Theoretical calculation shows that the sun phase angle, observation distance and the brightness magnitude of the targeted satellite change significantly because of no earth curvature effect and large separation distance in position. 仿真计算表明,天基观测由于不受地球曲率影响,且观测几何拉开,太阳相位角、观测距离变化范围较大,因此目标卫星视星等变化范围较大。