The Space Shuttle Discover was the the third orbiter to become operational at Kennedy Space Center, was named after one of two ships that were used by the British explorer James Cook in the 1770s ... during voyages in the South Pacific that led to the discovery of the Hawaiian Islands. Another of his ships was the Endeavour, the namesake of NASA's newest orbiter.
Discovery benefited from lessons learned in the construction and testing of Enterprise, Columbia and Challenger. At rollout, its weight was some 6,870 pounds less than Columbia. Two orbiters, Challenger and Discovery, were modified at KSC to enable them to carry the Centaur upper stage in the payload bay. These modifications included extra plumbing to load and vent Centaur's cryogenic (L02/LH2) propellants (other IUS/PAM upper stages use solid propellants), and controls on the aft flight deck for loading and monitoring the Centaur stage. No Centaur flight was ever flown and after the loss of Challenger it was decided that the risk was too great to launch a shuttle with a fueled Centaur upper stage in the payload bay.
[Summary provided by NASA]