A guidance strategy for rendezvous and docking to the space station in the Earth-Moon NRHO orbit

With the development of space technology,it is possible to build a space station in Earth-Moon space as a transit for Earth-Moon round-trip and entering in the deep space.Rendezvous and docking is one of the key technologies for building an Earth-Moon space station.A guidance strategy for rendezvous and docking from the Earth orbit to the space station in the Earth-Moon NRHO orbit is proposed in this paper,which is suitable for engineering applications.Firstly,the rendezvous and docking process is divided into three sections,i.e.,the large-range orbit transfer section,far-range guidance section,and close-range approaching section.The suitable terminal of large-range orbit transfer is selected according to the eigenvalue of NRHO orbit state transition matrix.The two-impulse guidance method based on the relative motion equation in the three-body problem is adopted for the far-range guidance section.The impulse time and amplitude are solved with the optimization algorithm.The linear constant three-body relative motion equation is proposed for the close-range approaching section,and the rendezvous and docking is completed by a two-stage linear approximation.Finally,a simulation analysis is carried out,and the simulation results show that the adopted dynamics equations and the designed guidance law are effective,and the three flight phases are naturally connected to accomplish the rendezvous and docking mission from the Earth orbit to the space station on the Earth-Moon NRHO.

Contact Tracking Control Strategy for Space Manipulator with Snare-Type End-Effector

The capture operation performed by a snare-type end-effector mainly relies on three flexible cables.This paper solves the dynamics modeling problems of flexible cable used in the snare-type end-effector and provides a contact tracking control strategy for the impact phase of snare capture.To describe the motion of flexible cable,a dynamics model is established by considering both tensile and bending resistance properties.On this basis,a virtual spring concept is introduced to represent the contact between flexible cables and the target grapple shaft,and a contact dynamics model is established approximately by polynomial function with the variables of penetration and start-end distance of flexible cable.Thereafter,a contact tracking control strategy is proposed to improve the reliability of space snare capture.The target grapple shaft and flexible cable can keep in contact at the initial contact point during the whole capture process and thus reduce the possibility of pushing the target away.Experiments are carried out to verify the effectiveness of the proposed method.

Making Public Space in High-density Environment: Strategy and Methodology of Landscape Urbanism

High concentration of population and other elements brought by high urbanization has pushed the future construction of urban public spaces to be both "compact" and "ecological". Theory and methodology of landscape urbanism provides a new perspective for the construction of public spaces in high-density urban environment. Based on the concept and basic standpoints of landscape urbanism, this paper elaborated its potential value in spatial connection, functional integration and vitality promotion, and also analyzed practical strategies of landscape urbanism from three perspectives of structure, fold and stage by combining with typical cases, so as to provide references for designing urban public spaces in high-density environment.

Strategy research on new urban space development and new deepwater terminal in Hengsha

From a strategic perspective,the paper presents a forward-looking thinking supported by interdisciplinary of modern logistics,estuary and coast,environment and ecology,economic management and mathematical statistics. It leads to a reasonable solution to space expansion by reclamation. Construction of new deepwater terminal is the best usage of land resources and can strengthen the status of Shanghai as an international shipping center,thus support the preparation and strategic decision of future urban development of Shanghai.

Space Strategy of the Trump Administration

Since the end of the Cold War, each US administration has promulgated its national space policy. In March 2018, the Trump administration published the outline of its National Space Strategy,1 which will not only reshape American space technology and space economy, but also have an important impact on global space governance.

Design Strategy of Underground Space of Urban Rail Transit Complex Based on Integration Concept

With the accelerated development and utilization of urban underground space,the underground space design of complex based on rail transit has attracted much attention.By sorting out the integration concept and constructing the logical framework of integrated design,the integrated design strategy is proposed from the aspects of function,transportation,space and environment on the urban scale,and the evaluation points of integrated design effect are put forward from the aspects of accessibility,coordination,openness and symbolism.

Application of Soft Power Strategy on Asian Civilization Spaces

While increasing contact between peoples and cultures,globalization does not weaken the diversity of world's civilizations.Soft power can serve as a lubricant to prevent the clash of civilizations and enhance dialogues between civilizations.The article summarizes the three components of China's soft power:cultural promoting,foreign assistance and the thought of"a harmonious world."Taking Uzbekistan as an example,the author also illustrates the path of the Islamic nations to implement"soft power"strategy.

