How do spaceships work in space when there is no air to push against?

Answer 1

"Spacecraft use rocket propulsion to move. Rocket engines do not push against air. Off hand I can't think of any engines that push against air. Many engines use air to get the oxygen needed to burn their fuel, but rocket fuel has oxygen in it.

If you put a firecracker beside a small block of wood, when the firecracker goes off it will knock the block of wood away from it. Explosions push the things near them away. You can think of a rocket engine like a series of explosions. These explosions push the rocket along.

Another analogy is like shooting a shotgun. If you have ever shot a shotgun, you know that it has a lot of "kick." That is, when you shoot the gun it pushes your shoulder back with a great deal of force. That kick is a reaction. If you were wearing roller skates or standing on a skateboard when you shot the gun, then the gun would be acting like a rocket engine and you would react by rolling in the opposite direction".

This person has not really understood the question, properly. The reason rocket propulsion allows movement at all is because of Newton's third law of motion; "If body A exerts a force on body B then body B exerts an equal and opposite force on body A".

For propulsion, exhaust gases are forced out of the engine and propelled in a direction which is opposite to that of the desired direction of motion. This also pushes the air in that same direction and so air molecules push back on the engine with an equal force, driving it forwards.

The problem you have in space is that there is no air and so how can a spacecraft mannouvere itself? The answer is that it pushes off its own exhaust gases which it creates. So I would imagine that there is a momentary period at the begining where the craft will remain stationary until the there are enough exhaust gases to allow propulsion.