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25 April 2022, Volume 42 Issue 2 Previous Issue    Next Issue

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Review of blackout mitigation methods for vehicles during atmospheric reentry YU Minghao, QIU Zeyang 2022, 42 (2):  1-12.  doi: 10.16708/j.cnki.1000-758X.2022.0016 Abstract ( 432 )   PDF (2375KB) ( 1407 )   Save In order to help researchers better understand the mitigation methods of blackout and its development status, blackout mitigation methods adopted in current aerospace fields were introduced systematically and comprehensively. Firstly, the formation causes and research status of blackout problem were briefly introduced, and then the propagation mechanism of electromagnetic wave in plasma was also expounded. Secondly, the basic principles, advantages and disadvantages of 14 technical methods used to mitigate the blackout were introduced and discussed in detail. Those methods include variation of aerodynamic design of aircrafts, addition of the crossed electric and magnetic fields, standing wave detection, increment of the incident frequency, and terahertz technology, etc. Next, the abovementioned 14 methods were classified and evaluated from six aspects, e.g., power consumption, size quality, communication effect and engineering practicability, etc. Finally, several suggestions are put forward for the future study of the blackout problem. Related Articles | Metrics

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Analysis of motion strategies and performance of astronauts in weightless environments LI Zhichang, HUANG Zhuoran, LI Jianfei, CAO Zhe, WEI Cheng 2022, 42 (2):  13-21.  doi: 10.16708/j.cnki.1000-758X.2022.0017 Abstract ( 244 )   PDF (6864KB) ( 197 )   Save The coordination and balance of astronauts′ motions during missions in space are different from those in the ground environment due to the microgravity environment. The characteristics of astronauts′ movement in microgravity environment were studied, the dynamics of astronaut attitude adjustment strategy was analyzed, and the human performance in the process of movement was evaluated. Specifically, in the absence of external force/moment actuation, the human body must rely on the limbs to achieve the active control of torso posture according to a certain coordinated motion strategy. On the other hand, in order to analyze the motion strategies, the dynamics principles of human wholebody movement process need to be studied. Firstly, the dynamics model of human multirigid body system was established based on NewtonEuler method, and secondly ,the closedloop control system based on MBDyn software and computational moment method was established, which can simulate and calculate the complex motion process of human body. Finally, using the above theory and system, the feasibility of the human body relying on the limbs to actively adjust the posture according to a certain motion strategy was verified, and the dynamics of each joint was obtained, which provides some theoretical support for the design of astronauts′ motion in the future mission. Related Articles | Metrics

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Influence of gaseous medium on cushion characteristics of airbags LI Bo, ZHU Meifang, LEI Jiangli, HE Qingsong, WANG Fei 2022, 42 (2):  22-29.  doi: 10.16708/j.cnki.1000-758X.2022.0018 Abstract ( 137 )   PDF (3933KB) ( 165 )   Save China has developed a set of combined cushioning airbags for the test ship of its new human spacecraft. The return cabin of the new spacecraft was taken as research object, and a dynamic model of the cushioning process of combined airbags with inner airbags was established based on the theories of fluid mechanics and thermodynamics. Then, the validity of this model was verified by MSCDytran.Through simulation calculation, the influence of two inherent gas parameters that affect the airbag cushioning characteristics, gas freedom and molar mass, was analyzed. The research results show that, compared with the degree of gas freedom, molar mass has a greater impact on the cushioning characteristics, i.e. the smaller the molar mass of the gas, the faster the exhaust speed of the airbag and the smaller the required vent area. But by adjusting the vent area of airbags, several common gases can be used as airbag cushioning medium to achieve similar cuadjusting shioning effects. The maximum deviations of buffer  and rebound speed do not exceed 02g and 012m/s respectively. Research results of the article can provide references for the selection of gas medium in engineering applications of cushion airbags. Related Articles | Metrics

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Consistency analysis of WAAS satellites broadcast messages WANG Qizhou, LI Rui, ZHANG Jingcan, ZHANG Chao 2022, 42 (2):  30-38.  doi: 10.16708/j.cnki.1000-758X.2022.0019 Abstract ( 169 )   PDF (11245KB) ( 109 )   Save Satellite based augmentation system (SBAS) is built on the basis of traditional GNSS in order to further improve accuracy, integrity, continuity and availability. At present, many SBASs have been established around the world. Among them, the system which provides the longest service is the WAAS of the United States. WAAS has 38 reference stations, 3 master stations, 6 ground uplink stations and 3 GEO satellites. In order to guarantee system redundancy, each WRS has three independent receivers. The system structure of WAAS was introduced, and the similarities and differences of different types of message data transmitted by different GEO satellites in WAAS were compared. The consistency of message broadcasting and the impact on users due to different GEO broadcast messages were analysed. Also, the specifications and constraints of WAAS on user selection of SBAS signals in minimum operational performance standards were analysed. The essential difference between SBAS and traditional widearea difference system was revealed from the perspective of applying requirements, and it was pointed out that integrity realtime monitoring is based on establishing a sufficiently reliable ground monitoring network and satellite communication link. Related Articles | Metrics

