Shuttle Columbia breaks apart, all 7 astronauts killed.(Chicago Tribune)

Byline: Tim Jones

The homeward-bound space shuttle Columbia broke up in orange flames and contrails of smoke over Texas on Saturday, killing all seven astronauts aboard and leaving investigators baffled over what went wrong on a mission that was only 16 minutes away from a successful completion.

Echoing the tragedy of the space shuttle Challenger that stunned the nation 17 years ago this week, Columbia exploded at an altitude of about 39 miles as it was traveling 18 times the speed of sound, en route to Cape Canaveral, Fla. The force of the explosion scattered debris across hundreds of square miles in Texas and Louisiana and, according to witnesses, shook houses in the area around Nacogdoches, Texas.

The incident provoked an outpouring of sympathy from a nation grappling with the memories of terrorist attacks and the looming prospect of war. Flags were lowered to half-staff. Americans interrupted their normal weekend routines to monitor developments on television and, in Texas and Florida, create memorials to the fallen astronauts.

In a televised address to the nation, an emotional President Bush paid homage to the astronauts, saying "the crew of the shuttle Columbia did not return safely to earth but we can pray that they are safely home."

NASA and an independent review panel said they will investigate the disaster. While officials said it was too early to speculate about the cause of the explosion, early indicators pointed to debris that damaged the left wing during the launch. That could have been responsible for the loss of temperature sensors in the left wing's hydraulic system.

Investigators have all but ruled out terrorism as a cause because the shuttle's high altitude and extreme speed effectively put it out of range of an attack from the ground.