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