2012 Vol. 32, No. 4

Display Method:
Variation Characteristics of Cusp Configuration Based on T96 Modelormalsize
LI Hui, WANG Chi, ZHANG Beichen
2012, 32(4): 461-468. doi: 10.11728/cjss2012.04.461
Abstract(2054) PDF 582KB(1055)
Based on the T96 model, we obtained the topology of the Earth's cusp and defined some parameters (e.g., minimum magnetic latitude of the equatorial boundary, latitudinal width, flare angels in the meridian and terminator plane, inclination, flatness, central magnetic local time) to describe its configuration. The influences of the solar wind dynamic pressure, the interplanetary magnetic field and storm intensity on the cusp's configuration are further studied. As the increasing of the solar wind dynamic pressure and storm intensity, the cusp's minimum magnetic latitude of the equatorial boundary, inclination, and the flatness all decrease, while the latitudinal width and flare angles in the midnight-noon and dawn-dusk directions increase. With the increasing of southward IMF, the equatorial boundary, latitudinal width, flare angle in the midnight-noon direction and inclination all decrease, while the flare angle in the dawn-dusk direction and flatness both increase. However, the situations of northward IMF are contrary. The magnetic local time of the cusp is controlled by IMF By. When By is positive/negative, the cusp moves toward dusk/dawn side. And there is a good linear correlation between the magnetic local time and IMF By. By comparing to some former observational results, the cusp obtained from the T96 model is nearly in accordance with the observations.
Statistical Studies of Magnetic Reconnections at Boundaries of Interplanetary Small-scale Flux Ropes
QI Yu, YAO Shuo, HE Jiansen, TIAN Hui, TU Chuanyi
2012, 32(4): 469-476. doi: 10.11728/cjss2012.04.469
Abstract(2220) PDF 703KB(1136)
Recently, the improvement on space and time resolution of in-situ instruments makes the small-scale flux ropes the hot point in the study of solar wind. Previous works analyzed the in-situ measurements from WIND between 1995 and 2005, and they reported two different lists of small-scale flux ropes with only 4 cases in common. The two lists were selected by human vision and by computer program, respectively. A recent work surveyed the list from human vision, finding magnetic reconnections in the boundary layers of 42% small-scale flux ropes. In order to reveal the magnetic reconnection properties at small-scale flux ropes' boundaries from both lists, we analyzed the computer selected list, finding magnetic reconnection happened at the boundaries in 41% of the flux ropes. Furthermore, other properties also indicate the two flux rope lists have almost the same trend statistically. These properties include magnetic reconnection shear angle, decrease of magnetic field magnitude and observational time scale of reconnection exhaust. Since more samples give more confident results, we combine the magnetic reconnection events in both lists, totally 71 magnetic reconnection exhausts. Our result shows 70% with a magnetic field strength depression larger than 20%, about 66% of the magnetic reconnection events are associated with a magnetic field shear angle larger than 90°. This indicates that the magnetic reconnection at the boundaries of the small-scale flux ropes are more likely to be anti-parallel than the reconnection events in the solar wind. Meantime, this result supports the previous work result based on the human vision selecting list. Our discussion first demonstrated the leading edge magnetic reconnections and the trailing ones have similar signatures, implying boundaries of small-scale flux ropes are different from the magnetic clouds. Therefore, the small-scale flux ropes do not expand as their larger scale counterpart- the magnetic clouds.
