11.03.2024

In 1977, a team of scientists and engineers at NASA’s Jet Propulsion Laboratory altered the course of space exploration when they launched the Voyager 1 and Voyager 2 spacecraft into the cosmos.

Their primary mission was to photograph Jupiter and Saturn, two of the four outer planets of our solar system, which had not yet been closely observed.

Instead of stopping there, the probes continued on, photographing Uranus and Neptune. The Voyagers sent back other amazing photographs, including Io’s volcanoes, Enceladus’s water-polished surface, and the Earth as a small pixel set against an inky, black universe.

The Voyagers would become the first human-made objects to enter interstellar space, leaving our sun’s domain. To the astonishment of many, the spacecraft have kept operating for the past 46 years.

Now, well into its twilight years, Voyager 1 is very sick. But amid weeks of concern at JPL – where a mission team, dwindling in number, talks with the crafts – a hopeful sign has finally emerged.

The elderly spacecraft has been speaking in gibberish since November 2023, and the Voyager engineering team has yet to fix the problem. As though a stroke left Voyager 1 with aphasia, it can hear the messages being sent from Earth but can’t respond coherently, providing no information on its health or status.

The issue likely lies in the flight data system (FDS), which compiles information about the spacecraft’s health, operational status and scientific observations into a string of 1’s and 0’s that are sent to Earth. Until recently, Voyager 1 had been transmitting a repetitive string of nonsense, indicating that the FDS may be “stuck”.

Without restoring communication, the Voyager team cannot tell what the probe needs to stay alive; consigning Voyager 1 to a lonely, unknowable demise.

“The likely cause of the issue is some type of corrupted bit structure in the FDS computer. We don’t know where that corruption is,” explained Dr. Suzanne Dodd, project manager for the Voyager Interstellar Mission, who describes this issue as the most serious she’s seen since joining the team in 2010.

In the past couple of weeks, Voyager 1 has shown promising signs of improvement. The probe is finally transmitting patterns of 1’s and 0’s that look familiar to the engineers.

“They’re not exactly what we would expect,” Dodd said. “But they do look like something that can show us that the FDS is at least partially working.”

When a crisis emerges at JPL, a “tiger team” is assembled to help attack the problem, temporarily aiding the mission team. Voyager’s longevity poses a unique challenge for the team. Almost every engineer and programmer who helped build the Voyagers have either retired or died.

“So a lot of what the tiger team has had to do is go back and look through old documentation,” Dodd said. “Try to recreate how the code was done and why the code was done that way.”

Once the team finally decides on the right command to send Voyager 1, it takes around 22.5 hours for that command to travel the 15 billion miles to the spacecraft. By the time a response is received on Earth, nearly two days have elapsed. The team currently sends commands around once a week, further slowing their efforts.

According to Dodd, the team is “extremely hopeful”, though she pointed out that the solution will “take more commanding and it will take more time.”

‘The Little Engine that Could’

The Voyager team has significantly dwindled in size and stature over the years. Since its kickoff in 1972, around 1,200 JPL employees have contributed to the mission; in the first five years, 950 employees were involved. Today, the Voyager team consists of only 12 full-time employees.

The entire Voyager mission was made possible by the discovery of a Caltech doctoral student who realized that once every 175 years, the alignment of our solar system’s four outer planets allows a spacecraft to slingshot from one to another, gaining momentum from each planet’s gravity en route. This “gravity assist” trajectory takes only 12 years to traverse, as opposed to the 30 years it would otherwise take to photograph all four planets.

Each time a Voyager probe approached a new planet, JPL became the center of international science news. Reporters and camera crews flocked to the campus, peppering exhausted engineers and scientists with questions as they hurried between labs and conference rooms.

Jupiter, Saturn and Uranus were reached in quick succession, bringing 24-hour media attention to JPL once a year from 1979 to 1981. Eight years later, the mission reclaimed the spotlight when Voyager 2 flew by Neptune, completing Voyager’s primary mission. After photographing Neptune, the mission slipped into the shadows, dwindling in size as engineers and scientists moved on to other projects.

There was a time when a catastrophic malfunction on Voyager would have immediately captured headlines. JPL announced the current crisis impacting Voyager 1 in early December 2023. The issue only made headlines this past week.

The demise of the Voyagers would be a loss felt by many.

“It’s the Little Engine that Could, that everybody is rooting for around the world,” Dodd explained. “And we just get the pleasure of being part of the team that gets to operate it for the rest of the world.”

Scientifically, the loss of the Voyagers would represent the loss of the only in situ data collection from interstellar space. According to Dodd, a spacecraft will not cross the interstellar boundary “for decades to come.”

At the celebration of Voyager’s 45th anniversary two years ago, JPL Director Laurie Leshin told an audience full of former Voyager engineers and scientists that the field of modern planetary science is “all about the foundation that Voyager laid.”

JPL’s Voyager’s 1-2 45th launch anniversary brought those who work on the missions together Thursday, Aug 25, 2022. As of the month of August 2022 the Voyager prob’s have gone 15 billion miles and takes 21 hours to send a command signal and 21 hours to receive a replay back to JPL that is till in contact with the probes. (Photo by Gene Blevins/Contributing Photographer)

She pointed out that the Galilieo, Juno, Cassini and Europa Clipper missions “are built upon the discoveries of Voyager.”

The Voyager probes do not have long to live. Soon, they will power down, aimlessly floating through space. Each Voyager carries “golden records”, gold LPs containing a sampling of Earth’s music, culture and the planet’s pulsar-based coordinates, in the hopes that intelligent life might learn about the planet.

While humans will undoubtedly outlive the Voyagers’ systems, the probes’ final mission, to preserve a record of Earth, may outlive humanity.

At the anniversary celebration, Ann Druyan, creative director of the Voyager Interstellar Message, reminded the audience that Voyager is “the epic achievement that will speak for us, perhaps even beyond the time that our species and our planet can speak for itself.”

Fast Facts on Voyager (Source: Jet Propulsion Laboratory)

• Launched in 1977, Voyager 1 and its twin, Voyager 2, are the two longest-operating spacecraft in history.
• Commands from mission controllers on Earth take 22.5 hours to reach Voyager 1, which is exploring the outer regions of the solar system more than 15 billion miles (24 billion kilometers) from Earth.
•  Each craft are much farther away from Earth and the sun than Pluto.
• The primary mission was the exploration of Jupiter and Saturn. After making a string of discoveries there — such as active volcanoes on Jupiter’s moon Io and intricacies of Saturn’s rings — the mission was extended.
• Voyager 2 went on to explore Uranus and Neptune, and is still the only spacecraft to have visited those outer planets. The adventurers’ current mission, the Voyager Interstellar Mission (VIM), will explore the outermost edge of the Sun’s domain.
• Voyager 1 and 2, a kind of time capsule, intended to communicate a story of our world to extraterrestrials. The Voyager message is carried by a phonograph record, a 12-inch gold-plated copper disk containing sounds and images selected to portray the diversity of life and culture on Earth

Quelle: Pasadena Star News