Viewing a single comment thread. View all comments

MetallicDragon t1_j6j7y4l wrote

Reply to comment by iheartbbq in NASA tested new propulsion tech that could unlock new deep space travel possibilities by Creepy_Toe2680

>Oh, twice huh. H2 weighs 2 grams per mole, it will need to be ejected at nine times the velocity of a water molecule at 18 g/mol to have equal the force.

Or just with 9x the mass flow rate. And thrust doesn't matter too much in space, what matters is fuel efficiency. A weaker nuclear rocker might need to do longer burns, but for the same mass of fuel as a conventional engine, it will get you going a lot further.

3

Shrike99 t1_j6jstqe wrote

>Or just with 9x the mass flow rate

You need 9x the molar flow rate, not the mass flow rate. And since hydrogen has 1/9th the molar mass of water, it ends up cancelling out.

2