空间科学学报

2008 Vol. 28, No. 4

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Shear Rate Determination of Flow Near Magnetopause

Li Linghan, Chen Tao

2008, 28(4): 273-282. doi: 10.11728/cjss2008.04.273

Abstract(2699) PDF 4147KB(1202)

Abstract:
Shear rate of flow near magnetopause is related to the degree of energy transfer near magnetopause. Many numerical simulations near magnetopause have to use shear rate of flow as an important input parameter. However, up to now it is still hypothetical and not realistic. By simultaneous multipoint observations of Cluster, using methods of linear interpolation and barycentric coordinates, we have determined shear rate of flow near magnetopause, an observational spatial parameter that can not be obtained until Cluster. Observational spatial distribution of shear rate of flow at dawn side and dusk side of magnetopause, magnetosphere and magnetosheath nearby has been analysed. Data analysis demonstrates that shear rate of flow as large as velocity difference of 330\,km/s over the distance of 100 km can exist near magnetopause sometimes even under quiet solar wind and geomagnetic conditions. Under many circumstances shear rate of flow near magnetopause is small, with the spatial velocity difference of dozens of km/s over the distance of 1000 km. The method we have adopted here can be used widely to determine shear rate of flow at any location.

Simulation on the Penetration of Energetic Particles Into the Magnetosphere

Tang Pengju, Xu Ronglan, Wang Chi

2008, 28(4): 283-287. doi: 10.11728/cjss2008.04.283

Abstract(2704) PDF 1910KB(1183)

Abstract:
The study on the penetration of interplanetary energetic particles into the magnetosphere, is one of the key problems in magnetospheric and space weather study. Most of the previous works concentrated on the statistical investigation of the penetration of energetic particles into magnetosphere under different interplanetary conditions. In this paper, the new-developed code is used to calculate the trajectories of energetic particles' penetration into the magnetosphere based on T89 model with different energies and pitch angles. The preliminary results show that only those particles moving along the magnetic field lines can penetrate and reach the earth's surface. The particles will be reflected earlier with larger deviation angle with respect to the magnetic field lines. The particles with higher energies can penetrate into the magnetosphere with larger distribution of the pitch angle, but only those with directions along the magnetic field lines can reach the ground. All these results are in consistent with theoretical predictions.

3-Dimensional Drift Shell Splitting During the Geomagnetic Disturbance

Huang Chaoyan, Xu Ronglan, Han Jianwei

2008, 28(4): 288-294. doi: 10.11728/cjss2008.04.288

Abstract(2772) PDF 3766KB(904)

Abstract:
Based on the theory of magnetospheric particle dynamics, the guiding center and magnetic field line tracing methods are used to calculate the drift shell splitting of the particle motion in the radiation belt. The results show that the two methods are the same. Therefore the 3-dimensional drift shell splitting during the geomagnetic disturbances is studied using magnetic field line tracing method. The initial location of the particles is ≤ 9Re with different initial pitch angles. Different magnetic disturbance index Kp and solar wind pressure, corresponding to T89c and T96 magnetic field model, are compared to each other. The results show that drift shell splitting varies with initial position, pitch angles, Kp index and solar wind pressure. The details are: (1) The drift shell splitting is stronger when the radius distance increases. Particles staring from noon will be trapped stably; otherwise, particles starting from night will escape from the magnetopause, when the initial radius distance and pitch angle are large. (2) When the initial pitch angles on the magnetic equatorial plane increase, the drift shell of particles starting from noon align inward, but from night align outward. (3) Drift shell splitting becomes obvious when Kp index or solar wind pressure increase, and the basic character and trend under these two disturbance parameters are the same.

