What Happened on April 10th
During preparations for the maiden voyage of the Columbia space shuttle, NASA engineers were monitoring a glitch in the shuttle’s computer systems. Synchronization between the main and backup AP-101 flight control computers was found to be the culprit behind the bug. Two gears were discovered to be out-of-sync – and repair would take at least a day to resolve the problem. Liftoff was re-scheduled for two days later, and countdown and launch on April 12 proceeded with no further setbacks. Columbia landed safely at Edwards Air Force Base in the Mojave Desert after orbiting Earth 34 times. NASA’s five space shuttles each housed 4 IBM AP-101 computers, with a fifth serving as a backup flight system computer. The AP-101s were built around transistor-transistor logic (TTL) semiconductor circuits and used the same architecture as the IBM System/360 family of computers. An earlier version of the AP-101 was first announced by IBM in 1966 as the 4Pi computer.