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. 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 orbiters left wing during the launch of STS-107 fatally compromised the vehicles thermal protection system.