NASA scientists claim to have identified the source of the trouble preventing humanity’s most distant emissary, Voyager 1, from returning its science data. However, locating the exact location of the problem, let alone fixing it, is still frustrating. A 45-hour round trip to relay messages doesn’t help, nor does the fact that only one radio dish, with other calls on its own time, is powerful enough for Voyager 1 to hear it at these distances.
Late last year, Voyager 1 began sending a random series of 1s and 0s instead of the Flight Data System (FDS) messages it was supposed to report its science observations.
“The spacecraft is receiving and executing commands sent from Earth; however, the FDS is not communicating properly with one of the probe’s subsystems, called the telemetry modulation unit (TMU),” a NASA statement announced at the time . “As a result, no scientific or engineering data is being sent back 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 some sort of sci-fi movie, this would be a hint that Voyager 1 had become sentient and had either gone on strike or was calling 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 was obsolete shortly after it was launched in 1977.
Voyager 1 has three computers. In a testament to Moore’s Law, their combined processing power wouldn’t use a smartphone. It would be surprising if they would still be working as they are if they were kept in a clean room protected from all types of radiation. Instead, they are now exposed to high-energy particles without even the minimal shielding of the solar wind.
The FDS receives data from the spacecraft’s surviving sensors and combines them to send to Earth via the Telemetry Modulation Unit.
“[The problem’s] likely somewhere in FDS memory, Suzanne Dodd, Voyager’s project manager since 2010, told Ars Technica. “Some was returned or corrupted. But without the telemetry, we can’t see where the FDS memory corruption is.”
“It would be the greatest miracle if we get him 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’ve been a project manager.” However, the successful re-establishment of communications with Voyager 2 last year offers hope, albeit from a milder problem.
These ideas include trying to return the FDS to the operating mode it used during its flyby of the giant planets, in the hope that this will reveal where the memory problem lies. Voyager’s usually small crew has pulled in people from other parts of NASA to prepare to do so, but Dodd noted that the people who want the most are not available.
“Not to be a bore, but a lot of Voyager people are dead,” she noted, leaving the current operators to search through the poorly kept archives. “We have sheets and sheets of schematics that are paper, all yellowed in the corners and all signed in 1974,” Dodd said.
Dodd lamented the lack of a ground-based simulator that could be used to test the commands before they are sent to Voyager 1. She also noted that the mission’s dwindling power supply and other fragile parts mean that it didn’t last long. There’s no point in taking the rescue effort too slowly if it means finding the solution just before the mission fails for another reason.
Despite weight restrictions when launched, the Voyagers had two FDSs each, but Voyager 1’s backup failed in 1981 (fortunately after it had passed Saturn). At the time, most people at NASA thought that Voyager 1 had done its job, since, unlike its twin, it would not pass by any other world.
Instead, the two Voyagers have mapped the heliopause, studied ultraviolet sources far from interference from the Sun, and probed magnetic fields that far from the Sun. Two of Voyager 1’s instruments have failed, and five have been turned off by ground control as “no longer a priority.” Four, one less than Voyager 2, are still operational, or at least were before the FDS failure. The magnetometer and the cosmic ray system in particular have proven invaluable on the extended mission. They are probably still collecting data, but they need a functioning FDS to get that information back to us.