A brief look at the four Space Shuttle flights

* STS-1 (Space Transportation System flight test 1) April 12-14, 1981. Astronauts John Young and Robert Crippen completed 36 earth orbits at a 166-mile altitude in a 54-hour mission which accomplished all 135 flight objectives.

* STS-2, Nov. 12-14, 1981. Joe Engle and Richard Truly completed 36 orbits at a 157-mile altitude after fuel-cell problems cut the planned 124-hour mission to a 54-hour ''minimum mission,'' which meant cutting back on mission objectives.

* STS-3, March 22-30, 1982. Jack Lousma and Gordon Fullerton completed 130 orbits at a 147-mile altitude after stretching their 7-day trip into 8 days due to poor landing conditions on Day 7. The extra time both demonstrated Columbia's flexibility and gave added time for experiments.

* STS-4 is planned as a 7-day, 112-orbit mission which will include climbing from an initial 149-mile altitude into a 189-mile orbit.