An artist's depiction of NASA's Voyager 2 probe. (Image credit: NASA/JPL-Caltech) NASA just made an interstellar tweak to the Voyager 2 spacecraft, known as the "Big Bang", to keep its remaining 50-year-old science instruments running a little longer.Voyager 2 and its twin launched in 1977, called Voyager 1, rely on a form of nuclear battery known as a radioisotope thermoelectric generator that uses the heat produced by the decay of plutonium. But the supply of plutonium on each probe drops at a...