NASA studied this McDonnell Douglas/Martin Marietta concept for a fully reusable space transportation system during the Shuttle research effort in 1969-1972. This two-stage system featured two piloted fly-back vehicles, a booster and an orbiter, both using liquid propellant. The booster would carry the orbiter to a set altitude, then detach to return to base. After separation, the orbiter's engines would ignite for final ascent into orbit. This concept had a second configuration for heavy payloads (such as large space station components) that did not need an astronaut crew; the booster, augmented by six solid rocket boosters, would launch a large disposable cargo carrier. NASA transferred a variety of concept models to the Museum after settling on the final Space Shuttle design.
This object is on display in James S. McDonnell Space Hangar at the Steven F. Udvar-Hazy Center in Chantilly, VA.