The AMSAT-OSCAR 7 (AO-7) satellite was launched into orbit on November 15, 1974 on a Delta 2310 rocket from Cape Canaveral as a secondary payload. Like many AMSAT spacecraft, it demonstrated a number of firsts:

* Satellite-to-satellite relay communication via AO-6.
* Early demonstrations of low-budget medical data relay and Doppler location of ground transmitters for search-and-rescue operations were done using this satellite.
* The Mode-B transponder was the first using “HELAPS” (High Efficient Linear Amplification by Parametric Synthesis) technology was developed by Dr. Karl Meinzer as part of his Ph.D.
* First to fly a Battery Charge Regulator (BCR).

The spacecraft went silent in 1981, presumably when its batteries gave out. However, in 2002 it was discovered to be working again and remains semi-operational till today: Ham Radio in Space: AO-7 “Zombie” Satellite Again Enjoying Its Time in the Sun – ARRL Letter

The ham satellite organization theorizes that AO-7’s batteries shorted when they failed, but the short circuit subsequently opened, allowing the satellite to return to life. This means AO-7 only works when it’s receiving direct sunlight and shuts down when in eclipse. Since the satellite became undead, terrestrial users have enjoyed numerous contacts via AO-7.

“AO-7 is alive and doing okay,” satellite observer Frank Griffin, K4FEG, reported this week. “This season’s eclipse cycle has ended.” Griffin explained that the eclipse period, during which AO-7 falls silent, lasts about 9 weeks, from mid-spring to mid-summer. According to its operating plan, AO-7 switches to Mode B (70 centimeters up/2 meters down) at 0000 UTC.