Irwin Stambler gives some information on this Lockheed ten-passenger cargo carrier in Orbiting Stations. As described, the vehicle would launch initially from a hot-water-propulsion rocket sled. Two nested fly-back boosters take the payload stage to orbit. I put the image scanned from the book on Flickr, it’s a hair wider than AFMC’s version and shows the artist’s signature. So, not so much a mystery as it is a spacecraft without a name. More here on Aerospace Projects Review, and more again here on Secret Projects.
Lockheed’s L-2000 SST design, loser in the competition with Boeing for US/SST contract, was result of decade of tunnel testing, incorporating best features of fixed wing double-delta concept proved out in SR-71. Lockheed’s philosophy was simplicity in design for better safety and economy.
How to build an SST! Brilliant Lockheed designer Clarence L. (Kelly) Johnson, who created such successful planes as the U-2, SR-71, F-104 and the Constellation, amused fellow aircrafters with satirical drawing portraying design problems encountered with the SST.