Effect of the Earth Movement on the Measured Moon Trajectory

All lunar theories within the framework of classical mechanics are based on the assumption of an inertial frame of reference,which is physically non-existent and has scarcely been examined in previous studies.This paper aims to examine the consequence of giving up the assumption of the existence of an inertial frame and the relevant influence on the measured moon trajectories.The general formulation of the lunar orbit is built from the perspective of the new general system theory(NGST),where the moon is modelled as a 6-DOF living body and active forces are introduced.This formulation can be retrograded to the framework of classical mechanics.Firstly,we calculate the active forces on the moon when a fixed earth movement and a fixed moon movement are assumed in the god-coordinate system.Then we investigate what will happen to the measured moon trajectory in the human-coordinate system when the earth movement and other parameters are perturbed in several cases.It is found that the results are sometimes inconsistent with the explanations using inertia forces in classical mechanics but can be well explained by NGST.We also discovered that the active forces on the moon should be adjusted constantly to maintain the stable measured moon trajectory.

Spatiotemporal characteristics and driving mechanisms of land use/land cover(LULC)changes in the Jinghe River Basin,China

Understanding the trajectories and driving mechanisms behind land use/land cover(LULC)changes is essential for effective watershed planning and management.This study quantified the net change,exchange,total change,and transfer rate of LULC in the Jinghe River Basin(JRB),China using LULC data from 2000 to 2020.Through trajectory analysis,knowledge maps,chord diagrams,and standard deviation ellipse method,we examined the spatiotemporal characteristics of LULC changes.We further established an index system encompassing natural factors(digital elevation model(DEM),slope,aspect,and curvature),socio-economic factors(gross domestic product(GDP)and population),and accessibility factors(distance from railways,distance from highways,distance from water,and distance from residents)to investigate the driving mechanisms of LULC changes using factor detector and interaction detector in the geographical detector(Geodetector).The key findings indicate that from 2000 to 2020,the JRB experienced significant LULC changes,particularly for farmland,forest,and grassland.During the study period,LULC change trajectories were categorized into stable,early-stage,late-stage,repeated,and continuous change types.Besides the stable change type,the late-stage change type predominated the LULC change trajectories,comprising 83.31% of the total change area.The period 2010-2020 witnessed more active LULC changes compared to the period 2000-2010.The LULC changes exhibited a discrete spatial expansion trend during 2000-2020,predominantly extending from southeast to northwest of the JRB.Influential driving factors on LULC changes included slope,GDP,and distance from highways.The interaction detection results imply either bilinear or nonlinear enhancement for any two driving factors impacting the LULC changes from 2000 to 2020.This comprehensive understanding of the spatiotemporal characteristics and driving mechanisms of LULC changes offers valuable insights for the planning and sustainable management of LULC in the JRB.

Trajectory Tracking of Vertical Take-off and Landing Unmanned Aerial Vehicles Based on Disturbance Rejection Control

We investigate the trajectory tracking problem of vertical take-off and landing (VTOL) unmanned aerial vehicles (UAV), and propose a practical disturbance rejection control strategy. Firstly, the nonlinear error model is established completely by the modified Rodrigues parameters, while considering dynamics of the servo actuators. Then, a hierarchical control scheme is applied to design the translational and rotational controllers based on the time-scale property of each subsystem, respectively. And the linear extended state observer and auxiliary observer are used to deal with the uncertainties and saturation. At last, global stability of the closed-loop system is analyzed based on the singular perturbation theory. Simulation results show the effectiveness of the proposed control strategy. © 2014 Chinese Association of Automation.

Chang'e 4 Lands at the Far Side of the Moon

Chang’e 4 began its travel to the moon at 02:23 Beijing time on December 8,2018 atop a LM-3B launch vehicle from the Xichang Satellite Launch Center.After separated from the carrier rocket,Chang’e 4 entered the Earth-moon transfer orbit with perigee of 200 km and apogee of 420 000 km.

