空间科学学报

1999 Vol. 19, No. 2

Previous Issue | Next Issue

Select articles

Display Method:

Cover

A PRELIMINARY ANALYSIS OFSOLAR MICROWWE EVENTS WITHDOUBLE-PEAK STRVCTURES

XU Fuying, WU Hongao

1999, 19(2): 97-101. doi: 10.11728/cjss1999.02.097

Abstract(2270) PDF 328KB(935)

Abstract:
In this paper, a preliminary analysis of eleven microwave eveals with donblepeak structures during the periods of Jan. 1989—Dec. 1990 are made. The resultsshown that the evolution of peak in most double-peak events with frequency exhibited a competition trend. Such a observing character may be interpreted resonablyby property of cross-spectra due to different distribution of nonthermal electronsor same distribution of nonthermal electrons but different optical thickness at samefrequency. Therefore, a deduction may be obtained that two peaks in the microwaveevents with double-peak structures originate from different source region, respectively.

ELECTRON DRIFT MOTION IN THESPACECRAFT PHOTO SHEATH OFMAGNETIZED PLASMA

CAO Jinbin, ZHOU Guocheng, WANG Xueyi, SHEN Chao

1999, 19(2): 102-107. doi: 10.11728/cjss1999.02.102

Abstract(2033) PDF 414KB(1035)

Abstract:
By using one second order drift approximation theory, we for the first time studythe drift motion of electrons in the photo sheath of spacecraft in a magnetizedplasma, and the structure of the magnetic bottle in the photo sheath. Resultsshow that the stronger the magnetic field, the weaker the electric potential of thespacecraft and the smaller the cross section of the magnetic bottle in the infinityis. In the photo sheath, the electric potential barrier has an important influence onthe current collection of the spacecraft.

MODELING STUDY OF NIGHT-TIMEENHANCEMENTS IN f₀F₂ AT LOW-LAfITUDES

LIU Libo, WAN Weixing, TU Jiannan

1999, 19(2): 108-113. doi: 10.11728/cjss1999.02.108

Abstract(2016) PDF 421KB(1043)

Abstract:
The nighttime anomalous enhancements in f₀F₂ are simulated in this paperusing a 2D low-latitude ionospheric theoretical model. The number densities, velocities of ions and electrons are calculated in the model by solving the plasmatransport equations. Typical characteristics of pre-midnight and post-midnight increases appeared in the values of calculated f₀F₂ near the equatorial anomaly crestlatitudes. The larger the peak electron densities, the stronger the enhancement is,which is in consistent with observed results. It is shown that the transport of plasmainduced by E×B vertical drift and the field-aligned neutral winds is important inthe formation of nighttime increases in f₀F₂ at crest latitudes.

THE WAVELET EXTRAPOLAfION TECHNIQUEUSED IN TRANSFORM RECONSTRUCTION FORCOMPUTERIZED IONOSPHERIC TOMOGRAPHY

XU Zhengwen, WU Jian, CAO Chong

1999, 19(2): 114-121. doi: 10.11728/cjss1999.02.114

Abstract(1725) PDF 525KB(956)

Abstract:
The limitations caused by data acquisition system geometry in computerizedionospheric tomography (CIT) in general bring some problems such as incompletedata obtained, nonuniform samples in pseudo-projections, incomplete spectrum infrequency domain. If direct FOurier method is used for reconstruction, the nonuniform samples in pseudo-projections must be uniformed and unknown region in twodimensional frequency domain must be estimated. With reference of Fourier extrapolation technique, the wavelet extrapolation technique is presented in this paper.Theoretical analysis and simulation are also shown, they demonstrate inverse abilityand feasibility of the method. Both theoretical analysis and reconstruction resultsshow much superiority of the wavelet transform extrapolation technique.

THE NONLINEAR PROPAGATION OF GRAVITYWAVE PACKETS IN THE SHEARED AMBIENT

ZHANG Shaodong, YI Fan, WANG Jingfang

1999, 19(2): 122-127. doi: 10.11728/cjss1999.02.122

Abstract(2208) PDF 410KB(1262)

Abstract:
By using a two-dimentional Full-Implicit-Continucus-Eulerian (FICE) scheme,a numerical simulation of nonlinear propagation of a Gaussian gravity-wave-packetin sheared ambient is carried out. The numerical analysis shows that for an initiallygiven upgoing gravity-wave-packet, in absence of a critical layer, although there exists nonlinear interaction during the propagation, the whole wave packet and thewave-associated energy keep moving upward, while the wave front moving downward. Wave-associated perturbation velocity increases with the increasing height,and the vertical wavelength decreases with the increasing height. The propagationpath of wave energy flux coincides well with the ray path predicted by the lineargravity wave theory, but the magnitude of wave energy propagation velocity is evidently smaller than the group velocity derived from the linear gravity wave theory.This indicates that the nonlinear propagation characteristics of gravity wave packetsin sheared ambient are essentially linear.

