Table of Content

    15 March 2011, Volume 31 Issue 2 Previous Issue    Next Issue
    Theories and Simulations in Substorm Research: A Review
    R. A. Wolf
    2011, 31 (2):  125-149.  doi: 10.11728/cjss2011.02.125
    Abstract ( 2212 )   PDF (1177KB) ( 1655 )   Save
    Both theory and simulation have played important roles in defining and illuminating the key mechanisms involved in substorms. Basic theories of magnetic reconnection and of interchange and ballooning instabilities were developed more than 50 years ago, and these plasma physical concepts have been central in discussions of substorm physics. A vast amount of research on reconnection, including both theoretical and computational studies, has helped provide a picture of how reconnection operates in the collisionless environment of the magnetosphere. Still, however, we do not fully understand how key microscale processes and large-scale dynamics work together to determine the location and rate of reconnection. While in the last twenty years, it has become clear that interchange processes are important for transporting plasma through the plasma sheet in the form of bursty bulk flows and substorm expansions, we still have not reached the point where simulations are able to realistically and defensibly represent all of the important aspects of the phenomenon. More than two decades ago it was suggested that the ballooning instability, the basic theory for which dates from the 1950s, may play an important role in substorms. Now the majority of experts agree that regions of the plasma sheet are often linearly unstable to ideal-MHD ballooning. However, it is also clear that kinetic effects introduce important modifications to the MHD stability criterion. It is still uncertain whether ballooning plays a leading role in substorms or has just a minor part. Among the different types of simulations that have been applied to the substorm problem, global MHD codes are unique in that, in a sense, they represent the entire global substorm phenomenon, including coupling to the solar wind and ionosphere, and the important mechanisms of reconnection, interchange, and ballooning. However, they have not yet progressed to the point where they can accurately represent the whole phenomenon, because grid-resolution problems limit the accuracy with which they can solve the equations of ideal MHD and the coupling to the ionosphere, and they cannot accurately represent small-scale processes that violate ideal MHD.
    Related Articles | Metrics
    A revisit of the phobos events
    Wing-Huen Ip
    2011, 31 (2):  150-153.  doi: 10.11728/cjss2011.02.150
    Abstract ( 2416 )   PDF (147KB) ( 1325 )   Save
    The magnetic field disturbances detected by the Phobos-2 spacecraft in 1989 have been suggested to be caused by a ring of dust and/or gas emitted from the Martian moon, Phobos. The physical nature of these ``Phobos events'' is examined using results from related investigations over the last twenty years. It is concluded that there is no clear evidence at present to support the association of magnetic field disturbances in the solar wind with Phobos. The situation will be further clarified taking advantage of the multi-spacecraft observations of the Yinghuo-1(YH-1), Mars Express and MAVEN missions beginning in 2012. It is expected that many novel features of solar wind interaction with Phobos (and possibly also Deimos) itself will also be revealed.
    Related Articles | Metrics
    Forward Modeling Method of CME and Discussion About the Projection Modified Method
    Gui Bin;Shen Chenglong;Wang Yuming;Ye Pinzhong Wang shui
    2011, 31 (2):  154-164.  doi: 10.11728/cjss2011.02.154
    Abstract ( 2192 )   PDF (686KB) ( 964 )   Save
    In this paper, the three-dimension velocity of 21 well-structured Corona Mass Ejections (CMEs) were obtained by Forward Modeling based on STEREO-SECCHI observations during 2007---2008. By measuring the height of the projected front in STEREO-A and STEREO-B sky plane and using the projection modified method, modified velocities of these CME, which were treated as 3D velocity before, were also obtained. Comparing the 3D velocity obtained from the Forward Modeling method and the modified velocity, it is found that the 3D velocity and the modified velocity are almost the same when angular distance, which is defined as the angle between the line connecting CME source region and Sun center and the line connecting observer and Sun center, is greater than 50º; that when the angular distance is less than 50º, the difference is obvious. The latter result shows that the modified method can not be used for the CMEs with angular distance less than 50º. It is found that the projected velocity is almost the same as the 3D velocity when the angular distance is greater than 65º. This result implies that the CME event with angular distance larger than 65º could be treated as a limb event.
