out the astrophysics missions to be started during the latter half of the 1990s and beyond.

The success of the U.S. space astrophysics program depends on a proper balance between large, moderate, and small missions. Large missions such as the Great Observatories have capabilities that cannot be matched by smaller missions. They provide leaps in capability needed to solve many of the problems at the frontiers of the universe. Large missions involve many researchers in innovative instrument development, support broad community participation in creative observing, attract students, and capture the public imagination. For example, data from the Einstein Observatory have been analyzed in more than 1,000 published papers, nearly all of which were written by individuals or by small groups of investigators. Large missions in astronomy provide for “small science with big facilities.” Amortized over their lifetimes, large missions can be efficient and cost-effective.

However, large missions are also complex and expensive. NASA and the scientific community must be alert to possible technical and management simplifications to assure scientific success on the fastest schedule and at the lowest cost. The manufacturing flaw in the HST mirrors constitutes a sober lesson, but HST problems must be viewed alongside a list of stunning successes in other complex missions such as the Viking and Voyager planetary flybys and the High-Energy Astronomical Observatory (HEAO) program, including the Einstein Observatory. The astronomical community and NASA must use the lessons of HST, and of other complex NASA science projects, to learn how to improve the management of future large missions.

At the same time, moderate and small missions add a vital dimension to NASA's space science program: the ability to deploy new instrumental technology into space on relatively short time scales. Smaller programs can provide new approaches to well-defined scientific problems of great significance that are not easily addressed with the large missions. The opportunity for rapid access to space allows for quick responses to scientific and technical developments, stimulates progress in technology, and attracts young instrumentalists who are essential for a successful future in space science. Many of the outstanding astronomical missions of the past were of moderate or small size, such as the Uhuru x-ray telescope, the International Ultraviolet Explorer (IUE), the Infrared Astronomical Satellite (IRAS), and the Cosmic Background Explorer (COBE) satellite. The small suborbital program made major contributions to the study of Supernova 1987A.

  • The committee recommends that NASA continue to develop a vigorous program of moderate and small missions of limited complexity and shorter development times, with increased use of expendable launch vehicles.

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