22 October 1999 Roll Angle System (RAS) for the High-Energy Solar Spectroscopic Imager HESSI
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Abstract
The purpose of the HESSI RAS is to provide information on the roll angle of the rotation spacecraft. Precise knowledge of the roll angle is a necessary ingredient for image reconstruction. The RAS is a continuously operating star scanner that points out radially and observes stars at 75 degrees from the Sun direction using a commercial lens and a fast CCD. The passage of a star image over the CCD charges one or several pixels above threshold and the timing of this signal defines the roll angle, once the star has been identified by comparing its pixel position and amplitude with a star map. Roll angles at intermediate times are inferred by assuming uniform rotation. With a limiting star magnitude of mv equals 3 we expect to observe at least 1 star per revolution over 1 year; on the average we will detect about 10 stars/revolution.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Reinhold Henneck, Reinhold Henneck, Jacek Bialkowski, Jacek Bialkowski, F. Burri, F. Burri, Martin Fivian, Martin Fivian, W. Hajdas, W. Hajdas, A. Mchedlishvili, A. Mchedlishvili, P. Ming, P. Ming, Knud Thomsen, Knud Thomsen, J. Welte, J. Welte, Alex Zehnder, Alex Zehnder, M. Dettwyler, M. Dettwyler, F. Buerki, F. Buerki, Gordon J. Hurford, Gordon J. Hurford, David W. Curtis, David W. Curtis, David H. Pankow, David H. Pankow, "Roll Angle System (RAS) for the High-Energy Solar Spectroscopic Imager HESSI", Proc. SPIE 3765, EUV, X-Ray, and Gamma-Ray Instrumentation for Astronomy X, (22 October 1999); doi: 10.1117/12.366530; https://doi.org/10.1117/12.366530
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