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I'm not sure where you got this fact, but HTV-2 had two independent RF communication systems and flew close to Mach 20.

I do agree with you that the Air Force wants hypersonic flight vehicles. Looks like air-breathing hypersonics are the priority.

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Past Mach 10, a layer of plasma is formed on the leading surface of the aircraft, which RF cannot traverse. This is also why atmospheric reentry occurs in a blackout. There's a good explanation of the phenomenon here:

http://www.scientificamerican.com/article.cfm?id=piercing-th...

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