• Voyager still operates using assembly code written nearly half a century ago
• NASA maintains interstellar spacecraft with less memory than a smartphone image today
• The engineers who built Voyager are disappearing faster than the spacecraft itself

Launches in 1977, NASA's twin Voyager spacecraft continues operating with onboard computers which run assembly language written for custom General Electric processors.

Each spacecraft carries three separate computer systems, with a total memory of roughly 64 to 70 kilobytes across all three - less storage than a single small image file on a modern smartphone today.

NASA's Suzy Dodd has compared operating Voyager to flying an Apple II, capturing how primitive the computing resources have become by modern standards.

What the spacecraft actually runs and why the language matters

The popular shorthand often says Voyager runs on Fortran, but that description blurs two different things together.

The spacecraft's low-level flight work depends on assembly language programming on highly specialised hardware designed in the early 1970s.

Fortran has been associated with ground systems and older mission tooling, not with the onboard flight software itself.

When NASA went looking for a replacement engineer in 2015, the job posting covered both assembly language skills and a deep understanding of the spacecraft's unique hardware architecture.

Forty-nine years of continuous operations have produced knowledge gaps that matter far more than the programming language itself.

Around the start of the interstellar mission after Voyager 2's flyby of Neptune in August 1989, the flight software was updated to make each spacecraft more autonomous.

That version, augmented by command sequences the team uploads every few months, is the basis of what is running now on both probes.

However, the team has shrunk and aged dramatically across decades, and much of the original paper documentation has been lost or fragmented over time.

Original engineers are no longer available to help

Larry Zottarelli was the last original Voyager engineer still working on the project when he retired in 2016 at the age of 80.

All of the other original engineers are dead or over 90, like Dr. Gary Flandro, an aerospace/trajectory engineer who is now living in retirement.

Dodd told Live Science in early 2024 that the people who built the spacecraft are not alive anymore, leaving a shrinking team to maintain code that no one fully understands.

The Voyager signal now takes more than 23 hours to reach Earth, and by the time NASA receives the next status check, the spacecraft will already be 1.5 million kilometres further into interstellar space.

The mission continues, but the institutional memory that built it is fading faster than the plutonium power sources that keep the probes alive.

Each passing year takes more of that knowledge with it, and when the last engineer who understands the assembly code retires or passes away, NASA will be left with paper documentation, a diminishing signal, and a spacecraft that no one alive can truly repair.

Via SpaceDaily

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