空间科学学报

Abstract:
Three-dimensional Magnetohydrodynamics (MHD) modeling is a key method for studying the interplanetary solar wind. This paper develops a new solar wind MHD model driven by multiple observations. The computation region of this model is from 0.1 Astronomical Unit (AU) to 1 AU. The model solves the ideal MHD equations in a six-component grid system by using the Total Variation Diminution (TVD) Lax-Friedrich scheme. In the new model, the physical parameters at the inner boundary are determined as following:the magnetic field is derived using the magnetogram synoptic map from GONG; the electron density is derived from the Polarized Brightness (PB) observations from LASCO; the velocity is deduced using an Artificial Neural Network (ANN) tactic with both the magnetogram and PB observations, and the temperature is derived from the magnetic field and electron density by a self-consistent method. We use this model to simulate the interplanetary solar wind during CR2062. The results show various observational characteristics, and are in good agreement with the OMNI and Ulysses observations. Thus, this model can be used to provide more realistic interplanetary solar wind and will be helpful for the research on space weather prediction.

Automatic Detection of Sunspots and Extraction of Sunspot Characteristic Parameters

LI Ling, CUI Yanmei, LIU Siqing, LEI Lei

2020, 40(3): 315-322. doi: 10.11728/cjss2020.03.315

Abstract(1598) PDF 6244KB(111)

Abstract:
Sunspots are solar features located in active regions of the Sun, whose number is an indicator of the Sun's magnetic activity. With a substantial increase in the size of solar image data archives, the automated detection and verification of various features of interest are becoming increasingly important for the reliable forecast of solar activity and space weather. In order to use high time-cadence SDO/HMI data and extract the main sunspot features for forecasting solar activities, we constructed an automatic detecting sunspot procedure with a mathematical morphology tool and calculated sunspot group area and sunspot number. By comparing our results with those obtained from Solar Region Summary compiled by NOAA/SWPC, it is found that sunspot group area and sunspot number computed with our algorithm are in good agreement with the active region values compiled by SWPC, and the corresponding correlation coefficients of sunspot group area and sunspot number are 0.77 and 0.79, respectively. In this study, high time-cadence feature parameters obtained from HMI data can provide timely and accurate inputs for solar activity forecasting.

Observation of a Dual Reconnection Exhaust Inside the Boundary Layer of Magnetic Cloud at 1 AU

ZHOU Zilu, SONG Xiaojian

2020, 40(3): 323-330. doi: 10.11728/cjss2020.03.323

Abstract(1491) PDF 6316KB(60)

Abstract:
Magnetic reconnection is prevalent in the low speed and low proton beta solar wind and is usually associated with Interplanetary Coronal Mass Ejections (ICME). In this paper, a dual reconnection exhaust in the front boundary of a Magnetic Cloud (MC) was observed by WIND spacecraft on 18 October 1995. The Alfvénic accelerated or decelerated plasma jets were examined using Walén relation near the boundary of the exhausts, which are consistent with the characteristics of the interplanetary reconnection exhausts reported in recent literatures. As a consequence, multiple reconnection exhausts could be abundant ahead of the MCs and complex 3D boundary layers would form instead of single reconnections exhausts. Such complex structures may bring some difficulties in searching for reconnection events in the magnetic cloud boundary layers.

Observations of TEC Depletion, Periodic Structure of TEC, ROTI and Scintillation Associated with ESF Irregularities over South China

DENG Kun, MA Yonghui, LIU Minbo, GUO Zhixiong, WANG Shu

2020, 40(3): 331-340. doi: 10.11728/cjss2020.03.331

Abstract(1126) PDF 8251KB(39)

