空间科学学报

2009 Vol. 29, No. 2

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Solar Wind Electrons Reflected by the Lunar Crustal Magnetic Field

Feng Yongyong, Xu Ronglan, Zhao Hua

2009, 29(2): 161-165. doi: 10.11728/cjss2009.02.161

Abstract(5012) PDF 567KB(1927)

Abstract:
In this paper, the solar wind electrons which are moving toward the moon surface are traced to study the reflection of these electrons due to the crustal magnetic field of the moon. The magnetic field in the solar wind Bsw is supposed to be perpendicular with the moon surface, and the crustal magnetic field is supposed as a small dipole field with a moment Mcb, where Mcb are parallel, anti-parallel, and ±90° correspond to the direction of the Bsw. The calculation shows that the reflection number of the electrons varied with the angle between Mcb and Bsw. When Mcb is parallel with Bsw, the number of the reflected particles is the largest. The number decreases when the angle between Mcb and Bsw increases. These results are expected to provide some important information for the remote measuring of the lunar crustal magnetic field by using electron reflectometry technique.

Simultaneous TC-1 and Cluster Observations of FTE on 13 March 2004

Zhang Qinghe, Liu Ruiyuan, Huang Jiying, DUNLOP M W, Hu Hongqiao, Hu Zejun, BOGDANOVA Y V, WALSH A

2009, 29(2): 166-174. doi: 10.11728/cjss2009.02.166

Abstract(4739) PDF 883KB(1443)

Abstract:
This paper analyzed the observations of the FGM and PEACE on TC-1 and Cluster Spacecraft between 12:15 and 12:25 UT on 13 March 2004. In this interval, the TC-1 spacecraft located in the magnetosheath southward the sub-solar magnetopause, and observed a standard magnetosheath FTE with a positive to negative bipolar characters at about 12:19 UT. The Cluster spacecraft array was encountering the plasma boundary layer near the high-latitude magnetopause in the northern hemisphere, crossing the magnetopause into the magnetosheath at about 12:23 UT. It also observed a standard magnetospheric FTE with a positive to negative bipolar characters at about 12:21 UT. With the similar features of the magnetic field structures and plasma data, these two FTE might be the same FTE moving through TC-1 and then Cluster. Since all 4 Cluster spacecrafts observed the FTE, the four-spacecraft techniques Minimum Directional Derivative/Difference (MDD) and Spatio-Temporal Difference (STD) were applied to calculate the dimension, motion and scale of these FTE. The inferred northwardly reconnected flux tube for the FTE is shown to move north-east and tailward with a quasi-2D structure and a scale of 1.21 Re. Whilst, the FTE motions are shown to be consistent with the expected motion of reconnected magnetic flux tubes over the surface of the magnetopause, arising from a predominantly low-latitude reconnection site during the prevailing upstream conditions. According to the predictions of the Cooling model, the motion of the FTE observed by TC-1 spacecraft is inferred, which implied that the speed and size of flux tube increase with its poleward moving.

Gyrosynchrotron Emission of Space Plasma Clouds

Sun Weiying, Wang Chuanbing, Wu Ji, Wang Shui

2009, 29(2): 175-182. doi: 10.11728/cjss2009.02.175

Abstract(3841) PDF 588KB(1542)

Abstract:
The high density plasma clouds with strong magnetic field will appear as CMEs propagating in the interplanetary space. The plasma clouds radiate electromagnetic wave in radio wave band. In order to study the characteristics of CME propagation, the gyrosynchrotron emission mechanism, which is the main radio radiation mechanism of the plasma clouds, is studied. The physical parameter of the plasma clouds (e.g., electron density, electron temperature, magnetic field and energy distribution) inside the CMEs can be derived according to the emission intensity or brightness temperature of them. In this paper, the emission, absorption and polarization characteristics of gyrosynchrotron emission as the optical depth are studied. The gyrosynchrotron emission process of isotropy and anisotropy plasma clouds with thermal and nonthermal electrons are also studied and summarized. Moreover, the expression of gyrosynchrotron emission intensity and brightness temperature is also provided as the refractive index is not equal to 1.

