Space Shuttle Columbia that remained fitted to the avionics suite, and an internal airlock that, originally fitted into the other orbiters, was later removed in favor of an external airlock to facilitate Shuttle/Mir and Shuttle/International Space Station dockings. Due to its weight, "Columbia" could not have used the planned Centaur-G booster (cancelled after the loss of "Challenger"). The retention of the internal airlock allowed NASA to use "Columbia" for the STS-109 Hubble Space Telescope servicing mission, along with the Spacehab double module used on STS-107. Due to "Columbia's" heavier weight, it was less ideal for NASA to use it for missions to the
Space Shuttle Magnus (Mission Specialist 1), and Rex Walheim (Mission Specialist 2); they conducted the 135th and last space Shuttle mission on board "Atlantis", which launched on July 8, 2011, and landed safely at the Kennedy Space Center on July 21, 2011, at 5:57 AM EDT (09:57 UTC). NASA announced it would transfer orbiters to education institutions or museums at the conclusion of the Space Shuttle program. Each museum or institution is responsible for covering the cost of preparing and transporting each vehicle for display. Twenty museums from across the country submitted proposals for receiving one of the retired orbiters. NASA also