BY CHARLES W. PETIT

NEWS BRIEFINGS For additional information including news, analysis, and links visit our briefing on the Columbia space shuttle crash. Read more about Space Exploration.

In a spectacle that stunned a nation the space shuttle Columbia disintegrated in a multiple fireball as it streaked across the clear blue sky over north central Texas during reentry from orbit shortly after 9 a.m. Saturday.

A crew of seven astronauts–six American and one Israeli–were aboard the shuttle, which was returning from a 16-day science mission. There was no chance of survival. The presence on Columbia of Ilan Ramon, a former Israeli Air Force combat pilot and his country's first astronaut, inevitably triggered speculation about terrorism. But NASA and other government officials rushed to say the space plane, flying at an altitude of 38 miles and a speed of more than 12,000 miles per hour, was well beyond the reach of any terrorist's missile. Sabotage may be a remote possibility, but security at and before launch was extra tight. Instead, initial suspicions focus on a failure in the left wing, and the possibility that its heat protecting tiles were damaged by insulation seen falling from the big, external fuel tank during launch from Kennedy Space Center two weeks ago.

A thundering roar accompanied the disaster as jagged pieces of shuttle tumbled at hypersonic speed and their sonic booms merged into a continuous rumble. A cloud lingered in the sky for hours, drifting southeast toward Louisiana.

Many of the small pieces of debris that survived the breakup reached Earth in a swath of ground more than 100 miles long, some in the town of Nacogdoches in east Texas–one landed near a high school, another went through the roof of a dentist's office. Officials including military units cordoned them off until federal personnel can gather them up. NASA asked residents of east Texas and bordering areas, if they see any possible wreckage, to stay clear. One reason is the possibility of toxic gases from propulsion and power unit fuels. More important, they want nobody but experts to move debris, and provided a phone number (281-483-3388) to report wreckage.

The loss of the oldest of America's four space planes and its occupants not only dealt a shocking body blow to an already bruised and grieving nation's psyche, but leaves NASA and the U.S. government with a gargantuan task to keep America's program of human space flight on track. President Bush, in a solemn, brief statement later in the morning, praised the courage of the astronauts and vowed, "The cause for which they died will continue ... our journey to space will continue." NASA officials said, however, that until they understand the accident, they are suspending flights by America's three remaining shuttles, Atlantis, Discovery, and Endeavour.

Bill Readdy, the agency's space flight director, said the first hint of trouble for him and other top NASA officials in Florida was loss of communication with the craft over Texas, just minutes before the spacecraft's intended touchdown on its Florida runway. Gaps in communication are not rare, particularly during re-entry, when a radio-absorbing fireball envelops the craft. "We were standing along the runway getting ready to celebrate a very successful mission," he said later. Only after the shuttle had failed to appear on the radar screen or in the sky on its final approach near the scheduled landing time of 9:16 a.m. did the mission's overseers in Florida know something horrible had occurred.

But engineers watching data come in at centers in Houston and Cape Canaveral had noted problems a few minutes earlier. Over a period of several minutes during re-entry, just before the spacecraft suddenly broke up, various sensors in the shuttle's left wing went dead. Data from sensors monitoring temperature and pressure for the elevons, or flaps, on the left wing were lost at 8:53 a.m. Then at 8:59, sensors monitoring pressure and temperature of the tires in the left-wing wheelwell also went offline. Such data losses are not rare, and controllers say the craft seemed to continue flying normally . "It had been a fantastic mission," said shuttle program manager Ron Dittemore.

NASA flight director Milt Heflin, almost overwhelmed with emotion during a post-accident briefing, says that it was only when he and other ground controllers tried to contact the crew in the following few minutes, including an attempt on a reliable ultra-high-frequency radio circuit, did he realize "we had a really bad day." By that time, ordinary citizens in Texas were watching in wonder and growing horror as the space shuttle's trail across the sky shed multiple, smoking pieces.

The accident occurred when the spacecraft was under great stresses. Heating from friction with the air was at its peak, and automated controls were putting the craft through a series of turns to help slow it down in the thin upper atmosphere. Some reports from witnesses who had watched the craft's trail over California moments earlier said it appeared that the shuttle, encased in a cloud of glowing plasma, may have already been shedding pieces there. However, NASA experts said the plasma fireball around a shuttle is turbulent and hard to read. They said there is, as yet, no solid evidence that it was breaking up before it approached the skies over Texas.

NASA administrator Sean O'Keefe briefed President Bush early Saturday, and coordinated an investigation with multiple Federal agencies including the new Department of Homeland Security to collect debris. Readdy vowed, "We must find what happened, fix it, and move on."

The loss comes almost exactly 17 years after the previous fatal shuttle flight, the loss of the Challenger with seven on board at takeoff, on Jan. 28, 1986. No shuttle flew after that accident for 2½ years. A similar delay now would pose immense problems for the 16-country International Space Station program, led by NASA. While Russian vehicles can rotate crews and take supplies to the station, which now has two American and a Russian on board, only the shuttles can carry equipment to keep expanding the half-built station. Columbia, the oldest of the shuttles with the smallest cargo capacity, was not used on the space station project.

Major questions include whether to alter or even abandon the space station project, and whether to replace the Columbia with a new shuttle or accelerate development of a new generation of cargo and human-carrying space ships. The Columbia made its first flight April 12, 1981, and space agency leaders hoped the shuttles would remain the mainstay of U.S. human spaceflight until 2015 and perhaps many years longer.

In initial briefings, shaken NASA engineers said they must now take another look at film of the piece of foam insulation seen tumbling from the external tank and passing near the shuttle's left wing at takeoff. "It looks like it impacted the left wing somewhere between the mid and outward portion of the span," Dittemore said. Several panels of NASA engineers had looked at the film during the mission, he said, and concluded it was not enough to seriously damage the wing or the tiles covering it. His team had told the shuttle crew to be sure to take pictures of the external tank when it was ejected from the shuttle upon reaching orbit, to see how much foam was lost. But the reason was to see if the tank design needs change to prevent such loss of insulation, not worry that it had hurt the shuttle.

As of now, Dittemore said, NASA's officials believe that the insulation should not have done much damage to the wing. But, he added, "as we look at that in hindsight, the impact was on the left wing, and certainly all the indications [of trouble during reentry] were on the left wing, so we can't discount that there might be a connection. But we cannot rush to judgment on it."

The Columbia, while old in years, was like all the shuttles considered to be a fresh vehicle. On its 28th mission, it was designed to fly much more often than it has. Its final flight had been on the schedule for four years, and some of its crew had trained for it that long. In its cargo bay was a sophisticated science lab called SpaceHab that kept the crew busy with experiments during the entire mission. Intended to help maintain space research momentum until the space station is complete, the mission had by all reports gone exceedingly well.

The last voice communication with the crew came at about 9 a.m., when their instruments told about the data loss from sensors in the left wing landing gear, which was still folded into the wing. The crew acknowledged to ground control that they saw the reading. Then their radio link went dead.