Performance Improvement of a Flexible Telescope Through Metrology and Active Control

A radio telescope is a flexible structure under the influence of gravity, temperature, and wind. Even after all passive means of telescope construction have been applied, the residual structural deformations of a high precision telescope may still lead to focus, pointing, and path-length errors and a loss in gain that exceed the performance specifications. Gravity-induced deformations can be calculated and corrected with high precision. While the time-variable nature of temperature- and wind-induced deformations can only partially be explored in numerical simulations, their control requires the input from metrology. Corrections can be made through the telescope control system but also, to some extent, through deformable mirror surfaces. The progress in metrology and the correction of certain telescope errors are described.