Identifying water vapor sources of precipitation in forest and grassland in the north slope of the Tianshan Mountains,Central Asia

Identifying water vapor sources in the natural vegetation of the Tianshan Mountains is of significant importance for obtaining greater knowledge about the water cycle,forecasting water resource changes,and dealing with the adverse effects of climate change.In this study,we identified water vapor sources of precipitation and evaluated their effects on precipitation stable isotopes in the north slope of the Tianshan Mountains,China.By utilizing the temporal and spatial distributions of precipitation stable isotopes in the forest and grassland regions,Hybrid Single-Particle Lagrangian Integrated Trajectory(HYSPLIT)model,and isotope mass balance model,we obtained the following results.(1)The Eurasia,Black Sea,and Caspian Sea are the major sources of water vapor.(2)The contribution of surface evaporation to precipitation in forests is lower than that in the grasslands(except in spring),while the contribution of plant transpiration to precipitation in forests(5.35%)is higher than that in grasslands(3.79%)in summer.(3)The underlying surface and temperature are the main factors that affect the contribution of recycled water vapor to precipitation;meanwhile,the effects of water vapor sources of precipitation on precipitation stable isotopes are counteracted by other environmental factors.Overall,this work will prove beneficial in quantifying the effect of climate change on local water cycles.

Relationship Between Land Use Changes and the Production of Dust Sources in Kermanshah Province,Iran

Recognizing land use changes(LUC)and evaluating their relationship with producing dust sources are considered effective to manage the environment.Taking Kermanshah Province,Iran as study area,dusty days from 2008 to 2015 were selected and dust sources were identified applying thermal-infrared dust index(TDI),hybrid single-particle lagrangian integrated trajectory(HYSPLIT),false color composite(FCC)and true color composite(TCC)of MODerate resolution Imaging Spectroradiometer(MODIS)images.Afterwards,the land use change map was produced using Landsat images in 2000 and 2015.Then,the distribution and frequency of the sources in each land-use change class and important dust production areas were specified.Eventually,two non-parametric tests including Chisquare and Kruskal-Wallis were applied to examine the relationship between LUC and dust sources.Results indicated that the distribution of dust sources was not identical in the study area,and the sources were mainly generated in the areas where land-use change had occurred.In fact,different classes of LUC have different contributions to dust production,and the highest contribution refers to the deflation in gentle slope areas and lowlands where the rangeland has been converted into agriculture land.The findings from this study are useful to manage and control dust in the identified sources.

An experimental investigation of one-and two-degree of freedom VIV of cylinders

In the paper,an experiment investigation was conducted for one-and two-degree of freedom vortex-induced vibration（VIV） of a horizontally-oriented cylinder with diameter of 11 cm and length of 120 cm.In the experiment,the spring constants in the cross-flow and in-line flow directions were regulated to change the natural vibration frequency of the model system.It was found that,in the one-degree of freedom VIV experiment,a ＂double peak＂ phenomenon was observed in its amplitude within the range of the reduced velocities tested,moreover,a ＂2T＂ wake appeared in the vicinity of the second peak.In the two-degree of freedom VIV experiment,the trajectory of cylinder exhibited a reverse ＂C＂ shape,i.e.,a ＂new moon＂ shape.Through analysis of these data,it appears that,besides the non-dimensional in-line and cross-flow natural vibration frequency ratios,the absolute value of the natural vibration frequency of cylinder is also one of the important parameters affecting its VIV behavior.

Determination of the controlled landing trajectory of Chang’E-1 satellite and the coordinate analysis of the landing point on the Moon

Based on the tracking observations of radio ranges and VLBI delays of Chang’E-1 (CE-1) satellite during the controlled landing on the Moon on March 1, 2009, the landing trajectory and the coordinates of the landing point are determined by positioning analysis. It is shown that the landing epoch (the emission epoch of the last signal) of CE-1 satellite on the Moon was at UTC8h13m6.51s. The lunar longitude, latitude and surface height of the landing point in the lunar primary axes frame are respectively 52.2732°, 1.6440° and –3.56 km (the reference lunar radius is 1738 km). The uncertainties are 0.0040°, 0.0168° and 0.18 km. The corresponding uncertainty in the tangential direction of the lunar surface is 0.52 km and the three-dimensional (3D) positioning uncertainty is 0.55 km. It is accordingly deduced that even with the present technical specifications of the radio ranges and VLBI delays, the 1 km 3D positioning precision could be guaranteed for the lander in the second stage of China’s Lunar Explora- tion Project. Concerning the trace determination of the rover on the lunar surface, because only telemetry signal will be emitted, VLBI would be the sole tracking technique from the Earth. The application of the constraint of geocentric distance is shown to be helpful to improving the positioning precision. It is worthy to pay close attention to the applications of the same beam VLBI technique, the lunar topographic model and the on-board observations of the lander and rover to the position/trace determination of the rover.

