tug out of service for several years.


Byron:

"I pretty much agree, though I think that cargo will be moved in as small of chunks as is possible."

No. Cheap cargo launch is constrained by Hohmann windows, so non-premium products would be stocked up and then launched in one go in large chunks. For cargo between gas giants and Earth, this means one chunk per year in each direction.


"People won't ship full asteroids unless it's pretty much all metal, and likely not even then."

Keep in mind there are asteroids of different sizes. They probably come in considerably smaller sizes than we can currently detect. Some might be small enough that you can plausibly treat the entire rock as a piece of cargo, although I don't know if it would be economical to collect such small and widely-spaced rocks as opposed to setting up a mining station on a large asteroid (which is technologically more complicated, but requires less space travel).

Milo said...

Thucydides:

"No ships are needed at all for cargo, only a mass driver or tether at either end."

You're assuming that mass drivers are cheaper than ships. A large amount of thrust is probably easier to apply when you're able to perform it in-flight over the course of hours or days or even weeks, which is still "instantaneous" relative to a Hohmann trajectory, as opposed to having to supply the full thrust before your cargo mass leaves the muzzle of your gun. Also consider the engineering challenges of using a mass driver for deceleration - effectively trying to slow down a bullet by catching it with your own gun barrel.

And again, attaching the engine to the cargo costs you nothing except for the opportunity cost of having that engine out of service for several years. If you can afford a huge interplanetary mass driver, you can probably afford several barge engines.


"The delta V to go from the Earth to the Moon and back is also 4 X that of going just to the Moon;"

Is not, unless you want the full round-trip to take the same amount of time the one-way trip took. If you're willing to have the round-trip time take twice as long (once to get there and once to get back), which is also how terrestrial vehicles behave, then it only costs 2x of the delta-vee. Furthermore, a mature moonbase would be able to refuel your propellant.


"and the Moon is pretty depleted in most items a space civilization needs like water, carbon, and nitrogen"

It has water. Not enough to cover the entire surface in a thriving rainforest, but enough that we can probably build an "oasis" that is large enough to support a decently-sized moonbase.

Nitrogen and carbon are bigger issues, admittedly.


"One suggestion that does make sense is to make the Moon a fortress with the sensors, weapons and base facilities to protect the Earth from impacts from natural or man made objects."

I analyzed lunar fortress tactics here. Luna would make an attractive forward base (even if just to mine reaction mass) for anyone attacking and especially blockading Earth, therefore fortifying it against being captured is important. If weapon ranges are long enough, one can also make use of the lack of atmosphere and lower gravity to get more efficient surface-to-orbit weapons.

Building those defenses, though, requires a fair amount of industry and construction ability, and probably some human operators. Once you have that, you already have most of the infrastructure needed for a moonbase. At that point it costs you little to develop the other economic uses of a moonbase.

I expect that civilian colonization of Luna will come first, and the fortifications will be developed by Luna's government once the colony is sufficiently mature and politically significant to have a government. (Which may or may not be independant.)

Milo said...

"I see cargo shipping, at such scales and with such potential for destruction as being reserved for national interplanetary transport systems. Much like today, where you pay NASA to get your satellite into space, you'd have several large asteroid mining companies renting cargo space onboard these large cargo ships, with leftovers for smaller enterprises."

Yes. Due to the need to launch cargo in large chunks, as I described to Byron above, there would be only a (relatively) small number of barges in service, carrying all the planet's cargo. The shipping company might or might not be privatized, but it isn't possible for everyone who has cargo to ship to operate their own transports.


"On the time-scale of decades, I'd be worried if the enterprise assuring the transport of several million tons of rock and ice, heading my way, becomes bankrupt due to separate investments and finds itself incapable of assuring my end, and I'd have to go dispatch some rescue ships to divert/catch it."

A spacelaunch company going bankrupt would have little if any effect on ships already in transit, which still have all the fuel they loaded on them before they went bankrupt - it just means they won't have the funds to launch new ones. The biggest issue would be ensuring that those ships continue to be supervised by ground control (which is relatively cheap).

Most likely there will be some legal mechanism in place to ensure bankrupt companies only fully dissolve once their last ship has arrived at its destination.


