The inquiry into the space shuttle Columbia tragedy continues, with thousands of pieces of debris so far reported to authorities from locations ranging from central Texas to western Louisiana. Each fragment will help investigators piece together what went wrong on the shuttle's return to Earth Saturday morning, under what were arguably perfect weather conditions for landing.

The first indications of trouble reached NASA's mission control eight minutes before nine o'clock EST, when sensors on the left side of Columbia's fuselage recorded a temperature spike. A few minutes later, temperature increases totaling 60 degrees were detected on the left side of the shuttle, which was significantly greater than the increase recorded on the right. Minutes later the control system started to tilt Columbia, apparently in response to increased drag detected on the shuttle's left. The anomalous data from the left side drew attention to an incident that occurred during the shuttle's launch: a piece of foam insulation from the external fuel tank hit Columbia's left wing about 80 seconds after lift-off. A leading theory holds that the impact of the roughly 2.7-pound block may have damaged the shuttle's heat-resistant tiles.

"All the analysis that we conducted over the course of the 16-day mission led us to conclude that there were no 'safety of operations' considerations and that's what the flight engineers all determined during the course of that time," says NASA Administrator Sean O'Keefe. "Having said that, we are not ruling this out. The investigating team is looking at that theory as well as lots of others." In addition to NASA's internal review panel, an independent inquiry board has been appointed to look into the disaster. In the meantime, all shuttle plans have been shelved. After the 1986 Challenger explosion, it was more than two years before another space shuttle took off.