Voyager 1 heard us from over 20 billion kilometers away, the furthest a spacecraft has ever been.
What came as a surprise to many is that we are still able to communicate with it. Just recently, NASA’s scientists sent instructions to activate backup thrusters that have been inactive for almost four decades. After 19 hours and 35 minutes the connection was established, and the scientists heard back from the spacecraft.
“The Voyager team got more excited each time with each milestone in the thruster test. The mood was one of relief, joy and incredulity after witnessing these well-rested thrusters pick up the baton as if no time had passed at all”, said Todd Barber, a JPL propulsion engineer.
Voyager 1 was launched on September 5th 1977, and for over 40 years the attitude control has been the work of the main thrusters.
The craft needs to stay oriented in a very specific was so it can communicate with the Earth, and that’s exactly what the thrusters do. However, over time, they have degraded to the point that they require more puffs in order to deliver the same attitude adjustments.
It’s always a good idea to have a back-up plan, because once you send something into space, you can’t retrieve it for repair. That’s why the spacecraft Voyager 1 had additional thrusters that were used for trajectory correction maneuvers (TCM), but first the team had to be sure they are still in function.
“The Voyager flight team dug up decades-old data and examined the software that was coded in an outdated assembler language, to make sure we could safely test the thrusters,” said JPL chief engineer Chris Jones.
The TCM thrusters are identical to the control thrusters, but are located in the back of the spacecraft and are also used very differently. The last time they were used was while Voyager 1 was passing by Saturn back in 1980.
But not only did they work for attitude control, they were just as good as the thrusters intended for the purpose.
“With these thrusters that are still functional after 37 years without use, we will be able to extend the life of the Voyager 1 spacecraft by two to three years,” said Voyager project manager Suzanne Dodd.
Encouraged by this success, the team now plans on conducting the same test on Voyager 2, which is expected to enter interstellar space sometime in the next few years.