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he new SR-72 will use a turbine-based combined cycle (TBCC) that will employ the turbine engine at lower speeds, and use a scramjet at higher speeds. A scramjet engine is designed to operate at hypersonic velocities by compressing the air through a carefully designed inlet, but needs to be traveling supersonic before it is practical to begin with. So far research projects from NASA, the Air Force and other Pentagon entities have not been able to solve the problem of transitioning from the subsonic flight regime, through hypersonic flight with a single aircraft. Same problem as Reaction Engines is trying to solve, so I am not sure whether they actually cracked it. In any case, nice pictures. Not sure why the exhaust color is purple in color. Its not running on Argon I believe.

Weird article. Intermediate thruster stage (Ramjet) is missing. Scramjet has supersonic combustion and a normal turbine delivers subsonic flows. Even with afterburner - the Scramjet inlet would decelerate the flow down to subsonic velocity with "normal" subsonic combustion. The only thing I can imagine is that the Scramjet stage is bi-functional and covers both, subsonic and supersonic combustion. But the article doesn't say anything about it.

In order to overcome the communication blackout problem suffered by hypersonic vehicles, a matching approach has been proposed for the first time in this paper. It utilizes a double-positive (DPS) material layer surrounding a hypersonic vehicle antenna to match with the plasma sheath enclosing the vehicle. Or in more easy language, basically one provides an antenna as capacitor, in combination with the plasma sheath (an inductor), they form an electrical circuit which becomes transparent for long wavelength radiation (the communication signal). The reasons is that fluctuations are balanced by the twin system, preventing absorption/reflection of the incoming radiation. Elegant solution, but will only work on long wavelength communication, plus I am not sure whether the antenna needs active control (as the plasma sheath conditions change during the re-entry phase).