Abstract:  The effective emissivity of multilayer insulator（MLI） is widely used in spacecraft thermal analysis and thermal design, and the empirical range of effective emissivity is 0.02 to 0.04 which is only related to numbers of layers and has nothing to do with temperature. The working condition of empirical range of effective emissivity is that the hot side temperature of MLI is within -10℃ to 50℃ and that the cold side is without solar heat flux. More condition deviation led to larger calculation deviation made by empirical range of effective emissivity.In order to solve the problem, the thermal performance equation of MLI normal heat transfer was proposed. The equation was made up of thermal radiation item and heat conduction item, and the acquisition method for the coefficient of radiation item and conduction item was described. As an example, the native 10-layer MLI was discussed, and the coefficients of the MLI were obtained,which was useful in engineering. The equation was examined in many working conditions. By using the equation, the cause of the problem was obtained, and the deviation was dropped from 20℃ to 5℃ in high and low temperature zone. The blade radiation model was well replaced by hybrid heat transfer model. Finally, the problem of how to design the operating conditions of MLI thermal balance test was briefly discussed.

Key words: multilayer insulator, thermal performance equation, blade radiation model, effective emissivity, hybrid heat transfer model, conduction item, radiation item