Table of Content

    15 May 2019, Volume 39 Issue 3 Previous Issue    Next Issue
    Global Space Weather Roadmap and Its Enlightenment to China
    LIU Siqing, LUO Bingxian
    2019, 39 (3):  275-282.  doi: 10.11728/cjss2019.03.275
    Abstract ( 2564 )   PDF (1571KB) ( 12039 )   Save

    With the development of technology, space weather has an increasingly impact on global technology infrastructure such as power systems, communication and navigation systems and aerospace assets. Humans need to strengthen their understanding of space weather events, improve space weather forecasting capabilities, and optimize infrastructure designs to mitigate the impact of space weather on society. Based on these requirements, the Committee on Space Research (COSPAR) of the International Council for Science (ICSU) and the International Living With a Star (ILWS) Steering Committee jointly established an expert group to study and develop a global road map for 2015-2025 on space weather. This paper introduces and interprets the roadmap and discusses the implications of the roadmap for the development of space weather in China.

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    Model and Impact Risk Assessment of Meteoroid for Marsormalsize
    LI Hao, KONG Xiangsen, ZHAO Chuan
    2019, 39 (3):  283-294.  doi: 10.11728/cjss2019.03.283
    Abstract ( 2694 )   PDF (3678KB) ( 14689 )   Save

    A Meteoroid is a small rocky or metallic body in the space. In the solar system, most meteoroids are fragments from comets or asteroids. In the space between Earth and Mars, the speed of meteoroid ranges from 24.13km·-1 to 42.2km·-1. The high speed meteoroid may cause catastrophic damage to Mars probes. In this paper, the meteoroid environment models for the flight from Earth to Mars and the flight in the near-Mars orbits are established respectively. The meteoroid environment models are established based on the zodiacal light observations by the space probes Helios I and Ⅱ, and the observed orbital parameters of comets. The assessment method of meteoroid impact risk for the Mars orbiter mission is also established using the finite element method. A Mars probe with relative anomalous shape is proposed, and the meteoroid impact risk of this assumed Mars probe is predicted for demonstration purpose.

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    Study on Geoeffectiveness of Interplanetary Coronal Mass Ejections by Support Vector Machine ormalsize
    YE Yudong, FENG Xueshang
    2019, 39 (3):  295-302.  doi: 10.11728/cjss2019.03.295
    Abstract ( 2521 )   PDF (1514KB) ( 15544 )   Save

    As arriving at the Earth, Interplanetary Coronal Mass Ejections (ICME) will interact with the Earth's magnetosphere and cause geomagnetic storms. The ICME event set is obtained by Richardson and Cane's Near Earth ICME list, and the input features are extracted based on interplanetary solar wind and magnetic data during ICME disturbance. A total of 483 ICME events from 1996 to 2006 are chosen in this study. 13 magnetic and kinetic features are finally selected for the training of the machine learning model. Rank of each feature's Fisher score indicates that the duration of the south-directed interplanetary magnetic field that is larger than 10nT and the increase of solar wind speed at the upstream shock or wave disturbance is closely related to the geoeffectiveness of ICME events, which is consistent with those former statistical results. The trained Radial Basis Function Support Vector Machine (RBF-SVM) can determine whether an ICME event could trigger moderate or stronger geomagnetic storms (Dst ≤ -50nT) effectively with an accuracy of 0.78±0.08. The results show that RBF-SVM can be used as a powerful tool in further analysis, and the better prediction of the geoeffectiveness of ICME will be obtained.

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    Transport Time for the Geomagnetic Storm Caused by CME
    MENG Chen, LU Jianyong, WANG Ming, GU Chunli, JI Haisheng
    2019, 39 (3):  303-309.  doi: 10.11728/cjss2019.03.303
    Abstract ( 2605 )   PDF (1660KB) ( 14577 )   Save

    The transport time is defined as the interval time between the occurrence of CME and the maximum value of the geomagnetic storm. In view of the 89 CME-Dst events collected from 1997 to 2015, the impact of CME speed, energy, and flare type on the transport time is analyzed. Using the non-linear fitting and the nonlinear regression of the Support Vector Machine (SVM), the Curve Fitting (CF) model and the Support Vector Machine (SVM) model for the CME transport time are built. In these models, 62 CME-Dst events during 1997-2006 are used as model input, and the remaining 27 CME-Dst events are used to test the model prediction. The results show that the prediction accuracies both of CF model and SVM model reach at about 85.2%, and the average absolute error of CF model is 13.77h while the SVM model is 13.88h. Comparing with the ECA model (its prediction accuracy is 77.8%, and the average absolute error is 14.55h), the accuracy of these two models is higher and the error is smaller than that of the ECA model. Therefore, CF model and SVM model can predict accurately the geomagnetic storm explosion with 1~5 days in advance.

