NASA studied this North American Rockwell concept for a two-stage, fully reusable space transportation system during the Shuttle research effort in 1969-1972. It featured two piloted fly-back vehicles--a large booster and a smaller orbiter, both with delta wings and pop-up jet engines for powered return to landing. The booster would lift the orbiter to a set altitude, then separate and depart as the orbiter ignited its engines to continue ascent into space. All liquid propellants were carried inside each vehicle. NASA transferred a variety of concept models to the Museum after settling on the final Space Shuttle design.