Science & Technology

The First Men on the Moon Almost Didn't Make It There

When Apollo 11 astronauts performed their final descent to the moon 49 years ago, they almost didn't make it. Neil Armstrong and Buzz Aldrin were just a few minutes from a historic landing when their spacecraft's computer got overloaded. A quick decision by a smart computer engineer saved the day.

Columbia and Eagle

Let's back up a moment to the late 1960s. NASA and the Soviet Union were engaged in a race to send humans to the moon first. Why? A lot of it was wrapped up in political prestige — the first nation to reach the moon would be recognized the world over for their powerful technology. Plus, a moon landing was a great chance to stimulate the economy and invent new technologies.

NASA's moon program was called Apollo, and it actually consisted of many missions. Some of them were engineering missions to test out the spacecraft, while others were exploration missions that did real and simulated moon landings. The first moon landing was designated as Apollo 11, which set its target on the Sea of Tranquility near the moon's equator. On July 20, 1969, the world watched as the Apollo 11 astronauts began their descent on this extraterrestrial world.

Apollo 11 was made up of two spacecraft. The command/service module was designed to bring the crew all the way to the moon and then back again, through the fiery reentry of Earth's atmosphere. It was called Columbia and was commanded by Michael Collins, who stayed behind while his crewmates went to the surface.

The other spacecraft was a lunar module called Eagle, commanded by Neil Armstrong and co-piloted by Edwin "Buzz" Aldrin. Eagle was designed to fly to the moon's surface and then back again to Columbia — that is, as long as Armstrong and Aldrin could do so safely. Spoiler alert: Eagle made it, but not without some drama.

Program Alarm 1202

Eagle was in its automatic descent to the surface when one of the astronauts sent a cryptic message: the computer on board was showing a "1202 alarm." The astronauts weren't sure what this alarm meant, because it was obscure and computers weren't very user-friendly back then. But engineers on the ground knew a 1202 meant the computer was overloaded.

You can get a sense of what the engineers were thinking in a 1994 perspective of the alarm on the Apollo Lunar Surface Journal from Fred Martin, who was part of Intermetrics Inc. and involved in the Eagle computer design. "The alarms continued to appear at intervals of approximately 10 seconds," Martin recalled in his account. "Everyone was tense and anxious."

A NASA software engineer called Jack Garman made the "gutsy call" to tell Mission Control to push on, Martin said. Garman's instinct was based on his experience with the system; he felt that if the computer wasn't making certain calculations, they weren't necessary for the landing. With NASA and the world holding its breath, the astronauts made their way to the surface, alarms blaring. Just moments before touching down, Armstrong took over the computer's control and manually steered Eagle to a safe landing at 4:17 p.m. Eastern Time on July 20, 1969.

The world erupted in celebration, but NASA — business-like and anxious for its astronauts' safety — called Intermetrics about 10 seconds after Eagle was secured on the surface. "What were those alarms? We're launching [from the moon] in 24 hours and we're not going with alarms," Martin recalled them saying. It took some simulations and some old-school printouts to figure out the cause, but it was traced back to one astronaut not putting a switch in the correct position before landing. Eagle's liftoff from the moon, happily, had no such alarms.

Ready to relive that historic day? NASA has a restored video of the entire moonwalk and related activities, lasting about three hours. The entire thing is on YouTube.

For the full story, check out the book "Moonshot: The Flight of Apollo 11" by Brian Floca. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Side-by-Side View of Apollo 11 Landing with LRO Data Reconstruction

Written by Elizabeth Howell July 19, 2018

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