Power pack: nuclear power in space The Engineer

With plutonium-238 supplies running low, the race is on to find new power sources for spacecraft
Most of us have a clear image of what a real-world spacecraft looks like. Whether it’s a communications satellite, an Earth observation platform or even the International Space Station, the picture that would generally spring to mind is of a relatively small, probably irregular-shaped body dwarfed by the spreading oblongs of solar panels, providing the power for whatever systems are on board.
That’s fine for Earth orbit or the inner Solar System. But what happens if you need to send a spacecraft further away, where the sun is too weak to provide enough power, or to a place where there is no constant access to sunshine, such as the dark side of the Moon or to Mars?