Soft X-ray telescope (SXT) built on the principle of grazing incidence optics was launched on-board AstroSat on September 28, 2015, and made operational on October 26, 2015. The telescope optics consists of two conical sections of approximate paraboloid and hyperboloid mirror segments arranged in Wolter type-I design. It comprises a total of 320 mirror segments made from aluminum foil of 0.2 mm thickness coated with gold on the front (reflective) side by the replication process that was first used in the Suzaku Observatory. The mirrors focus X-rays in the energy range of 0.3–8.0 keV on to a charged coupled device-based focal plane camera assembly at a distance of 2 m. We present here the pre-launch, ground-based calibration, and evaluation of SXT optics carried out at the X-ray Optics Laboratory at the Tata Institute of Fundamental Research. The SXT optics assembly was calibrated and evaluated experimentally, using scans by a collimated optical beam from a laser source, as well as using a full-aperture optical beam from an inverse telescope. A collimated beam of a red laser source was used to ensure the accuracy of mounting of individual mirror segments and the full aperture beam white light-emitting diode (LED) source was used to estimate the point spread function (PSF) of all 320 mirrors together. The approximate PSF obtained during the ground calibration was around 136.6 arcsec. These results were in accordance with the results obtained during the in-orbit calibration post launch.

基于掠入射光学原理的软X射线望远镜（SXT）于2015年9月28日在AstroSat上发射升空，并于2015年10月26日投入使用。 望远镜光学系统由近似抛物面和双曲面两个圆锥截面组成Wolter I 型设计中排列的镜段。它包括总共 320 个镜段，由 0.2 毫米厚的铝箔制成，正面（反射）侧镀金，通过最初用于朱雀的复制工艺天文台。反射镜将能量范围为 0.3-8.0 keV 的 X 射线聚焦到距离 2 m 的基于电荷耦合器件的焦平面相机组件上。我们在此介绍了在塔塔基础研究所 X 射线光学实验室对 SXT 光学器件进行的发射前、地面校准和评估。使用来自激光源的准直光束以及来自逆向望远镜的全孔径光束进行扫描，对 SXT 光学组件进行了校准和实验评估。红色激光源的准直光束用于确保单个反射镜段的安装精度，全孔径光束白色发光二极管 (LED) 源用于估计所有 320 个反射镜的点扩散函数 (PSF) . 在地面校准期间获得的近似 PSF 约为 136.6 弧秒。这些结果与发射后在轨校准期间获得的结果一致。