2016 Vol. 36, No. 2

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Exploring the Dynamic X-ray Universe: Scientific Opportunities for the Einstein Probe Mission
2016, 36(2): 117-138. doi: 10.11728/cjss2016.02.117
Time-domain astrophysics will enter a golden era towards the end of this decade with the advent of major facilities across the electromagnetic spectrum and in the multi-messenger realms of gravitational wave and neutrino. In the soft X-ray regime, the novel micro-pore lobster-eye optics provides a promising technology to realise, for the first time, focusing X-ray optics for wide-angle monitors to achieve a good combination of sensitivity and wide field of view. In this context Einstein Probe, a soft X-ray all-sky monitor mission, was proposed and selected as a candidate mission of priority in the space science programme of the Chinese Academy of Sciences. This paper reviews the most important science developments and key questions in this field towards 2020 and beyond, and how to achieve them technologically. It also introduces the Einstein Probe mission, including its key science goals and mission definition, as well as some of the key technological issues.
Statistical Study on IMF By Control of the FAC in the Magnetotail
CHENG Zhengwei, SHI Jiankui, LIU Zhenxing
2016, 36(2): 139-146. doi: 10.11728/cjss2016.02.139
Abstract(949) PDF 890KB(1093)
Using the magnetic field data from Cluster spacecraft and the Interplanetary Magnetic Field (IMF) data from ACE spacecraft, the effect of IMF By component (IMF |By|<10nT) on the Field-Aligned Current (FAC) occurrence rate and density at the Plasma Sheet Boundary Layer (PSBL) in the magnetotail is investigated. 1657 FAC cases from July to October in 2001 and 2004 were selected for analysis. We present that the IMF By component plays a very important role in controlling the occurrence rate and density of the FAC in the PSBL in the magnetotail. The FAC occurrence is higher (about 55.6%) when the IMF By is positive compared with that when the IMF By is negative. When the IMF |By| is more than 4nT, the occurrence rate of FAC is about 77.4%. The FAC occurrence in the magnetotail has an obvious positive correlation with the IMF |By|, and when the IMF By is positive, this correlation is better. The FAC density also has an obvious positive correlation with the IMF |By|, and when the IMF By is positive, this correlation is better. The above results show that the IMF By component has strong control on the occurrence and density of the FAC cases in the magnetotail, and that the change of FAC is closely associated with the duskward IMF (the IMF By is positive).
Seed Point Selection through Equal Line Integral of Magnetic Field Intensity Algorithm for Visualization of Geomagnetic Field
GAO Guangda, HU Xiaoyan, ZHONG Jia, ZOU Ziming
2016, 36(2): 147-152. doi: 10.11728/cjss2016.02.147
Abstract(1151) PDF 1101KB(1169)
Drawing the magnetic lines as streamlines is a general method of visualizing geomagnetic field. A key factor to evaluate the effect of the geomagnetic field visualization is whether the space distribution of geomagnetic field lines is consistent with that of magnetic field intensity, while the distribution of geomagnetic field lines is determined by seed point selection. The traditional algorithms that select seed points with uniform angles on magnetic meridian circles cannot objectively reflect the space distributions of magnetic field intensity. This paper proposes an algorithm of selecting seed points with equal line integral of magnetic field intensity. The algorithm is applied to draw the geomagnetic field lines with the data from T96 model and IGRF model. The redundant magnetic field lines existing in the result are removed. Statistical analysis and comparison between the space distribution of magnetic field lines and the geomagnetic field intensity reveals that this algorithm can effectively visualize the geomagnetic field.