    Related Articles | Metrics
    Simulation of Electrons' Trajectories in the Lunar Electric and Magnetic Field
    Feng Yongyong;Zhao Hua;Liu Zhenxing
    2011, 31 (2):  165-169.  doi: 10.11728/cjss2011.02.165
    Abstract ( 2023 )   PDF (592KB) ( 1348 )   Save
    The increasing interest in lunar exploration requires a better understanding of environment at the lunar surface. Like any object in plasma, the surface of the Moon charges to an electric potential that minimizes the total incident current. Surface charging is an universal process affecting all airless regolith-covered bodies. However, there are still many details that remain unclear and need to be discussed to understand those possible processes such as ion sputtering and electrically-driven dust transport. There are also many subjects that require further study, such as the temporal and spatial variation of lunar surface charging. Simulation and analysis of trajectories of the electrons under different conditions would help to predict surface potential, which in turn would benefit the understanding of the lunar environment. In this paper, the solar wind electrons which are moving toward the moon surface are traced to study the effect of surface potential on solar wind electrons reflected by the lunar crustal magnetic field. Statistic of number of electrons that reflected under different conditions is also analyzed. The calculations and simulations show that the variation of either magnetic field or potential difference does play an important role in the changing traces of electrons. Furthermore, the changes by the variations could be told from analysis of the results. Thus, the magnitude of crustal field and potential could be inferred from the data of instrument of LP (Lunar Prospector satellite). New devices could also be designed or developed in the coming lunar projects. Surface potentials are not always present on the Moon, so we could collect and analyze data under different conditions and thus obtain more precise results. However, there is one more important circumstance needed to be considered that the craft would be charged in the lunar environment. How to eliminate the influence of charged craft and get a more precise result are important problems for us to explore in the future.
    Related Articles | Metrics
    Research of Geospace Magnetic Field Response to the Solar Wind Disturbances
    Ding Liuguan;Jiang Yong;Xu Fei
    2011, 31 (2):  170-175.  doi: 10.11728/cjss2011.02.170
    Abstract ( 2391 )   PDF (510KB) ( 1280 )   Save
    The goespace magnetic field response to the solar wind disturbances including interplanetary shocks, solar wind dynamic pressure increase and decrease is analyzed comparatively. The geosynchronous magnetic field has positive response to all the disturbances strongly near the noon meridian, and has positive response in the nightside of the magnetosphere weakly. However negative responses were sometimes observed in the nightside. From our results, the geomagnetic index SYM-H always shows positive response to the disturbances of solar wind. The amplitude of geosynchronous response d Bz could be determined by the square root of the solar wind dynamic pressure near the noon meridian with good correlation the same as the geomagnetic indices. The d Bz at the geosynchronous orbit near local noon and the amplitude of sudden impulses (dSYM-H) on the ground are highly correlated under the circumstances action of IP shock or solar wind dynamic pressure increase, differentiating from the dynamic pressure decrease distinctly. It is shown that the IP shocks have some commonness with the solar wind dynamic pressure increase in affecting on the geospace magnetic field.
    Related Articles | Metrics
    Prediction of Relativistic Electron Flux at Geosynchronous Orbit Based on Magnetic Field
    Rui Lei;;Yu Peng;Zhao Hua
    2011, 31 (2):  176-181.  doi: 10.11728/cjss2011.02.176
    Abstract ( 2336 )   PDF (520KB) ( 1008 )   Save
    There is a good correlation between the relativistic electron flux and the P-component (perpendicular to the orbit plane and points northward) of magnetic field at geosynchronous orbit, and more importantly, the later happened 1~2 day earlier than the former. So the relativistic electron flux can be forecasted by the magnetic field measurement onboard. Firstly, the physical mechanisms possibly governing the correlation have been analyzed in this paper. Secondly, by analyzing the data of GOES11 (an geosynchronous orbit satellite which longitude is 135ºW), the best advanced time and linear correlation will be found out. Finally, a quantitative prediction model is developed. The outputs are hourly-averaged flux on four typical time periods 24 hours later. These four typical time periods are: midnight (23:31 LT---00:30 LT), morning (05:31 LT---06:30 LT), noon (11:31 LT---12:30 LT), evening (17:31 LT---18:30 LT) of local time. The relativistic flux of model has two energy spectrums which are >0.6 MeV and >2 MeV. The model Prediction Efficiency (PE) is about 0.7. This prediction model is of great application to synchronous satellites.