Statistical Analysis of Multi-spacecraft Observations on CIR Evolution
WANG Jingjing, LUO Bingxian, LIU Siqing, GONG Jiancun
2012, 32(4): 477-487. doi: 10.11728/cjss2012.04.477
Abstract(2323) PDF 772KB(1270)
STEREO-BEHIND (STB) and STEREO-AHEAD (STA) drifted behind and ahead of ACE around the Sun, with longitudinal separation increasing day by day. CIR driven by high speed solar wind from coronal holes swept STB, ACE, and STA sequentially. Currently, solar wind observations on ACE are the direct basis for Earth space environment forecasting. Based on interplanetary magnetic field and solar wind observations on STB and ACE, assuming high speed stream transmitted uniformly and radially from coronal holes, characteristics of CIR travel time from STB to ACE with their longitudinal separation increased from 0° to 70° was discussed. Statistical variation characteristics of high speed stream parameters were analyzed. The following was found out. Firstly, CIR arrival time on ACE could be predicted by CIR observations on STB. The average and maximum errors of travel time was 0.217d and 0.952d, respectively. 61% of all events reached ACE earlier than theoretical travel time. The maximum errors of travel time increased with longitudinal separation. The errors of travel time was related to observation differences in CIR speed on STB and ACE. The average and maximum errors of travel time were reduced to 0.194d and 0.489d respectively after being corrected by speed variances. Secondly, Linear correlation coefficient of maximum CIR speed on STB and ACE was 0.84. Characteristic parameters of the same CIR on STB and ACE such as speed and proton temperature showed the least difference, while proton density and total pressure showed relatively large difference. The average and maximum range of difference on CIR characteristic parameters observed by STB and ACE, such as maximum speed, maximum proton temperature, maximum total pressure, maximum magnetic field and maximum magnetic southward components, increased with longitudinal separation, while they decreased on maximum proton density. Thirdly, CIR events with larger maximum range and average of observation difference between STB and ACE concentrated in longitude 10°, 25° and 47°, corresponding to CR2059-2060, CR2065-2066, CR2077-2078, which had larger errors on travel time. These results showed that, there was a strong similarity between CIR observations on STB and ACE. Therefore, CIR observations on STB could be used as reference of CIR characteristics on ACE, and provided basis for forecasting of Earth space environment disturbance.
Analysis on Relativistic Electron Flux Enhancement Event at GEO in April 2010
ZHENG Jinlei, ZHONG Qiuzhen, CHEN Liangxu, LIU Siqing, DING Zhu
2012, 32(4): 488-500. doi: 10.11728/cjss2012.04.488
Abstract(2429) PDF 2441KB(1298)
The relativistic electron flux enhancement event at GEO in April 2010 is analyzed in contrasting with other 6 similar events from 2004 to 2010. Solar wind and geomagnetic conditions which might trigger this event were analyzed. Analytical results indicate that the relatively weaker magnetic storms were prone to make the high flux part of relativistic electrons closer to GEO orbit, and whistler wave acceleration mechanism probably played important roles. The injection depth of seed electrons was closely related to magnetic storm intensity. Dst index curve is well fitted with the lower edge of higher flux region of 30~100keV electrons. The injection depth of seed electrons determined the region where mass of >300keV electrons appeared. Because of the relatively weak storms in the relativistic electron flux enhancement event, the seed electrons injected into a shallow region which was close to geosynchronous orbit, leading to relativistic electron flux abnormally enhancement in geosynchronous orbit. The intense substorms in relativistic electron flux enhancement event at GEO in April 2010, which generated sufficient seed electrons and enhanced the wave-particle interaction, was an essential factor leading to relativistic electrons flux enhancement.
Study of the Instantaneous Change of Secondary Cosmic Ray During Thunderstorm
XU Bin, BIE Yeguang, ZOU Dan
2012, 32(4): 501-505. doi: 10.11728/cjss2012.04.501
Abstract(1931) PDF 432KB(1049)
Coincident study on the Atmospheric Electric Field (AEF) change and EAS particle increase during thunderstorm is very important in understanding the acceleration of secondary cosmic rays particle caused by AEF. From April to August, 2006, thunderstorms were frequently recorded at Yangbajing Cosmic Ray Observatory. This work analyzed the correlation between AEF and scaler mode counting rate during thunderstorm when the AEF has violent change. The results revealed that the counting rate of four channels had different feedback on the violent change of AEF, which showed that their energy and most components were different. In general, counting rate in channels of n=1, 2 are found to have large increase varying from 1% to 9%, while there was less or no significant changes for channels of n=3, n≥ 4. These preliminary results were very important to the further study of the acceleration mechanism of secondary cosmic rays.
