Commissioning and initial performance of the H.E.S.S. II drive system

The H.E.S.S. observatory was recently extended with a fifth telescope located at the center of the array - H.E.S.S. II. With a reflector roughly six times the area of the smaller telescopes and four times more pixels per sky area, this new telescope can resolve images of particle showers in the atmosphere in unprecedented detail and explore the gamma-ray sky in the poorly studied regime around a few tens of Giga electron-volt. H.E.S.S. II has been equipped with a high-performance drive system that can deliver the high torque necessary to accelerate and slew the 600 tonnes telescope while keeping a good tracking accuracy. A modular design with a high degree of redundancy has been employed to achieve stability of operation and to ensure that the telescope can be moved to a safe position within a short period of time. Each axis is driven by four 28 kW servo motors which are pair-wise torque-biased and synchronized through a state of the art Programmable Logic Controller (PLC). With this system, a fast repositioning and a minimal settling time has been achieved - crucial when studying transient sources such as gamma-ray bursts which are a prime target for this telescope. This contribution will report on the successful commissioning of the H.E.S.S. II drive system in the first half of 2012 at the H.E.S.S. site in Namibia. The technical implementation and the performance of the drive system will be presented.