3 ms·
> but they will need hundreds of tons of radiators and shielding. NTRs do not need radiators, they can keep cool using the prop. And the mass of shielding is m
by Tuna-Fish 6y ago
> but they will need hundreds of tons of radiators and shielding.
NTRs do not need radiators, they can keep cool using the prop. And the mass of shielding is measured in hundreds of kg to single-digit tons, not hundreds of tons. (You can very effectively reduce your shielding needs by putting the engine on a spar.)
The rest of your concerns are still valid. NTRs seem like they would work better if you are going to asteroids, or other such targets that don't have an atmosphere you can use to brake with, but I do not see the appeal for trips to Mars, where a more compact atmospheric-capable ship can shed half the trip Δv using a heat shield.
- rbanffy 6y ago> they can keep cool using the prop They stay hot after shutdown and you'll still need to cool them to avoid damage. If you use your propellant/coolant for that, the ISP will drop further.
- Tuna-Fish 6y agoYou plan for that in your burn, essentially doing a very low-powered long tail in it. Yes, doing this will slightly reduce Isp, but assuming you can alter the size of the throat on your bell, this effect is just single-digit seconds on the entire burn, compared to the "hundreds of tons of radiators" the GP referred to.
- rbanffy 6y agoA variable geometry nozzle would help a lot here, by keeping a lower volume of propellant to still be ejected at a high speed. May be a good idea after all.
- valuearb 6y agoYou need heavy radiators or your entire ship quickly becomes uninhabitable when the engine is running. We’ve never built a NTR capable of shedding all its heat through its propellant. In fact, we’ve never operated one in space, only on Earth where cooling is trivial.