Primary objective of the Spacelab-2 mission was to verify the performance of Spacelab's systems and to determine its interface capability with the Space Shuttle vehicle. 4 inches. 19th Space Shuttle Mission8th Flight of Challenger Crew:C. Gordon Fullerton, CommanderRoy D. Bridges, Jr., PilotF. Story Musgrave, Mission SpecialistKarl G. Henize, Mission SpecialistAnthony W. England, Mission SpecialistLoren W. Acton, Payload SpecialistJohn-David F. Bartoe, Payload Specialist