Keeping the lights on
The twin Voyager spacecraft left Earth nearly five decades ago; Voyager 2 left our planet Aug. 20, 1977, with Voyager 1 following shortly after on Sept. 5. Both spacecraft are powered by three radioisotope thermoelectric generators (RTGs) and have a host of instruments collecting and sending scientific data back to Earth. (In Voyager 1’s case it takes about 20 hours and 33 minutes for that data to reach us!)
Now, the RTGs aboard the Voyager spacecraft turn heat into electricity in order to power the probes. That heat comes from the decay of plutonium-238 radioisotopes. However, at this point in their lifetimes, the generators are producing about 40 percent less electricity than when they were first launched.
To keep them running for as long as possible, NASA began aggressively planning which systems to shut off in 2019. But the agency has been tackling the problem of diminishing power for decades now. “After 45 years in flight,” says Cofield, “the power budget is getting to the point where the team has to turn off whatever they can to keep the spacecraft running and doing science.”