Improvement of the Vitality of Public Space under the Background of Urban Renewal

As an indispensable part of urban development,urban renewal plays an important role in terms of promoting urban society,economy,culture,etc.,and has a profound impact on the sustainable development of cities and the happiness index of residents.Public space,as an important part of a city,plays a more critical role in urban renewal.The vitality of public space not only reflects the degree of urban cultural inheritance,but also shows the level of urban economic development,so it is an important issue that must be paid attention to in urban renewal work.In this paper,starting from the concept of urban renewal,public space and vitality,the influencing factors and methods of studying the vitality of public space under the background of urban renewal,as well as its advantages and limitations,were discussed,and some strategies for enhancing the vitality of public space under the background of urban renewal were finally put forward.It is expected to provide some reference and practical significance for the research and practice of urban renewal and the enhancement of the vitality of public space.

Identity of Urban Spaces: Assessment and Evaluation

As a major symbol of civilization,the city was built by man for his security and comfort.It is not only a settlement,but also an urban development which has been identified with the spirit that has been breathed into the community.Urban identity which is also known as collective identity,has gained meaning through the content of objective manifestation and the creation of flashbacks,citizens’memories and mental associations.That is what makes urban dwellers become citizens.Although the identity of the city is a result of civic culture,it still has an influence on the process of citizenship and can also be a reason for developing criteria related to the participation and assessment of its inhabitants.According to the view that identity is a set of traits and characteristics that distinguishes the dignity of a person and a society from other individuals and communities,a city becomes characterized and independent by adhering to these criteria.Despite the importance of identity as one of the richest qualitative aspects of urban life that gives meaning and fulfilment to the human quiddity,this complicated and expanded concept has still not been seriously considered,especially in relation to urban spaces.In fact,identity in architecture and urban spaces has recently diminished,since the main focus lies on building spaces for optimized profit and not for high quality living areas.In this research paper,parameters affecting urban identity are evaluated,and strategies and guidelines to promote these parameters are finally presented.

Analysis of Urban Public Building Space Design Strategies in the Digital Age

Urban public building spaces involve various aspects of people’s daily activities and interactions,making the rationality and scientific nature of the design of these spaces crucial.This article first discusses the role and impact of digitization in the design of public building spaces,covering aspects such as digital design methods,visual expression and presentation,augmented reality’s spatial interaction experience,and integrated design and construction.Following that,it analyzes the process of digitized urban public building space design by exploring topics like digital space design and modeling,visual representation of digital spaces,digital performance analysis of spaces,and the integration of digital projects.This article aims to provide insights and references for urban public building space design in the digital era.

存量优化视角下葑门横街更新的织补策略研究

中国式城市化的进程给老旧街区发展带来了机遇与挑战,其交通不畅、空间失活、基础设施陈旧等问题明显。随着城市空间逐渐从增量建设向存量优化转型,老旧街区作为存量空间的重要组成部分,其更新改造成为城市建设工作中的重点之一。文章立足存量优化的视角,选取了符合城市更新发展趋势的织补理论,针对苏州葑门横街道路交通、街巷空间、功能业态、文化属性方面的问题,归纳出其更新改造的织补要素,提出了物质和文化层面的织补策略。文章有利于完善和发展织补理论在城市老旧街区小规模渐进式更新中的应用与可持续发展,为城市老旧街区的更新提供更多的基础理论与科学依据。

Strategies for multi-step-ahead available parking spaces forecasting based on wavelet transform

A new methodology for multi-step-ahead forecasting was proposed herein which combined the wavelet transform(WT), artificial neural network(ANN) and forecasting strategies based on the changing characteristics of available parking spaces(APS). First, several APS time series were decomposed and reconstituted by the wavelet transform. Then, using an artificial neural network, the following five strategies for multi-step-ahead time series forecasting were used to forecast the reconstructed time series: recursive strategy, direct strategy, multi-input multi-output(MIMO) strategy, DIRMO strategy(a combination of the direct and MIMO strategies), and newly proposed recursive multi-input multi-output(RECMO) strategy which is a combination of the recursive and MIMO strategies. Finally, integrating the predicted results with the reconstructed time series produced the final forecasted available parking spaces. Three findings appear to be consistently supported by the experimental results. First, applying the wavelet transform to multi-step ahead available parking spaces forecasting can effectively improve the forecasting accuracy. Second, the forecasting resulted from the DIRMO and RECMO strategies is more accurate than that of the other strategies. Finally, the RECMO strategy requires less model training time than the DIRMO strategy and consumes the least amount of training time among five forecasting strategies.

