> But nuclear reactors aren't usually anywhere near 7 times heavier than their fuel. On not on earth, but Soviet spatial reactors[1] weren't too far from that:

> But nuclear reactors aren't usually anywhere near 7 times heavier than their fuel. 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. [1]: https://en.m.wikipedia.org/wiki/BES-5 https://en.m.wikipedia.org/wiki/BES-5