Transit 5B-5 entered orbit on December 13, 1964, as part of the US Navy’s early satellite-navigation program. Its navigation mission failed after only a few weeks, but the spacecraft remained in orbit.
More than six decades later, amateur radio observers still report receiving a telemetry signal near 136.658 MHz when the satellite is illuminated by the Sun. That makes it one of the oldest spacecraft from which a signal is still observed.
What is still operating
The spacecraft is not providing navigation services and nobody is commanding it. The surviving signal is telemetry from uncontrolled hardware, received intermittently as orbital and lighting conditions permit.
The community-maintained SatNOGS database entry for Transit 5B-5 records the launch date, orbital identity, and reported transmitter frequency. The Signal Identification Wiki describes observations of the signal and notes that it appears when sunlight reaches the spacecraft.
The power-source correction
An earlier version of this article said Transit 5B-5 was powered by a SNAP-3 radioisotope generator. That was incorrect. Transit spacecraft from the period used different power systems, and Transit 5B-5’s surviving transmission is associated with its solar power.
The distinction matters because the signal is not evidence of a nuclear generator operating continuously for six decades. It is evidence that parts of an early solar-powered telemetry system can still function intermittently long after the mission ended.
A signal, not an active mission
Calling Transit 5B-5 active can be misleading. It remains in orbit and sometimes emits a receivable signal, but it is not an operational satellite under Navy control. Amateur observers listen to it as a piece of spaceflight history, not as a current government service.
The accurate story is still remarkable: hardware launched in 1964, declared unsuccessful as a navigation mission, can occasionally be heard by people with suitable radio equipment more than sixty years later.
Editor’s note: This article was substantially corrected on September 14, 2026. The earlier version gave the wrong launch date and power source and overstated the satellite’s current operational status.
