Earlier Rejection from NASA.
At the start of the film, it's shown that when the civilian NASA agency was formed, Colvin and his buddies were "replaced" by chimps for the first space missions.
What I don't get is why they just didn't do why they just didn't apply to become astronauts themselves later on? The original seven astronauts from the Mercury program were all selected from a cadre of military test pilots. If they didn't make that selection, they could have applied for the astronauts classes in 1962, 1963 or 1966.
The film makes it look that as soon as NASA was formed, they somehow didn't qualify. They were all experienced military test pilots with the requisite college degrees. One or more of them would surely have been accepted by NASA.