"Flash idea! We have a nuclear electric/thermal/fusion/whatever drive accelerate the cargo net separately from the outer planets on the inward leg, using a tug. On the other end of the cargo net (I'm using net as it's so denuded of structure, a net is all that's left) we'd have a solar electric ion drive, providing fantastic Isp, but cheap nonetheless. As it approaches inner solar system, we can use the increased sunlight as energy for the ion drive, something we can't do all the way from Jupiter or Saturn."

For nuclear reactors, power density is more difficult to come by than energy density. What this means is that once your nuclear reactor is powerful enough to last you for one burn, it probably has enough fuel for two burns, making it pointless to put solar panels on a ship that already has a nuclear reactor. A solar-electric thruster would also have very low acceleration.


"This leads to a situation where you have E-t-O ships being big, heavy and slow, then returning much less loaded and proportionately faster, zipping back for a second load."

Nah. You'd still be trying to go for Hohmann orbits. Thus, heavier loads would be more expensive to ship, but not faster or slower.


"Okay now please tell me what's the problem. I've got the full post that I've been notified as too long. By the time I break it up into two, I find the original post attempt strangely successful."

What error message did you get?

If after clicking publish, you're returned to the message-entry form with a red error message under it, then your message is too long. Edit it down with the conveniently supplied form and publish again.

If after clicking publish, you're shown a page that's almost completely empty except for an error message, with no form, then your message went through fine. This is a spurious error message, ignore it. Just go back and reload the thread.

Also, you can click preview before publishing. This'll tell you properly if your message is too long without the above confusion.

Rick said...

I deleted some dupes - I hope I only got the dupes.

Blogger seems to give over-length warnings, then post the comment anyway. If you get the warning, instead of splitting your post and re-posting it, save it in Notepad or equivalent (just in case), then refresh the comments and see if the original post showed up.

Thucydides said...

Actually, the ISO containers in space idea is far more efficient than a ship, since you effectively have eliminated virtually all structure, fuel, remass and engines (although a small engine for course correction might be supplied. I'd go for a magnetic or electrostatic sail to minimize mass and power).

You are right a Hohmann orbit has very limited windows, but shipping cargos worth $8 million/kg like 3He would allow you to explore alternatives like the "interplanetary highway", which open a much wider range of options. If you are really keen to FedEX your products, then invest in a large enough magnetic or electrostatic sail to get enough delta V to sail to the market after boosting from the mine/factory, a very minimal "ship" with a small fraction of the cost of a "barge" or container ship.

Using some form of mass catcher to decelerate cargoes should not be such a big deal; the device would look like a huge funnel, or even rings in orbit separated by tens or hundreds of kilometers. A rotating tether would also work, and be mechanically simpler.

The Lunar "Fortress" could be simplicity itself, a telescope and radar array, and a nest of nuclear "shaped charges" which blast material at the offending object at a large fraction of c.

Citizen Joe said...

I toyed around with a mass catcher/launcher system which was many rings with shock absorbers between them. Catching and launching caused a LOT of heat build up so the rings used water ice as ballast and heat sinks. A catch scenario would usually eject a big cloud of steam into space nearby which would slowly condense back around the station.

Byron said...

I was thinking about throwing around big asteroids. I admit that small ones will likely be diverted whole, but those won't do much damage to Earth. Turbo, what's this about 1 or 2 km/s. Stuff coming from the asteroid belt will be going a lot faster. If it's NEOs, then not as much, but big rocks will still be dangerous.
The thing about a mass driver as opposed to engines is that you're not strictly tied to the Hohmann windows. Cargo not in the windows will be more expensive, but it will still get there. I just can't see people only launching cargo every couple years. Economies will not work that way. People will launch as often as possible, because nobody wants trade goods sitting for years in a warehouse, waiting for the next window. They'll just figure out a way to launch them on different orbits. It might be more expensive, but people aren't that patient.
Note: the above only applies in cases of large amounts of interplanetary commerce. If all we have is a few researchers, and maybe a trinket vendor or two, then the above does not apply. I'm assuming we're in a setting that has enough people to have wars and such. We really need an actual setting, because as often as not, these debates seem to spring from different assumptions about environment.

Milo said...

