Three American astronauts — commander Jim Pruett (Crenna), "Buzz" Lloyd (Hackman), and Clayton "Stoney" Stone (Franciscus) — are the first crew of Saturn derived space station. While returning to Earth, the main engine on the Apollo spacecraft One fails. Mission Control determines that Apollo does not have enough backup thruster capability to initiate atmospheric reentry, or to re-dock with the station and wait for rescue. The crew is marooned in orbit.
NASA debates how a rescue flight can reach the crew before their oxygen runs out in approximately two days. In the VAB is ready another Saturn 1B with Apollo capsule for the next Ironman mission.
Ted Dougherty (Janssen), the Chief Astronaut, demands that something be done. The President of the United States of America agrees with Dougherty and tells that failing to try a rescue mission will kill public support for the manned space program.
While the astronauts' wives (Lee Grant, Mariette Hartley, and Nancy Kovack) agonize over the fates of their husbands, all normal checklist procedures are bypassed to prepare the Ironman-II rescue mission for launch. A hurricane headed for the launch area threatens to cancel the mission. However, the eye of the storm passes over the Cape at the last minute during a launch window, permitting a launch with Dougherty aboard.
Pruett (Richard Crenna) subdues an unruly Lloyd (Gene Hackman) in Ironman-1 There is insufficient oxygen left for all three astronauts to survive until Dougherty arrives. There is possibly enough for two. Pruett and his crew then debate what to do. Stone tries to reason that they can somehow survive. Lloyd offers to leave since he is "using up most of the oxygen anyway", but Pruett overrides him. He orders everyone into their spacesuits. He want leaves the ship, ostensibly to attempt repairs.
But a Soviet spacecraft Soyuz suddenly appears and its cosmonauts tries to make contact. It can do nothing but deliver oxygen since the Soviet ship is too small to carry additional passengers. One of two Soviet Cosmonauts perform an EVA and carries the oxygen packs to the Apollo. The hatch is open so the packs can be attached to the spacesuits connectors.
Dougherty arrives with Ironmen-2 and he and the cosmonaut transfer the three Ironman astronauts into the Apollo rescue capsule . Both the Soyuz and the Apollo return to Earth, and the final scene fades out with a view of the abandoned Ironman-1 adrift in orbit.
