On April 20, 2024, engineers at the Jet Propulsion Laboratory celebrated around a conference table strewn with laptops and snacks. One man raised both fists above his head. Their Voyager 1 spacecraft had sent readable health reports for the first time in five months. The repair command had left Earth on April 18. Even a successful fix needed almost two days to announce itself.[2]

At more than 15 billion miles away, Voyager took about 22 and a half hours to receive a radio signal, with another 22 and a half hours for the reply. The team could send instructions, but nobody could reach inside the computer. When a memory chip stopped working, they had to persuade the spacecraft to work around a broken part it would carry with it.[2]

Since November 14, 2023, the spacecraft had been receiving commands and otherwise operating normally while sending home unusable science and engineering data. Its flight data subsystem, one of three onboard computers, packaged those reports. The team could still give Voyager orders; they had lost the readable reports that would tell them how it was doing.[2]

In early March, the engineers sent a "poke" command that prompted a readout of the computer's memory. They found that about 3 percent had been corrupted. An April 4 update identified a single chip as the suspected culprit, possibly struck by an energetic particle or simply worn out after 46 years. The cause of its failure was uncertain.[1]

By the April repair, the team had identified the failed chip and decided to move its affected software elsewhere in memory. There was room, but no single available location could hold the whole section. They divided the code, fitted the pieces into different places, and adjusted them so they could still work together. References elsewhere in memory also had to point to the new locations. Moving the pieces meant changing the instructions for finding them.[2]

On April 18, the team relocated the code that packaged engineering data. Those health and status reports came back readable on April 20, giving the engineers their first chance in months to check the spacecraft's condition. Science measurements would have to wait for more work on the remaining affected software.[2]

On May 19, another command began restoring the science reports. Two instruments returned to normal immediately; two needed additional work. By June 13, all four were sending usable science data. Engineers still had timekeeping software to resynchronize and a digital tape recorder to maintain. The spacecraft that had flown past Jupiter and Saturn had more chores waiting for its distant caretakers.[3]

In the April celebration photograph, the team is surrounded by the equipment of a much shorter working day: open laptops, drinks, a whiteboard covered in diagrams. Hands are clapping around the table, and the man at the back has both arms in the air. Far beyond that room, the failed chip remains aboard Voyager. The engineers have given its software other places to go.[2]

Sources

  1. NASA: Engineers Pinpoint Cause of Voyager 1 Issue, April 4, 2024
  2. NASA: Voyager 1 Resumes Sending Engineering Updates, April 22, 2024
  3. NASA: Voyager 1 Returning Science Data From All Four Instruments, June 13, 2024

Image: Voyager flight team celebrating on April 20, 2024, at JPL. Credit: NASA/JPL-Caltech. Cropped from the original photograph.