When NASA’s Juno spacecraft arrived at Jupiter this summer, engineers did a victory dance — and not just because their mission would return the best Jovian data ever. They were also celebrating Juno’s solar panels — the biggest on any planetary probe — taking the mission farther than any other sun-powered spacecraft.
Juno’s solar technology represents a giant leap in space exploration. Before its success, far-out craft used nuclear power. The Cassini mission to Saturn, the twin Voyagers’ trips beyond the solar system, Curiosity’s rove around the Martian surface, New Horizons’ pass by Pluto and Galileo’s close encounter with Jupiter were all brought to you by the radioactive element plutonium-238.
NASA uses dense plutonium “pellets” for fuel. As the atoms decay, they release high-speed helium nuclei and then become smaller uranium atoms. The ejected helium particles smash into the atoms around them. That collision creates heat that the spacecraft transforms into electricity.