Investigation on Es Properties in Representative Region of China
KONG Qingyan, CHEN Yue, LIU Wen, FAN Junmei
2012, 32(4): 506-512. doi: 10.11728/cjss2012.04.506
Abstract(2030) PDF 672KB(1254)
In this paper, the characteristics of sporadic E layer (Es) is discussed, using data measured from China vertical stations of Haikou (20.02°N, 110.20°E), Lhasa (29.39°N, 91.08°E) and Changchun (43.54°N, 125.19°E) for one solar period between January 1976 and December 1986. The diurnal, seasonal and solar activity variations of Es occurrence probability with critical frequencies greater than several special values (f0Es > 3, 5, 7, 9MHz) are discussed. The obscure property is also analyzed. The results show that: the most significant occurrence probability presented during daytime in summer months, and does not depend significantly on solar activity. The distribution regularity is of great difference with different stations, and in most cases, Lhasa has the biggest occurrence probability. As to the blanketing property, three stations also have different distribution characteristics, except for that the obscure probability in summer is bigger than other seasons and is bigger in solar minimum than solar maximum too.
Observations of the Global Ionospheric Response During the January 2009 Stratospheric Sudden Warming Event
LEI Xiaolong, FU Yang, XUE Zhengang, DU Xiaoyong
2012, 32(4): 513-523. doi: 10.11728/cjss2012.04.513
Abstract(2173) PDF 1183KB(1175)
A major Stratospheric Sudden Warming (SSW) in January 2009 was the strongest and most prolonged on record. In the period of this warming event, the solar activity and geomagnetic disturbance are extremely low. Hence it provides a good opportunity to investigate the response of the ionosphere to SSW event. The Kriging method is adopted to construct map of NmF2, hmF2, and integrated Vertical TEC (VTEC) within height ranging from 110km to 750km with data derived form COSMIC radio occultation system. And global TEC maps in the Sun-fixed coordinate are also withdrawn from IGS GIMs. By comparing these maps, it can be found that NmF2, hmF2 and TEC increase in the morning hours and decrease in the afternoon and night. Under fixed location and local time bins, cases during SSW and non-SSW days from global COSMIC observations are compared, which shows that NmF2, hmF2, and VTEC during SSW days, on average, increase 17%, 12%, 10km in the morning , decrease 10%, 15%, 16km in the afternoon, and decrease 19%, 23%, 11km in the afternoon respectively. According to the results of comparison of IGS GIMs during SSW and no SSW days, the main difference occurs in the middle and low latitude region, moves along with UT time and corresponds to the position of ionospheric anomaly. It also can be found that increase of TEC (VTEC and IGS TEC) is stronger in the northern hemisphere than in the southern hemisphere during the morning time. Furthermore, the phenomenon that NmF2, hmF2 and TEC (VTEC and IGS TEC) are decreased in the night hours has never been mentioned by previous studies. So altimeter observations by the OSTM/JASON-2 satellite are used for further verification and the phenomenon is validated at last.
Methods for Extracting Backscatter Ionogram Leading Edges
FENG Jing, LI Xue, QI Dongyu
2012, 32(4): 524-531. doi: 10.11728/cjss2012.04.524
Abstract(2115) PDF 2688KB(1182)
Algorithms for automatic backscatter ionogram scaling are established. The algorithms are used in the backscatter sounding system developed by China Research Institute of Radiowave Propagation (CRIRP) and show good results. The autoscaling system has been developed in two overall stages. The first stage is the automatic cleaning of a raw ionogram, which filters the raw ionogram to remove the interferences and noises. The second stage is to extract features from the clean ionogram, such as the propagation modes, the leading edges, etc., and this paper describes part of this work. Methods for extracting backscatter ionogram leading edges are presented. For a single layer or the lower one of two layers, the leading edge is extracted by edge identification algorithm on the ionogram with interferences and noises removed. For the upper one of two layers, the leading edge is extracted by power and gradient algorithm based on Gaussian-fashion weights on the ionogram just after interference suppression. The methods given in this paper have high accuracy and are easy to implement. They are applied successfully in several projects.
