Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： Solar energetic particles(SEPs) pose one of the most serious hazards to spacecraft systems and constrain human activities in space. Thus, it is of importance to forecast SEP events. Several theories and numerical models are applied to simulate SEP events. Each model makes some assumptions to simplify the complex acceleration and transportation processes within such events. In general, SEP will interact with ambient solar wind and background magnetic field during transportation. It is recognized that interplanetary transport effects must be taken into account at any analysis of SEP propagation. In the previous simulation, it always assumed Parker magnetic field and fixed solar wind speed as the input parameters. However, these assumptions are too simple when compared with the real conditions. In order to get better results, it is necessary to use more accurate background conditions. Recently, we change the fixed solar wind speed into spatial-dependent speed profile based on Parker's theory, and replace the Parker magnetic field with another Parker-like magnetic field based on in situ data at 1 AU. By solving the focused transport equation with simulation of time-backward stochastic processes method, our results show that:(1) Under fast solar wind speed assumption, it is clear that the omnidirectional flux decreases faster than that for the situation with slow solar wind speed in the decay phase. We suggest that it is due to the adiabatic cooling effect. Fast solar wind speed has a significant effect on the adiabatic cooling, which leads the SEPs to lose energy more quickly during transportation. However, slow solar wind speed has less impact on the time profiles of SEP flux and anisotropy. We also compare the time profiles of SEP event observed at different observatories and energies, the results remain the same as previous;(2) When applying in situ data of magnetic field observed by WIND during different Carrington Rotations, the omnidirectional flux time profiles vary greatly, and the main results are as followings:the peak flux appears to be delayed, multi-peak occur, anisotropy also has some differences.We think it results from the magnetic field polarity, which affects the pitch angle, and, furthermore, modulates the momentum. The characteristics are similar in solar minimum and solar maximum, while the peaks seem to be more when solar activity is active. We conclude that the real magnetic field polarity may exert a significant influence during the propagation of SEP. In the future, we will try to use the real-time background conditions which obtain from MHD models in our simulations, in order to make a thorough study of the SEP propagation.
Peer Review Status:
Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract：基于RMAP协议对SpaceWire高速总线进行了架构设计与实现。首先给出了SpaceWire高速总线的整体设计;其次对SpaceWire编解码器中的DS编码进行了优化;然后根据RMAP协议的基础要求,设计了RMAP SpaceWire总线的工作流程与实现方法;最后通过仿真平台对该设计进行仿真测试。仿真测试表明:设计实现了RMAP SpaceWire高速总线的基础功能,数据链路传输速度可以达到79.84 Mb/s。
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract：针对数传、测距一体化的调制方式高斯最小频移键控复合伪码测距(Gaussian minimum shift keying+pseudo-noise,GMSK+PN)信号的信噪比估计,提出了一种精度较高、复杂度较低的快速算法。该算法采用层状结构分解的方式,将信号分解为若干信号单元,对每一个分解的信号单元进行功率分配计算或信噪比估计,最后快速准确地计算出整个信号的信噪比。信噪比在1~13dB之间时,估计误差小于0.5dB。利用Simulink仿真工具,验证了该算法的有效性。
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract：
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract：针对地月系L2点不同任务需求下的低耗能转移轨道设计问题,基于不变流形理论与混合优化技术,深入研究了不同月球借力约束与不同幅值Halo轨道的入轨点(简称HOI点)对转移轨道飞行时间与燃料消耗的影响,给出了HOI点选择策略。首先结合任务要求并考虑月球引力影响,在月球借力点施加不同约束条件,通过微分修正算法调整Halo轨道的稳定流形,设计月球到Halo轨道的转移轨道。采用遗传算法与微分修正算法相结合的混合优化策略,在同时考虑地球停泊轨道高度、倾角、升交点赤经与航迹角等多约束条件下,对燃料最优的地月转移轨道进行研究。最后,分析月球借力高度、借力方位角和不同HOI点对平动点转移轨道飞行时间与燃耗变化量的影响,对于考虑月球借力的地月平动点转移轨道设计与应用具有重要的参考价值。
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： 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穘T-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.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： 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.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract：为了研究大面积等离子体片的分层特性,利用脉冲磁约束线形空心阴极放电装置,在150 Pa氦气中产生了持续时间为200μs、面积为60 cm×60 cm的大面积等离子体片。采用快帧法和旋转空心阴极法利用郎缪尔探针首次获得了等离子体片分层时厚度方向电子密度分布及其演化构成的二维分布图;基于获得的二维分布图,研究了分层等离子体片厚度方向电子密度的分布特征与磁场强度和放电电流的关系。实验发现,等离子体片分层时厚度方向电子密度呈现双峰曲线分布特征;当放电电流为2 A,磁场强度为1.5×10-2,2.25×10-2,3×10-2T时,双峰间距分别为0,3.2,8.4 mm;当磁场为3×10-2T,电流为1,2,3,4 A时,双峰间距分别为8.6,8.2,6.8,5 mm。结果表明:分层等离子体密度峰值间距随着磁场的增强和放电电流的降低而增大。
