i have some accelerometers that i've tested at sonic speeds (less than 1500fps), which record the Cd as the pressure spikes during the flight. assuming a hypersonic vehicle could be built (it's beyond my capabilities), i have no doubt my electronics could record atmospheric pressure changes, as well as changes in the weight/drag of my rocket in relation to the atmosphere at mach 5, 6, 7...etc...the fastest rocket i feel i could make without failure would be mach 2ish. mach 3 would be pushing it, but hypersonic is out of the question for now. (for me anyway).