Three American astronauts – commander Jim Pruett (Richard Crenna), "Buzz" Lloyd (Gene Hackman), and Clayton "Stoney" Stone (James Franciscus) – are the first crew of an experimental space station on an extended duration mission. While returning to Earth, the Apollo Command/Service Module#Service Propulsion System ''Ironman One'' fails. Mission Control Center determines that ''Ironman'' does not have enough fuel remaining to use the reaction control system as a backup to initiate atmospheric reentry. Nor is there sufficient fuel to re-dock with the station and wait for rescue. The crew is effectively marooned in orbit.