Abstract:
The observations of Global Positioning System (GPS) scintillation, Total Electron Content (TEC) depletion, the periodic structure of TEC and Rate of TEC Index (ROTI) over south China were presented. Data were collected from GPS observations at stations of Shenzhen and Guangzhou from 2011 to 2012. This study reported that the ratio of simultaneous occurrences of TEC depletions with strong scintillations was higher than that of TEC depletions with weak scintillations in vernal and autumnal equinoxes of 2011 over South China. The number of the periodic structures of TEC with depletion contained was greater than that with no depletion contained corresponding to strong scintillations. The structure of the slab of plasma irregularities could be responsible for the simultaneous occurrences of TEC depletion with strong scintillations and ROTI. Before and during the occurrences of strong scintillation, there was Large-Scale Wave Structure (LSWS) which provided the seed ionization perturbation to trigger ESF irregularities and contributed to the periodic structure of TEC.

Performance Analysis of BDS Single Frequency Ionosphere Model

XU Longxia, LI Xiaohui, HE Lei

2020, 40(3): 341-348. doi: 10.11728/cjss2020.03.341

Abstract(2148) PDF 6392KB(210)

Abstract:
With the construction of BDS-3, the single-frequency ionospheric model of BDS-2 (BDSKlob) which is only suitable for the correction of ionosphere delay in Chinese area is no more applicable. The BDGIM model is proposed for the correction of ionosphere delay globally in BDS-3. The performance of BDGIM model is compared with BDSKlob and GPSKlob (the ionospheric model of GPS) in different areas for day and night in the time period of 1-31 March 2019. The results show that the correction ratio of BDGIM model of BDS-3 is over 75% in China while that of BDSKlob is 59%. Its global correction ratio is 60% which is superior to the correction ratio 49% of GPSKlob. As far as the Root Mean Square (RMS) of ionosphere is concerned, the global average value of BDGIM model is less than that of GPSKlob. The RMS of vertical ionospheric error of BDGIM is less than 6 TECU in all the other areas excluding the high latitude area of south hemisphere.

Analysis of the Effectiveness of Launch Traffic Model to the Space Debris Environment

SHEN Dan, LIU Jing

2020, 40(3): 349-356. doi: 10.11728/cjss2020.03.349

Abstract(1489) PDF 5789KB(111)

Abstract:
The future launch will directly affect the space debris environment, and it must be rationally planned for maintaining the long-term sustainable development of outer space. In this paper, the Space Object Long-term Evolution Model (SOLEM) and Monte Carlo method are used to quantitatively analyze the effects of the launch number, launch mass and launch area of space objects on the future space debris environment, and increase in the numbers of collisions and space debris caused by large constellations are studied. The simulation results show that the main factors affecting the collision are the number of launches, the launch area, and the launch mass, which will affect the number of debris generated by the collision. Deployment of large constellations will have a great impact on the space environment. These provide a theoretical basis for rational planning of the future launch.

Characteristics of the Near-surface Atmospheric Electric Field over the Top of a Flat Mountain in Xilin Hot Volcano Geopark

U Han, CHEN Tao, LI Renkang, HE Zhaohai, ZHANG Huawei, LUO Jing, LUO Fushan, WANG Naiquan, DONG Wei

2020, 40(3): 357-363. doi: 10.11728/cjss2020.03.357

Abstract(1436) PDF 5356KB(70)

Abstract:
The intensity of the atmospheric electric field is an important parameter of atmospheric electricity. Accurate measurements of the atmospheric electric field are important for the monitoring and warning of thunderstorms and earthquakes. In this paper, the electric field data obtained by a balloon experiment of measuring the near-surface atmospheric electric field on 27 August 2015 is used to study the distribution of the atmospheric electric field with height within 500m near the Earth surface. The results show that fair-weather atmospheric electric field value over the top of a flat mountain rises exponentially with height. Both the values and range of the atmospheric electric field are large, especially within the height of 100m, and the value can reach 1kV·m^-1 or more. In addition, the empirical formula is used to derive the atmospheric conductivity near the surface of the Earth. Influenced by heavy ions in the air, the conductivity is much smaller than the average of global atmospheric conductivity. The results of this experiment not only enrich the observations of the atmospheric electric field under special terrain condition, but also reveal the distribution of electric field with height in the near-surface atmosphere of an extinct volcano in Xilin Hot, Inner Mongolia Area, China.

