Imagine you had a car sitting in storage since 1980, and suddenly you needed to start it up. Now imagine that it revs up like a charm as soon as you turn the key.
That’s the scenario NASA is using as a comparison for this week’s startup of a thruster system that’s been sitting dormant on the Voyager 1 probe for 37 years.
One important difference: Voyager’s key had to be turned by remote control from a distance of 13.1 billion miles.
Voyager 1 is traveling through interstellar space, 40 years after its launch on an unprecedented “grand tour” of the solar system. For most of that time, NASA has relied on the attitude control thruster system to keep the spacecraft in the correct orientation.
The attitude control thrusters deliver brief pulses, or “puffs,” that last for mere milliseconds but ensure that Voyager 1’s antenna remains pointed back at Earth.
Over the past three years, Voyager’s mission managers at NASA’s Jet Propulsion Laboratory have been noticing that the thrusters’ performance was degrading. More puffs were required to provide a given amount of energy.
When presented with the problem, propulsion experts said the best solution was to turn to a different system traditionally used for trajectory control maneuvers, or TCM. The last time the TCM thrusters were fired up was on Nov. 8, 1980, to adjust the probe’s course for its Saturn flyby.
“The Voyager flight team dug up decades-old data and examined the software that was coded in an outdated assembly language, to make sure we could safely test the thrusters,” JPL chief engineer Chris Jones said in a news release.
On Tuesday, the Voyager team essentially turned the key. They transmitted the commands for the TCM thrusters to fire up for 10-millisecond pulses and reorient the spacecraft. It took 19 hours and 35 minutes for the commands to reach Voyager 1, and just as much time for Voyager to beam the results of the test back to NASA’s Deep Space Network antenna in Goldstone, Calif.
Those results, received on Wednesday, showed that the thrusters worked perfectly.
“The Voyager team got more excited each time with each milestone in the thruster test,” JPL propulsion engineer Todd Barber said. “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 relief and joy was felt as well at Aerojet Rocketdyne, which built the MR-103 thrusters. Much of the work on the thrusters was done at Aerojet’s facility in Redmond, Wash.
— Aerojet Rocketdyne (@AerojetRdyne) December 1, 2017
Mission managers plan to start using the TCM thrusters routinely for attitude control in January. In order to do that, they’ll have to turn one heater for each thruster, which represents a significant draw on the spacecraft’s aging power system. When there’s no longer enough power to operate the heaters, the team plans to switch back to the attitude control thrusters.
Thanks to the backup system, “we will be able to extend the life of the Voyager 1 spacecraft by two or three years,” said Suzanne Dodd, JPL’s project manager for Voyager.
The Voyager team is likely to conduct a similar test for Voyager 2, the twin to Voyager 1. That spacecraft’s attitude control thrusters aren’t yet as degraded as Voyager 1’s. But it’s always a good idea to check the spare before you need it, right?