A conversation going on in another thread about dropping things from orbit as kinetic energy weapons got me curious about how much atmospheric drag would slow down such a weapon. Suppose you have a heavy (a few tons?) mass that's falling directly down toward Earth (normal to the surface) at orbital velocities, and the object has been designed to minimize drag and hit at the highest possible speed. Does anyone have any idea how much such an object might slow down? It would only be in the thicker parts of the atmosphere for something like 10 seconds, so it intuitively seems like there wouldn't be time for it to slow down much, but I don't really have any idea how to calculate it. I suspect that the simple drag equations that I learned in physics class would be insufficient for something traveling at 10+ km/sec.