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[Cryxis, Prince of Doom]

Me and my friends have been discussing this tricky subject, Can a rail gun launch a space craft with a live crew of human beings without killing everyone onboard from initial launch.

[Cryxis, Prince of Doom]

we are also going on the bases that a space craft has been created that can withstand the high speed launch from a rail gun

[DJ]

It's the acceleration, not speed, that kills. So yeah, you just need a really, really long rail gun.

[Cryxis, Prince of Doom]

even with a realy long rail gun, you go from 0- holy **** in a split second just by turning the gun on

[GiglameshDespair]

The answer is kind of. It probably wouldn't be all the way into orbit by magnetic rail alone, but it would certain provide a cheaper way of gaining altitude than rockets - it would use them to actually achieve orbit and continue on to wherever. This kinda stuff is typically referred to as mass drivers in the sort of civilian space context. So searching something like that might be informative.

There have been designs made for this sort of thing, but obviously, none have got past the designing stage. It would be very expensive to build.

On Earth

In contrast to cargo-only chemical space gun concepts, a mass driver could be any length affordable, with relatively smooth acceleration throughout, optionally even lengthy enough to reach target velocity without excessive g forces for passengers. It can be constructed as a very long and mainly horizontally aligned launch track for spacelaunch, targeted upwards at the end, partly by bending of the track upwards and partly by Earth's curvature in the other direction.

Natural elevations, such as mountains, may facilitate the construction of the distant, upwardly targeted part. The higher up the track terminates, the less resistance from the atmosphere the launched object will receive.[12]

The 40 megajoules per kilogram or less kinetic energy of projectiles launched at up to 9000 m/s velocity (if including extra for drag losses) towards Low Earth Orbit is a few kilowatt-hours per kilogram if efficiencies are relatively high, which accordingly has been hypothesized to be under $1 of electrical energy cost per kilogram shipped to LEO, though total costs would be far more than electricity alone.[9] By being mainly located slightly above, on or beneath the ground, a mass driver may be easier to maintain compared with many other structures of non-rocket spacelaunch. Whether or not underground, it needs to be housed in a pipe that is vacuum pumped in order to prevent internal air drag, such as with a mechanical shutter kept closed most of the time but a plasma window used during the moments of firing to prevent loss of vacuum.[13]

A mass driver on Earth would usually be a compromise system. A mass driver would accelerate a payload up to some high speed which would not be enough for orbit. It would then release the payload, which would complete the launch with rockets. This would drastically reduce the amount of velocity needed to be provided by rockets to reach orbit. Well under a tenth of orbital velocity from a small rocket thruster is enough to raise perigee if a design prioritizes minimizing such, but hybrid proposals optionally reduce requirements for the mass driver itself by having a greater portion of delta-v by a rocket burn (or orbital momentum exchange tether).[9] On Earth, a mass driver design could possibly use well-tested maglev components.

To launch a space vehicle with humans on board, a mass driver's track would need to be several hundreds of kilometers long if providing almost all the velocity to Low Earth Orbit, though lesser length can provide major launch assist. Required length, if accelerating mainly at near a constant maximum acceptable g-force for passengers, is proportional to velocity squared.[14] For instance, half of the velocity goal could correspond to a quarter as long of a tunnel needing to be constructed, for the same acceleration.[14] For rugged objects, much higher accelerations may suffice, allowing a far shorter track, potentially circular or helical (spiral).[15] Another concept is a large ring design whereby a space vehicle would circle the ring numerous times, gradually gaining speed, before being released into a launch corridor leading skyward.

[Telgin]

even with a realy long rail gun, you go from 0- holy **** in a split second just by turning the gun on

That depends entirely on the power of the gun.  It's possible to use weaker magnetic fields to give a more gradual acceleration that can still achieve extreme maximum velocities.

[GlyphGryph]

I think their second record was by far their best, they just haven't been the same since they went pop with that song "Rocking the Rocket".

[da_nang]

Problem is, if we're launching a heavy object, even with a fairly long rails, the current will be huge and might possibly melt the rails.

[10ebbor10]

even with a realy long rail gun, you go from 0- holy **** in a split second just by turning the gun on

You're thinking for use as actual guns.

Actually, he's thinking of railguns as actual guns. They're not. Actual guns have split second acceleration. Railguns have gradual acceleration over the entire length of the barrel.

Anyway, things like these exist in many varieties. Here's one based on maglev technology Link.

On the original question:

Me and my friends have been discussing this tricky subject, Can a rail gun launch a space craft with a live crew of human beings without killing everyone onboard from initial launch.

I depends on your definition of launch, and space craft.  (perhaps also, without killing everyone on board). Some of the nessecairy information required is:
- Does the rail gun have to provide all the acceleration, or can we use an auxiliary engine.
- Do we start at sea level, or are we allowed to construct a 20 km high rail gun.
- What is space? Anything above 100 km, or an actual orbit, or even escape velocity.

In the worst case scenario (ie, no auxiliary power, sea level launch, into orbit and at escape velocity), arceleration won't be you primary problem. Deceleration will be. After all, your spacecraft will suddenly find itself plowing through the sky at speeds somewhat greater 11 km/s, which is slightly problematic.

