Pretty straight forward question really. What are rail guns, how do they work and how likely is it that they will replace stage one rockets in the future? Why have they not done so already? Is it feasible? Or would the astronauts just get pasted due to the extreme acceleration?
In: Technology
This isn’t really an ELI5-answerable question, but I’ll try.
> What are rail guns, how do they work
A rail gun is a gun that uses electricity to shoot something instead of a chemical like gunpowder. This is similar to a gauss gun, but a gauss gun uses the electricity to create magnets that shoot the something instead of electricity directly.
If you’re not actually 5, see https://en.wikipedia.org/wiki/Lorentz_force for more details.
> how likely is it that they will replace stage one rockets in the future? Why have they not done so already? Is it feasible? Or would the astronauts just get pasted due to the extreme acceleration?
Almost zero chance. A “gun” of any sort is pretty bad at putting things into orbit. First, things shot by guns start out really fast then slow down due to friction. This is opposite the best way to get into space because it gets easier to go fast the higher you go, so a gun wastes a lot of power going fast when it’s hard and slows down when it gets easy.
Second, starting fast only gets you *into* space. To stay there for any length of time you have to go fast again. So to use a gun you would need to shoot a rocket so the rocket could do the second go-fast part. This is more complicated and less efficient than just using rockets the whole way.
Finally, because guns get slower they have to go really, really fast at first and that’s hard to live through. Especially for humans, but also for delicate electronics and other things you might find on a space ship.
There is a really good reason most space ships use rockets. To move around while in space you need one anyway, and making a rocket take care of the launch as well is relatively simple.
ELI15:
A gun system has zero acceleration ability after the projectile is fired, that is, the projectile is in *free-fall* after being shot. This means your speed is highest immediately after firing, which is when the atmosphere is thickest and losses due to friction are the worst. As the atmosphere thins out and friction decreases, the projectile has already slowed down and has no ability to take advangate of it.
To get into a stable orbit *around* the earth instead of just acting like a really-fast baseball and crashing back to earth you need a second acceleration phase–usually called the “circularization burn” near your peak altitude. A projectile itself cannot provide this, so you would have to shoot something like a rocket anyway. While you’re building a rocket, it’s relatively simple to build a second one for the launch instead of a completely different launch system. Also, as we’ve seen recently, the first stage is the easiest to recovery and reduce costs on, so the “waste” of a stage can be pretty low.
Finally, the acceleration profile of a gun-launch would be massive. Earth’s escape velocity is about 11 km/s. Ignoring atmospheric friction, that’s the speed your projectile would need to be moving when it left the gun. If we assume a 5 km-long gun, that requires an acceleration of over 1000 Gs (12 km/s^2). There aren’t many machines, and no humans, that can survive that. This part is a bit hand-wavy as escape velocity is for *leaving* Earth, and most space flight is concerned with *orbiting* Earth, but the fact that we’re at least two orders of magnitude away from “safe” even without having to deal with friction should be pretty telling.
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