Thucydides:

"Actually, the ISO containers in space idea is far more efficient than a ship,"

You can have it both way, with an ISO container pushed by a tugboat that has little structural mass of its own.


Byron:

"The thing about a mass driver as opposed to engines is that you're not strictly tied to the Hohmann windows. Cargo not in the windows will be more expensive, but it will still get there."

That also applies to engines. You need more propellant and energy, but Hohmann barges use quite little of both under normal conditions, so they can probably be turbocharged quite a bit - even if not to the same levels as actual express liners.


"I just can't see people only launching cargo every couple years."

Actually, for most routes the duration of the trip is a bigger issue than the frequency of windows. For an Earth-Saturn trip, a Hohmann trajectory takes about 6 years and can be performed once a year. Therefore, unless you apply enough brute force with your engines to be able to perform a steep orbit significantly more than six times faster than a Hohmann trajectory, it's pointless to complain about having to wait for launch windows.

If there's a lot of demand for cargo that takes less than six years to arrive, then there might be several scheduled transports at different durations. (One 6 year transport service, one 3 year transport service, one 1 year transport service, etc.) These would each have once-a-year launch windows for optimal efficiency, but these won't be the same once-a-year launch windows.

Doing the Saturn-Earth route in significantly less than one year requires a super-expensive engine barely less powerful than the ones on your passenger liners - you know, the one that have a power density comparable to the most high-end estimates of fusion reactors.


"Note: the above only applies in cases of large amounts of interplanetary commerce. If all we have is a few researchers, and maybe a trinket vendor or two, then the above does not apply."

I would say the opposite. You can afford to ship small trinkets on fast express ships, probably tucked in some corner of your existing passenger liners. If you have large amounts of bulk cargo, however, then it becomes crucial to ship all that mass in an efficient manner.


"We really need an actual setting, because as often as not, these debates seem to spring from different assumptions about environment."

Yes indeed.

However we can still try to debate about which environments would lead to one kind of situation, and which environments would lead to another kind of situation.

Or you could work in reverse: start with a situation you want to bring about, and then try to figure out if there's an environment that justifies it.

Milo said...

I said:

"Doing the Saturn-Earth route in significantly less than one year requires a super-expensive engine barely less powerful than the ones on your passenger liners - you know, the one that have a power density comparable to the most high-end estimates of fusion reactors."

Oh right, you were talking about mass drivers, not engines. Even so, can you imagine what kind of huge mass driver it would take to launch many kilotons of cargo at several hundren km/s? This would be analogous to trying to fire a space gun that uses the Tsar Bomba as a propellant charge.

Turbo10k said...

What I meant about the tug and the ion engine:

The Tug uses a high energy density drive, up to torch if needed. It accelerates the massive cargo net, then returns to base to accelerate the second one. This uses up the several cycles a Nerva or such is capable of. On the net, opposite end, we have some solar panels and an Ion drive with Fantastic Isp. Instead of a heavy acceleration over a week or so, it takes a long slow weak deceleration using its ion drive. This way, you decelerate cheaply, AND keep tug at base for second use. Otherwise you'd have to build one for each net :/ Not economic if you're shipping rock.

Milo-Mass drivers at those scales would probably be massive coil guns replacing high power with incredible length.

Thucydides-Most, if not all, current sf setting want fast interplanetary transport, space war and exoplanets, then work back from there to provide audience with enough technoblabble to keep 'em happy.

Citizen Joe-For such a large mass driver to exist, I think it should be built in space, operated in orbit or around a space hab to save on structural support. However, getting materials to build it as well as lots of ice to replace the one you lost as steam favours a large planetary body...Where did you put it? Also, how long does it take to recondense the steam? Based solely on gravity pulling it together, it'll take as long as it took comets to form out of protoplasma or something. Not economic if you can fire it once then wait several decades for the shock absorbers to recondense...

Milo said...

Turbo10k, look at it this way.

Your approach:
1. Accelerate cargo+tug to interplanetary speeds.
2. Fully reverse tug's direction and have it return to the planet it took off from.
3. Wait a long time, doing nothing and expending no resources (at least for that cargo batch).
4. Have a different tug set out from the destination planet, intercept match speeds with the cargo, and latch on to it.
5. Decelerate cargo+tug to the destination planet's reference frame.

