Measurements of dynamic pointing variations of a large radio telescope

Details Measurements of dynamic pointing variations of a large radio telescope Measurements of dynamic pointing variations of a large radio telescope

Jul 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000spie.4015..467s&link_type=abstract

Proc. SPIE Vol. 4015, p. 467-475, Radio Telescopes, Harvey R. Butcher; Ed.

Computer Science

2

Scientific paper

Next generation radio telescope designs face two serious technical challenges in pointing accuracy. The first is that improved resolution requires more precise pointing, and the second is that increased size makes that pointing accuracy even harder to achieve. New telescopes, such as the 50 m LMT/GTM, require sub-arcsecond pointing in significant wind, whereas current large radio telescopes point only to a couple of arcseconds without wind. A commonly proposed solution to the pointing problem is laser metrology. In this approach, structural deformations are measured, enabling correction of the resulting pointing errors. These measurements are typically slow, allowing only quasi-static effects to be removed. However, the low natural frequencies of large structures allow a significant response to the frequency content of the wind. This effect is difficult to calculate accurately because of both the limited knowledge of the actual wind power spectrum and the complex interaction of the wind with the structure. To investigate the dynamic behavior of large radio telescope in the wind, we conducted pointing measurements with the Nobeyama Radio Observatory (NRO) 45 m telescope. We measured the pointing error in elevation and cross-elevation as a function of time and wind speed, and examined the frequency content of the results. We present results which confirm that the dominant wind effects are at low frequencies, suitable for elimination via a laser-based system. However, the resonant behavior of the telescope is clearly visible in the data, and these dynamic errors are the dominant effects above about 0.1 Hz, even in modest (approximately 4 m/s) wind. As a result, an understanding of this dynamic behavior will be essential for the design of future large telescopes and metrology systems.

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