Description
The surface area of the GBT is a 100 by 110 meter active surface with 2,209 actuators (a small motor used to adjust the position) for the 2,004 surface panels. The panels are made from aluminium to a surface accuracy of better than 0.003 inches (76.2 micrometers) RMS. The actuators adjust the panel positions to correct for distortions due to gravity which change as the telescope moves. Without this so-called "active surface", observations at frequencies above 4 GHz would not be as efficient.
Unusual for a radio telescope, the primary reflector is an off-axis segment of a paraboloid. This is the same design used in the familiar direct-broadcast satellite (e.g., DirecTV) antenna: the reflector is a piece of a much larger paraboloidal figure, chosen such that the entire primary reflector has a clear view of the sky, unobstructed by the secondary mirror, feed system, or support structures.
The offset support arm houses a retractable prime focus feed horn in front of the 8 m subreflector and eight higher-frequency feeds on a rotating turret at the Gregorian focus. Operational frequencies range from 290 MHz to 100 GHz.
Read more about this topic: Green Bank Telescope
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