Study of Ionospheric TEC Horizontal Gradient by Means of GPS Observations

Huang Wengeng, Chen Yanhong, Shen Hua, Zhuang Chunbo

2009, 29(2): 183-187. doi: 10.11728/cjss2009.02.183

Abstract(5601) PDF 596KB(1946)

Abstract:
Dual-frequency GPS receiver can automatically correct time delay error caused by ionospheric Total Electron Content (TEC). But it cannot eliminate signal scintillation error caused by ionospheric irregularities. Even for differential GPS systems, ionospheric error is one of major sources in GPS positioning, for example, error from ionospheric TEC gradient, which will affect accuracy and degrade performance of GPS application system. In this paper, the magnitude of ionospheric TEC horizontal gradient is studied by means of GPS observations. The vertical TEC, and its horizontal gradient and ROTI index over NTUS station, which located in equatorial anomaly region, are derived from GPS observation provided by IGS network. It is found that, between post-sunset and around midnight, the ionospheric TEC has great fluctuation, and intense radio waves scintillation, which is represented by big ROTI index, takes place during this periods. Furthermore, the steep TEC horizontal gradient and its fast variation with respect to time appear. By comparison, the ROTI index, ionospheric TEC horizontal gradient and vertical TEC correlate very well with each other, and their variations characteristics result from density irregularities produced by plasma instability in ionosphere. It is suggested that when scintillation events are investigated, ionospheric TEC gradient is also one of considerable parameters.

Study of High Precision and Continuous Ionosphere Model Determination

Fan Guoqing, Wang Wei, Xi Xiaoning, Wei Lidong

2009, 29(2): 188-194. doi: 10.11728/cjss2009.02.188

Abstract(4400) PDF 756KB(1703)

Abstract:
This paper presents a new idea to determine polynomial ionosphere model with the circumstance that lacking of real observation data in special region. Besides real observation data, grid data calculated by global ionosphere model has been used as a background. The weight of two kinds of data has been discussed, and then mathematical model has been established. Secondly, the model continuity between two segments have been discussed, and then a smoothing method to calculate ionosphere delay has been studied, which uses two groups of time weighting neighbored model coefficients. Finally, the availability of the model was proved by mathematic experimentation.

Autocorrelation Method for Interpolation of Ionospheric Characteristic Parameters

Feng Jing, Liu Wen, Jiao Peinan, Fan Junmei

2009, 29(2): 195-201. doi: 10.11728/cjss2009.02.195

Abstract(3821) PDF 578KB(1152)

Abstract:
The autocorrelation method considers the ionospheric characteristic of interest as a realization of a random process, modeled as the sum of a periodical component and a random Gaussian process, assuming stationarity during the period of interest. Then the process is defined by its autocorrelation function. Based on the autocorrelation analysis theory, a proper steady ionospheric parameter is uesd and the corresponding autocorrelation model which is positive definite is also established in this paper. On this basis, an interpolation method for ionospheric missing data is presented. This method improves the interpolation accuracy of the method given by Muhtarov and Kutiev in 1999. It generally decreases the error by 1~2 percent, and even by nearly nine percent sometimes. Therefore it largely advances the effect of interpolation for ionospheric historical missing data. Furthermore, the variation rules of the interpolation error along with seasons, solar activites and latitudes are analysed.

Short-term Forecast of f₀F₂ Based on Ionospheric Storm Empirical Model and Kalman Filter

Xu Tong, Wu Jian, Wu Zhensen, Huang Chaojun, Wei Guohui, Feng Jian

2009, 29(2): 202-207. doi: 10.11728/cjss2009.02.202

Abstract(4235) PDF 657KB(1399)

Abstract:
With the time weighted accumulation index ap(τ), an empirical storm model of the relative deviation of f0F2 from its monthly median is established. It shows good accuracy only at strong geomagnetic disturbed condition in summer and equinoxes, but less accuracy result for winter. The wide used method in weather, ydrography, etc., Kalman filter, is used to update the coefficients of the empirical model and expected to make better improvement. The test with the ionosound data of hourly values from 1986 to 1995 at Changchun illustrates that the root-mean-squre error of the forecasted values in one hour advance is 0.76 MHz in winter, 0.68 MHz in summer and 0.61 MHz in equinoxes, respectively. The root-mean-squre error in different seasons are from 0.87 MHz to 1.43 MHz in the case of ap(τ)>100, i.e. the super strong geomagnetic disturbed condition. Simultaneously the method is compared with IRI2001 including the STORM model for several disturbed events, which shows the ability of updating the model coefficients and prospect of application.

