But because Voyager 1's last planetary encounter was Saturn, the Voyager team hadn't required using the TCM thrusters since November 8, 1980. The radio waves traveled for 19 hours and 35 minutes before reaching Voyager 1 13 billion miles away; 19 hours and 35 minutes after that, they got the results of their little experiment.
Voyager 1, NASA's farthest and fastest spacecraft, is the only human-made object in interstellar space, the environment between the stars. According to Suzanne Dodd, NASA's program manager for Voyager, the fact that the thrusters still worked after more than three decades will allow the probe's mission to be extended out years longer than previously anticipated. Over the next few years it completed fly-bys of Jupiter, Saturn, and Titan-Saturn's largest moon.
"The Voyager team got more excited each time with each milestone in the thruster test", stated JPL engineer Todd Barber, adding, "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", cited by Ars Technica.
After reviewing decades-old data and software "that was coded in an outdated assembler language", JPL engineers, led by JPL Chief Engineer Chris Jones, determined it was safe to attempt to fire them. Back then, the TCM thrusters were utilized in a more constant firing mode; they had never been used in the brief explosions necessary to orient the spacecraft.
Yesterday, NASA announced that it has successfully fired up four of Voyager 1's backup thrusters, which haven't been used since 1980, which should extend its life by a couple of years.
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Aerojet Rocketdyne developed all of the Voyager's thrusters. Humanity's farthest and longest-lived spacecraft are celebrating 40 years in August and September 2017.
The spacecraft had been relying on its primary thrusters to keep it oriented, but these have degraded over time.
The engineers fired up the thrusters on Tuesday and tested their ability to turn Voyager using 10-millisecond pulses. They will do so by switching over to backup TCM thrusters in early January of next year.
Voyager 2 is also on course to enter interstellar space, likely within the next few years, and now, its attitude control thrusters are still functioning well.
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. Voyager 1 was already operating on its backup branch of attitude control thrusters. The attitude control thrusters now used for Voyager 2 are not yet as diminished as Voyager 1's, however.