As well-prepared as they considered themselves and the astronauts to be, NASA officials viewed the first lunar landing with concern. Gene Kranz, the legendary NASA Flight Director, recalled in a 1999 interview conducted for the NOVA television special, To the Moon: “Going through my mind was a very simple equation: Today we are either going to land, we are going to abort, or we are going to crash.”
As if on cue, the Eagle’s descent to the lunar surface promptly confronted Apollo 11 with its two most serious tests – either of which had the potential to kill the mission. At an altitude of just over 7,000 feet, about five miles from the landing site, the LM pitched over to assume its vertical landing posture, the ghostly lunar surface visible through the downward-angled windows. It descended about another 1000 feet and then the guidance computer sounded an alarm. The light that came on in the LM was coded 1202, an “executive overflow” alarm, which meant the computer was having trouble completing its work in the cycling time available.
The Apollo 11 Command/Service Module Columbia shown in a photo taken from the Lunar Module Eagle after undocking while in orbit around the moon. NASA Langley Research Center photo
Almost nobody knew what a 1202 was and in the first row of consoles at the Mission Control Center – “the Trench” – it fell to 26-year-old Guidance Officer (GUIDO) Steve Bales to make the split second decision – Go or No Go.
At Kranz’s insistence, Bales and the other controllers then wrote down every possible computer error code and the correct response to each – a list Garman had beneath his console glass during Apollo 11.
“GUIDO?” Kranz shouted, seeking an answer. The Eagle was burning up its descent fuel. Luckily, Bales was aided by 24-year-old Jack Garman, an expert in the guidance computer software, who knew immediately that the computer would complete its work as long as the alarm didn’t sound too frequently – a signal that it was overwhelmed. “It’s okay,” he assured Bales, who shouted “Go!” to the Capsule Communicator (CapCom), astronaut Charlie Duke.
“We are Go on that alarm, Eagle,” Duke said.
The Lunar Module Eagle, with astronauts Armstrong and Aldrin aboard, its legs extended for landing, is pictured from the Command/Service Module Columbia as it departs lunar orbit for the surface of the moon. NASA photo
A few months earlier, Garman had suggested to the simulation supervisor, Dick Koos, that flight controllers should be tested on their reactions to computer error codes. Koos did, throwing a 1202 alarm at Kranz and his flight controllers on the last day of simulations, two weeks before the launch date. Bales, incorrectly, had called an abort – and, Kranz wrote later, “I was ready to kill Koos.” At Kranz’s insistence, Bales and the other controllers then wrote down every possible computer error code and the correct response to each – a list Garman had beneath his console glass during Apollo 11.
Meanwhile, as Armstrong eased the LM down toward the moon, he and Aldrin could see that the chosen landing area, the vast Mare Tranquillitatis (Sea of Tranquility) – which had been selected because of its relative smoothness – wasn’t as smooth as advertised. Worse, the Eagle had come in slightly faster than anticipated, overshooting the target site and sailing over a crater strewn with boulders that would wreck the LM. Armstrong swiftly overrode the computer and assumed manual control. There was no time to discuss the decision with Mission Control in Houston; there was precious little reserve fuel for the descent stage and Armstrong would need every available second of it.
Armstrong, who had crashed the LM many times during simulation, was, despite his outward calm, feeling the stress of the moment; his heart rate had climbed from a normal rate of 77 to 156. “Thirty seconds,” Duke radioed.
The Eagle diverged from the programmed path, coasting over the boulder field, searching for a clear landing spot as the fuel level dropped nearer to zero. In Houston, Charlie Duke called out the remaining fuel: “Sixty seconds.” Mission Control watched in silence, stunned at the telemetry data that told them the LM had not landed yet, but was throttling rapidly over the surface. Armstrong, who had crashed the LM many times during simulation, was, despite his outward calm, feeling the stress of the moment; his heart rate had climbed from a normal rate of 77 to 156. “Thirty seconds,” Duke radioed.
A grainy frame from television footage of astronauts Armstrong and Aldrin erecting the American flag on the moon. NASA image
Finally, Armstrong saw what he needed – a clear spot just beyond a small crater. He brought the Eagle down slowly, kicking up sheets of gray dust that enveloped the LM. The lander’s downward-pointing feelers touched the surface of the moon, tripping the circuit that illuminated the blue indicator light in the cockpit. “Contact light,” Aldrin called. Armstrong cut the engine, and the four footpads came down on the lunar soil.
“We copy you down, Eagle,” said Charlie Duke.
His heart rate beginning to slow a bit, Armstrong’s voice was calm and clear: “Houston, Tranquility Base here. The Eagle has landed.”
The Moon Walk
After the tense moments spent waiting for the Eagle to land, Kranz recalled, many in Mission Control simply burst into tears after the LM landed and he himself admitted to having some trouble getting out the words that would begin the next sequence for the astronauts and Mission Control: the Stay or No Stay decision. Armstrong and Aldrin, once down, immediately prepared the ship for the contingency of an emergency launch.