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PhD Candidate Talks About the Physics of Space Battles
darthvader100 writes "Gizmodo has run an article with some predictions on what future space battles will be like. The author brings up several theories on propulsion (and orbits), weapons (explosives, kinetic and laser), and design. Sounds like the ideal shape for spaceships will be spherical, like the one in the Hitchhiker's Guide movie."
The point that nukes wouldn't generally be useful is a good one. And the point that kinetic weapons would be ideal also makes sense. However, I'm not completely convinced by the emphasis on orbital mechanics. In order for that make sense, one needs space travel to be cheap enough and convenient enough that one can easily have lots of ships in space. If that's the case, one needs efficient enough propulsion systems that will make orbital mechanics not matter as much. They'll still matter probably (and certainly matter more than they do in standard scifi) but I'm not at all convinced they'll matter as much as he makes it out.
Also, he doesn't address the issue that long-range kinetic impactors can make most space combat irrelevant if they are going fast enough. There's not much Earth could do if there were large mass drivers on say Demos and Phobos sending fairly small projectiles at targets on the Moon or Earth or targeting large space installations. Again in this situation orbital mechanics would matter. But when the planets are in the correct positions, such setups would render local space combat irrelevant.
That assumes that there aren't technological advances that allow spacecraft to brute force the problem. Launch delays in terms of orbits mostly occur because of energy and fuel requirements. If you've got propulsion licked, you can pretty well launch when you wish.
That isn't going to work for stealth spacecraft which are a trivial engineering problem next to propulsion. Space is huge, you're going to need very very powerful sensors to find anything the size of a ship.
Correct. Burning fuel just to change the ships' direction is a waste. Utilising conservation of angualar momentum with a gyroscope is efficient and technologically feasible. Sapcecraft that are large and non-sperical are going to be very difficult to manoeuvre. Concentrating most of the ships mass in tight near the center is the way to mitigate this problem.
I don't think kinetic impactors are the way to go here. A high energy neutral particle beam is demonstrated to work effectively and doesn't spread out too much over a vast difference. (not more than a few cm over 1000 km) There is no hope of stopping it either. A few GEV beam of particles shows no mercy and can punch through several meters of shielding.
Lasers ablate material off the hull which obscures the target. Not quite the most effective weapon.
modified plasma window technology can function as a shield in a sense. Thick armor on the hull impedes the ship's ability to rotate.
Ammo is a problem. How many impactors can you have on an orbital defense platform? Just use particle beam technology to wipe out the ground force.
Only if you don't plan on re-entry as a sphere is non-optimal for utilising the effect that shaceship one was supposed to use; that is using a flat surface to force a ubble of air to pool in front of the craft and buffer against the heat.
Sigs are too short to say anything truly profound so read the above post instead.
I thought Neal Stephenson's Gap series had very good handling of space battles. Outside of lasers the weapons were pure fantasy physics, but the battle tactics that resulted from them were pretty realistic. Battles took place at distances on the order of light-minutes, such that your knowledge of the enemy ship's position was perhaps minutes old, your light-speed weaponry took minutes to reach them, and it took that much time again for you to know if you scored a hit. Defensive tactics consisted of trying to move your ship in unpredictable patterns. Ships were often cylindrical so they could have rotational gravity, but this was off for battle. Kinetic weapons existed, but were rarely used since at distances where they had a chance of hitting anything, it would have been basically like two old ships broad-siding each other only with deadly energy beams and in space.
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The problem is that reducing the profile in one direction means you have to make it larger in a different dimension. Now, that's not much of a problem when you're fighting 2D land-battles, but zero-gravity gives you the ultimate 3D battle-space. If your enemy is smart enough to put one fleet directly in front of you while having another flank from the top or bottom, all you've done is make your ships easier to hit.
If you're looking at it purely from the perspective of presenting the smallest profile possible, your best bet would be a needle-shape. Very long, and as thin as possible. However, that runs into other problems, such as maneuverability.
the peace treaty was signed in december 1814. but a major battle in the war, the one that made andrew jackson's name, took place in new orleans AFTER the peace treaty. the combatants didn't hear about the peace until february 1815
http://en.wikipedia.org/wiki/Battle_of_New_Orleans
i think we'll see a return of that in space warfare. sure the wide open vacuum of space changes everything, but so does the sheer vastness of it all. in future space battles, it wouldn't be surprising for a peace to be signed, the agreement beamed to combatants at light speed... and yet the battle still rages on for weeks, months, maybe even years. the battlefield might be lightyears away from the capitols
i don't even know if the idea of central command will work. we're used to modern tom clancy style special operations nowadays where forces engage the enemy while analysts watch them in realtime in pentagon/ cia warrooms as infrared images on massive screens, caught from spy satellites high above
but you can't do that in space
so warfare in space will deevolve from this sort of highly vertically integrated command and control aspect. you can't, for example, have a commander on earth relaying instructions to his troops on mars in real time, simply because the radio signal takes 10-20 minutes, one way (depending upon orbital locations)
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There's little radiant thermal energy directly from a nuke, and even in the atmosphere where there's a lot more, a sheet of bright white posterboard would be 100% eccective as a defense. Drop and cover.
