A Survey of Research on Service-Spacecraft Orbit Design

On-orbit service spacecraft orbit problem has been addressed for decades. The research of on-orbit service spacecraft orbit can be roughly divided into orbit design and orbit optimization. The paper mainly focuses on the orbit design problem. We simply summarize of the previous works, and point out the main content of the on-orbit service spacecraft orbit design. We classify current on-orbit service spacecraft orbit design problem into parking-orbit design, maneuvering-orbit design and servicing-orbit design. Then, we give a detail description of the three specific orbits, and put forward our own ideas on the existed achievements. The paper will provide a meaningful reference for the on-orbit service spacecraft orbital design research.

CALCULATING METHOD OF SERIES FOR TRUE ANOMALY OF A SPACECRAFT ELLIPTIC ORBIT

The transcendental equation of a true anomaly was written in a power series instead of a differential form. When the sufficient condition of the iterative convergence is satisfied, the relationship between the true anomaly and the time was gotten by the iterative method. And for the others, the transcendental equation of an eccentric anomaly was solved by the iterative method. After the eccentric anomaly had been calculated, the relationship between the true anomaly and the time was gotten with the numerical integral method. The approximate equation, which included the first five terms in general expansion, was written for the spacecraft quasi-circular orbit. And the true anomaly as the function of the time was also gotten by the iterative method. The numerical simulation results show that these methods are efficient.

Orbit Design for Twin-spacecraft Space VLBI

Space Very Long Baseline Interferometry(S-VLBI) is an aperture synthesis technique utilizing an array of radio telescopes including ground telescopes and space orbiting telescopes.It can achieve much higher spatial resolution than that from the ground-only VLBI.In this paper,a new concept of twin spacecraft S-VLBI has been proposed,which utilizes the space-space baselines formed by two satellites to obtain larger and uniform uv coverage without atmospheric influence and hence achieve high quality images with higher angular resolution.The orbit selections of the two satellites are investigated.The imaging performance and actual launch conditions are all taken into account in orbit designing of the twin spacecraft S-VLBI.Three schemes of orbit design using traditional elliptical orbits and circular orbits are presented.These design results can be used for different scientific goals.Furthermore,these designing ideas can provide useful references for the future Chinese millimeter-wave S-VLBI mission.

Effectiveness-based orbital optimization for servicing spacecraft

Effectiveness-based system development is an essential technology developing concept advanced by some countries,such as the U.S.A.Making use of Analytic Hierarchy Process,this paper brings forward a methodology for orbital optimization based on effectiveness in the case of the orbital deployment for the Servicing Spacecraft(SSC),which needs to accomplish many types of tasks and whose orbit is affected by kinds of factors with contradictions in orbital parameter selection.Firstly,the possible tasks of SSC are decomposed and their degrees of importance are given by the times,probabilities,values of their applications.Then,the supporting capabilities are discussed from the viewpoint of orbit design,and the determination of their weights is put forward.Finally,the relationships between the orbital parameters and the effectiveness are established by using effective function,and three synthesizing methods for a single task and its capabilities are presented.

Randomization-based algorithms for servicing spacecraft motion planning on elliptical orbit

Randomization-based motion planning algorithms are presented to solve problems of servicing spacecraft maneuvering in proximity to servicing targets on an elliptical orbit.The feasible trajectories of position and attitude for spacecraft are obtained by these algorithms under a variety of constraints.The state transition matrix is applied to computation of relative motion on elliptical orbits without performing numerical integration.The pseudo body coordinate system is built for identifying the planners on three coordinate axes with different functions.Finally,motion planning algorithm for translation and attitude taking account of the dependent variable (i.e.time) is used to obtain feasible trajectories.As the simulation examples indicate,the effectiveness of these methods is verified for relative motion while getting close to large structures,and the paper concludes with a detailed analysis of the results.

Multi-Feature Fusion Based Relative Pose Adaptive Estimation for On-Orbit Servicing of Non-Cooperative Spacecraft

On-orbit servicing, such as spacecraft maintenance, on-orbit assembly, refueling, and de-orbiting, can reduce the cost of space missions, improve the performance of spacecraft, and extend its life span. The relative state between the servicing and target spacecraft is vital for on-orbit servicing missions, especially the final approaching stage. The major challenge of this stage is that the observed features of the target are incomplete or are constantly changing due to the short distance and limited Field of View (FOV) of camera. Different from cooperative spacecraft, non-cooperative target does not have artificial feature markers. Therefore, contour features, including triangle supports of solar array, docking ring, and corner points of the spacecraft body, are used as the measuring features. To overcome the drawback of FOV limitation and imaging ambiguity of the camera, a "selfie stick" structure and a self-calibration strategy were implemented, ensuring that part of the contour features could be observed precisely when the two spacecraft approached each other. The observed features were constantly changing as the relative distance shortened. It was difficult to build a unified measurement model for different types of features, including points, line segments, and circle. Therefore, dual quaternion was implemented to model the relative dynamics and measuring features. With the consideration of state uncertainty of the target, a fuzzy adaptive strong tracking filter( FASTF) combining fuzzy logic adaptive controller (FLAC) with strong tracking filter(STF) was designed to robustly estimate the relative states between the servicing spacecraft and the target. Finally, the effectiveness of the strategy was verified by mathematical simulation. The achievement of this research provides a theoretical and technical foundation for future on-orbit servicing missions.

