Longest-serving satellite OSCAR-7 marks 50 years in orbit

Longest-serving satellite OSCAR-7 marks 50 years in orbit
by Clarence Oxford
Los Angeles CA (SPX) Nov 12, 2024

Launched on November 15, 1974, OSCAR-7, a microsatellite, continues its mission 50 years after its launch, serving as a vital asset for amateur radio operators globally. It holds the title of the oldest operational satellite, predating the launch of NASA's Voyager 1 and Voyager 2 by three years.

OSCAR-7 belongs to a series of amateur radio satellites known as OSCARs (Orbital Satellites Carrying Amateur Radio), built by volunteers from the Radio Amateur Satellite Corporation (AMSAT). Many of these contributors have affiliations with significant U.S. space organizations such as the Goddard Space Flight Center. AMSAT's innovation led to the novel use of secondary payloads to stabilize the center of gravity during launches. Despite being constructed primarily on basement workbenches by AMSAT volunteers, OSCAR-7 had to meet rigorous space-readiness standards to be integrated alongside the primary payload, NOAA-4/ITOS-G.

Engineered with CMOS technology, OSCAR-7 was initially projected by NASA engineers to last just one to three years due to its non-radiation-hardened components. However, the satellite not only outlasted its expected lifespan but also contributed notable advancements. It enabled early ground-to-satellite-to-satellite-to-ground communications by orbiting close to its predecessor, OSCAR-6, facilitating unique message relays between satellites.

A major achievement attributed to OSCAR-7 was its role in the early testing of Doppler-based location of emergency signals. Through collaboration with the COSPAR/U.S. SARSAT teams, simulated emergency location transmitters (ELTs) were transmitted and analyzed, demonstrating that passing signals through the satellite could accurately determine beacon locations. This technology laid the groundwork for the COSPAR/SARSAT system, which has since been credited with saving over 57,000 lives during more than 17,000 emergency incidents.

OSCAR-7's primary mission ended in 1981 when battery failure cut off power. However, in June 2002, it unexpectedly resumed operation, detected first by an amateur radio operator who identified its telemetry signal. This revival was confirmed globally and attributed to a possible change in the battery's state that allowed solar power to reach the onboard systems once more.

Endearingly called the "Sleeping Beauty" of satellites, OSCAR-7 has continued to offer scientific insights, including confirming orbital disturbances long hypothesized by NASA researchers. Despite its recent erratic telemetry and unpredictable transponder behavior, OSCAR-7's legacy as a pioneering satellite remains secure.