SPACE SHUTTLE COLUMBIA TRAGEDY

In a nationally televised White House address, President Bush said “our entire nation grieves” over the tragedy.

“The Columbia’s lost,” he said. “There are no survivors.”

The crash marked the first fatal accident in America’s space program since the 1986 Challenger explosion, which also claimed seven lives. That disaster grounded the shuttle fleet for almost three years and raised deep questions about the risks of space flight.

This time, Bush vowed that the astronauts’ deaths would not spell an end to space exploration.

“The cause in which they died will continue,” he said. “Our journey into space will go on.”

WHAT WENT WRONG?

Speaking from Kennedy Space Center in Florida, where the 100-ton shuttle had been scheduled to land, NASA Administrator Sean O’Keefe said Columbia broke up in flames as it re-entered the Earth’s atmosphere over Texas, spreading debris all over the state.

He described the crew as having performed their mission brilliantly, and said in a broken voice, “The loss of this valued crew is something we will never be able to get over.”

In its first hours, the investigation focused on Columbia’s left wing.

“The first indications of a potential problem occurred minutes before 8 o’clock Central Time (9 a.m. ET),” shuttle program manager Ron Dittemore told reporters. “The first indications were the loss of temperature sensors and the hydraulic sensors on the left wing.”

He said those failures were followed within minutes by several other problems, including the loss of sensors for tire pressure and temperature. Just as Mission Control was discussing the tire concerns with the crew, contact was lost at 9 a.m. ET.

After the shuttle launched on Jan. 16, mission managers said a piece of insulating foam had broken off from the external fuel tank and might have hit the left wing. At the time, NASA said the incident did not raise safety concerns.

“We can’t discount that there might be a connection,” shuttle program manager Ron Dittemore told reporters. But he cautioned that “we can’t rush to judgment on it.”

He said that Columbia had performed “flawlessly” during its 16-day science mission. The only technical glitch reported before Saturday was a problem with the shuttle’s dehumidifiers.

A U.S. official told NBC there was no indication of terrorism.

WITNESSED BY THOUSANDS

Thousands of witnesses watched in horror as Saturday’s tragedy unfolded. Across Texas and New Mexico, search-and-rescue teams fanned out over a wide area to investigate reports of debris. Most of the wreckage apparently landed in an area of many thousands of square miles between Waco and the Louisiana border.

In Nacogdoches, Texas, residents found bits of metal strewn across the city. Dentist Jeff Hancock told The Associated Press that a metal bracket about a foot long had crashed through his office roof.

“It’s all over Nacogdoches,” said barber shop owner James Milford. “There are several little pieces, some parts of machinery ... there’s been a lot of pieces about 3 feet wide.”

In Dallas, NBC News’ Jim Cummins reported that a loud explosion was heard at about the same time NASA lost contact with the spacecraft — a time when the shuttle was descending to 200,000 feet, traveling at 12,500 mph.

Soon after that, witnesses described seeing the Columbia disintegrating in flames along the way.

Janet Smith-Bozart, who was driving near Dallas, described the shuttle’s descent in an interview with MSNBC.

“I thought at first it might be a meteor coming into the atmosphere and then I realized it was much too big and much too slow for that,” she said.

“Essentially the entire thing just broke apart and the whole thing just disappeared. ... Eventually it just sort of faded and there was no more contrail or anything.”

Explosions were widely reported across Texas.

“It was like a car hitting the house or an explosion. It shook that much,” John Ferolito, 60, of Carrolton, north of Dallas, told AP.

SUDDEN DISAPPEARANCE

Columbia had been scheduled to land at 9:16 a.m. ET — the 113th mission in the 22-year-old shuttle program and the 28th flight for Columbia, which was NASA’s oldest shuttle. February 1 — Former space shuttle Commander Rick Hauck describes the process by which shuttles re-enter the earth’s atmosphere.

During the shuttle’s descent, it’s not uncommon for voice and radar contact to be lost for a brief period. But when Mission Control couldn’t re-establish communications, even after the shuttle’s scheduled landing time, NASA announced that “a contingency for the space shuttle has been declared.”

Flight controllers were ordered to pull out emergency procedures and retain all their records, a move aimed at securing evidence for the investigation to come.

NASA also advised anyone seeing crash debris to notify local authorities. The agency warned the public not to touch the debris, saying that it could be contaminated with toxic fuel.

GIRDING FOR THE WORST

Family members of the shuttle crew, which included the first-ever Israeli astronaut, were gathered on the Florida landing strip to greet their loved ones when news of the mishap emerged. NASA officials quickly huddled the relatives into a shuttle and kept them in seclusion at the Kennedy Space Center.

An official of the Department of Homeland Security, speaking on condition of anonymity, told NBC News there was no indication that terrorism might have been involved.

Nevertheless, the Pentagon and Joint Chiefs of Staff were convening a “domestic event conference” for any possible response to the Columbia incident, NBC’s Jim Miklaszewski reported. The Federal Emergency Management Agency was put in charge of the search operation in Texas, in cooperation with local authorities.

In addition to NASA’s internal investigation, an independent panel with representatives from the Air Force and Navy as well as the Transportation Department and other federal agencies would look into the causes of the tragedy, NASA’s O’Keefe said.

Speaking on condition of anonymity, a U.S. official told NBC’s Miklaszewski that a heat spike appeared on military satellite data around the time shuttle was re-entering. The readings would be examined to see if they correlate to the shuttle’s breakup. The highly sensitive infrared satellite, known as the DSP, originally was developed to detect the heat spike of Soviet intercontinental missile launches. It also has been used to detect the heat signature of oil fires, volcanic eruptions and the explosion of TWA Flight 800 in 1996.

A BLOW TO PROGRAM

Just in the last week, NASA observed the anniversary of the 1967 Apollo 1 fire (Jan. 27) and the 1986 Challenger explosion (Jan. 28).

The Challenger disaster, which occurred during a live TV broadcast of the launch, nearly ended the shuttle program. A series of investigations ultimately determined that a gas leak in the right booster rocket was blamed for the Challenger blast. In the explosion, the crew module separated intact from the fireball, went into a 2½-minute free fall from 50,000 feet, and plunged into the sea.

NASA put the shuttle program on hold after the Challenger accident until 1988. The agency has put the odds of a catastrophic accident during launch — the most dangerous part of any shuttle mission — at 1 in 438.

The Associated Press and Reuters contributed to this report.