Observations of Ionospheric Irregularity Zonal Velocity in Hainan

Chen Yanhong, Huang Wengeng, Gong Jiancun, Ma Guanyi, Sun Chuanli, Shen Hua

2008, 28(4): 295-300. doi: 10.11728/cjss2008.04.295

Abstract(3358) PDF 1947KB(1588)

Abstract:
To investigate the drift velocity of the equatorial ionospheric irregularity in low latitude of China, three single-frequency GPS receivers at Hainan (19.3ºN, 109.1ºE) were operated under the corporation of CSSAR, China and NICT, Japan. Distances between the receivers were 91 m and 104 m respectively. The GPS receivers sampled GPS signal intensity at a rate of 20 Hz. Drift velocities of irregularities were measured using cross-correlation analysis with the time series of the GPS signal intensity observed from March to November of 2007. The results indicate that the ionospheric scintillation mainly occurrs in spring and autumn. The zonal drift velocity is mainly eastward at night. It varis from 50 m/s to 150 m/s, and decreases with time. During the generation phase of plasma bubbles, the drift velocity is relatively scattered, which could be related to the random fluctuations of the plasma irregularities. And at the beginning of the scintillation, the plasma has a large vertical velocity, which can also cause the uncertainty of the zonal drift velocity. The characteristic of the drift velocity is consistent with the observational results in other stations at low latitude region.

Response of Middle and Upper Atmosphere to Pulse Disturbance From Lower Atmosphere

lUO Yao, Xiong Jiangang, Wan Weixing

2008, 28(4): 301-310. doi: 10.11728/cjss2008.04.301

Abstract(2612) PDF 2346KB(932)

Abstract:
By using a two-dimensional Full Implicit Continuous Eulerian (FICE) scheme and taking the atmospheric basic motion equations as the governing equations, a numerical model for nonlinear propagation of Acoustic Gravity Wave (AGW) disturbance in two-dimensional polar coordinates is solved. Results of numerical simulation show that the AGW packets propagate steadily upward and keep its shape well after several periods. This shows that FICE scheme is reliable for simulating the nonlinear propagation of AGW disturbance in a two-dimensional compressible atmosphere. The response of middle and upper atmosphere to the pulse disturbance of lower atmosphere in background winds or without background winds is simulated by using this model, and obtain the distribution of a certain physical quantity in time and space from earth's surface to 300 km above. The results reveal that the response of ionosphere occurs at a large horizontal distance from the source and the disturbance becomes greater with increasing of height. The situation when the direction of the background wind is opposite to or the same as the direction of disturbed velocity of gravity-wave is studied. The results show that gravity wave propagating against winds is easier than those propagating along winds and the background wind can accelerate gravity wave propagation. Just upon the source, an acoustic wave component with period of 6min can be found. These images of simulation are similar to observations of the Total Electron Content (TEC) disturbances caused by the great Sumatra-Andaman earthquake on December 26 in 2004.

Feasibility of Geosynchronous ATV Navigation Based on GPS

Fan Litao, Tang Jianguo, Wu Jie

2008, 28(4): 311-315. doi: 10.11728/cjss2008.04.311

Abstract(3004) PDF 1522KB(1174)

Abstract:
The GPS is used to determine the orbit of Geosynchronous Autonomous Transfer Vehicle (GATV). The visibility of the GPS satellites relative to the vehicle is analyzed in this paper. Moreover, inertial error, pseudorange and delta pesudorange models are established in the earth centered inertial coordinate system. The adaptive kalman filter with a fading factor is applied for the vehicle orbit determination. Simulation results show that even slope-lobe signal is used, GPS satellite visibility becomes lower as the vehicle flies higher. Usually, the visibility can not be improved effectively by increasing the receiver antenna gain and direct orbit determination is infeasible with only one epoch GPS observation. It is indicated that by using kalman filter, in the conditions of 1 km initial position deviation, 1 m/s initial velocity deviation, 10 m pseudorange mean square error and 0.05 m/s delta pseudorange mean square error, the final position deviation is smaller than 50 m while the velocity deviation is smaller than 0.02 m/s.

