利用磁性Jacobi场比较定理估计轨道球的体积

本文运用磁性Jacobi场与轨道球的体积公式的关系,估计轨道球的体积。主要利用磁性Jacobi场比较定理从上面来估计在Kähler磁场上轨道球的体积,其思想是将磁性Jacobi场放大,从而给出轨道球的体积。

小球轨道运动实验在教学中的拓展运用

“小球轨道运动”是中学物理实验教学中的一个演示实验。操作简单，富有趣味，突出反映物体运动的位移、路程、速度、时间等物理量之间的关系。在分析该实验过程、对实验结果进行理论推导的基础上，对实验进行拓展，提出值得探究的问题，将演示实验巧妙地转变为探究实验。

Imaging simulation and analysis of attitude jitter effect on topographic mapping for lunar orbiter stereo optical cameras

The geometric accuracy of topographic mapping with high-resolution remote sensing images is inevita-bly affected by the orbiter attitude jitter.Therefore,it is necessary to conduct preliminary research on the stereo mapping camera equipped on lunar orbiter before launching.In this work,an imaging simulation method consid-ering the attitude jitter is presented.The impact analysis of different attitude jitter on terrain undulation is conduct-ed by simulating jitter at three attitude angles,respectively.The proposed simulation method is based on the rigor-ous sensor model,using the lunar digital elevation model(DEM)and orthoimage as reference data.The orbit and attitude of the lunar stereo mapping camera are simulated while considering the attitude jitter.Two-dimensional simulated stereo images are generated according to the position and attitude of the orbiter in a given orbit.Experi-mental analyses were conducted by the DEM with the simulated stereo image.The simulation imaging results demonstrate that the proposed method can ensure imaging efficiency without losing the accuracy of topographic mapping.The effect of attitude jitter on the stereo mapping accuracy of the simulated images was analyzed through a DEM comparison.

球笼式等速万向节不同夹角下强度分析

采用准静态接触仿真分析方法,对不同工作夹角的情况下的球笼式等速万向节分别进行应力分析,得到各零件的应力分布和薄弱点,并将仿真结果与试验相对比,验证模型的准确性及合理性。结果表明:当夹角达到30°时,保持架受到钟形壳和星形套的挤压,单侧钢球出现与球道脱离的趋势;当夹角达到45°时,该侧2个钢球与球道几乎完全脱离,同时另外一侧2个钢球与保持架也发生脱离。由于受挤压作用,大夹角下保持架应力主要位于两根筋上。

On simulation of precise orbit determination of HY-2 with centimeter precision based on satellite-borne GPS technique

The HY-2 satellite carrying a satellite-borne GPS receiver is the first Chinese radar altimeter satellite, whose radial orbit determination precision must reach the centimeter level. Now HY-2 is in the test phase so that the observations are not openly released. In order to study the precise orbit determination precision and procedure for HY-2 based on the satellite- borne GPS technique, the satellite-borne GPS data are simulated in this paper. The HY-2 satellite-borne GPS antenna can receive at least seven GPS satellites each epoch, which can validate the GPS receiver and antenna design. What＇s more, the precise orbit determination processing flow is given and precise orbit determination experiments are conducted using the HY-2-borne GPS data with both the reduced-dynamic method and the kinematic geometry method. With the 1 and 3 mm phase data random errors, the radial orbit determination precision can achieve the centimeter level using these two methods and the kinematic orbit accuracy is slightly lower than that of the reduced-dynamic orbit. The earth gravity field model is an important factor which seriously affects the precise orbit determination of altimeter satellites. The reduced-dynamic orbit determination experiments are made with different earth gravity field models, such as EIGEN2, EGM96, TEG4, and GEMT3. Using a large number of high precision satellite-bome GPS data, the HY-2 precise orbit determination can reach the centimeter level with commonly used earth gravity field models up to above 50 degrees and orders.

