Jan. 16, 7:39 a.m. — Columbia rockets into orbit from Kennedy Space Center.

Feb. 1, 5:15 a.m. — Columbia fires braking rockets, streaks toward touchdown.

5:53 a.m. — NASA loses temperature measurements for shuttle's left hydraulic system.

5:58 a.m. — NASA loses measurements from three temperature sensors on shuttle's left side.

5:59 a.m. — NASA loses eight more temperature measures and pressure measures for left
inboard and outboard tires. One of the measurements remains visible to crew on a display panel; which crew acknowledges.

5:59 a.m. — Final transmission. Mission Control radios: "Columbia, Houston, we see your tire pressure messages and we did not copy your last." Columbia replies: "Roger, uh, ..."

6 a.m. — NASA loses all data and contact with Columbia at 207,135 feet.

6 a.m. — Residents of Texas, Arkansas and Louisiana report hearing "a big bang" and seeing flames in the sky.

6:16 a.m. — Columbia's scheduled landing time.

6:29 a.m. — NASA declares an emergency.

6:44 a.m. — NASA warns residents to stay away from possibly hazardous debris.

8 a.m. — Kennedy Space Center lowers flag to half-staff.

11:05 a.m. — President Bush announces: "Columbia is lost; there are no survivors."

Source: NASA.