Can it be used in the void/space?

As far as I know, yes. I've allowed a player to do so, when there was a hull breach and the majority of the party got sucked out into the void. The techpriest used it to collect people and fly them back to the ship.

Jump pack boosters create thrust , so technically it should work similar to a rocket. And thus indeed be usable in deep space.

https://en.wikipedia.org/wiki/Manned_Maneuvering_Unit

I would, however, make the player test to see if they can actually retain control, for the lack of gravity and resistance mean that, as per Newton's laws, the operator would have to counter their boost manually ... or risk missing the intended target or ungracefully slamming into a ship's hull.

Thanks guys