There is a quick back of the envelope calculation that we can do to understand this better. The force due to drag on an object is described by the following eq

There is a quick back of the envelope calculation that we can do to understand this better. The force due to drag on an object is described by the following equation (http://en.wikipedia.org/wiki/Drag_equation http://en.wikipedia.org/wiki/Drag_equation): F = (1/2)p(v^2)(C_d)A where p is the density of the fluid the object is moving in, v is the velocity of the object relative to the fluid, C_d is the coefficient of drag and A the cross-sectional area. C_d is around 1 for most geometries (http://en.wikipedia.org/wiki/Drag_coefficient http://en.wikipedia.org/wiki/Drag_coefficient). In the CAID report, the dimensions of the foam is estimated to be 19x11.5x11.5 inches, which is roughly 0.5x0.3x0.15 meters. Assuming the foam fell with the smallest surface pointing down (a bad assumption), we can estimate A to be 0.045 m^2. According to Wolfram Alpha, the density of air at 20km, the altitude at which the foam broke off, is 0.089 kg/m^3. The initial velocity of the foam was about 1568 mph which is around 700 m/s. Plugging all of this in to the above equation gives: F ~= 981 kg*m/s^2 The mass of the foam was estimated at 1.6 lbs, or around 0.7 kg, and using F=ma we can calculate the acceleration to be about 1400 m/s^2. The foam traveled for 0.16 seconds before striking the shuttle, and assuming that the above force was constant during that time (thus overestimating the change in velocity), that would result in a delta_v for the foam of 224 m/s, which is about 500 mph. This is all assuming of course I didn't make some trivial mistake with the math, which I probably did. It would be great if someone with more knowledge than me could chime in about drag near the speed of sound (or multiples of the speed of sound).