NASA still maintains some of the Voyager spacecraft code in a 1970s-era programming language that almost nobody on Earth fully understands anymore, and the handful of engineers who do are now in their 80s – Image for illustrative purposes only (Image credits: Unsplash)
The Voyager spacecraft continue their journey through interstellar space, but their survival now rests on a narrow set of skills that fewer people possess each year. Engineers must still work with assembly language written for custom processors built in the early 1970s, a level of programming that demands intimate knowledge of hardware long out of production. Without that expertise, even routine commands risk becoming impossible to craft safely. The situation has grown more pressing as the original team members reach advanced age and institutional records remain scattered across aging paper files.
The Actual Computing Systems Aboard Each Probe
Each Voyager carries three separate computer systems designed for specific roles. The Computer Command Subsystem handles overall operations, the Attitude and Articulation Control Subsystem manages orientation and instrument pointing, and the Flight Data Subsystem packages science and engineering measurements for transmission back to Earth. The last of these drew particular attention during Voyager 1’s extended communications outage that lasted from late 2023 into early 2024.
These systems run on purpose-built General Electric processors that use assembly language written specifically for the mission. Total memory across all three computers amounts to roughly 64 to 70 kilobytes, a capacity smaller than many single photographs taken by modern smartphones. Project manager Suzy Dodd has likened the task to operating an Apple II computer from the same era, underscoring how limited the onboard resources remain after nearly five decades in flight.
Knowledge Gaps That Have Accumulated Over Time
After Voyager 2’s final planetary encounter at Neptune in 1989, engineers updated the flight software to allow greater autonomy during the long interstellar phase. That core version, supplemented by command sequences uploaded every few months, still governs both spacecraft today. Yet much of the supporting documentation from the 1970s and 1980s existed only on paper and has been lost or fragmented during repeated office relocations.
The people who originally designed and built the hardware are no longer available. Current staff must therefore reconstruct necessary details through whatever records survive, a process that resembles an archaeological effort. This loss of context creates practical difficulties whenever unexpected behavior occurs or new commands must be developed.
The Current Team and Its Shrinking Support Network
The flight team at NASA’s Jet Propulsion Laboratory remains small but includes engineers who joined the project well after launch. Suzy Dodd herself began working on Voyager sequences in 1984 and returned as project manager in 2010. Larry Zottarelli, the last original engineer still active on the mission, retired in 2016 at age 80 after decades focused on the Flight Data Subsystem.
Younger engineers possess general technical ability, yet few have both the inclination and the opportunity to master assembly programming on these obsolete custom processors. The team maintains a short roster of retired specialists who can be consulted during emergencies, though that list continues to shrink. The core challenge lies less in the code being unreadable and more in the narrowing pool of people who understand its precise interaction with the aging hardware.
What Comes Next for the Mission
Power output from the radioisotope thermoelectric generators declines by about four watts each year, forcing the gradual shutdown of instruments to preserve basic spacecraft functions. Engineering data may continue to reach Earth for several years after the last science measurements stop. Current projections indicate the probes could remain within range of the Deep Space Network until around 2036, depending on available transmit power.
The 50th anniversary of the launches arrives in September 2027, marking the next major public milestone. Beyond that point, the succession question becomes increasingly urgent. The mission’s remaining lifespan will be measured in years rather than decades, and the window for passing critical knowledge forward is closing.
The Human Stakes Behind the Technical Challenge
Succession planning now centers on identifying engineers willing to invest time in a mission with a known endpoint. The conditions that produced the original team, including extended hands-on work with early digital hardware, no longer exist in standard training programs. As a result, the institutional memory required to keep the Voyagers operational rests with a dwindling group whose experience cannot be easily replicated.
This reality highlights a broader pattern in long-duration spaceflight: hardware endurance often outlasts the human expertise needed to maintain it. The Voyagers have already exceeded every original expectation, yet their continued operation depends on preserving skills that are themselves approaching retirement.