    Related Articles | Metrics
    Index Forecasting Method Based on Neural Network Techniques
    Chen Chun;Sun Shuji;Xu Zhengwen;Zhao Zhenwei;Wu Zhensen
    2011, 31 (2):  182-186.  doi: 10.11728/cjss2011.02.182
    Abstract ( 1938 )   PDF (503KB) ( 988 )   Save
    Magnetic storm has always been one of the key issues of solar-terrestrial space physics for the past half century. The Dst index is the longitudinally averaged magnetic field depression at low latitudes. It is the primary measure of the magnitude of magnetic storms, and provides a convenient way to monitor the magnetospheric ring current. By using artificial neural network and considering the effects of the period of the geomagnetic activity, this paper brought out a method of forecasting Dst index, an hour in advance. The inputs of the network include time, season, Dst index and the first difference and the second difference of Dst index, the mean value of 27 days ago at t time, and the output is the observed Dst index data at next time. The trained net then can forecast Dst index 1 h ahead. Some examples are presented by using the Dst index data in 1985, 1986, 1990, 1991, respectively. The results indicate that the predicted Dst index has good agreement with observed data and the corresponding root mean errors of the model comparing with the measurement were 4.00 nT, 3.72 nT, 5.35 nT and 6.82 nT, respectively. In addition, the error analysis indicates that the predicted root-mean-square error of Dst index is smaller in low solar activities than in high solar activities.
    Related Articles | Metrics
    Variations of Ionospheric Parameters During the Total Solar Eclipse on 22 July 2009
    Ding Zonghua;Sun Shuji;Chen Chun;Li Na;Xu Zhengwen
    2011, 31 (2):  187-193.  doi: 10.11728/cjss2011.02.187
    Abstract ( 2028 )   PDF (656KB) ( 1033 )   Save
    The variations of ionospheric parameters including fmin, f0F2 and TEC during the total solar eclipse of 22 July 2009 are investigated. The results show that the fmin drops quickly after the eclipse commencement and then gradually restores to the normal value. The f0F2 and TEC decrease greatly during the eclipse maximum. These phenomena are probably caused by the fact that the solar electromagnetic radiation decrease sharply during the solar eclipse. The f0F2 and TEC show some positive disturbance which is more notable near to the equatorial abnormal crest region on about 5~6 hours and some negative disturbance on about 9~10 hours after this eclipse. Combining the analysis of the solar and geomagnetic activity, we think that it seems difficult to further investigate the eclipse ionospheric effect since the space weather events including magnetic storm and electric field penetration are accompanying this event.