Mitigating Deep Dielectric Charging Effects at the Orbits of Jovian Planets

Deep dielectric charging/discharging,caused by high energy electrons,is an important consideration in electronic devices used in space environments because it can lead to spacecraft anomalies and failures.The Jovian planets,including Saturn,Uranus,Neptune and Jupiter’s moons,are believed to have robust electron radiation belts at relativistic energies.In particular,Jupiter is thought to have caused at least 42 internal electrostatic discharge events during the Voyager 1 flyby.With the development of deep space exploration,there is an increased focus on the deep dielectric charging effects in the orbits of Jovian planets.In this paper,GEANT4,a Monte Carlo toolkit,and radiation-induced conductivity(RIC)are used to calculate deep dielectric charging effects for Jovian planets.The results are compared with the criteria for preventing deep dielectric charging effects in Earth orbit.The findings show that effective criteria used in Earth orbit are not always appropriate for preventing deep dielectric charging effects in Jovian orbits.Generally,Io,Europa,Saturn(R_S=6),Uranus(L=4.73)and Ganymede missions should have a thicker shield or higher dielectric conductivity,while Neptune(L=7.4)and Callisto missions can have a thinner shield thickness or a lower dielectric conductivity.Moreover,dielectrics grounded with double metal layers and thinner dielectrics can also decrease the likelihood of discharges.

Spot beam handover trigger and channel allocation scheme in GEO mobile satellite communication

An effective spot beam handover trigger and channel allocation scheme is proposed for GEO mobile satellite communication based on its characteristic and application. By using both signal strength and terminal location information, necessary handover is triggered promptly and accurately to reduce the negative effect of long signaling delay. Then handover decision is made with the handover queuing and channel allocation strategy. An adaptive channel resource allocation scheme is considered to optimize resource utilization with guarantee of emergency communication, which is significant for emergency rescue and disaster relief. Simulation results show that the proposed scheme prevents unnecessary handover effectively and has favorable adaptability to emergent requirement of satellite communication.

Evaluation of CHAMP Satellite Orbit with SLR Measurements

The technique of Evaluating CHAMP satellite orbit with SLR measurements is presented. As an independent evaluation of the orbit solution, SLR data observed from January 1 to 16, 2002 are processed to compute the residuals after fixing the GFZ’s post science orbits solutions. The SLR residuals are computed as the differences of the SLR measurements minus the corresponding distances between the SLR station and the GPS-derived orbit positions. On the basis of the SLR residuals analysis, it is found that the accuracy of GFZ’s post science orbits is better than 10 cm and that there is no systematic error in GFZ’s post science orbits.

On Applications of Selenodesy to Lunar Detection

According to the history of lunar detection, the relationship between selenodesy and lunar detection is reviewed , and the focus of the lunar detection and the lunar detection plan of China are summarized. The key techniques of selenodesy are presented, and the applications of selenodesy to the lunar detection are discussed.

Earth Gravity Field Recovered from CHAMP Science Orbit and Accelerometer Data

The earth gravity field model CDS01S of degree and order 36 has been recovered from the post processed Science Orbits and on-board accelerometer data of GFZ’s CHAMP satellite. The model resolves the geoid with an accuracy of better than 4 cm at a resolution of 700 km half-wavelength. By using the degree difference variances of geopotential coefficients to compare the model CDS01S with EIGEN3P, EIGEN1S and EGM96, the result indicates that the coefficients of CDS01S are most close to those of EIGEN3P. The result of the comparison between the accuracies of geopotential coefficients in the above models, indicates that the accuracy of coefficients in CDS01S is higher than that in EGM96.The geoid undulations of CDS01S and GGM01C up to 30 degrees are calculated and the standard deviation is 4.7 cm between them.

Reducing Influence of Gravity Model Error in Precise Orbit Determination of Low Earth Orbit Satellites

Based on the orbit integration and orbit fitting method, the influence of the characters of the gravity model, with different precisions, on the movement of low Earth orbit satellites was studied. The way and the effect of absorbing the influence of gravity model error on CHAMP and GRACE satellite orbits, using linear and periodical empirical acceleration models and the so-called "pseudo-stochastic pulses" model, were also analyzed.

