Apollo 11 – The Big Leap

Launch date: July 16, 1969
Landing date: July 24, 1969

And the day has come. History is watching. The effort of hundred thousands of people and the dreams of other millions rest on one single mission, on three man.

On July 20, 1969, an ancient dream was about to be fulfilled as Commander Neil Armstrong and his right-hand man, Buzz Aldrin, descended towards the first manned touchdown on the Moon. Beginning at about 35,000 feet (10,670 m) above the surface, a series of alarming warning on Eagle’s computer set everyone on edge…

“Program alarm”, said Armstrong. “1202”.

At mission control in Houston, a 26-year-old Steve Bales was sitting at the Guidance console, monitoring Eagle’s systems via remote telemetry. Another code, 1201, also came out. “What’s a 1201?”, the senior flight controller asked. Bales needed a few seconds to think, but Eagle’s crew needed an immediate answer. Should they abort the landing? Bales had not time left for thinking. Making the bravest decision of his life, he spoke into his headset for all mission controllers to hear. “We’re ‘Go’ on the alarm”. This meant, astronauts to carry on with their descent. Then Eagle started its way to the surface. Bales had recalled similar alarms showing up during one of the many trainings simulations, and he thought that it was not a threat to the mission.

Just as Bales was recovering, Charlie Duke, CapCom at that moment, radioed a warning up to Eagle’s crew. “You only have 60 seconds-worth of fuel remaining”. Unsure whether the astronauts had got the message, he called out another warning. “Thirty seconds”. Chief astronaut Deke Slayton, standing behind Duke, said softly to him, “Shut up, Charlie, and let ’em land”.

With less than a hundred feet remaining before touchdown, Eagle apparently was pitching forward at a very steep angle and skimming over the ground at 30 miles (48 km) per hour. Had the astronauts lost control of their ship?

At last, Aldrin radioed, “Contact light. Mode control to auto. Engine arm off”. Those were the first words spoken by a human on another world. Sadly for Aldrin, we prefer to remember Armstrong’s words a few moments later. “Houston, Tranquility Base here. The Eagle has landed”.

A fascinating reply from Duke seems not to have been much remarked on at the time. “Roger, Tranquility, we copy you on the ground. You got a bunch of guys about to turn blue. We’re breathing again. Thanks a lot”.

Later Armstrong explained what happened on those last seconds before touchdown. The Eagle’s guidance computer was taking them right into a crater with a large number of holes and rocks. He had to manually nudge Eagle forward to hover a few feet over the surface until he could find a safe place to land.

But what really made this safe landing was something more genius: the 1201/1202 sequence alarms. This was the “kill and recompute from a safe place” restart approach of the revolutionary software running in the Eagle’s guidance computer. Just seconds before the alarms triggered, the computer was overloaded with interrupts caused by incorrectly phased power supplied to the lander’s rendezvous radar. These 1201/1202 alarms indicated “executive overflows”, meaning the guidance computer could not complete all of its tasks in real time and had to postpone some of them.

The priority alarm displays interrupted the astronauts’ normal displays to warn them that there was an emergency “giving the astronauts a go/no go decision (to land or not to land)”. Steve Bales knew the astronauts were seeing these alarms and that is why he shouted the GO to land. This might sound obvious nowadays, but back on 1969 the software development was at its earliest stages and to create a code smart enough to recognize which tasks are more critical than others, reorder them and execute them was nearly science fiction.

The brain behind this was a 33-year-old woman Margaret Hamilton; pioneer in software engineering (a term which was coined by her) and her work is a fundamental part to understand how software is develop today. She and other women that time were key in programming. Another example was Grace Hopper, inventor of COBOL programming language, US Navy rear admiral and also remembered by coining the term debug after finding out that one of her lab’s computer was malfunctioning because a moth.

Hamilton later wrote of the incident with the landing of Apollo 11 and describes perfectly the importance of her software:

The computer (or rather the software in it) was smart enough to recognize that it was being asked to perform more tasks than it should be performing. It then sent out an alarm, which meant to the astronaut, ‘I’m overloaded with more tasks than I should be doing at this time and I’m going to keep only the more important tasks’; i.e., the ones needed for landing … Actually, the computer was programmed to do more than recognize error conditions. A complete set of recovery programs was incorporated into the software. The software’s action, in this case, was to eliminate lower priority tasks and re-establish the more important ones … If the computer hadn’t recognized this problem and taken recovery action, I doubt if Apollo 11 would have been the successful moon landing it was.

Margaret Hamilton

Armstrong and Aldrin tried to rest, but they were too keyed up to sleep. After two hours of preparations for the EVA, the Eagle was depressurized, hatch opened and Armstrong began his descent to the lunar surface. Once he jumped into the surface, the whole world heard his words:

19 minutes later it was the turn of Aldrin to step out of the Eagle. His first impression was to take a picture of his first step in the Moon; the bootprint picture we all remember. Both astronauts began the multiple surface operations: mount the TV cameras, collect soil and rock samples, experimental walkthrough the surface, deploy seismic experiment device to measure moonquakes and a retroreflector used for the Laser Ranging experiment to measure the exact distance between Moon and Earth for the first time.

After 21 and a half hours, the Eagle lifted off lunar surface to rejoin Collins onboard of the Columbia module in lunar orbit and being the journey back to Earth. Apollo 11 splashed down in the Pacific Ocean on 24 July 1969 at 16:50:35 UTC at 400 miles of Wake Island and 24 km (15 mi) from the recovery ship USS Hornet. The performance of the spacecraft was excellent throughout the mission. The primary mission goal of landing astronauts on the Moon and returning them to Earth was achieved. Armstrong was a civilian on his second spaceflight (he’d previously flown on Gemini 8), Aldrin was a USAF Colonel on his second spaceflight (Gemini 12), Collins was a USAF Lt. Colonel also on his second flight (Gemini 10).

Finally the ancient dream was accomplished. The primary goal of the Gemini and Apollo projects was achieved flawlessly and within deadlines. The immense hard work of thousand of men and women was finally recognized and inserted in a memorable place in human history. The legacy of this shows what humans can achieve if we really focus. When the society falls to its darkest stage or we only see horrendous actions, examples like this must be present with all of us and poke our lives; continue growing as species and look up to these bright moments which are the ones pushing us forward.

But this must be just the beginning. We need to set our next goal to push further our boundaries, our next giant leap. Is it Mars? is it Titan? Predictions says it would be the red planet but we must go back to the Moon first. There is much more to discover and study over there to understand the early stages of our planet and solar system. I believe humans will need to leave Earth and make a new home on another planet. In the next 100 years we will embark in our greatest ever adventure and a stablished crew on the Moon will be the real first step: our destiny is in the stars.