[Bauglir]

After all, your spacecraft will suddenly find itself plowing through the sky at speeds somewhat greater 11 km/s, which is slightly problematic.

The upside is that you'll be able to ignore some of the problems traditional aircraft have to put up with. Geese will vaporize before they have an opportunity to actually strike your vehicle, probably!

[da_nang]

Problem is, if we're launching a heavy object, even with a fairly long rails, the current will be huge and might possibly melt the rails.

1$ of electrical energy per kilogram.

I suppose that if something's big enough, it could cause those problems.

I think the more immediate one is how we make a near-vacuum that large, without leaks, and plasma shields that won't disintegrate.

Well, to move a 1000 kg vehicle at 1 m/s^2 you'd be looking at a current at the magnitude of 10 kA - 100 kA.

[10ebbor10]

After all, your spacecraft will suddenly find itself plowing through the sky at speeds somewhat greater 11 km/s, which is slightly problematic.

The upside is that you'll be able to ignore some of the problems traditional aircraft have to put up with. Geese will vaporize before they have an opportunity to actually strike your vehicle, probably!

Doubt it actually. The plasma cone isn't that strong.

[Talvieno]

The answer is a flat no. I don't care if we're talking "slow acceleration" or not - "slow acceleration" for a railgun would still be absurdly fast.

The human body can safely survive roughly around 50 G's for a sustained period, although it will slowly damage your eyes and other particularly delicate internal organs. A human can survive 175 G's for a split second, but will still suffer massive internal trauma including (but not limited to by any means) broken bones - but they still survive it. (sources: http://en.wikipedia.org/wiki/John_Stapp, http://en.wikipedia.org/wiki/David_Purley)

A railgun accelerates a round in excess of 60,000 G's. <--- You get in a railgun, you're dead. (source: http://en.wikipedia.org/wiki/Railgun)


Magnetic acceleration, on the other hand, like that used by a maglev, is a different story... but it still probably wouldn't get you into space.

we are also going on the bases that a space craft has been created that can withstand the high speed launch from a rail gun

Good luck with that. Not even the solid metal slugs fired from today's prototype railguns survive even the atmospheric friction - they blow to bits as they're flying through the air, and superheat the air around it to the point that the air catches fire just from the friction:


However, this might interest you: (from the Railgun page on Wikipedia)

Spoiler (click to show/hide)

Electrodynamic assistance to launch rockets has been studied.[16] Space applications of this technology would likely involve specially formed electromagnetic coils and superconducting magnets.[17] Composite materials would likely be used for this application.[18]

For space launches from Earth, relatively short acceleration distances (less than a few km) would require very strong acceleration forces, higher than humans can tolerate. Other designs include a longer helical (spiral) track, or a large ring design whereby a space vehicle would circle the ring numerous times, gradually gaining speed, before being released into a launch corridor leading skyward.

In 2003, Ian McNab outlined a plan to turn this idea into a realized technology.[19] The accelerations involved are significantly stronger than human beings can handle. This system would only be used to launch sturdy materials, such as food, water, and fuel. Note that escape velocity under ideal circumstances (equator, mountain, heading east) is 10.735 km/s. The system would cost $528/kg, compared with $20,000/kg[19] on the space shuttle (see Non-rocket spacelaunch). The railgun system McNab suggested would launch 500 tons per year, spread over approximately 2000 launches per year. Because the launch track would be 1.6 km, power will be supplied by a distributed network of 100 rotating machines (compulsator) spread along the track. Each machine would have a 3.3 ton carbon fibre rotor spinning at high speeds. A machine can recharge in a matter of hours using 10 MW. This machine could be supplied by a dedicated generator. The total launch package would weigh almost 1.4 tons. Payload per launch in these conditions is over 400 kg.[19] There would be a peak operating magnetic field of 5T – Half of this coming from the rails, and the other half from augmenting magnets. This halves the required current through the rails, which reduces the power fourfold.

Along with this: http://en.wikipedia.org/wiki/Mass_driver

edit: had some disassociated side-pane data in the wikipedia quote.

[Sheb]

Talvieno: you can choose your railgun's acceleration. Right now, the goal is to shoot an artillery shell or slug, so we go for quick acceleration, but we don't HAVE to.

[10ebbor10]

Stuff changes based on design, you know. Not each rail gun is the same. That high speed acceleration stuff are numbers for military rail guns, which preferably fire things very far very fast. ((I mean, to stay in the guns comparison, you're saying that based on numbers for a sniper rifle, machine guns can not exist. ))

A railgun is no more and no less than a pair of parallel conducting rails, along which a sliding armature is accelerated by the electromagnetic effects of a current that flows down one rail, into the armature and then back along the other rail. Acceleration is dependent solely on the weight of the object, and the current. Low current, and the object accelerates slowly, like a maglev.

With a long enough rail, and a vacuum tunnel it's perfectly possible to launch a spacecraft at near escape velocity. However, launching it from sea level is near impossible. You'd be experiencing a drag force of 5*10⁵N/m². Assuming a craft weight of 40 tons, you're surface area should be less than 2 m² (at which point you'll receive 25 g's of deceleration.) This is quite unrealistic.

Edit: Here's the Star Tram, which could take people to space..