Discovery launched from Kennedy Space Center on April 28, 1991 at 7:33 AM EDT and landed at Kennedy on May 6, 1991 at 2:55 PM EDT. The shuttle orbited 134 times at an altitude of 190 nautical miles at an inclination of 57 degrees and travelled 3.5 million miles. The mission lasted 8 days, 7 hours, 22 minutes, and 23 seconds.
This was a Department of Defense mission whose activities are not classified.
An unclassified payload included Air Force Program-675 (AFP675); Infrared Background Signature Survey (IBSS) with Critical Ionization Velocity (CIV), Chemical Release Observation (CRO) and Shuttle Pallet Satellite-II (SPAS-II) experiments; and Space Test Payload-1 (STP-1). Classified payload consisted of Multi-Purpose Release Canister (MPEC). Also on board was Radiation Monitoring Equipment III (RME III) and Cloud Logic to Optimize Use of Defense Systems-IA (CLOUDS-I).
The launch was originally scheduled for March 9, but during processing work at Pad A, significant cracks were found on all four lug hinges on the two external tank umbilical door drive mechanisms. NASA managers opted to roll back the vehicle to the VAB on March 7, and then to OPF for repair. Hinges were replaced with units taken from orbiter Columbia, and reinforced. Discovery returned to the pad on April 1, launch was re-set for April 23. The mission was again postponed when, during prelaunch external tank loading, a transducer on the high-pressure oxidizer turbopump for main engine number three showed readings out of specification. The transducer and its cable harness were replaced and tested. Launch was rescheduled for April 28.
Discovery was crewed by Commander Michael J. Coats, Pilot L. Blaine Hammond, and Mission Specialists Guion S. Bluford, Gregory L. Harbaugh, Donald R. McMonagle, and Charles L. Veach.