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Having previously discussed a stragetic perspective, now for technical aspects. Columbia was the oldest, heaviest of the fleet. It was also doing what most every space flight has not done - carrying a massive payload back to earth. A payload that increases structural stresses. Most shuttles return to earth empty.
It is obvious that some heat shield tiles were lost when the shuttle launched. In missions where shuttles weighed less, this was not a problem but proved risky based upon resulting heat damage. However this shuttle was probably the heaviest to ever return to earth. Potential for failure was greatest. Previous shuttles with much less weight did lose tiles and suffered serious burning of the aluminum structure. But that alone does not explain a failure so quickly. Add to those missing tiles a possible failure or excessive flexing in its old wings - again due its payload.
Shuttles cannot communicate with ground during reentry for the same reasons that capsules suffer blackouts. But NASA solved this problem by communicating through TDRSS during landing. Likely, telemetry data continued to be received after voice communication was lost. But it best will take weeks before even that data is understood. Clear from evidence, massive failure occured on the left wing where it joined the fuselage. Reasons for that failure must explain why a shuttle would attempt a landing knowing that heat shield tiles were missing. Unfortunately, a decision was being made with few options which might explain why the decision to land was still made. Considering the current political climate, jettisoning the lab was not an option even though, in hindsight, it might have saved the crew.
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