Voyager 1

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NASA knows what knocked Voyager 1 offline, but it will take a while to fix

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Hope returns —

“Engineers are optimistic they can find a way for the FDS to operate normally.”

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A Voyager space probe in a clean room at the Jet Propulsion Laboratory in 1977.

Enlarge / A Voyager space probe in a clean room at the Jet Propulsion Laboratory in 1977.

Engineers have determined why NASA’s Voyager 1 probe has been transmitting gibberish for nearly five months, raising hopes of recovering humanity’s most distant spacecraft.

Voyager 1, traveling outbound some 15 billion miles (24 billion km) from Earth, started beaming unreadable data down to ground controllers on November 14. For nearly four months, NASA knew Voyager 1 was still alive—it continued to broadcast a steady signal—but could not decipher anything it was saying.

Confirming their hypothesis, engineers at NASA’s Jet Propulsion Laboratory (JPL) in California confirmed a small portion of corrupted memory caused the problem. The faulty memory bank is located in Voyager 1’s Flight Data System (FDS), one of three computers on the spacecraft. The FDS operates alongside a command-and-control central computer and another device overseeing attitude control and pointing.

The FDS duties include packaging Voyager 1’s science and engineering data for relay to Earth through the craft’s Telemetry Modulation Unit and radio transmitter. According to NASA, about 3 percent of the FDS memory has been corrupted, preventing the computer from carrying out normal operations.

Optimism growing

Suzanne Dodd, NASA’s project manager for the twin Voyager probes, told Ars in February that this was one of the most serious problems the mission has ever faced. That is saying something because Voyager 1 and 2 are NASA’s longest-lived spacecraft. They launched 16 days apart in 1977, and after flying by Jupiter and Saturn, Voyager 1 is flying farther from Earth than any spacecraft in history. Voyager 2 is trailing Voyager 1 by about 2.5 billion miles, although the probes are heading out of the Solar System in different directions.

Normally, engineers would try to diagnose a spacecraft malfunction by analyzing data it sent back to Earth. They couldn’t do that in this case because Voyager 1 has been transmitting data packages manifesting a repeating pattern of ones and zeros. Still, Voyager 1’s ground team identified the FDS as the likely source of the problem.

The Flight Data Subsystem was an innovation in computing when it was developed five decades ago. It was the first computer on a spacecraft to use volatile memory. Most of NASA’s missions operate with redundancy, so each Voyager spacecraft launched with two FDS computers. But the backup FDS on Voyager 1 failed in 1982.

Due to the Voyagers’ age, engineers had to reference paper documents, memos, and blueprints to help understand the spacecraft’s design details. After months of brainstorming and planning, teams at JPL uplinked a command in early March to prompt the spacecraft to send back a readout of the FDS memory.

The command worked, and Voyager.1 responded with a signal different from the code the spacecraft had been transmitting since November. After several weeks of meticulous examination of the new code, engineers pinpointed the locations of the bad memory.

“The team suspects that a single chip responsible for storing part of the affected portion of the FDS memory isn’t working,” NASA said in an update posted Thursday. “Engineers can’t determine with certainty what caused the issue. Two possibilities are that the chip could have been hit by an energetic particle from space or that it simply may have worn out after 46 years.”

Voyager 1’s distance from Earth complicates the troubleshooting effort. The one-way travel time for a radio signal to reach Voyager 1 from Earth is about 22.5 hours, meaning it takes roughly 45 hours for engineers on the ground to learn how the spacecraft responded to their commands.

NASA also must use its largest communications antennas to contact Voyager 1. These 230-foot-diameter (70-meter) antennas are in high demand by many other NASA spacecraft, so the Voyager team has to compete with other missions to secure time for troubleshooting. This means it will take time to get Voyager 1 back to normal operations.

“Although it may take weeks or months, engineers are optimistic they can find a way for the FDS to operate normally without the unusable memory hardware, which would enable Voyager 1 to begin returning science and engineering data again,” NASA said.

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Humanity’s most distant space probe jeopardized by computer glitch

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An annotated image showing the various parts and instruments of NASA's Voyager spacecraft design.

Enlarge / An annotated image showing the various parts and instruments of NASA’s Voyager spacecraft design.

Voyager 1 is still alive out there, barreling into the cosmos more than 15 billion miles away. However, a computer problem has kept the mission’s loyal support team in Southern California from knowing much more about the status of one of NASA’s longest-lived spacecraft.

The computer glitch cropped up on November 14, and it affected Voyager 1’s ability to send back telemetry data, such as measurements from the spacecraft’s science instruments or basic engineering information about how the probe was doing. So, there’s no insight into key parameters regarding the craft’s propulsion, power, or control systems.

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

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

Voyager 2, which launched 16 days before Voyager 1 in 1977, isn’t quite as far away. It took a more leisurely route through the Solar System, flying past Jupiter, Saturn, Uranus, and Neptune, while Voyager 1 picked up speed during an encounter with Saturn to overtake its sister spacecraft.

For the last couple of decades, NASA has devoted Voyager’s instruments to studying cosmic rays, the magnetic field, and the plasma environment in interstellar space. They’re not taking pictures anymore. Both probes have traveled beyond the heliopause, where the flow of particles emanating from the Sun runs into the interstellar medium.

There are no other operational spacecraft currently exploring interstellar space. NASA’s New Horizons probe, which flew past Pluto in 2015, is on track to reach interstellar space in the 2040s.

State-of-the-art 50 years ago

The latest problem with Voyager 1 lies in the probe’s Flight Data Subsystem (FDS), one of three computers on the spacecraft working alongside a command and control central computer and another device overseeing attitude control and pointing.

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 package in binary code—a series of ones and zeros. A separate component called the Telemetry Modulation Unit actually sends the data package back to Earth through Voyager’s 12-foot (3.7-meter) dish antenna.

In November, the data packages transmitted by Voyager 1 manifested a repeating pattern of ones and zeros as if it were stuck, according to NASA. Dodd said engineers at JPL have spent the better part of three months trying to diagnose the cause of the problem. She said the engineering team is “99.9 percent sure” the problem originated in the FDS, which appears to be having trouble “frame syncing” data.

A scanned 1970s-era photo of the Flight Data Subsystem computer aboard NASA's Voyager spacecraft.

Enlarge / A scanned 1970s-era photo of the Flight Data Subsystem computer aboard NASA’s Voyager spacecraft.

So far, the ground team believes the most likely explanation for the problem is a bit of corrupted memory in the FDS. However, because of the computer hangup, engineers lack detailed data from Voyager 1 that might lead them to the root of the issue. “It’s likely somewhere in the FDS memory,” Dodd said. “A bit got flipped or corrupted. But without the telemetry, we can’t see where that FDS memory corruption is.”

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 make use of volatile memory. Each Voyager spacecraft launched with two FDS computers, but Voyager 1’s backup FDS failed in 1981, according to Dodd.

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

“Unfortunately, we haven’t cracked the nut yet, or solved the problem, or gotten any telemetry back,” Dodd said.

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