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Proceedings Paper

The GBT precision telescope control system
Author(s): Richard M. Prestage; Kim T. Constantikes; Dana S. Balser; James J. Condon
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Paper Abstract

The NRAO Robert C. Byrd Green Bank Telescope (GBT) is a 100m diameter advanced single dish radio telescope designed for a wide range of astronomical projects with special emphasis on precision imaging. Open-loop adjustments of the active surface, and real-time corrections to pointing and focus on the basis of structural temperatures already allow observations at frequencies up to 50GHz. Our ultimate goal is to extend the observing frequency limit up to 115GHz; this will require a two dimensional tracking error better than 1.3", and an rms surface accuracy better than 210μm. The Precision Telescope Control System project has two main components. One aspect is the continued deployment of appropriate metrology systems, including temperature sensors, inclinometers, laser rangefinders and other devices. An improved control system architecture will harness this measurement capability with the existing servo systems, to deliver the precision operation required. The second aspect is the execution of a series of experiments to identify, understand and correct the residual pointing and surface accuracy errors. These can have multiple causes, many of which depend on variable environmental conditions. A particularly novel approach is to solve simultaneously for gravitational, thermal and wind effects in the development of the telescope pointing and focus tracking models. Our precision temperature sensor system has already allowed us to compensate for thermal gradients in the antenna, which were previously responsible for the largest "non-repeatable" pointing and focus tracking errors. We are currently targetting the effects of wind as the next, currently uncompensated, source of error.

Paper Details

Date Published: 28 September 2004
PDF: 12 pages
Proc. SPIE 5489, Ground-based Telescopes, (28 September 2004); doi: 10.1117/12.552319
Show Author Affiliations
Richard M. Prestage, National Radio Astronomy Observatory (United States)
Kim T. Constantikes, National Radio Astronomy Observatory (United States)
Dana S. Balser, National Radio Astronomy Observatory (United States)
James J. Condon, National Radio Astronomy Observatory (United States)

Published in SPIE Proceedings Vol. 5489:
Ground-based Telescopes
Jacobus M. Oschmann Jr., Editor(s)

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