NASA studied this Lockheed concept for a two-stage, fully reusable space transportation system during the Shuttle research effort in 1969-1972. Unlike similar designs that perched the orbiter on top of a booster vehicle, this one attached the orbiter underneath. The booster would lift the orbiter to a set altitude, then separate and depart as the orbiter ignited its engines to continue its ascent into space. Both piloted vehicles would return to land. The upswept wings on these vehicles also differed from other design concepts. NASA transferred a variety of concept models to the Museum after settling on the final Space Shuttle design.