On the 20 July 1969, Neil Armstrong and Buzz Aldrin approached the surface of the moon in their fragile Lunar Module, the Eagle. It was a fraught descent. Aldrin was calling out computer data to Armstrong as they approached, but the computer played up- and only cool heads meant that the landing was not abandoned. And as he approached the surface, Armstrong spotted that their landing site was strewn with boulders the size of small cars. In his attempt to find a clear site to land, Armstrong almost used up all his fuel reserves, which would have meant that they could not return home, or crashed among the boulders.