Voyager 2 comes back online, 11.5 billion miles from home
Plenty can go wrong when you're floating through interstellar space, billions of miles from Earth, running on a radioisotope thermoelectric generator and coming up on 43 years since the last time anyone laid a spanner on you. Last week, Voyager 2 shut itself down into a safe mode after an unexplained delay in a calibration maneuver caused two high-powered systems to come on at the same time, overdrawing the power supply.
Figuring out what went wrong and deciding what to do next was a laborious process, mainly because communications to and from Voyager, traveling at the speed of light, take 17 hours each way. So, any time you give this extraordinary spacecraft a command, you need to wait about 34 hours before you know if it had the desired effect.
Now, NASA has announced that it's turned Voyager 2's scientific instruments back on and resumed collection of scientific data. The rest of the craft is still under review, and the team is slowly running diagnostics to determine when everything else can be switched back on.
Such are the foibles of working with humanity's earliest interstellar machines, particularly given that the twin Voyager spacecraft left Earth back in 1977, and their incredible journey thus far and the observations they have sent back to us from the outer reaches of the solar system have been achieved using technology from before the age of the personal computer.
These kinds of problems will eventually become more common. Their power supplies relies on the decay of densely-packed radioactive plutonium oxide spheres, which at the time of launch were able to supply a constant 470 watts of power. That figure has been slowly dropping over time as the fuel has decayed; its half-life of 87.7 years means Voyager 2 is losing about 4 watts a year right now.
By mid-2019, power was down to about 280 watts, and NASA decided to turn off one of the onboard heaters, which was designed to keep its cosmic ray subsystem instrument within its optimal operating conditions. Remarkably, that system has continued to operate despite dropping to temperatures well below what it was ever tested for, and despite the reduced power available, Voyager is still sending back data from five instruments, many years after anyone expected we'd still be in touch with it. The original Voyager team did an exceptional job on this machine, building in failsafes like this safe mode that have kept it in terrific condition.
At some point, it'll no longer have enough power to heat up its own fuel lines, and it'll lose the ability to aim its antenna back at Earth to speak or listen. Then, off it'll soar into the vastness of interstellar space as a lonely record of our civilization. That'll do, Voyager 2, that'll do. You've done us proud.