Imagine trying to start a car that's been sitting in a garage for decades—and the car is 13 billion miles away. That's what NASA attempted to do this week with the Voyager 1 spacecraft—and it worked.
Four of the thrusters on Voyager 1—the only human-made object ever to reach interstellar space—have been dormant since 1980, just three years after it and its twin probe, Voyager 2, were launched into the universe bearing the sights, sounds, and music of Earth on the Golden Record.
For the past 40 years, Voyager 1 has been using "attitude control thrusters" to keep the spacecraft's antenna oriented to Earth so that it can communicate with us, and us with it. The thrusters fire tiny pulses lasting for just milliseconds. For the past three years, they've been degrading, worrying the Voyager team.
Propulsion experts Carl Guernsey and Todd Barber, from NASA's Jet Propulsion Laboratory in Pasadena, California, considered different interventions and how the spacecraft might respond to them. They proposed attempting to start the four "trajectory correction maneuver," or TCM, thrusters located on the back of the spacecraft, hoping they could take over the job of correctly orienting Voyager. In the early days of the mission, these thrusters, identical in size and functionality to the attitude control thrusters, were used to keep the probe's instruments targeted on Jupiter, Saturn, and their moons as the spacecraft flew by them.
They pored over decades-old data and deciphered outdated software code to make sure they could attempt to turn on the TCM thrusters without causing damage to Voyager. Then, on Tuesday, engineers fired them up and tested their ability to orient the spacecraft, using 10-millisecond pulses. They had to wait 19 hours and 35 minutes for the data to make it to Earth, but eventually they got the good news: The TCM thrusters were up to snuff.
Now that the back thrusters are operational, Voyager 1 just got another two to three years of life, Suzanne Dodd, mission project manager at NASA's Jet Propulsion Laboratory, said in a statement. The plan is to shift the orientation work to the TCM thrusters in stages beginning in January. Each requires a heater to operate, and turning on the heaters requires power, which is a strain on the aging probe. So when there's no longer enough power for them, the job will switch back to the attitude control thrusters.
The engineers will likely attempt the same move with Voyager 2 when its attitude control thrusters start to break down; currently, they're in better shape than Voyager 1's. Now in the periphery of our solar system in what's known as the heliosheath, Voyager 2 will enter interstellar space in the next few years. As the twin crafts fly deeper into the universe at more than 36,000 mph, they'll keep talking to Earth for at least a little while longer.