If you tried to start a car that’s been sitting in a garage for a couple years, you’d have to clean and replace parts then hope. But a set of thrusters aboard the Voyager 1 spacecraft successfully fired up after 37 years in the deep chill of interstellar space. In that same time interval, I’ve gone through six cars. Voyager’s one mean machine!
Voyager 1, NASA’s farthest and fastest spacecraft, is the only human-made object currently in interstellar space, beyond the influence of the sun in the environment between the stars. The spacecraft, which has been flying for 40 years, relies on small devices called thrusters to orient itself so it can communicate with Earth. These thrusters fire in tiny pulses, or “puffs,” lasting just milliseconds, to subtly turn the spacecraft so that its antenna points at our planet. Last Wednesday, the Voyager team was able to use a set of four backup thrusters, dormant since 1980.
“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 Suzanne Dodd, project manager for Voyager at NASA’s Jet Propulsion Laboratory, Pasadena, California in a recent press release.
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, a tune-up’s not an option, so the Voyager team assembled a group of propulsion experts at NASA’s Jet Propulsion Laboratory to study the problem and agreed on a solution: try another set of thrusters that had been asleep for 37 years.
“The Voyager flight team dug up decades-old data and examined the software that was coded in an outdated assembler language, to make sure we could safely test the thrusters,” said Jones, chief engineer at JPL.
In the early days of the mission, Voyager 1 flew by Jupiter, Saturn, and important moons of each. To accurately fly by and point the spacecraft’s instruments at a smorgasbord of targets, engineers used “trajectory correction maneuver,” or TCM, thrusters that are identical in size and functionality to the attitude control thrusters, and are located on the back side of the spacecraft. But because Voyager 1’s last planetary encounter was Saturn, the Voyager team hadn’t needed to use the TCM thrusters since November 8, 1980. Back then, the TCM thrusters were used in a more continuous firing mode; they had never been used in the brief bursts necessary to orient the spacecraft.
On Tuesday, Nov. 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 traveling at the speed of light to reach a radio antenna in Goldstone, California, that’s part of NASA’s Deep Space Network. Come Wednesday the 29th, they discovered the TCM thrusters worked perfectly as if no time had passed at all.
NASA plans to switch to the TCM thrusters in January. To make the change, Voyager has to turn on one heater per thruster, which requires power, which is in limited supply for the aging probe. When power’s no longer available 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. It’s set to enter interstellar space in the next few years. Both spacecraft are headed in the direction of nearby red dwarf star systems in northern Ophiuchus, a summertime constellation. Each Voyager carries a copy of the Golden Record, a 12-inch gold-plated copper record with sounds and images (and greetings in 55 languages) from all over the Earth.