    Related Articles | Metrics
    Penetration characteristics of VLF wave from atmosphere into the lower ionosphere
    Zhao Shufan;Sheng Xuhui;Pan Weiyan;Zhang Xuemin
    2011, 31 (2):  194-200.  doi: 10.11728/cjss2011.02.194
    Abstract ( 2340 )   PDF (557KB) ( 1226 )   Save
    Many papers have indicated that earthquake happens associated with a width frequency band of VLF (Very Low Frequency), ULF (Ultra Low Frequency), ELF (Extremely Low Frequency) electromagnetic radiation, which have been recorded by satellites in the ionosphere and low magnetosphere. In this paper, the reflection and transmission coefficient of the homogeneous half-space ionosphere has been calculated using propagation matrix method. Simultaneously the Booker quartic equation is solved to get the refractive index in the ionosphere. The analysis of the factors which influence the reflection and transmission coefficient of the ionosphere and the propagation characteristics in the ionosphere of VLF wave have been performed, such as wave frequency, incident angle, geomagnetic inclination, electron density and collision frequency in the ionosphere to provide fundamental basis for further studies on numerical calculation of propagation of ULF/VLF waves in the stratified ionosphere and support the study of seismo-ionosphere coupling mechanism. The results show that it is easier for the TE (Traverse Electric) wave radiated by vertical electric dipole to penetrate into the ionosphere, but the TM (Traverse Magnetic) wave radiated by horizontal electric dipole is reflected again and again in the ground-ionosphere waveguide. It is easier to observe the VLF wave anomaly when the electron density is lower or at the high-latitude region. The O wave experiences severer attenuation than X wave, so X wave is a penetration mode whereas O wave is a non penetration mode in the ionosphere. The attenuation of the two characteristic wave decrease as the decrease of the angle between the geomagnetic field and wave vector, that is to say the attenuation is the smallest when longitudinal propagation. When the geomagnetic field is considered, the ULF/VLF wave related with earthquake can penetrate into the ionosphere which is confirmed by the satellite observation. But the further physical mechanism will be delved in the future.
    Related Articles | Metrics
    New Hybrid Method for High Resolution TEC Measurement With the Tri-band Beacon
    Zhao Haisheng;Xu Zhengwen;Wu Jian;Wang Zhange; Liu Kun;Li Na;Chen Jinsong
    2011, 31 (2):  201-207.  doi: 10.11728/cjss2011.02.201
    Abstract ( 2046 )   PDF (684KB) ( 1262 )   Save
    The ionospheric Total Electron Content (TEC) is one of the key parameters of ionospheric sounding results. As the main input parameter, the measurement precision of TEC will directly affect the Computer ionospheric Tomography (CT) imaging result. In the past, the dual-band technique was mainly used for TEC measurement. However, due to the solution of the phase integral constant and error of the system hardware delay, the TEC results cannot satisfy the high accuracy requirement of reconstruction imaging by using the ionospheric CT. The newly developed tri-band technique throws new light on the space-based ionospheric sounding techniques. A new method is proposed for inversing TEC on the basis of combining the propagation delay and phase with the tri-band beacon. By using the fusion of advantages of both detecting random electron density fluctuations and computing phase integral constants with the tri-band beacon, it further improves the measuring resolution of the ionospheric TEC. Simulation results show that the CT resolution is improved by using the three-frequency measurement based on this method.
    Related Articles | Metrics
    Analysis of Properties for Radiowave Polarization Plane Rotation
    Zhao Hongmei;Jiang Changyin;Wang Jian
    2011, 31 (2):  208-213.  doi: 10.11728/cjss2011.02.208
    Abstract ( 1954 )   PDF (708KB) ( 977 )   Save
    The radiowave polarization plane rotation is caused by the ionospheric dispersion and the double refraction. Begin with the ionosphere refraction index, the formula of radiaowave polarization plane rotation angle is derived in this paper. Using the measured electron density, magnetic induction intensity module of geomagnetic field, and magnetic obliquity profiles, the radiaowave polarization plane rotation angle is simulated for fixed height carrier under different angles between antenna side-view and earth normal, different regions, different frequency bands, different time slots, and different solar activity cases, which is described by column diagraphs and tables. The simulation results and the rules and properties of radiowave polarization plane rotation angle are analyzed and summarized in its seasonal, temporal, regional, frequency-domain aspects. (1) The rotation angle will decrease as the frequency arises, and will increase as the angle between antenna side-view and earth normal arises. (2) The rotation angle will increase as the sun polar activity arises, larger in the day and smaller at night. (3) At night, the rotation angle in summer is the largest and in winter is the smallest as in high and middle latitude, larger in spring and autumn and smaller in summer and winter as in low latitude. (4) In the day, the rotation angle in winter and spring is larger that in summer and autumn as in high latitude, larger in spring and autumn and smaller in summer and autumn.
