(CNN) –– NASA engineers successfully fired a set of thrusters that Voyager 1 hadn’t used in decades to fix a problem that could prevent the 47-year-old spacecraft from communicating with Earth billions of kilometers away.
When Voyager 1 launched into space on September 5, 1977, no one expected that the probe would still be working today.
As a result of its exceptionally long mission, Voyager 1 is experiencing problems as its components age in the frigid outer reaches beyond our solar system. When a problem arises, engineers at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, have to be creative while keeping an eye on how the spacecraft will react to the changes.
Voyager 1, the farthest spacecraft from Earth today, is about 15 billion miles away. The probe operates beyond the heliosphere (the bubble of the Sun’s magnetic fields and particles that extends far beyond Pluto’s orbit), where its instruments take samples directly from interstellar space.
Earlier this year, engineers noticed a problem when a fuel tube inside one of Voyager’s thrusters became clogged. If the thrusters are clogged, they cannot generate enough force to keep the spacecraft stable. Voyager’s thrusters keep the spacecraft oriented so it can communicate with Earth.
Unless Voyager 1 is positioned so that its antenna points toward Earth, the spacecraft cannot “listen” for commands from mission control or send data, according to Calla Cofield, media relations specialist at JPL.
“If the nozzles that keep the antenna pointed at Earth were to clog, that would mean the end of the mission,” he said.
The team realized they would have to command the spacecraft to switch to a different set of thrusters, but the solution would not be simple.
This is not the first time that Voyager 1 has had to switch to a different set of thrusters. Fortunately, the spacecraft has three sets of thrusters: two for attitude thrusters and one dedicated to trajectory correction maneuvers.
Voyager 1 used thrusters for a variety of purposes during flybys of planets such as Jupiter and Saturn in 1979 and 1980.
Now the spacecraft follows an unchanged trajectory away from our solar system, so it only needs a set of thrusters to help keep its antenna pointed at Earth. To power the thrusters, liquid hydrazine is turned into a gas and released in about 40 short puffs per day to maintain Voyager 1’s proper orientation.
Over time, engineers discovered that the fuel tube inside the boosters could become clogged with silica, a result of aging of the fuel tank’s rubber diaphragm. As the nozzles become clogged, they generate less power.
In 2002, the team ordered Voyager 1 to switch to a second set of attitude boosters when the first one showed signs of clogging. Engineers switched back to a set of trajectory correction nozzles in 2018 when the other set also appeared clogged.
But when the team recently checked the condition of Voyager’s trajectory correction jets, they were even more clogged than the previous two sets of jets.
When the team originally switched the trajectory correction nozzles on Voyager six years ago, the tube opening measured 0.25 millimeters wide. But now, according to NASA, the obstacle has reduced it to 0.035 millimeters, which is half the width of a human hair.
It was time to go back to another set of position nozzles.
As Voyager 1 and its twin Voyager 2 aged, the mission team slowly shut down non-essential systems on both spacecraft to conserve power, including heaters. As a result, Voyager 1’s components are cooler, and the team knew they couldn’t simply command Voyager 1 to immediately switch to one of the thrusters without doing something to warm them up.
But Voyager 1 doesn’t have enough power to turn the heaters back on without turning off something else, and its science instruments are too valuable to turn them off and risk not turning them back on, the team said.
They then realized that one of the spacecraft’s main heaters could be turned off for about an hour, which would allow the engineers to turn on the heaters and make the switchover safely.
That plan worked, and on August 27 Voyager 1 once again relied on one of its original boosters to stay in contact with Earth.
The team has taken steps to reduce the use of the thrusters and hopes to get another two to three years of use out of the original set, said Todd Barber, Voyager’s propulsion engineer.
Once the spacecraft has exhausted this set of thrusters, Voyager 1’s remaining option is a second set of thrusters, which are already throttled.
“Any decisions we have to make in the future will require much more analysis and caution than before,” Voyager project manager Suzanne Dodd said in a statement.
Voyager 2 also underwent propulsion changes in 1999 and 2019, and “the situation there is less severe,” Barber said. Voyager 2 traveled more than 20 billion kilometers from Earth.
Information collected by these long-duration probes helps scientists understand the shape of the comet-like heliosphere and how it shields Earth from charged particles and radiation in interstellar space.
