Current Issue

2022, Volume 42,  Issue 5

Gaia数据揭示太阳的过去和未来
2022, 42(5): 841-841.
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NASA公布Artemis-3载人登月任务候选着陆区
2022, 42(5): 841-841.
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美欧更新火星采样返回计划行动框架
2022, 42(5): 842-842.
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美航空航天安全咨询小组预警国际空间站过渡计划
2022, 42(5): 843-843.
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NASA揭示近几十年来南极冰层损失情况
2022, 42(5): 843-843.
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俄欧终止ExoMars项目合作
2022, 42(5): 843-843.
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中国科学院征集空间科学(三期)卫星工程候选项目
2022, 42(5): 845-846.
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ESA发布“新世界”空间探索路线图
2022, 42(5): 846-848.
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第二届中国空间科学大会在太原举办
2022, 42(5): 1038-1038.
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Review
Ocean Surface Current Multiscale Observation Mission
DU Yan, DONG Xiaolong, JIANG Xingwei, ZHANG Yuhong, ZHU Di, WANG Minyang, WU Wei, WANG Xiangpeng, ZHAO Zhangzhe, XU Xing’ou, TANG Shilin, JING Zhiyou, LI Yineng, CHEN Kun, CHEN Wen
2022, 42(5): 849-861. doi: 10.11728/cjss2022.05.2022-0047
Abstract:
OSCOM innovatively proposed the Doppler Scatterometer (DOPS) measurement principle, which could detect ocean surface current, ocean surface vector wind, and ocean surface wave spectrum (abbreviation: current-wind-wave) simultaneously. Using DOPS, a real-aperture radar, by a dual-frequency (Ka-Ku) with conically scanned rotating multi-pencil-beam antenna, OSCOM could conduct the integrated observations of current-wind-wave with a swath of more than 1000 km and a high-resolution of kilometer spatial scale. OSCOM will break through the research bottlenecks of ocean sub-mesoscale and non-equilibrium dynamics, ocean multi-scale interactions, and air-sea coupling, and support the theoretical research in ocean sciences and climate change. With the launch of the OSCOM, the application of sea surface current observations will improve the numerical model study, laying the foundation for numerical simulation, assimilation, and forecasting of oceanic non-equilibrium dynamical processes, achieving significant improvements in ocean and ocean-atmosphere coupled models. The application of OSCOM current observations, together with the other multi-source satellite dataset, including the high-resolution SST and ocean surface color, will provide support for the research in marine biogeochemical cycles and carbon budget, meeting the need of the national strategy. The implementation of OSCOM scientific satellite is of vital significance to the advance of the study and the application of satellite observations in Earth Science, leading to the implementation of the applied satellites in China.
Space Physics
Solar Flare Short-term Forecast Model Based on Long and Short-term Memory Neural Network
HE Xinran, ZHONG Qiuzhen, CUI Yanmei, LIU Siqing, SHI Yurong, YAN Xiaohui, WANG Zisiyu
2022, 42(5): 862-872. doi: 10.11728/cjss2022.05.210315028
Abstract:
Solar flares are a kind of violent solar eruptive activity phenomenon and an important warning device of space weather disturbance. In space weather forecasting, flare forecasting is an important forecast content. This paper proposes a flare prediction model based on long and short-term memory neural network, which uses the time sequence of magnetic field changes in the solar active area in the past 24 h to construct samples, and analyzes the time series evolution of magnetic field characteristics through the long and short-term memory neural network to predict whether ≥M-level flares will occur in the next 48 h. This paper uses a data set for all active area samples from May 2010 to May 2017, and selects 10 magnetic field characteristic parameters of SDO/HMI SHARP. In the modeling process, six feature parameters with high weight, gain rate and coverage rate were selected as input parameters through XGBoost method. Through test comparison, the false report rate and accuracy rate of the model are similar to the traditional machine learning model, and the accuracy rate and critical success index are better than the traditional machine learning model, which are 0.7483 and 0.7402 respectively. The overall effect of the model is better than that of the traditional machine learning model.
