53rd Space Shuttle Mission3rd Flight of Endeavour Crew:John H. Casper, CommanderDonald R. McMonagle, PilotMario Runco, Jr., Mission SpecialistGregory J. Harbaugh, Mission SpecialistSusan J. Helms, Mission Specialist The primary payload was NASA's Tracking and Data Relay Satellite-6 (TDRS-6), the fifth satellite in the TDRS cluster. TDRS-6 was deployed using an Inertial Upper Stage (IUS) booster.