Columbia was an "old crotchety beast" in the terms of another engineer. Possibly (I'm not certain) the oldest in the fleet.
The possibility occurs that someone could have planted a bomb. Certainly no missile at that altitude/velocity.
Now the entire Shuttle fleet will be grounded; we will have to evacuate the Space Station and it will have to be done via Soyuz.
--Boris
My mom called and woke me up to tell me about this. From the spiraling reports on Drudge I'm guessing some aerodynamic instability- maybe damage to a control surface that made the vehicle uncontrollable. I'm guessing we we'll be doing CFD analyses to see what defect in the control surfaces could cause loss of control.