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.
L. Apollo is pictured here by an artist of The Martin Co., one of three leading Space Age manufacturers awarded study contracts on project by NASA. Apollo was a god of Ancient Greece, son of Clymene and Titan. This is nicely appropriate, since Martin produces the mighty Titan intercontinental ballistic missile.
R. The Apollo lunar spacecraft planned to carry 3 crewmen on round trip between earth and the moon is shown above here enroute among the stars. Protruding fan-shapes are solar arrays to gather energy from sun for use aboard. Apollo was said to have been the triumphant participant in Olympic games. Homer called him the “god of prophecy.”