Presidents have to prepare for all sorts of contingencies. Including the possibility, in Richard Nixon's case, that the Apollo 11 astronauts might not safely return from the moon.

This contingency speech — found in the National Archives by the excellent blog Letters of Note — provides a chilling look at what might have been, starting with its blunt headline: "In Event of Moon Disaster."

"Fate has ordained that the men who went to the moon to explore in peace will stay on the moon to rest in peace," Nixon's speechwriter William Safire began. "These brave men, Neil Armstrong and Edwin Aldrin, know that there is no hope for their recovery."

Given Apollo 11's success, it's easy to overlook the fact that a mission failure was quite possible. The module used to ferry astronauts from the Apollo spacecraft to the moon's surface, in particular, was developed in a hurry — and as it descended, its computer malfunctioned, spitting out error messages and forcing Neil Armstrong to land the craft without radar data.

Here's the speech, which was first revealed on Meet the Press in 1999: