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Hundreds of things had to go according to plan for Apollo 11 to land astronauts on the Moon and return them to Earth successfully. The flight proceeded mostly generally as planned, but there were a number of potential missionstoppers that the general public only learned about later.


The story of humanity’s first visit to another world is one that is well known. But this grand saga, one filled with drama and grandeur, often omits many details–the small moments of apprehension, concern, and sometimes even fear–which attended the mission of Apollo 11, carrying the first crew to attempt a landing on the Moon.


Neil Armstrong, Buzz Aldrin, and Michael Collins departed Earth from the Kennedy Space Center on July 16, 1969. Three days later they were in lunar orbit. On July 20, Armstrong and Aldrin entered the Lunar Module (LM), and fired its descent engine to initiate their long fall to Mare Tranquilitatis, dozens of miles below them.

The Apollo 11 Lunar Module Eagle was passing 33,000 feet (about 10,000 meters), headed to the Moon below, when the first alarm went off. The Eagle’s guidance computer had become overloaded and locked up, displaying a numeric error message on its display: “1202.” After a flawless launch, a by-the-numbers transit across 240,000 miles (386,243 kilometers) of space to the Moon, and having braked the Command and Service Module (CSM) Columbia into lunar orbit, a computer malfunction could cause America’s first landing on the Moon to be scrubbed over a few errant electrons.

Neil Armstrong, who was piloting the Eagle, looked at the readout with concern, as Buzz Aldrin, his comrade in this great adventure, continued to watch the computer, as he had been throughout. Neither man knew what the alarm meant—only that it represented a potential mission scrub and could cause them to cut short the landing attempt. Landing on the Moon was not something that could be eyeballed, like setting down at a local airstrip on Earth. If the computer failed, they would have to abort, staging the LM and making an emergency ascent back to Mike Collins and the waiting CSM in orbit, a potentially dangerous maneuver.

“Program Alarm,” Armstrong said, with the slightest edge of tension in his voice. “It’s a 1202.”

The radio signal between the LM and Mission Control had been weak, so Aldrin repeated, “1202.” In Houston, flight controllers scrambled to discern what the 1202 code meant, as nobody had recognized it immediately. Then a call came from a team of engineers in an operations support room adjacent to Mission Control, and Steve Bales, the controller responsible for the navigation computer, told Flight Director Gene Kranz that it was okay to proceed. Relieved but still concerned, Kranz assented.

What the 1202 computer alarm looked like to Armstrong and Aldrin aboard the Lunar Module. This is a modern reproduction of the Apollo Guidance Computer.
Nick Howes
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Apollo 11 50th anniversary Special Edition