On his second mission, Bobko was the commander of STS-51-D which launched from Kennedy Space Center on April 12, 1985. The mission was to deploy two communications satellites, perform electrophoresis and echocardiograph operations in space, in addition to accomplishing other experiments. When one of the communications satellites malfunctioned, the first unscheduled spacewalk was made to activate the satellite which required rendezvous and operations with the remote manipulator arm. After 168 hours of orbital operations, "Discovery" landed on Runway 33 at Kennedy Space Center on April 19, 1985.