(CNN) –– NASA engineers have successfully fired a set of thrusters that Voyager 1 hasn’t used in decades to solve a problem that could prevent the 47-year-old spacecraft from communicating with Earth billions of miles away.
When Voyager 1 blasted off into space on September 5, 1977, no one expected the probe to still be operational today.
As a result of its exceptionally long mission, Voyager 1 experiences 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 also being careful about how the spacecraft will react to the changes.
Voyager 1, the spacecraft currently farthest from Earth, is about 15 billion miles away. The spacecraft operates beyond the heliosphere—the bubble of magnetic fields and particles from the Sun that extends far beyond the orbit of Pluto—where its instruments sample interstellar space directly.
Earlier this year, engineers detected a problem when the fuel tube inside one of Voyager’s thrusters became clogged. If the thrusters are clogged, they can’t generate as much force to keep the spacecraft stable. Voyager’s thrusters keep the spacecraft oriented so it can communicate with Earth.
If Voyager 1 is not positioned so that its antenna is pointing toward Earth, the spacecraft cannot “hear” commands from mission control or send data, according to Calla Cofield, a media relations specialist at JPL.
“If the thrusters that keep the antenna pointed toward Earth were to become clogged, that would mean the end of the mission,” he said.
The team realized it would have to send commands to the spacecraft to switch to another set of thrusters, but the solution would not be simple.
This is not the first time Voyager 1 has had to switch to another set of thrusters. Fortunately, the spacecraft has three sets of thrusters: two attitude thrusters and one dedicated to trajectory correction maneuvers.
Voyager 1 used the thrusters for a variety of purposes while flying by planets such as Jupiter and Saturn in 1979 and 1980, respectively.
The spacecraft is now on a steady trajectory away from our solar system, so it needs only a set of thrusters to help keep its antenna pointed toward Earth. To power the thrusters, liquid hydrazine is converted to a gas and released in about 40 short puffs per day to keep Voyager 1 pointing correctly.
Over time, engineers discovered that a fuel line inside the boosters can become clogged with silicon dioxide, a result of the fuel tank’s rubber diaphragm aging. As the boosters become clogged, they generate less thrust.
In 2002, the team ordered Voyager 1 to switch to its second set of attitude thrusters when the first one showed signs of clogging. Engineers switched back to the trajectory correction thruster set in 2018 when the second set also appeared clogged.
But when the team recently checked the status of Voyager’s trajectory correction thrusters, they were even more clogged than the previous two thruster sets.
When the team initially replaced Voyager’s trajectory correction thrusters six years ago, the tube’s opening measured 0.25 millimeters wide. But now, the blockage has shrunk it to 0.035 millimeters — half the width of a human hair, according to NASA.
It was time to rotate back to another set of attitude thrusters.
As Voyager 1 and its sister spacecraft, Voyager 2, have aged, the mission team has been slowly shutting down nonessential systems on both spacecraft to conserve power, including the heaters. As a result, Voyager 1’s components are cooler, and the team knew it couldn’t simply send a command to Voyager 1 to immediately switch to one of the attitude thrusters without doing something to warm them up.
However, Voyager 1 does not have enough power to turn the heaters back on without shutting down something else, and its science instruments are too valuable to turn off and risk never turning 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 engineers to turn on the thruster heaters and safely perform the switchover.
This plan worked, and on August 27, Voyager 1 again relied on one of its original thrusters to maintain contact with Earth.
The team took steps to use fewer 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 the other set of attitude thrusters, which is already clogged.
“All of the decisions we will have to make in the future will require much more thought and caution than ever before,” Voyager project manager Suzanne Dodd said in a statement.
Voyager 2 also underwent thruster changes in 1999 and 2019, and “the situation there is less severe,” Barber said. Voyager 2 has traveled more than 20 billion kilometers from Earth.
The information gathered by these long-duration probes helps scientists understand the comet-like shape of the heliosphere and how it shields Earth from energized particles and radiation in interstellar space.
