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. Last Updated: 07/27/2016

NASA Says Tank Foam Not to Blame

HOUSTON -- NASA is casting a wider net in the space shuttle investigation now that it has essentially ruled out a theory that a breakaway piece of foam may have caused Columbia to rip apart.

Other possibilities abound, from an accidental triggering of explosive devices on board to a collision with a piece of space garbage, or perhaps a flaw in a wing that caused the spacecraft to swing out of control and disintegrate moments before landing.

Shuttle program manager Ron Dittemore said every theory was being examined.

"Was it something that happened after launch? Was it something that happened during the entry? Or was it something that happened during ascent [launch] and we didn't see it? Those are all possibilities," he said Wednesday at a news conference.

For days, the investigation centered on a 1-kilogram chunk of foam insulation that peeled off the external fuel tank during launch and smashed into Columbia's wing. The theory was that the collision damaged the thermal tiles that keep the craft from burning up during re-entry.

But Dittemore said a rigorous analysis concluded that the impact would not be strong enough to doom the shuttle.

In one of several factors being examined, investigators have noted that during Columbia's descent, its automatic control system struggled to maintain the craft at the precise angle required for a safe return to Earth.

The autopilot added "more and more flight control muscle" in an attempt to keep Columbia pointed straight, Dittemore said, but just before the last signals from the spacecraft reached Earth, it was clear "we were beginning to lose the battle."

Dittemore said engineers are also exploring the possibility that increases in temperature detected on Columbia's left side may have somehow caused the loss of control and breakup of the shuttle.

Just minutes before Columbia fell apart, temperature rises were detected in the left landing gear compartment and on the left side of the fuselage.

Dittemore said the landing gear compartment contains small explosives designed to deploy the gear if the normal system fails.

If heat accidentally triggered the explosives, it could have been catastrophic, but Dittemore said this was unlikely.

Another scenario involved orbiting garbage. A collision from even a small object could have hit the shuttle like a bomb. Dittemore said small pieces of junk have damaged space shuttles in orbit, although it is rare.

He said important clues may come from the space shuttle debris being collected on the ground.

Pieces of the left wing, tiles and voice or data recorders would be particularly useful in solving the mystery of the disaster, but none have been found yet, Dittemore said.

Dittemore also said engineers are still trying to resurrect the final 32 seconds of signals Columbia sent.

"Perhaps this 32 seconds will help us understand some sequence of events," he said.