I have unretired briefly to do this for the United States Air Force (USAF).
The Delta 9 reusable launch vehicle concept consists essentially of a SpaceX Falcon 9R clone, implemented in hydrogen fuel, using recently developed and tested Blue Origin BE-3 engines.
The intent of such a program is to produce separate propulsion, airframe and operations sectors for the emerging commercial space flight industry in the same way our current airline industries are structured. This specific vehicle is designed in such a way as to motivate our legacy aerospace companies to begin participating substantively and competitively in this new commercial spaceflight industry, within their respective market niches and areas of expertise, while driving the industry forward with substantial Air Force funding, in much the same way that NASA has done with the COTS program, but focused more on specific Department of Defense space launch needs, with near term operational time frames (2018). The most obvious existing tank suitable for modification into the required launch vehicle would be the Boeing Delta IV Medium, but alternative airframe providers and technologies would not be ruled out.
So yeah, I’m a rocket scientist and a space architect. Now all I need is a rocket.