My approach would perform only steps 1, 3, and 5, skipping 2 and 4. Your approach costs strictly more than mine, since you perform all the burns I do and more.

Additionally my approach is more failure-tolerant, due to not being so reliant on an accurate intercept course on step 4, and due to the cargo having engines attached for emergency course corrections if necessary (even though it would have those engines idling and using no fuel under normal conditions).

The disadvantage of my approach is, as I said, the opportunity costs of having the tug be out of service for up to several years.

Once you're already on a course to a planet, it's easier and cheaper to keep going there than to stop and return to where you started, even if you're still only 0.001% of the way to your destination.


"This way, you decelerate cheaply, AND keep tug at base for second use. Otherwise you'd have to build one for each net :/ Not economic if you're shipping rock."

This depends on how many cargo shipments you make. For an Earth-Saturn Hohmann route (yearly launches in each direction that take about 6 years to arrive), you would need about a dozen barges in your entire fleet. That may sound like a lot, until you realize that it's the backbone of multiple planets' economy, at which point it suddenly sounds like quite small compared to the number of merchant ships in existance today or in the Age of Sail. If you do have fleets of merchant ships all over the place, then objections totally evaporate.

If you're using steeper-than-Hohmann routes, then you need even less barges in your grand fleet. If you launch cargo less than once a year (which is perfectly reasonable if they take 6 years to arrive), then you again need less barges. Similarly Earth-Jupiter takes less barges, while Earth-Uranus takes more.


"Mass drivers at those scales would probably be massive coil guns replacing high power with incredible length."

Okay. Let's say we want to accelerate something to 300 km/s (for an Earth-Saturn duration of 100 days). Let's furthermore say that your mass driver has a length equal to the entire circumference of Earth, 40000 km.

You then need to perform the entire acceleration in 266.666 seconds, or 4.444 minutes. To accomplish this, you need a continuous acceleration over this time period of 1125 m/s/s, or more than 100 Earth gravities.

(If you want to do the math for other numbers: acceleration = 1/2 * muzzle velocity^2 / barrel length. This assumes equal acceleration over the course of the barrel, which may be the case for some mass drivers but would not be so for, say, chemical guns.)

Milo said...

Errata: 300 km/s is the total delta-vee for the Earth-Saturn trip, not the delta-vee at each end. Thus the described mass driver is actually for a 50-day trip, not a 100-day trip. The 100-day trip would "only" need to accelerate at 28 gees.

But maybe looking at a steep orbit is unfair. Okay, so...

An Earth-Saturn Hohmann has a delta-v of 10.29 km/s at Earth and 5.44 km/s at Saturn.

To accomplish the Earthside acceleration, our superhuge accelerator would need an acceleration of 1.32 m/s/s, which sounds reasonable until you remember that this accelerator is still 40000 km long.

So let's build a more modest accelerator merely spanning the length of Great Britain, or 968 km. Now we need an acceleration of 54.68 m/s/s, or 5.57 gee, sustained for just over three minutes. Perhaps possible, but is that really easier or cheaper than getting the same effect from a much smaller chemical or nuclear-thermal rocket? Also remember that you're subjecting your cargo to 5.57 gee-forces, and any smaller accelerator will need even bigger forces. I hope it isn't fragile!

Turbo10K said...

"which sounds reasonable until you remember that this accelerator is still 40000 km long."

But it's only wires. Nearly no support structure and could be made cheaply. Or better, it could have power beamed onboard. Might be a feat to construct, but wouldn't be a difficulty.

The point I had for suggesting massive mass drivers was that energy density would be less. You's still have to expend equal amount of joules, but over more time and distance. I think it goes down proportionately with distance and squared with time?

"Perhaps possible, but is that really easier or cheaper than getting the same effect from a much smaller chemical or nuclear-thermal rocket?"

Depends on how the engine costs per load (plus propellant) and how much it weighs, again, per load. Adding a high-thrust engine means increase in structure, so it all depends on economy. I see your example used in transport between outer planets, or between moons or space habs in the asteroid belt. However, inner planets have fabulous energy production, AND the benefits of solar power. My inter-system barge combined the two. High-power density tugs at one end, free energy ion drives decelerating it slowly as it approaches inner planets.