Research on Positioning of High Earth Orbital Satellite Using GNSS

Qin Honglei, Liang Minmin

2008, 28(4): 316-325. doi: 10.11728/cjss2008.04.316

Abstract(3541) PDF 4171KB(1741)

Abstract:
The GNSS as a navigation and positioning method has global, all-weather, real time and high precision characteristics. Using it on the high earth orbital satellites in positioning can provide precise orbit and attitude determination, overcome the disadvantage of complex equipment and high cost which using ground measurement and control system to positioning, make it possible to autonomous navigation . New and exciting opportunities become possible if satellites are able to autonomously determine their own orbit. For example, precise onboard orbit determination opens the door to satellites flying in formation. However, receivers in low Earth orbit have virtually the same view of the navigation satellite constellation as receivers on the ground. But satellites orbiting at geostationary altitudes and higher have a severely limited view of the main beams of the GNSS satellites. The main beams are either directed away from these high-altitude satellites or they blocked to a large extent by the Earth. So, using much weaker signals is a fundamental requirement for a high orbital altitude GNSS receiver, but it is certainly not the only challenge. Other unique characteristic of this application must also be considered. On the one hand, dynamic characteristics will be more different at high Earth orbit. High dynamic situation makes it difficult to use weaker signals. On the other hand, Position Dilution of Precision (PDOP) figures are much more higher at geostationary and higher altitudes because visible navigation satellites are concentrated in a much smaller region with respect to the spacecraft antenna. Spacecraft navigation receiver must be designed to withstand a variety of extreme environmental conditions. In this paper, positioning of high earth orbital satellites using GNSS is researched. The visibility of navigation satellites, dynamic characteristics, Geometric dilution of precision are analyzed using single GNSS and integrated GNSS. Through simulation and analyzing, it is verified that using GNSS can realize the positioning of HEO satellite and obtain enough positioning precision requirement.

Study on Location and its Algorithm Using Time Difference of Arrival by Sounding Rocket

Hu Shengbo, Meng Xin, Yao Xiujuan, Yang Xuan, Bian Chunjiang

2008, 28(4): 326-329. doi: 10.11728/cjss2008.04.326

Abstract(3196) PDF 1037KB(809)

Abstract:
The requirements of space environment exploration are increasing, but usual receiving and tracking equipment are ponderous and with bad agility, and more and more unsuitable for multi-purpose situation, in which more flexibilities are needed. Locating methods based on time difference of arrival are presented by sounding rocket, and a constrained weighted least squares location algorithm is given. The methods have the characteristics of reliable receiving, good agility, high locating precision and low cost. And the methods can be used to locate sounding rocket, receive and process the exploring data for multi-purpose situation.

Determination of X Ray Pulsar Pulse Time of Arrival at Spacecraft

Yang Tinggao

2008, 28(4): 330-334. doi: 10.11728/cjss2008.04.330

Abstract(3472) PDF 922KB(1427)

Abstract:
X ray pulsar can be used for spacecraft autonomous navigation. Pulsar clock can be used to stabilize onboard clock. Utilization in space of X ray pulsar clock is based on high precision determination of pulsar pulse Time of Arrival (TOA) at spacecraft. A method to obtain X ray pulsar pulse profile with individual photon arrival time records by onboard X ray detect system was discussed. In the case that an onboard clock is used as time reference for X ray pulsar timing recorded individual photon arrival time (spacecraft proper time) should be converted to barycentric dynamic time (TDB). Doppler effect due to orbit velocity of spacecraft during observation period may blur observed pulse profile. To mitigate smearing effect to pulse profile further transformation of recorded photon arrival time to Solar System Barycenter (SSB) is required using estimated approximate spacecraft position by spacecraft dynamics. Then obtained X ray pulsar pulse profile is compared with its standard template pulse profile to derive an observed pulse arrival time. Algorithm of determining X ray pulsar TOA at spacecraft with high precision was reviewed. Detailed analysis method to determine TOA in Fourier frequency domain was introduced and compared to analysis method in time domain.

Study on the Influence of Lunar Wheel Configuration for Traction Ability

Li Jiangqiao, Zou Meng, Li Yinwu, Jia Yang, Huang Jianbo

2008, 28(4): 335-339. doi: 10.11728/cjss2008.04.335

Abstract(2821) PDF 374KB(929)

Abstract:
It is important to research the relationship on the vehicle-terramechanics in lunar surface circumstances for the lunar rover to work normally. Based on the indices of the traction performance, the comparative indoor test were made in simulated lunar soil for different configuration wheels. The test results show that, the drag bar pull and efficiency coefficient is increasing with the wheel width and diameter. The draw bar pull increased with the rug height, but the efficiency coefficient reduces when the slip radio is bigger than 20 %. The draw bar pull and efficiency coefficient will reduce with the rug distribution increases when the rug distribution is more than 20 %.

