Apollo 18, the fictitious moon mission that failed, was in the real world a canceled mission that could have landed on the moon in 1973. It was not the name for the Apollo component of the Apollo-Soyuz Test Project, NASA's rendezvous with a Russian Soyuz spacecraft in 1975.
Norman Grant (James Garner) was a Republican senator in the book upon which this was based, but the character's political affiliation, along with other factors, were changed to suit Garner's personal (Democratic) politics.
James Garner, upon hearing that a small group of Marines were being used as extras, insisted on meeting them.
As a Korean War combat vet himself, he wanted to talk to them. He graciously spent his lunch break with them telling stories, answering questions and signing autographs.