Power pack: nuclear power in space

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?

Probes and craft in these regions run off nuclear power. This has a long history, the first nuclear power system for satellites was launched in 1961 and nuclear-powered craft include the Pioneer and Voyager probes, Galileo, Cassini, Ulysses and the New Horizons probe, currently on its way to Pluto; as well as the 1970s Viking landers, the Spirit and Opportunity Mars rovers, and the scientific instruments used on the Moon by the Apollo 12 to 17 crews. These are all still where they were left, apart of course from those to be used by Apollo 13, which are somewhere in the Pacific Ocean.