Voyager - the interstellar Godwit is nearly one light-day away
The Voyager spacecraft are now in deep interstellar space, further away from the earth than any other artifact made by humanity. In exactly four months (November 18th) Voyager 1 will be a full light-day1 away from us. Launched in 1977, to take advantage of planetary alignment that happens once every 175 years, these probes were a budget-curtailed version of the Grand Tour program (conceived in 1964!) that aimed to visit all the outer planets. NASA has built and launched many observatories and probes that are amazing fusions of imagination, science, engineering and sheer determination (c.f the Parker Solar probe, or JWST or the Hubble ST or the Mars Rovers). But the Voyager crafts are in a class by themselves.
The Interstellar Age by Jim Bell is a great history of the Voyager missions. The NASA Voyager mission page is a treasure trove of information and provides current status. The identical probes, Voyager 1 & 2, have outlived their design lifetimes (5 years) by more than four decades. There are so many different connections between the Voyagers and other topics I have discussed in these newsletters.
There are so many fascinating aspects to the design of the Voyager, each worthy of deep study. Each Voyager spacecraft comprises approximately 65,000 individual parts, representing a highly complex electro-mechanical assembly for its time. The Golden Record on the craft is probably the greatest concept album of all time. The Voyager spacecraft was the first unmanned planetary mission to utilize a distributed computing architecture. This architecture divides onboard management among three dual-redundant, custom-engineered computer systems. I recently answered a question from an FAA colleague about moving all compute for NAS systems into a central capability. I cannot emphasize enough my admiration for the distributed architecture of the current NAS and the resiliency and local survivability that architectural choice provides us. There is a lot to learn from the decision to distribute the compute infrastructure on the Voyager into three separate (and redundant) systems. Due to those choices the inventive team at JPL has found ways to keep the craft operating over decades despite multiple unanticipated malfunctions of components of the craft. Over the decades, the JPL flight team has had to engage in a kind of long-distance forensic engineering to recover from critical failures, including:
In 1977, right at the launch phase of Voyager 2, a problem caused its spectrometer mirrors to physically warp, severely degrading its sight. Recognizing they couldn't reach it, engineers creatively repurposed a small heater intended for an entirely different phase of the mission to fix the issue, snapping the optics back into focus before the planetary flybys. The planetary flybys were the primary purpose of the mission.
In 1978 when Voyager 2’s backup radio receiver tracking loop capacitor failed, the craft lost its ability to automatically track drifting frequencies from Earth. JPL engineers solved this by meticulously calculating thermal and Doppler frequency shifts hour by hour, choosing to manually "tune" the ground transmitter to the exact shifting frequency the probe could hear. This continues to this day.
In 2023-24 after a single memory chip handling packaging software failed and caused Voyager 1 to transmit absolute binary nonsense, the team spent five months operating blindly. They successfully rewrote the flight software, slicing the program into tiny fragments, tucking them into various tiny vacant pockets across healthy memory. They reprogrammed Voyager 1 from 15 billion miles away!
Decades of aging caused a fuel tank rubber diaphragm to emit a byproduct that mixed with propellant and left residue clogs, choking the attitude-control thrusters down to half the width of a human hair. Engineers pulled up original 1970s blueprints to execute a high-stakes change to alternate back-up propulsion lines. They had to come up with this creative workaround a couple of times (in 2017 and 2024). The thrusters are key because the crafts antenna has to be pointed back to earth for it to communicate with NASA.
Last year when Voyager 1's active "roll" attitude-control engines began failing due to physical wear, threatening a permanent misalignment from Earth, JPL engineers formulated a daring remote rescue command. They successfully revived a completely separate set of backup roll thrusters that had been left dormant and untouched since 2004, stabilizing the probe's orientation.
These recoveries show that the JPL team does not look at Voyager as a collection of static parts, but as an adaptive, evolving system. A system launched in 1977 has continued to evolve remotely (with guidance from the JPL engineers on earth for sure). The design choices made a long time ago allowed this wonderful set of adaptations to take place. This remote adaptation isn't just a triumph of human coding; it brings to mind one of the most extreme endurance strategies in the natural world: the flight of the bar-tailed godwit.
The bar tailed godwit leaves Alaska at the end of the northern summer, flies south, non-stop, to Tasmania or New Zealand. To prepare for this journey their digestive system shrinks (won’t be eating for a while), kidneys atrophy (to reduce weight), and their exercise organs grow (have to sustain that grueling flight). During the flight, once they exhaust their massive fat reserves, godwits literally consume their own internal organs and flight muscles for protein and metabolic water. Towards the end of the trip even the heart and lungs decrease in size as the bird's overall body mass drops and requires less oxygen transport. The Voyager spacecraft are following a similar strategy. To keep them alive as their plutonium-238 power sources decay, NASA engineers are engaged in a decades-long process of "instrument triage." Most recently, Voyager 2's Low-Energy Charged Particle instrument was shut down in 2025, and Voyager 1's followed in early 2026.
On November 18th, a signal from Voyager 1 will be received by NASA’s Deep Space Network (DSN) a full day after transmission by the craft. The DSN itself is a fascinating engineering marvel. The transmitter on the Voyagers operates at 22 Watts. That is about the power of the light bulb inside your fridge. In contrast, your local FM station broadcasts at 50,000-100,000 watts. Because radio waves spread out like an expanding sphere as they travel through space (following the inverse-square law), the vast majority of that 22-watt signal misses Earth entirely. By the time the signal completes its day long journey across the solar system, the tiny fraction hitting DSN antennas is unimaginably weak. NASA engineers measure the received power at roughly 1 attowatt, which is 1 x 10^-18 watts.
Written out fully, the power striking the massive, 70-meter ground dishes looks like this: 0.000,000,000,000,000,001 Watts. What NASA accomplishes daily is to imagine capturing a whispered conversation from 1,000 miles away and an hour ago, all while standing in the dead center of a roaring rock concert.
In an age obsessed with noisy, central compute, Voyager reminds us of the quiet, enduring majesty of brilliant, distributed design.
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