used between segments of the SRB casing. Failure of the O-ring allowed hot combustion gases to escape from between the booster sections and burn through the adjacent ET, leading to a sequence of catastrophic events which caused the orbiter to disintegrate. Repeated warnings from design engineers voicing concerns about the lack of evidence of the O-rings' safety when the temperature was below had been ignored by NASA managers. On February 1, 2003, Columbia disintegrated during re-entry, killing all seven of the STS-107 crew, because of damage to the carbon-carbon leading edge of the wing caused during launch. Ground control engineers had made three separate requests for high-resolution images taken by the Department of Defense that would have provided an understanding of the extent of the damage, while NASA's chief TPS engineer requested that astronauts on board Columbia be allowed to leave the vehicle to inspect the damage. NASA managers intervened to stop the Department of Defense's imaging of the orbiter and refused the request for the spacewalk, and thus the feasibility of scenarios for astronaut repair or rescue by Atlantis were not considered by NASA management at the time. Criticism The partial reusability of the Space Shuttle was one of the primary design requirements during its initial development. The technical decisions that dictated the orbiter's return and re-use reduced the per-launch payload capabilities. The original intention was to compensate for this lower payload by lowering the per-launch costs and a high launch frequency. However, the actual costs of a Space Shuttle launch were higher than initially predicted, and the Space Shuttle did not fly the intended 24 missions per year as initially predicted by NASA. The Space Shuttle was originally intended as a launch vehicle to deploy satellites, which it was primarily used for on the missions prior to the Challenger disaster. NASA's pricing, which was below cost, was lower than expendable launch vehicles; the intention was that the high volume of Space Shuttle missions would compensate for early financial losses. The improvement of expendable launch vehicles and the transition away from commercial payloads on the Space Shuttle resulted in expendable launch vehicles becoming the primary deployment option for satellites. A key customer for the Space Shuttle was the National Reconnaissance Office (NRO) responsible for spy satellites. The existence of NRO's connection was classified through 1993, and secret considerations of NRO payload requirements led to lack of transparency in the