From the horses mouth, so to speak
Ben Rich, former head of Skunk Works and lead designer of the U2, SR-71, F-117........etc
"The funding for the competition [between Lockheed/Rockwell and Northrop/Boeing to build a stealthy, long-range successor to the B-1 bomber] came out of a secret stash in the Air Force budget. A young colonel working in the Air Force "black program" office at the Pentagon, named Buz Carpenter, arbitrarily assigned the funding the codename Aurora. Somehow this name leaked out during congressional appropriations hearings, the media picked up the Aurora item in the budget, and the rumor surfaced that it was a top secret project assigned to the Skunk Works - to build Americas first hypersonic airplane. That story persists to this day even though Aurora was the code name for the B-2 competition funding. Although I expect few in the media to believe me, there is no code name for the hypersonic plane, because it simply does not exist."
And earlier in that chapter;
"....during one very slack period in the mid-1980's, the Reagan administration was ready to sign up the Skunk Works on a three-year feasibility study for developing a hypersonic plane, which, by definition, mean a aircraft capable of flying faster than five times the speed of sound. The Reagan science advisors were proposing an airplane that flew at Mach 12 and offered me a million dollars per Mach number to show how it could be done. The trouble was that I couldn't design such a vehicle if they offered me 12 billion. That project was nothing but a simple-minded boondoggle from start to finish."
This book is 13 years old but, Ben Rich was a pioneer of building Stealth aircraft, and was largely responsible for the SR-71's staggering performance, described as being 30 years ahead of its time. I doubt such a plane is even possible using conventional means, I guess that's not to say that there aren't new breakthroughs in technology since then...
Great book by the way, tells the mind-blowing story of the development and use of the SR-71, F-117, U2 aircraft, as well as snippets like the test pilot sent into the desert in a Cessna to find a suitable site for testing secret aircraft projects, say a dry-lake bed for instance, where Skunk Works did their test flights, during which all personnel on the airbase were told to go inside their windowless offices as these aircraft were so top-secret at the time.
Amazon.co.uk: Skunk Works: Ben R. Rich, Leo Janos: Books