Historical Land Use/Cover Changes and the Hemeroby Levels of a Bio-Cultural Landscape: Past, Present and Future

The urbanization of a campus landscape has required much space for this expansion, reinforcing the status of geographical space as a limited resource. We analyzed the effects of land cover change assessed over temporal dataset on composition and configuration dynamics of UFSCar (Federal University of São Carlos) campus landscape, based on a descriptive view of the hemeroby levels, over a 54-year period (1962-2016), in order to understand the impacts of past anthropogenic induced landscape change and inform decision making with regard to biodiversity management. The classification of land use/cover dynamics, over time, was obtained based on screen digitizing of aerial photos and LandSat imagery. An ordinal scale ranging from ahemerob to metahemerob was applied to assess the hemerobiotic state of each land use type. Currently, The UFSCar landscape campus configures a biocultural mosaic in different stages of hemeroby. Thus a campus landscape dynamics model, which can be denoted as “forestry-conservation-urban model”, anthropogenic landscape is replaced by natural one, later by land cover reflecting the spatial anthropization process. Through time, two hemerobiotic trajectories were identified, in which 1) an euhemerob landscape matrix is substituted by an ahemerob one, resulting in increased naturalness of the campus landscape, and then 2) metahemerob patch types will later on increasing as a consequence of ongoing urbanization. Expressive amount of ahemerob patches in campus landscape fulfills one of the conditions for maintenance of the capacity for self-regulation and sustainability of a biocultural landscape. This framework provides an essential tool supporting with essential information about current and historical landscape sustainability for campus landscape management and support decision making process. The main institutional challenge for campus landscape sustainable management lies in the balance between the competitors of the campus landscape matrix: conservation x urbanization.

Nomenclature for lunar features at the Chang＇e-3 landing site

Nomenclatures for lunar features always accompany the progresses of human lunar exploration,which has an important dual meaning in culture and science. The naming of lunar features not only can commemorate the outstanding contributions of academics,masters in various fields, and popularize the traditional cultures of ethnic groups all over the world, but also have a critical function of providing accurate indicative information on features with special morphology, origin, nature and scientific value. However, nomenclature for features at the Chang'e-3 landing site, which has a more arbitrary form without many constrains posed by a uniformed system, is unlike the features for other morphological units.This paper originated from the actual needs for the description of scientific exploration activities, interpretation of scientific research and dissemination of scientific results. Some prominent morphological units with great scientific importance and identification purpose were chosen from the images taken by the terrain camera, panorama cameras and landing camera onboard the Chang'e lander and Yutu rover. A nomenclature system was established under the three enclosures, four quadrants and twenty-eight lunar lodges' system of the Chinese ancient sky division method. Finally, a standard feature names set waspublished after some necessary approval procedures by the International Astronomical Union.

Agriculture and Forest Transition: Understanding of Land Use Change in a Cultural Landscape

Land use trajectory analysis provides both the time and kind of land cover changes to monitor land use dynamics. Land cover change trajectories for three different dates (1965, 1989 and 2014) extracted from satellite images by vectorization of the thematic information were studied This study was carried out on a cultural landscape (S?o Carlos municipality, SP, Brazil) with three major land use-cover classes (forest, agriculture and other uses). The results showed the spatio temporal variability of landscape pattern and forest and agriculture change trajectories. Analysis based on these landscape trajectories demonstrates that agriculture and forest cover changes have been caused by human activities. The results reflect the conflicting interactions between environmental and human systems in the study area. A key question is that the pressure exerted on forest land use-cover depends on the incentives that move society from a conflicting relation with a municipal territory. A more sustainable landscape transition and trajectory for S?o Carlos municipality are extremely dependent on the regulatory role of the government through strategies related to the implementation of specific categories of legally protected areas (Legal Reserves and Areas of Permanent Preservation).

