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Conceptual design of reflector structure for the large adaptive reflector Loewen, Nathan

Abstract

The Large Adaptive Reflector (LAR) is a very large radio telescope proposed by the Dominion Radio and Astrophysical Observatory in Penticton, B C . Two innovative components make the L A R unique from traditional radio telescopes. Firstly, the focal receiver is supported by an airborne helium balloon. The position of the focal receiver is controlled by multiple tethers running to the ground. Secondly, the ground-based reflector structure is "adaptive" in nature, which allows it to be configured in a continuous range of parabolic shapes. The reflector structure is required to be 300m in diameter, with a surface height range of 0 to 15 meters above a level reference plane. The reflector surface must be accurate to within 9mm rms from the ideal paraboloid shapes. The realistic design of the reflector structure with emphasis on fabrication and economy is the focus of this paper. The driving factor in the conceptual design is minimizing the cost per unit area while meeting the surface accuracy requirements under a wide range of operating conditions. Since an adaptive structure of this magnitude is unprecedented, solutions cannot be easily derived from existing structures. Therefore, the methodology of converging towards a design solution must involve creativity, as well as a systematic way of eliminating less optimal solutions. The approach taken here first defines the load requirements, which are mainly governed by environmental loads such as thermal, wind, and snow loads. Various materials and general structural configurations are then compared for their suitability to this application. Once a preliminary design is developed, an analysis is carried out that gives quantitative results for structural performance. Methods of structural fabrication, and dynamic motion of the structure are also considered.

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