S73-20774 (1 March 1973) --- Astronaut Charles Conrad Jr., commander of the first manned Skylab mission, goes through a checklist of experiment activity during Skylab training at Johnson Space Center. Conrad is standing in the Multiple Docking Adapter (MDA) in the Mission Simulation and Training Facility at JSC. He is working at the "materials processing in space" facility in the MDA. Photo credit: NASA