Designed to be reflown as many as 100 times, the U.S. space shuttle originally had been expected to reduce the high cost of spaceflight into low Earth orbit. After the system became operational, however, the vehicle's operating costs and the time needed for refurbishment between flights proved to be significantly higher than early projections. Between 1981 and 1985 a fleet of four orbiters—Columbia (the first to fly in space), Challenger, Discovery, and Atlantis—was put into service. On January 28, 1986, Challenger, carrying seven astronauts, exploded shortly after liftoff, killing all aboard including a private citizen, schoolteacher Christa McAuliffe (McAuliffe, Christa Corrigan). (See disaster (Challenger disaster).) The presidential commission appointed to investigate the accident determined that a joint seal in one of the solid rocket boosters had failed as a result of mechanical design problems, which were exacerbated by the unusually cold weather on the morning of the launch. Hot gases leaking from the joint eventually ignited the fuel in the shuttle's external tank, causing the explosion. After the accident, the shuttle fleet was grounded until September 1988 to allow NASA to correct the design flaws and implement associated administrative changes in the shuttle program. In 1992, Endeavour, a replacement orbiter for the destroyed Challenger, flew its first mission. NASA has announced that the space shuttle program will end in 2010 and that subsequent manned missions will use a vehicle called Orion, which will be similar to the Apollo spacecraft.

On February 1, 2003, Columbia broke up catastrophically over north-central Texas at an altitude of about 60 km (40 miles) as it was returning from an orbital mission. All seven crew members died, including Ilan Ramon, the first Israeli astronaut to go into space. (See disaster (Columbia disaster).) Once again the shuttle fleet was immediately grounded. The accident investigation board concluded that, during the launch of the shuttle, a piece of insulating foam had torn from the external tank and struck the orbiter's left wing, weakening its thermal protection ability. When the orbiter later reentered the atmosphere, it was unable to withstand the superheated air, which penetrated the wing and destroyed it, leading to the vehicle's breakup. As in the analysis of the Challenger disaster, the Columbia accident was seen as the result of both mechanical and organizational causes that needed to be addressed before shuttle flights could resume. (For additional information on the space shuttle, see space exploration.)