the NASA Ground Track

It is becoming apparent that the genesis of this Shuttle accident was not unlike that of the Challenger....too many people (who should have known better) disregarding the environmentals pre-launch.

It has been admitted that the Columbia sat on its launch pad much longer than any other Shuttle before it (39 days) and that the weather was the coldest Florida weather for over 50 years. I recall seeing deep snow on the TV at the time. That's a lot of freeze/melt/re-freeze cycles for the foam insulation - which undoubtedly as a result was rain-soaked, freeze-cracked and was ready to separate in large icy spear-like stalactites under the stresses of max Q (81 secs into launch). Of course, once the liquid hydrogen was loaded, the foam was then frozen in place. It took the post-launch thermodynamic heating to thaw it and it then separated along its cyclic fault-lines. If you look here (link) you will see that it has happened before and damaged the RCC leading edge in a similar fashion to what is here suggested may have happened to STS-107.Once you read into the NASA specifications for the RCC leading edge, it becomes apparent that it was "toughened" - but only against high temperatures (as part of the TPS) - and never against IMPACT. They never took the required precautions against launch debris impact - probably because the spec for its "raison d'etre" was always to revolve around its resistance to re-entry heating.

A likely fix would be to affix a vulcanized (and wedge-shaped) sacrificial strip along the RCC Leading Edge (even a non-aerodynamic and deflective one). That reasonably practical fix would provide launch debris impact protection yet quickly burn away on re-entry. A pointy impact of an icy stalactite on that RCC L.E. probably did what you would expect any pointy impact to do to what's essentially nothing more than a toughened graphite, i.e. shatter it. Because it is only "bolted on" (via inconel attachments), loss of its structural integrity (by shattering) would have led to it being rapidly eroded away. But how?

If you read the NASA blurb here, they describe it as being critically coating-protected against oxidization. Once an RCC section was shattered on launch, that section’s oxidization destruction on re-entry was assured. Unfortunately that section was right ahead of the port wheel-well’s outboard forward corner. Superheated white-hot RCC pieces detaching was what the Owens Valley Astronomer would have seen in the pre-dawn darkness. The underlying aluminium wing surface is only rated to 175 odd degrees. No wonder the wheel-well was pierced and the events in there set in train (see here and here.

Further Reading on the Thermal Protection System is here.

This is an excerpt from the most recent set of modifications made to the Shuttle Fleet. These documents were obtained just prior to NASA pulling all information about the shuttle from the net on that fateful Saturday. Read carefully.

" The area aft of the reinforced carbon-carbon nose cap to the nose landing gear doors has sustained damage (tile slumping) during flight operations from impact during ascent and overheating during re-entry. This area, which previously was covered with high-temperature reusable surface insulation tiles, will now be covered with reinforced carbon-carbon.
The low-temperature thermal protection system tiles on Columbia's midbody, payload bay doors and vertical tail were replaced with advanced flexible reusable surface insulation blankets.
Because of evidence of plasma flow on the lower wing trailing edge and elevon leading edge tiles (wing/elevon cove) at the outboard elevon tip and inboard elevon, the low-temperature tiles are being replaced with fibrous refractory composite insulation (FRCI-12) and high-temperature (HRSI-22) tiles along with gap fillers on Discovery and Atlantis. On Columbia only gap fillers are installed in this area."