But those thrusters had not been used in 37 years.
As humanity's first visitor to interstellar space, NASA's Voyager 1 has revealed itself to be a trooper, answering commands that take nearly 20 hours to arrive, and performing routine tasks and transmitting data back (another 20-hour one-way call) to the home planet.
NASA made the decision to activate the disused thrusters because the thrusters they had been using to adjust the spacecraft's antenna weren't functioning well anymore.
Experts at the agency's Jet Propulsion Laboratory (JPL) in California made a decision to turn to four backup thrusters that were last used on Nov 8, 1980.
The spacecraft had been relying on its primary thrusters to keep it oriented, but these have degraded over time. The Voyager team used a set of four backup "trajectory correction maneuver", or TCM thrusters that are located on the back side of the spacecraft.
The spacecraft - now over 141 times the distance between the earth and the sun - is expected to go dark some time in the next five years as the remaining energy is depleted.
After reviewing decades-old data and software "that was coded in an outdated assembler language", JPL engineers, led by JPL Chief Engineer Chris Jones, determined it was safe to attempt to fire them. The team waited eagerly as the test results traveled through space, taking 19 hours and 35 minutes to reach an antenna in Goldstone, California, that is part of NASA's Deep Space Network.
All of Voyager's thrusters were developed by Aerojet Rocketdyne. Now, the Voyager team is able to use a set of four backup thrusters, dormant since 1980. The same kind of thruster, called the MR-103, flew on other NASA spacecraft as well, such as Cassini and Dawn.
The Voyager missions discovered the first active volcanoes beyond Earth, at Jupiter's moon Io, and hints of a subsurface ocean on Jupiter's moon Europa.
So the Voyager 1 engineers came up with a new plan. The JPL will also test out the TCM thrusters on Voyager 1's twin, Voyager 2, although NASA says that that spacecraft's attitude control thrusters are in better shape. According to NASA, the re-awakened thrusters were just as effective as the attitude control thrusters. NASA's Jet Propulsion Laboratory (JPL) said today that engineers began noticing in 2014 that the attitude control thrusters were degrading. To make the change, Voyager has to turn on one heater per thruster, which requires power - a limited resource for the aging mission.
Illustration of the paths of Voyager 1 and 2. JPL is a division of Caltech in Pasadena.