One-step Ahead Prediction of f₀F₂ Based on Phase Space Reconstruction

Kong Qingyan, Liu Wen, Jiao Peinan, Fan Junmei

2009, 29(2): 208-212. doi: 10.11728/cjss2009.02.208

Abstract(3771) PDF 558KB(1217)

Abstract:
One-step ahead prediction of critical frequency f0F2 is presented, using samples of about 5856 observations of f0F2 with 15-minute time resolution taken from a station in the low latitude, from March 2005 to April 2005. Based on phase space reconstruction of chaotic time series, and according to the theory that near trajectories have similar characteristics, the k-nearest neighbor method is taken to forecast f0F2 15 minutes ahead. Training method and self-adaptive-select method are attempted to define the neighbor numbers used for prediction, and for these neighbors, averaging method and regression ones are taken to treat them. The forecasting errors for those methods are compared. It is shown that one-step ahead forecasting method based on phase space reconstruction can reach high accuracy. In addition, the method has the advantage of easy to implementing with high processing speed. So it is quite suitable for quasi real-time prediction.

Ionospheric Electro-magnetic Disturbances Prior to Yutian 7.2 Earthquake in Xinjiang

Zhang Xuemin, Qian Jiadong, Ouyang Xinyan, Cai Jin'an, Liu Jing, Shen Xuhui, Zhao Shufan

2009, 29(2): 213-221. doi: 10.11728/cjss2009.02.213

Abstract(4172) PDF 1070KB(1606)

Abstract:
Based on the observing data of electro-magnetic field and other plasma parameters on DEMETER satellite of France, the anomalous variations in ion temperature Ti, ion density Ni, Very Low Frequency (VLF) magnetic spectral values and so on were analyzed before Yutian 7.2 earthquake in Xinjiang. The analysis on Ti shows that the abrupt abnormal signals above epicentral area occur frequently in a much wider space, so they are with lower reliability as seismic precursors. Using revisited orbit method to compare the shapes of the density of H+, it is found that all curves in a year are with consistent shape, but the peak amplitude in summer and autumn is 1 times of that in spring and winter. Compared the curves of Ni in 2008 with those in 2007 and 2006, apparent increases were exhibited at peak value regions in one month prior to Yutian earthquake with the amplitude rising to more than a magnitude relative to the other two years since February, and it continued to the earthquake occurrence. As for the magnetic spectrum data, orbits were selected in the distance of 2000\,km and single frequency (400 Hz) values were extracted and arranged to a time series according to their record date and common latitude scale (0~60°N). The results show that during 2 days before the earthquake, the spectrum values at 400 Hz increased approximately by an order of magnitude, reflecting an obvious electro-magnetic emission occurred in ionosphere before the earthquake. It is illustrated after processing the three components of ELF electric and magnetic field on March 20 by vector analysis that, some left-rotated polarization electro-magnetic signals existing at the observing period reflect that the variation of ion density in ionosphere was accompanied by the emission of ELF electro-magnetic signals. Summing up, the variation process of these ionospheric parameters is consistent to the coupling mechanism of earthquake preparation and ionosphere at present.

Effects of Solar UV Radiation on Space Optical Films

Wang Yingjian, Wang Yongmei

2009, 29(2): 222-228. doi: 10.11728/cjss2009.02.222

Abstract(4124) PDF 721KB(1327)

Abstract:
Optical remote sensing is an important means for spaceborne remote sensing, and optical films also have been applied widely in temperature control and energy supply systems of satellite. Their performance in space environment plays an important role for satellite operation in orbit, especially for satellite life and safety. This paper gives the physical mechanisms of the effects of solar UV radiation on optical films, and analyses its rule of this effects. In addition, the influences of atom oxygen erosion, energetic particles and electrostatic charging on the optical films degradation induced by under solar UV irradiation have been analyzed. The experimental results about the effects of solar UV radiation on space-based optical system coatings are also reviewed. Finally the suggestions for contamination protection are provided.