THE EFFECTS OF THE VERTICAL WAVELENGTHOF THE GRAVITY WAVES ON ESF

ZHANG Tianhua, ZHANG Donghe, XIAO Zuo

1999, 19(2): 128-133. doi: 10.11728/cjss1999.02.128

Abstract(2198) PDF 311KB(1291)

Abstract:
The results of numerical simulation show that not only gravity waves are theseeds of ESF, but also their vertical amplitudes and the wavelengths of gravity wavesinfluence the evolution of ESFin different ways. The work we done gave a nonlinearexplanation on the various morphological features of ESFs.

ON FEATURES OF THE MAGNETOSPHERICCOUPLING EXAMED BY GEOMAGNETIC DWITH HIGH TIME RESOLUTION

SHEN Changshou, ZI Minyun, GAO Yufen, SUO Yucheng, WU Jian

1999, 19(2): 134-140. doi: 10.11728/cjss1999.02.134

Abstract(2210) PDF 501KB(1307)

Abstract:
Minutely mean values of geomagnetic data from each 11 stations nearby100°E GMand 300°E GMmeridians respectively are used to analyze the detailedfeatures of magnetospheric disturbances during a magnetic storm on November 26,1994. It is shown by the evolutions of H- and z-components, that the variationso f both region 1 and region 2 field-aligned currents are very important processesin the magnet osphere-ionosp here coupling. The coupli ng effect s in t he auror al areaare distinct obviously from that in mid--and lowWelatitudes. And the influence degreefor stations along different meridians is neither the same. The disturbance energyfrom the magnetosphere and the shielding effect of the region 2 field--aligned currentmay cause an abrupt intensification of ionospheric currents, and an eastward fieldand current may appearg which could last for about half an hour, in mid-andlow-latitudes at night side. Meanwhile, ionospheric plasmas of the F-region will belifted by E×B drift effect, which then leads to a simultaneously enhancement of h'F(minimum vertual height for F-region) at many stations nearby a same meridian.

CHANGE OF THE THERMOSPHERECOMPOSITION AND DENSITY DURING SEVEREGEOMAGNETIC ACTIVITIES

QIN Guotai, SUN Lilin, LI Hong

1999, 19(2): 141-147. doi: 10.11728/cjss1999.02.141

Abstract(1942) PDF 437KB(1143)

Abstract:
In this papers the Ap values for three geomagnetic activities of Jul. 6, 1974,Mar. 2, 1982 and Sept. 6, 1982, and thermospheric composition data from AECand DE-Bare used to search the change of the thermospheric composition anddensity during severe geomagnetic activities. The results show that the fluctuationof thermospheric density is very clear during severe geomagnetic activities. Andthe magnitude of this change increases as the altitude increases. At near 600km,the change can be four times of the original values, the change of N2 density is thelajrgest in all of the thermospheric compositions; while the abundance of O (No/N_all)decreases notably during severe geomagnetic activities.

AN ACCURATE MAfHEMAfICAL MODEL FORSATELLITE EPHEMERIS

YANG Weilian

1999, 19(2): 148-153. doi: 10.11728/cjss1999.02.148

Abstract(1775) PDF 395KB(1465)

Abstract:
An accurate mathematical model for calculating satellite ephemeris is givenin this paper, which is designed to apply to near the Earth and approximatelycircular orbits. The model uses 10 constant parameters to fit the secular and longperiodical variations of the orbit, while the short periodical variations caused bytesseral harmonics of the geopotential field are based on the known theoreticalresults. By sorting the terms with same frequency the formulae become quite simple.In addition, the model is also flexible to use and can be justified with differentaccuracy requirements up to 50 meters.

