How do MMU's work?

Question

How does an MMU (manned manuvering unit) work?
it uses nitrogen as propellant, but what does it it push against to go?

Answer 1

It works on the same principle as a rocket engine. For every action there is an equal and opposite reaction. Basically the escaping nitrogen pushed on the MMU and the MMU pushes off from the escaping nitrogen. The nitrogen and MMU react against each other. Perhaps it would be easier to imagine if the MMU were firing bullets from guns. The recoil is caused by the bullets pushing off from the MMU. Now think of the nitrogen molecules as trillions of tiny bullets.

Answer 2

The nitrogen gas does not have to push against anything. It follows the principle of for every action, there is an equal and opposite reaction. The gas jet goes one one and the astronaut goes the other way. It is much the same as any rocket engine works, but at a greatly reduced energy level....mass is ejected one way, the object travels the opposite way.

Answer 3

The propellant pushes on the rocket of course. As the fuel goes out the nozzle the rocket is pushed the opposite way with an equal and opposite force. Basic Isaac Newton stuff (his second law).
You could achieve propulsion in space by standing (with your feet locked in) on the spaceship and then throw a baseball in the opposite direction you want to go. The spaceship would have achieved a "thrust" equal to the force of the baseball. Think of two ice scaters standing close together. One is an adult and the other a child. They push each other away. The child would move faster than the adult but they would have gained the same amount of energy (or impulse).