Space Shuttle Challenger (OV-099) was a Space Shuttle orbiter manufactured by Rockwell International and operated by NASA. Named after the commanding ship of a nineteenth-century scientific expedition that traveled the world, Challenger was the second Space Shuttle orbiter to fly into space after Columbia, and launched on its maiden flight in April 1983. It was destroyed in January 1986 soon after launch in an accident that killed all seven crewmembers aboard. Initially manufactured as a test article not intended for spaceflight, it was utilized for ground testing of the Space Shuttle orbiter's structural design. However, after NASA found that their original plan to upgrade Enterprise for spaceflight would be more expensive than upgrading Challenger, the orbiter was pressed into operational service in the Space Shuttle program. Lessons learned from the first orbital flights of Columbia led to Challengers design possessing fewer thermal protection system tiles and a lighter fuselage and wings. This led to it being lighter than Columbia, though still heavier than Discovery. During its three years of operation, Challenger was flown on ten missions in the Space Shuttle program, spending over 62 days in space and completing almost 1,000 orbits around Earth. Following its maiden flight, Challenger supplanted Columbia as the leader of the Space Shuttle fleet, being the most-flown orbiter during all three years of its operation while Columbia itself was seldom used during the same time frame. Challenger was used for numerous civilian satellite launches, such as the first tracking and data relay satellite, the Palapa B communications satellites, the Long Duration Exposure Facility, and the Earth Radiation Budget Satellite. It was also used as a test bed for the Manned Maneuvering Unit (MMU) and served as the platform to repair the malfunctioning SolarMax telescope. In addition, three consecutive Spacelab missions were conducted with the orbiter in 1985, one of which being the first German crewed spaceflight mission. Passengers carried into orbit by Challenger include the first American female astronaut, the first American female spacewalker, the first African-American astronaut, and the first Canadian astronaut. On its tenth flight in January 1986, Challenger disintegrated 73 seconds after liftoff, killing the seven-member crew of STS-51-L that included Christa McAuliffe, who would have been the first teacher in space. The Rogers Commission convened shortly afterwards concluded that an O-ring seal in one of Challengers solid rocket boosters failed to contain pressurized burning gas that leaked out of the booster,