HOUSTON, Texas (CNN) -- Seven astronauts were killed today when space shuttle Columbia broke up about 38 miles above Texas on its way to Kennedy Space Center in Florida.
President Bush said in a televised address to the nation Saturday the news had brought "great sadness to our country," but pledged, "Our journey into space will go on."
"These men and women assumed great risk in the service of all of humanity," Bush said. "In an age when space flight has come to seem almost routine, it is easy to overlook dangers. ... These astronauts knew the dangers and faced them willingly."
Bush said the nation grieved for their families.
"The crew of the shuttle Columbia did not return safely to earth, yet we can pray that all are safely home," the president said. (Full story)
Earlier, NASA Administrator Sean O'Keefe said there was no indication the tragedy was "caused by anything or anyone on the ground."
Shuttle Commander Rick D. Husband, Pilot William C. McCool, Payload Commander Michael P. Anderson, Mission Specialists David M. Brown, Kalpana Chawla and Laurel Clark and Israel's first astronaut, Ilan Ramon, were killed.
O'Keefe said it was "too early to speculate about the exact cause," but said a team was already being assembled to delve into data and debris.
"We have assured [the families] that we will begin the process immediately to recover their loved ones and understand the cause of this tragedy," O'Keefe said.
O'Keefe said that NASA officials had been waiting eagerly for the shuttle to land because "we couldn't wait to congratulate them" for their extraordinary performance.
"The loss of this valiant crew is something we will never be able to get over," he said. (Full story)
Flags at the White House and NASA headquarters were lowered to half-staff in tribute to the crew.
No indication of terrorism
An administration official said the shuttle's altitude made it "highly unlikely" it fell victim to a terrorist act. FBI officials also were quick to discount the possibility of foul play or terrorism. (Full story)
"We have no information at this time that indicates that this was a terrorism incident," said Gordon Johndroe, press secretary for the Department of Homeland Security. "Obviously, the investigation is just beginning, but that is what we know now."
Homeland Security Director Tom Ridge went to the White House shortly after hearing of the disaster. He made phone calls to officials in Arizona, New Mexico, Oklahoma and Louisiana about the possibility of falling debris in their states.
U.S. officials said the Federal Emergency Management Agency (FEMA) would play the lead role in investigating the disaster, working closely with the military.
Video of the shuttle streaking over Dallas showed Columbia disintegrate into trails of flaming debris.
Reports of debris stretched from Corsicana southeast of Dallas into Louisiana. Officials warned that debris could be hazardous and should be avoided. Authorities in Plano, Texas -- north of Dallas -- were investigating the possibility shuttle debris may have caused an apartment fire there.
In Nacogdoches, Texas, police reported "numerous pieces of debris" both inside the city limits and in Nacogdoches County.
Residents as far east as Shreveport, Louisiana, reported seeing and feeling an explosion.
"As we seen [Columbia] coming over, we seen a lot of light and it looked like debris and stuff was coming off the shuttle," Benjamin Laster, of Kemp, Texas, told CNN.
"We seen large masses of pieces coming off from the shuttle as it was coming by," Laster said. "The house kind of shook and we noticed a sonic boom ... and then we seen a big continuous puff of vapor or smoke stream come out and then we noticed a big chunk go over."
The crew of STS-107, the last Columbia mission, walked out for launch on January 16.
NASA officials at the Johnson Space Center in Houston said they last had contact with the shuttle about 9 a.m. ET, and it had been expected to touch down at about 9:16 a.m. ET.
Dozens of people, including several officers, reported seeing "a ball of fire," Bowie County Sheriff's office dispatcher Jodine Langford said. "They saw it go out and then break into pieces," she said. (Witnesses' reports)
The Israeli Embassy in Washington has dispatched a small team to Florida to be with Col. Ilan Ramon's wife, four children and his parents, a spokesman for the Israeli embassy told CNN.
Ramon's family members had traveled from Israel to watch the planned return of the shuttle to the Kennedy Space Center Saturday morning. (Full story)
Former Sen. John Glenn, who was the first American to orbit Earth and returned to space at age 77, told The Associated Press he had he met Husband while training for his own 1998 mission. He said he was watching the landing on television with his wife. (Full story)
Columbia is the oldest of NASA's shuttle fleet, first launched in 1981. It was on its 28th mission. The shuttle underwent an extensive, 17-month overhaul that began in September, 1999.
It rejoined the shuttle fleet in February, 2001 and flew its first mission after the upgrades in March, 2002.
Infomation from: CNN
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