May 2022, Volume 7 Issue 4
    

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  • Topic：Very Long Baseline Interferometry Technology
    Research Progress of VLBI Technology and Application to China Lunar Exploration Project
    HONG Xiaoyu, ZHANG Xiuzhong, ZHENG Weimin, WANG Guangli, LIU Qinghui, WANG Na, ZHANG Hongbo, WANG Min, SHU Fengchun
    2020, 7(4): 321-331. https://doi.org/10.15982/j.issn.2095-7777.2020.20200030
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    The Unified S-Band (USB) measurement and control system with ranging and velocity measurement capabilities and the VLBI system with high precision angle measurement capabilities are jointly used to undertake the orbit determination for the missions. The measurement accuracy is increasing constantly. The orbit determination for Chang'E-1、Chang'E-2、Chang'E-3、Chang'E-4 and Chang'E-5 test spacecraft missions have been completed successfully. It has made important contributions to CLEP and laid a solid foundation for the subsequent exploration of the Moon and planets.
  • Topic：Very Long Baseline Interferometry Technology
    High-Precision VLBI Orbit Measurement Technology in the Chang'E-4 Mission
    WANG Guangli, HONG Xiaoyu, LIU Qinghui, LI Bin, MA Jun, SU Yan, HAO Longfei
    2020, 7(4): 332-339. https://doi.org/10.15982/j.issn.2095-7777.2020.20200026
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    Chang'E-4（CE-4）achieved the soft landing and patrol survey on the far side of the Moon for the first time in the world. The S-band ΔDOR measurement technology is used in the relay satellite mission，and the new S-band ΔDOR observation data processing system is developed. During the prober mission，the VLBI system realized fast time-sharing observations for the relay satellite and lander-rover combination prober for the first time；and the Tianma radio telescope is used to calibrate the relay satellite antenna in orbit. Considering the characteristics of CE-4，the key technical issues to be solved by the VLBI technology are analyzed，and specific measures are proposed. The analysis of the measurement results during the real-time mission of the two spacecraft show that these technical measures play important roles in the accomplishment of mission goals.
  • Topic：Very Long Baseline Interferometry Technology
    Contribution of VLBI for the Orbit Determination to Chinese Lunar Exploration Project
    HUANG Yong, LI Peijia, HU Xiaogong
    2020, 7(4): 340-346. https://doi.org/10.15982/j.issn.2095-7777.2020.20200022
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    The S/X-band radiometric range/Doppler and very long baseline interferometry（VLBI）techniques are used in Chinese lunar exploration to track the probe. Measurement accuracy is improved for the application of new equipment and techniques. VLBI data plays a very important role in the orbit determination（OD）and lander positioning. VLBI data can improve short arc OD accuracy comparing with the range/Doppler data only. For the lunar orbit，Combining VLBI data helps to improve orbit accuracy especially in along-track and normal directions. Results also indicate that VLBI data contribute more to the OD when the probe is at the edge-on view than at the face-on view. Overlap analysis shows that the position consistency is about 20 m and better than 3 m in the radial direction for CE-3/CE-4 lunar orbit. The statistical positioning method is applied to determine the position for the CE-3 lander combined with 1 h range and VLBI data，and the accuracy is better than 50 m compared to the result of LRO camera.
  • Topic：Very Long Baseline Interferometry Technology
    S/X Cryogenic Receiver Technology for VLBI Satellite Tracking
    LI Bin, ZHONG Weiye, WANG Shengwang, ZHANG Lijun, LIANG Shiguang
    2020, 7(4): 347-353. https://doi.org/10.15982/j.issn.2095-7777.2020.20200029
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    The high sensitivity cryogenic receiver is the important equipment to improve the measurement accuracy of the satellite tracking for Chinese Lunar Exploration Project. The low noise amplifiers of front end are cooled to 15 Kelvin. The equivalent noise temperature of cryogenic receiver is one order of magnitude lower than the traditional equipment working at room temperature， greatly improving the sensitivity of radio telescope. Several advanced technologies have been adopted to simultaneously realize highly sensitive dual-band observations on the same target，including S/X dual-band feed horn，cryogenic low noise amplifier based on HEMT，cryogenic polarizer and low temperature superconducting filter. The measured receive noise of S-band is 8 K in the frequency range 2.19～2.3 GHz，and the system noise is 53 K at zenith. The measured receiver noise of X-band is 13 K in the frequency range 8.2～9.0 GHz，and the system noise temperature is 32 K at zenith. The S/X cryogenic receivers have been applied successfully for VLBI satellite tracking in Chinese Lunar Exploration Project.
