While the Orion capsule of the Artemis mission is about to skim the Moon with computers 20,000 times faster than those of the Apollo era, humanity tends to glorify the race for computing power. However, the most dizzying space feat in our history does not rely on the latest generation microprocessors. Far, very far beyond the borders of our solar system, two spacecraft launched in 1977 continue to transmit invaluable data. The Voyager 1 and 2 probes, which carry the oldest American government computers still in operation, prove every day that the engineering of half a century ago is capable of defying eternity.
An electronic brain from the era of audio cassettes
To grasp the technological miracle that the Voyager probes represent, one must delve into the context of their birth. When launched in 1977, the first movie Star Wars had just arrived in theaters and personal computers were in their infancy with the Apple II. It is with this technology from another era that Voyager 1 became, in 2012, the very first human-made object to enter interstellar space, joined by its twin six years later.
Situated over 24 billion kilometers from their home planet, these pathfinders navigate thanks to an archaic computer architecture that would amuse any modern engineer. Each probe is equipped with six rudimentary computers (distributed in three redundant systems), custom-designed by General Electric.
Their total computing power? Barely 68 kilobytes. That is a memory capacity lower than what is required to store the smallest photograph on a current smartphone. For comparison, a mid-range modern smartphone has approximately 125,000 times more RAM than the combined systems of these two probes. And to top it off, the scientific data is still recorded on an ancient 8-track digital magnetic tape.
The inexorable nuclear countdown
If the computers miraculously survived cosmic radiation and absolute cold for almost five decades, the probes face another implacable enemy: energetic hunger. At such a distance from the Sun, light is just a bright star among others, rendering solar panels completely useless.
The survival of the Voyager probes relies on radioisotope thermoelectric generators (RTGs). These mini nuclear reactors convert the heat emitted by the natural decay of plutonium-238 into electricity. Ingeniously designed without any moving parts to avoid mechanical wear, these generators have an inherent limit in nuclear physics: over the decades, the radioactive material decays and the electrical power decreases inexorably.
To delay the inevitable fate, NASA is now forced to act like a surgeon operating billions of kilometers away. To save the last available watts, engineers must make the difficult decision to amputate the probes of their senses. They proceed with the gradual extinction of heating systems and certain scientific sensors, such as Voyager 2’s famous plasma study instrument, recently turned off.
Space debris carrying an eternal message
Despite these drastic rationing measures, the agony of the probes is mathematically programmed. In the early 2030s, the generators will no longer provide enough energy to power the communication systems. The ancient computers from 1977 will permanently shut down, and NASA will lose contact with its two explorers forever.
They will then begin a silent drift, becoming simple metallic debris sailing through the Milky Way. But that would be to forget their ultimate mission. Fixed on the side of each probe is the Golden Record, a copper disc coated with gold. These artifacts contain images of our world, greetings spoken in 55 human languages, and a selection of musical works. Silent and lifeless, the Voyager probes will continue their journey for billions of years, carrying this precious message in the abyss of the universe, in the faint hope that some distant intelligence will one day encounter our memory.