Breakthrough Made on the Nondestructive Testing of Orbital Spacecraft

Lanzhou Institute of Physics, a subsidiary of CAST, conducted ground testing on its newly developed eddy current nondestructive testing equipment, demonstrating an important breakthrough had been made with the nondestructive testing of orbital spacecraft. The equipment works steadily and has met the design requirements for space applications. It was also announced by the Institute that the equipment would be used during the next lunar exploration mission to detect the status of

基于Orbiter的航天器升力式再入特性仿真

升力式再入是指航天器进入大气层时产生一定可控升力,对提高落点精度具有重要意义。为了研究升力式再入的动力学特性,采用Orbiter模拟器的应用程序接口,在其飞行动力学模型基础上,对航天器从低轨道升力式再入返回过程进行仿真。通过仿真试验,分析热流、过载、动压等参数的变化规律,初步摸清了升力式再入的动力学特性,并对升力式再入和弹道式再入仿真结果参数进行了比较和分析,结果表明升力式再入能很好解决过载和热流峰值高的问题。

Corrugation Stuffed Shield for Spacecraft and Its Performance

A corrugation stuffed shield system protecting spacecrafts against meteoroid and orbital debris （M/ OD） is presented. The semi-empirical ballistic limit equations （BLEs）defining the protection capability of the shield system are given, and the shielding performance is also discussed. The corrugation stuffed shield （CKS） is more effective than stuffed Whipple shield for M/OD protection, and its shielding performance will be improved significantly as increasing the impact angle. Orbital debris up to 1 cm in diameter can be shielded effectively as increasing the impact angle to 25° at the corrugated angle of 30°. The results are significant to spacecraft design.

An improved nonlinear control strategy for deep space formation flying spacecraft

This paper aims to provide further study on the nonlinear modeling and controller design of formation flying spacecraft in deep space missions. First, in the Sun-Earth system, the nonlinear formation dynamics for the circular restricted three-body problem （CRTBP） and elliptic restricted three-body problem （ERTBP） are presented. Then, with the Floquet mode method, an impulsive controller is developed to keep the Chief on the desired Halo orbit. Finally, a nonlinear adaptive control scheme based on Nonzero set- point LQR and neural network is proposed to achieve high precision formation maneuver and keeping. The simulation results indicate that the proposed nonlinear control strategy is reasonable as it considers not only the orbit keeping of the Chief, but also the formation modeling inaccuracy. Moreover, the nonlinear adaptive control scheme is effective to improve the control accuracy of the formation keeping.

Angles-only relative navigation in highly elliptical orbits

For angles-only relative navigation system only measures line-of-sight information,there are inherent problems in the ability to determine the range between Chaser and Target. Angles-only relative navigation is an attractive alternative for inspecting or rendezvous with noncooperative target,if adequate accuracy can be achieved. Angles-only relative navigation model considering J2 perturbation is presented for tracking and rendezvous with noncooperative target in highly elliptical orbit. Impulsive out-of-plane maneuvers of the Chaser are used to improve the navigation accuracy. The first impulse burns in cross-track directions to change the orbit inclination of the Chaser. The second impulse burns after one orbit period to change the orbit of the Chaser back. The simulation results show that the relative navigation system without maneuvers can't correct the initial state errors,while impulsive out-ofplane maneuvers of the Chaser improves the navigation accuracy. Angles-only relative navigation with chaser vehicle maneuvers to improve observability is effective when the spacecrafts are in highly elliptical orbits.

Refueling Test System Completed In-orbit Verification

The in-orbit verification of a refueling test system has been completed successfully.The test system based on a surface tension tank was developed by the Beijing Institute of Control Engineering（BICE）,CAST and launched into spacewith the Tianyuan 1 satellite aboard a LM-7 carrier rocket on June 25.The lifetime of any spacecraft is constrained by fuel it carried.

Thruster direction controlling of assembled spacecraft based on gimbal suspension

The attitude control system design and its control effect are affected considerably by the mass-property parameters of the spacecraft. In the mission of on-orbit servicing, as fuel is expended, or the payloads are added or removed, the center of mass will be changed in certain axe; consequently, some thrusters＇ directions are deviated from the center of mass（CM） in certain plane. The CM of assembled spacecraft estimation and thruster direction control are studied. Firstly, the attitude dynamics of the assembled spacecraft is established based on the Newton-Euler method. Secondly, the estimation can be identified by the least recursive squares algorithm. Then, a scheme to control the thrusters＇ directions is proposed. By using the gimbal installed at the end of the boom, the angle of the thruster is controlled by driving the gimbal; therefore, thrusters can be directed to the CM again. Finally, numerical simulations are used to verify this scheme. Results of the numerical simulations clearly show that this control scheme is rational and feasible.