    Related Articles | Metrics
    Boundedness of Formation Configuration for Nonlinear Three-body Dynamics
    LI Peng;SONG Yongduan
    2011, 31 (2):  214-222.  doi: 10.11728/cjss2011.02.214
    Abstract ( 1940 )   PDF (281KB) ( 1115 )   Save
    The configuration boundedness of the three-body model dynamics is studied for Sun-Earth formation flying missions. The three-body formation flying model is built up with considering the lunar gravitational acceleration and solar radiation pressure. Because traditional linearized dynamics based method has relatively lower accuracy, a modified nonlinear formation configuration analysis method is proposed in this paper. Comparative studies are carried out from three aspects, i.e., natural formation configuration with arbitrary departure time, initialization time and formation configuration boundedness, and specific initialization time for bounded formation configuration. Simulations demonstrate the differences between the two schemes, and indicate that the nonlinear dynamic method reduces the error caused by the model linearization and disturbance approximation, and thus provides higher accuracy for boundedness analysis, which is of value to initial parameters selection for natural three-body formation flying.
    Related Articles | Metrics
    ew Method to Analyse the Orbital Abnormal of LEO Satellite Using TLE Data
    Yang Xu;Liu Jing;Wu Xiangbin;Wang Ronglan;Yu Youcheng;Wang Rendong;Zhang Yao;Li Dawei
    2011, 31 (2):  223-228.  doi: 10.11728/cjss2011.02.223
    Abstract ( 2620 )   PDF (487KB) ( 1145 )   Save
    Finding the orbital abnormal of orbiting satellite accurately and in time has great meanings. The presented method can find the orbital abnormal of debris or spacecraft effectively, which provide data supports to analyse and verify the collision event computed by space debris collision avoidance system. The orbital abnormal also includes the orbit maneuver and other orbit change. This paper discussed how to analyse the orbital abnormal of LEO satellites using TLE data. Then, a method of using the satellite adjacent elements plus compositive criterion are presented. The basic idea of compositive criterion method is to get each sub criterion and turnover rate using a certain period data of satellites, and each satellite has its own criterion instead of using an settled criterion to all satellites. Analysis showed that compared to using a single element threshold method, the compositive criterion method decreases the missing discrimination and also has a high accuracy of right discrimination. This paper also briefly analyzed other kinds of orbit using the same method.
    Related Articles | Metrics
    Gyro Fault Diagnosis Algorithm Based on Vector Observation
    Hu Di;Dong Yunfeng
    2011, 31 (2):  229-235.  doi: 10.11728/cjss2011.02.229
    Abstract ( 2110 )   PDF (598KB) ( 964 )   Save
    Using reaction wheels to control the attitude and thrusters for station-keeping, the satellite's inertial may be changed. A vector observation algorithm based on kinematics applied to the gyro fault diagnosis is presented in the paper. Using the Generalized Rodrigues Parameters (GRPs) to describe the satellite's attitude may avoid that the mode of quaternion is not equal to one. Using quaternion to compute the satellite's kinematics can also avoid the GRPs' complex integral. Both small change and slow decrease of angular velocity range is simulated when gyro's rapid and slow change faults occur. The result shows that the algorithm can estimate body's angular velocity effectively and diagnose the gyro fault accurately under the two situations above. The algorithm is not affected by body's inertial and control torque with a smaller amount of calculation, and have a potential value to the engineering application.
    Related Articles | Metrics
    Study of Ionosphere Using GPS Data and its Application to Analysis About Earthquake
    Xing Nan;Wang Xiaoya;Hu Xiaogong
    2011, 31 (2):  236-245.  doi: 10.11728/cjss2011.02.236
    Abstract ( 2182 )   PDF (1023KB) ( 1105 )   Save
    To obtain VTEC as well as DCB, a method is developed by using ground-based GPS data with multiple-arc method and Kriging interpolation. Assisted by multiple-arc method, VTEC was calculated every 30 minutes as local variables, and DCB was calculated every day as global variables. Kriging method, taking the spatial information of VTEC into account, helps us to establish a 2D model and get DCB of both satellites and receivers. The result shows itself reliably in comparison with IGS result, but more stable and precise in resolution. Meanwhile, grounded on 3-variable spline basis function, we unfold electron density into a linear combination of a set of grid point. With its contribution, CT result of ionospheric electron density was made by MART. This result is consistent with CHAMP result get by occultation method. These two ways are applied to the data of Yangtze River triangle region in May, 2008 when the shocking earthquake happened in Wenchuan. A simple statistic analysis reveals the response of ionosphere to the signal associated with earthquake but occurred before it.
