The VST tracking system and its preliminary performance

The 2.6m VST telescope is in installation phase in the ESO observatory of Cerro Paranal. After preliminary tests in Europe performed jointly by INAF and ESO the tracking system was considered at the readiness level to be shipped to Chile. The motion control system has already been reintegrated in Chile and is operational again. The final tuning is going to be performed after the integration of all the telescope subsystems, still in progress. Therefore here the focus is especially on tests performed in Italy. This paper describes the solutions adopted for the telescope main axes control as well as the preliminary tracking results. Available test data are related to encoder feedback. Tests have been performed tracking coordinates of virtual objects. A comprehensive test case to evaluate the performance of different controllers was needed to proceed in a systematic way. A tracking map derived from the VLT commissioning experience has been used, spanning all the different conditions for axes positions and speeds, including meridian crossing and tracking near the blind spot.