Voyagers 1 and 2 have the distinction of being in space for 42 years and still operating. And even though they’re 18 billion km (11 billion miles) from the Sun, they’re still valuable scientifically. But they’re running out of energy, and if NASA wants them to continue on much longer, they have some decisions to make.
The Energy Problem
The energy issue is becoming more and more critical over time for the Voyagers. Not only do their scientific instruments require energy, but the spacecraft need to keep themselves warm in the frigid environment of space. The pair of spacecraft aren’t solar powered: that wouldn’t be possible so far from the Sun. They rely on radioisotope thermoelectric generators (RTG) for their energy.
Each of the Voyager probes has three RTGs, and they use plutonium 238 for their fuel source. As that isotope decays, it produces heat which is converted to electrical energy. Each Voyager launched generating 470 watts at 30 volts DC, but over time that degrades. Not only is the fuel steadily depleted, but the thermocouples used in the system degrade over time. As of 2011, both Voyagers were generating just under 270 watts, which is about 76% of the power they started out with.
While that 270 watts