基于分阶段自编码器与注意力机制的舰载机着舰航迹实时预测模型

航空母舰舰载机着舰过程中应沿相对固定的航迹下滑,以保证触舰点位于舰艉拦阻系统所在的区域,因此舰载机航迹是着舰信号官进行指挥决策的重要依据之一。舰载机航迹实时预测有助于着舰信号官判断着舰作业发展态势,及时形成正确的航迹纠偏引导指令。为此,提出一种基于分阶段自编码器与注意力机制的着舰航迹实时预测模型。第一阶段采用降噪自编码器对历史航迹数据进行特征提取;第二阶段基于长短期记忆网络构建时序自编码器,同时引入注意力机制对不同时刻的编码器输出分配不同的权重,自适应学习其对最终预测结果的影响强度。通过仿真实验将所提模型与6种基线模型进行对比,结果表明,所提模型的综合性能优于基线模型,能够满足着舰航迹实时准确预测的应用需求。

Characteristic analysis and design of near moon abort trajectory for manned lunar landing mission

The safety of astronauts would be severely threatened if the lunar-landing spacecraft were under an emergency during the near moon phase of flight, which was far from the Earth. For the problem of mission abort caused by the main engine (service propulsion system, SPS) failure during lunar orbit insertion, firstly, the family of trajectories resulted from SPS premature shutdown and corresponding abort trajectories were analyzed; then an algorithm that can be applied to the near moon abort trajectories was proposed using patched-conic technique. The characteristics of the abort trajectory, such as energy consumption and return time of flight, were analyzed and presented. Finally, simulation examples were given to demonstrate various cases of near moon SPS failure. The results of the simulation have validated the approach proposed.

飞行训练典型科目轨迹仿真实现

飞行训练科目是飞行学员学习飞行技能、掌握飞机性能、检验飞行技术能力的有效途径。针对科目训练过程中轨迹随意性大、评分标准不统一、事后讲评效果差的实际问题,构建基于捷联惯导微分方程离散化的轨迹仿真系统,对几种典型训练科目的、特点和标准等因素进行梳理,完成训练科目细分动作的时间序列化,实现标准起落航线、小速度飞行、懒八字等几种典型飞行训练科目的轨迹仿真。结果表明:论文构建的轨迹仿真系统,能准确反映训练科目的训练目标和飞行特征,为提升训练讲评质量及后续量化评估奠定基础。

近30年来滇中城市群生态用地变化轨迹时空演变特征及其驱动机制

[目的]生态用地在维持生态平衡和支撑经济发展方面发挥着重要作用。研究滇中城市群生态用地的时空演变特征和驱动机制对优化生态安全格局、推进云南生态文明建设、筑牢国家西南生态安全屏障具有重要现实意义。[方法]利用Google Earth Engine(GEE)云平台对滇中城市群1990—2020年生态用地进行识别的基础上,采用变化轨迹分析、热点分析和地理探测器对滇中城市群生态用地时空变化轨迹和驱动机制进行了探索。[结果](1)滇中城市群生态用地变化以非生态用地与林地互换为主,并集中发生在林地和非生态用地的过渡地带,而生态用地内部之间(林地和草地)的转换主要发生在研究区北部和南部的山地区域。(2)生态用地变化以低频次变化为主,高频次较少,频次变化在元江干热河谷、金沙江干热河谷区域、滇东滇东南喀斯特地带表现出明显的聚集效应。(3)耕地面积变化是影响滇中城市群生态用地变化的主要驱动力,社会经济因素对生态用地的影响力显著高于自然因素,在自然环境、耕地扩张、生态修复政策等多重驱动下,多因子交互作用对生态用地变化更具解释力。[结论]滇中城市群生态用地破碎,自然环境的改变和人类活动的日益增强极易导致生态用地发生变化,亟需分区域合理制定生态保护措施,筑牢国家西南生态安全屏障。

