The design and performance of the Gondola Pointing System for the Sunrise II Balloon-Borne Stratospheric Solar Observatory

With its 1m aperture, the Sunrise Balloon-Borne Stratospheric Solar Observatory was the largest space-based solar telescope. It was designed to study the magneto-convective processes of the sun at resolutions higher than 100km and the payload took data during a flight from June 12 to June 17, 2013. To achieve its science requirements, the telescope had to point to an accuracy of 26" for extended periods of time. Pointing of the instrument was effected by the Sunrise Pointing System (PS). The PS used measurements provided by a Lockheed Intermediate Sun Sensor (LISS) and passed the data through a cascade of up to four digital filters to calculate the best voltages to drive the azimuthal and elevation motors. All filter settings could be modified in flight to adapt to changing conditions. Using this design, the PS met its requirements, pointing the instrument with an accuracy better than 26" for 60% of the flight and for continuous time periods of up to 99min. In this paper, we detail the design and performance of the PS during the 2013 flight.