Prediction of Partial Ring Current Index Using LSTM Neural Network
LI Hui, WANG Runze, WANG Chi
2022, 42(5): 873-883. doi: 10.11728/cjss2022.05.210513061
Abstract:
The local time dependence of the geomagnetic disturbances during magnetic storms indicates the necessity of forecasting the localized magnetic storm indices. For the first time, we construct prediction models for the SuperMAG partial ring current indices (SMR-LT), with the advance time increasing from 1 h to 12 h by Long Short-Term Memory (LSTM) neural network. Generally, the prediction performance decreases with the advance time and is better for the SMR-06 index than for the SMR-00, SMR-12, and SMR-18 index. For the predictions with 12 h ahead, the correlation coefficient is 0.738, 0.608, 0.665, and 0.613, respectively. To avoid the over-represented effect of massive data during geomagnetic quiet periods, only the data during magnetic storms are used to train and test our models, and the improvement in prediction metrics increases with the advance time. For example, for predicting the storm-time SMR-06 index with 12 h ahead, the correlation coefficient and the prediction efficiency increases from 0.674 to 0.691, and from 0.349 to 0.455, respectively. The evaluation of the model performance for forecasting the storm intensity shows that the relative error for intense storms is usually less than the relative error for moderate storms.
Simulation of ENA Imaging Measurements on a Geosynchronous Orbit
LU Li, YU Qinglong, ZHOU Ping, JIA Shuai, CHANG Yuan
2022, 42(5): 884-890. doi: 10.11728/cjss2022.05.210414051
Abstract:
Geosynchronous orbit is located in the ring current region, where the energetic particle emission environment challenges the ion deflection design limit of the Energetic Neutral Atom (ENA) imager. Therefore, there is no measurement record of ENA imaging in this area before. On the basis of possessing the patent of high-energy ion deflection technology, ENA imaging under different Kp index in geosynchronous orbit is simulated. The simulation images show the characteristics of low-altitude ENA emission source and the rough sketch of magnetosphere. Due to the north-south conjugation observation of geosynchronous orbit, the simulated ENA images at different positions all have north-south symmetry. Aiming at the unsolved problems, such as the input source of ring current energetic ions during geomagnetic activities and its evolution process, we analyzed the possible results of ENA imaging combined with in-situ particle measurements in the same satellite, as well as the subversion effect of any north-south asymmetry of ENA map on the inversion model.
Research on the Spatio-temporal Coding Scheme for the Dynamic Earth’s Magnetosphere
WANG Cifeng, HU Xiaoyan, ZOU Ziming, LI Yunlong, BAI Xi
2022, 42(5): 891-900. doi: 10.11728/cjss2022.05.210825093
Abstract:
The spatio-temporal subdivision model for the dynamic Earth’s magnetosphere is proposed to realize the multi-layered subdivision for the dynamic and irregular physical space of the magnetosphere drawing on the idea of the global discrete grids for the geoscience data. The distortion of the grids can be convergent within a certain number of subdivision times. Therefore, the subdivision model can be taken as a formalization for the spatio-temporal characteristics of the Earth’s magnetosphere in a certain range. On this basis, encoding and expressing the spatio-temporal grids obtained by subdivision for computer storage and processing is another key problem in constructing the basic spatio-temporal framework for the organization and management of large-scale observation data of the Earth’s magnetosphere. Due to the specific spatio-temporal characteristics, the classical geoscience coding schemes have trouble in fully reflecting the spatio-temporal relations between the grids. Therefore, it is difficult to support the basic spatio-temporal computing between the grids. In this paper, an efficient coding scheme is designed for the drift shell subdivision grids combining the basic ideas of the integral coordinate coding and the Morton coding schemes. On this basis, the spatio-temporal framework for the dynamic Earth’s magnetosphere is constructed which lays the foundation for the efficient organization and processing of geomagnetic data. The experiments carried out show that, the coding efficiency of the scheme is relatively high and it can support efficient neighbor relationship calculation. It provides a solution for the organization and computing of the multi-source, multi-layered, heterogeneous and large-scale observation data of the dynamic Earth’s magnetosphere.
