24.04.2024
NASA’s Voyager 1 spacecraft is depicted in this artist’s concept traveling through interstellar space, or the space between stars, which it entered in 2012.
Credit: NASA/JPL-Caltech
After some inventive sleuthing, the mission team can — for the first time in five months — check the health and status of the most distant human-made object in existence.
For the first time since November, NASA’s Voyager 1 spacecraft is returning usable data about the health and status of its onboard engineering systems. The next step is to enable the spacecraft to begin returning science data again. The probe and its twin, Voyager 2, are the only spacecraft to ever fly in interstellar space (the space between stars).
Voyager 1 stopped sending readable science and engineering data back to Earth on Nov. 14, 2023, even though mission controllers could tell the spacecraft was still receiving their commands and otherwise operating normally. In March, the Voyager engineering team at NASA’s Jet Propulsion Laboratory in Southern California confirmed that the issue was tied to one of the spacecraft’s three onboard computers, called the flight data subsystem (FDS). The FDS is responsible for packaging the science and engineering data before it’s sent to Earth.
After receiving data about the health and status of Voyager 1 for the first time in five months, members of the Voyager flight team celebrate in a conference room at NASA’s Jet Propulsion Laboratory on April 20.
The team discovered that a single chip responsible for storing a portion of the FDS memory — including some of the FDS computer’s software code — isn’t working. The loss of that code rendered the science and engineering data unusable. Unable to repair the chip, the team decided to place the affected code elsewhere in the FDS memory. But no single location is large enough to hold the section of code in its entirety.
So they devised a plan to divide the affected code into sections and store those sections in different places in the FDS. To make this plan work, they also needed to adjust those code sections to ensure, for example, that they all still function as a whole. Any references to the location of that code in other parts of the FDS memory needed to be updated as well.
The team started by singling out the code responsible for packaging the spacecraft’s engineering data. They sent it to its new location in the FDS memory on April 18. A radio signal takes about 22 ½ hours to reach Voyager 1, which is over 15 billion miles (24 billion kilometers) from Earth, and another 22 ½ hours for a signal to come back to Earth. When the mission flight team heard back from the spacecraft on April 20, they saw that the modification worked: For the first time in five months, they have been able to check the health and status of the spacecraft.
During the coming weeks, the team will relocate and adjust the other affected portions of the FDS software. These include the portions that will start returning science data.
Voyager 2 continues to operate normally. Launched over 46 years ago, the twin Voyager spacecraft are the longest-running and most distant spacecraft in history. Before the start of their interstellar exploration, both probes flew by Saturn and Jupiter, and Voyager 2 flew by Uranus and Neptune.
Quelle: NASA
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Update: 7.05.2024
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Engineers found space in the geriatric spacecraft’s memory to deal with a stuck bit
Voyager 1 whizzes through interstellar space at 17 kilometers per second.
On 14 November 2023, NASA’s interstellar space probe Voyager 1 began sending gibberish back to Earth. For five months, the spacecraft transmitted unusable data equivalent to a dial tone.
In March, engineers discovered the cause of the communication snafu: a stuck bit in one of the chips comprising part of Voyager’s onboard memory. The chip contained lines of code used by the flight data subsystem (FDS), one of three computers aboard the spacecraft and the one that is responsible for collecting and packaging data before sending it back to Earth.
JPL engineers sent a command through the Deep Space Networkon 18 April to relocate the affected section of code to another part of the spacecraft’s memory, hoping to fix the glitch in the archaic computer system. Roughly 22.5 hours later, the radio signalreached Voyager in interstellar space, and by the following day it was clear the command had worked. Voyager began returning useful data again on 20 April.
NASA engineers managed to diagnose and repair Voyager 1 from 24 billion kilometers away—all while working within the constraints of the vintage technology. “We had some people left that we could rely on [who] could remember working on bits of the hardware,” says project scientist Linda Spilker. “But a lot of it was going back through old memos, like an archeological dig to try and find information on the best way to proceed.”
