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 Atlantis Space Shuttle Atlantis Space Shuttle "Atlantis" (Orbiter Vehicle Designation: OV‑104) is a Space Shuttle orbiter vehicle belonging to the National Aeronautics and Space Administration (NASA), the spaceflight and space exploration agency of the United States. Constructed by the Rockwell International company in Southern California and delivered to the Kennedy Space Center in Eastern Florida in April 1985, "Atlantis" is the fourth operational and the second-to-last Space Shuttle built. Its maiden flight was STS-51-J from 3 to 7 October 1985. "Atlantis" embarked on its 33rd and final mission, also the final mission of a space shuttle, STS-135, on 8 July 2011.