catbarf on 26/8/2010 at 18:14

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Technically yes, but gases disperse so rapidly in a vacuum that the gas would likely be too thin to support combustion by the time the first spark is becoming a spreading fire. In any case it would be a quick puff and flash of light, but it wouldn't resemble a fire or explosion.



Depends entirely on what propulsion method is used. If it's a primitive chemical rocket, then it needs combustible fuel. But if it's an ion drive, or a nuclear saltwater rocket, or a VASIMR, or NERVA, then no combustible materials are involved, just whatever resource is needed to power the engine (electricity, nuclear fuel rods, etc.) and reaction mass to throw out the back of the ship (likely water).



I would love to see such a realistic movie, but there are three issues with the above. The first is that projectile weapons, due to their travel time, would have a maximum effective range of no more than a hundred kilometers or so- as opposed to lasers and missiles which have effective ranges measured in the thousands and tens of thousands of kilometers (Even rather conservative estimates on future development of laser technology would allow economically-sized lasers from lunar orbit to be hitting spacecraft in Earth orbit with enough focus to do damage). The second is that putting windows on a space ship is really, really dumb, what with all that lethal solar radiation and the fragility of transparent materials. And the third thing is that any space ship would need airtight bulkheads and damage control or it could be destroyed by a piece of debris in planetary orbit.

A space battle would more likely come down to firing lasers, missiles, and railguns at one another until enough damage is done that the reactor fails, the radiators get shot off and the ship has to turn off its reactor to avoid melting, the weapons or targeting systems are destroyed, the ship surrenders, or a lucky shot kills the crew.

Anyone else read (http://www.projectrho.com/rocket/) Project Rho?

Matthew on 26/8/2010 at 18:43

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Well this sounds like a fascinatingly exciting movie guys

Matthew on 26/8/2010 at 18:50

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Oh well if you're having trippy babies then I'm interested

Sulphur on 26/8/2010 at 19:01

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Well, technically lasers can work. Not exactly like in the movies (they're not that slow, being made of, well, light), but yeah

SPACE MONOLITH BABIES - as real as the future, dagnabbit

catbarf on 26/8/2010 at 19:50

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We have all of those right now except the nuclear saltwater rocket, and that's in the research stage. I also forgot to mention the Orion drive, which uses nuclear detonations as a method of propulsion, and is available now.

There are various reasons why these devices aren't used in commercial rockets. Ion engines and the VASIMR have low thrust but high specific impulse- they're 'fuel efficient' but can't get you off the ground (Although the VASIMR has 'gears' that allow it to be either high-thrust or high-impulse, but not both at once). NERVAs rely on nuclear reactors and produce large amounts of radioactive exhaust, and the Orion works by dropping nuclear bombs out of your ship, so they're not suitable for use in atmosphere for ecological reasons.



The problem isn't tracking, it's distance. If your cannon has a muzzle velocity of 1000m/s, it'll take exactly 100 seconds to reach the target. If the target can produce 1G of thrust (9.8m/s^2) and is trying to avoid you, then depending upon how much thrust they apply their location could vary up to 49km from where you aimed- and that's just along the axis of thrust. If they can move laterally with maneuvering thrusters, or simply turn and apply thrust in a new direction, you have another axis to miss the target in.

And this is ignoring that because the shells are slow, the enemy has ample time to detect them, figure out where they're going, and get out of the way or simply incinerate them with a point defense laser.

But, most importantly, compared to lasers, guns are incredibly inaccurate, even in a vacuum. Being able to get the shell on target from 100km away would be impressive, even if the target is moving at a constant velocity. Even a variance of 0.1% will put the shell 100m from where it was supposed to go.

Sneak attacks on transports and stations would get around the first two issues, but since space is very empty, there's no practical way to hide. You can't get rid of heat, only shift it around, so your multi-million-degree exhaust will stand out like a beacon. Even with no engine running, a 273K habitation module is easy to spot amongst the 3K background. So, there's really no way to avoid detection and creep up to point-blank range.



It's been suggested, but assume your target is 100km away, as in the example. Assume their ship is 100m long, so you need to have no more than 100m in between each shot. So basically, you need a projectile every 100m along a 49km stretch (that's 490 shells) to be able to prevent them from dodging. In one axis. Assuming every shot goes precisely on target.

A better idea would be to get up to a relative 3km/s (pretty slow in space terms), fly towards them, and then dump something (anything) in their path- be it chunks of scrap metal or cat litter, at 3km/s it has an energy release equal to its own mass in TNT.



If the laser in question is powerful enough to harm your hull, a bit of confetti in the way won't stop it.