Hello, I'm sure you're familiar with the good old Nuclear reactor. It's a fission reactor that makes a lot of power in conjunction with its steam turbines. The nuclear energy system is unlocked on Nauvis, and in the context of Space Age, that makes it an early-to-mid game unlock. For the planet Nauvis, nuclear power is great for the whole game. Water is endless, and uranium is plentiful. For space platforms it's not ideal because it takes a lot of water and a fair amount of space. Solar panels are so good in space, especially near the sun, that it's harder to justify a reactor on a small platform. If you're mainly going around Fulgora then nuclear becomes more competitive because Fulgora has more ice from asteroids and less solar energy. Later, when you head to the 4th new planet, nuclear becomes a much better option because the solar power is so low and ice is more abundant. At that point, you've had nuclear as an option for all the 5 planets (although you probably don't use it on all of them), and a few space routes, so it's time to unlock a new and exciting energy system.