4 ms·
The implied goal is to send humans to places in the solar system. That means life support, food, water, etc. So a lot of mass anyway. Worse, the longer the trip
by marcinzm 6y ago
The implied goal is to send humans to places in the solar system. That means life support, food, water, etc. So a lot of mass anyway. Worse, the longer the trip the more mass you need to bring onboard. Nuclear would allow for the shortest trip durations while ion engines would be the longest. With ion engines you have the issues of micro-gravity health risks on the crew, psychological risks and the need for a lot more supplies.
- bryanlarsen 6y agoFor super long trips, efficiency is king. Coupled with the ability to ability to burn continuously, solar-electric and nuclear-electric are way more efficient than nuclear-thermal. Ion engines may have low thrust -- just use a lot of them. Nuclear-thermal's Achilles heel is that you can't use it to boost off Earth. So you need a high thrust chemical engine to get it into space. It's hard to make the numbers work -- nuclear-thermal may be more efficient than that chemical engine, but it's dead mass while you're boosting it out of the Earth's gravity well. If instead you can use the same chemical engine to get to Mars that you used to boost yourself out of Earth, you don't have that dead mass. If you want to get to Mars fast, just boost some extra fuel on an extra ship. Nuclear-thermal looks nice on paper; it's probably the highest efficiency high thrust engine that's achievable with today's materials. But it's hard to find a good use case for it. A manned Earth->Mars run used to be it; but SpaceX's plan for in-space-refueling shortens the trip time just as much, if not more.