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    Solar Wind Parameters and Auroral Hemispheric Power of Magnetic Storm during ICME
    LI Xiangyu, NIU Chao, XU Buyun, KANG Zhiqian, LIU Daizhi
    2019, 39 (3):  310-315.  doi: 10.11728/cjss2019.03.310
    Abstract ( 2459 )   PDF (3072KB) ( 14771 )   Save

    Based on three types of ICME-driven magnetic storms, including fierceness magnetic storm (SA type), strong magnetic storm (SB type) and delayed main phase storm (SC type) from 1995 to 2004, temporal superposition of the solar wind speed, the electric field EK-L, the interplanetary magnetic field and the auroral hemispheric power at the 1AU are conducted, and compared with the -vBz coupling function and the Newell coupling function respectively. The results show that there is a relative quiet period of the solar wind, auroral hemispheric power, interplanetary magnetic field and magnetic layer in the early stage of ICME arrival. However, the background solar wind speed, the southward component of the interplanetary magnetic field and the auroral hemispheric power of the SA magnetic storm are higher than those of the other two magnetic storm types. It indicates that the large coronal mass ejection has an effect on the interplanetary magnetic field, the background solar wind, and HP before the ICME arrives. After the rapid start of the magnetic storm, the low slope, delayed peak of the EK-L electric field of SC type magnetic storm and the northward component enhancement of the interplanetary magnetic field are the manifestations of the main phase delay of the magnetic storm.

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    Prediction of High-energy Electron Flux of Geosynchronous Orbit Based on Empirical Mode Decomposition
    QIAN Yedong, ZHANG Hua, YANG Jianwei, WU Yewen
    2019, 39 (3):  316-325.  doi: 10.11728/cjss2019.03.316
    Abstract ( 2774 )   PDF (2941KB) ( 14580 )   Save

    During the recovery of a magnetic storm, the relativistic electrons with MeV energy diffuse from the outer radiation belt to geosynchronous orbit. The electrons which energy are larger than 2MeV could penetrate the surface of satellites and accumulate inside them. Such an electron flux effect could cause satellites to be unable to function properly or to fail completely. Relativistic electrons change very rapidly during the magnetic storm and are very non-stationary. These effects are reduced by empirical mode decomposition method. Data in 2008-2009 are used as the training set, and data in 2010-2013 are used as the testing set. The result shows that the average prediction efficiency of the testing set is 0.81. The solar activity is complex in 2013, and the prediction efficiency is up to 0.81. The prediction efficiency of electron flux has been greatly improved by using empirical decomposition method.

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    Analysis of Stratospheric Gravity Wave Parameters Based on COSMIC Observationsormalsize
    WANG Yizhou, HUANG Yingying, LI Huijun, LI Chongyin
    2019, 39 (3):  326-341.  doi: 10.11728/cjss2019.03.326
    Abstract ( 2593 )   PDF (10967KB) ( 12108 )   Save

    Using the temperature profiles between 30°N and 40°N latitude observed by COSMIC satellites from 29 December 2006 to 3 January 2008, the disturbances and potential energy (Ep) of Gravity Waves (GWs) in lower stratosphere are calculated by vertical running windows method, double-filter method and single-filter method, respectively. The altitude and longitude distributions, and multi-time scale variations of these parameters are obtained. The spatial characteristics of background temperature and horizontal wind fields are analyzed to investigate the possible origins of GWs. The disturbances and potential energy (Ep) of GWs in lower stratosphere obtained by the above three methods are compared. The results are as follows. The errors of GW perturbations calculated by vertical running windows method are relatively large, because it can only remove the disturbances with large vertical scales, while can not remove small vertical scales in derived GW disturbances. The double-filter can well suppress both large-scale background and small-scale disturbances in temperature profiles. GW disturbances obtained by a single-filter does not include large vertical scale background, but still contain some small vertical scale disturbances. The double-filter method cannot obtain altitude variations of Ep, while the single-filter method can give altitude variations of monthly averaged Ep. The relationships between GWs' parameters (including disturbances and Ep) and background temperature and horizontal wind fields are revealed.

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    A Model for Real-time Calculation of the Atmospheric Neutronormalsize
    CHEN Shanqiang, LIU Siqing, CHEN Dong, LIN Ruilin, SHI Liqin, CAO Yong
    2019, 39 (3):  342-348.  doi: 10.11728/cjss2019.03.342
    Abstract ( 2684 )   PDF (4015KB) ( 13154 )   Save

    In order to evaluate the global distribution of atmospheric neutron at 0~100km altitude for real time, the propagation of cosmic rays in the geomagnetic field and the atmosphere is analyzed. By using the TSY05 and MAGNETOCOSMICS model, the real-time calculation of global geomagnetic cut-off rigidities with 1h resolution is realized. The spherical shell geometry model is established at intervals of 1km using NLRMSISE-00 model, and the spectrum distribution of secondary particles generated by different particles is calculated by the Monte Carlo simulation techniques, namely, the Geant4 toolkit, then an atmospheric neutron database is created. Compared with EXPACS model, the validity and reliability of the database are verified. Based on the observed or predicted space environment parameters, the energy spectra of the cosmic ray and the solar proton event in the synchronous orbit are calculated, and the effective vertical cut-off rigidities in function of latitude and longitude at the altitude of 100km. The atmospheric neutron and effective dose are calculated by using linear interpolation per hour.

