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NASA probe Voyager 1 swaps engines in a tricky situation on its flight through interstellar space

Idris Bevan September 12, 2024

The distant and cold space probe Voyager 1 used a clever engine trick to make it easier to call home.

Voyager 1, the farthest human-driven object currently flying through interstellar space, was experiencing problems with its engines that made it difficult for the spacecraft to stay pointed at Earth on its return flight. If Voyager 1 could not switch to a different engine, the 47-year-old spacecraft would continue on its own without any help from Earth. To make matters worse, Voyager 1 is so old that sudden changes could damage the spacecraft.

“Any decisions we have to make in the future will require much more analysis and caution than before,” Suzanne Dodd, Voyager project manager at NASA’s Jet Propulsion Laboratory, which manages the mission, said in a statement Tuesday (Sept. 10).

The findings from Voyager 1 are crucial for space exploration because they tell us more about interstellar space, the region of the cosmos beyond the reach of gravity or the Sun’s particles.

But the spacecraft’s aging nuclear power source has weakened significantly and no longer has much power, so JPL engineers began a rescue plan to improve the spacecraft’s pointing capabilities without jeopardizing the remaining functional science instruments.

Voyager 1 and its twin Voyager 2 launched their first missions to explore the distant solar system in 1977. Together they flew past the four largest outer planets of the solar system until 1989 and, with age-related adjustments, continue to send scientific data from afar after both left the solar system in the early 2010s.

two blue and large planets next to each other in one image

An image of Uranus on the left and Neptune on the right, taken by the Voyager 2 spacecraft. (Photo credit: Patrick Irwin)

As with humans, the aging process brought changes to Voyager’s systems. The fuel lines for the engines have been prone to clogging for over 20 years. This happens when a rubber membrane in the spacecraft’s fuel tanks wears down and creates a silicon dioxide byproduct that clogs the line.

Fortunately, each Voyager has three thruster branches available: two attitude branches, originally intended for orientation, and a trajectory correction branch, intended for course changes in space. To be clear, engineers have handled the unexpected for decades by creatively repurposing parts of Voyager. But this new thruster situation brought additional challenges.

a diagram showing a bubble around the Sun and the positions of Voyager 1 and 2 and depicting the area of the heliosphere

Artist’s impression of the parts of the heliosphere, or sphere of influence of the Earth’s sun. Also pictured (not to scale) are NASA’s Voyager 1 and Voyager 2 spacecraft, currently in interstellar space. (Image credit: NASA)

On Voyager 1, a fuel tube in the first branch of the attitude engine began to clog in 2002, requiring a switch to the second branch, NASA officials wrote in the same statement. When the second branch developed problems in 2018, all of Voyager 1’s orientation maneuvers switched to the trajectory correction maneuvers branch.

However, through use, this single branch of the trajectory correction system became severely clogged, even worse than the attitude drive branches before it.

Therefore, JPL decided to switch back to the attitude control system, but less power was available than in 2002. Voyager 1 is running only with the most necessary systems and even some of its heaters have been turned off.

The necessary shutdown of some heaters and the reduced radiant heat from the smaller number of running systems in the spacecraft meant that Voyager 1’s inactive engine branch was so cold that even turning it on could cause damage.

JPL engineers remotely surveyed Voyager 1 and concluded that turning on one of the heaters for an hour would be enough. The command worked, and on August 27, one of the attitude thrusters successfully pointed Voyager 1 toward Earth for the first time in six years.

Voyager 1 recently required a different kind of creative troubleshooting: In June, engineers solved a data transmission problem that had plagued the spacecraft for months.

Engineers at the Jet Propulsion Laboratory (JPL) plan to keep the twin Voyager spacecraft operating at least until the mission’s 50th anniversary in 2027, Dodd told reporters at a meeting of the space science community’s Outer Planets Assessment Group in June, according to SpaceNews.

The group generally deals with exploration activities in the outer reaches of the solar system. It can provide advice to NASA, but the agency does not necessarily follow recommendations, according to NASA.