Possible wing damage appears to be focus as 3 shuttle probes begin.(The Dallas Morning News)

Byline: Ed Timms

It didn't seem like much at the time: as Columbia rumbled off the launching pad 17 days ago, a chunk of insulation apparently flecked off the main fuel tank and struck the space shuttle's left wing.

But after Columbia broke apart Saturday, much of the speculation about what caused the tragedy focused on damage to the heat-absorbing tiles on that wing.

NASA shuttle project manager Ron Dittemore on Saturday that insulation had struck the wing during takeoff.

"As we look at that now in hindsight, we can't discount that there might be a connection," said Dittemore, speaking in Houston. "But we have to caution that we can't rush to judgment, because a lot of things in this business that look like the smoking gun turn out not to be close."

Still, the wing appeared to be the focus as at least three separate investigations were planned _ one by NASA, one by an independent panel of government and military experts and one by a House committee.

As the shuttle descended through the atmosphere at about 18 times the speed of sound, extremely high temperatures build up on the leading edges of the shuttle's wings. The tiles are designed to protect the wing.