Planned date: 01 April 1974 - Crew: Brand, Lind & Lenoir - 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 - the CSM systems would
not have been powered down. 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.