Apollo 11

While Eagle sat on the surface, Columbia kept going round.

Once an orbit the Moon came between Michael Collins and everyone: Houston, Armstrong and Aldrin, and every other human being alive. Forty seven minutes, completely out of touch.

The press called him the loneliest man in history. He spent his life correcting them.

In Carrying the Fire: I feel this powerfully: not as fear or loneliness, but as awareness, anticipation, satisfaction, confidence, almost exultation. I like the feeling.

Go back a minute, to a light coming on in the cabin.

That light triggered a countdown. Sixty seconds remaining. Thirty seconds remaining. They weren't counting down to empty tanks; they were counting down to "bingo", the mandatory safety threshold where they had to abort the landing and fly back.

Touchdown came just nine seconds after the final warning call.

Afterwards they reconstructed the tanks and found roughly forty five seconds of engine time. Houston had believed twenty five.

The sensors hadn't broken. In the low gravity, the remaining fuel was sloshing around, repeatedly uncovering the gauge and tricking the computer into thinking they were nearly dry.

Every word of that descent reached the ground intact. But the clock they were racing against was a mirage.

Six hours and thirty nine minutes later, Armstrong went down the ladder and put his left boot in the dust.

About six hundred million watched, roughly one person in six then alive.

He said one small step for man, one giant leap for mankind. He maintained ever after that he had said a man, the version that makes sense. The a is not audible, and has never been settled.

Aldrin came down after him, looked out and commented on the magnificent desolation.

Bolted behind the ladder, a plaque: Here men from the planet Earth first set foot upon the Moon. July 1969, A.D. We came in peace for all mankind.

They left an Apollo 1 patch for Grissom, White and Chaffee.

And two Soviet medals, handed to Frank Borman in Moscow by Gagarin's widow and Komarov's. Two men who died on the way to this, honoured by the country that got there first.

William Safire wrote a speech for Nixon in case the ascent engine failed to light: Fate has ordained that the men who went to the Moon to explore in peace will stay on the Moon to rest in peace. Declassified decades later, never read aloud.

The other thing that's missing is the tape.

What six hundred million people saw was a makeshift broadcast patched together from a specialised signal meant for engineers. The true master recordings were vastly superior, but they were scrubbed and reused because magnetic tape was a finite resource in a government agency. An official search later turned up nothing.

The ultimate technical monument to human engineering was wiped by an archivist who needed a blank cassette.

One of the things they set down is not a monument.

The laser ranging retroreflector is a panel of corner cubes, a shape that returns light along the path it came in on. Point a laser at the Sea of Tranquility and a handful of the photons come back, about two and a half seconds later. Observatories have done it since 1969.

It transmits nothing. It has no power and nothing to say. It waits, and it answers.

Sputnik transmitted the truth in a code almost nobody understood. Vostok spoke clearly and held back the fact that mattered. Apollo was heard by six hundred million, the best recording of it was taped-over, and the thing they left behind is still replying.