An Improved Algorithm for Nowcast of Kp Index
WANG Geng, LUO Bingxian, LIU Siqing, GONG Jiancun
2016, 36(2): 153-166. doi: 10.11728/cjss2016.02.153
Abstract(1156) PDF 3307KB(1298)
The planetary three-hour-range Kp index is widely used in space weather services. Due to the two weeks' time delay of the release of Kp index, the real-time estimation of the Kp index becomes essential for space weather forecasting organizations. In this paper, an improved algorithm for real-time Kp estimation on the basis of Takahashi's procedure was developed. The new algorithm improved the accuracy of Kp estimation by distinguishing the day-to-day variations of geomagnetic field's regular variation and taking account of both the diurnal and seasonal variations of magnetic disturbance. The statistical result shows that the Prediction Efficiency (PE) increased from 0.77 to 0.84 using Fredericksburg's data, from 0.88 to 0.92 using the nine stations network's data. Using the data from Beijing Ming Tombs observatory (BMT) from 2000 to 2006, the PE increased from 0.70 to 0.80 compared with the Takahashi procedure. The error of the estimations differs from universal time, season and the scale of magnetic disturbance. The RMS error reached maximum for Kp=7. Analysis of Kp using the SuperMAG indices indicated that the asymmetric distribution of Kp stations affects the Kp nowcast performance.
Modeling and Analysis of the Power Sectra of Ionospheric Amplitude Scintillations over Haikou Station and Its Application
ZHANG Hongbo, SHENG Dongsheng, LIU Yumei, SUN Shuji, XU Tong
2016, 36(2): 167-174. doi: 10.11728/cjss2016.02.167
Abstract(1168) PDF 2192KB(1009)
The amplitude data of UHF-band ionospheric scintillations were recorded at a low-latitude station of China, Haikou station (geographic: 20.00°N, 110.33°E), during the high sunspot activity year of 2013. Based on these data, the Welch algorithm of the Fast Fourier Transform methods was used to analyze the scintillation intensity power spectra, and four types of typical intensity power spectra were found and presented. A nearly sinusoidal fluctuation in the east-west horizontal direction was found in the irregularity structure by analyzing the contour map of spectral density as a function of local time and spatial scale. The spectral index p of the ionospheric amplitude scintillations was extracted for the year of 2013, and the variation of the spectral index p was analyzed by statistical method and an empirical model of the spectral index p over Haikou station was put forward, which was applied in the empirical Climatological Model of Scintillation Occurrence Probability (CMSOP) over the low-latitude of China. Finally the prediction of ionospheric scintillation occurrence over Haikou station from CMSOP is compared with the observations.
Mid-latitude Planetary Waves Observation from MST Radar Measurements in the Troposphere and Lower Stratosphere
TANG Lei, HUANG Chunming
2016, 36(2): 175-187. doi: 10.11728/cjss2016.02.175
Abstract(1132) PDF 3710KB(1226)
Characteristics of the Planetary Waves (PW) in the Troposphere and Lower Stratosphere (TLS) were investigated with Mesosphere-Stratosphere-Troposphere (MST) radar wind measurements in Xianghe (116.9°E, 39.8°N) from January 2012 to December 2014. Spectral analyses show that the TLS region is dominated by quasi-16-day and quasi-10-day PW, while the former ones are more significant. In the troposphere regions (above 17km height), the PW with dynamic periods are primarily observed, which last less than three months and don't indicate significant seasonal variation. Meanwhile, the amplitudes of the PW in the zonal direction exceed those in the meridional direction. In the lower stratosphere regions, intense PW mainly occur in the zonal component in winter. The amplitudes in the stratosphere are generally smaller than those in the troposphere. This paper also discusses the propagation characteristics of PW based on MST radar data and MERRA reanalysis data. The result shows that zonal component of the quasi-16-day PW observed in February and March 2014 propagated eastward with a zonal wave number of 2 (the horizontal wave length was about 15324.7km). The corresponding phase velocity was 11.1m·s-1 (positive eastward). The quasi-16-day PW propagated upward vertically with a 64km vertical wave length. In addition, the observation in May 2014 showed that the quasi-10-day PW in the zonal component propagated eastward with a zonal wave number of 1. Its horizontal wave length, phase velocity and vertical wave length were 30649.4km, 35.5m·s-1 and 50km respectively.
