Weight edit As the second orbiter to be constructed, and the first able to fly into space, Columbia was roughly 8,000 lb (3,600 kg) heavier than subsequent orbiters such as Endeavour , which were of a slightly different design, and had benefited from advances in materials technology. In part, this was due to heavier wing and fuselage spars, the weight of early test instrumentation 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 (canceled 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. citation needed Due to Columbia's higher weight, it was less ide...