The mission was sham. The murders were real.

What if one of the greatest space adventures was really a hoax? The whole world is watching the first manned flight to Mars prepare. Suddenly, its astronauts are taken from the craft to an abandoned desert hanger where NASA's director tells them their life support systems have failed. Because of the mission's success is crucial to future space programs, he orders them to take part in a simulated Martian landing as cameras roll. If they refuse, their families will be harmed.
The phony flight goes well until an uninformed NASA technician spots a computer discrepency. He mentions it to a reporter friend who smells a story and starts to investigate. When their rocket disintegrates and the world thinks them dead, the astronauts realize their lives are in danger. They escape and separate- hoping one of them will survive to expose the sensational fraud.