光学系统设计是星敏感器设计的关键，光学系统参数决定将影响星敏感器的性能指标，而参数的选择需要考虑天空背景辐射、图像传感器参数等多种因素。采用Modtran软件仿真分析了不同情况下的天空背景辐射。在此基础上，通过引入能量集中度以及传感器噪声，推导出更精确的可探测极限星等公式，并深入分析了星敏感器可探测极限星等、探测概率以及探测精度与各影响因素的关系。对典型设计参数的可行性进行了分析，分析结果可为全天时星敏感器光学系统设计提供参考。

The selection of optical-system parameters plays a key role in star sensors, which can affect the sensor′s performance. When determining the parameters, sky background radiance and parameters of image sensors should be considered. Sky background radiance under different situations is simulated by Modtran. A more accurate formula to estimate the detectable stellar magnitude limit is proposed, considering the effects of energy focusing degree and sensor noise. With this formula, the factors affecting the detectable stellar magnitude, detection probability and accuracy are deeply analyzed. The feasibility of typical optical-system parameters is studied. The results offer important references in the determination of optical system of all-day used star sensors.