Sea Level Pressure Retrieval in Mid-to-low Latitude Regions Using FY-3C/MWHTS Data

ZHANG Zijin, DONG Xiaolong

2020, 40(3): 364-375. doi: 10.11728/cjss2020.03.364

Abstract(1148) PDF 10311KB(27)

Abstract:
Sea level pressure is an important meteorological factor and plays a key role in Numerical Weather Prediction (NWP), tropical cyclone forecasting and solar activity studies. However, until recently, sea level pressure data have mainly been provided by in-situ measurements. It is of great significance to obtain sea level pressure with a high spatial and temporal resolution by means of remote sensing. In this study, we investigated the retrieval of sea level pressure over mid-to-low latitude (40°S-40°N) regions using the observations from the Microwave Humidity and Temperature Sounder (MWHTS) onboard the Fengyun-3C (FY-3C) satellite. Sea level pressure sounding is achieved by MWHTS 118.75GHz channels due to their ability to measure the total columnar oxygen absorption. The sensitivity of the MWHTS 118.75GHz channels to surface pressure was analyzed using the radiative transfer equation. Compared with the channels far into the oxygen absorption band, the channels lie on the wing of the band are more sensitive to the change of surface pressure. A statistical retrieval algorithm based on the Back-Propagation (BP) neural networks was established. In-situ buoy measurements and reanalysis data were used to assess the retrieval performance. Results showed that the proposed retrieval algorithm can estimate sea level pressure over mid-to-low latitude areas (40°S-40°N) with the accuracy of 2.0, 3.0, and 3.5hPa for clear-sky, cloudy and rainy conditions, respectively. In addition, several tropical cyclone retrieval experiments showed that the proposed method was useful in the early identification of tropical depression.

Gravity Independence Analysis Based on Bubble Departure in Flow Boiling

YUE Shuwen, DU Wangfang, LI Kai, ZHAO Jianfu

2020, 40(3): 376-381. doi: 10.11728/cjss2020.03.376

Abstract(1068) PDF 5057KB(69)

Abstract:
The density difference between gas and liquid phases in the flow boiling phenomenon leads to the important influence of gravity on the flow and heat transfer performance. Therefore, the study of gravity effect is of great significance for the space application of flow boiling. The Bower-Klausner-Sathyanarayan gravity independent criterion, i.e. BKS criterion, is revisited. It is pointed out that BKS criterion has congenital defect in theory and cannot reflect the gravity effect correctly. Using the same departure model of growing vapor bubble in flow boiling as adopted in BKS criterion, but neglecting the sliding effect of bubble along the heating wall, the departure diameters of single bubble in the initial segment after the boiling incipience under different flow directions in normal gravity are calculated. A new gravity independent criterion based on Froude number is concluded, which is in better agreement with the experimental results. The new criterion is in principle consistent with the dominant force criterion.

Numerical Simulation of Two-phase Heat Flow and Water Distribution for Water Electrolyzer in Microgravity

LIU Xiaotian, WU Chuanjia, MA Peng, WANG Shuangfeng, LI Mingyu, YIN Yongli

2020, 40(3): 382-393. doi: 10.11728/cjss2020.03.382

Abstract(1525) PDF 16651KB(89)

Abstract:
Water electrolysis technology is a green-hydrogen process, and it is also a critical oxygen filling technology for medium- and long-term manned space missions. To study the effect of gravity on the performance of solid polymer water electrolyzer, the 3D two-phase model and the system model of electrolyzer were established. The water distribution, flow and temperature field were simulated and the effects of microgravity and normal-gravity on the electrolyzer were analyzed. When the electrolyzer placed in microgravity or horizontally, the numerical simulation of the electrolyzer with single-cell showed that the flow and the temperature fields in the electrolyzer are distributed uniformly. However, when the electrolyzer was placed vertically and water supplied horizontally, the water shortage appeared in the electrolyzer due to the oxygen gathered in the upper part. The numerical simulation of the system model indicated that the water distribution of the system is nonuniform in both normal-gravity and microgravity conditions. When the electrolyzer system was placed horizontally, the system flow rates firstly decrease then increase from the bottom cell to the top cell. While when the electrolyzer system was placed in microgravity or vertically, the system flow rates always increase from the bottom cell to the top cell.

