Space shuttle Columbia broke apart in flames 200,000 feet over Texas on Saturday, killing all seven astronauts just minutes before they were to glide to a landing in Florida.
"Columbia is lost; there are no survivors," President Bush announced to a stunned nation.
Bill Readdy, NASA's associate administrator for space flight and a former shuttle commander, said it was too early to speculate about what had destroyed Columbia. A senior U.S. official, speaking on condition of anonymity, said there was no immediate indication of terrorism.
NASA Administrator Sean O'Keefe, his voice breaking at times, said Bush had talked to the families of the astronauts who had been waiting at Kennedy Space Center for the crew's return.
"We trust the prayers of the nation will be with them and with their families," O'Keefe said. "A more courageous group of people you could not have hoped to know than the families of these crew members, an extraordinary, extraordinary group of astronauts who gave their lives."
Neither he nor Readdy took reporters' questions.
The six Americans and one Israeli, that country's first astronaut, who were aboard Columbia were 16 minutes from landing when the shuttle broke apart. They had been expected to touch down in Florida at 9:16 a.m.
At 9 a.m., Mission Control abruptly lost all data and voice contact with the shuttle and crew. At the same time, residents of Texas, Arkansas and Louisiana reported hearing "a big bang" and seeing flames in the sky.
The final radio transmission between Mission Control and the shuttle gave no indication of any trouble.
Mission Control radioed: "Columbia, Houston, we see your tire pressure messages and we did not copy your last."
Columbia's commander, Rick Husband, calmly responds: "Roger, buh ..."
Then the transmission goes silent for several seconds, followed by static.
Military satellites with infrared detectors recorded several flashes as Columbia broke apart, according to a defense official who spoke only on condition of anonymity. It was unclear whether those "spikes" of heat indicated an explosion, the burning of pieces of debris re-entering the atmosphere or something else.
Television footage showed a bright light followed by smoke plumes streaking through the sky. Debris appeared to break off into separate balls of light as it continued downward.
Hours after the shuttle had been expected to land, the giant screen at the front of Mission Control showed a map of the Southwest United States and what should have been Columbia's flight path. The U.S. flag next to the center's countdown clock was lowered to half-staff.
"A contingency for the space shuttle has been declared," Mission Control somberly repeated over and over from Houston.
At Kennedy Space Center, O'Keefe met with the astronauts' families. Six of the seven astronauts were married, and five of them had children.
NASA officials, meanwhile, warned people on the ground to stay away from any fallen shuttle debris. EPA spokesman Joe Martyak said he didn't know what toxic chemicals could be amid the debris because the shuttle can undergo reactions from the intense heat of reentry.
The shuttle flight was the 113th in the shuttle program's 22 years and the 28th flight for Columbia, NASA oldest shuttle.
In 42 years of U.S. human space flight, there had never been an accident during the descent to Earth or landing. On Jan. 28, 1986, space shuttle Challenger exploded shortly after liftoff.
(China Daily, February 2, 2003)