Towards the next HST: Fine Guiding Results from the BRRISON Mission

The Balloon Rapid Response for ISON (BRRISON) mission is expected to make observations from altitudes near 125,000 ft (35 km, above 99.5% of the atmosphere) for several hours. Previous balloon missions have provided quantitative evidence that wavefront errors are negligible from this altitude. In order to take advantage of the space-like seeing conditions in the stratosphere, a balloon-borne telescope should be stabilized at a level that is comparable to the telescope's diffraction limit. The stabilization problem consists of two separate tasks: measuring the time-varying pointing error signal and correcting those pointing errors. BRRISON is equiped with coarse and fine pointing systems: a pair of star trackers and an IMU to control the elevation and azimuth pointing of the telescope and a high-speed sCMOS guide camera and a fine steering mirror to compensate for finer image motion. We will report on the precision and bandwidth of the pointing error signal and of the fine steering mirror's corrections. Expected targets include Jupiter and Comets Encke and ISON, in filters inherited from the Hale-Bopp campaign to isolate OH (310 nm) and CN (385 nm) features.