The energy directly from a nuke is mostly expresses as gamma and x-rays. These are planty damaging, but fall off with the square of distance. You'd need to get a pretty large nuke in pretty close to your target to produce more radiation than bad weather. Space this close to the Sun is harsh, radiation-wise.
So the solution is to use the energy of a nuke, but overcome the range^2 thing: nuke-pumped X-ray lasers. This is not a new idea - it's why Reagan's missile defense program was called "Star Wars". For all I know, we have this weapon in orbit already.
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It depends on what axis of maneuverability you're talking about. A vehicle will have a low moment of inertia around its narrow axes but poor about its long axes. Of course, that's why the flak concept is so important -- to make it harder to miss. One concept that the US military threw around for a bit was launching what basically amounted to a missile full of sand/grit into orbit, esp. one counter to the Earth's rotation. You want to ensure damage -- how about being nailed by hundreds of chunks of rock moving at a relative velocity of over 15,000 meters per second? It'd render LEO inaccessible for years.
As for your comments about making yourself more exposed in one axis while decreasing it in others, I think the author actually addressed that point well. Until we have tech that allows for virtually unlimited thrust at virtually no cost, there *will* be orientation implicit in space. You don't just go whatever direction you want in a gravity well, you still need to factor in launch windows, etc.
On that front, I'm reminded of an old game I used to play, called VGA Planets. A very fun multiplayer game, although everyone's empires tended to become too unwieldy to manage after many turns, and players would start to drop out until there was nobody left. In the game, you built various starships (freighters, warships, crew transports, etc) and dispatched them to various star systems to colonize their planets. Your planets and starbases had long-range radar and could detect incoming ships (some being stealthier than others) -- the closer it came, the more data you could get about it. By paying attention to the ship's trajectory and velocity, you could forecast where it was likely to be in future turns, and dispatch warships for an intercept and capture. A clever countermeasure, therefore, was to not always take the optimal route between planets, but to slightly offset your angle and velocity each turn so that if someone tries to set up an ambush, you sail past it. As a counter to the countermeasure, some players would send multiple warships and spread them out along the route, since capturing an unescorted Large Deep-Space Freighter didn't exactly require a powerful fleet. And I would have fun by setting the callsign for my most powerful warships, "Large Deep-Space Freighter", hoping that people who weren't paying enough attention to what they were seeing would mistake the callsign for the ship class (it actually worked several times).
Any way, the reality with space combat is much more boring. There's no way a Mars colony could become truly independent from Earth for many, many centuries. Try to trace back the resources needed to, say, run a CPU fab, or even a nuclear fuel cycle. Modern technology is produced from an unfathomably large web of interconnected part and resource dependencies that we have spread across the entire Earth. And future tech will be even more complicated to produce. So the reality is that if Mars wants to rebel, all Earth needs to do is cut off shipments to them and they'll slowly wither away as things break that they can't replace.
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Actually, nuclear weapons are likely to be far more lethal at great distance in space than in the atmosphere. The atmosphere absorbs most of the radiation from a nuclear weapon. The vacuum of space doesn't. It continues on and on, at dangerous levels for hundreds or even thousands of miles.
A ~50 megaton blast releases ~1e18 joules of energy. At 1000 miles, that's spread over 12.6 million square miles, or about 30 joules per square meter. 1 rad is 0.01 joules per kilogram, so a 100kg mass taking up 0.5 square meters would receive 15 rads. If we assume a Q factor of 5 for a nuclear weapon, that's 75 rem. That's enough to cause radiation sickness. Cut the distance in half (500 miles) and that's 300 rem -- the LD50 for humans.
The danger radius for nuclear weapons in space is *big*. Even if you add in enough shielding to reduce radiation exposure by 95%, and drop the nuclear weapon yield tenfold to 5 MT, you'd still kill over half the crew of the spacecraft from a dozen miles away. You don't really need to be even close. And radiation poisoning is not a nice way to go.
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As far as I know Independence War series (1 & 2) are the only PC games that implemented 100% true Newtonian physics. They took care of movement, heat issues, detection by heat and visual, whole shebang.
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