SPACE CENTER, Houston (AP) -- NASA investigators are looking closely at whether the chunk of foam insulation that hit the shuttle on liftoff was coated or saturated with ice, which would have made the object more destructive than the space agency ever imagined.
The theory is that some sort of defect in the insulation allowed rain to penetrate the foam while the shuttle was on the launch pad. Then, the theory goes, ice formed between the foam and the super-cold hull of the fuel tank.
Ice infiltration might explain what caused a 20-inch piece of foam to pop off during the launch. But more important, it might explain how a piece of foam that was thought by NASA to weigh only 2 1/2 pounds might have caused catastrophic damage to the thermal tiles under the left wing.
Columbia was on the launch pad for five weeks, from Dec. 9 until Jan. 16, when it took off with seven astronauts on their science mission. That was not unusually long, but it rained heavily during the period, and some insiders are speculating that rain might have gotten behind the foam.
Ice routinely forms on the outside of the 154-foot tank after NASA begins filling it with super-cold liquid hydrogen and oxygen fuel in the final hours of the countdown.
But the men sent out to inspect the tank for ice, right before liftoff, would have had no way of seeing - or knowing - whether any ice lay behind the foam.
Shuttle program manager Ron Dittemore said earlier this week that engineers were trying to determine whether any ice was on the piece of foam that came loose 81 seconds into the flight. Ice would have made the foam heavier and more dangerous.
Steven Schneider, an aeronautics and astronautics professor at Purdue University, said Wednesday that all the focus seems to be on the foam itself, "but there has to be something that wasn't so obvious.''
"Maybe instead of being just plain foam, it had a whole lot of ice inside the foam that maybe was unexpected and surprised them,'' he said.
Schneider said it is also possible that the flying object seen in the launch video is not foam at all, but a totally different piece of debris, like solid ice.
He also said it is possible that the object somehow damaged the seal on the left landing gear door, setting off the deadly cascade of events.
High temperatures were detected inside the left wheel well 24 minutes before Columbia broke apart 39 miles over Texas on Saturday.
Michael Kostelnik, a top NASA spaceflight official, said ice could be dangerous if it came loose during liftoff. But he said to the best of his recollection, "ice was not an issue'' - at least any ice that could be observed.
Kostelnik again defended the engineering analysis that was conducted during Columbia's 16-day flight regarding the potential safety threat from the foam. The one week of reviews concluded that any damage from the foam to the thermal tiles beneath Columbia's left wing was minor and posed no hazard.
But that conclusion was based in part on the assumption that the foam weighed 2 1/2 pounds.
"I am sure when those photo analysis were reviewed, there was concern,'' Kostelnik said. But he added: "I am very comfortable that this team did as good as they could to understand what this anomaly was. ... I believe that we made the right decision at that time. It will yet to be determined, perhaps there was a mistake there. We don't know that.''
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