Radiation Shielding Method of Energetic Particles for Ultraviolet Photomultiplier of the Sun Synchronous Orbit
YU Yingqing, WANG Yongmei, FU Liping, KONG Chunyang, LI Xiaoyin, WANG Yue
2012, 32(4): 532-536. doi: 10.11728/cjss2012.04.532
Abstract(1992) PDF 496KB(731)
The radiation environment of space accounts much for ultraviolet Photomultiplier Tube (PMT) performance degradation and even invalidation. The ultraviolet PMT's anti-radiation shielding methods depend on the environment of space radiation, spacecraft's orbital altitudes and their life expectancy as well as the type of ultraviolet PMT. Energetic particles environment of the sun synchronous orbit and Monte-Carlo simulation calculation are used in simulating PMT model's shielding effects. Our calculation results are supported an optimization design of shielding compositions for UV PMT on Sun-synchronous orbit. The simulations have determined an optimized shield constituted by an Aluminum-Tungsten-Aluminum tri-layer. And each thickness is 2mm, 0.5mm, 2mm. In a sun-synchronous environment, the dose received by PMT will be decreased from 9.98× 106rad to 8.41× 102rad, and this optimized multilayer structure could meet our performance requirements.
Numerical Simulation on Single Bubble Pool Boiling in Different Gravity Conditions
ZHAO Jianfu, LI Zhendong, ZHANG Liang
2012, 32(4): 537-543. doi: 10.11728/cjss2012.04.537
Abstract(1963) PDF 592KB(1190)
In this paper, the growth processes of a single bubble on a fixed single site and the relative heat transfer under different gravity are numerically investigated for saturated water at 0.1MPa. A simplified lubrication theory is used to predict the contribution from the micro-wedge area underneath the growing bubble, while vapor and liquid phases in other macro-area are treated as one fluid by using the continuum interface model. The Level Set Method and constant superficial contact angle are used to capture the interface between the vapor and liquid phases and the motion of contact line on the heating wall, respectively. The numerical results indicate that the equivalent diameter is proportional to about (1/3~1/2)-power of the growing time in spite of whatever gravity levels. But gravity has great influences on both the departure diameter and the growing time. The bubble departure diameter is proportional inversely to about 1/3-power of gravity, while the growing time is proportional inversely to about 4/5-power of gravity. The area-averaged heat fluxes are approximately proportional to the 3/2-power of the wall superheat when the number density of active nucleation sites fixes. Furthermore, this trend has no change with the decrease of gravity.
Experimental Study on Growth of an Isolated Bubble Utilizing Short-term Microgravity Drop Tower
LI Jing, ZHAO Jianfu, XUE Yanfang, WEI Jinjia, DU Wangfang, GUO Dong
2012, 32(4): 544-549. doi: 10.11728/cjss2012.04.544
Abstract(2030) PDF 576KB(991)
Pool boiling in short-term microgravity has been studied experimentally utilizing the Drop Tower Beijing of the National Microgravity Laboratory of Chinese Academy of Sciences, which can provide a microgravity period of 3.6s. The growth process of an isolated bubble in microgravity has been presented and analyzed in detail. A P-doped N-type square silicon chip with the dimension of 10mm×10mm×0.5mm with a smooth surface was used for the heater element. Subcooled FC-72 with a concentration of air of 0.0046 moles gas/mole liquid was used as the working fluid. Electric heating with constant current was used to input the heat into the heater element. Analyses on high-speed images of the growth process of an isolated bubble and on the data of heat transfer obtained in the experiments have also been conducted. It is found that the bubble growth model based on classical thermal-controlled mechanism can describe the early period of bubble growth observed in the experiments. The value of the empirical parameter in the relative model is inside the range reported in the literature, which indicates that gravity has a much slight influence during the early period of bubble growth. For large size bubble in microgravity, however, much accurate data can be provided.
