NASA studied this concept for a fully reusable launch vehicle during the design studies of 1969-1971. In this two-part design, the three-engine orbiter was mounted on a larger fifteen-engine piloted booster. All engines would ignite for launch, and the booster would separate at some point during ascent and return to land while the orbiter continued to space. Both craft burned liquid oxygen and liquid hydrogen propellants, and each had retractable wings and turbofan engines for return flight. NASA transferred a variety of concept models to the Museum after settling on the final Space Shuttle design.