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cso:telescope:dsos:dsos [2012-09-25 12:09] sradford |
cso:telescope:dsos:dsos [2013-08-28 08:32] (current) sradford [Instructions] |
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| + | ====== Dish Surface Optimization System ====== | ||
| + | The CSO is one of a very few radio telescopes with an active surface correction system. | ||
| + | This Dish Surface Optimization System (DSOS) improves the telescope efficiency by | ||
| + | altering the primary mirror surface to correct for static imperfections and for changes in gravitational deformation as the telescope moves in zenith angle (elevation). | ||
| + | The consequent improvement in the telescope's aperture efficiency is significant at shorter wavelengths, in particular at 350 µm wavelength. | ||
| + | |||
| + | ===== Instructions ===== | ||
| + | |||
| + | * [[userproc]] | ||
| + | * {{DSOS_Test.pdf|Test procedures}} 2011-09-27 | ||
| + | |||
| + | |||
| + | ===== Description ===== | ||
| + | |||
| + | The CSO's 10.4 m primary mirror is made up of 84 hexagonal panels with aluminum skins and honeycomb cores. | ||
| + | The panels are connected to the backing structure by 99 steel rod standoffs. | ||
| + | Each standoff is fitted with a (Peltier) heating/cooling assembly so it can be elongated (heated) or contracted (cooled). | ||
| + | A controlled potential is applied to each of the 99 assemblies to adjust the shape of the primary mirror. | ||
| + | The necessary standoff lengths were determined from holography measurements of the telescope over a range of zenith angles. | ||
| + | |||
| + | Holography measurements indicate the DSOS improves the surface accuracy of the telescope to about 11 µm rms | ||
| + | compared to about 25 µm rms without the system. | ||
| + | This would correspond to an improvement in aperture efficiency from 33% to 79% at the 350 µm wavelength. | ||
| + | The CSO's holography instrument, however, operates in the range of roughly 230 to 460 GHz. | ||
| + | Additionally improvement in efficiency does not translate linearly to higher frequencies. | ||
| + | As a result, of course, efficiency measurements at the 350 µm wavelength range were done. | ||
| + | About a 71% best and 60% average improvement in peak signal power was measured. | ||
| + | Which is about 56% efficiency. | ||
| + | These excellent results were measured with instruments mounted on the Cassegrain focus. | ||
| + | Instruments mounted on the Nasmyth focus (N2) also see marked improvements but do not benefit as much from the newer correction table. | ||
| + | Steps are being taken to determine the adjustments of the DSOS to best optimize performance of the telescope out to N2. | ||
| + | The DSOS has been in operation on the CSO since February 2003. | ||
| + | Observers using SHARCII and the 850 GHz heterodyne receiver have been able to detect new weak and/or distant objects including with the help of this unique active optics system. | ||
| + | |||
| + | * [[http://www.cso.caltech.edu/dsos/DSOS_MLeong.html|Background information]] | ||
| + | |||
| + | ===== Results ===== | ||
| + | |||
| + | |||
| + | ==== References ==== | ||
| + | |||
| + | |||
| + | CSO Technical Briefing, Hilo, HI, October 2007 | ||
| + | |||
| + | |||
| + | {{2007-leong.pdf|Update to the CSO Submillimeter Active Optics System}},\\ | ||
| + | Leong, M. M., 2007, CNC/USNC/URSI North American Radio Science Conference, Ottawa | ||
| + | |||
| + | {{2006-leong.pdf|A CSO Submillimeter Active Optics System}},\\ | ||
| + | Leong, M., Peng, R., Houde, M., Yoshida, H., Chamberlin, R., and Phillips, T., 2006, Proc. SPIE 6275, 62750P | ||
| + | [[http://adsabs.harvard.edu/abs/2006SPIE.6275E..21L|ADS]] | ||
| + | |||
| + | {{2004-leong.pdf|A CSO Submillimeter Active Optics System}},\\ | ||
| + | Leong, M., 2005, USNC/URSI National Radio Science Meeting, Boulder, p. 426 | ||
| + | |||
| + | {{2003-leong.pdf|Dish Surface Optimization System: Surface Correction on a 10.4-meter Leighton Primary Mirror}},\\ | ||
| + | Leong, M., Houde, M., Peng, R., Yoshida, H., Chamberlin, R., Phillips, T. G., 2003, | ||
| + | in AMOS Conference Proceedings, ed. P. Kervin, and J. Africano, AFRL/MEDB, Kihei, HI | ||
| + | |||
| + | {{2002-staff.pdf|A method for implementing the CSO surface correction hardware: Memo No. 1}},\\ | ||
| + | CSO Staff (M. Leong, R. A. Chamberlin, M. Houde, R. Peng, T. G. Phillips, H. Yoshida), 2002 October 18 | ||
