@valorum got the answer right: Beyond the Stars (1989)
Plot summary from Wikipedia:
Eric is the teenage son of a computer scientist who worked for the Apollo program, which sent the first humans to the Moon. Eric, determined to become an astronaut himself one day, befriends Paul Andrews, the thirteenth man on the Moon. Paul is avoided by other astronauts nowadays because he was very rude and distant when he returned from space. Eric slowly learns that during his excursion on the Moon Paul discovered something that he keeps as a secret.
Thank you for all the insights, I was very little at the time, so my memory is very limited and fuzzy, I basically just remember the rocket model.