Artist’s impression of a Voyager probe. Credit: NASA
Two calls from space have reached our planet in recent days. One came from the small Japanese lander Slim, which has been lying on the lunar soil since January 20th. The other from an old acquaintance, NASA’s Voyager 1 probe, over 24 billion km away – the farthest artifact there is. For different reasons, both calls – although highly anticipated – were far from a given.
Let’s start with the latter. Launched into space on 5 September 1977, just two weeks after the twin probe Voyager 2, and having long since arrived beyond the boundary of the heliosphere, therefore into interstellar space, it is not the first time that Voyager 1 has shown understandable signs of fatigue. The latest, however, was worrying scientists at NASA’s Jet Propulsion Laboratory more than usual: in fact, since November 14, 2023 https://twitter.com/NASAJPL/status/1734617628545564771. Or rather, it was no longer able to send readable data: in Pasadena, California, the mission control center knew that the probe continued to receive commands and function normally, but the telemetry packages, both scientific and engineering, were completely unusable.
The person responsible, NASA engineers established last month, this time was one of the three on-board computers of the probe: the Fds (from the English flight data subsystem), i.e. the flight data subsystem. Made up of two 16-bit machines, the FDS has the task of packaging scientific and engineering data before sending it to Earth. A task that he evidently could no longer carry out correctly. An engineer from NASA’s Deep Space Network, the network that manages the radio antennas that communicate with the two Voyager probes and many other spacecraft, had however managed to decode the signal, discovering that it contained a copy of the entire FDS memory same. Valuable information: by comparing it with one of the readings prior to the malfunction, it was possible not only to understand the exact cause of the problem, but also how to resolve it. The malfunction was caused by the breakage of a chip responsible for managing a portion of the FDS memory: since there was part of the FDS code in those memory banks, no longer being able to access it had rendered the scientific and engineering data unusable.
How to do? Since the chip was impossible to repair, the mission engineers decided to move the code to another portion of memory. However, since there was no free space large enough to house it internally, they had to divide it into smaller parts and readjust it to ensure that it could continue to function, although no longer contiguous but broken up into many segments. Not an easy task and unacceptable errors, having to install everything on a computer from half a century ago and 24 billion km from the nearest repair service.
The team therefore got to work transferring only part of the code, the one dedicated to packaging engineering data. The upload began last April 18, but since traveling at the speed of light a radio signal takes over 22 hours to reach the probe and the same amount to return back, only two days later – April 20 – it was possible to obtain a response: The change was successful. For the first time in five months, it was possible to verify the state of health of the spacecraft. Over the next few weeks, the remaining portions of code will also be relocated, so that even the flow of scientific data from the most remote human outpost can resume regularly.
Third awakening for the Slim lunar lander
In the meantime, as we were saying, after a long and cold lunar night – over 14 Earth days in the dark and with temperatures reaching 170 degrees below zero – on 23 April signs of life also arrived from the Japanese Slim lander. Jaxa made it known https://twitter.com/SLIM_JAXA/status/1783330118683050427 understandably enthusiastic, considering that the small module was not designed to last so long, nor had he taken into account that it would have to spend its stay on the Moon with its nose facing downwards.
And instead he not only woke up but also – as soon as he reopened his eyes – found the energy, thanks to solar panels, to take a photo and send the image to the ground: we can see it in the tweet above. What Slim has just left behind is his third lunar night, and to make sure whether he really got through it unscathed, an analysis of his conditions and the inevitable deterioration due to the alternation of daytime and very cold nights. In any case, for Japan – the fifth country in the world, after the Soviet Union, the United States, China and India, to have successfully made a landfall soft on our satellite – it is already a success beyond all expectations.
