The first Space Shuttle, Enterprise (OV-101), is a test vehicle designed to operate in the atmosphere; it is not equipped for space flight. Enterprise was rolled out at Rockwell International's assembly facility in Palmdale, California in 1976. In 1977, it entered service at NASA's Dryden Flight Research Center, Edwards Air Force Base, for a nine-month-long approach and landing test program. 

Upon completion of the approach and landing tests, Enterprise was used for vibration tests at Marshall Space Flight Center in Alabama and for launch complex fit checks at Kennedy Space Center in Florida and Vandenberg Air Force Base in California.  In 1985, NASA transferred Enterprise to the Smithsonian Institution's National Air and Space Museum. Since then Enterprise has been placed on display at the National Air and Space Museum's Steven F. Udvar-Hazy Center, near Washington's Dulles International Airport .

Columbia (OV-102), the first of NASA's orbiter fleet, was delivered to Kennedy Space Center in March 1979. Columbia initiated the Space Shuttle flight program when it lifted off Pad A in the Launch Complex 39 area at KSC on April 12, 1981. It proved the operational concept of a winged, reusable spaceship by successfully completing the Orbital Flight Test Program - missions STS-1 through STS-4.

Columbia was destroyed over east Texas on its landing descent to Kennedy Space Center on Feb. 1, 2003, at 8:59 a.m. EST at the conclusion of a microgravity research mission, STS-107.

Columbia was named after a small sailing vessel that operated out of Boston in 1792 and explored the mouth of the Columbia River. One of the first ships of the U.S. Navy to circumnavigate the globe was named Columbia. The command module for the Apollo 11 lunar mission was also named Columbia.

Number of flights (28)
Upgrades and overhauls  Post Challenger upgrades 02/1986 - 09/1988
      08/1991 - 02/1992    10/1994 - 04/1995    09/1999 - 05/2000

The Space Shuttle Challenger (STA-099, OV-99), was delivered to Kennedy Space Center in August 1982.  Challenger was destroyed during the launch of mission 51-L on January 28, 1986. An O-Ring seal on the right solid rocket booster began leaking due to a combination of poor inspection and low environmental temperature at the launch site, spraying hot gases onto its attachment point to the main fuel tank and causing structural failure 73 seconds after lift-off. The booster rocket broke free and slammed into the external fuel tank, rupturing it. The shuttle stack was then ripped apart by aerodynamic forces, and the external tank's fuel ignited into a fireball. Although there is some small evidence that members of the crew may have survived the Shuttle's initial breakup, cabin pressurization was lost and at the altitude where the breakup took place all crewmembers would have died from lack of oxygen before the free-falling crew cabin struck the Atlantic Ocean. On March 9 United States Navy divers found the largely intact but heavily-damaged crew compartment with the bodies of all seven astronauts inside.  In January, 1987 the recovered remains of Space Shuttle Challenger were transported to abandoned Launch Complex 31/32 on Cape Canaveral Air (Force) Station, where they were sealed in two 80-foot deep Minuteman missile silos and adjacent underground equipment rooms. The remains are expected to be stored there indefinitely.

Number of flights (10)                   Upgrades and overhauls  None

Discovery (OV-103), the third of NASA's fleet of reusable, winged spaceships, arrived at Kennedy Space Center in November 1983. It was launched on its first mission, flight 41-D, on August 30, 1984. It carried aloft three communications satellites for deployment by its astronaut crew.

Other Discovery milestones include the deployment of the Hubble Space Telescope on mission STS-31 in April 1990, the launching of the Ulysses spacecraft to explore the Sun's polar regions on mission STS-41 in October of that year and the deployment of the Upper Atmosphere Research Satellite (UARS) in September 1991.

Discovery is named for two famous sailing ships; one sailed by Henry Hudson in 1610-11 to search for a northwest passage between the Atlantic and Pacific Oceans, and the other by James Cook on a voyage during which he discovered the Hawaiian Islands.

Number of flights (31)
Upgrades and overhauls  Post Challenger upgrades 02/1986 - 09/1988
                                     09/1995 - 06/1996

03/08/2004
¹Return to Flight preparations continue on orbiter Discovery in the processing facility at KSC. Following the decision by NASA management to remove and X-ray the Rudder Speed Brake actuator gears, the four actuators were removed from the vehicle and sent to the Integrated Transfer and Launch X-ray Facility for X-ray beginning Monday. The X-ray will determine if the gears were installed correctly.  The Body Flap actuators are installed, with a fit check set for today. The Body Flap re-installation is scheduled for Friday. Build-up of Reinforced Carbon-Carbon (RCC) panels and associated fittings is ongoing. The first RCC panels are scheduled to be hung starting early next week.

Atlantis (OV-104), was delivered to Kennedy Space Center in April 1985. It lifted off on its maiden voyage on Oct. 3, 1985, on mission 51-J, the second dedicated Department of Defense flight. Later missions included the launch of the Galileo interplanetary probe to Jupiter on STS-34 in October 1989, and STS-37, with the Gamma Ray Observatory (GRO) as its primary payload, in April 1991.

Atlantis is named after a two-masted sailing ship that was operated for the Woods Hole Oceanographic Institute from 1930 to 1966.

Number of flights (25)
Upgrades and overhauls  Post Challenger upgrades 02/1986 - 09/1988
                                     11/1997 - 09/1999

03/08/2004
¹Processing of Atlantis continues at KSC in preparation for its future mission. Installation of the C-shaped T-seals that fit between each RCC panel is beginning on the left-hand wing leading edge. Right-hand RCC spar fittings are being installed, with the first panels being placed on the vehicle starting next week.

Remote Manipulator System hi-potential voltage tests are ongoing. Installation of window No. 2 is scheduled for next week.

Authorization to construct the fifth Space Shuttle orbiter as a replacement for Challenger was granted by Congress on August 1, 1987. Endeavour (OV-105), first arrived at KSC's Shuttle Landing Facility May 7,1991, atop NASA's new Shuttle Carrier Aircraft (NASA 911). The space agency's newest orbiter  began flight operations in 1992 on mission STS-49, the Intelsat VI repair mission.

Endeavour is named after the first ship commanded by 18th century British explorer James Cook. On its maiden voyage in 1768, Cook sailed into the South Pacific and around Tahiti to observe the passage of Venus between the Earth and the Sun. During another leg of the journey, Cook discovered New Zealand, surveyed Australia and navigated the Great Barrier Reef.

Number of flights (18)
Upgrades and overhauls  07/1996 - 02/1997

03/08/2004
¹Space Shuttle Endeavour is in its Orbiter Major Modification period, which began in December 2003. Thermal Protection System blankets are being removed to support removal and inspection of the Rudder Speed Brake actuators. RCC panels continue to be removed from the vehicle and returned to the vendor for inspection.