Launched: 1974 April. Number crew: 3 .

Main objective would be to conduct some new scientific experiments and boost Skylab into a higher orbit for later use by the shuttle. The marginal cost of such a mission would have been incredibly low; but NASA was confident that Skylab would stay in orbit until shuttle flights began in 1978 - 1979. But the shuttle was delayed, and faster atmospheric decay than expected resulted in Skylab crashing to earth before the first shuttle mission was flown.

• Skylab 5 (cancelled) - . Crew: Brand, Lenoir, Lind. Nation: USA. Related Persons: Brand, Lenoir, Lind. Program: Skylab. Flight: Skylab 5. Spacecraft: Apollo CSM.

  After completion of the three programmed Skylab flights, NASA considered using the remaining backup Saturn IB and Apollo CSM to fly a fourth manned mission to Skylab. It would have been a short 20 day mission to conduct some new scientific experiments and boost Skylab into a higher orbit for later use by the shuttle. But NASA was confident that Skylab would stay in orbit until shuttle flights began in 1978 - 1979. But the shuttle was delayed, and Skylab crashed to earth before the first shuttle mission was flown.