The Spectrometer/Telescope for Imaging X-rays (STIX) is a remote sensing instrument on Solar Orbiter that observes the hard X-ray bremsstrahlung emission of solar flares. This paper describes the STIX Aspect System (SAS), a subunit that measures the pointing of STIX relative to the Sun with a precision of ± 4 ″ $\pm 4''$ , which is required to accurately localize the reconstructed X-ray images on the Sun. The operating principle of the SAS is based on an optical lens that images the Sun onto a plate that is perforated by small apertures arranged in a cross-shaped configuration of four radial arms. The light passing through the apertures of each arm is detected by a photodiode. Variations of spacecraft pointing and of distance from the Sun cause the solar image to move over different apertures, leading to a modulation of the measured lightcurves. These signals are used by ground analysis to calculate the locations of the solar limb, and hence the pointing of the telescope.

中文翻译：

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STIX 视向系统 (SAS)：用于在太阳轨道器上成像 X 射线 (STIX) 的光谱仪/望远镜的光学视向系统

X 射线成像光谱仪/望远镜 (STIX) 是太阳轨道器上的一种遥感仪器，用于观测太阳耀斑的硬 X 射线轫致辐射发射。本文描述了 STIX 视向系统 (SAS)，它是一个子单元，它以 ± 4 ″ $\pm 4''$ 的精度测量 STIX 相对于太阳的指向，这是准确定位重建的 X 射线图像所必需的在太阳上。SAS 的工作原理基于一个光学透镜，该透镜将太阳成像到一个板上，该板上有小孔，这些小孔以四个径向臂的十字形配置排列。穿过每个臂孔的光由光电二极管检测。航天器指向和与太阳距离的变化导致太阳图像在不同的孔径上移动，导致测量光曲线的调制。地面分析使用这些信号来计算太阳边缘的位置，从而计算望远镜的指向。