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212 the programs and facilities needed to carry out this work. Any exercise of this kind is based on certain assumptions, and it is important to state clearly what these are. We have taken as our point of departure pro- grams that would begin in fiscal year 1983 or later, and we have not evaluated ongoing programs approved by pre- vious advisory committees. The most important such project in radio astronomy is the 25-m millimeter-wave telescope proposed by the NRAO and appearing in the President's original budget for fiscal year 1981 but subsequently removed for budgetary reasons. A large millimeter-wave telescope was one of the high-priority recommendations of the previous astronomy survey (the Greenstein report), and the 25-m project has been thoroughly reviewed and approved by the advisory mech- anisms of the National Science Foundation. The present report of the Panel on Radio Astronomy is predicated on the assumption that the 25-m telescope will be con- structed during the early or middle Years of the 1980's. II. SUMMARY OF RECOMMENDATIONS A. Highest Priority The Panel selected four facilities as being of the highest priority for radio astronomy in the 1980's. In order of importance these are: 1. A Very-Long-Baseline (VLB) Interferometric Array of about ten 25-m antennas widely spread over the United States, designed to form radio images at ultrahigh angular resolution of quasars, galactic nuclei, interstellar masers, and a variety of stellar sources and to extend measurements of proper motion and statistical parallax over much of the Galaxy. The resolution of this Array at its shortest operating wavelength of about 1 cm will be only 0.3 milliarcsecond--several orders of magnitude better than that of any other image-forming astronomical telescope. 2. A submillimeter telescope of about 10-m aperture located at a dry, high-altitude site. The purpose of this telescope is to open the almost unobserved wave- length range from 0.3 to 1.0 mm to astronomical investi- gation. Molecular line emission in this region may approach the Fraunhofer spectrum of the Sun in richness, and there is a variety of continuum sources including the

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213 planets, interstellar dust clouds, quasars, radio sources and the cosmic background radiation. 3. A near-Earth-orbiting verY-long-baseline-inter- ferometrY VLBI station consisting of a deployable tele- scope in the 25-m class. As a rapidly moving additional element of the ground-based Array, this station will sig- nificantly enhance the angular resolution, dynamic range, latitude coverage, and time response of the system, and it will serve as a prototype for stations in highly ellip- tical orbit projected for the 1990's. 4. A large steerable radio telescope in the 100-m class designed to operate at wavelengths of 1 cm and longer. The equivalent of a large optical reflecting telescope, this general-purpose instrument combines large collecting area with wide frequency coverage and has important applications in nearly every area of radio astronomy. These include studies of the Sun, Moon, planets, pulsars, distant 21-cm galaxies, molecular clouds in our own and other galaxies, and the cosmic background radiation. Special Category 5. The Panel recommends the construction of a two- element heterodyne interferometer to observe through the 10- m atmospheric window. The purpose of this instrument is to resolve stars and other small infrared sources, to study circumstellar dust and molecules, and to undertake precision astrometry, including testing of the General meory of Relativity. B. Other Recommendations The Panel identified the following projects as being of major importance to radio astronomy but of less urgency than the above: 6. A program of antenna and receiver development for a 10-m-class submillimeter telescope in near-Earth orbit, to be launched in the 1990's. 7e The inclusion of radio spectrographs and polari- meters on the Star Probe and Solar Coronal Explorer, to observe plasma processes in the solar corona and the solar wind. 8. A millimeter-wave telescope in the 5-10-m class in the southern hemisphere for the study of galactic struc- ture and molecular sources not visible from the United States.