"additionally my approach is more failure-tolerant, due to not being so reliant on an accurate intercept course on step 4"

The cargo net uses its own ion engines to decelerate, so no intercept is involved.

Also, keeping the tug is more interesting for a smaller, private company who wants to accelerate two or more nets with a single tug withing the Hohmann window. A robotic, single way ion engine costs much less than a tug...

Turbo10K said...

"which sounds reasonable until you remember that this accelerator is still 40000 km long."

But it's only wires. Nearly no support structure and could be made cheaply. Or better, it could have power beamed onboard. Might be a feat to construct, but wouldn't be a difficulty.

The point I had for suggesting massive mass drivers was that energy density would be less. You's still have to expend equal amount of joules, but over more time and distance. I think it goes down proportionately with distance and squared with time?

"Perhaps possible, but is that really easier or cheaper than getting the same effect from a much smaller chemical or nuclear-thermal rocket?"

Depends on how the engine costs per load (plus propellant) and how much it weighs, again, per load. Adding a high-thrust engine means increase in structure, so it all depends on economy. I see your example used in transport between outer planets, or between moons or space habs in the asteroid belt. However, inner planets have fabulous energy production, AND the benefits of solar power. My inter-system barge combined the two. High-power density tugs at one end, free energy ion drives decelerating it slowly as it approaches inner planets.

"additionally my approach is more failure-tolerant, due to not being so reliant on an accurate intercept course on step 4"

The cargo net uses its own ion engines to decelerate, so no intercept is involved.

Also, keeping the tug is more interesting for a smaller, private company who wants to accelerate two or more nets with a single tug withing the Hohmann window. A robotic, single way ion engine costs much less than a tug...

Byron said...

When I said trinket vendors, I was trying to think of an early industry on Mars, or somewhere. Replace it with whatever will go there first.
If we have near-torch passenger ships, then why are we shipping stuff via Hohmann? If we replace the liner module with something 1000 times heavier, the trip should be 10 times as long. That's considerably shorter than a Hohmann, and gives you a lot of cargo.
And my every few years comment was made with Mars in mind, not Jupiter. People will be even harder-pressed to go out that far via Hohmann. I seriously doubt that serious trading colonization will take place more than a few months travel away. Trading in this case means that it maintains commerce with the mother world, excluding isolationist colonies. Travel is not just time in transit, but the time between when I decide to send a package and it's arrival. I seriously doubt that many people will go farther than that, as they didn't previously. If you look, during the age of discovery, it was about 8 months to India, the outer limit of colonization, and only then because it was richer than the other areas around it. The point is, even if passengers can move faster, cargo speeds will limit the spread of colonies.

Milo said...

Turbo10k:

"You's still have to expend equal amount of joules, but over more time and distance."

No, less time and distance. A rocket can afford to accelerate slowly over the course of many times the size of Earth, taking a few hours or days or even weeks to build up speed, which is still nothing compared to month-or-year-long journeys. Our 40000 km accelerator (I repeat, equal to the circumference of Earth) has mere minutes to build up to 300 km/s. An ion thruster can accelerate at 2 milligee for a week.

Even a nuclear-thermal rocket, while accelerating over the wastefully short times and distances of a mass driver, has the advantage of bringing its engine with it instead of needing large static infrastructure that is capable of providing high accelerations along its full length. Fission-thermal rockets may be preferable over fission-electric ones for Hohmann transfers, several-month Mars missions, and similar low-delta-vee journeys, simply because of their higher power density.


"A robotic, single way ion engine costs much less than a tug..."

Think of my barges as robotic, single way ion engines, that can eventually (years later) be recycled and sent on another robotic, single way mission.


Byron:

"If we have near-torch passenger ships, then why are we shipping stuff via Hohmann?"

Because stuff is worth less, per ton, than human beings, while getting shipped in much larger amounts. Therefore you have to be more mindful of shipping that stuff economically, so shipping costs stay lower than the stuff is worth.

Also, people need life support that scales with how long they stay in space, so turbo-charging your engines, however difficult, may still prove to be cheaper due to life support savings. Unless your cargo happens to be perishable (due to the highly corrosive environment of hard vacuum?), it doesn't have to worry about that. Perishable cargo will probably get made locally rather than shipped through space, unless it's green-fuming Rigellian brandy.