Research on Long-distance MSTID Event Observed by Multi-instruments over Mid-latitude Regions of China
LUO Ji, XU Jiyao, WU Kun, YUAN Wei, WANG Wei, ZHANG Jiaojiao
2022, 42(5): 901-912. doi: 10.11728/cjss2022.05.210722080
Abstract:
Ionospheric plasma irregularities have always been one of the research focuses in space physics. These irregularities usually have impacts on satellite communication, navigation as well as positioning system. It is of great importance to study the morphological features and the evolutions of these ionospheric irregularities. Medium Scale Travelling Ionospheric Disturbance (MSTID) is one kind of irregularities which usually be wave-like perturbations of the ionospheric plasma in the F-region. The evolution of mid-latitude MSTID is complicated, especially over China. In recent years, with the rapid development of the Chinese Meridian Project and the All-sky Imager Observation Network, more and more instruments have been added to the study of the ionosphere over China. This paper reports a long-distance propagating MSTID event over northeastern China on the night of 17 October 2018. The MSTID were simultaneously observed by multi-instruments, including the all-sky imager, Swarm satellites, High-frequency radar as well as Digisonde. The MSTID lasted for more than 4 hours (12:02-16:23 UT) in the field view of the airglow imager, showing typical wavelength, the phase velocity of 176.3~322.5 km, 67.0~154.1 m·s–1. The MSTID event was possibly generated at high latitude and propagated southwestward to the lower latitude, which was observed by the all-sky imagers in Yichun and Xinlong stations.
Studies for Mesopause Temperature Distribution Characteristics Based on the Sodium Lidar Data
GUO Shangyong, HU Xiong, YAN Zhaoai, CHENG Yongqiang, TU Cui
2022, 42(5): 913-918. doi: 10.11728/cjss2022.05.210901096
Abstract:
As the boundary of mesosphere and thermosphere, mesopause is an important area for studying the middle and upper atmosphere, many energy coupling processes happen here, study for the temperature distribution characters will improve our understanding of the climatology of this region. This paper studies the annual and seasonal temperature distribution characteristics based on the Langfang sodium lidar data in 2013. Results show that, the annual mean mesopause locates at around 97.5 km with the temperature 191.2 K. Under the influence of exothermic chemical reactions, there is a relative maximum temperature 198 K at 91 km on the annual profile. The seasonal temperature at mesopause region is influenced by solar radiation and atmospheric dynamics. In winter, solar radiation is the primary factor, producing a higher mesopause of 181 K at 99 km altitude. In summer, the rising atmosphere from lower altitude makes a colder mesopause at 88 km altitude with the temperature 177 K. Harmonic analysis demonstrates a strong change in annual amplitudes over a rather small altitude range, coupling with the annual phase profile, and it is shown that dynamics in lower mesopause region and solar radiation in upper mesopause region play the key role in determining the thermal structure respectively.
Global Stratospheric Gravity Wave Characteristics by Aura/MLS and TIMED/SABER Observation Data
YANG Wenkai, YANG Junfeng, GUO Wenjie, YANG Xiaohua, XIA Zhongfei, ZHANG Bingyan, CHENG Xuan, HU Xiong
2022, 42(5): 919-926. doi: 10.11728/cjss2022.05.210906098
Abstract:
Gravity waves are one of the main atmospheric waves in near space environment and have an important impact on the global atmosphere circulation. The limb-sounding instruments on the satellites provide the atmospheric temperature, which can be used for the research of the gravity waves. The data from the Microwave Limb Sounder (MLS) on Aura and the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) on TIMED from 2012 to 2014 are used to study the global distribution characteristics of atmospheric gravity waves at the height of 20~50 km. The gravity wave activities derived from the two observations are similar to each other. Gravity waves change significantly with season, latitude and altitude. Gravity waves at high latitudes in the winter hemisphere are strongest, and that at high latitudes in the summer hemisphere are weakest. There are also obvious gravity wave activities over the equator and the subtropics in the summer hemisphere. The results show that the strength of gravity wave increases with altitude. In general, the value of gravity wave activity intensity derived from TIMED/SABER is greater than that from Aura/MLS.
