Kennedy Space Center
On February 1, 2003, "Columbia" and her crew of seven were lost during re-entry over Texas during the STS-107 mission (the 113th shuttle flight); a vehicle breakup triggered by damage sustained during launch from Pad 39A on January 16, when a piece of foam insulation from the orbiter's external fuel tank struck the orbiter's left wing. During reentry, the damage created a hole allowing hot gases to melt the wing structure. Like the "Challenger" disaster, the resulting investigation and modifications interrupted shuttle flight operations at KSC for more than two years until the STS-114 launch on July 26, 2005.
STS-61-C
STS-61-C saw "Columbia" return to flight for the first time since the STS-9 mission in November 1983, after having undergone major modifications over the course of 18 months by Rockwell International in California. Most notable of these modifications was the addition of the SILTS (Shuttle Infrared Leeside Temperature Sensing) pod atop "Columbia's" vertical stabilizer, which used an infrared camera to observe reentry heating on the shuttle's left wing and part of its fuselage. The camera was only used for a few more missions after STS-61-C, but the pod remained on "Columbia" for the remainder of its operational life. Smaller and more discreet modifications were also added at various points throughout the shuttle. The bulky ejection seats, which had been safed after STS-4, were replaced with conventional seats and head-up displays for the commander and pilot were installed.