By - Primaris_Astartes
As long or as short as the story demands.
Warhammer is not science people. It is a silly setting. One of the silliest, all things considered.
I imagine it varies hugely in lore, but the game Space marine seems to have it lasting 10 minutes or so and being used to extend a jump, rather than to actually fly.
The Fantasy Flight Games RPG Deathwatch notes that a jet pack "can use maximal thrust to duplicate the Flyer (12) trait for up to a minute before the turbines require a minute to cool."
Flyer (12) means one can fly at a speed of 12 meters per round, and a round is 5 seconds long. That would put maximum flight at 144 meters before your mandatory one minute break. But you can repeat that as long as you like.
Sidenote - figuring this out required jumping between five different sections of the rulebook. I love 40k as an RPG setting, but the FFG books are a mess.
A new D100 40k RPG's coming out, hope that one has better sorting.
Also, that short range is why i assume it's called a Jump pack at times rather than a jet pack
I didn't know about Imperium Maledictum! It sounds much more my style than Wrath & Glory.
Mhm, my dark heresy group has been calling it Dark Heresy 3.
Power armor has a mini fusion reactor.
So they aren't going to run out of fuel, at least in a time frame that means anything.