The directorial debut fro Robert Altman, the guy who went on
to make some TV series called M*A*S*H.

The film is based on an actual project using a Gemini to land a
man on the Moon before the Soviets. A relatively small unmanned
base was sent ahead so the astronaut had some place to stay
and survive until picked up by another landing party in about
one month's time.

One of the images in the article Raoul links to has an image of
this concept, and you can find out a lot more about it here:

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

As Gemini is one of my favorite manned spacecraft, I think
it would have been great and actually made a lot of sense if
they modified it to orbit and land on the Moon. After all, the
whole point of putting a man on the Moon by 1970 was to
do it as quickly as possible to beat the Soviets, not establish
a long term base and extensive science exploration, as the
program quickly showed.

As for Countdown, while it sometimes got to be a bit melodramatic,
the film should be a bigger hit with space buffs than it seems to
be, considering it depicted manned spaceflight realistically just as
Marooned did one year later.

Hey, and this year is its 40th anniversary! Is it out in DVD?