18 July 2000 Calibrating the imaging system of the high-energy solar spectroscopic imager (HESSI)
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The primary object of HESSI is to study the explosive energy release in solar flares. HESSI will image flares with spatial resolution ranging between 2 and 35 arcseconds over the energy range 3 keV to 20 MeV. The system is based on Fourier-transform imaging in connection with high-resolution Ge-detectors. HESSI uses 9 Rotating Modulation Collimators, each consisting of a pair of widely separated (1.55 m) grids mounted on the rotating spacecraft. The grid pitches range from 34 micron to 2.75 mm in steps of sqrt(3). This gives angular resolutions that are spaced logarithmically from 2.3 arcseconds to 3 arcmin, allowing sources to be imaged over a wide range of angular scales. In our design the most critical performance parameter, the relative twist between the two grids of each pair--can be very precisely monitored on ground (on a level of several arcseconds) by a special Twist Monitoring System (TMS). Extensive measurements and cross-calibrations between the TMS and several coordinate measuring machines before and after the environmental tests demonstrated the precision and stability of the alignment to be on the order of 5 arcseconds.
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Knud Thomsen, Knud Thomsen, Jacek Bialkowski, Jacek Bialkowski, F. Burri, F. Burri, Martin Fivian, Martin Fivian, W. Hajdas, W. Hajdas, A. Mchedlishvili, A. Mchedlishvili, P. Ming, P. Ming, J. Welte, J. Welte, Alex Zehnder, Alex Zehnder, } "Calibrating the imaging system of the high-energy solar spectroscopic imager (HESSI)", Proc. SPIE 4012, X-Ray Optics, Instruments, and Missions III, (18 July 2000); doi: 10.1117/12.391588; https://doi.org/10.1117/12.391588


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