Cross-Layer Design and Ant-Colony Optimization Based Routing Algorithm for Low Earth Orbit Satellite Networks

To improve the robustness of the Low Earth Orbit(LEO) satellites networks and realise load balancing, a Cross-layer design and Ant-colony optimization based Load-balancing routing algorithm for LEO Satellite Networks(CAL-LSN) is proposed in this paper. In CALLSN, mobile agents are used to gather routing information actively. CAL-LSN can utilise the information of the physical layer to make routing decision during the route construction phase. In order to achieve load balancing, CALLSN makes use of a multi-objective optimization model. Meanwhile, how to take the value of some key parameters is discussed while designing the algorithm so as to improve the reliability. The performance is measured by the packet delivery rate, the end-to-end delay, the link utilization and delay jitter. Simulation results show that CAL-LSN performs well in balancing traffic load and increasing the packet delivery rate. Meanwhile, the end-to-end delay and delay jitter performance can meet the requirement of video transmission.

An Automatic Cycle-Slip Processing Method and Its Precision Analysis

On the basis of analyzing and researching the current algorithms of cycle-slip detection and correction, a new method of cycle-slip detection and correction is put forward in this paper, that is, a reasonable cycle-slip detection condition and algorithm with corresponding program COMPRE (COMpass PRE-processing) to detect and correct cycle-slip automatically, compared with GIPSY and GAMIT software, for example, it is proved that this method is effective and credible to cycle-slip detection and correction in GPS data pre-processing.

A distributed routing algorithm based-on simplified topology in LEO satellite networks

In this paper, a distributed muting strategy based on simplified topology （DRBST） was proposed for LEO satellite networks. The topology of LEO satellite networks was simplified aiming at minimizing intersatellite links handover number. To optimize the route based on the simplified topology, we considered not only the transmission delay but also the queuing delay and the processing delay, which were analyzed using Markov chain and determined using a novel methodology. The DRBST algorithm was simulated in a LEO satellite networks model built using OPNET. The simulation results demonstrate that the low complexity DRBST algorithm can guarantee end-to-end delay bound. Moreover, the muting protocol cost is much less than traditional algorithms.

Global Water Vapor Content Decreases from 2003 to 2012： An Analysis Based on MODIS Data

Water vapor in the earth′s upper atmosphere plays a crucial role in the radiative balance, hydrological process, and climate change. Based on the latest moderate-resolution imaging spectroradiometer(MODIS) data, this study probes the spatio-temporal variations of global water vapor content in the past decade. It is found that overall the global water vapor content declined from 2003 to 2012(slope b = –0.0149, R = 0.893, P = 0.0005). The decreasing trend over the ocean surface(b = –0.0170, R = 0.908, P = 0.0003) is more explicit than that over terrestrial surface(b = –0.0100, R = 0.782, P = 0.0070), more significant over the Northern Hemisphere(b = –0.0175, R = 0.923, P = 0.0001) than that over the Southern Hemisphere(b = –0.0123, R = 0.826, P = 0.0030). In addition, the analytical results indicate that water vapor content are decreasing obviously between latitude of 36°N and 36°S(b = 0.0224, R = 0.892, P = 0.0005), especially between latitude of 0°N and 36°N(b = 0.0263, R = 0.931, P = 0.0001), while the water vapor concentrations are increasing slightly in the Arctic regions(b = 0.0028, R = 0.612, P = 0.0590). The decreasing and spatial variation of water vapor content regulates the effects of carbon dioxide which is the main reason of the trend in global surface temperatures becoming nearly flat since the late 1990 s. The spatio-temporal variations of water vapor content also affect the growth and spatial distribution of global vegetation which also regulates the global surface temperature change, and the climate change is mainly caused by the earth's orbit position in the solar and galaxy system. A big data model based on gravitational-magmatic change with the solar or the galactic system is proposed to be built for analyzing how the earth's orbit position in the solar and galaxy system affects spatio-temporal variations of global water vapor content, vegetation and temperature at large spatio-temporal scale. This comprehensive examination of water vapor changes promises a holistic understanding of the global climate change and potential underlying mechanisms.