Effect of Initial Liquid Hydrogen Temperature on the Pressure Changes in the Cryogenic Propellant Tank

WANG Yanhui, ZHOU Binghong

2020, 40(3): 394-400. doi: 10.11728/cjss2020.03.394

Abstract(1450) PDF 5135KB(58)

Abstract:
The cryogenic propellant tank will be in microgravity environment for more than several hundred seconds during the MECO (Main Engine Cut-off) phase. Liquid hydrogen propellant works near its saturation temperature, which can easily cause phase transition due to heat transfer and other effects, thus affecting the pressure change of the tank. The effects of different initial cryogenic propellant temperatures on tank pressure and temperature are studied by establishing a three-dimensional CFD model. The results show that the larger the difference between the temperature of the propellant near the gas-liquid interface and the saturation temperature under the current gas pressure is, the greater the pressure drop rate is. As the gas pressure drops, the overall temperature of the ullage gas decreases, the pressure drop rate also gradually decreases, and the pressure change curve tends to flatten out. When the initial liquid propellant temperature is lower than the equilibrium temperature, the higher the initial liquid propellant temperature is, the higher the equilibrium pressure is.

Research on Multi-priority Astronomical Observing Satellite Task Replanning Method for Dynamic Requirement

LIU Yong, JAUBERT Jean, WU Haiyan, FENG Zhun, LI Hu

2020, 40(3): 401-407. doi: 10.11728/cjss2020.03.401

Abstract(1527) PDF 4958KB(68)

Abstract:
In view of multi-priority astronomical observation satellite task scheduling, the dynamic insert of high-priority tasks and adjustment of original mission planning and scheduling due to unpredictable events are analyzed. For the SVOM (Space multi-band Variable Object Monitor) satellite mission planning, a method based on the rolling-horizon optimal strategy is proposed for single-satellite ToO (Target of Opportunity) tasks rescheduling. High-priority tasks should be processed first in each rolling cycle. By using rollback operation, the tasks influenced should be rescheduled or deleted. In this paper, the total time of satellite mission planning and the total time of ToO planning are considered comprehensively in the objective function. The solution has certain significance for quick responding to high-priority ToO tasks and improving service quality.

Adaptive Passive Control for Large-angle Attitude Maneuver of Liquid-filled Spacecraft

WANG Hongwei, SONG Xiaojuan, LI Changjie

2020, 40(3): 408-418. doi: 10.11728/cjss2020.03.408

Abstract(1045) PDF 5467KB(51)

Abstract:
In this paper, the large-angle attitude maneuver of three-axis stabilized liquid-filled spacecraft based on adaptive passive control is studied. The liquid sloshing is equivalent to the viscous spherical pendulum model, and the dynamic model of the coupled system is established by using the law of conservation of angular momentum. In view of the fact that gyroscope faults or gyroscope-free configuration lead to no angular velocity measurement of spacecraft attitude, considering the characteristics of unknown external disturbance, the moment of inertia uncertainty and the un-measurable characteristics of liquid sloshing displacement, the adaptive output feedback passive control law is designed for large angel attitude maneuver of spacecraft. The adaptive update laws are used to compensate for external disturbances and estimate state variables for liquid sloshing. The Lyapunov method and LaSalle invariant lemma prove that the control law can not only ensure the asymptotic stability of the closed-loop system but also ensure the two desired equilibrium positions are stable. Finally, simulation results verify the effectiveness of the proposed control method.

