空间科学学报

2006 Vol. 26, No. 1

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A 3rd Order WENO GLM-MHD Scheme for Magnetic Reconnection

FENG Xueshang, ZHOU Yufen, HU Yanqi

2006, 26(1): 1-7. doi: 10.11728/cjss2006.01.001

Abstract(3004) PDF 2413KB(1038)

Abstract:
A new numerical scheme of 3rd order Weighted Essentially Non-Oscillatory （WENO） type for 2.5D mixed GLM-MHD in Cartesian coordinates is proposed. The MHD equations are modified by combining the arguments as by Dellar and Dedner et al to couple the divergence constraint with the evolution equations using a Generalized Lagrange Multiplier （GLM）. Moreover, the magnetohydrodynamic part of the GLM-MHD system is still in conservation form. Meanwhile, this method is very easy to add to an existing code since the underlying MHD solver does not have to be modified. To show the validation and capacity of its application to MHD problem modelling, interaction between a magnetosonic shock and a denser cloud and magnetic reconnection problems are used to verify this new MHD code. The numerical tests for 2D Orszag and Tang＇s MHD vortex, interaction between a magnetosonic shock and a denser cloud and magnetic reconnection problems show that the third order WENO MHD solvers are robust and yield reliable results by the new mixed GLM or the mixed EGLM correction here even if it can not be shown that how the divergence errors are transported as well as damped as done for one dimensional ideal MHD by Dedner et al.

Three Dimensional Simulation of the Steady Solar Wind in Carrington Rotation 1935

XIANG Changqing, FENG Xueshang, YAO Jiusheng

2006, 26(1): 8-13. doi: 10.11728/cjss2006.01.008

Abstract(2797) PDF 2880KB(1217)

Abstract:
A three-dimensional MHD simulation is conducted to study the steady solar wind in Carrington Rotation (CR) 1935 by using the three-dimensional numerical magnetohydrodynamic (MHD) model introduced by Feng et al. The numerical results demonstrate that the neutral current sheet has two peaks and two valleys, which is consistent with the result of PFSS model at Wilcox Solar Observatory (WSO). The obtained proton number density at 2.5 Rs is of the same order of magnitude as the result estimated from K-coronal brightness during the CRs 1733-1742 in 1983made by Wei et al. The radial velocity profile along heliocentric distance is consistent with that of low solar wind speed deduced by Sheeley and Wang et al. However, it is not able to reproduce the fast-speed flow in coronal holes and slow solar wind in streamers because of oversimplified energy equation adopted in our model. Future efforts must be made to remedy this deficiency.

Energetic Ions Flux Distribution Properties of the Earth's Ring Current Region

WANG Xinyue, SHEN Chao, LIU Zhenxing

2006, 26(1): 14-20. doi: 10.11728/cjss2006.01.014

Abstract(2419) PDF 4464KB(956)

Abstract:
In order to investigate the distribution of ring currents ions, Shen and Liu＇s model of ring currents ions distribution simulation is used to research 10-100 keV ion＇s distribution property. Without calculating loss, based on the ions distribution of plasma sheets injection region and near earth injection region, we obtained the flux distribution of ring currents region main composition, such as H^＋, O^＋, He^＋, during the main phase of a magnetic storm. Different ions have the same structure of flux distribution under the same conditions. Ions flux will become intensity if the electric field improves. 10 keV energetic ions widely distribute in ring current even if electric field is considerably weak. 40 keV energetic ions and other higher energetic ions form steady flux distribution with improved electric field. And the intensity of high energetic ions （≥ 40 keV） flux will exceed thelow energetic ions relatively if the electric field is intense enough. Ions flux intensity will reach the maximum when the pitch angle is 90°.

