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The Robert C. Byrd Green Bank Telescope of the National Radio Astronomy Observatory is the world's premiere single-dish radio telescope operating at centimeter to long millimeter wavelengths. This paper describes the history, construction, and main technical features of the telescope.

We report on the design and construction of the Penn Array Receiver, a 64 element array which will be a 90 GHz facility instrument for the 100 m Green Bank Telescope. Each array element is a transition edge sensor bolometer. Detector noise will be background limited by the random arrival of photons and in one hour we expect to be able to map a 5 arcminute square of sky to 80 μ Jy at a resolution of 8 arcseconds. No feed horns are used, instead cooled high-density polyethylene lenses and a cold (3 K) Lyot stop control the illumination of the telescope. Capacitive mesh filters act as IR blockers and define a bandpass of 86-94 GHz. The array elements are spaced by 0.5 f λ so that the sky is fully sampled in a single pointing of the GBT. This significantly simplifies the scanning patterns needed for sparser arrays. The detectors are cooled to 0.25 K using a pulse tube cooler and helium sorption refrigerators. The cryogenics along with all the electronics and the computer system have been successfully operated on the GBT. By February, detailed tests on the response of the detectors will allow us to further develop the data processing techniques needed to remove atmospheric noise from the data and beam measurements of the cryostat will confirm that the optical design is correct. We are also developing better control software to automatically bias the SQUID multiplexed readout.

A 100-m-diameter, fully steerable, offset dual reflector radio telescope is under construction at the Green Bank, West Virginia, facility of the National Radio Astronomy Observatory (NRAO). Significant performance improvement is expected of the offset design over that possible with symmetrical antennas. The antenna will be capable of operation from below 300 MHz to above 40 GHz. To take full advantage of the offset design, ultra-low-noise cryogenic receivers will be constructed and installed. The trade-offs made in the design of the microwave optics are summarized, and plans for receivers and associated equipment are described. >