Research On Thermal Control Technology Of Ultra-large Diameter In-orbit Assembly Telescope

With the development of Astronomy,in order to obtain high-quality images of weak signals deeper in the universe,the resolution of telescopes is increasingly required.In order to obtain higher resolutions,the diameter of telescopes will also become larger.However,the carrying capacity of the launch vehicle and the envelope size limit the increase of the telescope’s aperture.In-orbit assembly technology has become an effective way to resolve this contradiction.Various countries have started to study the technology of in-orbit assembling telescopes.The thermal control system is an important guarantee for the normal operation of the telescope in orbit and obtains high-quality images.Due to thermal control methods such as coating multiple layers,it will interfere with the assembly process.Traditional thermal control measures cannot fully meet the thermal control needs of the in-orbit assembled telescope.Therefore,the research on the thermal control technology of the in-orbit assembled telescope should also be launched simultaneously.In this paper,a certain 10m orbit assembled telescope is taken as the research object,and the thermal control technology of the orbit assembled telescope is studied.The orbital environmental characteristics of the telescope are the basis and prerequisite for the thermal design of the telescope.First,the thermal environment characteristics of the Halo orbit at the second Lagrangian point of Sun and Earth are analyzed.The external heat flow of the orbit is calculated to guide the thermal design and thermal design simulation verification.In this orbit,the main external heat sources such as the sun are located on the same side and the side facing away from the sun is free of strong visible light and heat radiation.Based on this characteristic,the research of multi-layer film sunshield was carried out.The sunshade is used to block the sunlight,and the telescope is cooled to the working temperature through passive radiation.The parameters of the shape,size,number of layers,material,and opening angle of the sunshield were determined.As an infrared telescope,in order to observe low-temperature targets in the depths of the universe,the detector is required to be at extremely low operating temperatures.The focus plane was thermally designed and two schemes were proposed:radiant cold plate radiant cooling and refrigerator cooling.By comparing and analyzing the advantages and disadvantages of the two schemes,a radiant cold plate radiant cooling scheme was selected because of its higher reliability and stability.Then,the thermal design was verified by thermal simulation.First,the high and low temperature conditions of the telescope were determined according to the changes of the heat flow outside the orbit.Then the thermal analysis finite element model of the telescope was established by using UG/SST software to calculate the temperature level of the telescope.The results show that under low temperature conditions,the heat of1290 W/m~2 from the sun is blocked by the sunshield,and the radiation intensity reaching the low temperature region is only 0.036 W/m~2.The temperature of the primary mirror,secondary mirror and each structural component is lower than 50K,which meets the needs of thermal control.However,the temperature of some sub-mirrors of the main mirror is higher than 50K under high temperature conditions,which cannot fully meet the thermal control requirements.In order to meet the thermal control needs of thermal design,it is necessary to optimize the thermal design parameters.However,due to the large number of parameters,the optimization process is complicated and difficult.In order to improve the optimization efficiency and reduce unnecessary work,sensitivity analysis was performed on the parameters of the telescope’s main heat transfer channel.After analysis,many parameters were divided into sensitive parameters,relatively sensitive parameters and insensitive parameters.Then,optimize high-sensitivity parameters and ignore insensitive parameters.The optimized design meets the needs of thermal control.