Current Sheet Structure and Motion Observed by Cluster on September 15, 2001

LEI Jinnguo, LU Li, LI Zhongyuan, LIU Zhenxing, A. Balogh, H. Réme

2006, 26(1): 21-27. doi: 10.11728/cjss2006.01.021

Abstract(2705) PDF 5786KB(1181)

Abstract:
Multiple crossings of the neutral sheet were observed by the Fltax Gate Magnetometer （FGM） and the Cluster Ion Spectrometry experiment （CIS） onboard the Cluster li at （-19, 4,-1） Re from 0430 UT to 0515 UT on September 15, 2001. The high-speed proton flow, which reversed from tailward to Earthward, was detected during the multi-crossings. Using a linear gradient/curl estimator technique the cross-tail current was obtained. The peak of the current density reached 28 nA/m^2. A large-scale wave propagating duskward and the thin current sheet flapping in the vertical direction were investigated, the thickness of the current sheet ranged from 0.3 Re to 0.2 Re, and had a tendency of being thinner. The velocity of the proton bulk flow in the x direction exceeded 1000 km/s during the magnetic field reconnection. By using the multi-point timing analysis and Minimum Variance Analysis, the structure and motion of the magnetotail current sheet were estimated.

Lidar Study of the Background Na Layer Over Wuhan: Long Term and Nighttime Variations

PENG Caihua, YI Fan, ZHANG Shaodong

2006, 26(1): 28-34. doi: 10.11728/cjss2006.01.028

Abstract(2852) PDF 3523KB(1197)

Abstract:
Based on the lidar observations from April 2001 to December 2004 over Wuhan, the long term （time scale longer than one year） and nighttime variations of background Na layer are presented, and their possible causes are also discussed. The observation results of long term variation show that Na abundance has a maximum value in November, which is approximately 2 times of the minimum value （1.6 × 10^9 cm^-2） in May; Na centroid height reaches a maximum value in August, which is about 1.4 km higher than the yearly average value （91.2 km）; the average value of rms width is 4.5 km, and its maximum and minimum values occur in December and March, respectively; Both of the Monthly averaged centroid height and rms width show a quasi-semiannual variation, but with contrary phase variations. Except the long term variations, the background Na layer also exhibits obvious nighttime variation： Na abundance increase with the nighttime except a short duration near the dawn time with a maximum value of 2.9 ×10^9 cm^-2 at 0540 LT; the height of peak value decreases with the nighttime; the centroid height of Na layer increases slowly with the nighttime until the time of 0520 LT, then it decreases rapidly to the value at the time of 2000 LT; the magnitudes of the fluctuations for the averaged Na layer abundance, height of peak, centroid height and rms width in the nighttime are 1.2 × 10^9 cm^-2, 3km, 0.3km and 0.8km, respectively.

Numerical Study on the Propagation of Gravity-Wave Packet in Time-Variant Background Fields

HUANG Kaiming, ZHANG Shaodong

2006, 26(1): 35-42. doi: 10.11728/cjss2006.01.035

Abstract(2618) PDF 2713KB(1068)

Abstract:
By using 2nd order operator-splitting scheme,numerical simulations of nonlinear propagation for a Gaussian gravity-wave packet in time-variant background temperature and wind fields are carried out individually. The simulation results show that the time-variant background fields influence little on the spacial structure of the wave packet, and the polarization relations of each wave disturbance components agree well with that of the linear gravity wave theory. Propagating in a time-variant background temperature field, the propagation paths of the gravity-wave packet are obviously different from the paths derived from the linear wave theory, and the variational tendency of the horizontal and vertical group-velocities are little difference is found in the variation of wave opposite to prediction of the linear theory, and a frequency between the simulation result and the dispersion relation of gravity wave.These indicate that the linear wave theory isn＇t feasible to describe quantitatively the nonlinear propagation of the gravity wave packet in time-variant background fields. While in a time-variant background wind field, the background impacts more significantly on the wave frequency than in time-variant background temperature field, and the propagation paths is more close to the paths of the linear theory than that in a steady-state background field.

