LAUNCH VEHICLE

rocket system that boosts a spacecraft into Earth orbit or beyond the gravitational dominance of the Earth. A wide variety of launch vehicles have been used to lift payloads ranging from a few pounds to the giant Skylab and Soyuz space stations. Many of the early launch vehicles were originally developed as intercontinental ballistic missiles, including the Atlas rocket that served as a booster for the U.S. Mercury (q.v.) series and the Titan rocket modified for the U.S. Gemini (q.v.) program. Most launch vehicles used to lift heavier spacecraft consist of two or three rocket propulsion systems mounted one on top of the other. The Saturn V, which carried Apollo spacecraft to the Moon, was made up of three stages, the first two of which were equipped with a single engine. In such a system, the propellant tank and the vehicle structure in each stage are cast off as soon as the fuel is depleted, in order to lighten the load. The U.S. space shuttle (q.v.) system that became operational in 1981 represents a significant technical advance over traditional launch vehicles. Unlike the Saturn V, it can make more than one flight, since most of its principal components are designed to be recovered and refurbished for repeated use.