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    Principle and Accuracy Problems of Gravitational Redshift Experiments in Space
    ZHANG Yuanzhong
    2019, 39 (3):  349-353.  doi: 10.11728/cjss2019.03.349
    Abstract ( 2711 )   PDF (1177KB) ( 14517 )   Save

    In this paper, the problems about the principle and accuracy in the experiments of space gravitational redshift are analyzed. Firstly, according to Einstein Equivalent Principle (inertial force is equivalent to gravity), the main part of Earth's gravity inside the spacecraft is cancelled out by inertial force, so that the microgravity inside the spacecraft is much smaller than the gravity at its orbit. For this reason, the gravitational potential of the space borne clock should be taken as an effective gravitational potential corresponding to the microgravity. However, in Ref.[4] (GP-A experiment) and Ref.[5] (Radio astron satellite program), the gravitational potential of the clock is simply taken as the gravitational potential at the orbit. Secondly, testing the relativistic redshift requires a comparison between theoretical prediction and experimental measurement. The accuracy of this test is determined by the larger error. Therefore, if improving just the experimental precision but not the accuracy of the Earth Gravitational Model, then the test accuracy cannot be improved.

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    Demonstration and Analysis of LEO Real-time Kinematic Precise Orbit Determination with Priori Orbit Constraint ormalsize
    SHI Yishuai, HAO Jinming, JIAO Wenhai, DONG Ming, JIAO Bo, LIU Weiping
    2019, 39 (3):  354-364.  doi: 10.11728/cjss2019.03.354
    Abstract ( 2602 )   PDF (3116KB) ( 10758 )   Save

    Real-Time Precise Orbit Determination (RTPOD) of Low-Earth-Orbit (LEO) satellites can greatly expand their ability to perform complex scientific missions, such as real-time environment monitoring, maneuver control and satellite autonomous navigation. In this paper, the model of real-time kinematic precise orbit determination is introduced. We present a conception that the LEO Priori Orbit Constraint (POC) is used in the process of RTPOD for the sake of improving the accuracy, convergence speed and stability. The broadcast ephemeris, predicted part of ultra-rapid ephemeris and real-time precise ephemeris are adopted respectively to propose 6 different RTPOD solutions, which are then demonstrated and analyzed using the observations from Swarm A/B/C satellites during 7 days. The results show that the accuracy is improved in turn by using broadcast ephemeris, IGU and IGC ephemeris. Moreover, adding POC can further enhance the result while using the same ephemeris. The IGC+POC solution using the priori orbit with a 1m standard deviation reaches an accuracy of 6.12cm, 5.55cm and 4.98cm in the radial, along and cross component, respectively, which is comparable to the post-processing kinematic POD. Analyses based on different priori orbits indicate that the ideal priori orbit should appear less noise and long-term systematic biases, and short-term systematic biases show little influence on constraint results. Furthermore, adding POC can remarkably speed up the convergence. The convergence of IGC solution needs about 31min on average, whereas the average convergence time after adding POC with a 1m standard deviation is about only 4min, which is beneficial to the fast re-convergence after the occurrences of cycle slip, loss of lock and communication link interruption, and is of great significance in practical application scenarios.

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    Orbit Determination for Geostationary Earth Orbit Targets Based on the CCD Drift-scan Photoelectric Telescope at One Single Stationormalsize
    YU Yong, LUO Hao, MAO Yindun, ZHAO Xiaofen, TANG Zhenghong
    2019, 39 (3):  365-372.  doi: 10.11728/cjss2019.03.365
    Abstract ( 2285 )   PDF (2733KB) ( 14282 )   Save

    As a passive measurement method, the ground-based photoelectric observation is not limited by the equipment on the satellite and can be used to measure most of Geostationary Earth Orbit (GEO) targets above the station. The ground-based photoelectric observation has the advantages of low operating cost, strong intuition and high measurement precision, hence it can play an important role in monitoring the GEO targets. In order to evaluate the actual monitoring ability for GEO targets based on the photoelectric telescope at one single station, observation experiments of 3 Beidou GEO satellites are carried out by 1.56-meter telescope with CCD drift-scan photoelectric technology of Shanghai Astronomical Observatory. The external precisions are estimated by the precise ephemeris of the satellites. The results show that the accuracy of the celestial positioning of the GEO satellites is better than 0.3" in both azimuth and elevation. In the case of single observation pass, although the accuracy of orbit prediction is low, the orbit determination accuracy during observation arc is better than 100m. The effect of orbit improvement based on multi-pass of observations is obvious. In the absence of orbit control, the orbit determination accuracy is better than 50m, and the prediction precision of extrapolating to 4-day is about the order of hundreds of meters. In addition, the accuracy of the orbit prediction of the GEO target in the case of different observation time span is quantitatively evaluated, which can provide the reference for the practical application of the CCD drift-scan photoelectric telescope at one single station.