Modeling and Measurement of Rigid Wheel-soil Interaction for a Lunar Rover

Tao Jianguo, Hu Ming, Gao Haibo, Deng Zongquan, Quan Qiquan

2008, 28(4): 340-344. doi: 10.11728/cjss2008.04.340

Abstract(3010) PDF 1976KB(1407)

Abstract:
Based on soil's press-sinkage and shear models of terramechanics and passive earth pressure of soil mechanics, mathematical models of wheel-soil interaction are constructed for a rigid wheel of lunar rover moving or steering on deformable soil. For analysis of effect of soil parameters and wheel slips to rigid wheel locomotion, the wheel's performance parameters on different soil are computed through these models, such as drawbar pull, moving torque and steering torque to different slips. A novel test-bed is set up to test wheel's performance parameters, and experimental results of a rigid wheel on the soil validate the effectiveness of presented models.

Adaptive Mode Method in Inverse Dynamics of a Rotating Flexible Manipulator With High-frequency Excitation

Li Qing, Wang Tianshu

2008, 28(4): 345-349. doi: 10.11728/cjss2008.04.345

Abstract(2316) PDF 1347KB(1270)

Abstract:
In dynamics and control of space flexible manipulators, high computing speed is always required for solving inverse dynamics. However, when the flexible multibody system suffers from high-frequency excitation such as contact impact, high order modes have to be counted to ensure adequate precisions while the computing speed is lowered down. To increase the computational efficiency of such problems, an adaptive mode method was proposed with an application in inverse dynamic modeling of a rotating flexible manipulator. In the process, the axial displacement caused by transverse deformation of the beam-like model was considered, and high order mode coordinates were reduced gradually as they damped off in the proportion of total energy due to structural damping. The control laws of driving torque for the rotary manipulator articulation were computed to account for its validity. Additionally, the influence of gravity was investigated.

Numerical Simulation of Thermocapillary Convection in an Evaporating Liquid Layer Under Microgravity Condition

Ji Yan, Liu Qiusheng, Zhu Zhiqiang

2008, 28(4): 350-355. doi: 10.11728/cjss2008.04.350

Abstract(3329) PDF 1745KB(1231)

Abstract:
A new model of the evaporation of a pure liquid layer underlying its own vapor is proposed and analyzed. The liquid layer is subjected to horizontal temperature gradient under microgravity condition. The thermocapillary convection is coupled with the evaporation, adding complication in the interfacial mass and heat transfer. An analytical expression for temperature distribution is given in pure evaporation case without considering thermocapillarity. For the case of both evaporation and thermocapillary convection, a finite difference algorithm is developed to solve simultaneously the thermal and flow fields in the liquid layer at various evaporation Biot number and Marangoni number until the steady state solution is achieved. The influence of evaporation Biot number and Marangoni number on the interfacial mass and heat transfer has been discussed. Three regimes of the coupling between evaporation and thermocapillary convection are found and explained from our numerical results.

Optimizing Process of the Images Captured by the Solar X-EUV Imaging Telescope

Liu Xin, Li Baoquan

2008, 28(4): 356-360. doi: 10.11728/cjss2008.04.356

Abstract(3453) PDF 1304KB(1069)

Abstract:
The solar X-EUV imaging telescope is mainly used to monitor and predict the solar activities that affect the space weather. The observed materials will be dedicated to the space weather forecast. For the space adaptability of the telescope, the image captured by CCD will be affected by the noise formed in structure modulation. This essay focuses on the optimizing process of the images captured by the telescope. It discusses the physical meaning of Fourier transform and its application in the image processing. With two-dimensional discrete Fourier Transform, images are transformed into frequency domain. With Butterworth wave-isolation filter, the program was designed and adjusted in practice, thus the periodicity noise in the image is smoothed to reduce the distortion of images as less as possible. The optimized images are favorable for further analysis of the solar activities.