I've seen in some videos of astronauts that they used to use a jetpack type system to maneuver in the vacuum of space around the ISS and other satellites using pressurized gas.
Gaseous nitrogen was used as the propellant for the MMU. Two aluminium tanks with Kevlar wrappings contained 5.9 kilograms of nitrogen each, enough propellant for a six-hour EVA depending on the amount of maneuvering done. Typical MMU delta-v (velocity change) capability was about 80 feet per second (25 m/s).
This is perhaps a convoluted question because of the circumstances that surround my asking of this question. I was explaining to a friend that we don't really "pilot" shuttles to the moon or other objects, rather it is like a calculated throw, a one time launch that will get us to the object because of our velocity, direction, and the gravitational pull of objects in space. To that, she raised the question, "Well why do jetpacks work in space if there is nothing to push against?".
To my knowledge, there isn't anything for the gas to push against. The best answer I could muster was that expelling gas from a pressurized container still results in a force, and according to Newton's Third Law, there is an opposite force pushing the astronaut away. This can also theoretically be accomplished by throwing an object to propel yourself away from the direction of the thrown object.
I would like to know more specifically how a pressurized container creates force if there is nothing to push against, if indeed there is nothing to push against. Another question may arise from this answer, but I will save it for it's own thread.