Ability Over Appearance: Several of the main actors top 6 feet (183 cm) (Dennis Quaid and Scott Glenn in particular). However, none of the actual astronauts were over 5'11" (180 cm), as that was the maximum height allowed by the cramped Mercury capsu—er, spacecraft. Gus Grissom, who was 5'5" (165 cm) in real life, was portrayed by the 5'10" (178 cm) Fred Ward.
Fatal Method Acting: The stuntman portraying Chuck Yeager's bailout of the crashing F-104. His helmet filled with smoke, and he didn't get his parachute deployed. Also a strange bit of Truth in Television, as Yeager actually collided with his seat after ejecting, and his helmet filled with liquid explosive materials, similarly filling his helmet with smoke and burning his face to a cinder. The aftermath is portrayed in the Out of the Inferno shot listed on the main page.
Hey, It's That Guy!: Only applies to Cincinnati Bengals fans. Gonzalez is played by Anthony Munoz, who was an All-Pro offensive lineman at the time.
Negated Moment of Awesome / What Could Have Been: In both real life and discussed in the film, Chuck Yeager was passed over for the space program. Despite being someone who is now considered to be one of the greatest pilots in the history of aviation, NASA was looking for college graduates. Yeager never attended college, nor West Point or Annapolis, but instead was an enlisted man recruited as a pilot and therefore field-commissioned after the US entered the war. Could anybody imagine how utterly awesome it would've been had Chuck Yeager become an astronaut?note Hopefully he wouldn't have been one of the ones in the Apollo 1 fire, though.
Towards the end of the movie, Alan Shepard tells his wife Louise, in a "one of these days..." manner, "I'm going to the moon...". Shepard would be the only one of the Mercury Seven who would go to the moon, on Apollo 14 note He was stated to be on the first Gemini mission, but got grounded due to an inner ear condition. After the docs cleared him, Shepard was initially assigned to Apollo 13, NASA execs moved him to Apollo 14 to give his crew more time to train.
During the astronaut tryouts in the movie, Gordon Cooper gloats about breaking the record for holding one's breath, only to realize that John Glenn and Scott Carpenter are still going after he's done. In real life, Cooper did hold his breath the longest, since he was the only non-smoker in the Mercury Seven.
At the movie's end, before Cooper lifts off on his mission, he's shown dozing off. Cooper was the first astronaut to sleep in outer space.