Nuclear ground-orbit vehicle

[Fred Brackin]

Originally Posted by gjc8

Using it once or twice isn't gonna hurt things to badly, especially compared to the assorted nuclear testing done historically.

If you need it for emergency earth-to-orbit vehicles, fine. But if you regularly use it to launch satellites, etc, my impression was it will add up to a serious problem.

The actual problem for NERVA rockets and ground to orbit was sucky power-to-weight ratio even though they had superior fuel efficiency.

Maybe 2, maybe 3x better fuel use for somewhere between 10 and 30x as much engine weight (greater cost too of course). That was with hydrogen too. Water ameliorated the power-to-weight problems while giving away the fuel efficiency. Heat water with a nuclear reactor or create it by combusting H2 and O2 and efficiency is the same at the same temperature.

The real attraction of NERVAs occurs when you can run them for long times but don't have to achieve high Gs. Some of the prototypes were run for 30 minutes to an hour. The Shuttle's main engines with their 8 minute burn times are pretty much unique (and consequently complex and expensive). 2 minutes is more common for liquid fuel rockets.

So 3 Gs for 8 minutes favors chemical rockets. Once you're in space 48 minutes at 0.5 Gs gives you the same Delta-V with 1/6th as much NERVA engine.

It's not obvious that the fuel can't have a sealed barrier between the it and the water/hydrogen reaction mass. Bombarding water/hydrogen with neutrons and gamma rays doesn't create problematic materials. If the actual reactor materials stay inside the engine there are no real pollution problems.

Now, nuclear salt water rockets are an all-around stupid idea but the NERVA type aren't so bad.