Study on Dynamic Coupling Characteristic of Flexible Spacecraft
LU Yuying, LIU Zhuyong, HONG Jiazhen
2012, 32(4): 550-554. doi: 10.11728/cjss2012.04.550
Abstract(2030) PDF 447KB(1130)
Dynamic forward recursive formulation of rigid-flexible coupled multi-body system is an important modeling theory of dynamics, which will not only reduce the workload but also avoid the accumulated error, and is apt to the exact solution when applied to complex systems because it retains the influence caused by elastic vibration of flexible parts to the center of mass and moment of inertia. In this paper, the general type of forward recursive formulation to rigid-flexible coupled spacecraft system was applied, and the higher accuracy in calculation was expounded. Finally, through numerical calculation, advantage of the forward recursive method in handling the coupling program of flexible system than that of the traditional method was verified.
Small Eccentricity Artificial Frozen Orbit Design With Transverse Continuous Low-thrust
MA Qingtian, LI Junfeng, BAOYIN Hexi
2012, 32(4): 555-559. doi: 10.11728/cjss2012.04.555
Abstract(2437) PDF 434KB(1119)
The non-critical inclination natural frozen orbit requires that the argument of perigee is 90 degrees, the eccentricity e has a magnitude of order 1×10-3 and the eccentricity has a corresponding relationship with inclination and semi-major axis, thus the variety of selection of the orbit parameters is greatly restricted by these rigorous requirements. This paper suggests that small eccentricity artificial frozen orbit be presented by applying transverse continuous low-thrust with constant amplitude and half orbit period switching direction, thus the rigorous requirements on orbit elements are relaxed. The transverse continuous thrust aT used to maintain the small eccentricity artificial frozen orbit is proportion to the square root of semi-major axis and in converse proportion to eccentricity. Considering aT near critical inclination, it is proportional to the displaced inclination Δi, and the fuel used to maintain the orbit is small. Moreover the transformational relation between qusai-mean orbit elements and instantaneous orbit elements should be considered during the simulation.
Orbit Design of Space-based Visible Sensor Satellite for Monitoring the Objects in Geosynchronous Belt
TANG Yi, WU Meiping, LI Xian, FU Xiaofeng
2012, 32(4): 560-566. doi: 10.11728/cjss2012.04.560
Abstract(1933) PDF 657KB(1089)
Based on the analysis of the optical and positional characteristics for geosynchronous objects, this paper motivates the location chosen for the search fence and the Space-Based Visible (SBV) sensor operating strategy. The relationship among the size of the search fence, the time required to search the fence region and the times of the observation is deduced firstly. Then, according to the requirement of the space mission and the characteristics of SBV sensor, this paper selected the surveillance orbit type and established the constraint conditions of the system parameters. Finally, the range of altitude for the surveillance orbit is provided on the constraint conditions, and the observational efficiencies of all possible surveillance orbits are simulated. The results of simulation indicate that the percentages of coverage for objects in geosynchronous belt of the surveillance orbits are above 90% when the orbital parameters are suitable. The percentages of coverage are above 95% when the field of view for SBV sensor is about 4° × 4° or the size of the search fence is above 40°.
A Class of QC-LDPC Codes With High Performance and Low Complexity in Deep Space Communication
GUO Rui, HU Fangning, LIU Jilin
2012, 32(4): 567-574. doi: 10.11728/cjss2012.04.567
Abstract(1858) PDF 483KB(1123)
A class of QC-LDPC codes with high error performance and low complexity was proposed. Firstly, a global matrix M with extern Approximate Lower Triangular (eALT) method was designed. Each 1 in the global matrix M was replaced by a permutation matrix, and each 0 was substituted by a null matrix to reduce the number of small stopping set and error floor. Then, In order to lower the complexity of searching cyclic shift coefficient, a Zig-Zag based method was put forward, which uses a given formula to generate coefficient and does not need search by computer. At last, the linear encoding process was given with the proposed QC-LDPC. Simulation result shows that the proposed method can reduce the number of small stopping set, increase the minimum distance of LDPC codes, and achieve very low error floor with linear encoding complexity. What's more, the cyclic shift coefficient was generated by structured method.
