You have to understand, G-forces is just a measure of the acceleration a body is undergoing, put into terms of the acceleration of objects in the Earth's gravitational field close to the surface.
Perhaps you're thinking that when they say a jet takes off with 5G acceleration, if this number would change in space. The answer is not really (assuming the jet works in space) because this acceleration is horizontal so it isn't really affected by gravity. Assuming the jet managed to produce the same amount of thrust, the "G-force" or accelerations felt by any passengers, would be the same as on earth.