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Chinese Journal of Space Science
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15 May 2010, Volume 30 Issue 3
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Causes of Martian Magnetic Field and the Distribution
Tong Dongsheng;Chen Chuxin
2010, 30 (
3
): 193197. doi:
10.11728/cjss2010.03.193
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2599
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A model of currents around Mars is proposed, upon which the distribution of magnetic field in Martian equatorial plane is calculated. In this model, there exist currents in the Martian magnetopause, the Martian ionosphere and the current sheet in the Martian magnetotail based on the observational data from satellite and appropriate assumptions. According to the continuity of the current, these currents satisfy the relation that the total current in the Martian magnetopause is equal to the summation of the total current in the Martian ionosphere and the total current in the Martian magnetotail. Superposition of the magnetic field generated by these currents and solar wind magnetic field constitutes magnetic field in the Martian equatorial plane. Results obtained through the model of Martian currents are consistent with observational results through satellite and those gained by other methods.
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Model Research of 10.7 cm Solar Radio Flux 27day Forecast
Wen Jing;Zhong Qiuzhen;Liu Siqing
2010, 30 (
3
): 198204. doi:
10.11728/cjss2010.03.198
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2541
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The midterm forecast of daily solar active index is always complex and difficult in space environment forecasting operation. A new 27day forecast model of 10.7 cm solar radio flux F10.7 index) based on the observation and general evolution of the solar active regions has been built to improve the AutoRegress (AR) method. The area and longitude of an active region has been used as control parameters in the new model. The sunspot decay rate suggests a simple way to forecast the area of active region in next solar rotation. The new model is tested in the following two cases: (1) F10.7 index is much larger than usual as unexpected solar active regions appear on the disk; (2) F10.7 index becomes quite peaceful because the dominant solar activity regions disappear. The result indicates that the relative errors of the new model were mainly 5%~9 % smaller than those of AR model under these two conditions. That means it is possible to improve the operational forecast model of solar index using the information of solar active regions.
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Research on the Solar Proton Fluence Model
Li Tingting;Shi Liqin;Liu Siqing
2010, 30 (
3
): 205210. doi:
10.11728/cjss2010.03.205
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2445
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Solar Proton Event (SPE) has great influence on the human space activities. Establishing prediction model for total fluence of solar protons accumulated during a mission and taking protective measures are of vital significance for the security of the spacecraft and astronauts. Based on a data set of proton events from the last four solar cycles, a new statistical model is designed to predict the proton fluence for space mission analysis. The energy ranges considered are E>10 MeV and E>30 MeV, respectively. Because of the quasirandom nature of the occurrences, and spectra of SPE, solar proton mission fluence must be treated statistically. The purpose of this analysis is to derive the probability of exceeding various proton fluence as a function of proton energy and mission duration. Compared with commonly used JPL model, solar activity levels are taken into account to obtain the occurrence probability of proton events. The new model can access proton fluence in different phase, and is more consistent with the distribution of proton events.
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CESE Method for Resistive Magnetohydrodynamics
Liu Yuanxin;Ji Zhen;Feng Xueshang;Zhou Yufen
2010, 30 (
3
): 211220. doi:
10.11728/cjss2010.03.211
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2397
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In this paper, the 2.5dimensional resistive Magnetohydrodynamics (MHD) equations were solved to simulate two magnetic reconnection problems in single current sheet by applying the spacetime Conservation Element and Solution Element (CESE) method. Three different versions of CESE method are employed: (1) the original CESE method, (2) the Courant Number Insensitive Scheme (CNIS) CESE method, (3) the high order CESE method. The numerical results obtained from the abovementioned approaches are discussed in the aspect of the divergence of the magnetic field. The numerical results indicate that no obvious differences exist among the three approaches in the configuration of the magnetic field. However, for the divergence of the magnetic field, the results obtained from the three approaches differ from each other. In respect to keeping the divergence of the magnetic field small, the CNIS method is better than the others. It is hoped that these conclusions might be helpful for the design of algorithm where the magnetic reconnection problems should be included, since the controlling of the divergence of the magnetic field is one of the key issues in MHD simulation.
