In August 1993, Smith completed one year of astronaut candidate training. He served as the Astronaut Office representative for the Space Shuttle main engines, the solid rocket boosters, the external tank, and Shuttle safety from April to November 1993. In September 1993, Smith became the first member of the 1992 astronaut class to receive a flight assignment.
Smith served as a mission specialist aboard the Space Shuttle Endeavour on Mission STS-68, September 30 to October 11, 1994. Smith's responsibilities were split between Shuttle systems, Space Radar Lab 2 (SRL-2, the flight's primary payload), and several experiments located in the crew cabin. Smith was one of two crewmen trained to perform a space walk had one been required. As part of NASA's Mission to Planet Earth, SRL-2 studied the Earth's surface and atmosphere, creating radar images of the Earth's surface environment and mapping global carbon monoxide pollution. Endeavour circled Earth 183 times and traveled 4.7 million miles during the 11 day, 5 hour and 46 minute flight.
From November 1994 until March 1996, Smith was assigned to duties at the Kennedy Space Center as a member of the astronaut support team. The team was responsible for Space Shuttle prelaunch vehicle checkout, crew ingress and strap-in prior to launch, and crew egress post landing.
Smith performed three space walks as a member of the February 1997 STS-82 Discovery crew which serviced the Hubble Space Telescope (HST). The crew completed five space walks in order to dramatically improve the scientific capability of the telescope and to replace degraded support equipment. HST's orbit was also increased 8 miles by the crew. The flight orbited the Earth 150 times covering 4.1 million miles in 9 days, 23 hours, 37 minutes and Smith's three space walks totaled 19 hours, 10 minutes.
Carried SIR-C SAR. Landed at Edwards Air Force Base on October 11. Payloads: Space Radar Laboratory (SRL) 2, five Getaway Special payloads, Chromosome and Plant Cell Division in Space (CHROMEX) 5, Biological Research in Canisters (BRIC) 01, Cosmic Radiation Effects and Activation Monitor (CREAM), Military Application of Ship Tracks (MAST), Commercial Protein Crystal Growth (CPCG).
After a spectacular night launch, the Shuttle completed its rendezvous with Hubble Space Telescope on February 13. Over the next four days five spacewalks were undertaken to renovate Hubble.
The Hubble Space Telescope was released back into orbit at 06:41 GMT on February 19. Discovery landed on Runway 15 at Kennedy Space Center at 08:32 GMT on February 21.
Hubble Space Telescope Servicing Mission 2 - NICMOS installation.
Hubble Space Telescope Servicing Mission 2 - Data interface unit replacement.
Hubble Space Telescope Servicing Mission 2 - Insulation blanket repair.
Hubble Space Telescope (HST) servicing mission SM-3A, delayed repeatedly by technical problems with the shuttle fleet after the near-disastrous previous launch. Finally launched after the last possible day to avoid Y2K computer problems; one spacewalk was cancelled so that the shuttle could return by December 28. Hubble was in a 591 km x 610 km x 28.5 deg orbit at launch. After separation of the external tank ET-101 the Orbiter was in a 56 km x 587 km x 28.5 deg transfer orbit. The OMS 2 burn at 0134 UTC raised the orbit to 313 km x 582 km. The payload bay contained:
Replaced all six of the gyroscopes on Hubble.
Completed part of the installation of new insulation to the Hubble space telescope. The rest was deferred to the next servicing mission.