We are constructing an 8 by 8 bolometer camera, as a 90 GHz facility instrument for the 100 m Green Bank Telescope (GBT). The bolometers use transition-edge-superconducting (TES) sensors read
out with a time-based SQUID multiplexing system. The receiver will be one of the first astronomical instruments to use such detectors. Our TES bolometers require cooling below 290 mK. To obtain these temperatures we use He3 and He4 sorption refrigerators that cycle from a two-stage pulse-tube cryocooler. The He3 stage has an operating temperature of 252 mK and a hold time of 77 hours with a 10 microwatt load. A combination of the large collecting area of the GBT and the low noise of the detectors will enable us to map 15 arcsecond by 15 arcsecond areas of sky to 200 microJansky in one hour.
The NRAO Robert C. Byrd Green Bank Telescope is a new 100 meter radio telescope that is now in routine astronomical operation. This paper gives a status report on astronomical performance, operational capabilities, development plans, and early scientific highlights. The telescope is now in regular operation to frequencies of 50 GHz, which achieves the base design goal of the facility. Both the surface and pointing accuracies allow good performance at that frequency. The active surface of 2004 movable panels is in regular use at all frequencies above ~8 GHz and significantly improves both gain and diffraction beam shape at high and low elevation angles. Receivers exist at most primary observing frequencies ranging from ~290 MHz to 50 GHz. A 256k-channel correlation spectrometer with up to 16 independent inputs is in routine use for spectroscopy. Backends for pulsar observing, broadband continuum, Very Long Baseline Interferometry, and planetary radar reception also exist. An advanced development program for enhancing the performance of the GBT is also underway. This program includes the Precision Telescope Control Project that will extend operation to 115 GHz or 2.6 mm wavelength (see the paper by Prestage and Constantikes in this volume), a 26-40 GHz receiver, a 68-92 GHz receiver, a fast sampling continuum backend built by a Caltech/NRAO collaboration, and a 64-pixel bolometer camera developed by a consortium of UPenn, NASA-GSFC, NIST, UCardiff, and NRAO. Software development projects for enhanced user interfaces and data handling are underway, and plans to implement queue-based dynamic scheduling and remote observing are being developed. The status of these projects and their anticipated scientific impact will be discussed.
The 100-m NRAO Green Bank Telescope will be completed in early 2000. The GBT is the most ambitious, single radio telescope ever constructed and has a large number of unique design and performance features. This paper will review those features, which include an offset feed (clear aperture) design, an active surface, a closed-loop laser metrology system for surface figure and pointing control, broad frequency coverage from approximately 100 MHz to 115 GHz, a versatile receiver selection mechanism, and a new multi-input, 256k-channel autocorrelation spectrometer. The status of the project, the commissioning schedule, plans for early operations, the initial instrumentation suite, and plans for future instrumentation will be reviewed. Through most of its frequency range, the GBT will offer a considerable advance in sensitivity and image fidelity compared with exiting telescopes. Scientific areas for which the GBT will have a large impact will be discussed.