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 Columbia disaster crew of two. Less than a year after the accident, President Bush announced the Vision for Space Exploration, calling for the space shuttle fleet to complete the ISS, with retirement by the year 2010 following the completion of the ISS, to be replaced by a newly developed Crew Exploration Vehicle for travel to the Moon and Mars. NASA planned to return the space shuttle to service around September 2004; that date was pushed back to July 2005. On July 26, 2005, at 10:39 am EST, Space Shuttle "Discovery" cleared the tower on the "Return to Flight" mission STS-114, marking the