"If we replace the liner module with something 1000 times heavier, the trip should be 10 times as long. That's considerably shorter than a Hohmann, and gives you a lot of cargo."

My "near-torch" Earth-Saturn express is about 100 days. Make that 10 times longer, and your trip takes 2.7 years, or a little under half of a Hohmann transit. That's not that much better. Make it 10000 times heavier instead of 1000 and you're almost to a Hohmann trajectory.

Turbo10k said...

"The point is, even if passengers can move faster, cargo speeds will limit the spread of colonies."

Usually, a cargo ship is sent to set up an unmmaned space hab, followed by the first colonists, engineers and lab coats, totally dependant on home worlds. Then we wait for civilians to fill it up before any more expansion happens (unless you have a parallel project). This is because it is better (economically and logistically) to have a full hab than any number of half filled ones.

I think human factors, economic and how determined the civilians are to leave the homeworld in face of privation and isolation, are more limiting to colonization than technological factors.

Also, the cargo tug and hohmann transfers are all in a near future setting (in around 100 to 500 yrs) where we have colonised up to Saturn using only Space habs and nuclear electric. Torch tugs would mean you could have a single, one piece 'hard' cargo ship, capable of 6 month Jupiter-Earth going in and out inner solar system without regard of gravity slings and transfer energies. You do have a several gigawatts under the boot anyway...

PS: Please note difference between 'soft' and 'hard' ships. A hard warship is like the Star Destroyer or the Space shuttle, very dense and with integral armour. 'Soft' ships are more like Odessey 2001 or the ISS-propellant tanks on the outside, little armour aside from a faceplate, griders making up most of its structure...More realistic but not so cool.

Milo said...

Byron:

"And my every few years comment was made with Mars in mind, not Jupiter. People will be even harder-pressed to go out that far via Hohmann."

I thought we agreed Mars was a boring place to go to?

A Hohmann to mars take 8.6 months and comes up once every 14 months (so unlike Earth-Saturn, the synodic period is longer than the trip time).

That's a little too long for humans, unless they're really bold, but a near-future-tech fission-thermal or fission-electric rockets can do a steeper transit in a couple months.

For cargo... hmm. I'd say just accept the a-little-under-two-year wait time on cargo, but if you want to go faster, you can try for these expensive nuclear rockets to broaden your launch window and reduce the trip to a couple months. I don't know how to calculate pessimal trip times assuming a maximally inconvenient launch window - which is important, because unless you can cope with the 2.2 year synodic period, you're not going to get any benefit out of faster cargo transport.

What kind of propulsion systems are you assuming for this setting?

Serious space scientists have actually proposed sending the cargo for a Mars exploration mission first, then sending the astronauts later on a faster orbit so they arrive at around the same time.


"I seriously doubt that many people will go farther than that, as they didn't previously."

In the Age of Sail, people didn't have unmanned cargo ships. That put an additional limit on cargo trip durations.


"If you look, during the age of discovery, it was about 8 months to India, the outer limit of colonization, and only then because it was richer than the other areas around it."

Hmm. This isn't that far off from a Mars Hohmann. Except that India didn't have launch windows.


"The point is, even if passengers can move faster, cargo speeds will limit the spread of colonies."

The thing is that for bulk cargo (helium-3, asteroid metals, ammonia, MacGuffinite, whatever) throughput is much more important than latency - if 100 kilotons of MacGuffinite arrive every year, you don't particularly care if they were launched yesterday or 5 years ago. What it does, however, mean, is that while stable shipping lines can have high throughput cheaply, new upstart colonies have a very hard time entering the market, since they take years to get "revved up". What I might do in this situation is send the first few cargo shipments on a steeper orbit, as a sort of "look, I have stuff to trade!" proof of concept to help me win contracts, then gradually shift more and more into Hohmann orbits as my company is established.

For passengers, communications, and smaller express packages, latency is more important. Fortunately, unlike the Age of Sail, we can now communicate at the speed of light rather than sending couriers, so that just leaves passengers and express packages. (For passengers, it isn't even so much latency as actual trip time - many people would rather wait 6 months planetside for a launch window and then embark on a 3 month journey, rather than immediately starting on an 8 month journey. Not only do you get to spend less time cooped up in a tin can, but life support is also cheaper.)

