The Voyager mission team fired up a set of four backup thrusters aboard the Voyager 1 spacecraft last Tuesday, November 28, 2017. The thrusters had been dormant since 1988. If you tried starting a car that’d been sitting that long, you might not expect it to respond. But – on Wednesday, November 29 – mission controllers learned that Voyager 1’s thrusters did respond. Suzanne Dodd, project manager for Voyager at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, said:
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.
Voyager 1 was launched in 1977. It’s the most distant spacecraft from Earth and likely to remain so. It took advantage of a cyclical positioning in the outer planets, during which they were all temporarily on the same side of the sun, and thus passed Jupiter in 1979, Saturn in 1981, Uranus in 1986 and Neptune in 1989.
Voyager 1 was judged to have crossed the heliopause on August 25, 2012 to enter interstellar space, the space between the stars.
The spacecraft relies on the thrusters to orient itself so it can communicate with Earth. These thrusters fire in tiny pulses, or “puffs,” lasting mere milliseconds, to subtly rotate the spacecraft so that its antenna points at our planet. A statement from JPL said:
Since 2014, engineers have noticed that the thrusters Voyager 1 has been using to orient the spacecraft, called ‘attitude control thrusters,’ have been degrading. Over time, the thrusters require more puffs to give off the same amount of energy. At 13 billion miles from Earth, there’s no mechanic shop nearby to get a tune-up.
The Voyager team assembled a group of propulsion experts at NASA’s Jet Propulsion Laboratory, Pasadena, California, to study the problem. Chris Jones, Robert Shotwell, Carl Guernsey and Todd Barber analyzed options and predicted how the spacecraft would respond in different scenarios. They agreed on an unusual solution: Try giving the job of orientation to a set of thrusters that had been asleep for 37 years …
On Tuesday, November 28, 2017, Voyager engineers fired up the four TCM thrusters for the first time in 37 years and tested their ability to orient the spacecraft using 10-millisecond pulses. 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.
Lo and behold, on Wednesday, November 29, they learned the TCM thrusters worked perfectly — and just as well as the attitude control thrusters.
Jones, chief engineer at JPL, said the team had to look back at historical data to devise its plan to use the thrusters:
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.
Barber, a JPL propulsion engineer, commented:
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.
JPL said the plan going forward is to switch to the TCM thrusters in January. To make the change, Voyager has to turn on one heater per thruster, which requires power — a limited resource for the aging mission. When there is no longer enough power to operate the heaters, the team will switch back to the attitude control thrusters.
The thruster test went so well, the team will likely do a similar test on the TCM thrusters for Voyager 2, the twin spacecraft of Voyager 1. The attitude control thrusters currently used for Voyager 2 are not yet as degraded as Voyager 1’s, however.
Voyager 2 is also on course to enter interstellar space, likely within the next few years.
Bottom line: Space engineers devised and successfully carried out a plan to fire up thrusters aboard Voyager 1 – needed to communicate with Earth – thus extending the life of the mission by several years.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.