The Space Shuttle Columbia disaster was a fatal incident in the United States space program that occurred on February 1, 2003, when the Space Shuttle Columbia (OV-102) disintegrated as it reentered the atmosphere, killing all seven crew members. The disaster was the second fatal accident in the Space Shuttle program, after the 1986 breakup of Challenger soon after liftoff.

During the STS-107 launch, a piece of the insulative foam broke off from the Space Shuttle external tank and struck the thermal protection system tiles on the orbiter's left wing. Similar foam shedding had occurred during previous Space Shuttle launches, causing damage that ranged from minor to nearly catastrophic,:121 but some engineers suspected that the damage to Columbia was more serious. Before reentry, NASA managers had limited the investigation, reasoning that the crew could not have fixed the problem if it had been confirmed. When Columbia reentered the atmosphere of Earth, the damage allowed hot atmospheric gases to penetrate the heat shield and destroy the internal wing structure, which caused the orbiter to become unstable and break apart.After the disaster, Space Shuttle flight operations were suspended for more than two years, as they had been after the Challenger disaster. Construction of the International Space Station (ISS) was put on hold; the station relied entirely on the Russian Roscosmos State Space Corporation for resupply for 29 months until Shuttle flights resumed with STS-114 and for crew rotation for 41 months until STS-121.

NASA ultimately made several technical and organizational changes, including adding a thorough on-orbit inspection to determine how well the shuttle's thermal protection system (TPS) had endured the ascent, and keeping a designated rescue mission ready in case irreparable damage was found. Except for one final mission to repair the Hubble Space Telescope, subsequent shuttle missions were flown only to the ISS so that the crew could use it as a haven if damage to the orbiter prevented safe reentry.

Space Shuttle Columbia (OV-102) was a Space Shuttle orbiter manufactured by Rockwell International and operated by NASA. Named after the first American ship to circumnavigate the upper North American Pacific coast and the female personification of the United States, Columbia was the first of five Space Shuttle orbiters to fly in space, debuting the Space Shuttle launch vehicle on its maiden flight in April 1981. As only the second full-scale orbiter to be manufactured after the Approach and Landing Test vehicle Enterprise, Columbia retained unique features indicative of its experimental design compared to later orbiters, such as test instrumentation and distinctive black chines. In addition to a heavier fuselage and the retention of an internal airlock throughout its lifetime, these made Columbia the heaviest of the five spacefaring orbiters; around 1,000 kilograms (2,200 pounds) heavier than Challenger and 3,600 kilograms (7,900 pounds) heavier than Endeavour. Columbia also carried ejection seats based on those from the SR-71 during its first six flights until 1983, and from 1986 onwards carried an external scientific instrument bay on its vertical stabilizer.

During its 22 years of operation, Columbia was flown on 28 missions in the Space Shuttle program, spending over 300 days in space and completing over 4,000 orbits around Earth. While it was seldom used after completing its objective of testing the Space Shuttle system, and its heavier mass and internal airlock made it unideal for planned Shuttle-Centaur launches and dockings with space stations, it nonetheless proved useful as a workhorse for scientific research in orbit following the loss of Challenger in 1986. Columbia was used for eleven of the fifteen flights of Spacelab laboratories, all four United States Microgravity Payload missions, and the only flight of Spacehab's Research Double Module. The Extended Duration Orbiter pallet was used by the orbiter in thirteen of the pallet's fourteen flights, which aided lengthy stays in orbit for scientific and technological research missions. Columbia was also used to retrieve the Long Duration Exposure Facility and deploy the Chandra observatory, and also carried into space the first female commander of an American spaceflight mission, the first ESA astronaut, the first female astronaut of Indian origin, and the first Israeli astronaut.

At the end of its final flight in February 2003, Columbia disintegrated upon reentry, killing the seven-member crew of STS-107 and destroying most of the scientific payloads aboard. The Columbia Accident Investigation Board convened shortly afterwards concluded that damage sustained to the orbiter's left wing during the launch of STS-107 fatally compromised the vehicle's thermal protection system. The loss of Columbia and its crew led to a refocusing of NASA's human exploration programs and led to the establishment of the Constellation program in 2005 and the eventual retirement of the Space Shuttle program in 2011. Numerous memorials and dedications were made to honor the crew following the disaster; the Columbia Memorial Space Center was opened as a national memorial for the accident, and the Columbia Hills in Mars' Gusev crater, which the Spirit rover explored, were named after the crew. The majority of Columbia's recovered remains are stored at the Kennedy Space Center's Vehicle Assembly Building, though some pieces are on public display at the nearby Visitor Complex.