Study on Dynamics Property of Smoke Particles in Vacuum and Microgravity

CHEN Ning, PAN Gongpei, CHEN Houhe, GUAN Hua, XUE Feng

2006, 26(1): 43-47. doi: 10.11728/cjss2006.01.043

Abstract(2251) PDF 1692KB(1166)

Abstract:
The dynamics of smoke particles can be effectively described by the Stokes sedimentation theory and diffusion coefficient expression in normal conditions; but in vacuum and microgravity, the forementioned principles are not applied any longer. In order to study the applicability of the IR smoke in outer space, by analyzing the vacuum and microgravity effects of the smoke particles, we can simulate approximately the dynamics property of smoke particles using molecule dynamics theory. On the basis of correlative theory, the force between particles is related to the space between them. When the space is less than ten times balance space, the force is large enough to form steady smoke, otherwise, the force is too small, smoke particles cannot form steady smoke. According to the Maxwellian distribution function, a function model of space between particles is established. Based on the model, the effects of smoke materials radius r, consistency ρ and the moving time of particles t on the space between smoke particles are discussed by Mathematica method. The results show that the space reduces with the increasing of the r and ρ, the smoke screen stability will increase gradually; the more long t is, the more the space is large, the smoke screen stability will decrease.

Study of Multisensor Image Fusion Technology

WU Zhenyu, WANG Peng, MA Meng

2006, 26(1): 48-53. doi: 10.11728/cjss2006.01.048

Abstract(2726) PDF 1842KB(1331)

Abstract:
In this paper, it is paid attention to the image fusion technology, in the field of image fusion, there are two major algorithm, one is color transformation. Images can be represented differently in RGB color and IHS color, the elements of images in IHS color are calculated, and then achieve the fusion of different images. This method used to play a important role. From the 1980s, another new mathematic tool began to be developed. It is wavelet analysis. Image fusion based on color transformation and wavelet transformation have been achieved in the environment of Matlab. The characters of color transformation have been studied. The characters of fusion images got from different levels of wavelet transformations coefficients are studied and difference of different level wavelet transformations are analyzed, the relations between the wavelet transform levels and the ratio between the different images＇ space resolution are given in order to get good fusion images, and effects of different wavelet on image fusion are also analyzed.

An Adaptive Fuzzy Controller for Satellite Maneuver Control

WANG Shuquan, YIN Xunhe, ZHAO Guangheng

2006, 26(1): 54-58. doi: 10.11728/cjss2006.01.054

Abstract(2699) PDF 1829KB(1421)

Abstract:
An adaptive fuzzy controller for Satellite Maneuver Control （SMC） is outlined. The typical fuzzy controller has a quick transient response and a very good robustness quality, and can easily incorporate human expert knowledge in the form of fuzzy rule ＂intelligence＂. But to construct the fuzzy rule base we must hold enough expert knowledge in advance, sometimes it＇s a difficult work. So the adaptive method is incorporated into the fuzzy control system, thus by adjusting the parameters of the fuzzy system, a proper fuzzy rule base can be got. And because the analysis is based on the Lyapunov function, the system is insured to be stable. Comparison of the system＇s performances with no language information and with only one language information is given, shows that with only one language information the system can reach a very high quality. Finally, simulation results substantiate the robustness quality of the adaptive fuzzy control system.

Engineering Analysis on a Satellite Attitude Control Thruster Plume at High Altitudes

CHENG Xiaoli, WANG Qiang, YAN Xiqin

2006, 26(1): 59-63. doi: 10.11728/cjss2006.01.059

Abstract(2955) PDF 2233KB(1373)

