NASA studied this Grumman concept for a partially reusable space transportation system during the Shuttle research effort in 1969-1972. It featured two piloted fly-back vehicles - a large booster and a small orbiter - both with retractable jet engines for powered descent to landing. This design reduced the orbiter's weight and size by putting its propellants into disposable external fuel tanks that could be jettisoned after ascent. NASA transferred a variety of concept models to the Museum after settling on the final Space Shuttle design.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.