Citizen Joe said...

As with much of my designs, there is an ulterior motive to the ice cooling/flash vaporization of the mass catcher/launcher system. It gives a satisfying VWOOSH! when a ship arrives. The five mile long laser star idea started out with the stipulation that it be five miles long. Probably some sort of vicarious phallic representation by the original concept artist. But all of the requirements for the fusion drive made it justifiably long by using a linear accelerator instead of a torus. The concept designer wanted interstellar travel, which would have required more than simple light speed, it would have to be hundreds of times the speed of light. That lead to the Z-P drive in which longer distances (between stars) can be covered faster than shorter distances (between planets). The added special effects of time-space distorting around the FTL events makes for a very interesting visual effect as well as justifying a shock wave (which normally wouldn't travel through space). So ya, I push things to pseudo plausible and then just invoke the rule of cool and be done with it.

Byron said...

You seem to be insisting that if we don't ship cargo across the Atlantic by jet, it goes by sailing ship. There's an enormous difference between a ship taking 100 days to Saturn, and a 6-year cargo trip. The first we can't even begin to work on. The second we can do today. And you keep thinking in terms of early exploration. I'm speaking of mature, developed economies. They will undoubtedly have a faster means of shipping cargo than Hohmann orbits. Even if it's slower than passengers go, it won't be six years to Saturn if passengers make it in 100 days. As I said, the same engine with 1000 times the mass in cargo could make Saturn in 2.7 years, and given that people are a couple of tons apiece, then that's a lot of cargo. Some stuff might move by Hohmann, but that will be super-economy shipping, not the norm for trade goods.

Milo said...

"And you keep thinking in terms of early exploration."

I wasn't. Where did I appear to be talking about early exploration?

In fact, I pointed out a situation where mature, developed economy might use slower orbits than a new one.

Compare technologies used for scientific research versus technologies used for mass production. The scientific technologies are typically highly inefficient, because scientists are just interested in getting something to work that has never worked before, and "we'll let the engineers figure out how to make it more efficient later". A few early spaceflights can afford to be highly inefficient, but a mature economy needs to figure out how to make things cheap, not just make them work.


"As I said, the same engine with 1000 times the mass in cargo could make Saturn in 2.7 years, and given that people are a couple of tons apiece, then that's a lot of cargo."

For the same price, you can carry 11 times as much mass on a Hohmann orbit.


However...

Milo said...

However. Thinking about it some more, I did find something that can justify steep shipments - namely, if the cargo is more valuable than I've been assuming. If a Hohmann shipment costs only 0.1% of the amount the cargo is worth, then you can very easily quadruple (or more) your shipping costs to halve (or more) travel time, without really noticing any dent in your profit margin. If, on the other hand, space travel is expensive enough and cargo worthless enough that cargo is only barely worth shipping (which everyone keeps telling me is the likely prognosis for space trade) - for example, a Hohmann shipment costs 50% of what your cargo is worth - then you can still turn a profit from this trade, but even a small increase in shipment costs will notable influence your profit margins.

So what you have to do is figure out how much your cargo is worth, and how much a given amount of thrust costs.

Milo said...

It is exceedingly difficult to predict what the future will look like, although one thing stands out: the most likely technologies would make space travel cheaper (like fusion power) would be likely to also make local manufacture and production of goods cheaper, meaning your goods are worth less - unless they're something only available in particular places, like gas giant helium-3, or even Tellurian biomass.

But there is one situation where we can kinda sorta predict the economy: namely, when the thing being shipped is also the thing that makes your spaceships go. Let us pretend, for the moment, that helium-3 is so awesomely valuable that (A) it might be able to absorb steep trading costs, and (B) the helium-3 needed to power your reactor is the only significant cost associated with spaceflight, with propellant being dirt cheap and maintainance costs being neglible. According to some quick-and-dirty calculations, sending a ship on the 100-day Earth-Saturn trip costs a total of 54.432 TJ/ton of ship. Let's say 10% of this ship is your reactor, 63% is propellant, and 26% is helium-3 cargo. According to my previous calculation, helium-3 carries 200 PJ/ton for pure helium-helium fusion. (If you prefer, you can instead say you're using deuterium-helium fusion but your reactor isn't perfectly efficient.) A little more math tells me that this express ships needs to burn 0.1% of its cargo in helium-3... which sounds like a non-issue. So much for helium-3 Hohmann barges... unless, that is, propellant or maintainance costs are a serious issue.

