NASA scientists claim to have identified the source of the problems keeping humanity’s most remote emissary, Voyager 1, from returning its science data. However, finding the exact location of the problem, let alone fixing it, still proves frustrating. A 45-hour round trip to get messages through doesn’t help, nor does the fact that only one radio dish, with other calls in due course, is powerful enough for Voyager 1 to hear it over these distances.
Late last year, Voyager 1 began sending back a random series of 1s and 0s instead of the Flight Data System (FDS) messages that should have reported its science observations.
“The spacecraft is receiving and executing commands sent from Earth, but the FDS is not communicating properly with one of the probe’s subsystems, called the telemetry modulation unit (TMU),” a NASA statement said at the time. “As a result, no scientific or technical data is returned to Earth.”
Three months after the problems started, with some of the best engineers in the world working on the problem, it’s still happening.
In a certain kind of science fiction film, this would be an indication that Voyager 1 had become sentient and had either gone on strike or called for help. In the real world, it reflects the fact that one of the most powerful scientific instruments of all time runs on a computer system that became obsolete shortly after its launch in 1977.
Voyager 1 has three computers. In proof of Moore’s Law, their combined processing power could not power a smartphone. It would be amazing if they still worked as well if they were kept in a clean area, protected from all kinds of radiation. Instead, they are now exposed to high-energy particles without even the minimal protection of the solar wind.
The FDS takes the data from the spacecraft’s remaining sensors and combines it to transmit to Earth via the Telemetry Modulation Unit.
“[The problem’s] probably somewhere in the memory of the FDS,” Suzanne Dodd, Voyager project manager since 2010, told Ars Technica. “A piece has been turned or damaged. But without the telemetry we can’t see where the FDS memory corruption is.”
“It would be the greatest miracle if we got it back,” Dodd added. “We certainly haven’t given up. There are other things we can try. But this is, by far, the most serious since I became a project manager.” Nevertheless, the successful restoration of communications with Voyager 2 last year offers hope, albeit from a simpler problem.
These ideas include trying to switch the FDS back to the operating mode it used during its flight past the giant planets, in the hope that this will reveal where in the memory the problem lies. The usually small Voyager team has brought in people from other parts of NASA to prepare for this, but Dodd noted that the people they want most are not available.
“Not to be gloomy, but a lot of Voyager people are dead,” she noted, leaving the current operators to sort through archives that were not kept in the best order. “We have sheets and sheets of paper diagrams, all yellowed on the corners, all signed in 1974,” Dodd said.
Like, in a real version of Space cowboysAlthough one of the remaining former operators was called into retirement to fix the problem, NASA failed to capitalize on the publicity potential by disclosing it.
Dodd complained about the lack of a ground simulator that could be used to test commands before sending them to Voyager 1. She also noted that the mission’s dwindling power supply and other vulnerable components mean it won’t last that long. There’s no point in making the rescue attempt too slowly if it means finding the solution just before the mission fails for some other reason.
Despite the weight restrictions when launched, the Voyagers carried two FDSs each, but Voyager 1’s backup failed in 1981 (fortunately after it passed by Saturn). At the time, most people at NASA thought Voyager 1 had done its job because, unlike its twin, it would not pass by other worlds.
Instead, both Voyagers mapped the heliopause, studied ultraviolet sources far from solar interference, and probed magnetic fields as far from the Sun. Two of Voyager 1’s instruments have failed, and five have been disabled by ground control as “no longer a priority.” Four of them, one fewer than Voyager 2, are still operational, or at least were before the FDS failure. The magnetometer and cosmic ray system in particular proved invaluable during the extended mission. They are likely still collecting data, but need a functioning FDS to send that information back to us.