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While Apollo 11 astronauts made their historic descent onto the moon’s cratered surface 45 years ago, Al Ragsdale stood at Mission Control in Houston feeling a mix of excitement and dread.

Then a 25-year-old simulation engineer, Ragsdale knew exactly how the landing sequence was supposed to play out. He had personally operated a practice version of the spacecraft hundreds of times.

That meant he also knew that things were going wrong.

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“We got those program alarms,” said Ragsdale, who today works for a contractor at NASA’s Langley Research Center. “The alarm basically says, ‘The computer’s got a bug.’ You’re in a vehicle that’s being flown by the computer for the first 10 minutes or so of the landing. We knew that it was about 3,000 feet lower than it was supposed to be. So, you’ve got a computer that’s screaming, ‘I’ve got a problem!’ And you know that you’re lower than you should be.”

Astronaut Neil Armstrong took over manual control and flew a different path than the one planned, which meant he burned more fuel than expected. At the time, folks at Mission Control feared the lander would run out of gas short of its target, Ragsdale said. For a few tense moments, the outlook was not good.

“I was expecting them to abort,” said Ragsdale, who was invited to be on hand at Mission Control because of his experience with the lander simulators. “Those were my thoughts. I kept expecting the abort light to come on at any minute, but it didn’t.”

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Instead, the three-man crew of Apollo 11 — Armstrong, Edwin “Buzz” Aldrin and Michael Collins — accomplished one of the great feats in human history. Mankind’s giant, extraterrestrial leap took place July 20, 1969, when Armstrong became the first man to walk on the moon.

It was an achievement made possible by key contributions from NASA Langley personnel. The Hampton, Virginia, research center supplied the Apollo team with mission concepts, aerodynamic problem solving and crew training for the moon landing. John Houbolt at Langley championed the lunar-orbit rendezvous plan that proved to be a winning concept for the mission.

Leading up to the 45th anniversary of the first moon walk, Ragsdale has been recalling his experiences on that historic day. The 70-year-old engineer still does simulation work, although he’s now employed part time at NASA Langley by Analytical Mechanics Associates, Inc.

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He describes his work with Apollo 11 as life changing and has mementos that bring back images from July 1969 in vivid detail.

“I was writing down everything that was happening as it was happening,” Ragsdale said of landing day. “It’s kind of fun to look at now. I still find this exciting to remember and think about.”

Ragsdale holds a slightly yellowed page of his notes from that day. He also shows off his badge allowing access to Mission Control as well as a booklet of codes used to instruct the mission’s rudimentary computer system.

“People have forgotten a lot of the details,” Ragsdale said, “like how simple the computer was. Their computer, if you compared it to modern ones, the entire thing to get to the moon and back was 72 KB of memory. All of the program had to fit in that … Now, everybody’s got laptops and big screens and all like that. We had three numbers we could look at, three five-digit numbers we could see. … People forget that calculators hadn’t been invented yet, and a digital watch was a new invention when they landed on the moon.”

Considering the limitations of their tools and the risks involved, Ragsdale marvels at what was accomplished.

“To me it’s amazing that we made it on the first try,” he said. “The crew had only given themselves about a 50/50 chance. There were so many things that could go wrong. They were pretty sure they would survive, but they weren’t sure it would all be successful.”

The simulator that Ragsdale worked with in Houston contributed to the triumphant landing, as did the astronauts' training at the Lunar Landing Research Facility at NASA Langley.

“There was very much a feeling of teamwork,” Ragsdale recalls. “We were all working together. My feeling, looking back 45 years ago, was, ‘Hey, the team was successful! Let’s keep going.’ ”

To learn more about NASA Langley's role in the Apollo 11 mission, visit this site.