The Voyager 2 probe surrounded by its engineers, March 23, 1977.
© NASA/ JPL/ Caltech
The two Voyager probes left for space in the last century, at the twilight of the 1970s, when neither Thomas Pesquet nor Emmanuel Macron were born! After photographing Jupiter, Saturn, Uranus, Neptune, their multiple moons, taking the famous family photo of the Solar System and the legendary image Pale Blue Dot (A pale blue dota photograph of the Earth taken from the enormous distance of 6 billion kilometers), these spacecraft are still at work, 47 years after their takeoff. Alive, but injured, half of the scientific measuring instruments are now turned off in order to save energy.
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This solidity and efficiency obviously command respect, but where do they come from? How do NASA, JPL (American research center in charge of robotic space missions) and other teams of engineers on the ground manage to keep these two machines in service today, when they are both more 20 billion kilometers from us?
“We didn’t design them to last 30 years or 40 years [mais] so as not to fail”
Let us not forget that these ships carry the Golden Record, our message addressed to possible extraterrestrial civilizations, but above all the testimony of terrestrial life, from our strands of DNA to the song of whales through our mathematics. It took a year for the commission chaired by the famous astronomer and astrophysicist Carl Sagan to choose the elements to engrave in this disc plated with nickel, then gold.
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John Casani, head of the Voyager project from 1975 to 1977, explains in what state of mind and with what objective these indestructible machines were built at a time when computing was still rudimentary. Yes, indestructible, because it is estimated that Voyager 1 and 2 should survive the death of the Sun and our own planet…
John Casani in front of Voyager and the legendary Golden Record.
© Nasa / JPL / Caltech
One of the keys is redundancy: every part has its double, and even machines are doubles!
The principle of component redundancy is pushed to its peak since the Voyager probes themselves form a duo. Each “vital” system thus has its replacement, in case a problem appears. But that's not all!
The probe battery, responsible for powering everything, is a thermoelectric generator which operates thanks to the disintegration of the radioisotope plutonium 238. The latter releases a lot of heat per kilogram (thus transformed into electricity) and little gamma radiation. Its radioactive half-life being 87 years, this therefore leaves a certain margin. Unfortunately, nothing lasts forever: Voyager 1 and 2 lose about 4 W of power each year and will one day be as cold as the icy Universe…
This is the battery used by Voyager 1 and 2, running on plutonium 238.
© Nasa / JPL / Caltech
You can even follow Voyager 1 and Voyager 2 in real time thanks to this NASA page!
Solutions to aging must be creative!
In 1977, the computer languages were not those used today and, unsurprisingly, were less efficient, with some current two-line codes taking 15 in the languages of the time (notably assembly). However, computer engineers capable of coding in Fortran to communicate with Voyager probes are no longer common in the streets.
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Thus, during a big bug at the end of 2023, Voyager 1 sent data without any meaning, as if it were aphasic: no one understood anything about its signals. It took several months before the team figured out the problem and solved it from 15 billion miles away. The chip (FDS) which stored the memory was indeed damaged and the code had to be rewritten and then reinjected into the system. Clever and knowing that there was no longer enough memory space available, the computer engineers fragmented this crucial program into sub-parts and then put everything back into operation in the spring of 2024.
The joy of the engineering team when after five months of “space battle”, they managed to “cure” Voyager 1.
© Nasa / JPL / Caltech
Alas, Voyager 1 like Voyager 2 inexorably loses energy and cools down. One day, or rather one cosmic night, they will be too far away and exhausted for us to follow them. They will then drift for billions of years, taking with them the memory of our existence and these words from Carl Sagan's son: “Hello from the children of Earth”…
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