STS-37

The primary payload, the Gamma Ray Observatory (GRO), was deployed on flight day 3. GRO's high-gain antenna failed to deploy on command; it was finally freed and manually deployed by Ross and Apt during an unscheduled contingency space walk, the first since April 1985. The following day, the two astronauts performed the first scheduled space walk since November 1985 to test means for astronauts to move themselves and equipment about while maintaining the then-planned Space Station Freedom. GRO science instruments were Burst and Transient Source Experiment (BATSE), Imaging Compton Telescope (COMPTEL), Energetic Gamma Ray Experiment Telescope (EGRET) and Oriented Scintillation Spectrometer Experiment (OSSE).