Navigation and Control of the PRISMA Formation： In-Orbit Experience

This paper presents flight results and lessons learned from the Spaceborne Autonomous Formation Flying Experiment （SAFE） conducted by the German Space Operations Center in the frame of the Swedish PRISMA technology demonstration mission. PR1SMA involves two fully autonomous formation-flying spacecraft which have been launched in June 2010 in a dawn/dusk orbit at an altitude of 750 km. SAFE represents one of the first demonstrations in low Earth orbit of an advanced guidance, navigation and control system for dual-spacecraft formations. Innovative techniques based on carrier-phase differential GPS （Global Positioning System）, relative eccentricity/inclination vectors and impulsive maneuvering are validated and tuned in orbit to achieve centimeter accurate real-time relative navigation, reliable formation keeping at the meter level and flexible formation reconfiguration capabilities. The technologies demonstrated within SAFE are considered as key precursors of future distributed satellite systems for unrivaled remote sensing and space exploration.

A Hybrid Algorithm Based on Differential Evolution and Group Search Optimization and Its Application on Ethylene Cracking Furnace

To find the optimal operational condition when the properties of feedstock changes in the cracking furnace online,a hybrid algorithm named differential evolution group search optimization(DEGSO) is proposed,which is based on the differential evolution(DE) and the group search optimization(GSO).The DEGSO combines the advantages of the two algorithms:the high computing speed of DE and the good performance of the GSO for preventing the best particle from converging to local optimum.A cooperative method is also proposed for switching between these two algorithms.If the fitness value of one algorithm keeps invariant in several generations and less than the preset threshold,it is considered to fall into the local optimization and the other algorithm is chosen.Experiments on benchmark functions show that the hybrid algorithm outperforms GSO in accuracy,global searching ability and efficiency.The optimization of ethylene and propylene yields is illustrated as a case by DEGSO.After optimization,the yield of ethylene and propylene is increased remarkably,which provides the proper operational condition of the ethylene cracking furnace.

Dynamic Connectivity in Cislunar Communication Networking Based on Geosynchronous Orbit Relay Satellites

The architecture of cislunar multi-hop communication networks, which focuses on the requirements of lunar full-coverage and continuous cislunar communications, is presented on the basis of Geosynchronous Orbit (GEO) satellite network relays. According to the geographical distribution of the forthcoming Chinese Deep Space Measuring and Controlling Network (DSMCN), two networking schemes are proposed and two elevation angle optimization models are established for locating GEO relay satellites. To analyze the dynamic connectivity, a dynamic network model is constructed with respect to the time-varying characteristics of cislunar trunk links. The advantages of the two proposed schemes, in terms of the Connectivity Rate (CR), Interruption Frequency (IF), and Average Length of Connecting Duration (ALCD), are corroborated by several simulations. In the case of the lunar polar orbit constellation case, the gains in the performance of scheme I are observed to be 134.55%, 117.03%, and 217.47% compared with DSMCN for three evaluation indicators, and the gains in the performance of scheme II are observed to be 238. 22%, 240.40%, and 572.71%. The results validate that the connectivity of GEO satellites outperforms that of earth facilities significantly and schemes based on GEO satellite relays are promising options for cislunar multi-hop communication networking.

Optimization of multi-revolution low-thrust transfer based on modified direct method

A modified direct optimization method is proposed to solve the optimal multi-revolution transfer with low-thrust between Earth-orbits. First, through parameterizing the control steering angles by costate variables, the search space of free parameters has been decreased. Then, in order to obtain the global optimal solution effectively and robustly, the simulated annealing and penalty function strategies were used to handle the constraints, and a GA/SQP hybrid optimization algorithm was utilized to solve the parameter optimization problem, in which, a feasible suboptimal solution obtained by GA was submitted as an initial parameter set to SQP for refinement. Comparing to the classical direct method, this novel method has fewer free parameters, needs not initial guesses, and has higher computation precision. An optimal-fuel transfer problem from LEO to GEO was taken as an example to validate the proposed approach. The results of simulation indicate that our approach is available to solve the problem of optimal muhi-revolution transfer between Earth-orbits.

All-digital Carrier Frequency Tracking Method in LEO DS/SS Communication

An efficient method to track the carrier frequency which is recommended to use in low earth orbit(LEO) direct-sequence spread-spectrum(DS/SS) communication system is given. The carrier frequency drifts quicker in LEO DS/SS communication system, its tracking problem becomes much more important especially in digital receiver with the limits of physical shape and power. Under the condition of coarse carrier frequency synchronization, a digital tracking method based on least square method(LSM) is proved to be a quick, simple and efficient method. Numerical results and charts are given.