There is a single satellite launched by the US Navy in 1964 that is still in orbit, still transmitting, and still being used by amateur radio operators around the world – and nobody at the Navy has been in charge of it for decades – Image for illustrative purposes only (Image credits: Unsplash)
Every day, people with modest radio equipment in their backyards tune in to a signal that has traveled through space since the mid-1960s. The source is a small satellite placed in orbit by the US Navy on December 28, 1964, from Vandenberg Air Force Base in California. That spacecraft, known as Transit 5B-5, was never meant to operate this long, yet it continues to send out its distinctive beacon without any official oversight. Its persistence offers a rare window into engineering choices made when space hardware was built to endure rather than to be replaced quickly.
Built for Submarines, Designed to Last
Transit 5B-5 formed part of the earliest satellite navigation network, created to give American submarines accurate position fixes anywhere on the globe. The system predated GPS by decades and relied on a constellation of similar spacecraft. Engineers expected each satellite to function for perhaps five years at most, given the harsh conditions of low Earth orbit and the limits of 1960s technology. The satellite weighed roughly 70 kilograms and followed a polar path that allowed repeated passes over populated areas.
By the time GPS assumed navigation duties, the entire Transit program had been retired in 1996. Official responsibility for Transit 5B-5 ended then, leaving the spacecraft without maintenance, commands, or monitoring from its original operators. Despite that absence of support, the satellite has remained in its original orbit and has never ceased its transmissions.
A Nuclear Power Source That Keeps Giving
The key to the satellite’s longevity lies in its power system, a SNAP-3 radioisotope thermoelectric generator fueled by plutonium-238. This device converts the steady heat from radioactive decay directly into electricity, without any reliance on sunlight or chemical batteries that degrade over time. Plutonium-238 has a half-life of about 88 years, so the generator still produces a substantial fraction of its original output more than six decades after launch.
Because the transmitter requires only minimal power, the satellite can continue broadcasting a telemetry signal at 136.65 MHz. There are no moving parts to fail, no propellant to exhaust, and no complex computer systems prone to glitches. The result is a simple, self-contained machine that drifts through space while steadily emitting its signal, year after year.
Amateur Operators Keep the Signal Alive in Practice
Today the only regular listeners are members of the amateur radio community who track the satellite with inexpensive software-defined radio receivers. These hobbyists decode the rhythmic tones into data about the spacecraft’s temperature and basic systems. One Canadian operator, Scott Tilley, has followed Transit 5B-5 for years and described it as the oldest satellite he has heard still transmitting.
Tilley noted that the spacecraft produces a pulsing tone that stands out clearly when it passes overhead. He has compared the experience to hearing the satellite “sing” as it moves across the sky. No special permissions or military contacts are required; anyone with basic equipment and patience can capture the same signal that was first sent when Lyndon B. Johnson was president.
What Enduring Design Reveals About Technology
The continued operation of Transit 5B-5 highlights a different approach to engineering than the rapid replacement cycles common today. Its creators accepted the high cost of a space launch and therefore built the satellite to exceed its expected lifespan by a wide margin. The nuclear power source and minimalist design have allowed it to outlast both its mission and the institution that launched it.
While the Navy has long moved on, the satellite itself shows no sign of stopping. It travels at roughly 17,500 miles per hour in a stable orbit, powered by decaying plutonium and broadcasting data that no longer serves any official purpose. For those who still listen, the signal represents a tangible link to an earlier era of space exploration, one in which hardware was expected to keep working long after its designers had retired.