Humanity’s furthest space probe is compromised by a computer glitch

Humanity’s furthest space probe is compromised by a computer glitch

Annotated image showing the various parts and tools of NASA's Voyager spacecraft design.
Zoom in / Annotated image showing the various parts and tools of NASA’s Voyager spacecraft design.

Voyager 1 is still alive out there, blasting out into the universe more than 15 billion miles away. However, a computer problem has prevented the dedicated mission support team in Southern California from learning more about the condition of one of NASA’s longest-lived spacecraft.

The computer glitch appeared on November 14, affecting Voyager 1’s ability to transmit telemetry data, such as measurements from the spacecraft’s science instruments or basic engineering information about how the probe works. Therefore, there is no insight into key parameters related to the vehicle’s propulsion, power or control systems.

“It would be the biggest miracle if we got it back. We certainly haven’t given up,” Susan Dodd, Voyager project manager at NASA’s Jet Propulsion Laboratory, said in an interview with Ars. “There are other things we could try. But this is, by far, the most dangerous since I’ve been project manager.”

Dodd became project manager for NASA’s Voyager mission in 2010, overseeing a small cadre of engineers responsible for humanity’s exploration of interstellar space. Voyager 1 is the farthest spacecraft ever, moving away from the Sun at 38,000 miles per hour (17 kilometers per second).

Voyager 2, which launched 16 days before Voyager 1 in 1977, isn’t all that far off. It took a more leisurely route through the solar system, flying by Jupiter, Saturn, Uranus and Neptune, while Voyager 1 gained speed during an encounter with Saturn to overtake its sister spacecraft.

Over the past two decades, NASA has dedicated Voyager’s instruments to studying cosmic rays, magnetic fields, and the plasma environment in interstellar space. They don’t take pictures anymore. Both probes traveled beyond the heliosphere, where particles emitted by the Sun stream into the interstellar medium.

No other operational spacecraft currently explores interstellar space. NASA’s New Horizons probe, which flew by Pluto in 2015, is on track to reach interstellar space in the 2040s.

State of the art technology for 50 years

The final problem with Voyager 1 is with the probe’s flight data subsystem (FDS), one of three computers on board the spacecraft that works alongside a central command and control computer and another device that oversees attitude control and guidance.

The FDS is responsible for collecting science and engineering data from the spacecraft’s network of sensors and then combining the information into a single data packet in binary code — a string of ones and zeros. A separate component called a telemetry modulator sends the data beam to Earth through the Voyager dish’s 12-foot (3.7 m) antenna.

In November, data packets sent by Voyager 1 showed a recurring pattern of ones and zeros as if they were stuck, according to NASA. Engineers at JPL spent the better part of three months trying to diagnose the cause of the problem, Dodd said. She said the engineering team is “99.9 percent sure” that the issue originated in FDS, which appears to be having trouble “frame syncing” the data.

A 1970s-era scanned image of the Flight Data Subsystem computer aboard NASA's Voyager spacecraft.
Zoom in / A 1970s-era scanned image of the Flight Data Subsystem computer aboard NASA’s Voyager spacecraft.

So far, the ground team believes that the most likely explanation for the problem is a piece of corrupted memory in the DSF. However, because the computer is down, engineers lack detailed data from Voyager 1 that could lead them to the root of the problem. “It’s probably somewhere in the FDF’s memory,” Dodd said. “It’s flipped over or damaged a bit. But without telemetry, we can’t tell where the FDS memory is damaged.”

When it was developed five decades ago, Voyager’s flight data subsystem was an innovation in computing. It was the first computer on a spacecraft to use volatile memory. Each Voyager spacecraft was launched with two FDS computers, but Voyager 1’s FDS backup failed in 1981, according to Dodd.

The only signal Voyager 1 Earthbound engineers have received since November is the carrier tone, which essentially tells the team that the spacecraft is still alive. There is no indication of any other major problems. Changes in the modulation of the carrier signal indicate that Voyager 1 is receiving commands sent from Earth.

“Unfortunately, we have not yet cracked the nut, resolved the problem, or recovered any telemetry,” Dodd said.

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