I was going to dump this on the X-51 thread, but didn't want to sound like a conspiracy loonie at the time, and now that thread seems to have gone dormant. I suppose now my little theory will fit right in, and I lost track of the X-51 thread, so if somebody already posted this idea, I apologize for the repetition.<br /><br />I believe it was recently posted that the X-51 is basically stepping into the gap left by the cancellation of the X-43 project. I also think that somebody said that project was more closely aligned with the Air Force than NASA. At the time this depressed me because I was taking it to mean that this was the deathknell of 'open', non secret research into scramjets and their applications into a potential spaceplane. Call it a coping mechanism, fit me for a tin foil hat, and call me crazy but I developed a small theory wherein the X-51 project actually serves the opposite purpose, that of bringing classified material to light for other project which have no need for classification. <br /><br />It's not all that unthinkable to say that it is possible the Air Force, DARPA, CIA, Skunk Works, or whoever else you want to include has had an effort to develop a viable spaceplane ever since the space shuttle turned out to be a disappointment. Perhaps the Air Force decided they'd like the cross range capability, reusability, and payload return capabilities built into the shuttle, but without the cumbersome proceedure of launching a spaceplane vertically on a rocket stack. With the combined requirements of cross-range capability, payload return and very low launch infrastructure it'd seem that a HOTOL Single Stage To Orbit or Two Stage to Orbit vehicle would be an ideal solution. There certainly would be other routes to those requirements, such as a two stage air dropped reusable capsule, which although sacrificing cross range capability would open up the possibility of higher altitude flights. <br /><br />Even if the Air Force, DARPA et al never achieved