Basic story is that the Americans are trying to land a shuttle on Mars but they are not ready or unable to be ready for it so they fake it in a TV studio. Pictures 'beamed through space' etc. Problem is that the shuttle explodes on impact back with Earth so the astronauts would have all died. Except that, of course, they are alive and well and never been in Mars.
After the film "capricorn one" came out, suddenly there were loads of conspiracy theorists screaming that the Apollo moon landings were a hoax. A lot of "facts" on these conspiracists' websites are actually from the film, not from real life.