A comment on "Marooned", the movie that was made about a moon mission disaster which was released after the Apollo 11 landing but prior to the Apollo 13 real-life disaster, mentioned that the movie is not available on DVD and rarely, if ever, appears on television. I believe that the same is true of this movie (at least regards TV screenings) and it's for the same reason. "Marooned" and "Countdown" are movies that are so much of their period that they scarcely make any sense at all to 21st Century minds. Of course, we all know about the Cold War, and most cold war movies involve international espionage which is timeless.
Countdown is a movie about the Space Race which dominated the daily agenda at least as much as conventional Cold War conflicts like the Korean and Vietnam wars. The plot concerns a situation in which the Soviets succeeded in their aim to send a manned rocket to the Moon before the Americans were ready to fly Apollo. However, contact with the cosmonauts has been lost, and there is still a chance for NASA to fulfill Kennedy's challenge of "sending a man to the Moon and returning him safely to the Earth" - as well as the kudos gained from discovering and being the ones to tell the Soviets what happened to their men.
An interesting sideline on this is that the actually successful method of moon exploration used, ie send three men to lunar orbit and then two can travel to the surface in a smaller ship, is certainly not the only solution, and this movie explores a different one forced by necessity. Since Apollo is not ready and there is no lunar lander capable of taking off from the moon, why not send a less complex ship with only one man, and let him stay on the moon, kept alive by an environment habitat sent on ahead by unmanned rocket and by provision of supplies by further unmanned ships? Such a scenario had already been envisioned by science fiction authors like Arthur C. Clarke as being the most efficient way to explore our satellite. Certainly nobody had previously imagined that we would send men to the Moon for a matter of a few days in a ship which could not carry more than a few hundred pounds of samples back to Earth. By exploring this other methodology this movie succeeds in highlighting the true nature of our Lunar adventure. The point was not to expand the human frontier or to increase the sum of scientific knowledge - the point was to get a man on the moon and safely back before the Russians did.