The VASIMR engine in the video I was watching could theoretically get from the Earth to Mars in 40 days, but solar wasn’t sufficient to power it. So, that’s why they would want to use a nuclear reactor instead of solar. Since it seems multiple countries, including the US are still interested in a manned mission to Mars, it seems getting their quickly if it’s an option might be a good thing. This thread was merely to ask why we couldn’t use a reactor off the shelf, so to speak since I didn’t see the issues until they were pointed out (which is why this was in GQ and I am not a nuke guy in any way). I was wondering why they were talking about having to build one from scratch and go through rigorous testing when we have reactors on ships and have for decades. I see now why it wouldn’t work. But they were pretty clear that they needed more than solar could provide for their energy budget.
You’d be better served by making solar work. You can see this intuitively. If you get over a kilowatt per square meter, and you can make that square meter of panel weigh just a kilogram (it’s a very, very thin sheet with the circuitry embedded in it), you can make this work. No moving parts , the array would probably look like a very fragile flower with thin cables connecting all the pieces of it to a central truss.
The other option is to just truck a massive amount of fuel to space. You can also intuitively see that this will work. It’s better to do the Mars orbital transfer burn over 30 minutes at 1/3 G with inefficient engines so you have all the velocity right up front than to accelerate at a glacial rate for months.
So SpaceX’s concept is to basically build a reusable, 2 piece ‘space truck’ that is a very large spacecraft that can land and refuel after delivering a payload. So it would make multiple trips to bring enough cryogenic fuel to the spacecraft that will go to Mars, such that it has the delta V of a fully loaded upper stage on Earth or more. 3-5 kilometer/second or more. And then it’s going to burn a big chunk of this right away, bringing the transit time down to 80 days.
Yeah, in theory with the most amazing high power nuclear-electric system you could do 30 days, but what you are talking about is actually really hard to do. Only exotic designs have that kind of power density. You would need to do something like droplet radiators, where you have long booms and the reactor coolant is a liquid metal mix. It gets sent into space as cooling droplets of metal, allowed to fly freely through space for a few hundred meters as tiny micro-droplets, and then gets recovered by a collection boom. This is a theoretical method, only studied in a few NASA papers, that would have to be developed from scratch, but it would work because it lets you have the radiator area of a square kilometer or more without actually carrying the mass for anything but the long booms that make it work.
Even with Elon-Time, if SpaceX had the money they could probably be doing passenger runs to Mars around 2030. This kind of exotic nuclear power technology would take decades and many billions to develop.
And the only advantage of it is less radiation. Once the astronauts touch down on Mars, their rad dose is halved, right away (because the bulk of Mars itself blocks half the radiation) and then if they are living in actual buried habitats, it could be a lot less still.