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Feasibility study of spacecraft gravity center offset compensation by intentional xenon temperature control WANG Jue, WANG Min, GUO Tingting, ZHONG Xiaoqing, WEN Zheng, WEI Xin 2022, 42 (2):  39-45.  doi: 10.16708/j.cnki.1000-758X.2022.0020 Abstract ( 137 )   PDF (3400KB) ( 134 )   Save The gravity center offset of spacecraft was generally compensated by adding some balancing weight. The balancing weight was not able to provide other support for spacecraft mission, thus it reduced the loading efficiency of spacecraft. For the spacecraft equipped with high density gas cylinders, e.g. xenon, a new method was raised to compensate the offset of gravity center of spacecraft by the intentional temperature control of xenon cylinders, so as to reduce the use of balancing weight. The gravity center offset compensation ability influenced by the temperature control of xenon cylinders was positively related to xenon mass ratio and xenon cylinders′ centroid spacing. Under the condition of application for spacecraft, the gravity center offset with magnitude order of tens of millimeters can be compensated by the temperature control of xenon cylinders and the minimum compensation error was approximately 2mm. References for gravity center compensation of electric propulsion spacecraft can be provided. Related Articles | Metrics

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General relativistic theory for laser phase comparison between satellites under orbit perturbations LIANG Jian, JIA Qian, LIU Lei, TANG Shuo 2022, 42 (2):  46-55.  doi: 10.16708/j.cnki.1000-758X.2022.0021 Abstract ( 177 )   PDF (3914KB) ( 195 )   Save For intersatellite laser ranging from picometers to nanometers level, this paper established the oneway and twoway laser phase comparison models between satellites in GCRS. The general relativity effect was considered in the established models induced by orbit perturbations. In the vicinity of the Earth, simulation studies of satellites with different orbital altitudes were carried out to investigate the phase comparison error resulting from the general relativity effect. Then, the intersatellite laser ranging error was obtained by the phase comparison error. Simulation results show that the minimum laser ranging error of general relativity effect is of the order of 100 picometers, and the maximum error is of the order of 1 micron. It can be concluded that the higher the orbit height, the smaller the intersatellite laser ranging error of general relativity effect, and the larger the distance between satellites, the larger the intersatellite laser ranging error of general relativity effect. Related Articles | Metrics

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Site-specific tropospheric zenith total delay forecast based on N-BEATS 2022, 42 (2):  56-63.  doi: 10.16708/j.cnki.1000-758X.2022.0022 Abstract ( 165 )   PDF (10573KB) ( 204 )   Save High-precision priori tropospheric delay can reduce the convergence time of precise point positioning. Based on a highprecision and high-resolution numerical meteorological database, the deep learning method N-BEATS algorithm was used to predict the site-specific tropospheric zenith total delay. Nine IGS tracking stations were selected. It covered 18.5 years from January 2002 to June 2019. Based on the N-BEATS algorithm, three forecast strategies were designed with different input arcs. The first 17.5 years of the entire period were used for model training. The last year’s data was used for validation. The results show that the average forecast residuals of different forecast arcs shorter than 12hours are mostly in the sub-millimeter range. As the forecast arc increases, the average forecast residual increases. The strategy with a longer input arc shows better performance than the other two strategies with shorter arcs. The standard deviations of the forecast residuals of 2hours, 4hours, and 6hours are approximately 5mm, 9mm, and 13mm, respectively. Related Articles | Metrics

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Research on satellite positioning technology based on BeiDou-3 navigation satellite system ZHAO Pengfei, CHEN Gaofeng, LI Xiaojuan, WANG Dabao, LIU Ning, WANG Huicong 2022, 42 (2):  64-70.  doi: 10.16708/j.cnki.1000-758X.2022.0023 Abstract ( 197 )   PDF (3247KB) ( 242 )   Save The transmission link between BeiDou navigation satellites and user satellite, and the relationship between the capture sensitivity and the incoherent accumulation were analyzed. A fourtime incoherent accumulation was used and capture sensitivity reached -130dBm, together with positioning time less than 5 minutes. Based on the capture sensitivity, a STK model was set up to simulate the number of captured BeiDou navigation satellites for the user satellite whose orbit was of sun synchronous in a full orbital period. The results show that more than 4  satellites could be captured during the full orbital period. Positioning accuracy and speed accuracy are 2.59m and 0.00378m/s respectively. The first test of on-orbit satellite positioning was carried out right after BeiDou navigation satellite system completed deployment at the end of 2020. Six or more visible BeiDou navigation satellites were captured. Positioning accuracy of 2.77m and speed accuracy of 0.006m/s were achieved, showing good consistency with the simulated results. The study proves that the algorithm can be used for satellite positioning applications and  that it satisfies the positioning requirement based on Beidou navigation system. Related Articles | Metrics