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    Design of VHF System Spaceborne SVOMormalsize
    LIU Yang, WU Hao, YU Xianyong, LI Zongde, DAI Yuanyuan
    2019, 39 (3):  373-380.  doi: 10.11728/cjss2019.03.373
    Abstract ( 2558 )   PDF (3360KB) ( 15709 )   Save

    The on-board VHF system is an important part of the SVOM satellite. It provides a quasi-real-time VHF-band information access channel for the location information and the important data of the scientific target which is detected by payloads. In this paper, the design of VHF system on-board SVOM is introduced. The equipment design, software design and modulation algorithm design are described in detail. SVOM VHF system is the first application of 4CPFSK modulation in VHF band for spaceborne data transmission in China. Test results show that the implementation of the VHF system can meet the application requirements of the satellites and provides a solution for the real-time transmission of important data of space science satellites.

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    Method of Temperature Control and Its Validation for Atomic Clock Cabin on Navigation Satellite
    LIN Shifeng, LI Kai, JIANG Guizhong, WU Jian, MA Errui
    2019, 39 (3):  381-387.  doi: 10.11728/cjss2019.03.381
    Abstract ( 2520 )   PDF (2788KB) ( 14455 )   Save

    Atomic clock, as an important part of the navigation satellite, provides high-accuracy and high-stability time frequency source for the satellite. For the continuity and stability of atomic clock operation in orbit, the satellite thermal control system should provide a suitable temperature environment for it. In this paper the thermal control design and the control algorithm of atomic clock are introduced, and the results of thermal simulation and tests based on the atomic clock thermal control for the navigation satellite are provided. Temperature data in orbit show that the thermal design of cabin for atomic clock is suitable. Thermal simulation results and the tests are effective. In addition, the temperature of atomic clocks in orbit meets the requirement and is nearly one order of magnitude better than that of the indicator.

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    Life Prediction and Analysis of Momentum Wheel Based on Wiener Process Degradation Modelingormalsize
    XU Jingbo, TAN Xueqian, WU Zhen, SUN Danfeng, JIANG Ningxiang, SUN Dan
    2019, 39 (3):  388-398.  doi: 10.11728/cjss2019.03.388
    Abstract ( 2630 )   PDF (1863KB) ( 13171 )   Save

    Momentum wheel as a key actuator for satellites, its reliability and life span directly affect the success or failure of satellite missions in orbit. For the life prediction and analysis of momentum wheel products, due to the limited number of samples, long test cycle and high cost, it is impossible to obtain enough life sample data. Therefore, combined with engineering experience and existing ground life test data, the Wiener process degradation model is used to model the reliability of the momentum wheel product, and its life expectancy is estimated and analyzed. The results show that this model provides an effective method for predicting the life of a momentum wheel and is suitable for life prediction and analysis of high reliability, long life products.

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    Finite Time Control of Space Robot with Elastic Base and Flexible Arms
    HUANG Xiaoqin, CHEN Li
    2019, 39 (3):  399-406.  doi: 10.11728/cjss2019.03.399
    Abstract ( 2531 )   PDF (2124KB) ( 15977 )   Save

    Based on the finite time control, the trajectory tracking and flexible vibration suppression of a free-floating space robot system with two flexible arms and elastic base are discussed. Because of the multiple dynamic coupling relationship between the elastic base and the two flexible arms, the system is a highly nonlinear system. Firstly, the connection between the elastic base and the first arm is regarded as a linear spring, and the dynamic model of the system is derived from the Lagrange equation of the second kind and the assumed mode method. Secondly, by applying the two time-scale assumptions of singular perturbation theory, the system is decomposed into a slow subsystem which represents the rigid motion and a fast subsystem which represents the elastic base and two arms vibration. For the slow subsystem, a finite-time controller based on the nominal model is designed to realize the rigid desired trajectory tracking. Due to the finite time convergence property of the integral sliding mode surface, it has faster convergence speed and stronger robustness than the traditional asymptotic convergence control method. For the fast subsystem, the linear quadratic optimal control method is adopted to suppress the vibration of the elastic base and the two flexible arms simultaneously. Lyapunov theory is used to prove that the proposed control algorithm can enable the tracking error converging to the origin within a finite time. Finally, the simulations verify the effectiveness of the control method.

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