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： 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.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： 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.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： The characteristics of current high orbit GPS (Global Positioning System) signal are of poor availability and low positioning accuracy. Positioning of high Earth orbit satellites using GPS/Beidou combined system is studied. The visibility of navigation satellites and the Geometric Dilution of Precision (GDOP) are analyzed. Through simulation and analyzing, it is verified that the GPS/Beidou combined system has better performance than that of single GPS system. On one hand, the GPS/Beidou combined system can receive more satellites' signal than single GPS system. On the other hand, GDOP of the GPS/Beidou combined system is smaller than that of single GPS system. At the same time, the use of high-precision atomic clock in the satellite receiver can realize positioning of three satellites, and reduce the technology requirements of receiver.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： With the ever-increasing of space data, a reasonable data-arrangement is strongly required for high efficiency in data accessing and visualization. In this paper, basing on the characteristics of solar-wind data, a SDOG-R grid model is employed, which is radial independent division in the adaptive SDOG grid. For huge Sun-Earth space, it is divided into multi-resolution grids. The original data, which is output from a SIP-CESE solar wind model, are re-sampled, and put into the subdivided grids. The grid model is applied to both regular and irregular sampling data, and fully maintains the characteristics of original data to the best and encodes grids with an improved CDZ curve. Specific examples of data organization are given. The experiments prove that the grid model not only resolves the problem that grids are too dense at two poles and the spherical center, but also meets the need for higher resolution in radius than in latitude and longitude. Besides, 3D LOD spatial data model can not only provide multi-resolution data, but also significantly improve the large-scale mass data retrieval and access efficiency, and can support the organization and management of massive spatial data effectively.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： This paper introduces the structure and working principle of the Neutral Atom Imaging System-High （NAIS-H） which is in the MIT project. Based on the testing needs of the instrument， we have designed ground test equipment， including the circuit system and the host computer system. In this paper， we show the structure and working principle of the ground test for NAIS-H， and tell structure and java programming of the sub modules of the host computer system in detail， such as API communicating system， data analyzing system and data saving system. At last， we test the equipment， and the result shows the ground test system has good performance and achieves the design requirement.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： For the small satellites formation flying， the distance between satellites must be determined and an adequate inter-satellites communication medium must be used to transmit the science data. In order to minimize device complexity， this paper studied a system capable of simultaneously transmitting high rate telecommunication and ranging. through simulations by Simulink in different ranging modulation index， obtained the bit error rate of telecommunication data. By analyzing the characteristics of GMSK+PN signal， an effective demodulation scheme for GMSK+PN is developed by this paper.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： CCD is the core component for realizing space soft X-ray exploring mission. According to the requirements for space soft X-ray exploring， the scientific CCD42-10 BI AIMO produced by E2V Company has high sensitivity， low noise and high readout speed， and a driving circuit based on FPGA is designed. This design is developed on the XC3S500E hardware platform， using VHDL language to describe the driving timing. The CCD is driven by EL7202 chips. The simulation and testing results indicate that the CCD performed stably， and the design matches the driving requirements of CCD42-10 BI AIMO.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： In order to save channel resources， asynchronous digital multiplexer， which can multiplex different rate， different burst time slot digital source， has been widely applied. Aims to reduce the maximum extent possible source packet data transmission delay， improve channel utilization， design scheme of a greedy asynchronous dynamic digital multiplexer is proposed. The priority scheduling strategy of sources is given too. Two kinds of multiplex model are described by hardware description language. Simulations for greedy dynamic multiplexer and virtual channel multiplexer， under the condition of different physical frame length and two source model， have been carried out by Modelsim. The simulation results show that， for the average transmission delay and delay jitter， the greedy dynamic multiplexing is superior to the virtual channel multiplexing， and is more effective in saving resource of source cache.