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Onboard orbit propagation and micro-thrust calibration for small satellites ZHANG Junhua, CHEN Jianlin, SUN Chong, YUAN Jianping 2022, 42 (2):  71-81.  doi: 10.16708/j.cnki.1000-758X.2022.0024 Abstract ( 284 )   PDF (3405KB) ( 418 )   Save To accurately address the orbit motion of small satellites in low Earth orbit, a kind of high-precision orbital propagation algorithm and on-orbit thrust calibration algorithm based on the consideration of complex perturbation forces were designed. Firstly, the dynamic model for small satellites was established considering the gravitational force of the sphere Earth and several perturbations. The variable-step Runge-Kutta integrator was employed in the orbit propagation. Then, using the unscented kalman filter (UKF), an on-orbit calibration algorithm was designed to calibrate the micro-thrust with errors in real time. To validate the effectiveness and accuracy of the proposed orbit prediction method, its results were compared with those of STK programs in a great number of simulation scenarios. The numerical simulation shows that the joint orbit determination and electric thrust calibration are quite precise. Related Articles | Metrics

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Impedance control of space manipulator based on improved neural network QI Yifan , JIA Yinghong, ZHAO Baoshan, ZHONG Rui, HONG Wenqing 2022, 42 (2):  82-90.  doi: 10.16708/j.cnki.1000-758X.2022.0025 Abstract ( 390 )   PDF (3739KB) ( 503 )   Save  An impedance control method based on improved neural network was proposed oriented to compliance control of space manipulators under the condition of uncertain environmental information and unknown collision model. Based on the closed-loop equation of impedance control system, the reasons why precise force control can’t be achieved under the condition of uncertain environmental information and unknown collision model were analyzed. The weight matrices in the neural network were adjusted by particle swarm optimization algorithm to improve the convergence speed and optimization performance of neural network. An impedance controller based on the improved neural network was proposed, which accomplished compliance control. The improved neural network can adjust the impedance parameters on line to achieve better compliance control effect. Numerical simulation results show that the proposed controller can reduce the force control error and position control error effectively, and has a better anti-jamming capability for force feedback interference signal than traditional impedance controller. Related Articles | Metrics

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A novel DOR beacon for deep space navigation and positioning GAN Jiangying, SHU Fengchun, WU Yajun, TONG Fengxian, GUO Shaoguang, WU De 2022, 42 (2):  91-98.  doi: 10.16708/j.cnki.1000-758X.2022.0026 Abstract ( 202 )   PDF (5835KB) ( 185 )   Save Very long baseline interferometry (VLBI) is one of the important approaches of navigation and positioning of deep space probes. The differential one-way ranging (DOR) beacons and delta differential one-way ranging (Delta-DOR) measurement systems, which accurately determine the angular distance of the deep-space detector with respect to the extraterrestrial radio source, are often used in VLBI observations of deep space probes. Phase dispersion is one of the main sources of error that reduce the accuracy of measurement. A new DOR beacon (PN-DOR) was developed based on the pseudorandom noise modulation method and the design and implementation of the beacon were carried out. Moreover, the optimization methods of the Gold code bandwidth, polynomials, the shaping filters coefficients and the DOR signal modulation index were analyzed in the time and frequency domain. The PN-DOR beacon can effectively reduce the delay error induced by phase dispersion and improve the Delta-DOR measurement accuracy, thus meeting the needs of high-precision navigation and positioning of future deep-space probe missions of China. Related Articles | Metrics

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Urban road extraction of multi-level segmentation based on optimal feature selection LEI Huimin, ZHANG Hesheng 2022, 42 (2):  99-107.  doi: 10.16708/j.cnki.1000-758X.2022.0027 Abstract ( 144 )   PDF (9092KB) ( 108 )   Save In order to solve the problem that the feature dimension is too high in the process of road extraction, a kind of feature selection method based on ReliefF filtering and Wrapper encapsulation was put forward. The particle swarm optimization algorithm (PSO) was used as the search algorithm of Wrapper, and the optimized random forest algorithm (OPRF) was used as the classifier of Wrapper to form the PSO OPRF encapsulated subsets evaluator. The feature subset selected by ReliefF was evaluated, the feature dimension was reduced, and the optimal feature subset was selected. According to the selected features, the urban road network was extracted by multilevel segmentation and classification. Taking GF-2 remote sensing images of some urban areas of Taiyuan city, Shanxi province as data sources, the road extraction quality obtained by using the proposed feature selection method was compared with that obtained by using only ReliefF algorithm, using traditional random forest as a classifier, and using J48 decision tree as a kind of method on classifier feature selection. The results show that the road extraction quality is the best for the proposed method, and the extraction qualitiy of three types of road are up to 0.959, 0.853 and 0.931, respectively. Related Articles | Metrics

