NASA: Space ‘electronic surgery’ operation revives Voyager 1 | The science

Last November, the antennas following the course Voyager 1 They started receiving unintelligible gibberish. It’s not that the connection is broken; It’s just that this string of ones and zeros, computer language, didn’t make sense. The probe was more than 24 billion kilometers away from us. In these circumstances, it is fantastic that the last bug that prevented us from understanding the information he was sending could be fixed. From the end of April Voyager 1 calling home again, and one of the main telephones here on Earth is on the outskirts of Madrid, in Robledo de Chavela, which pointed its six antennas at the damaged probe for the first time.

After several weeks of analysis, the problem could be related to a faulty memory chip. Like some large dinosaurs, probes Voyager They have three brains: one to decode orders sent to it, another to control navigation and antenna orientation, and a third to format and transmit data to Earth. The latest decision affected the latter. Of the three, it is the most complex, with a total memory capacity of 69 kilobytes. Not megabytes or gigabytes. Kilobytes. Smaller than the floppy disk of that time.

The solution was to change the position of some software routines using electronic surgeryto avoid using a damaged chip. The patch did not fit in any free memory space, so it had to be divided into smaller segments, distributed across all memory banks, trying, however, not to affect other functions. Currently, the deep space network antennas – in California (USA), Canberra (Australia) and Robledo – periodically communicate with the two spacecraft, either to download information from their detectors or to perform maintenance work. No one knows exactly how long they can do this.

The remaining devices continue to operate and transmit information, with the exception of the failed plasma sensor. The ship and its twin Voyager 2, embarked on an expanded mission to explore space, not only interplanetary, but also interstellar. It becomes increasingly difficult to communicate with them. Its very weak signal (which attenuates as the square of the distance) is obscured by background noise coming from space. Since their launch, the size of the antennas has been increased and the sensitivity of the receivers has been pushed to the limit so that their very faint noises can be picked up.

For this reason, for the first time in history, six radio frequency antennas at NASA’s Deep Space Madrid complex were tested to simultaneously receive data from the spacecraft. Voyager 1 20 April. Combining the receiving power of several antennas makes it possible to collect very weak signals from distant spacecraft: at the moment, five antennas are needed to transmit scientific data and, as reported Voyager 1 moves away, all six antennas will be required.

The signals arrive encrypted along with an error correction system—a series of extra bits that are interleaved with the data itself to ensure its integrity. But this extra bit is only for error detection; The larger number of bits also allows them to be automatically corrected. Voyagers first used a recovery system that required as many extra bits as the data itself. This was almost equivalent to handing them over in duplicate. New algorithms have reduced this burden to just 20%: one bit of verification for every five bits of information.

The problem is that at the distance they are at, the transmission speed is very low. Information arrives at a speed of only a few hundred bits per second. Sending an order to these ships takes 22 and a half hours, and the antennas must radiate many kilowatts of power to ensure that Voyager’s antenna (a dish only three meters in diameter) can hear anything.

Four decades of travel

It’s been more than 40 years since it visited its last target, Saturn’s moon Titan, and there hasn’t been much to see in space since. It wasn’t until the early 1990s that flight controllers turned on their cameras to record family photo all planets of the solar system visible from afar. They then turned off the power system to save energy.

The Voyagers are the only two ships that have so far left the Sun’s influence and entered an unknown environment. Two other probes Pioneer 10 And eleven, they started earlier, but on a slower trajectory, which allowed Voyager to overtake them; That New Horizonswhich Pluto explored is also on the road to retreat, but the road is still long.

At the end of 2004 Voyager 1 It passed through a shock wave created when the solar wind (a jet of subatomic particles ejected by the Sun) collides with the interstellar wind. This is not a clear limit, but it is a limit that is easily detected by on-board instruments. Voyager 2 He did this in 2007.

Eight years later magnetometer Voyager 1 discovered that the galactic magnetic field began to dominate the solar magnetic field. Thus, it escaped from the “bubble” of our star and finally entered interstellar space. It is still moving very fast: about 550 million kilometers per year, or almost four times the distance from Earth to the Sun.

At that time Titan was the main target, so the trajectory Voyager 1 It was set up to fly over him at a short distance. This made it impossible to direct it towards more distant planets and it was thrown in the same direction in which the Sun moves relative to nearby stars.

Instead of this Voyager 2 (in the range almost 19 o’clock at the speed of light) was not subject to this obligation and, after Jupiter and Saturn, was able to head to Uranus and Neptune. All the photographs we have of these planets and their family of moons were taken by this single probe. Now its trajectory is moving more or less in the opposite direction from the satellite, plunging into the southern hemisphere, so that only antennas located in Australia can track it. Voyager 1 (To 22 and a half hours at the speed of light) visible from all stations.

Probe computers were developed at a time when microprocessors as we know them today did not exist. Since then, documentation and programming instructions have not been digitized. These are thick manuals or simple data tables stored for forty-odd years in some archive at the Jet Propulsion Laboratory. Time has turned them yellow, but the worst thing is that those who wrote them – and understood them – have retired or disappeared. Today, very few technicians are familiar with these programming techniques. Old machine code or, at best, assembly code. No high-level languages ​​like Python or Java. Only ones and zeros.

At its peak, in the late 1980s, the team responsible for the care of the ships reached 300 people; Today there are only a dozen servants left who have miraculously managed to restore contact with the venerable device. The same ones who saved Voyager 2 when he lost contact with Earth for several weeks in 2023.

The nuclear reactors powering both probes will have enough fuel for perhaps another couple of years. His hydrazine reserves, which allow him to point his antenna toward Earth, will likely last longer since they are only consumed in short, random bursts of a few milliseconds. And then? All that opens before them is the vast emptiness of space. For 40,000 years Voyager 1 It will pass less than 2 light years from an unnamed star AC+79 3888 in the constellation Giraffe; After about 3000 centuries Voyager 2 This will happen near Sirius, the brightest in our sky.

His further course is unpredictable. It is possible that they will be trapped in orbit within the Milky Way itself, carrying with them two golden disks created by Carl Sagan containing photographs and sounds of Earth and the distant hope that someone will be able to collect them and interpret them into the future when our civilization no longer.

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