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： In order to ensure the success of space exploration mission， the small satellite formation requires reliable inter-satellite communications. Based on 802.11， small satellite formation network protocol architecture was designed. Firstly， network protocol stack was built according the OSI stack layers， the key parameters of physical layer and data link layer of was tuned to meet the requirement of inter-satellite communication， the network layer routing protocol was analysed， and then the satellite network formation model was made and analysed. With the aid of the network simulation tool NS3， performance of four typical formation network was simulated. Simulation results show that the network protocol architecture ensures inter-satellite communications based on 802.11. Although network performance varies greatly in different flyning formations， it can be adjusted according to the task requirements.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： In the measurement of space particle， the interference caused by the particles is an important factor of the measure accuracy decline in the space particle detection， Anti-coincidence cup technology is an important means to eliminate particle interference. The paper introduces the origin of spatial interference particles and theory of anti-coincidence cup measuring system.An output pulse readout circuit based on A225F is designed， achieving in reshaping the quasi-Gaussian waveform at a high counting rate.The details of the application of A225F is described in the paper.The simulation and experimental results prove the reasonableness of the design.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： The capability of the modern payloads on satellite is getting stronger and stronger， and the motor has been used widely. The life and reliability of the motor equipped on satellite would be the main characters that restrict long-time work of the satellites. So the design of motor system on satellites should be not only satisfied with the application requirements， but also the requirements of life and reliability should be fully taken into account simultaneously. In this paper， a two-phase hybrid stepper motor control system based on FPGA is introduced. In order to improve control accuracy and suppress low-frequency vibration， the system was designed based on subdivision control method and an acceleration process was designed to ensure that motor started properly. Large current was used to stop the motor quickly and small current was used to keep the motor motionless. The test results showed that this system has the advantages of low-power consumption， starting and stopping steadily.
Peer Review Status:Awaiting Review
Subjects: Geosciences >> Space Physics submitted time 2016-04-22
Abstract： Schmidt and Angel lobster-eye X-ray imaging system can realize total reflection focusing and imaging by simulating lobster-eye microchannel structure. Compared with traditional way of X-ray imaging, it is provided with large field of detection view, high resolution and energy acquisition ability. This paper studies on two lobster-eye basic structures. Based on the principle of grazing incidence, we analyzed Angel and Schmidt structure of light entering focal plane and space resolution. We use tracepro simulation software to model and verify the several focusing and imaging property parameters of these two lobster-eye structures, such as receiving/transmitting light, maximum/cross arm, maximum/background, cross arm/background. The theoretical analysis and simulation results show, when the focal length is longer and channel length-width ratio is about 50. Due to multiple reflection, focusing and imaging signal-to-noise ratio of some main parameters of Schmidt is higher than Angel model, and the spatial resolution is lower. When the focal length is shorter and channel length-width ratio is about 10. Due to simple reflection, focusing and imaging signal-to-noise ratio of some main parameters of Schmidt is lower than Angel model, and the spatial resolution is almost the same.
Peer Review Status:Awaiting Review
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