Atmospheric Drag Coefficient Modification for Orbit Prediction Precision Improvement of LEO Space Objects
CANG Zhongya, XUE Bingsen, CHENG Guosheng, ZHU Xiaolu
2016, 36(2): 188-195. doi: 10.11728/cjss2016.02.188
Abstract(1380) PDF 1736KB(1513)
Atmospheric drag is the primary disturbing force to LEO space objects since the atmospheric density is still considerable. This paper proposes a new method based on space environment indices and neural network model to modify drag coefficient. According to TLE (Two Line Element) sets, by simulating the orbit prediction and comparing prediction semi-major axis to real-time value, the optimal values of drag coefficients (B0sup*) are selected. It is found that optimal values are one or two days ahead the values in TLE, and they are all corresponded with F10.7 and Ap indices. Based on historic data, the neural network is built for drag coefficient correction to improve the orbit prediction precision. Result shows that the neural network model could timely response to space environment disturbance. This method is applied in Tiangong-1 (TG-1) and International Space Station (ISS) orbit prediction to verify its validity and universality, and it shows that the orbit prediction accuracy is improved by 50%~60% during geomagnetic disturbance while the errors are biggest. Generally, this method could improve the orbit prediction precision by 30%, the and success rate of improvement is about 80%.
Guidance, Navigation and Control Technology for Lunar Surface Exploration
XING Yan, TENG Baoyi, LIU Xiang, MAO Xiaoyan
2016, 36(2): 196-201. doi: 10.11728/cjss2016.02.196
Abstract(1516) PDF 2734KB(1287)
The lunar rover of Chang'E-3 probe was the first explorer of China roaming on the surface of extratellurian celestials, which had the totally different Guidance, Navigation and Control (GNC) technology from the Earth orbital spacecrafts. The main requirements of the rover for GNC system included autonomous navigation, environment perception, obstacle recognition, path planning, emotion control, and so forth. Several key technical breakthroughs had been achieved in GNC system of Chang'E-3 lunar rover-Jade Rabbit, such as autonomous position and attitude determination, multi-wheel motion control on lunar surface, Binocular Stereo Vision based autonomous environment perception and path planning, structure-light vision based obstacle avoidance, and lunar terrain and light condition analog simulation for experimentation on Earth, etc. In this paper, we discussed the mission overall requirement, key technology, and ground experiment of guidance, navigation and control system of Chang'E-3 Lunar Rover.
Comparative Analysis of Two Representative Computation Models for Deep Dielectric Charging
WANG Song, TANG Xiaojin, WU Zhancheng, YI Zhong
2016, 36(2): 202-208. doi: 10.11728/cjss2016.02.202
It is of great importance to analyze the deep dielectric charging for spacecraft using computer simulation. The general methodology is as follows. The first step is to get the charge deposition in dielectric through particle transport simulation, and then to compute the charged electric potential and electric fields according to the potential computation model. In the preliminary stage, researchers usually employed the RIC model or its improved versions for analysis, whereas the simplified model based on current conservation law has played the dominant role in recent years. In order to study the equivalence between these two classical models, the computation method for each model is presented with verification by comparing the results of a benchmark model with the published results. Then, theoretical analysis is made that the simplified model is a further simplified version of the RIC model, and they can lead to the same charging outcome providing the same total conductivity is used. Finally, through computing the charging process of a dielectric panel with three different grounding conditions under GEO severe electron radiation, sufficient simulation verifications are provided. The obtained conclusions can make beneficial reference for the evaluation of satellite deep dielectric charging.
Designing and Implementing of the Payload Self-exploration
LIANG Yaoming, MA Miao, WANG Lianguo, SHEN Weihua, ZHU Yan
2016, 36(2): 209-214. doi: 10.11728/cjss2016.02.209
Abstract(1230) PDF 849KB(2084)
The payload of the satellite has different working modes. In order to obtain the optimum working state, it needs to be switched constantly between each mode. When switching, many working state parameters need to be configured, such as, 28 Front Electronic Ends (FEE), neutron acquisition and processing circuit, the trigger system circuit, high voltage powers and payload data management system. To improve the switch flexibility of payload exploration mode and lower the complexity of parameter configuration during switching, the management project is studied for payload self-exploration of the satellite by analyzing the working modes of this explorer. The designing method is based on event-driven which are combined by programming-experts on the ground and perform-units on the satellite. Software realization result is given out for the payload self-exploration. Meanwhile, the reliability and security measures are studied. The test results show that the function is implemented. It can be used on the satellite to explore space anytime and anywhere. It reduces the dependency on the remote control center.