  • Topic：Very Long Baseline Interferometry Technology
    Real-Time Correlator Technologies of VLBI
    ZHENG Weimin, ZHANG Juan, XU Zhijun, LIU Lei, TONG Li, ZHANG Xiuzhong
    2020, 7(4): 354-361. https://doi.org/10.15982/j.issn.2095-7777.2020.20200027
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    Real-time correlator is the core facility of data processing center of China’s Lunar Exploration Project (CLEP) VLBI subsystem. Software and hardware ones are developed to ensure the successful tracking in all CLEP missions by the main and standby operation mode. The software correlator is a specially designed parallel computing program which runs on a high performance cluster server platform. The hardware one is a special high speed signal correlator based on a FPGA platform. They all adopt FX type structure，with real-time data receiving，decoding，correlation processing，phase correction signal extraction，real-time monitoring and other functions. When the accuracy of the prediction delay model is not enough，the correlator can reconstruct the delay model automatically by the special fringe search module and the processor is guided to complete the related processing of the detector signal. After engineering verification, the real-time data rate of the Lunar probe VLBI measurement orbit reached 512 Mbps.
  • Topic：Very Long Baseline Interferometry Technology
    Ionospheric TEC Correction for VLBI Based on GNSS Density Network
    ZHOU Weili, SONG Shuli, LI Peijia, ZHANG Zhibin, HUANG Chao, HUANG Yong, WANG Guangli
    2020, 7(4): 362-370. https://doi.org/10.15982/j.issn.2095-7777.2020.20200056
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    Very long baseline interferometry（VLBI）is one of the key technologies for orbit determination of Chang'-E satellites in China's lunar exploration project. Ionospheric delay is one of the main errors of VLBI orbit determination. The ionospheric delay correction method based on GNSS inversion is given，which is used in the Chinese VLBI Network. Because there are few stations of international GNSS service（IGS）in China，in order to meet the demand of lunar exploration，more stations are will be builtin China and a new global ionospheric correction model（SHAO）is constructed. Compared with the CODE model，the maximum difference of ionospheric delay Root Mean Square Error（RMSE）on CVN stations is 1.23 ns during the ionospheric quiescence. During the active period of the ionosphere，the maximum difference of the ionospheric delay RMSE on CVN station is 16.80 ns. When the ionosphere is active，the VLBI orbit determination residual based on the SHAO model increases from 6.07 ns to 3.33 ns in S1 band，9.10 ns to 7.07 ns in S2 band，0.70 ns to 0.60 ns in X0 band compared with CODE model.
  • Article
    Analysis and Selection of Landing Areas for Mars Mission
    WANG Yue, WANG Biao, WANG Xun, PAN Chenan, YAO Peiwen, LI Chenfan, LI Bo
    2020, 7(4): 371-383. https://doi.org/10.15982/j.issn.2095-7777.2020.20190708001
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    In this paper，based on the（Digital Elevation Model）data，remote sensing imagery and geological units，the priority landing areas were selected by combining the engineering constraints（terrain factors，ground bearing capacity，elevation and latitude）and scientific significance，and geological background of these priority landing areas was studied. Firstly，terrain factors（including slope and roughness）of the tentative sub-area were extracted derived from DEM data. And the areas meeting engineering constraints，which have lower slope（< 7.38°），roughness value（< 0.0096），stronger ground bearing capacity，elevation（< –2 km）and latitude（0～30°N），were selected. Then，based on the two research focuses of life and geology，the areas containing the scientific significance were chosen as the priority landing areas（a～h）. Among them，a and b priority landing areas are located in the Chryse Planitia，c～g priority landing areas are located in the Isidis Planitia and h priority landing area is located in the Nepenthes Planum. Finally，the geological backgrounds of the eight areas were studied，and three priority landing areas（e～g）were considered as the highest priority landing areas because of their flat terrain，location at the boundary of two geological units and detection of the distribution of hydrous minerals.
