Eli5: How do rail guns work and why are they not used to launch things into space?

Question

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

Answer 1

Rail guns use electromagnets to accelerate things to high speeds.

An electromagnet is just lots of loops of wire, often around an iron core. When you pump electricity through it, it becomes magnetic. When you turn the electricity off, it stops being magnetic.

Now imagine having a row of these, with a ball bearing sitting at one end. You turn on the first 3 magnets, say, and the ball begins to roll. When the ball reaches the first magnet, you turn it off and turn on mag number 4. The ball accelerates more. It reaches 2, which you turn off and turn on 5. Rinse and repeat. This makes the ball accelerate a lot, until it shoots past then end of the row of (now all off) electromagnets. This is essentially how a rail gun works. It speeds things up by using electromagnets. (This is also how the Large Hadron Collider works, but in a loop.)

Now to rockets. Rockets work by constantly fighting against the force of gravity. They throw a load of expanding gas out the back, and this has pushes them up the way. (Contrary to common belief, they aren’t pushing on the ground at all. It just happens to be in the way.)

The term “launch” is probably a bit misleading, because it gets used to describe releasing rockets *and* projectiles, like our rail gun friend. A projectile is something that gets launched, but doesn’t then have any propulsion. It’s essentially falling. You *could* launch something in to space by throwing it really, *really*, hard. But the speed you need is called the escape velocity. On Earth, the escape velocity is over 11km/s. That is, to launch something to space by throwing it, you would need to make it go over 11km in a second. And that’s forgetting about drag.

So, the reason we don’t use rail guns is because you’d need the make the rocket go stupidly quick through the atmosphere. Either that or build a rail that goes all the way in to space. On the other hand, using rockets to constantly fight against gravity, spaceships can accelerate at a much gentler pace (relatively speaking) the whole way up.