"Contact light”

"Okay.” continued Aldrin. "75 feet, and it’s looking good. Down a half, six forward.” They were 23 metres up and almost hovering.

’’Sixty seconds,” called Duke as mission control continued their countdown to the land-or-abort call.

’’60 feet, down 2’A,” called Aldrin. “Two forward. Two forward. That’s good.”

Armstrong had found his spot and was taking the LM down. Like all the commanders, he wanted to land with the LM still moving gently forward so that he could always see where he was going. It was felt unwise to land going backward as it posed the risk of falling into a crater or striking a boulder that could not be seen.

“40 feet, down 2 A,” said Aldrin. “Picking up some dust.”

This was new. This was wdien the people in and around mission control realised that this was for real. No one had ever thought to mention it during the great many simulations they had run. The descent engine’s exhaust plume was blowing a substantial blanket of flying dust that wafted around the small stones scattered across the landing site. They were in a new environment and already discovering new things.

Jack Ciarman later related the phenomenal impact Aldrin’s words had. "We’d watched hundreds of landings in simulation, and they are very real.” Up to this point, and because he was used to the apparent reality of the simulations, Garman had not fully appreciated the fact that what was happening was no simulation.

Then Aldrin mentioned the dust. "And we’d never heard that before.’’ recalled Garman. "It’s one of those, ‘Oh, this is the real thing, isn’t it?’ I mean, you know it’s the real thing, but it’s going like clockwork, even with problems. We always had a problem during descent. A problem happens, you solve the problem, you go on. no sweat. Then Buzz Aldrin says, ’We’ve got dust now’.’ My god, this is the real thing. And you can’t do anything, of course. You’re just sitting down there. You’re a spectator now. Awesome. Awesome.”

On Apollo 15. as Falcon was being brought down onto the plain at Hadley. Scott thought the dust seemed completely enveloping. From his perspective, it was like flying in a fog. "At about 50 to 60 feet [15 to 18 metres], the total view’ outside was obscured by dust. It was completely IFR." Scott was comparing the experience to instrument flight rules, a mode of aircraft flying that pilots adopt when the weather closes in and restricts their visibility. He therefore had to take his attention from the view outside and use the displays in front of him.

As Young brought Orion down the final few metres on Apollo 16, Duke talked him through the dust.

“Okay, down at three [feet per second], 50 feet, down at four." They seemed to be dropping faster. "Give me one click up," advised Duke. Young operated the ROD switch and temporarily found he was hovering above a blanket of flying dust. "Come on. let her down. You levelled off," said Duke. “Let her on down. Okay, six per cent. Plenty fat." They had no problem with propellant.

“We did hover for a short period of time there,” commented Young after the flight, "at about 40 feet [12 metres] off the ground, and the [horizontal velocity] rates were practically zero and there was blowing dust. Vou could still see the rocks all the way to the ground, the surface features, even the craters, which really surprised me."

As Young brought the LM down, he just barely missed a 25-mcirc crater and landed with Orion’s rear footpad right on its edge. It was only when he and Duke got outside and could sec all around the LM that they realised how close they had come to being dangerously tilted over.

“I’m glad you weren’t 10 feet [further back], said Duke. "Whew me!"

“W’e were going forward," said Young, thankfully.

“Yeah, we were landing going forward."

Back on Apollo 11, Armstrong was only 10 metres above the surface and Aldrin was still feeding him data. “Thirty feet, 2 ‘A down." By this time, and since 70 metres altitude, Aldrin could view’ the LM’s shadow when he glanced up as it moved across the landscape. Since they always landed with a low, morning Sun behind them, the approaching shadow could be a useful tool to help to judge the final few metres. However, Armstrong could not see it because he was flying with the LM yawed to the left and the way his window was heavily recessed severely limited his field of view to the right.

“Four forward. Four forward," continued Aldrin. "Drifting to the right a little. 20 feet, down a half."

“Thirty seconds." called Duke. For all their telemetry, the flight controllers simply did not have the situational awareness that the crew’ enjoyed. With only 30 seconds remaining before the land-or-abort call, mission control was beginning to hold its collective breath.

“Drifting forward just a little bit," said Aldrin. coaching his commander down.

"That’s good."

Just then, one of the probes attached to three of the LM’s footpads struck the surface and lit an indicator in the cabin. Their footpads were less than two metres above the surface. "Contact light,” called Aldrin.