Basic Problems Research in Stratospheric Airship Design
YU Chunrui, QIAO Kai, LIU Dongxu
2022, 42(5): 927-932. doi: 10.11728/cjss2022.05.211015106
Abstract:
Stratospheric airship is a new kind of long-endurance near-space vehicle, which has the characteristics of high flight altitude, long endurance time, outstanding carrying capacity and good cost-effectiveness ratio. Because of its unique flight performance, stratospheric airship possesses extremely extensive and important prospects in application, such as the fields of Earth observation and communication relay. However, design and development of stratospheric airship is a difficult task of system engineering because this vehicle system is highly complex, and the basic problems and solutions of its conceptual design are not completely clear. To solve these problems, this paper introduces the basic characteristics of stratospheric wind field, temperature, and pressure, and then combs the influence of stratospheric environment on the preliminary design of stratospheric airship. Also, the differences between stratospheric airship and conventional low-altitude airship are pointed out by summarizing the remarkable characteristics of stratospheric airship from the aspects of aerodynamics and thermodynamics. Finally, the influence of fundamental problems on the conceptual design of stratospheric airship is discussed to provide reference for the development of stratospheric airship technology.
Design of a Comprehensive Observation Equipment for Atmospheric Electric Field
LI Lei, SU Jianfeng, CHEN Tao, LI Wen, WANG Shihan, TI Shuo, LUO Jing, SUN Hailong, DONG Wei, WU Wei
2022, 42(5): 933-940. doi: 10.11728/cjss2022.05.210824090
Abstract:
The atmospheric electric field is an important parameter in space physics, which can reflect the integrated response of the near-surface atmosphere to meteorological activity, solar activity and geological activity. In this paper, a self-designed and developed integrated atmospheric electric field observation equipment is introduced, which integrates meteorological observation and atmospheric electric field, and can simultaneously measure multiple parameters including temperature, relative humidity, wind speed and atmospheric electric field. The observation results can be used for scientific research on lightning activities, geological hazards, and magnetic storm activities. In this paper, the detection principle, data reception, storage and transmission, and electric field calibration of the integrated atmospheric electric field observation equipment were described, the measured data of the equipment at the Beijing Xialing station has been analyzed , then it was compared with the FAMEMS-DF02 electric field instrument acquired by the National Space Science Center and the meteorological data released by the China Meteorological Network. The results show that the error corresponding to 99% of the moments for each meteorological parameter does not exceed ±10%, and the average error does not exceed ±3%, while the average error of the electric field data is ±0.166 kV·m–1. Finally, error analysis and discussion are conducted for the comparison results.
Microgravity and Material Science
Metabolic Network Flux Balance Analysis of the Microgravity Influence on the Growth of Arabidopsis Thaliana
WANG Zhihan, RUAN Yao, ZHANG Qingye, ZHANG Hongyu
2022, 42(5): 941-951. doi: 10.11728/cjss2022.05.210714077
Abstract:
As a typical space environmental factor, the influence mechanism of microgravity on plants is a research hotspot in space life science. The microgravity environment directly or indirectly affects plant metabolism and induces many physiological adaptations. With the development of systems biology, the metabolic network model enables the modeling of plant metabolism in microgravity. In this study, the flux balance analysis method was used to study the metabolic networks of different tissues of the model plant Arabidopsis thaliana, and to explore the mechanism of the effect of microgravity on the growth and development of Arabidopsis thaliana. By comparing the biomass yield of Arabidopsis thaliana under space and ground conditions, it was found that the biomass of etiolated seedlings, seedlings, shoots, roots, and hypocotyls is decreased by 33.00%, 51.52%, 6.89%, 12.53%, and 11.70%, respectively, consistent with the growth trend of Arabidopsis thaliana in the space environment. Enrichment analysis of metabolic pathways showed that microgravity down-regulated Arabidopsis thaliana’s carbon fixation pathway, while up-regulated the pentose phosphate pathway. This result preliminarily analyzed the mechanism of microgravity influence on the growth and development of Arabidopsis thaliana and demonstrated the potential of the flux balance analysis method in the study of the biological effects of microgravity.