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Study of Computerized Ionospheric Tomography Under Ionospheric Storm Conditions
Yu Xiao;Ou Ming;Liu Dun;Ma Baotian;Deng Zhongxin;Chen Li;Zhen Weimin
2010, 30 (
3
): 221227. doi:
10.11728/cjss2010.03.221
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2337
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The characteristics and development of the lowandmid latitudinal ionospheric storm during the magnetic storm in November, 2004 are studied using GPS observations from 6 stations along 115°E meridian. The results from tomographic reconstruction method show that the ionospheric storm during this magnetic storm mainly exhibits the positive storm phase, and the positive deviations of electron density are not only latitude dependent but also height dependent. The Equatorial Anomaly (EA) crest moves poleward as a result of enhanced energy deposition into the high latitude ionosphere. The electron density and TEC gradually recover to the quiet level in the first recovery phase. These results are in good agreement with previous studies, and the ionospheric effects can be attributed to the storm circulation theory superimposed with the movements of EIA crest.
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Empirical Orthogonal Function (EOF) Analysis on the Thermospheric Total Mass Density Retrieved From CHAMP Observation
Zhou Xu;Wan Weixing;Zhao Biqiang;Yue Xin'an;Ren Zhipeng
2010, 30 (
3
): 228234. doi:
10.11728/cjss2010.03.228
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2619
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The Empirical Orthogonal Function (EOF) analysis was applied to study the thermospheric total mass density at the altitude of 400 km with the data obtained from German CHAMP satellite during the interval from 2003 to 2007, when the solar activity is in declining period. The solar cycle and yearly variations of the thermospheric total mass density ρ are obtained. It is found that the total mass density ρ was obviously affected by the solar activity, the correlation coefficient between solar cycle variation component of ρ and F10.7 index can reach 94.5%. At the mid and highlatitudes, the amplitude of solar cycle variation is larger in the south hemisphere than in the north. The amplitude of the solar cycle variation is decreased as the latitudes change from low to high. At low latitudes there exists a structure of double crests which is recently known as the Equatorial Mass density Anomaly (EMA). In the yearly variation of the total mass density, there is a seasonal variation that the density is larger in summer than in winter. The amplitude of the yearly variation of density ρ increases with solar F10.7 index as well as the absolute latitude. Comparing the result of CHAMP data with the output of NRLMSISE00 model under the input of the same condition of observation, it is found that both the solar cycle and the yearly variations of thermospheric total mass density are in good agreement. Even though, the latitude difference of the solar cycle variation of ρ is a little bigger from NRLMSISE00 than CHAMP data and there is no EMA structure in NRLMSISE00 model. Furthermore, there is an obvious semiannual variation component while analyzing the NRLMSISE00 data without 130daywide sliding window. Thus it is considered that, with the restriction of CHAMP orbit, the 130daywide sliding window may smooth out the semiannual component, as well as the higher. It is concluded that the present results are meaningful in the study of the thermospheric climatology.
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Classical Theory of Atmospheric Tides and Development of Some Related Modern Models
Liu Renqiang
2010, 30 (
3
): 235242. doi:
10.11728/cjss2010.03.235
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2471
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Roughly based on the historical order of advances in tidal theory, the classical theory that involves a 2D steady and variable separable basic partial differential equation, which is reduced from a set of starting equations linearized under an assumption without dissipations and background winds, and its global wave mode solutions expanded in Hough functions was reviewed at first. Then a modern numerical model (i.e., GSWM), which was mainly developed by Forbes and Hagan beginning from a linearization under realistic conditions of various dissipations and nonzero background winds and so is still 2D steady in essence but cannot be solved by the method of separation of the latitude and height variables, was introduced. At last, a developing tendency that people have begun in recent years to employ some GCM (e.g. TIMEGCM, MUAM, CMAM and WACCM), which pay more attentions to the middle and upper atmosphere, to study the tidal nonlinearity and nonmigrating tides etc. was summarized. Also given are some analyses about the characteristics of respective tidal models and differences between them by incorporating the understanding of the author. Along the way, it can be seen that during half a century starting from first principles people have made persistent efforts to disclose the realistic structural characteristics of the global atmospheric tides and the mechanisms for tidal long and shortterm variability, while this kind of endeavor is closely connected with the advances in observations of atmosphere especially the wind and temperature fields in the MLT by using from groundbased radars to instruments on board satellites.
