“Alarms Went off in the Spacecraft.” How IBM Computer Whizzes Saved Apollo 11
Fortune - Sun 21 Jul 04:49 GMT

"July 20th was our D-Day,” says a retired IBM engineer who remembers the man who saved an almost-aborted moon landing.

  But as the Apollo 11 mission neared the moment of truth, beginning its descent toward the lunar surface, crisis struck.

  “We knew what it felt like for the air to be sucked out of building 30 because an abort had been called when it shouldn’t have,” Ahr says, referring to the instant onset of depression that befell workers inside the facility where IBM’s so-called real-time computer complex, the mechanical brains of the mission, was housed, when a test-run went awry.

  “It’s always more chaotic or emphatic or disconcerting when it happens during a real mission," Ahr adds.

  Jack Garman, a NASA computer specialist and avionics expert trained on IBM's computers, had been asked by Gene Kranz, the mission's chief flight director, to write down all possible error conditions to prepare for any contingency.

  "It took 10-to-15 seconds the first time [the alarm] occurred for him to say ‘Keep going,’" Ahr remembers.

  Each time an alarm triggered, as the Apollo mission's lunar module descended faster toward the Moon's surface, Garman told his superiors to continue the mission.

  The Apollo 11 mission "was an incredible accomplishment,” says IBM Research’s Kelly.