Green Bank Telescope: the largest fully steerable single dish in the world, 100 x 110 m.
The Robert C. Byrd Green Bank Telescope (GBT) is the world's largest fully mobile radio telescope. It is part of the National Radio Astronomy Observatory (NRAO) at Green Bank, West Virginia (USA). The telescope honors the name of Senator Robert C. Byrd.
The telescope sits at the heart of the United States national radio quiet zone, a large area where all radio transmissions are either limited or banned outright, to help the telescope function properly.
Description
The surface area of the GBT is 100 by 110 meters with a separate actuator for each of the 2,004 surface panels. The panels are made from aluminum to a surface accuracy of less than 0.003 inches RMS. Infrared lasers are used to measure the position of each plate so that if one is to move even slightly out of place the actuator can move it back into it proper posistion, resulting in a surface that can be kept in an optimal state throughout an observation with the telescope. A laser alignment system also allows for precise knowledge of the posisitioning of the dish by utilizing reflectors in the mountains and around the base of the telescope itself.
The telescope is unusual in that the mirror is not a symmetrical dish, but is a section of a much larger parabolic figure with the receiver where the prime focus would be of the entire mirror. As a result, the support for the receiver does not in any way obscure the mirrors view of the sky.
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