一种地外天体着陆凸轨迹曲率滑模制导方法

针对复杂地外天体表面安全着陆问题,提出了凸轨迹曲率滑模制导方法。该方法考虑着陆轨迹形状对着陆安全性的影响,将曲率约束引入到滑模面设计中,实现着陆器系统状态位于滑模面上时,轨迹形状为凸。首先,针对曲率约束进行等效转化和松弛,提出了曲率松弛项,并利用曲率松弛项设计了曲率滑模面,满足三维凸轨迹条件。其次,推导了曲率滑模反馈制导律,滑模状态可在有限时间内收敛到零,在该制导律作用下,着陆器将以凸轨迹状态完成精准软着陆。最后,通过蒙特卡洛仿真验证了所提算法的有效性和鲁棒性。

深度神经网络辅助的垂直回收火箭在线轨迹优化方法

针对垂直回收火箭在线轨迹规划的计算效率和初始敏感问题,提出一种深度神经网络辅助的在线轨迹优化算法。考虑火箭动力下降段的气动阻力,使用变分法和庞德里亚金极小值原理推导最优性条件,首次证明最优推力矢量幅值存在Bang-Bang特征。在此基础上,设计离线训练和在线优化两步求解框架。一是离线训练深度神经网络,在初值大范围波动条件下,有监督学习Bang-Bang特征的结构参数;二是在线规划最优轨迹,将训练好的深度神经网络作为辅助求解器,生成伪谱离散法的分段点,嵌入序列凸优化算法求解。该算法将最优推力的与伪谱法的分段特性有机结合,提高了有限离散点下的求解精度。仿真结果表明,该算法能有效提升在线轨迹规划的求解效率和初值适应性。

渤海湾海陆风环流及臭氧特征分析

利用2023年夏季在乐亭县开展的观测实验数据和相关气象数据及环境数据,分析渤海湾地区海陆风环流及其对臭氧污染的影响。结果表明,海陆风环流可以影响臭氧在海陆间输送,可能导致渤海湾上空及沿海地区臭氧污染。HYSPLIT后向轨迹模拟解析共有5条主要气团轨迹影响到实验观测地区,其中有2条偏南方向气团通过短距离输送进入实验地区,对该区域的臭氧污染贡献率高达65%。

类星舰飞行器翻转着陆轨迹优化

星舰是美国太空探索技术公司(SpaceX)研制的新一代可重复使用航天运输系统。该类型飞行器的着陆过程与传统航天器截然不同,具有姿态机动大、约束条件多、精度要求高的特点。首先研究了类星舰飞行器翻转着陆段的动力学模型,将发动机摆角响应引入动力学方程来抑制发动机摆角振荡问题。接着,基于凸优化方法设计了可以考虑姿态机动和典型约束条件下类星舰飞行器飞行时间自由的翻转着陆轨迹优化算法。为了提高算法的收敛性,使用虚拟控制、在目标函数中惩罚信赖域并给出了初值选取方法。最后,结合数值优化结果,分析了不同初值选取方法、发动机摆角响应、着陆发动机个数和优化目标选取对翻转着陆过程的影响。

综合直接侧力控制着舰

提出了一种新的着舰控制方法,即综合直接侧力控制着舰。首次将直接侧力应用到着舰研究上,并将美军MAGIC CARPET着舰控制的纵向控制理念拓展到侧向控制上,对侧向直接力舵面和侧向常规舵面进行综合控制设计,实现侧向三通道解耦。在直接侧力通道上设计了横向轨迹增量控制,让横向杆位移直接正比于横向对中漂移速率。对HUD显示符号进行改进,使飞行员更直观地观察着舰态势。设计着舰飞行模拟环境,实时模拟飞行员操纵。模拟结果显示:飞行员能如MAGIC CARPET纵向控制一样,以“一杆操纵”策略很简便地完成对中修正,同时能很好地跟踪侧向甲板运动和抵抗侧风干扰,且整个过程航向角和滚转角基本不变。相对于常规着舰,该方法大大降低了飞行员操纵负担,且提高了着舰性能。