RBF Neural Network in Electrostatic Levitation Position Control
LU Xiaoxiao, LIU Xiaoke, LI Hu, ZHENG Fu, SUN Zhibin, YU Qiang
2022, 42(5): 952-960. doi: 10.11728/cjss2022.05.210927103
Abstract:
With the characteristics of nonlinearity and time variation, the position control system of electrostatic levitation facility cannot suppress the disturbance effectively by using traditional control methods. To solve this problem, a RBF-PID control strategy combining neural network and PID control method was proposed. Firstly, the mechanical analysis on the spherical sample was researched, and the mechanism model of the position control system of electrostatic levitation was deduced. Then, the position control system of electrostatic levitation was constructed, based on the RBF-PID controller. The control parameters were adjusted in real-time according to the simulation results. The simulation results show that it takes 0.12 s to make the sample stable when its surface charge suddenly changes from 10–9 C to 3×10–9 C. The experimental results show that when the sample is in the heated status, the mean absolute error of control system is 0.0416 mm by adjusting the parameters in real time, and the control effect is 70% better than that of traditional PID controller .The proposed RBF-PID control strategy has a high identification accuracy, and it has stronger robustness and stability compared with the traditional PID control strategy.
Space Exploration Technology
Forward Simulation and Comparative Experiment Analysis of Polarimetric GNSS Radio Occultations Detecting Rainfall Events
SU Doudou, BAI Weihua, DU Qifei, SUN Yueqiang, TAN Guangyuan
2022, 42(5): 961-972. doi: 10.11728/cjss2022.02.210409049
Abstract:
Studies have proved that the Global Navigation Satellite System (GNSS) Polarimetric Radio Occultation (PRO) technology has the possibility of detecting rainfall. This study uses GPM DPR products as rainfall rate data to collocate with the latest PAZ satellite observation data, and selects representative rainfall events with a wide range of rainfall and matching with RO events. By selecting 7 raindrop shapes such as TB, and 5 raindrop size distribution models such as MP, the T-matrix method is used to simulate these rainfall events. The Pearson correlation coefficient, root mean square error, and other parameters between the simulated polarimetric phase shift and the observation data calibrated using linear trend, or the observation data calibrated using antenna pattern are calculated respectively. The Pearson correlation coefficients between the simulated value and the calibrated value using linear trend, or the calibrated value using antenna pattern are 0.9994 and 0.9933, respectively. The root mean square error between the simulated value and the calibrated value using linear trend, or the calibrated value using antenna pattern are 0.3429 and 1.2765, respectively. The comparative analysis results show that there is a high correlation between the simulated value and the polarimetric phase shift measured by PAZ and the simulated results are closer to the polarimetric phase shift calibrated using linear trend. The results show that adopting MP or JD as the raindrop size distribution model and SC or PB as the raindrop shape can get higher accuracy when simulating events with a small rainfall rate (below 1 mm·h–1). For events with high rainfall rates (above 1 mm·h–1), selecting the MP or SS raindrop size distribution model and the TB raindrop shape can simulate the best results.
