Power

Rechargeable batteries store energy from the solar arrays to power a spacecraft through eclipse, at night, or during peak demand. Lithium-ion has largely replaced older nickel chemistries.

The subsystem that generates, stores, and distributes electricity — from solar arrays or radioisotope generators, through batteries, to every instrument and heater on board.

A device that generates electricity by combining hydrogen and oxygen, producing water as a by-product. Fuel cells powered the Apollo and Space Shuttle missions, useful for short crewed flights needing high power.

A nuclear power source that converts the heat of decaying plutonium-238 directly into electricity. RTGs let missions operate far from the Sun or through the lunar night — powering Voyager, Cassini, and the nuclear Mars rovers Curiosity and Perseverance (the earlier rovers were solar-powered).

Panels of photovoltaic cells that convert sunlight into electricity — the primary power source for most spacecraft in the inner Solar System. Beyond Jupiter, sunlight becomes too weak and other sources are needed.