    Related Articles | Metrics
    Inter-satellite Real-time Relative Positioning Method Based on Augmented
    Liu Yang;Xu Yu
    2011, 31 (2):  246-253.  doi: 10.11728/cjss2011.02.246
    Abstract ( 2038 )   PDF (625KB) ( 996 )   Save
    The real-time inter-satellite relative positioning method based on augmented GPS can achieve the level of centimeter in case of having the orbit dynamic model. In view of its difficulty of full-filing the high-precision requirement of orbit dynamic model currently, this paper proposes a new high-precision real-time relative positioning method which uses tripe-difference functions of GPS to get the time transform matrix of state vector, then uses UKF (Unsented Kalman Filter) to estimate the inter-satellite real-time relative positions. Simulation results show that comparing the precision of decimeter level of the relative positioning using the usual sequent point estimation method, the new method can achieve the relative positioning precision of centimeter level when the inter-satellite distance is less than five kilometers.
    Related Articles | Metrics
    Motion Equation of Satellite in XNAV
    Fei Baojun;Pan Gaotian;Xiao Yu;Han Chunhao
    2011, 31 (2):  254-259.  doi: 10.11728/cjss2011.02.254
    Abstract ( 2176 )   PDF (484KB) ( 1272 )   Save
    In X-ray pulsar-based navigation model for satellite autonomous position determination, whether in theory or in view of measurement precision, the equations of time-of-arrival measurement and satellite's motion, observation equation and state equation must all base on same reference system. In the solar system Barycentric Reference Systems (BCRS), that is an inertial frame in DSX system, current time measurement equation can be used, but the perturbing acceleration of satellite consists not only the multipole of Earth, gravitation perturbation of Sun and Moon and radiation pressure of Sun, but also relativistic effect. Because the satellite's position error caused by relativistic effect is about 10 meter in quantity order. In the Geocentric Reference Systems (GCRS), that is a non-inertial frame, the relativistic effect term can be neglected in the motion equation of satellite. Because the error caused by this effect is about 10 centimeter. But time measurement equation in BCRS must transform to GCRS. As a result of the above, the navigation model can be more precision and complete.
    Related Articles | Metrics
    Design for Fuzzy Variable Structure Controller of Hybrid Position and Force Control for Dual-arm Coordinated Space Robot Systems
    Chen Zhihuang;Chen Li
    2011, 31 (2):  260-268.  doi: 10.11728/cjss2011.02.260
    Abstract ( 2320 )   PDF (718KB) ( 2382 )   Save
    A kind of nonlinear dynamics model of free-floating dual-arm space robot system is based on Lagrange method, and the dynamics model of object is presented based on Newton-Euler method. Based on the results and closed kinematic chain constraints, the dynamics model of synthetical system is obtained, and the control problems for object to track the desired trajectory in workspace and adjustment of interactive forces due to the interaction between the object and the end-effectors are discussed. Because of the high complexity of structure and the uncertainty of parameter of such systems, the scheme of variable structure global sliding-mode control with better robustness to uncertainty and disturbance is proposed to track the desired trajectory of object, and the corresponded scheme of internal forces control is proposed synchronously. Therefore, the object position and internal forces can be regulated simultaneously. A fuzzy controller is designed to reduce shiver due to the inherent defect of sliding-mode control and ensure rapid response. The fuzzy controller can tune the sliding-mode control law parameters automatically according to the relationship between the system state and switch surface. The effect of the controllers is testified by computer simulation.
    Related Articles | Metrics