PRISMA—A formation flying project in implementation phase

The PRISMA project for autonomous formation flying and rendezvous has passed its critical design review in February–March 2007. The project comprises two satellites which are an in-orbit testbed for Guidance, Navigation and Control (GNC) algorithms and sensors for advanced formation flying and rendezvous. Several experiments involving GNC algorithms, sensors and thrusters will be performed during a 10 month mission with launch planned for the second half of 2009.The project is run by the Swedish Space Corporation (SSC) in close cooperation with the German Aerospace Center (DLR), the French Space Agency (CNES) and the Technical University of Denmark (DTU). Additionally, the project also will demonstrate flight worthiness of two novel motor technologies: one that uses environmentally clean and non-hazardous propellant, and one that consists of a microthruster system based on MEMS technology.The project will demonstrate autonomous formation flying and rendezvous based on several sensors—GPS, RF-based and vision based—with different objectives and in different combinations. The GPS-based onboard navigation system, contributed by DLR, offers relative orbit information in real-time in decimetre range. The RF-based navigation instrument intended for DARWIN, under CNES development, will be tested for the first time on PRISMA, both for instrument performance, but also in closed loop as main sensor for formation flying. Several rendezvous and proximity manoeuvre experiments will be demonstrated using only vision based sensor information coming from the modified star camera provided by DTU. Semi-autonomous operations ranging from 200 km to 1 m separation between the satellites will be demonstrated.With the project now in the verification phase particular attention is given to the specific formation flying and rendezvous functionality on instrument, GNC-software and system level.     

Flight demonstration of new thruster and green propellant technology on the PRISMA satellite

The concept of a storable liquid monopropellant blend for space applications based on ammonium dinitramide (ADN) was invented in 1997, within a co-operation between the Swedish Space Corporation (SSC) and the Swedish Defense Research Agency (FOI). The objective was to develop a propellant which has higher performance and is safer than hydrazine. The work has been performed under contract from the Swedish National Space Board and ESA. The progress of the development has been presented in several papers since 2000.ECAPS, a subsidiary of the Swedish Space Corporation was established in 2000 with the aim to develop and market the novel “high performance green propellant” (HPGP) technology for space applications. The new technology is based on several innovations and patents w.r.t. propellant formulation and thruster design, including a high temperature resistant catalyst and thrust chamber.The first flight demonstration of the HPGP propulsion system will be performed on PRISMA. PRISMA is an international technology demonstration program with Swedish Space Corporation as the Prime Contractor.This paper describes the performance, characteristics, design and verification of the HPGP propulsion system for PRISMA. Compatibility issues related to using a new propellant with COTS components is also discussed. The PRISMA mission includes two satellites in LEO orbit were the focus is on rendezvous and formation flying. One of the satellites will act as a “target” and the main spacecraft performs rendezvous and formation flying maneuvers, where the ECAPS HPGP propulsion system will provide delta-V capability.The PRISMA CDR was held in January 2007. Integration of the flight propulsion system is about to be finalized.The flight opportunity on PRISMA represents a unique opportunity to demonstrate the HPGP propulsion system in space, and thus take a significant step towards its use in future space applications. The launch of PRISMA scheduled to 2009.     

美国航天器交会技术研究

美国交会对接技术的发展可分为三个阶段：＂双子座＂与＂阿波罗＂飞船,航天飞机,以及后航天飞机时代的项目。自主交会技术的发展,首先基于多种制导和导航敏感器的研发,特别是用于最终逼近段的激光敏感器。制导、导航与控制系统的冗余,以及故障检测与隔离的方法,在轨迹安全性中起重要作用。文章研究美国自主交会方案,包括＂双子座＂,＂阿波...     

Flight demonstration of formation flying capabilities for future missions (NEAT pathfinder)

PRISMA is a demonstration mission for formation-flying and on-orbit-servicing critical technologies that involves two spacecraft launched in low Earth orbit in June 2010 and still in operation. Funded by the Swedish National Space Board, PRISMA mission has been developed by OHB-Sweden (formerly Swedish Space Corporation) with important contributions from the German Aerospace Centre (DLR/GSOC), the French Space Agency (CNES), and the Technical University of Denmark (DTU). The paper focuses on the last CNES experiment achieved in September 2012 that was devoted to the preparation of future astrometry missions illustrated by the NEAT and µ-NEAT mission concepts. The experiment consisted of performing the type of formation maneuvers required to point the two-satellite axis to a celestial target and maintain it fixed during the observation period. Achieving inertial pointing for a LEO formation represented a new challenge given the numerous constraints from propellant usage to star tracker blinding. The paper presents the experiment objectives in relation with the NEAT/µ-NEAT mission concept, describes its main design features along with the guidance and control algorithms evolutions and discusses the results in terms of performances achieved during the two rehearsals.     

