Alarms During the Landing 20 July 1969

You are advising flight director Gene Kranz as a guidance officer in Mission Control during Apollo 11’s descent to the Moon.

Minutes into the powered descent, the lunar module’s guidance computer shows a “1202” program alarm. Neil Armstrong radios for an explanation. The flight director needs a go or abort decision within seconds.

Known information

The alarm means the computer has more work than it can handle and has restarted, dropping lower-priority tasks.
In a recent training simulation, a similar alarm led to an abort call that the team afterwards judged unnecessary.
Engineer Jack Garman, working from a handwritten list of alarm codes, believes this alarm is acceptable as long as it does not occur continuously.
Navigation and guidance data coming back from the spacecraft still look good.
Aborting would mean firing the ascent engine to return to lunar orbit without landing.

Reveal what happened (spoilers: decide first)

Fact

What actually happened

Mission Control called ‘go’ and the descent continued. (Continue the descent)

Guidance officer Steve Bales, advised by Garman, called “go”. Further 1202 and 1201 alarms followed, and each time the decision was to continue. Armstrong took manual control to fly past a field of boulders, and the lunar module Eagle landed at 20:17 UTC on 20 July 1969.

Important

Possible consequences · Analysis and speculation, not fact

An abort would probably have ended Apollo 11 without a landing and handed the first landing attempt to a later mission. Whether that would have changed the programme’s timeline significantly is a matter of speculation.

History does not reveal what would definitely have happened under the other choice. Many factors could have changed the outcome.

Context · Why it was decided this way

The alarms were later traced to a switch configuration that caused the computer to process unnecessary rendezvous radar data, filling its memory. The software, designed to restart and keep the most important tasks running, did what it was built to do.

Bales later accepted the Presidential Medal of Freedom on behalf of the Mission Control team. He and others have credited the preparation done after the simulation for making a fast decision possible.