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Modeling and Analysis of Radiometer Effect on the Innersatellite
Liu Hongwei;Wang Zhaokui;Zhang Yulin
2010, 30 (
3
): 243249. doi:
10.11728/cjss2010.03.243
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1937
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Radiometer effect is a kind of thermal noise caused by temperature gradient. It is one of the main interfering factors to the innersatellite, and is important to measure gravitational field. By analyzing the cause, the model of innersatellite radiometer effect was established by the kinetic theory of gas molecules. In the model, the innersatellite radiometer effect was divided into two parts. One was the reaction force and its torque caused by gas molecules which escaped from innersatellite surface. The other was the force and its torque caused by collision of gas molecules which escaped from the cavity wall on the outersatellite. Then the influence of various parameters to innersatellite radiometer effect was analyzed and methods of reducing the innersatellite radiometer effect were found. The results showed that through lowering the pressure and temperature gradient in cavity, as well as using materials with low surfacemass ratio, the acceleration caused by radiometer effect could be reduced.
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Size Estimation of Space Object Based on Narrowband Radar
Yu Chunrui;Liang Diannong;Dong Zhen;Yu Anxi
2010, 30 (
3
): 250254. doi:
10.11728/cjss2010.03.250
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2219
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Earth orbiting spacecrafts have become an integral part of our everyday lives. A real and growing concern for the safety and reliability of these satellites is the threat from collision with other orbiting objects including space debris. Size estimation of space object is an important task in evaluating its danger of a possible collision with operational spacecraft. RCS (Radar Cross Section) includes much information of space object, and extracting the feature of the object size from the RCS time series of narrowband radar is very helpful to radar target identification. Unfortunately, it is very difficult to get the information of target shape and size from its RCS. In this paper, based on the research of the characteristic of the ellipsoid's RCS, a shape estimation method of space object is proposed, and the problem of size estimation is studied further with a new method of size estimation proposed. The result using real radar data shows that this method is feasible to estimate the shape and twodimensional sizes of the space object.
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Solving the Nearfar Problem for Positioning the High Earth Orbital Satellite With GPS
Liang Minmin;Qin Honglei;Li Feng
2010, 30 (
3
): 255262. doi:
10.11728/cjss2010.03.255
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1995
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Cross correlations caused by the limited dynamic range of the GPS Gold codes represent a significant ``nearfar'' problem when GPS is used for positioning of High Earth Orbital (HEO) satellite. The power differences among signals received by High Earth Orbital satellite from different GPS satellites will be up to tens of dB since the lobe amplitude of GPS satellite transmit antenna and transmission distance are both different. Based on the requirement of positioning of HEO satellite using GPS, a Maximum Likelihood (ML) estimator algorithm is used to resolve the nearfar problem introduced by the suboptimal sliding correlator solution. The GPS maximum likelihood estimator acquisition algorithm performs a simultaneous, twodimensional search of both the Doppler frequencies and GPS Gold codes. At first, simple cross correlator is used to detect the strong code signal. Then, a fine acquisition will be done to estimate the parameters of the strong code signal accurately. The maximum likelihood algorithm is used to cancel the strong code signal. As the nearfar problem has been dealt with by canceling the strong code signal, the acquisition of the weak code signal can still be completed. In order to show the good performance of the estimator, GPS signal received by HEO satellite is analyzed to generate a simulated signal. Also, simulations have been done to compare the performance of the maximum likelihood estimator and the Simple Correlator (SC) algorithm. The result shows that the maximum likelihood estimator can improve the twodimensional searching performance and decrease the interference arising from nearfar problem.
