GoKawiilThe popular version of this story has hardened into a fixed shape. NASA still runs the Voyagers on software written in a programming language nobody alive can read, kept going by a handful of engineers all in their eighties, with no one queued up to replace them.
In our reading of the record, parts of this are accurate. Parts are not. The underlying problem is real, and more specific than the headline suggests.
What the spacecraft actually run
The Voyager onboard computers run assembly language written for purpose-built General Electric interrupt-driven processors, designed and fabricated in the early 1970s. Three computer systems sit on each spacecraft: the Computer Command Subsystem, the Attitude and Articulation Control Subsystem, and the Flight Data Subsystem. The FDS is the one most often in the news, because it packages science and engineering data for transmission and was the subsystem at the centre of Voyager 1’s five-month communications failure in late 2023 and early 2024.
The popular shorthand often says Voyager “runs on Fortran.” That appears to blur two things: onboard flight software and ground-side tools. The spacecraft’s low-level flight work depends on assembly-language programming on highly specialised hardware. Fortran has been associated with ground systems and older mission tooling. When NASA went looking for a replacement engineer in 2015, the brief covered both, but Suzy Dodd’s specific concern in the same coverage was finding people who could program in assembly and understand the intricacies of the spacecraft.
The spacecraft’s onboard computing resources are tiny by modern standards. Across the Voyager computer systems, the total memory is often described as roughly 64 to 70 kilobytes, less than the size of a small image file today. Dodd has compared operating it to flying an Apple II. The comparison captures the basic point: the team is operating a deep-space probe with computing resources from another technological era.
What was lost, and when
Forty-nine years of operations have produced gaps that matter more than the language itself.
Around the start of the interstellar mission, after Voyager 2’s closest approach to Neptune in August 1989, the flight software was updated to make each spacecraft more autonomous and better suited to long-term operations with less hands-on attention from Earth. That version, augmented by command sequences the team uploads every few months, is the basis of what is running now.
The team has shrunk and aged across decades. More significantly, much of the original documentation has been lost or fragmented. Voyager paperwork from the 1970s and 1980s was largely paper, and each time the project moved offices, more of it disappeared. Dodd told Live Science in early 2024 that “the people that built the spacecraft are not alive anymore,” and that although the team has a “reasonably good set of documentation,” much of it is still on paper, making the search for records feel like “this archaeology dig to get documents.”
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