From The Unwanted Blog: “The McDonnell Douglas Model 176 was a generic spaceplane design derived from the FDL-7 (Flight Dynamics Lab – USAF Wright-Pat). It was incorporated into small spaceplanes adequate for taking a few crewmembers to a space station on up to Space Shuttle competitors. Above is one of two pieces of art (found in the NASA HQ historical archive) showing a late 1960′s concept for a Model 176 optimized for the ILRV (Integral Launch and Recovery Vehicle) role. ILRV was one of the immediate predecessors to the Space Shuttle program.
The Model 176 was a sleek dart-like design with stubby fins. While details varied from iteration to iteration, all (or nearly all) featured high aspect ratio variable geometry wings for landing.”
Much more on the Secret Projects web site here