All space vehicles, whether robotic probes or vehicles for human exploration, require electrical power. Electrical power is required to run the computers and control systems, to operate the communications system, to operate scientific instruments, and to power the life support equipment to keep humans alive and healthy in space. For missions to the surface of the Moon or the planets, power may be required to run rovers, or to process material into useful products such as fuel or oxygen. Advanced rocket engines such as ion drives also run on electrical power.

Electrical power sources can be categorized into three basic types: batteries and fuel cells, solar power systems, and nuclear power systems.

For short missions, power can be provided by batteries or fuel cells, which produce power from chemical energy. Fuel cells are similar to batteries, producing electricity from a fuel and...