Voyager 1 was launched by NASA on September 5, 1977, as part of the Voyager program to study the outer Solar System. On November 22, 2017, the probe was approximately 13 billion miles (21 billion kilometers), from the Sun. Voyager 1 is also the first human-made spacecraft to leave the solar system.
In its 40 year journey into interstellar space, Voyager 1 completed the objectives of its mission, including flybys of Jupiter, Saturn and Saturn’s large moon, Titan. It studied the weather, magnetic fields and rings of the two planets and was the first probe to provide detailed images of their moons.
NASA scientists have been relying on small thrusters, called “attitude control thrusters,” on the spacecraft to turn the probe so it can communicate with Earth. The thrusters fire in tiny pulses, or “puffs,” lasting mere milliseconds to turn the spacecraft.
Main thrusters are wearing out
However, after 40 years, the main thrusters have started wearing out, with scientists noticing it was taking more “puffs” to move the craft into position. However, Voyager 1 does have a set of four backup trajectory correction maneuver thrusters that haven’t been used since the 1980s.
The Voyager team assembled a group of propulsion experts at NASA’s Jet Propulsion Laboratory, Pasadena, California, to study the problem and come up with a “Plan B.” Chris Jones, Robert Shotwell, Carl Guernsey and Todd Barber analyzed options and predicted how the spacecraft would respond in different scenarios.
The propulsion experts ended up agreeing on an unusual solution – to try using four “trajectory correction maneuver” (TCM) thrusters, located on the back side of Voyager 1.
“The Voyager flight team dug up decades-old data and examined the software that was coded in an outdated assembler language, to make sure we could safely test the thrusters,” said Jones, chief engineer at JPL.
Plan B works perfectly
On November 28, 2017, Voyager engineers fired up the four TCM thrusters for the first time in 37 years, using 10-millisecond pulses. Then they set back and waited for the test results to travel through space. It took 19 hours and 35 minutes for the results to reach an antenna in Goldstone, California,
And on the next day, November 29, the Voyager team had their answer – The TCM thrusters worked perfectly. “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,” said Barber, a JPL propulsion engineer.
“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.
The plan right now is to switch to the TCM thrusters in January.
