NASA studied this concept for a partially reusable space transportation system during the Shuttle research effort in 1969-1972. The novel feature of this design is the placement of two external propellant tanks alongside the orbiter's fuselage. These disposable tanks would supply the orbiter after the piloted booster stage separated, and they would be jettisoned empty just before the spacecraft reached orbit. Putting the tanks outside reduced the size and weight of both the orbiter and the booster for improved performance during launch. Concept models like this reflected creative engineering approaches to balancing technical and cost requirements. NASA transferred a variety of concept models to the Museum after settling on the final Space Shuttle design.