Target Pre-screening Method for Asteroid Exploration Based on Minimum Orbital Intersection Distance
ZHANG Jiawen, ZHENG Jianhua, LI Mingtao
2022, 42(5): 973-983. doi: 10.11728/cjss2022.05.210906097
Abstract:
Asteroid exploration helps to study important scientific issues such as the evolution of the solar system, and the implementation of asteroid exploration during the transfer of deep space missions can increase scientific returns. Aiming at the problem of large calculation amount and low efficiency in the primary selection of asteroid exploration targets directly through orbit recursion, a target pre-screening method based on the minimum orbital intersection distance is proposed. After the formula for calculating minimum orbital intersection distance for hyperbolic orbit is derived, the theory is applied to the screening of asteroid exploration targets. Firstly, based on the shape and spatial position of the orbits of the probe and the asteroids, the geometric closest distances between their orbits are calculated, and the asteroid targets that may meet the approach distance criteria are pre-screened. Then, based on the orbit recursive model, the target asteroids whose real closest distance to the probe is less than approach distance criteria are selected. The simulation results show that this pre-screening method based on the minimum orbital intersection distance can effectively reduce the amount of calculation and reduce the calculation time, thus improving the efficiency of asteroid target determination.
Comparison of Initial Orbit Determination Methods with Very-Short-Arc Angle Observations from LEO Space Debris
LEI Xiangxu, XIA Shengfu, YANG Yang, WANG Xiaozhen, ZHANG Zhengyuan, LI Zhenwei, SANG Jizhang
2022, 42(5): 984-990. doi: 10.11728/cjss2022.05.211026108
Abstract:
Optical observation is the most common observation method for space objects. When optical telescopes work in scanning mode, the obtained observation arc length is usually very short, even less than 1% of the orbital period of the observed space object. And such angle observation arc is called Very-Short-Arc (VSA) angle observation. Based on the VSA of the near-circular LEO space debris, this paper studies the performance differences of commonly used methods for initial orbit determination. The influence of observation arc length on the success rate and error of different initial orbit determination algorithms is analyzed. The results can provide reference for initial orbit determination. Several commonly used methods, such as Laplace method, Gauss method, Gooding method and Range-Search (RS) algorithm, proposed in recent years, are compared and analyzed. The results of large-scale VSA show that the success rate of the RS algorithm is higher than 90%, and the statistical error of the semi-major axis of the initial orbit elements is only 25 km. Results show that the succeed rate of RS method is better than other algorithms. The research results can provide reference for subsequent observation data processing.
High Resolution Design and Realization of 400 MHz Bandwidth Surface Acoustic Wave Chirp Transform Spectrum Analyzer for Deep Space Exploration
RU Penglei, LIU Mengwei, GONG Junjie, WANG Wen, ZHU Haotian, ZHU Di, DONG Xiaolong
2022, 42(5): 991-1003. doi: 10.11728/cjss2022.05.210611071
Abstract:
Chirp Transform Spectrum analyzer (CTS) has the advantages of low power consumption and high stability, and has unique advantages in deep space exploration. The 180 MHz bandwidth chirp transform spectrum analyzer mounted on the Rosetta comet detector is the only back-end heterodyne real-time spectrum analyzer that has successfully completed space missions so far. Based on the principle of chirp transform spectrum analysis, a 400 MHz bandwidth Chirp transform spectrum analyzer was designed and built by combining the digital expander technology with the Surface Acoustic Wave (SAW) compressor technology. By analyzing the compression results in the frequency band, the phase difference between the expander and the compressor was introduced as an important factor affecting the compression waveform. According to the two key parameters of the pulse compression waveform, the main lobe width and the peak side lobe ratio, the optimal matching design of the digital expander and the analog SAW compressor are completed. The compression result of the system is optimized, so that the resolution of the system reaches the theoretical value of 100 kHz. FM signal and multi-frequency signal are used to test and verify the CTS system.
Finite Element Simulation Analysis of Damping Torque of Space Rotating Object
SHI Yongkang, HUANG Shaohua, LIAO Qian, CHEN Jinshan
2022, 42(5): 1004-1011. doi: 10.11728/cjss2022.05.210709075
Abstract:
In order to improve the efficiency of the damping torque in the process of electromagnetic braking, the damping torque of spherical shell is analyzed by using the electromagnetic field software MAXWELL. A two-dimensional Helmholtz coil Finite Element Model is designed and established, and the validity of the model is verified. The Finite Element Model is used to analyze the variation trend of damping torque under the influence of each factor individually. Then, the damping torque formula of the spherical shell model is modified. Simulation results show that the damping moment formula of spherical shell model have its applicable conditions, and is suitable for spherical shell with thickness to radius ratio less than 0.023. The calculation error of the new damping torque formula of spherical shell is smaller than the original.
