Early indications are heat problem caused shuttle tragedy.

Byline: Seth Borenstein

WASHINGTON _ It's too soon to say why the space shuttle Columbia exploded, but the early signs suggest that a heat problem enveloped the left wing and side of the spacecraft before it disintegrated more than 39 miles above north central Texas.

What caused the heat and subsequent explosion is still unknown, but a prime suspect is a slight mishap that occurred when the vehicle was launched on Jan. 16. At that time, some debris from the shuttle's external fuel tank slammed against the left wing, experts said.

No matter what the cause, safety experts have warned for years that a problem was coming. They told Congress that the shuttle program needed more money and newer equipment or else it faced rising safety risks. Six outside consultants on a safety panel issued such warnings; they were fired in March 2001.

NASA officials began sketching out the fragmentary details of what they knew about the crash at a press conference Saturday afternoon.

In the last seven minutes before NASA lost communication with the 21-year-old ship, Columbia seemed to be flying normally. There was no sign of loss of flight control before it exploded at Mach 18.3, about 13,000 mph, said shuttle program manager Ron Dittemore. The shuttle had performed "absolutely flawlessly" during its 16-day mission, he said.

Then temperature sensors and tire pressure sensors on the left side were lost "as if someone had cut the wire," said Dittemore.