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Voyager's 15 Billion Mile Software Update
In 1977, NASA launched two robotic space probes - Voyager 1 and Voyager 2 - on an ambitious mission to study the outer planets of our solar system. Now, over four decades later, these intrepid spacecraft are still out there, having traveled an astonishing 15 billion miles from Earth. But how can 40-year-old technology stay operational for so long, especially when the signals from Earth take over 20 hours to reach the spacecraft? The answer lies in the Voyager team's ability to send software updates across billions of miles of space.
To start with, the Voyagers were built to last. The engineers at NASA's Jet Propulsion Laboratory designed the spacecraft to be robust and reliable enough to visit Jupiter, Saturn, Uranus and Neptune. The Voyagers are powered by three radioisotope thermoelectric generators that convert heat from the natural decay of plutonium-238 into electricity. This provided plenty of power for the onboard computers, scientific instruments and communication systems. The computers are based on custom-designed, low-power CMOS chips that are incredibly resistant to radiation damage. Obviously, longevity was a major priority.
In addition, the software running on the Voyagers was designed to be updated during the mission. When the spacecraft were launched in 1977, the software was stored on cassette tapes. Commands from Earth were designed to trigger certain routines on the tapes, allowing new instructions to be uplinked. This meant the mission scientists could fix bugs and adjust the flight plan instead of being permanently locked into 1977 technology. The software was updated numerous times during encounters with the outer planets to optimize data collection and spacecraft operations.
For example, a critical software update was transmitted to Voyager 2 before it flew by Uranus in January 1986. This “inflight retargeting” allowed the spacecraft's instruments to image previously unknown moons that had been discovered in the planet’s rings. The new commands enabled Voyager 2 to pivot and take photos of these moons instead of just streaking by. This retargeting allowed Voyager 2 to beam home extremely valuable images and readings from these tiny icy worlds.
Remarkably, even after the Voyagers completed their “Grand Tour” of the outer planets, their software kept being updated. After Voyager 2 flew by Neptune in 1989, both spacecraft resumed their journey into the depths of interstellar space. There wasn’t much left to study out there, so the probes were “repurposed” by giving them new software instructions.