FIGURE 3.1 A decade of deferred maintenance and refurbishment has led to a variety of problems at the national observatories, including the deterioration of the railroad tracks used at the VLA to reconfigure the array for operation at different spatial resolutions. Courtesy of the National Radio Astronomy Observatory/Associated Universities, Inc.

The Very Long Baseline Array (VLBA), the highest-priority ground-based initiative recommended by the Field Committee (NRC, 1982), has been funded by NSF and will begin operating in 1992. The VLBA will provide detailed maps of the cores of active galaxies and quasars with sub-milliarcsecond angular resolution and will determine distances to objects in our own and other galaxies from measurements of H2O masers. The committee is confident that this next step in the application of very long baseline interferometry (VLBI) techniques will return exciting results.

The most spectacular closing of an old facility was the unanticipated collapse of the Green Bank 300-ft telescope. The replacement for the 300-ft telescope will be the Green Bank Telescope, a fully steerable instrument of comparable diameter. The telescope will incorporate novel design features, such as an active surface, that may eventually permit operation at wavelengths as short as 3 mm. The telescope will begin operation in 1995, initially at centimeter and longer wavelengths, for the study of pulsars, active galaxies, and 21-cm hydrogen emission in our own and in distant galaxies. The upgrade of the 1,000-ft Arecibo telescope will improve the sensitivity of that instrument by a factor of 3 to 4 for nonradar observations. Because of its large collecting area, the Arecibo telescope will continue to play a critical role in pulsar studies and



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