If you're carrying anything less valuable than high-energy-density fusion fuel, however...

Well, I'm not an economist.

Milo said...

Okay, let's try another look anyway. In today money, a good benchmark is that 3.6 GJ of grid electricity is worth $100. If your spaceship reactors are based on the same technology as grid power plants, then they may well approach this price - realistically they'll likely be less efficient, but let's ignore that. The total energy for a trip is (1/2 * propellant mass * exhaust velocity^2). This time, let's pretend that 40% of your ship is propellant, then this becomes (4/3 * payload mass * deltav^2). A typically Hohmannish delta-vee, 15 km/s, would cost 300 GJ/ton of cargo, or $8333/ton of cargo. The 100-day trip, 300 km/s, would cost $3333333/ton of cargo, or $3.33/gram of cargo. An intermediate 14-month, 60 km/s trip would cost $133333/ton cargo, $0.13/gram cargo. For comparison, one fairly-expensive-but-not-MacGuffinite material, boron (arbitrarily picked mainly due to its expense and potential value as armor), is worth $5/gram ($5000000/ton), so a 100-day shipment is a bad idea but the intermediate shipment can work. A much cheaper chemical which is nonetheless important in today's economy due to being produced in huge amounts, ammonia, is worth $150 per ton - though possibly far more than that when shipped to a planet/moon where nitrogen is scarce.

What this suggests is that even though doubling speed will quadruple energy costs, energy costs aren't the reason why space travel is currently so difficult. Power reactors, it seems, are a bigger issue than the fuel you're feeding them. Which means these calculations do a very poor job of estimating anything. They do, however, suggest that if the "quadruple price to double speed" rule holds (up to a certain maximum based on your available reactor technology), then there isn't so much justification for Hohmann barges after all. Everyone can easily tune their shipments to cost around 1% to 10% of the cargo's value, unless the stuff is so cheap that even a Hohmann costs more than that. I'll have to think this over some more, I was just taking for granted the "space travel is so expensive that any money you can shave off is worth it" thing.

So again: what you have to do is figure out how much your cargo is worth, and how much a given amount of thrust costs.

Milo said...

What I really want to do is figure out how to calculate trip times from pessimal launch windows... (Related to the current subject, this would help determine if shipping times faster than a year or so are ever worth it, given launch windows for a given trip duration only come up once a year anyway. It would also be useful in a very different context, for determining how quickly warships can deploy in an emergency.) I've already written a program that can calculate optimal launch window trip times given a certain delta-vee.



And sorry about taking up so many posts. I got a little rambly. Sudden paradigm shifts are disorienting...

Citizen Joe said...

Once again, with stable, fungible cargo, the time in transit isn't as important as the annual delivery. A thousand tons of He3 shows up every year, who cares how long it was in space. Well... that isn't quite true.

There is a finite but small chance that some stray rock will hit the barge and destroy it. The longer your barge is in space, the greater the chance of a catastrophic failure. Helium (to be specific) is also hard to hold because it tends to leak out. That will result in an annual loss of stored helium to vacuum. Helium would also need to be held in cryo (dewars) which takes energy to maintain the cold temperatures. That is also a time based cost. There might be a mortgage on the barge and equipment (robots etc). Deep space radiation can have deleterious effects to metal and electronics on an atomic level, which means you can't use that same barge forever.

In the end, slow transport is costly. However, He3 is a special case. Tritium, which is much easier to make than He3, has a half life of 12 years. So if you send tritium (in the form of heavy water) you can use the long time (and decay energy of tritium) to make He3. So rather than process and decay up a thousand tons of He3 and then ship it, you let it process on the way. This also works for wine making/aging. So if you're sending something on a slow boat, make sure that you're taking advantage of the slowness.

«Oldest ‹Older   1 – 200 of 234   Newer› Newest»