Posted by rbanffy 1 day ago
Starship is all about a lot of mass to Earth orbit. This is a little mass somewhere between interplanetary and interstellar design parameters. Yes, Starship could put it into Earth orbit, when expendable probably interplanetary, sure.
And it may well help launch it, but that’s where its relevance ends, it’s at the other end of the spectrum of what you would design for. For example, at this corner of the design space, chemical propellants aren’t a thing.
You can expand in parallel. If Starship works you can launch 100 spacecraft instead of 1, or in other words, you can expand your system by a factor of 100 "in parallel" and hence increase whatever you get from that small payload margin by a factor of 100.
Besides that there are other approaches like laser array + photon sail which more directly benefit from mass to LEO.
With 3.5% enriched uranium, about 1/8 of that mass on the power supply is fuel.
Yeah, it's not impossible. But nuclear reactors aren't usually anywhere near 7 times heavier than their fuel.
But then you'll get into severe storage and control problems. And that thing has to work for 13 years, untouched. There's a maximum somewhere on the middle.
Anyway, I don't think reactors on earth are anywhere close to 140 times the mass of the fuel either. And they don't have to use radiative cooling.
Remember that on Earth nuclear reactors create electricity by boiling water to turn turbines. Such a system will be far more difficult to design for space.
On not on earth, but Soviet spatial reactors[1] weren't too far from that:
> The fuel core of the reactor was 0.24 m in diameter, 0.67 m long and weighed, as an assembly, 53 kg,[1][2] and contained 35–50 kg of enriched uranium. The entire reactor, including the radiation shielding, weighed 385 kg.
The problem is yield, out of 100kW of thermal power it was only able to generate up to 3kW of electricity due to lack of efficient cooling in space.
Ok, a bit sci-fi but I had to say it.
It might even be possible to use a modulated retroreflector on the craft-- e.g. we fire a high power low divergence beam at the craft and it reflect it back. By modulating the reflection in can send back data with practically no power usage.
The angles accepted by the reflector could be fairly hard and so the difficult pointing problem would only exist on our end.