So NASA searched for a Plan B, eventually deciding to try using four "trajectory correction maneuver" (TCM) thrusters, located on the back side of Voyager 1. In a blog post, the agency explained that Voyager 1's main attitude control thrusters had been degrading, making it hard to reorient the spacecraft so that its antenna points back towards Earth.
The thrusters are used to orient itself so it is capable of continuing to send back communications to Earth.
At 13 billion miles from Earth, there's no mechanic shop nearby to get a tune-up. Then they waited 19 hours, 35 minutes for the test results to arrive at an antenna in Goldstone, California.
Although the Voyager 1's twin spacecraft-Voyager 2-launched just 16 days after Voyager 1, its standard thrusters appear to be in much better shape, NASA officials wrote.
Voyager 1 is the most distant human-made object, and scientists announced in 2013 the craft's crossing of the boundary between the sun's influence and interstellar space, making it the first mission to explore the void between the stars. NASA says they hope to extend Voyager 1's life by at least two or three more years.
Voyager 1 was launched in 1977 and flew past Jupiter and Saturn in 1979 and 1980 respectively.
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"The Voyager flight team dug up decades-old data and examined the software that was coded in an outdated assembler language, to make sure we could safely test the thrusters", said JPL's Chris Jones, who led the effort, in a JPL news release. However, we can still communicate with Voyager across that distance.
U.S. space agency NASA has said a set of thrusters aboard the Voyager 1 spacecraft, the only human-made object in interstellar space, have been successfully fired up after 37 years without use.
This week, the scientists and engineers on the Voyager team did something very special.
All of Voyager's thrusters were developed by Aerojet Rocketdyne. "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". The need to use them is not as immediate, however, because the primary thrusters of Voyager 2 have not significantly degraded. And the thrusters had never been tested for the 10-millisecond "puffs" needed for reorientation. They will do so by switching over to backup TCM thrusters in early January of next year.
To reawaken these dormant thrusters the team had to go back to the original Voyager documentation. Voyager 2 will join Voyager 1 in interstellar space in a few years, so discovering another way of reorienting these probes is a valuable technique for the future. The attitude control thrusters now used for Voyager 2 are not yet as degraded as Voyager 1's, however.