Multi-objective Optimization-based Thermal Design Of In-orbit Assembled Telescopes

Space telescopes are an important tool for human exploration of space,and increasing their aperture size is the most effective means of achieving higher levels of observation.The conflict between the need for astronomers to rapidly increase the level of observations and the manufacturing difficulties associated with the aperture size of space telescopes is also becoming increasingly evident.In-orbit assembled telescopes,due to their superior construction,not only reduce the difficulty of machining a single large reflector,but also break the size limits of launch vehicles.However,traditional thermal design concepts for space telescopes are not fully suitable for application to onorbit telescopes,and the thermal design should take into account the special characteristics of the structure and the corresponding interchangeability concepts.Therefore,it is important to investigate the thermal design of in-orbit assembled telescopes.In this paper,the structure and orbit of the in-orbit assembled telescope are first introduced.Based on the mechanical structure,the heat transfer path is analysed.Based on the orbit information,the variation of the BETA angle between the sunlight vector and the orbital plane of the satellite is calculated,and the shadow surface time in a single orbital cycle is analysed at different BETA angles.The out-of-arrival heat flow on the surface of the in-orbit assembled telescope was calculated and its trend was analysed.Based on the structure and orbital characteristics of the in-orbit assembled telescope,the difficulties of the thermal design tasks of the in-orbit assembled telescope were analysed.The thermal control design of the in-orbit assembled telescope was carried out.The thermal design of the hood was proposed,and the shape,material and number of layers of the hood were determined.A special radiant heating backplate was designed for the primary and secondary mirrors.A heat dissipation path was designed for the CMOS component part and the area of the radiative cooling plate was determined.The thermal simulation analysis of the in-orbit assembled telescope was carried out using finite element simulation software,and two operating conditions,high and low temperature,were defined.The simulation results show that the temperatures of the primary mirror,secondary mirror and CMOS temperature meet the thermal control index,but are close to the limit temperature of the index,and the thermal design needs to be optimised.A BP neural network agent model based on Bayesian optimization is established for the in-orbit assembly telescope.Based on this,a sensitivity analysis of the thermal design parameters is carried out,and the Spearman rank correlation coefficient method and the MIV method are applied to find the temperature sensitive thermal design parameters for the primary mirror,secondary mirror and CMOS respectively.Finally,a mathematical model for the multi-objective optimisation problem of the in-orbit assembled telescope is constructed,and the NSGA-II,MOEA\D and IBEA methods are applied to find the multi-objective optimisation of the thermal design parameters of the in-orbit assembled telescope.The optimized thermal design parameters have been substituted into the finite element model and the temperature of the primary mirror fluctuates from 19.7 to 20.5°C,the secondary mirror from 19.1 to20.8°C and the CMOS from 1.6 to 25.4°C.The temperature of the secondary mirror,primary mirror and CMOS all meet the thermal control index and the temperature fluctuation range is smaller than that before the optimization.The feasibility of applying the multi-objective optimization method to the thermal design parameters of the in-orbit assembled telescope is verified.