Regenerative Braking Strategy for Motor Hoist by Ultracapacitor

Rising concern in environmental issues on global scale has made energy saving in powered equipment a very important subject.In order to improve the energy efficiency and driving range of a motor hoist,a regenerative braking system is designed and discussed.The system takes a unique ultracapacitor-only approach to energy storage system.The bi-directional bride DC？DC converter which regulates current flow to and from the ultracapacitor operates in two modes：boost and buck,depending on the direction of the flow.In order to provide constant input and output current at the ultracapacitor,this system uses a double proportional-integral（PI） control strategy in regulating the duty cycle of PWM to the DC？DC converter.The permanent magnet synchronous motor（PWSM） drive system is also studied.The space vector pulse width modulation（SVPWM） technique,along with a two-closed-loop vector control model,is adopted after detailed analysis of PMSM characteristics.The overall model and control strategy for this regenerative braking system is ultimately built and simulated under the MATLAB and Simulink environment.A test platform is built to obtain experimental results.Analysis of the results reveals that more than half of the gravitational potential energy can be recovered by this system.Simulation and experimentation results testify the validity of the double PI control strategy for interface circuit of ultracapacitor and SVPWM strategy for PMSM.

An adaptive ant colony system algorithm for continuous-space optimization problems

Ant colony algorithms comprise a novel category of evolutionary computation methods for optimization problems, especially for sequencing-type combinatorial optimization problems. An adaptive ant colony algorithm is proposed in this paper to tackle continuous-space optimization problems, using a new objective-function-based heuristic pheromone assignment approach for pheromone update to filtrate solution candidates.Global optimal solutions can be reached more rapidly by self-adjusting the path searching behaviors of the ants according to objective values. The performance of the proposed algorithm is compared with a basic ant colony algorithm and a Square Quadratic Programming approach in solving two benchmark problems with multiple extremes. The results indicated that the efficiency and reliability of the proposed algorithm were greatly improved.

Review on strategies of space-based optical space situational awareness

Space-based optical(SBO)space surveillance has attracted widespread interest in the last two decades due to its considerable value in space situation awareness(SSA).SBO observation strategy,which is related to the performance of space surveillance,is the top-level design in SSA missions reviewed.The recognized real programs about SBO SAA proposed by the institutions in the U.S.,Canada,Europe,etc.,are summarized firstly,from which an insight of the development trend of SBO SAA can be obtained.According to the aim of the SBO SSA,the missions can be divided into general surveillance and space object tracking.Thus,there are two major categories for SBO SSA strategies.Existing general surveillance strategies for observing low earth orbit(LEO)objects and beyond-LEO objects are summarized and compared in terms of coverage rate,revisit time,visibility period,and image processing.Then,the SBO space object tracking strategies,which has experienced from tracking an object with a single satellite to tracking an object with multiple satellites cooperatively,are also summarized.Finally,this paper looks into the development trend in the future and points out several problems that challenges the SBO SSA.

Homing Strategy for a 4RRR Parallel Kinematic Machine

Returning home is the most important process of a parallel kinematic machine （PKM） with incremental encoders.Currently,most corresponding articles focus on the accuracy of homing process,and there lacks the investigation of the operation＇s safety.For a 4RRR PKM,all servoaxes would be independently driven to their zero positions at the same time based on the traditional homing mode,and that can bring serious interfere of the kinematic chains.This paper systemically investigates this 4RRR PKM＇s safety of homing process.A homing strategy usually contains three parts which are the home switches＇ locations,the platform＇s initial moving space,and each links＇ homing direction,and all of them can influence the safety of homing operation.For the purpose of evaluating and describing the safety of the homing strategy,some important parameters are introduced as follows：Safely homing ratio （SHR） is used to evaluate the probability of a machine＇s successfully returning home from an initial moving space;Synchronal rotational angle （SRA） is the four links＇ largest synchronal rotational angle with given directions from a given pose.Whether a machine can safely return home from a given pose can be judged by comparing the SRA with all four home switches＇ mounting angles.By meshing the initial moving space and checking the safeties of returning home from all the initial poses on the nodes,the SHR of this initial moving space can be calculate.For the sake of convenience,the platform＇s initial moving space should be as large as possible,and in this 4RRR PKM,a square zone in the center of the workspace with a giving initial rotation range is selected as the platform＇s initial moving space.The forward direction is selected as each link＇s homing direction according to custom,and the platform＇s initial rotational angle is selected as larger than 0° based on this 4RRR PKM＇s kinematic characteristics.The platform＇s initial moving space can be defined only by the side length of the initial moving square.By setting a probable searching step and calculating the SHR of the initial moving square,an optimal procedure of searching for the largest side length of the platform＇s initial moving square is proposed.The homing strategy proposed is based on a systemic research on the safety of homing process for PKM,and the two new indexes SHR and SRA can clearly describe the safety of homing operation.The homing operation based on this strategy is fast and safe,and the method can also be used in other PKMs with the situation of serious components＇ interference.

