Why is fuel needed to change the speed or direction of a probe in space?

1 Answer
Jan 2, 2016

When you push an object in space, it will continue to fly forever at a constant speed unless the force on gravity acts on it.

Explanation:

This is the reason why fuel is required in space. There is no air resistance to slow down the spacecraft in space, so it will continue "flying" and the fuel acts as a propeller.