The Astronaut (1972)

Includes spoilers: in the not too distant future the first American astronaut prepares to set foot on the planet Mars. The world is watching this event live on television (although there is several minute delay for radio waves to travel the distance, and NASA has their own delay to the public broadcast). Everything is a success, or so the world thinks. Meanwhile a man in the air force with a resemblance to the astronaut is recruited as a double, and is told what really happened: the astronaut died on Mars from unknown causes. NASA keeps this a secret so they can maintain funding and work to uncover the cause of death. The double is told the impersonation will be brief, but NASA keeps stringing him along with an unspoken threat. His home life is impossible since he does not want to deceive the wife and keeps his distance. They finally decide the only solution is to fake his death (although an unscrupulous NASA official arranges for a real death). But Russia announces they have launched their own Mars mission, based on America's success. A more scrupulous NASA official feels that continued silence is tantamount to murder and decides to reveal the whole truth to the President.