Retrieval strategy for failed satellite on tether’s optimal balance swing angle

A retrieval control strategy for failed satellite,which is connected to a servicing spacecraft by a tether,is studied.The Lagrange analytical mechanics based dynamics modeling for the system composed of a servicing spacecraft,a tether and a failed satellite,is presented under the earth center inertia coordinate system,then model simplification is conducted under the assumption that the failed satellite’s mass is far smaller than the servicing spacecraft’s,meanwhile the tether’s length is far smaller than the size of the servicing spacecraft’s orbit.Analysis shows that the retrieval process is intrinsically unstable as the Coriolis force functions is a negative damping.A retrieval strategy based on only the tether’s tension is designed,resulting in the fastest retrieval speed.In the proposed strategy,firstly,the tether’s swing angle amplitude is adjusted to 45?by deploying/retrieving the tether;then the tether swings freely with fixed length until it reaches negative maximum angle–45?;finally,the tether is retrieved by the pre-assigned exponential law.For simplicity,only the coplanar situation,that the tether swings in the plane of the servicing spacecraft’s orbit,is studied.Numerical simulation verifies the effectiveness of the strategy proposed.

Research on the Optimization of Public Spaces in Urban Villages Based on Space Syntax:A Case Study of Luochengtou Village in Handan City

This paper based on the theory of space syntax took Luochengtou Village in Handan City,Hebei Province for example,tried to figure out a proper way for the renewal of urban villages,and change the current dilemma of"one-size-fits-all"and"removing all"in most cases,and put forward that local conditions and regional characteristics must be considered to propose the renewal strategies more suitable for the targeted objects.Based on the space syntax Depthmap software and field investigation,the paper analyzed the accessibility,intelligibility and throughput of public spaces in Luochengtou Village,and put forward 3 optimization strategies in view of the problems such as insufficient public spaces,poor accessibility and intelligibility of roads,and poor activity of spaces,specifically,increasing public activity spaces,sorting out public space network,and creating active space nodes,so as to optimize public environment of the village,enhance villagers’sense of belonging,sense of safety and sense of identity.

The Impact of Urbanization on the Ecological Space of Traditional Villages and Restoration Strategies:Take Huangpu Village in Guangzhou as an Example

The rapid urbanization has brought tremendous impact on the ecological spaces of traditional villages,research on the influence process and restoration strategies will contribute to the protection and development of traditional villages.This paper took Huangpu Village for example,summarized the types and characteristics of its ecological spaces,analyzed the influence process and characteristics of urbanization on it,and then put forward 7 restoration strategies pertinently.It has some theoretical application value for the protection and development of traditional villages in the Pearl River Delta and other highly-urbanized regions.

Root phosphatase activity is a competitive trait affiliated with the conservation gradient in root economic space

Background:The diversity of resource acquisition strategies of plant roots determines the species coexistence patterns to a certain extent.However,few root physiological traits have been investigated,such as root phosphatase activity(PA)that affects plant phosphorus(P)uptake.Methods:Root PA and classical root functional traits were investigated for 21 coexisting species in a deciduous broad-leaved forest in warm temperate-subtropical transition zone,China.We analyzed the root order variation of absorptive fine root PA,clarified the attribution of root PA in root economic space(RES)and the different P acquisition strategies of co-occurring species based on the multidimensional RES theory,and determined the dominant factors affecting interspecific variation in root PA.Results:There was no distinct pattern of PA variation with root order in the first three root orders of absorptive fine roots,and root PA was constrained by phylogeny.Root PA is a competitive trait affiliated with the conservation gradient in RES.The tight linkages among root PA,mycorrhizal colonization,diameter,specific root length,and nitrogen concentration suggested trade-offs among P acquisition strategies of co-occurring species,i.e.species with long and fine roots acquire inorganic P by actively exploring the soil and secreting phosphatase to mineralize and hydrolyze organic P,while species with short and thick roots obtain P mainly by investing C in mycorrhizal partners.Conclusions:Collectively,our study provides an insight into the forest species coexistence in climatic transition zones,i.e.species coexistence mechanisms based on diverse phosphorus acquisition strategies.