ATTITUDE DETERMINATION USING TWOSATELLITES: MODELING AND SIMULATION

WU Jie, REN Xuan, HU Xiaoping, ZHENG Wei, ZHENG Chong

1999, 19(2): 154-159. doi: 10.11728/cjss1999.02.154

Abstract(1907) PDF 368KB(1077)

Abstract:
A new method of attitude determination using two satellites is presented inthis paper, that is to determine vehicle's attitude using carrier phase of two earthsynchronous satellites. The principle and the precision of attitude determinationusing two satellites are discussed in detail in this paper. Computer simulation statethat the mean square error of attitude determination using two satellites can be0.23° in yaw, 0.18° in pitch and 0.15° in rolling, under conditions of mean squareerror of carrier phase single difference be 0.02 cycle, antennas be 1 meter apart, andso on.

RESEARCH ON THE INTELLIGENT DIAGNOSISFOR SPACECRAFT BASED ON FAULT TREE ANDNEURAL NETWORK

JI Changwei, RONG Jili, HUANG Wenhu

1999, 19(2): 160-166. doi: 10.11728/cjss1999.02.160

Abstract(2053) PDF 464KB(1801)

Abstract:
Fault diagnostic system is of great importance in monitoring and controllingspacecraft in the ground control center. The bottleneck problem of knowledge acquisition for spacecraft fault diagnosis is solved by using fault tree knowledge. Thepaper presents a fault diagnostic method based on fault tree and neural networkmodel. Based on the hierarchical model of fault tree, knowledge representationmethod based on frame and generalized rule is presented, and the relevant certainand possible reasoning strategies are described. Learning diagnosis based on neuralnetwork model is used to confirm and verify the results from the possible reasoning. By using Borland C++ under Windows, a fault diagnostic prototype systemis developed, and the validity is also demonstrated by diagnosing a satellite powersystem fault imitation bench.

THE COMPUTATION OF ATOMIC OXYGEN FLUXAND FLUENCE ON THE SURFACES OFARTIFICIAL SATELLITES AND ITS DISCUSSION

FAN Quanfu, TIAN Jianhua

1999, 19(2): 167-172. doi: 10.11728/cjss1999.02.167

Abstract(2356) PDF 418KB(1361)

Abstract:
In this paper, a model for computing Atomic Oxygen (AO) flux and fluenceis developed under relatively ideal conditions. The effects of some factors (orbitaltitude, solar activity, incident angle and inclination) on AOflux and fluence aremainly discussed.

DYNAMIC CHARACTERISTICS ONDIFFERENTIAL CUSHION DAMPING ANDTRANSMISSION SYSTEM OF SPACE DOCKINGMECHANISM

ZHAO Yang, CAO Xibin, WANG Xinggui, SHAO Chengxun

1999, 19(2): 173-180. doi: 10.11728/cjss1999.02.173

Abstract(2052) PDF 411KB(1185)

Abstract:
The model of a differential cushion damping and transmission system is oneof the main fields of spacecraft docking dynamics. The dynamic characteristics ofthe differential cushion damping and transmission system are researched based onthe analysis of system kinematics relationship. A new applied dynamic modeling isgiven for docking dynamic simulation.

A DOUBLE LOOPS CONTROLLER DESIGNMETHOD FOR LARGE FLEXIBLE SPACECRAFT

LIU Chunmei, SHEN Yi, HU Hengzhang

1999, 19(2): 181-186. doi: 10.11728/cjss1999.02.181

Abstract(1746) PDF 378KB(1052)

Abstract:
In this paper, a double loops controller design method is provided in accordancewith the characteristics of large flexible spacecraft, such as low frequency, low damping and coupling between rigid body and flexible appendages. Optimal sliding-modecontrol method is used, and robust stability is considered. Finallyg numerical simulations show that vibration suppression and accurate pointing are accomplishedby using two separate control loops with certain robust property. Based on modetruncation modle of the flexible spacecraft.

CONTROL ON TRANSVERSE VIBRATION OFTETHER BY THE LONGITUDINAL MOTION FORTETHERED SATELLITE

GU Xiaoqin, TAN Zhaoyang

1999, 19(2): 187-191. doi: 10.11728/cjss1999.02.187

Abstract(1701) PDF 291KB(1562)

Abstract:
The transverse vibration of a tethered satellite is studied. The equation of thevibration is formulated. To suppress the transverse vibration of the tethered satellite, the longitudinal control force is gotten by Pontryagin's method. The controlforce to exert to the tether is produced by D'Alembert force of satellites, and satellites are accelerated by the change of the tether's length, which is controlled by themotor in the satellite. The numerical simulation results are included.