NASA's twelfth annual chronology of events in astronautics and aeronautics reflects a U.S. space program redefined to be less costly and perhaps less spectacular in the 1970s than in the previous decade-yet this volume records a continued and indeed matured response to the challenges of space, both in scientific exploration and in practical uses. The year 1972 closed with the triumphant end of the Apollo program. The mass of data from the manned explorations of the moon and data still being collected by instruments left on the moon's surface combined with events on earth to intensify awareness of our planet, especially the fragility of its environment and the preciousness of its resources. In addition to bringing insights into how the earth evolved and into the history and nature of the moon, the flights-culminating in the new space records and investigations of Apollo 16 and Apollo 17 during 1972-let us see our planet "as it really is," influencing long-range planning for future activities in space, as well as in many other areas of life. Several major events underscored the shift in emphasis from lunar exploration toward study of our planet. A major step forward in space applications, turning space knowledge and technology into practical benefits, was the launch of Erts 1 to begin global observation of the earth's resources and environmental factors. Data from Erts 1, from Skylab, and from remote-sensing aircraft were to be available to users worldwide. Weather and communications satellites-including Nimbus 5, Noaa 2, Anik 1 for Canada, and two Intelsats-were orbited to continue almost routine service to man from space. NASA's technology utilization program expanded the nation's technology base and attacked problems in health and medical care, air and water pollution, transportation, urban construction, and fire safety. Although a stretched-out space program reduced plans for a future Grand Tour of all the outer planets to a focus on Jupiter and Saturn, and the NERVA nuclear rocket program was reoriented toward a small, high-energy, nuclear propulsion system for planetary missions, 1972 produced significant firsts in space science. Pioneer 10 made the first probe of the Asteroid Belt and flew on toward its December 1973 rendezvous with Jupiter and eventual escape from the solar system. Pioneer 11 was to follow in 1973 for a meeting with Jupiter in 1974. Mariner 9, launched in 1971, completed its mission during 1972, photographically mapping the entire globe of Mars and sending back information that revised our understanding of that planet. We now know that Mars is geologically active; free-flowing water may have existed in its ancient past. Mariner 9 data laid the groundwork for 1975-1976 Viking missions to softland on Mars and search for evidence of life. Mariner 10, to be launched in late 1973, would make the first explorations of Mercury, flying by Venus on its way. Oao 3 (Copernicus) opened new channels of information into the distant reaches of the universe. The Orbiting Astronomical Observatory made the first ultraviolet observations of Uranus, observed a supernova, and, at this writing, has returned compelling evidence of the existence of black holes in space. Explorer 47 and 48 joined satellites launched in previous years to extend our knowledge of physics and astronomy. NASA's major efforts in aeronautics were directed chiefly toward quieter engines; efficient, short-haul air transportation; and reduction of exhaust emissions. The supercritical wing was flight-tested on the Navy T-2C trainer and the Air Force TF-8A jet aircraft in joint advanced transport technology projects to permit savings in structural weight and increases in cruise speed without increasing power. In the NASA-USAF program to develop technology for landing manned space vehicles horizontally, the M2-F3 lifting body completed its 27th and final flight, having reached a speed of 1718 kilometers per hour and a 21 800 meter altitude.