Abstract:
An engineering estimation method has been developed to calculate satellite attitude control thruster plumes at high altitudes, and the main exhaust gas species distributions are analyzed numerically. The grid generation technique is introduced to split the thruster nozzle exit section into cells, each of which is considered an independent point source, respectively. Hence, a modified free molecule model suitable for the nozzle exit local conditions is obtained. It consists of four primary formulae for density, mass flux, normal pressure and transitional energy flux, and three formulae for velocity, transitional temperature and internal energy flux. A nitrogen plume exhausted from a axisymmetric nozzle is firstly calculated. Numerical outlet conditions obviously influence upon analysis results for flow variables, especially, dynamic and thermodynamic variables. Then, an MBB 10N bipropellant thruster multi-species plume is investigated numerically. Comparisons are presented between the modified model and experiment, and good agreement is found for density distributions. Moreover, the levels of agreement are superior to those using the original single point source free molecule model. Pressure and internal energy vary more rapidly in the plume. It is unlike light molecule species that heavy molecule species mainly focus along the plume axis and their density distributions show a more dominant direction, i.e. axial direction.

Experiments Research on Orientation Determination by Twin-Star System

LU Liangqing, HU Dewen, WU Meiping

2006, 26(1): 64-79. doi: 10.11728/cjss2006.01.064

Abstract(2802) PDF 1347KB(1099)

Abstract:
Based on the previous work on AR （Ambiguity Resolution） method study and precision simulation analysis, a two-antenna 2.55 m-long baseline orientation prototype system is constructed using Twin-Star system, performed much static and dynamic experiments on it through orientation determination software developed by the author independently, and made precision analysis such as static relative precision, absolute azimuth accuracy, and dynamic azimuth stability. By experiments data processing, the paper has the results to show the feasibility of AR methods by static base rotation baseline and equivalent rotation baseline method developed by the author for vehicle dynamic environments, and the prototype has the following precision parameters： the relative precision better than 0.016 27° in azimuth, 0.012 97° in elevation, the absolute azimuth accuracy better than 0.35895°, and the dynamic azimuth stability better than 0.086 02°. The results also show that in real applications the Twin-Star orienting could provide precise azimuth information. This technology will widen the current function scope of ＂Beidou＂ Satellite System and has important application significance in military and civil background.

Identification Method to Improve Disturbance Model Parameters of Reaction Wheel

SUN Jie, ZHAO Yang, TIAN Hao

2006, 26(1): 70-74. doi: 10.11728/cjss2006.01.070

Abstract(2355) PDF 1836KB(1198)

Abstract:
Reaction wheel is one of the main disturbance sources that affect the precision of attitude control system of spacecraft. The purpose of setting up a disturbance model of reaction wheel is to predict the effects of the disturbance on the spacecraft, and then adopt corresponding control methods and isolation systems to restrain them. This paper presents the experimental disturbance model of reaction wheel. By analyzing the experimental data of reaction wheel, the parameters of the disturbance model, harmonic numbers and amplitude coefficients are determined. The energy compensation method is then given. The simulation results show that the identification accuracy of harmonic numbers does not exceed 0.04%. When adopting the amplitude spectrum method to compute the amplitude coefficients, the error is high up to 15.5%, however the error not over 1.1% when adopting energy compensation method. It indicates that the energy compensation method improves the identification accuracy of amplitude coefficients. This paper aims at providing a certain basis for improving the attitude control precision and stabilization of the spacecraft.

Hierarchical Nonholonomic Motion Planning of Dual-Arm Space Robots for Obstacle Avoidance via Lyapunov Methods

GUO Yishen, CHEN Li

2006, 26(1): 75-80. doi: 10.11728/cjss2006.01.075

Abstract(3043) PDF 1371KB(1151)

Abstract:
Based on Lyapunov methods, the hierarchical motion planning of free-flying dual-arm space robots for obstacle avoidance is discussed. The methods make full use of the nonholonomic nature of the system. With the momentum conversation and the Jacobian matrix, the system state equations and the control output equations for control design are established. And then the primary and secondary Liapunov functions are selected. The primary function insures the movement of the endeffectors from the start point to the end point. The secondary ascertains obstacle avoidance of the endeffectors. Combined the primary and secondary functions, the two endeffectors implement the specific movement and realize obstacle avoidance. A planar dual-arm space robot is simulated to verify the proposed methods.