ISIS Fourier telescope concept for imaging the sun and the sky in hard x rays and gamma rays

摘要

Abstract: The Marshall Space Flight Center, Alabama in a teaming arrangement with the Naval Research Laboratory, Maryland has developed the ISIS (impulsive solar imaging spectrometer) mission for viewing the sun and the sky in the EUV, soft, and hard x rays. The soft and hard x ray imaging as well as the gamma-ray spectroscopy will be provided by a three axis pointed Fourier telescope (i.e. a spatial modulation collimator). The EUV imager will be a supporting context instrument. This paper describes the optimized instrument concept and discusses the associated trades made in developing it. For example, the numbers of spatial frequencies measured versus the sensitivity needed for imaging weak sources is discussed in detail. ISIS builds upon the YOHKOH findings in that the telescope is tailored to image compact simple loop sources. Only two spatial frequencies need be measured, allowing substantial gains in sensitivity. In addition, this allows both the real and imaginary Fourier components to be measured, which is a vast improvement over approaches that measure only the real components. !5