Space Shuttle It weighed 3.4 metric tons (7,500 lb) less than the last run of lightweight tanks, allowing the Shuttle to deliver heavy elements to ISS's high inclination orbit. As the Shuttle was always operated with a crew, each of these improvements was first flown on operational mission flights. The solid rocket boosters underwent improvements as well. Design engineers added a third O-ring seal to the joints between the segments after the 1986 Space Shuttle "Challenger" disaster. Several other SRB improvements were planned to improve performance and safety, but never came to be. These culminated in the considerably simpler, lower cost, probably
Space Shuttle retirement Space Shuttle retirement The retirement of NASA's Space Shuttle fleet took place from March to July 2011. "Discovery" was the first of the three active space shuttles to be retired, completing its final mission on March 9, 2011; "Endeavour" did so on June 1. The final shuttle mission was completed with the landing of "Atlantis" on July 21, 2011, closing the 30-year Space Shuttle program. The Shuttle was presented to the public in 1972 as a "space truck" which would, among other things, be used to build a United States space station in low earth orbit in the early 1990s