NASA is reconsidering whether tank foam debris caused the Columbia disaster. That’s quite a shift from days earlier when the foam was the "leading candidate" -- an explanation that quickly became embarrassing. … Until 1997, Columbia’s external fuel tanks were insulated with a Freon-based foam. Freon is a chlorofluorocarbon (CFC) supposedly linked with ozone depletion and phased out of widespread use under the international treaty known as the Montreal Protocol.
Despite that [ugh! They say this in the States?] the Freon-based foam worked well and that an exemption from the CFC phase-out could have been obtained, NASA succumbed to political correctness. The agency substituted an allegedly more eco-friendly foam for the Freon-based foam.
NASA says computer modeling fails to show how foam insulation striking the thermal tiles could do enough damage to cause catastrophe -- apparently ignoring that [Aargh! Another one!] flaking foam substantially penetrated thermal tiles on an earlier flight.
NASA has even offered up the ultimate exculpatory theory -- that space junk or even a meteor could have hit the wing and damaged the thermal tiles.
The investigation into what happened to Columbia needs to be turned over to a truly independent and qualified commission -- and before the evidentiary trail starts to disappear.
A pity Richard Feynman isn't still around to do the job, as he did on the Challenger enquiry.