NASA studied this General Dynamics/Convair concept for a fully reusable space transportation system early in the Shuttle research effort of 1969-1972. This two-stage system featured three piloted fly-back vehicles, an orbiter sandwiched between two boosters, all using liquid propellants. All would ignite together for lift-off, and the boosters would detach and fly to land when their fuel was consumed while the orbiter continued on to space. All three vehicles had snap-out wings and jet engines for return flight. NASA transferred a variety of concept models to the Museum after settling on the final Space Shuttle design.