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21 July 2010 A control loop closure system for the Sardinia Radio Telescope active surface
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The Sardinia Radio Telescope (SRT) is a 64 meters (diameter) single dish radioantenna which is in the building phase in Italy. One of the most challenging characteristics of SRT is its capability to observe up to a frequency of 100 GHz thanks to its main reflector active surface. The active surface is composed by 1008 panels and 1116 mechanical actuators which may modify the segmented shape of the main reflector making possible the correction for wavefront distortions induced by the gravitational and thermal deformations. In order to observe at a frequency of 100 GHz the surface shape must be accurate below of a value of 150 μm r.m.s.. This value may be reached during the initial alignement phase using the microwave holography but it cannot be maintained during the scientific operations because of the (dynamical) deformations. In order to permit the observations at any time, a system able to measure the surface deformations with the necessary accuracy and a time-response of few minutes (the time-scale of the deformations) must be operative. We propose here three simple and robust methods to measure the relative deformations of the segmented panels with respect to an initial aligned surface (reference surface). The ultimate choice on which one of the three systems will operate on SRT will be taken after final testing on all of them. Prototypes of each system have been realized and two of them have been also successfully tested on the active optics radiotelescope of Noto (Italy). The test on the third system will be done in the next few months.
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Claudio Pernechele, Carlo Barbieri, Pietro Bolli, Franco Buffa, Tonino Pisanu, Sergio Poppi, Giampaolo Serra, Marco Morsiani, Juri Roda, Giampaolo Zacchiroli, Carlo Nocita, and Mario Paternò "A control loop closure system for the Sardinia Radio Telescope active surface", Proc. SPIE 7739, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation, 77391C (21 July 2010);

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