The Universe holds many mysteries. But since mid-May, it is a computer and not a stellar mystery that NASA has been trying to understand. The probe Voyager 1, sent in 1977, has an attitude problem. A midlife crisis for the oldest spacecraft still in operation?
The telemetry data, which reach the American space agency after more than twenty hours and 23 billion kilometers of travel, are distorted. The problem comes from the so-called “AACS” system. “This system controls the attitude, that is to say the way the probe is oriented in spacedescribes Rosine Lallement, astrophysicist at the Paris Observatory. In particular, it ensures that the communication antenna remains well pointed towards the Earth. » Now, the attitude data now reaching Earth is gibberish.
→ REREAD. Voyager 1 has officially left the solar system
“It’s a completely random message that doesn’t make any sense, says Michel Blanc, astrophysicist at Irap (Research Institute in Astrophysics and Planetology). It’s not even like the data indicates a wrong orientation, it’s completely incomprehensible. » However, the system works and the antenna is obviously well oriented since NASA manages to exchange without concern with the device. “If the system was faulty, we would have lost the link”, recalls the researcher.
An interstellar medium that would have broken the device
The probe also did not enter degraded mode and the scientific data, also transmitted via the antenna, correspond well to what is expected and predicted by theory. So where does the problem come from? “Something in the electronics or in the software must have taken a hitsays Rosine Lallement. Perhaps it is a reaction to collisions with high energy particles? »
Since August 2012, Voyager 1 has indeed entered the interstellar medium, the region between the stars, farther than any human objects sent into space. The probe has left the heliosphere, the Sun’s zone of influence. “Never has a mission lasted so long and never has a probe traveled in this environment. This necessarily confronts us with a lot of new things and a lot of unknowns,” philosopher the specialist of the heliosphere.
The twin device, the probe Voyager 2, broke through the barrier of the solar cocoon, the heliopause, in 2018. And does not seem to be experiencing any problems so far. Perhaps it is simply because its interstellar stay has been shorter and the device has suffered less attack from particles. Or maybe the part of the Universe where Voyager 2 advance behaves differently from that of Voyager 1the two probes not having gone in the same direction.
A possible fix if the “bug” comes from the software
To see more clearly, NASA has launched a diagnosis of the software and hardware of Voyager 1. If the defect is software, it will be possible to send a patch. “The on-board software is regularly improved, for example for the format and the compression of the data”, comments Michel Blanc. If the problem is hardware, it will be necessary on the other hand to hope that there is a redundancy. In 2017, NASA used secondary thrusters to replace the main engines. “It is also possible that the team never finds the source of the problem and simply adapts”, said Suzanne Dodd, in charge of the Voyager program at the American agency.
Anyway, the probe should only work for a few more years. Experts estimate that it will no longer produce enough energy to continue transmitting around 2025. Three plutonium nuclear batteries, RTGs (radioisotope thermoelectric generators), provide its power. Over time, they provide less than 250 watts, the equivalent of a few light bulbs. And long after losing contact with its home planet, some thirty-eight thousand years from now, Voyager 1 will pass “close” to a star in the constellation Ursa Minor. Far, very far from humanity, which had meticulously assembled it.