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Research on Spaceborne Deployable Antenna
Wang Hongjian;Liu Heguang;Zhang Dehai
2010, 30 (
3
): 263269. doi:
10.11728/cjss2010.03.263
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2448
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Due to the limited space of the fairing, HaiYang2 satellite microwave Calibration Radiometer Antenna (HY2 CRA) used deployable structure and two hinges to perform the stretching action. Many efforts had been also exerted to meet the demand of high gain, low noise, high beam efficiency, low loss etc. The offset paraboloid made of carbon fiber together with conical corrugated horns was selected for this antenna to reduce the total mass. The working frequencies were selected to be 18.7 GHz, 23.8 GHz and 37 GHz respectively with 600 MHz bandwidth. The new compact two septums Orthomode Transducers (OMT) were proposed and analyzed by full wave method, and these OMT were employed to meet the demand of the dual polarizations for all three frequencies. Finally the whole antenna was tested in the far field testing system. The technical renovation about working mode, key knowledge, design procedure, and measurement were analyzed in this paper.
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Fast Approach of Doppler Rate Estimation Based on Geometry and SAR Echo Data
Peng Tao;Zhang Hongqun;Wu Yewei;Han Jiawei
2010, 30 (
3
): 270274. doi:
10.11728/cjss2010.03.270
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1975
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Doppler frequency rate is one of the key parameters in the azimuth processing of SAR data. Once mismatched, it will cause serious defocusing in azimuth dimension and then result in the degradations of image quality. On the other hand, fast estimation for Doppler frequency rate is necessary for the sake of disaster mitigation. To meet the need of fast estimation of Doppler frequency rate, an approach based on geometry and SAR echo data is put forward in this article, which can simplify the estimation processing according to the relationship between the Doppler frequency rate and range. Besides, the selection strategy for block data used to estimate the Doppler frequency rate is discussed. In the end, corresponding results have been given.
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Robust Control for Spacebased Robot With External Disturbances and Uncertain Parameters in Joint Space
Chen Zhiyong;Chen Li
2010, 30 (
3
): 275282. doi:
10.11728/cjss2010.03.275
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2020
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The robust control problems were discussed for spacebased robot system whose base was not controlled. The underactuated dynamic equations of the system were derived through the Lagrange method and linear momentum conservation of the system. It was shown that the dynamic equations mentioned above can be linearly dependent on a group of inertial parameters. Based on the results and with the augmentation approach, a robust control scheme was developed for spacebased robot system with uncertain payload parameters and external disturbances to track the desired trajectory in joint space. The control scheme proposed doesn't require measuring the position, velocity and acceleration of the base with respect to the orbit due to an effective exploitation of the system dynamics. Besides, it is computationally simple, because the controller is always robust to the uncertain parameters and external disturbances rather than explicitly estimating them online. Therefore, the control scheme is prone to realtime and online applications in spacebased robot system. A twolink planar spacebased robot system was simulated to verify the proposed control scheme.
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Lossless Compression Algorithm for Droplet Images in Space Droplet Evaporation Experiment
Zhou Xiaobo;Yu Qiang;Cai Shijie
2010, 30 (
3
): 283288. doi:
10.11728/cjss2010.03.283
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2141
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In space droplet evaporation experiment, a great number of droplet images were captured, compressed and then transmitted to the ground station. To improve lossless image compression ratio in space droplet evaporation experiment, according to the high correlation between droplet images that were sequentially captured, an image sequence lossless compression algorithm based on JPEGLS algorithm and interframe prediction error coding was developed. In this algorithm, JPEGLS algorithm was applied to the first frame of the image sequence. Every single frame that follows was compared with its previous frame to get an interframe prediction error frame, and Golomb coding was applied to the interframe prediction error frame. In this way, lossless compression for droplet images sequence was realized. The result of experiments shows that the proposed algorithm is superior to JPEGLS in compression ratio and encoding time.
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