Selected by NASA in January 1990, Gregory became an astronaut in July 1991. Astronaut Gregory has served in the following technical assignments: Shuttle Avionics Integration Laboratory (SAIL); astronaut office representative for Landing/Rollout, T-38 Flying Safety; Kennedy Space Center Astronaut Support Personnel (ASP); and spacecraft communicator (CAPCOM) in mission control.
Gregory served as the STS-67 pilot on the seven-person astronomical research mission aboard the Space Shuttle Endeavour. Launching from the Kennedy Space Center on March 2, 1995, and landing at Edwards AFB on March 18, 1995, the crew established a new mission duration record of 16 days, 15 hours, 8 minutes and 46 seconds, while completing 262 orbits and traveling nearly seven million miles. This second flight of the ASTRO telescope primary payload included numerous secondary payloads as well. Upon completion of this, his first mission, Gregory has logged 400 hours in space.
Gregory currently serves as the astronaut office representative for rendezvous and proximity operations.
Carried Astro 2 astronomy payload with 3 UV telescopes.(attached to Endeavour).Payloads: Ultraviolet Astronomy (ASTRO) 2; Middeck Active Control Experiment (MACE); Protein Crystal Growth—Thermal Enclosure System (PCG-TES) 03; Protein Crystal Growth—Single-Locker Thermal Enclosure System (PCG-STES) 02; Commercial Materials Dispersion Apparatus Minilab/Instrumentation Technology Associates, Inc. Experiments (CMIX) 03; Shuttle Amateur Radio Experiment (SAREX) II; two getaway special experiments.