Immediately, the pair began a rehearsed series of tasks to turn Eagle from a flying machine to a home on the Moon.

‘’Shut down,” said Armstrong.

“Okay. Engine stop.” replied Aldrin.

By the lime Armstrong got the engine stopped, they had already settled onto the surface. No harm came to the engine, but he was struck by the unexpected way the lunar dust behaved in the exhaust gases in front of him. In an interview 32 years later, he talked about this surprising phenomenon: “I was absolutely dumbfounded when I shut the engine off. They just raced out over the horizon and instantaneously disappeared, just like it had been shut off for a week. That was remarkable. I’d never seen that. I’d never seen anything like that. And logic says, yes. that’s the way it ought to be there, but I hadn’t thought about it and 1 was surprised.”

On later flights, the commander was spring-loaded to stop the engine as soon as the probes touched the surface, particularly on the. l-missions where the longer engine nozzle provided only 30 centimetres of clearance to level ground.

“АСА out of detent,” was Aldrin’s next item, vvhieh referred to the controller in Armstrong’s hand. As they touched down, the LM adopted whatever attitude the surface dictated. However, the RCS thrusters w’ere still busily firing in a futile attempt to restore their previous attitude. By moving the stick, known as the attitude control assembly (АСА) out of its central position, Armstrong made the system think that the current attitude was also the desired attitude, and thereby stopped the jets from firing.

“Out of Detent. Auto.” said Armstrong.

“Mode control, both auto. Descent engine command override, off. Engine arm, off. 413 is in.” Aldrin’s litany of checklist instructions ended with an entry into the AGS, their secondary guidance system. Aldrin was entering a number into address 413 that told the machine they had landed and that it should take note of their current attitude in case they had to abort from it. The body-mounted gyros of the AGS were prone to drift and were unlikely to provide an accurate attitude by the time an abort might be called.

“We copy you dowm. Eagle." said Duke, spokesperson for an anxious mission control and a waiting Earth. Armstrong was not yet finished with the checklist.

“Engine arm is off,” he responded to Aldrin." Then to the w orld, he announced. "Houston, Tranquillity Base here. The Eagle has landed.”

Duke tvas caught by the moment and by Armstrong’s sudden change of call sign, despite having been forewarned. “Roger. Twan… Tranquillity. We copy you on the ground. You got a bunch of guys about to turn blue. We’re breathing again. Thanks a lot."

In the view of the public, the defining moment of the event would be when a human footprint deformed the lunar dust. This would have a human dimension; there would be a personal link to the hearts of all people who left footprints on Earth and a sense of the frailty of a mere human stepping out on a hostile alien world. The moonwalk would be the pinnacle of the whole achievement, itself a supremely difficult accomplishment.

Neil Armstrong didn’t view a moonwalk as being particularly difficult not in comparison to the rigours of gelling Eagle onlo the Moon in one piece. Speaking in 2001 to NASA historians, he weighed up how difficult the landing had been. ’‘The most difficult part from my perspective, and the one that gave me the most pause, was the final descent to landing. 1 hat was far and away the most complex pari of the flight. The systems were very heavily loaded at that time. The unknowns were rampant. The systems in this mode had only been tested on Harth and never in the real environment. There were just a thousand things to worry about in the final descent. It was hardest for the system and it was hardest for the crews to complete ihai part of the flight successfully.’’

Then somewhat humourously, he tried to enumerate the difficulty of the landing as compared to an excursion outside. “Walking around on the surface, you know, on a ten scale, was one. and I thought that the lunar descent on a ten scale was probably a thirteen.”

A final and eloquent perspective on the moment of touchdown comes from Jim Scotti, a planetary scientist who once asked Gene Cernan about the sounds he could hear as he landed on the Moon. Scotti wanted to know about the noise produced by the engineering that surrounded Cernan; pumps, switches, thrusters, and that big descent engine. The answer he got was not what he expected. Jim picks up the story. "What he heard in the moments after landing was… silence! You sec, before landing, he was so engrossed in the activity that he heard Jack calling out numbers and the occasional call from Houston and everything else blended into the background because he was so focused on the task of landing. At touchdown, however, the spacecraft fell silent and mission control was staying quiet to try not to interfere with what they expected was the final moments of touchdown. And Gene added: ‘And the guy standing next to me was struck silent staring out the window looking at the surface and he sure wasn’t saying anything!’”