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BF-1 satellite system design and technology characteristics BAI Zhaoguang, WANG Chongyu, FAN Dongdong, SUN Jiwen 2022, 42 (2):  108-116.  doi: 10.16708/j.cnki.1000-758X.2022.0028 Abstract ( 576 )   PDF (8151KB) ( 238 )   Save BF-1 is the first meteorological satellite based on global navigation satellite system-reflection (GNSS-R) signal measurement technology in China, The new L-band sea surface wind field information detection technology was adopted to provide services for national meteorology, disaster prevention and mitigation and other industries in wind field measurement and sea surface hurricane wind speed inversion. From the perspective of system design, the overall technical indicators of BF-1 satellite were introduced, and the recognition process and results of the satellite system configuration, the key index of the load and the orbital characteristics in combination with the demand analysis were expounded. The technical characteristics of filling the gap of sea surface highprecision wind field monitoring, the first sea launch, satellite ground integrated data inversion, innovative data center and so on were summarized. The wind speed measurement accuracy can reach 2m/s while the wind field measurement is available in the range from 2m/s to 70m/s.  At the same time, the on-orbit test, load performance comparison and follow-up development suggestions were introduced. The design process can be used as a demonstration of subsequent operational satellites and other satellite systems. Related Articles | Metrics

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Design and verification of key technologies for space-borne GNSS-R sea wind field observation payload WANG Yanguang, BAI Zhaoguang, ZHU Xueping, WANG Chongyu, HAN Lin 2022, 42 (2):  117-124.  doi: 10.16708/j.cnki.1000-758X.2022.0029 Abstract ( 190 )   PDF (3896KB) ( 285 )   Save At present, the sea surface wind field observation methods are limited. The space-based observation in view of global navigation satellite system-reflection (GNSS-R) provides a new approach for global wind field sensing. The GNSS-R sea surface wind speed sensing technology has the characteristics of allweather, low power consumption, wide coverage, multiple signal sources and low cost, which has gained widespread attention gradually. Since the designed GNSS system primitively aimed to provide global users with passive navigation services based on radio pseudo-range measurement, and not designed as a space-based remote sensing radiation source, the GNSS-R reflected signal had the cheracteristics such as scattered observation points, weak signal power and signal processing algorithm with large amount of calculations. Taking the BF-1 satellite as the research object, the GNSS-R signal processing algorithm and system were studied. In view of the characteristics of GNSS-R signal, the requirements and constraints of space-borne real-time processing, it was proposed to combine the dynamic phase compensation technology on the short-term cycle correlation and rotation transform to reduce the GNSS-R signal processing burden without distortion. The computational burden of the proposed algorithm was 1/8.99 of the one for the traditional circular correlation method, meanwhile a FPGA based GNSS-R signal processing system was designed. The pay load was tested on the ground and in orbit. The results show that the GNSS-R signal processing system and the proposed signal processing algorithm meet the satellite’s requirements (5-frame per second). The DDM results have be used in the wind field inversion effectively. Related Articles | Metrics

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Wind speed retrieval for BF-1 GNSSR satellites using geophysical model function method FAN Dongdong, LU Minjian, CHEN Chenxin, GAO Han, WEI Haoyun 2022, 42 (2):  125-133.  doi: 10.16708/j.cnki.1000-758X.2022.0030 Abstract ( 192 )   PDF (10828KB) ( 175 )   Save Global-scale high temporal and spatial resolution sea surface wind field detection is currently one of the hotspots in global meteorological research and forecasting. In traditional sea surface wind field detection technology, the measurement area is limited, and it is severely restricted by the weather condition. Based on the principle of wind speed retrieval from global navigation satellite system-reflectometry(GNSS-R), the wind speed retrieval model was constructed using the geophysical model function(GMF) method with the level 1 data of BF-1 as input and the wind speed data reanalyzed by the European center for mediumrange weather forecasts (ECMWF) as the reference wind speed. This paper analyzed the influence of different parameters of the level 1 product, such as satellite, observation antenna, specular incident angle, signal-to-noise ratio, etc., on the observation characteristics and wind speed, determined the GMF empirical model parameters and completed the model establishment. The generated retrieved wind speed data and their statistical characteristics were compared and analyzed with the results of cyclone global navigation satellite system(CYGNSS). The retrieved wind speed and the distribution characteristics of the retrieval deviation with respect to the incident angle and the reference wind speed are all consistent with the trend of CYGNSS results. This work preliminarily demonstrates the wind speed detection capability of the BF-1 satellite, which can provide a reference for subsequent detection performance improvement and constellation development. Related Articles | Metrics