Introduction T HE Space Shuttle was designed in the 1970s and is still the most efficient manned Earth-to-orbit vehicle available. However, operation of the Space Shuttle costs much more than planned. For future space missions, a new transportation system is desired to improve the operability and costs. The primary purpose of this study was to consider configurations for a new vehicle. Many ideas have been introduced." For example, the U.S. Air Force's concept Black Horse is a single-stage horizontal-takeoff spacecraft with aerial refueling, and Pegasus is a four-stage Earth-to-orbit vehicle using a reusable airplane as the first stage. Another example is the National Aerospace Plane concept, which used hypersonic airbreathing propulsion. This Note presents the results for two concepts designed to place small payloads in orbit with fully reusable vehicles. For these concepts, a vertical takeoff and horizontal landing (VTHL) single-stage-to-orbit (SSTO) concept and an assisted SSTO using a subsonic airplane for air launch are compared.