Countdown!

Was reminded, recently, of one of my favorite Sixties SF movies. It was inspired by an actual backup plan to use Gemini equipment for a Moon landing if Apollo fell too far behind to meet the "before this decade is out" goal.

http://en.wikipedia.org/wiki/Countdown_%281968_film%29

_Countdown_ is occasionally denounced as unrealistic, but there actually were such plans, many of them seriously explored:

http://www.astronautix.com/articles/bygemoon.htm