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 program shuttle design that best balanced capability, development cost and operating cost. Ultimately chosen was a design using a reusable winged orbiter, reusable solid rocket boosters, and an expendable external fuel tank for the orbiter's main engines. The shuttle program was formally launched on January 5, 1972, when President Nixon announced that NASA would proceed with the development of a reusable space shuttle system. The stated goals of "transforming the space frontier...into familiar territory, easily accessible for human endeavor" was to be achieved by launching as many as 50 missions per year, with hopes of driving down per-mission costs. The prime