Research on Communications at Low SNRs in Deep Space Explorations
JIANG Bin, BAO Jianrong
2012, 32(4): 575-584. doi: 10.11728/cjss2012.04.575
Abstract(1825) PDF 646KB(1049)
Compared with traditional wireless communications, deep space communications are challenged with difficult problems of extremely low Signal-to-Noise Ratio (SNR), high transmission delay and discontinuous reception of data which are mainly caused by large transmission loss, limited energy and changeful trajectory of the space probe, etc. Faced with these problems, the researches on several key techniques at extremely low SNR in deep space communications are introduced. And the techniques include deep space antenna arrays, coding and modulation, joint demodulation and decoding, fountain coding and the autonomous radio and so on to help solve the above problems. Finally, the development trends and related applications of them are prospected.
Method for Time-of-transmission Recovery Based on Assisted-GPS Positioning
CAO Hui, YUAN Hong
2012, 32(4): 585-591. doi: 10.11728/cjss2012.04.585
Abstract(2284) PDF 437KB(1080)
As we all known, time-of-transmission cannot be worked out successfully when GPS receiver isn't able to accomplish the bit synchronization, frame synchronization and navigation data demodulation. In this proposed algorithm, the time-of-transmission was recovered through the iterative LMS equation and ambiguity search with the assistance data, including ephemeris information and satellite clock corrections etc. The algorithm was derived strictly and its main steps were introduced. Then, the selection of search factor ω was discussed and the restrictions for the initial errors of approximate location (150km) and receiver's clock bias (180s) were eliminated. The algorithm was proved to be valid using simulation results, which indicates that this method can be used in the real GPS application with poor received signal or partial signal.
Adaptive Fitting of Colored Noises and Corresponding Covariance Matrices in Navigation
CUI Xianqiang, YANG Yuanxi, ZHANG Xiaodong
2012, 32(4): 592-597. doi: 10.11728/cjss2012.04.592
Abstract(2433) PDF 460KB(1189)
To use Kalman filtering for kinematic navigation and positioning, we have to deal with function model and stochastic model. The precision and reliability of kinematic Kalman filtering are affected remarkably from the function model and stochastic model errors. Adaptive fitting of both colored noise and covariance matrices by using moving windows are presented based on the assumption that the observation and dynamic model noises mainly include the colored noises with first order self-correlation character. The expressions to calculate the colored noise estimators and covariance matrices of the modified observations and predicted states are obtained. Feasibility and practicability of the model and algorithm are tested by an example. It is shown that the Kalman filtering, based on the adaptive fittings of the colored noises and covariance matrices, can be effective in resisting the influence of the colored noises on the navigation results.
Fault Tree Analysis of the Space Cable-strut Deployable Articulated Mast
HU Ming, DENG Guobing, CHEN Wenhua, QIAN Ping, LIU Dongxu, PAN Jun
2012, 32(4): 598-604. doi: 10.11728/cjss2012.04.598
Abstract(1871) PDF 536KB(1344)
Combined the application environment of the space cable-strut deployable articulated mast, the fault tree of the deployable mast is established by considering the deploying failure of the mast as the top event based on the analysis of its composition and deployment mechanism, whose quantitative and qualitative analysis is finished for the fault tree of the deployable mast. And then the results of the probability of failure, important degree of probability and criticality are obtained and the main factors leading to the deploying failure of the mast are found out. The results show that the accurate deploying of the mast is influenced by lack of driving force, jamming on its roller card of the corner wheel and precision failure, which provides the foundation for the deploying reliability analysis of the space cable-strut deployable articulated mast