70 degrees to plane is quite steep imo and could explain the appearance the perpindicular attitude in the video (if appearances are to be believed). As the object's attitude does not change through the video sequence, yet remains nearly perpindicular to the flight path it would seem it was no longer under control at that point. Then there's the semi-rectangular object spinning away from it in the lower right. Imo it appears to be proportional in size and shape to the shuttle's tail. I don't have the ability to capture frames from an .mpg otherwise I would post some of the frames which show the spinning object in focus with the main image.
If this this scenario is true it would indicate the shuttle's tail broke during a righthand/Southerly S-manuever leaving the craft perpindicular to the slipstream. As the video depicts it's L-side is the leading edge along it's flightpath which correlates to the thermal telemetry.