Minuscule Memory
Voyager 1 and its twin, Voyager 2—which also remains operational—were launched nearly 50 years ago, in 1977, to tour the solar system. Both spacecraft far surpassed their original missions of visiting Jupiter and Saturn, and in 2012, entered interstellar space.
“That mission literally rewrote the textbooks on the solar system,” says Jim Bell, a planetary scientist at Arizona State University and author of a book recounting 40 years of the mission. “We’ve never sent anything out that far, so every bit of data they send back is new.” The 1960s and 1970s technology, on the other hand, is now ancient.
Decades after the tech went out of vogue, the FDS still uses assembly language and 16-bit words. “These are two positively geriatric spacecraft,” says Todd Barber, a propulsion engineer for Voyager. Working to fix the issues, he says, is “like palliative care.”
Voyager’s flight data subsystem (FDS) and other computers were custom built for the mission by General Electric.JPL PHOTO 360-751AC
To first diagnose the issue, NASA’s engineers first tried turning on and off different instruments, says Spilker. When that proved unsuccessful, they initiated a full memory readout of the FDS. “That’s what led to us finding that piece of hardware that had failed and that 256-bit chunk of memory,” she says. In one chip, the engineers found a stuck bit, fixed at the same binary value. It became clear that the chip was irreparable, so the team had to identify and relocate the affected code.
However, no single location was large enough to accommodate the extra 256 bits. “The size of the memory was the biggest challenge in this anomaly,” says Spilker. Voyager’s computers each have a mere 69.63 kilobytes of memory.
To begin fixing the issue, the team searched for corners of Voyager’s memory to place segments of code that would allow for the return of engineering data, which includes information about the status of science instruments and the spacecraft itself. One way the engineers freed up extra space was by identifying processes no longer used. For example, Voyager was programmed with several data modes—the rate at which data is sent back to Earth—because the spacecraft could transmit data much faster when it was closer to Earth. At Jupiter, the spacecraft transmitted data at 115.2 kilobits per second; now, that rate has slowed to 40 bits per second, and faster modes can be overwritten. However, the engineers have to be careful to ensure they don’t delete code that is used by multiple data modes.
Having successfully returned engineering data, the team is working to relocate the rest of the affected code in the coming weeks. “We’re having to look a little harder to find the space and make some key decisions about what to overwrite,” says Spilker. When their work is completed, the Voyager team hopes to return new science data, though unfortunately, all data from the anomaly period was lost.
Built to Last
The cause of the stuck bit is a mystery, but it’s likely the chip either wore out with age or was hit by a highly energetic particle from a cosmic ray. Having entered interstellar space, “Voyager is out bathed in the cosmic rays,” Spilker says. Luckily, the spacecraft was built to take it, with its electronic components shielded from the large amount of radiation present at Jupiter. “That’s serving us quite well now in the interstellar medium.”
The 8-track tape aboard Voyager stores data about planets and plasma, not pop music. NASA/JPL-CALTECH
When Voyager was built, the 12-year trip to Uranus and Neptune alone was a “seemingly impossible goal for a 1977 launch,” says Barber. The longevity of Voyager is a testament of its engineering, which accounted for many contingencies and added redundancy. The mission also included several firsts, for example, as the first spacecraft with computers able to hold data temporarily using volatile CMOS memory. (An 8-track digital tape recorder onboard stores data when collected at a high rate.)
Importantly, it was also the first mission with a reprogrammable computer. “We take it for granted now,” Bell says, but before Voyager, it wasn’t possible to adjust software in-flight. This capability proved essential when the mission was extended, as well as when issues arise.
Going forward, the Voyager team expects to encounter additional problems in the aging spacecraft—though they hope to make it to the 50-year anniversary before the next one. “With each anomaly, we just learn more about how to work with the spacecraft and are just amazed at the capabilities that the engineers built into it using that 1960s and ’70s technology,” Spilker says. “It’s just amazing.”
Quelle: IEEE Spectrum