Study On High-precision Thermal Control Method Of Small Satellite

It is necessary to provide a good working environment to maintain the spacecraft the normal operation on orbit.With the development of space technology and the progress of spaceborne electronic technology,the requirements of thermal control precision become more and more strict,and some reaches the requirements of mK level and even higher.In recent years,with the rapid development of small satellites and micro satellites,the traditional thermal control technology combined with the auxiliary structure of the machine thermal integration design method,has not adapted to demanding requirements of the small satellite and micro satellites thermal control system on high precision,high reliability,light weight and low-cost.In order to solve the problem of the thermal control resource and the high-precision temperature control of small satellite,this paper focuses on the study of a novel low-cost high precision temperature measurement method,a new high-precision thermal control scheme on star sensor system and the design method of hierarchical structure of high precision thermal control system from three aspects of theory,simulation and experiment.From local to whole,it provides a solution for the high-precision thermal control method of the small satellite.Firstly,in order to solve the problem of insufficient temperature measurement on the micro-nano satellite and to reduce the weight of the temperature measuring cable net,this paper discusses the new low-cost temperature measurement scheme using the commercial digital temperature sensor instead of the thermistor temperature measuring.The adaptive experiment platform for multi-temperature measurement of space environment is established.The temperature measurement and spatial adaptability of DS18B20 based on 1-wire commercial digital temperature measurement sensor DS18B20 are studied.And the DS18B20 temperature measurement method was applied to the XW-2 micro-nano satellite.Design based on the micro-nano satellite interface,hardware and software was carried out.The ground and in-orbit experiments are verified for the temperature measurement system.Research results show the commercial digital temperature measuring device DS18B20 based on 1-Wire is consistent with that of thermocouple from-50? to 100? and temperature measurement accuracy is high in vacuum environment.Good stability can meet the requirements.The analysis of ground and in-orbit experimental data show the low cost temperature measurement technology can meet the requirements of temperature measurement.And compared with the traditional thermistor,the temperature measurement method saves nearly 32%of the weight of the measured cable net.The research of this paper provides a new method for measuring temperature of the equipment in the satellite,which lays the foundation for the precise temperature measurement application of the digital temperature sensor in the satellite.For a specific star sensor system,by analyzing and compareing three kinds of thermal control design schemes proposed in this paper,the thermal control design scheme based on high thermal conductivity structure integrated star sensor system is the optimal thermal control design scheme.For optimal thermal control design scheme,Influencing analysis was carried out from three aspects:the equivalent radiation rate of the multi-layer insulation material,the thickness of the high thermal conductivity structure and the thermal conductivity of the high thermal conductivity materials.The results show that the effect of multilayer equivalent emissivity is small,and the structure thickness and thermal conductivity have great influence.The further analysis results show the biggest star bracket on two temperature declined from 3.18? to 2.43 ?,the temperature control effect be improved,and the thermal conductive materials used by weight is 2.5 Kg to 0.7 Kg with 4 mm thickness of C-C graphite materials instead of copper.Finally,4mm thick c-c graphite materials were selected as the structural design materials for high thermal conductivity.The simulation results show that the scheme of the thermal control design can realize the biggest temperature difference on the star bracket is not greater than 2.43 ?,star sensor installed flange on-orbit mean temperature was 7.47 ??8.93?,which satisfies the temperature requirement very well,and that the design is reasonable.The thermal control design scheme can provide reference for the thermal control design of equipment with high-precision temperature control.In order to meet the needs of the future small satellite high-precision thermal control,a high precision thermal control method based on the hierarchical structure combined with high-precision of PID temperature control algorithm is proposed in this paper.The simulation and verification of this method is carried out by establishing a virtual satellite model.The basic principle of this method is to divide the satellite thermal control region into the peripheral thermal control zone,the transitional thermal control zone and the core thermal control zone.According to different thermal control indexes,the equipment should be placed in the corresponding thermal control area.The equipment with high-precision is placed in the core thermal control area.The thermal control areas are independent each other by using thermal insulation design.The high-precise temperature control of the sensitive unit in the core area is realized based on the above hierarchical thermal control combined with PID temperature control algorithm.The sensitive unit high precision temperature control model combining hierarchical structure with PID temperature control algorithm in the virtual satellite was established based on the above principle.Theoretical and simulation analysis was carried out.The influencing analysis of the key parameters influencing hierarchical structure thermal control was carried out according to the local hierarchical thermal control analysis model.Research results show that the thermal control technology based on the hierarchical structure combined with PID temperature control algorithm can realize the sensitive units temperature control precision better than ±0.01?.The key parameters influencing temperature control precision mainly include the inner emissivity of the transition section?,,outer emissivity of the central section ?c,effective emissivity from the transition section to the central section ?i/o,inner emissivity of the central section ?i,outer emissivity of the equipment ?eq,outer emissivity of the mounting plate ?d,electronic equipment power Pe,the conductivity coefficient of the equipment mounting insulation pad ?,equipment quantity m,equipmentpower Pe and compensate the heating power u(t)(Kp/TI(s)/TD(s))with PID temperature control algorithm.The larger parameters ?i,?eq and ?d,the lower temperature level and the shorter balance time.The larger parameter ?i/o,the longer balance time and the worse temperature control precision.And the parameter ?i/o has the maximum influence on the temperature control precision.The larger parameters ?i and Ec,the lower temperature level.The higher thermal conductivity ?,the worse temperature and the lower temperature.The larger parameter Pe,the higher temperature level and the longer balance time.The larger parameter m,the longer balance time.The PID temperature control algorithm is used to compensate the heating power u(t)(KP/TI(s)/TD(s)).Only the temperature control precision is affected,and the appropriate parameters can be selected to obtain better control accuracy.In order to further verify the effectiveness of the high precision temperature control method combining the hierarchical structure with PID temperature control algorithm,a prototype of high precision temperature control unit is developed.The high precision temperature control method based on hierarchical structure combined with PID temperature control algorithm is studied using experimental method.The results show that the high precision temperature control method combining hierarchical structure with the PID temperature control algorithm can realize the temperature control precision better than ±0.025 ?.The prototype performance of high precision temperature control unit meets the requirements.The experimental results are in good agreement with the simulation results which further validate the effectiveness of the high precision thermal control method proposed in this paper and the correctness of the simulation model based on the hierarchical structure combined with PID temperature control algorithm.The results can provide useful reference for the structure design of high precision thermal control of satellite.