Abstract: With respect to molecular contamination influenced by material outgassing due to Low Earth Orbit satellite in space environment,an on-orbit payload test is sampled from a spacecraft running on sun synchronous orbit.Details on orbit element variation such as semi major axis perturbance and Local Time of Descending Node shift and so on are discussed to analyze the temperature of the radiant cooler containing the earth shield,and the first and the second stage.Focusing on the second stage temperature varying,a model is built to estimate the environmental temperature of the molecularly contaminated radiant cooler.With the flight data,results illustrate that the second stage temperature has a zero value of about 75.53 K,and a natural degradation zero value closing to 26.71 K with a factor nearing 0.07 h^-1,and a molecular contamination zero value approximating to 6.90×10^-14K with a factor about 0.06 h^-1.After cooling about 90h,it is predicted that the minimum temperature of the device can be 75.62 K lower than the test result about 0.47 K.According to the estimation,the results prove that the radiant cooler performance due to the molecular contamination that can be totally ignored is excellent to satisfy the payload requirements.