Design of Magnetometer Based on GMI Effect in Fe-based Nano-crystalline Ribbon
LÜ Weiwei, WANG Jindong, ZHAO Hua
2016, 36(2): 215-220. doi: 10.11728/cjss2016.02.215
The magnetometer based on Giant Magneto-Impedance (GMI) effect becomes one of the hottest points on magnetometer research in recent years. Compared with other magnetometers, GMI magnetometer has the advantages of miniaturization, high sensitivity, quick response, high temperature stability and low power consumption. Based on the sensitive material of Fe-based nano-crystalline ribbon, a GMI probe and subsequent signal processing circuit have been designed and realized to compose a GMI magnetometer. Experimental results suggest that in the magnetic field ranging from-25000nT to 25000nT, the sensitivity is 0.176mV·nT-1, which attains the measurement requirement of a weak magnetic field. The magnetometer has advantages of small size and low power consumption so that could be used in space magnetic field measurement.
Research on the Control System of the Ground Attitude Simulation Light Source
WANG Xinghua, WANG Lingyun, WANG Bo, ZHANG Guoyu, SU Shi, SUN Gaofei, LIU Shi
2016, 36(2): 221-226. doi: 10.11728/cjss2016.02.221
The Sun sensor and the infrared Earth sensor are two important components of attitude control after satellite launch. The ground attitude simulation light provides solar simulation signal and infrared Earth analog signal for the two parts as a ground test equipment. This paper designs a set of ground attitude simulation light which consists of one solar simulation light including 4 light seams and one north as well as one south infrared Earth simulators to simulate the opening angle of 15.6°, and provides an analog Sun protection signal for south and north Earth sensors' Sun protection probes. Composition and the overall structure of the ground attitude simulation light control system are described in detail. Through analysis and calculation of each simulation, strict timing relationship between the sources is given, and through the experiments of each source simulation between sequential test, it can be shown that the simulation speed phase-locked error is no more than 1ms, and the angle error between light source simulation timing is less than 0.5°.
Design of Unfolded Mechanical Properties Testing System for Multidimensional Deployment Mechanism of Antenna
WANG Yajun, XU Zhigang, HE Yun, HE Xibin
2016, 36(2): 227-236. doi: 10.11728/cjss2016.02.227
Satellite antenna is a key component for satellite communications. In order to ensure the reliability of antenna deployment mechanism in orbit, its mechanical properties must be tested on the ground. To achieve this goal, this paper presents a mechanical performance testing system of antenna deployable mechanism which is in multidimensional framework style. The deployment process of antenna under high or low temperature and weightless environment of space can be simulated, and a loading test during the process could be carried on. The scheme and working principle of the testing system has been illustrated, as well as the innovative design of the three degrees of freedom mechanical arm and the loading mechanism. In addition, the mathematical model of the loading system has been built and simulated. Analyses show that the error of gravity balance is less than 2% FS (Full Scale) and error of the loading moment is less than 2%, thus the system can meet the test requirements of deployable mechanism. The testing system has made it a reality that the test of deployable mechanism has stepped from theoretical simulation stage across to the full-physical simulation stage, which is of great significance to ensure the satellite reliable communications in orbit.
Time Delay Estimation of Flexible Space Robot Robust H Control and Vibration Suppression
YE Bingneng, CHEN Li
2016, 36(2): 237-244. doi: 10.11728/cjss2016.02.237
Abstract(732) PDF 918KB(3569)
This paper discusses the trajectory tracking and vibration suppression of free-floating flexible space robot with uncertain system parameters, which combines the advantages of time delay estimation control and robust H control. Time-delayed estimation is used to achieve unknown dynamics of space robot system online and to perform a compensation during the tracking control. L2 gain control is employed to achieve L2 interference suppression of time-delay estimation error, which could further improve the robustness of the system. At the same time, theoretical analysis proves that the introduction of L2 gain control can suppress the influence of time delay estimation error on the system to satisfy the robust H performance, and ensures all signals in the closed-loop system to be bounded. In addition, the virtual control force is proposed to transform the original control scheme, which can achieve both tracking the desired trajectory and suppressing the flexible vibration control target through only one control input. Simulation results and comparison chart are given to illustrate the effectiveness of the proposed control scheme and the active vibration suppression of flexible.