  • Article
    Analysis and Design of the Communication System for Multi-Probes Joint Lunar Polar Exploration
    LIU Shi, LI Jionghui
    2020, 7(4): 384-390. https://doi.org/10.15982/j.issn.2095-7777.2020.20191029001
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    The communication system is one of the important subsystems of a lunar polar explorer. Because of the significant differences compared to the missions in lower latitudes，the features and requirements of communication design need to be clarified for lunar polar soft-landing explorations for the multi-spacecraft mission to explore the polar region of the Moon. In this paper，the communication system architecture，communication environment conditions and data volume and other mission requirements are analyzed，and the lunar polar area communication system link architecture is designed. The scheme is based on a set of lunar relay communication network. The link structure composed of the lunar communication network realizes the reliability and scalability of the system through the mutual backup of heterogeneous links and multi-center nodes，taking into account the optimal allocation of resources in the system. It can provide guidance for the implementation of future lunar polar region exploration and communication technology projects，as well as future lunar polar region exploration and communication technology projects.
  • Article
    A Union Design Method of Trajectory and Guidance for Launch Vehicles Adapted to Multi-Target Orbits
    WANG Ying, TANG Mingliang, HAO Chuanchuan, ZHU Liangcon, FENG Jihang
    2020, 7(4): 391-398. https://doi.org/10.15982/j.issn.2095-7777.2020.20200038
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    With the increasing of multi-satellite network launch missions and increasing multiple window launch missions，a union design method of trajectory and guidance is proposed in this paper，which can adapt for multiple target orbits. In this innovate method，one theory trajectory for one target orbit is designed，making a hypothesis which the satellite’ sentry point position is maintained unchanging for other target orbits，and then the terminal guidance parameters with requirements of other orbits are generated，and lastly the target orbits are reached by iterative guidance. The simulation results indicate that relative to the traditional method，this method can greatly reduce the calculation amount while making little impact on carry capacity，and has strong adaptation for multiple target orbit missions. This method can also adapt for temporary slightly target orbit adjustment.
  • Article
    Analysis on Space Power Synthesis Performance of Deep Space Antenna Array
    ZHANG Xuwang, ZHANG Wenchan, MA Wenqi, CHEN Shaoqing, LIU Youyong
    2020, 7(4): 399-406. https://doi.org/10.15982/j.issn.2095-7777.2020.20200052
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    Deep space antenna array is one of the important measures to realize deep space exploration and communication with a very long distance. Based on the signal model of antenna array，the space power synthesis performance characeristics of the deep space antenna array are studied. The effects of time delay and phase compensation error of each antenna signal on the space power synthesis performance are analyzed，and the effects of formation of antenna array on the position and amplitude characteristics of grating lobes are studied. The simulation test results show that the grating lobes of the uniformly distributed square antenna array are evenly distributed and have a large amplitude. As the degree of non-uniform distribution of the antenna array increases, the grating lobes will become scattered and the amplitude will decrease, but the main lobe changes will not Not obvious. The grating lobes of the circular antenna array are scattered, while the main lobe and grating lobes of the L-shaped antenna array are both elliptical. It provides a certain reference for the design of deep space antenna array system.
  • Article
    Design of Wide Range Input and Output Beam Power Supply for Ion Electric Propulsion
    CHEN Changwen, WU Rong
    2020, 7(4): 407-416. https://doi.org/10.15982/j.issn.2095-7777.2020.20200051
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    The power processing unit（PPU）of ion electric propulsion system on the deep space detector needs to adapt to wide range voltage input，wide range voltage output and wide range power output，which results in the increase of component stress， volume and weight and decrease of efficiency of PPU. According to the requirements of grid power supply for ion electric propulsion PPU of small objects detector in China，the input voltage is 60 ~ 110 V，the output voltage is 420 ~ 1 260 V，and the output current is 0.3 ~ 2.1 A. In this paper, the design of grid power supply is studied from the aspects of power module decomposition，soft switching topology selection，single-stage power converter topology design and two-stage power converter topology design. A comprehensive optimization scheme in efficiency，volume and reliability is proposed. The physical verification of the design of single power module of grid power supply is carried out. The results show that the optimized module decomposition and fixed output voltage can effectively reduce the component stress，optimize the efficiency of the converter working point and improve the reliability of the converter；when using the single-stage phase shifted full bridge and full bridge LLC to design wide range input converters，there are still some problems，such as high stress of semiconductor power components，high capacitance stress，and difficult processing of magnetic components；the buck / boost + full bridge LLC two-stage topology scheme can simplify the stress of high-voltage rectifier circuit and adapt to wide range input. It is a preferred scheme for wide range input and output Beam power supply.