Time Recovery Strategy of Navigation Satellite Based on Inter-satellite Link

CHEN Tingting, LIN Baojun, GONG Wenbin, CHANG Jiachao

2020, 40(3): 419-424. doi: 10.11728/cjss2020.03.419

Abstract(1381) PDF 4176KB(70)

Abstract:
When the Beidou navigation satellite is on autonomous navigation, the satellite time-frequency system abnormality will cause the load time system to power off and restart, which is an intrackable problem. For this reason, a new strategy is proposed using ranging and data transmission functions of the Beidou inter-satellite link. Due to the stability and accuracy of the current on-board computer crystal oscillator, the method of using ten-second stability for predicting crystal frequency drift to calculate satellite time instead of the crystal oscillator is proposed to make sure the satellite clock is stable during the restart time of the load system. With this method, total error can satisfy the allowable range of inter-satellite link construction error. After the load system is restarted, the on-board computer gives the navigation task processor a standard time and total error is calculated through error analysis system, which can also meet inter-satellite link standard. The satellite clock error can be fixed through the inter-satellite link to re-synchronize the satellite time and ground time.

Orbit Performances Validation for CFOSAT Scatterometer

DONG Xiaolong, ZHU Di, LIN Wenming, ZHANG Kuo, YUN Risheng, LIU Jianqiang, LANG Shuyan, DING Zhenyu, MA Jianying, XU Xingou

2020, 40(3): 425-431. doi: 10.11728/cjss2020.03.425

Abstract(1373) PDF 6942KB(98)

Abstract:
The first rotating fanbeam scatterometer onboard China-France Oceanography Satellite (CFOSAT) is able to observe Earth's surface at different incidence and azimuth angles using innovative observing geometry, and in turn to improve the retrieval of sea surface wind, soil moisture, sea ice extent, etc. After the CFOSAT was launched in October 2018, the performances of the CFOSAT Scatterometer (CSCAT) are being tested in orbit. This paper provides an overview of the CSCAT system, and then summarizes the key parameters of CSCAT tested in orbit, including calibration signal analyses, system noise analyses, and radar backscatter processing results analyses. Consequently, the first wind retrieval results of CSCAT are analyzed to assess the system performance. The wind speed accuracy of CSCAT is better than 1.5m·^-1, and the wind direction accuracy is better than 15°. The special resolution is better than 12.5km. All these results show that CSCAT generally works well in orbit and has a unique advantage in the monitoring of nearshore winds, soil moisture, and sea ice extent.

Gibbs Error Correction of the One-dimensional Synthetic Aperture Radiometer Based on CLEAN Algorithm

ZHANG Aili, WU Ji, LIU Hao

2020, 40(3): 432-437. doi: 10.11728/cjss2020.03.432

Abstract(729) PDF 4268KB(52)

Abstract:
For the one-dimensional (1-D) synthetic aperture microwave radiometer with a small number of antenna elements, the system has a limited number of sampling baselines, which causes the truncated sampling in the special frequency domain, resulting in significant Gibbs errors in imaging results, and then affects the imaging quality of the synthetic aperture radiometer. In practical applications, the windowing function is usually chosen to suppress the Gibbs error, but the windowing function also reduces the spatial resolution of the radiometer system. Therefore, a correction algorithm based on CLEAN algorithm is proposed in order to suppress the Gibbs imaging error of the synthetic aperture radiometer. As an application, this method is implemented to a currently completed 8-element one-dimensional linear synthetic aperture radiometer ground prototype system, and the effectiveness of the CLEAN algorithm in suppressing the Gibbs error in the radiometer imaging results has been verified through a series of simulation experiments. In this paper, the basic principle of CLEAN algorithm is introduced in detail, and the effectiveness of the algorithm is verified by simulation experiments.

2020 Vol. 40, No. 3

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