超低轨飞行器迎风面减阻构型优化研究

针对超低轨飞行器迎风面气动阻力过大的问题,在理论解求自由分子流气动阻力方法的基础上分析迎风面阻力的主要影响因素,计算不同长度下几种典型迎风面构型的气动阻力值并分析其变化原因。在此基础上设计迎风面构型的表达函数并引入智能算法对其迭代寻优。对构型存在的约束,引入罚函数机制以降低不可行解的适应度值。研究结果表明:此方法可获得最小阻力迎风面的近似最优解,在现有材料的约束下,相比锥形构型,优化方法最大减阻可达5%以上,并能有效增加飞行器头部容积;随迎风面高度上升,最小阻力构型从近台形逐渐向锥形转化。提出的构型优化方法,可为后续超低轨飞行器减阻构型设计提供参考。

航天器相对运动的教学设计与思政实践

航天器相对运动研究两个及以上航天器在太空中相对彼此的运动特性,在空间交会对接和空间站建设运营等领域有着广泛的应用。相对运动的教学工作面临理论公式繁多、运动特性反直觉、思政案例难设计等挑战。课程负责人设计了“历史背景—基础理论—思想实验—课堂讨论—编程实践—工程案例”的教学流程和方法,并在其中穿插融入了人类交会对接成就史和月球采样返回的中国方案等思政案例。教学实践表明,该教学和思政设计能有效提升学生的学习成效,使得思想政治教育与专业知识教育相辅相成。

基于事件触发学习的航天器定轨算法

针对通信和计算资源受限的航天器实时定轨问题,提出一种基于事件触发学习的无迹卡尔曼滤波航天器定轨算法。以无迹卡尔曼滤波方法为基础,设计随机事件触发机制驱动的自适应学习算法,实现有限系统动态学习频率下的实时定轨,在保证定轨精度的同时降低地面站与航天器双向通信次数,有效节省了航天器通信与计算资源。

空间操作任务的分布式仿真系统

针对非合作目标抓捕、在轨维护、空间装配等复杂空间操作任务的地面验证需求,构建一套分布式仿真系统,主要由后台仿真模型、前端视景演示系统和前端主控制器组成。为实现不同建模工具或编程语言之间的多学科模型耦合与交互,引入FMI(functional mock-up interface)标准进行系统集成,提高了系统的模块化程度、通用性与可移植性。为充分利用计算资源、提高仿真效率,分布式部署仿真子系统与模块,利用DDS(data distribution service)通信机制实现高效、可靠的数据交互。双臂空间机器人抓捕非合作目标的演示案例表明,该仿真系统能够高保真模拟从远距离导引到近距离操作的全过程,满足实时仿真的要求。

高轨大型航天器液体晃动等效建模方法研究

高轨航天器一般都带有大量液体燃料,在进行轨道机动时液体运动会对航天器的姿态产生不可忽略的扰动,建立简洁而精确的液体晃动动力学模型具有重要的工程应用价值.介绍在带有大型燃料贮箱的高轨航天器研制过程中液体晃动等效动力学建模若干问题的研究进展,包括应用于位保模式的任意形状三维贮箱液体晃动等效建模方法、姿态大角度机动下时变参数等效力学建模方法,给出基于静矩和惯量连续的变参数等效建模方法,并通过数值仿真验证了所提出方法的准确性.

基于TLE双行根数的航天器机动检测方法

由于不同功能的航天器承担的任务不尽相同、轨道亦不相同等原因,航天器不时需要变轨机动以确保完成任务.对于非合作航天器,其可能的变轨信息预先未知且难以预测,故需要准确快速判断航天器的变轨事件,以及时调整轨道探测策略.由于美国公布的双行根数具有来源稳定、更新频率快和容易获取等特点,本文结合航天器轨道动力学及变轨控制的特点,提出了基于TLE双行根数的航天器变轨机动检测方法,通过检测半长轴的变化量和相对距离最小值实现了在轨航天器轨道面内机动的检测.以METOP-A1和IRNSS 1G两个航天器在2019年6-9月的TLE根数为例,说明使用该方法开展机动检测的操作流程和步骤.同时大量仿真计算结果表明,该方法能够有效解决航天器在轨运行过程中面内机动时间和半长轴改变量的检测以及多次变轨识别的问题,检测精度与TLE根数自身精度及机动量大小相关.

低轨等离子体环境中航天器充电研究及在轨试验

低轨道等离子体环境与航天器相互作用下将产生高充电电位,引起航天器充放电效应并对航天器能源系统、电子系统及航天员出舱活动等产生危害。本文开展了等离子体环境与航天器相互作用机理和规律研究,通过理论计算和仿真分析,建立了低轨道航天器充电模型,并进行了在轨试验验证,为低轨航天器等离子试验模型提供了理论支撑,具有重要的科学意义。