The U.S. space agency, NASA, is suspending future shuttle flights until it knows what caused the loss of the shuttle Columbia and its seven- member crew. Columbia broke up over Texas Saturday minutes before it was to land in Florida after a 16-day research mission in Earth orbit.

Seven astronauts, including the first from Israel, went down to their deaths in a hail of shuttle debris over Texas. Dramatic videotapes from a Dallas television station show it streaking to Earth in several smoking pieces.

Shuttle officials say the first sign of a problem was the loss of readings from sensors that measure tire pressure and temperature and structural heat on the orbiter's left side as it at headed toward landing at 18 times the speed of sound. Chief flight director Milt Heflin says controllers lost all contact with the shuttle minutes later.

"We lost the data and that's when we clearly began to know that we had a bad day," he said.

News reports tell of shuttle remains strewn across a wide area of east Texas. NASA is sending technicians to Texas to collect it with help from national, state, and local emergency agencies. NASA administrator Sean O'Keefe has established both an internal and independent external review board to investigate the cause of the disaster.

"This is indeed a tragic day for the NASA family, for the families of the astronauts, and likewise tragic for the nation," said Mr. O'Keefe.

The head of the shuttle program, Ron Dittemore, says debris analysis is key to understanding what happened to Columbia. He pledged a non-stop effort to assess it and all related flight data.

"It's going to take us some time to work through the evidence and the analysis to clearly understand what the cause was," he explained. "We will be poring over that data 24 hours a day for the foreseeable future."

Pending the answer, NASA is suspending all space shuttle flights. It has stopped preparing orbiters for flight at the Kennedy Space Center launch site, including the one that was scheduled to exchange crews at the International Space Station in early March.

A Russian supply rocket, set for launch Sunday, is bringing supplies that NASA says will support the station crew through late June.

Seventeen years ago, the shuttle Challenger exploded shortly after launch, but the Columbia disaster is the first time a shuttle has been lost returning from orbit since the program began 113 missions ago in 1981.

At the U.S. Naval War College in Newport, Rhode Island, space expert Joan Johnston-Freese notes that takeoff and landings are the most dangerous times for space shuttles.

"That's when the maximum pressure and velocity occur," she said. "The shuttle lands as a large glider and control is always a challenge, but under those conditions of pressure and velocity, the shuttle is so super-heated at that point that it's a very volatile situation under the best of conditions."

As part of NASA's probe, technicians will look for any signs that an unusual launch incident may have damaged critical insulating tiles on the shuttle's left wing, the side of the shuttle where the sensor readings went dead. Insulation from the rocket that helped boost Columbia to orbit flew off and hit the wing during liftoff.

Shuttle manager Dittemore says that after exhaustive analysis early in the mission, flight engineers determined that it probably would have no affect on the flight. But given Columbia's loss, he did not dismiss the potential impact to the wing.

"We're going to go back and see if there is a connection. Is that the smoking gun? It is not. We don't know enough about it. A lot more analysis and evidence needs to come to the table," he emphasized. "It's not fair to represent the tile damage as the source. It's just something we need to go look at."

When the Columbia disaster occurred, NASA administrator O'Keefe was at the Kennedy Space Center in Florida awaiting the shuttle's return with the families and friends of the astronauts. What was to be a happy reunion turned into grief-stricken moments of consolation. Mr. O'Keefe paid tribute to the astronauts, whom he said dedicated their lives to facing scientific challenges for all of us on Earth.

"The loss of this valued crew is something we will never be able to get over and certainly the families of all of them," he said. "We have assured them we will do everything, everything, we can possibly do to guarantee that they work their way through this horrific tragedy."

Security had been tighter than usual at the landing site because the presence of Israeli astronaut Ilan Ramon prompted government fears that he might be the target of a terrorist attack. However, NASA says there is no indication that terrorism is involved in the shuttle loss.