The basic idea is straightforward: A nuclear reactor rapidly heats up a propellant, probably liquid hydrogen, and then this gas expands and is passed out a nozzle, creating thrust. But engineering all of this for in-space propulsion is challenging, and then there is the regulatory difficulty of building a nuclear reactor and safely launching it into space.
Hmm it seems like we are still relying on a propellant of some kind.
I mean, you will always need a propellant, E=MC^2 after all, even if you’re Pushing with light, you’re still losing mass as you expel that out the back, no matter how you cut it.
The real question is how much work you’re getting out of each unit of mass you toss out they back, and that depends on how fast you toss it. These kinds of engines (nuclear thermal engines) get about expel their reaction mass at about 8000 meters per second, the most efficient conventional engine pushes exhaust out at about 4500 meters per second. So, you’re getting a. It less than twice as much change in the crafts speed per unit of mass used for these kinds of engines.
That may not seem like a game changer, but a 50% increase in efficiency rapidly compounds since most of the mass you’re trying to move with propellant is… well other propellant.
Yeah, how much thrust would you get per kilo of liquid nitrogen? What sort of top speed? Sounds like it would take a decent amount I imagine.
This probably depends on how rapidly you can make the propellant material expand (more force) and how big you can build the expansion chamber/nozzle (more volume).
Practical space propulsion is pretty much just throwing shit out the back of your vehicle as fast as possible.
These kinds of engines get about double the exhaust velocity of high efficiency conventional rockets. (A hydrolox engine like that used on the space shuttle or the centaur upper stage getting an exhaust velocity of about 4500 m/s and a nuclear thermal getting about 8000m/s)
They had a nuclear rocket engine developed and ready to go back in the sixties. Better late than never, I guess.
