NASA studied this Lockheed Martin concept for a partially reusable space transportation system during the Shuttle research effort in 1969-1971. It featured a delta-wing orbiter vehicle flanked by two large external fuel tanks. It was called a stage-and-a-half vehicle because the orbiter would launch itself without a booster and fly all the way to orbit using its own rocket engines fed by the external fuel tanks (the half-stage), which would be jettisoned when empty. The reusable orbiter had retractable wings and air-breathing jet engines that deployed after reentry, enabling it to fly like an airplane to landing. NASA transferred a variety of concept models to the Museum after settling on the final Space Shuttle design.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.