Analysis and Calculation on Collision Breakup Characteristics of Orbital Spacecraft

Li Yiyong, Shen Huairong, Li Zhi

2009, 29(2): 229-233. doi: 10.11728/cjss2009.02.229

Abstract(4324) PDF 589KB(1494)

Abstract:
The collision breakup problem of orbital spacecraft is studied in this paper. The collision breakup algorithm of orbital spacecraft is presented based on NASA standard breakup model. Constraint conditions required for the breakup calculation are analyzed emphatically. Finally, the general utility simulation calculation program is implemented, and is verified to be correct by comparing with measured data of P-78 satellite breakup event. The research can be an important reference to predict and analyze damage characteristics of orbital collision events.

Research of the Evadible Period and Satellite Orbit Maneuver

Wang Jianfeng, Liu Jing, Liu Lin

2009, 29(2): 234-239. doi: 10.11728/cjss2009.02.234

Abstract(3043) PDF 558KB(1339)

Abstract:
With the expansion of the human's activity in exploring, utilizing the outer space, the total number of orbital space debris increases rapidly, which leads to an essential danger to the spacecrafts and astronauts in the future. Space environment protection is becoming the most important task in space navigation. In order to ensure the success of space mission, the low-orbit objects are more important. The forecast and alarm system of space debris is an important application of space object scouting around the earth. In order to avoid the collision between two objects, the orbit change of at least one of the two objects before their collision is necessary. In this paper, some analyses on the relationship between the increment of speed and variations of orbits are studied. Some strategies for orbit maneuvers are also given. At the same time, some research on the over pass durations from the ground stations is done. These works provide effective technique support for the forecast and alarm of space debris and spacecrafts.

Study on System of Space Information Based on Quantum Entanglement

Yan Yi, Pei Changxing, Han Baobin, Zhao Nan

2009, 29(2): 240-243. doi: 10.11728/cjss2009.02.240

Abstract(3083) PDF 492KB(1138)

Abstract:
Quantum communication is an unconditional secure manner of transmitting information. A system of space information based on quantum entanglement is presented. It is using stratospheric platform and geosynchronous satellite as quantum repeater to deliver entangled photon pairs. The communication link between sender and receiver is built by quantum entanglement, and quantum information is transferred by the principle of quantum teleportation. The characteristic of the system is discussed, and numerical analysis is made for the performance of transmitting information. The result shows that the system can effectively transmit information in security.

Weak Solar Scintillation Effects on Deep Space Communication

Zhao Na, Meng Xin, Hu Shengbo

2009, 29(2): 244-248. doi: 10.11728/cjss2009.02.244

Abstract(3931) PDF 554KB(1549)

Abstract:
Solar scintillation effects can be significant for deep-space telecommunication links at small Sun-Earth-Probe (SEP) angles. Severe scintillation can make the telecommunication link unavailable. The physical characteristics of solar conjunction and scintillation are presented, the Rician channel model is set up, and the Gaussian approaches of communications channel are obtained once Rician factor exceeds 10\,dB in deep space exploration due to weak solar scintillation. At last, we simulated the weak scintillation effects on telemetry signals at both X-band and Ka-band by the model.

Structural Analysis About a New Solar Sail

ZHENG Jinjin, SHENG Zhaoyu, ZHOU Hongjun, HUANG Wenhao, SHENG Lianguan

2009, 29(2): 249-256. doi: 10.11728/cjss2009.02.249

Abstract(3381) PDF 378KB(1898)

Abstract:
The article presents a structural analysis of a new space probe-solar sail. It was deployed successfully on ground. The loads for an outer space mission was introduced and expressed with equation. As a special state, the largest load around earth was used to analyze the model by the finite element method. Some results about strain and stress was obtained after setting some initial parameters. Compared to the results in the literature, the results presented here are significant.