The distant, cold Voyager 1 spacecraft used a clever trick with its thrusters to help it phone home.
Voyager 1, the most distant human-made object now flying through interstellar space, had thruster problems that made it difficult for the spacecraft to stay pointed toward Earth when communicating with the planet. Unless Voyager 1 could switch to a different set of thrusters, the 47-year-old spacecraft would continue to navigate alone without any help from Earth. Making matters worse, Voyager 1 is so old that sudden changes could damage the spacecraft.
“All of the decisions we'll have to make going forward will require much more thought and caution than ever before,” Suzanne Dodd, Voyager project manager at Agency's Jet Propulsion Laboratory, which manages the mission, said in a statement Tuesday (Sept. 10).
Voyager 1 science is critical to space science because it tells us more about interstellar space, the region of the cosmos beyond the reach of gravity or particles from the Sun.
But the spacecraft's aging nuclear power source is badly damaged and doesn't have much energy to run it. So JPL engineers embarked on a rescue plan to improve the spacecraft's steering capability without putting its remaining functional scientific instruments at risk.
Voyager 1 and its twin, Voyager 2, launched their initial missions in 1977 to study the distant solar system. Together, they flew by the four largest planets in the outer solar system in 1989 and continue, with adjustments for their age, to send back scientific information from afar even after both left the solar system in the early 2010s.
As with humans, aging has brought changes to Voyager’s systems. The fuel line on its thrusters has been prone to clogging for more than 20 years — that happens when a rubber diaphragm in each spacecraft fuel tank degrades, creating a silicon dioxide byproduct that clogs the line.
Fortunately, every Voyager has three propulsion branches available for use: two attitude branches originally designed for guidance and a trajectory correction branch designed for trajectory changes in space. To be clear, engineers have been overcoming the unexpected for decades by creatively reusing Voyager parts. However, this new thruster situation brought with it additional challenges.
On Voyager 1, a fuel tube on the first attitude propulsion branch began to clog in 2002, necessitating a switch to the second branch, Agency officials wrote in the same statement. When the second branch began to malfunction in 2018, all Voyager 1 attitude maneuvers switched to the trajectory correction maneuver branch.
But with use, this single branch of the trajectory correction system has become severely clogged, to an extent even worse than any of the previous attitude propulsion branches.
JPL therefore decided to return to the attitude propulsion system, but had to do so with less power available than in 2002. Voyager 1 is operating with only essential systems, and even some of its heaters have been turned off.
Between that necessary loss of some heaters — and the decrease in radiant heat due to fewer systems running on the spacecraft — Voyager 1's inactive attitude propulsion engine was so cold that even turning it on could cause damage.
After closely examining Voyager 1 from afar, JPL engineers determined that turning on one of the heaters for an hour would suffice. The command worked, and on August 27, one of the arms of the attitude thruster successfully reoriented Voyager 1 toward Earth for the first time in six years.
Voyager 1 recently needed another form of creative problem-solving; in June, engineers solved a data transmission problem that plagued the spacecraft for months.
JPL engineers plan to keep the twin Voyager spacecraft operational until at least the mission's 50th anniversary in 2027, Dodd told reporters in June at a meeting of the space science community's Outer Planets Assessment Group, according to SpaceNews.
The group is more broadly concerned with exploration activities in the outer reaches of the solar system; it can provide advice to Agency, but the agency does not necessarily follow recommendations, Agency said.