Improvement of the IRAM 30-m telescope from temperature measurements and finite-element calculations

Millimeter wavelength radio telescopes built in a conventional way from steel and aluminum require elaborate thermal control to guarantee small structural deformations and good observational performance. We describe the temperature monitoring system of the Institut de Radioastronomie Millimetrique 30-m telescope and the use of temperature measurements in finite-element calculations of structural deformations. These calculations reproduce with good precision the measured thermal deformations of the telescope and allow the investigation and localization of thermally important elements in the telescope structure. The data are used for calculation of temperature induced main reflector surface deformations and of the associated actual beam pattern, and for prediction and real-time correction of the focus. The pointing cannot be fully predicted since the available finite-element model does not include the Nasmyth focus cabin (and the concrete pedestal). The long-term investigation of the telescope's thermal behavior led to an improvement of the thermal control system and to a better performance of the telescope.