* The Apollo 1 launch-pad fire, during a training session, using a 100% pressurised oxygen atomosphere. Three dead. Grissom, White, and Chaffee. I can list them from memory.

* Apollo 11 suffered a lunar lander computer crash in the final seconds before landing, was programmed to land on what would have been unsurvivable terrain, and had fewer than 30 seconds of fuel left when it finally touched down.

* Apollo 12 was struck by lightning as it left the launch pad, knocking out much of the electrical system, which had to be reset. Fortunately they built things robustly.

* Apollo 13 had an oxygen tank explode as it was en route to the moon. The mission was aborted, though orbital mechanics meant that the astronauts still had to orbit the Moon, then return to Earth.

Any of 11, 12, or 13 could have ended with fatalities. One scenario for the command module pilot (Michael Collins in Apollo 11) was, if needs be, to leave his two crew members on the lunar surface and to return to Earth alone.