Trajectory Design of Solar Ring Mission Based on Libration Point Trajectory of Three-body System
JIANG Zhuole, WANG Yamin, ZHANG Yonghe
2022, 42(5): 1012-1019. doi: 10.11728/cjss2022.05.210830094
Abstract:
Solar observations in space are the key means to understand the origin of solar cycles, solar eruptions, and extreme weather events. In order to observe the Sun from the ecliptic plane at 360 degrees, scientists have proposed a 3D solar exploration mission. Aiming at the “Solar Ring” mission, a deployment method of “Solar Ring” orbit based on the low-energy trajectories associated with the libration point of the three-body system is proposed. Using the amplitude and off-orbit points of Sun-Earth L1/L2 Halo orbits as design parameters, the transfer time and deep-space maneuver as the cost function, the mission trajectories are constructed and optimized with the invariant manifolds of three-body system and contour maps. A global analysis of mission cost and the corresponding design variables is carried out. Simulation results show that the orbit deployment cannot satisfy the shortest transfer time and the smallest deep-space maneuver at the same time. The optimal transfer time solution under the orbit maneuver constraint is obtained, and a plan for launching and deploying orbits is designed based on the way of one rocket two spacecraft with the rocket of Long Match 3A.
Modeling and Verification of File Delivery Delay for LTP in Complex Deep Space Networks
YU Guo, DONG Zhenxing, ZHU Yan
2022, 42(5): 1020-1028. doi: 10.11728/cjss2022.05.211029109
Abstract:
Aiming at the problem that the models of file delivery time for Licklider Transmission Protocol (LTP) established in simplified scenarios can’t be directly applied to complex scenarios, a theoretical model of file delivery time for LTP in complex deep space networks is proposed. Previous research has focused mainly on establishment of a data transmission model for LTP in simplified scenarios with one to two hops or multihop scenarios with a custody mechanism of the Bundle Protocol (BP). However, the research results are not applicable to communications in complex deep space networks without the custody mechanism of BP that is more suitable for deep space communications with LTP. Firstly, the transmission mechanism of LTP in complex deep space networks is analyzed. Then, the theoretical model of file delivery time for LTP in complex deep space networks is established based on the analysis of the transmission mechanism before. Finally, a simulation verification platform is built to analyze the correctness and advantages of the model. The results show that the calculated results of the model are in good agreement with the experimental results, and the model proposed is more suitable for complex deep space networks than the models based on simplified scenarios.
Inherent Error and Temporal-Spatial Characteristics of GYGNSS Sea Surface Wind Speed
LIU Shuai, LIN Wenming, LU Yunfei
2022, 42(5): 1029-1037. doi: 10.11728/cjss2022.05.211101110
Abstract:
Global Navigation Satellite System Reflectometry (GNSS-R) is a new technique for the remote sensing of sea surface wind speed. In terms of operational applications, it is necessary to perform a detailed and quantitative analysis on the GNSS-R wind speed. In this paper, wind data of the Cyclone Global Navigation Satellite System (CYGNSS) mission are used to evaluate the capability of GNSS-R in wind remote sensing. First, the collocated buoy winds, as well as the European Centre for Medium-Range Weather Forecasts (ECMWF) winds, are used to analyze the climatologic and the temporal-spatial characteristics of CYGNSS wind speeds. Second, a triple collocation analysis is used to estimate the inherent errors and the calibration coefficients of GYGNSS wind. It shows that the quality of CYGNSS wind is promising for wind speed below 10 m·s–1, but degrades remarkably at high wind conditions. Moreover, the wind speed error is consistent in the temporal domain, but shows certain dependency on the geographic location. Overall, the inherent error of CYGNSS wind speed is about 1.79 m·s–1. The results are not only relevant for the operational application of CYGNSS wind product, but also important for the further inter-calibration of CYGNSS signal.