Temperature Response Analysis And Prediction Of Alpha Magnetic Spectrometer In-orbit

Alpha Magnetic Spectrometer(AMS)is a large and precise high-energy particle detector installed on the International Space Station(ISS)to detect dark matter and antimatter in the universe and explore the origin of the universe.AMS relies on six groups of ultra-high precision detectors to complete the particle detection,and the measurement accuracy of each detector is dependent on the proper operating temperature.Therefore,a stable and efficient thermal control system is critical to ensure the safe and stable operation of AMS.The thermal analysis of AMS in-orbit can not only provide support for the formulation of AMS thermal control strategy,but also provide theoretical basis and technical reference for the thermal management of other equipment on the ISS and even other spacecraft in low Earth orbit.This study analyzed the external thermal environment of AMS,and systematically investigated the heat flux and periodic and transient temperature response characteristics of AMS under the ISS full operating conditions by means of numerical simulation,neural networks and theoretical calculation,combined with the measured temperature data of AMS in-orbit.The main contents of the thesis are as follows:1.Based on the energy balance equation of AMS in-orbit,the factors affecting the periodic and transient external thermal environment of AMS were analyzed:the factors affecting the periodic thermal environment of AMS mainly include the ISS orbital altitude h,the orbital period t,solar radiation intensity,angle β,exposure factor SEF and shadow factor SF;apart from the above factors,the factors affecting the transient thermal environment of AMS also include angle θ and view factors of solar radiation,Earth albedo and Earth infrared radiation.Based on the spherical coordinate system,the view factors of AMS each surface were deduced,and this laid a foundation for the periodic and transient thermal analysis of AMS in-orbit.2.The simulation of the AMS temperature in-orbit under the ISS full operating conditions was implemented in Thermal Desktop and SINDA/FLUINT software.The periodic temperature variations on each AMS surface were investigated,as well as the effects of orbital parameters and ISS operating conditions on AMS temperature.The coldest and hottse working conditions of the AMS RAM and WAKE main radiators under the ISS normal operating condition were determined,and the thermal control suggestions to ensure the safe and stable operation of AMS were proposed.Results showed that the temperature of each AMS surface varied with angle β,and the largest difference of orbital average temperature of the same part at different angle βcan reach 31.7℃.The effects of orbital parameters and ISS operating conditions on each AMS surface were different.Under the ISS normal operating condition,the hottest working condition for the AMS RAM and WAKE main radiators was reached when the angle β was near-25°with the ISS orbital altitiude being 460 km at perihelion position,and the high-temperature warnings of the power distribution system(PDS)on the AMS WAKE main radiator could be trigged.To resolve the warnings,locking the ISS starboard solar arrays vertically can effectively decrease the temperature of the PDS.The research results provide a basis for formulating the AMS thermal control strategy.3.The in-orbit temperatures of each AMS surface and key parts under the ISS full operating conditions were studied using the back propagation(BP)neural network model.BP neural network models for AMS in-orbit under the ISS normal operating condition and ISS special operating conditions were constructed,respectively.The BP neural network models were trained based on the measured temperature data from January 1,2016,to December 31,2017,after the installation of the thermal blanket.The models that can quickly and accurately predict the periodic temperature on each AMS surface and key parts were obtained,and the models were applied to predict the orbital average temperature of these parts.The results showed that,under the ISS normal operating condition,the orbital average temperature on each AMS surface and key parts were:AMS top was from-12.4℃ to-4.3℃,port surface was from+2.7℃ to+14.2℃,starboard surface was from-9.8℃ to+29.4℃,RAM surface was from4.1℃ to+4.5℃,WAKE surface was from+0.4℃ to+24.2℃,the BOX-C was from+10.4℃to+20.1℃,and the PDS was from+18.6℃ to+40.4℃.All the orbital average temperatures were within the thermal control requirements in the full angle β range,which proves the effectiveness of the AMS thermal control system after the installation of the thermal blanket.The comparison between the results predicted by the BP neural network model and the results simulated by the numerical model showed that machine learning method is an effective and accurate method for AMS periodic thermal analysis.4.The theoretical model of the external heat flux of AMS in-orbit was established,and the transient variations in the external heat flux into each AMS surface were studied.The theoretical model was validated through a comparison with the measured temperature.Based on the validated model,the effects of ISS special operations on the AMS external heat flux were further examined.The influences of adding the thermal blanket on AMS components were investigated,and the transient temperature responses of the PDS with frequent temperature anomalies under the ISS full operating conditions were investigated.Results showed that the transient external heat flux on each AMS surface varied with the orbital position,and the effects of ISS special operations on different AMS surfaces were different.Locking the ISS solar arrays and adjusting the ISS flight attitude had a more significant impact on AMS external heat flux,than adjusting the ISS starboard radiator did.The total external heat flux at the PDS was the largest when the angle β was around-25°,which was the fundamental reason for the frequent high-temperature warnings occurred in this angle β range after installing the thermal blanket on AMS.The transient temperature response hysteresis of the PDS was about 230 seconds.Therefore,in order to ensure the safe and stable operation of the PDS,it is necessary to vertically lock the ISS starboard solar arrays about 4 minutes before its temperature breaks through the high temperature warning limit under the hottest condition.The results further improve the thermal control strategy of AMS.