Abstract: Demand for star sensor is increasing on near space vehicles. Compared with space environment, near space environment has new factors which influence star sensor’s detectability such as atmospheric extinction, sky backgroud light, high speed, high temperature, high angular velocity, etc. The factors which influence near space star sensor’s detectability are analyzed step by step. The influencing mechanism of detectability is obtained about FOV,sensitivity, SNR, image processing algorithm. The relation between SNR and environment/design factors is quantified. One method of parameter design for near space sensor is proposed. Finally one principle prototype for special requirement is designed， tested and verified. The results indicate the principle prototype can meet the application requirements.

Key words: near space, star sensor, detectability