基于MicroSim仿真平台的航天器交会对接物理仿真系统

航天器交会对接物理仿真是进行交会对接技术地面试验和验证的一种行之有效的方式,本文初步分析了利用微小卫星五自由度仿真平台M icroSim实现交会对接过程中测量方案、制导和控制策略以及GNC软件系统性能等仿真验证的物理仿真系统的可能性,简要介绍了M icroSim仿真平台,提出基于M icroSim仿真平台的航天器交会对接物理仿真系统总体方案。为建立我国的RVD物理仿真系统提供了一条快速低廉的有效途径。     

共面快速受控绕飞轨迹设计与控制

绕飞运动在航天器在轨服务与在轨支援、辅助航天员舱外活动、航天器编队飞行、空间交会对接等空间活动中具有重要应用。分析了快速受控绕飞的可行性和主要过程，建立了适用于目标航天器运行在圆轨道上的共面快速绕飞和进入绕飞与退出绕飞的轨迹设计模型，采用多速度脉冲控制方法和等角度，等时间控制方式对绕飞轨迹进行控制。仿真计算结果表明所提出的快速受控绕飞轨迹设计模型和控制方法可以实现对圆轨道目标航天器的共面快速受控绕飞。     

非合作空间目标自主交会凸优化制导技术

为解决非合作空间目标机动、自旋、章动等动态特性对自主交会过程带来的困难和挑战,在某飞行器姿轨控一体化推进系统配置的基础上,充分考虑各类约束后构建标准的凸优化自主交会数学模型;着重分析了非合作目标动态特性对制导误差的影响,设计相应的修正策略;以原始对偶内点法作为核心求解器,设计了具备状态预测和更新能力的制导算法;数学仿真验算表明,该方法合理可行,克服了动态特性造成的接近轨迹偏差,良好地适应了非合作交会任务。     

卫星交会的自主导航技术

论述卫星交会自主导航的飞行任务背景和概念 ,综述国内外学者正在进行探索研究的思路 ,以期引起国内学者的的注意、探讨和深入研究。     

火星轨道交会自主导航与制导方法

对火星采样返回任务中的火星轨道交会自主导航和制导技术进行了研究。采用光学自主导航敏感器测量的火星中心方向和视半径,相对敏感器测量的相对位置等观测量,设计了导航滤波器同时估计轨返组合体和上升器的轨道。在导航滤波器设计中,针对光学自主导航敏感器更新频率远低于滤波解算频率的问题,设计了一种连续观测量构造算法,确保每个滤波周期均可进行测量更新,以提高导航精度。基于导航滤波器估计结果,采用T-H制导设计了4脉冲共椭圆交会策略实施轨道控制,从而构成近程交会自主导航和制导方案用于完成火星轨道交会任务。通过数学仿真校验了所提出方法的有效性。     

方位角约束自主交会变结构制导律设计

针对空间交会视线相对运动动力学模型具有时变非线性和参数不确定性的特点,提出了一种基于非线性滑动模态的自主交会变结构制导算法。通过将视线运动模型划分为横向和纵向运动模型,分别设计了相应的非线性滑动模态。横向滑动模态是一种由视线角速率、视线角和时间构成的非线性函数,而纵向滑动模态则是由距离、速率以及时间构成的非线性函数。然后,根据Lyapunov稳定性理论分别推导了横向和纵向自主交会变结构制导规律。横向制导实现了带有末端方位角约束的自主接近;纵向制导保证了软交会所要求的距离和速度协同控制。仿真结果表明,设计的方法在只使用相对信息量的前提下克服了交会模型的耦合非线性和参数不确定性,并能适用于不同高度圆轨道和椭圆轨道上的V-bar和R-bar自主交会任务。     

Profiles of quick access to the orbital station for modern spacecraft

The problems of decreasing the duration of the autonomous flight of a spacecraft (SC) before the docking with an orbital station (OS) are considered in this paper. Modern SCs should be docked with the International Space Station (ISS) with an arbitrary initial phase angle; for this reason, the rendezvous of the Russian Soyuz-TMA spacecraft with the ISS is performed for 2 days. The paper presents to consideration some new flight profiles with essentially smaller duration. The results of modeling the developed rendezvous profiles are presented and solutions to emergency situations are considered.     

Autonomous navigation of formation flying spacecrafts in deep space exploration and communication by hybrid navigation utilizing neural network filter

Autonomous navigation of spacecrafts is a difficult task, however, which is a must in future deep space exploration. With multiple spacecrafts flying in space, this aim can be achieved by formation flying spacecraft (FFS) utilizing inverse time difference of arrival (ITDOA) and inverse difference Doppler (IDD) methods, which can locate the position of earth-station from one-way uplink signals in the FFS coordinate, and by way of conversion of coordinates, the position of FFS is achieved in earth-centered earth-fixed (ECEF) coordinate. The ability of neural network (NN) filter in navigation to extract position of spacecrafts from random measuring noise of signal arrival time and Doppler shift is studied with different radius of FFS and surveying parameters. The NN filter used by spacecraft group is new way of unidirectional autonomous navigation and is of high precision of hybrid navigation.     

Autonomous guidance and control of Earth-orbiting formation flying spacecraft: Closing the loop

Previous work on autonomous formation flying guidance and control identified three key challenges to overcome in order to obtain a fully autonomous guidance and control loop: an accurate but simple model of relative motion about elliptical and perturbed orbits, an efficient way of performing conflicting requirements trade-off with power-limited on-board computers, and finally an optimal or near-optimal control algorithm easy to implement on a flight computer. This paper first summarizes recent developments on each of these subject that help to overcome these challenges, developments which are then used as building blocks for an autonomous formation flying guidance and control system. This system autonomously performs trade-offs between conflicting requirements, i.e. minimization of fuel cost, formation accuracy and equal repartition of the fuel expenditure within the formation. Simulation results show that a complete guidance and control loop can be established using mainly analytical results and with very few numerical optimization which facilitates on-board implementation.     

地球同步轨道卫星编队飞行的区域性导航系统方案

卫星编队飞行组成虚拟平台 ,这是当前一个完全崭新和开拓性的研究课题。根据与时俱进 ,开拓创新的精神 ,本文提出一个地球同步轨道卫星编队飞行组成的区域性导航系统方案。这是至今为止在相同精度和相同覆盖区条件下卫星数量最少的 ,也是投资经费最低的导航系统方案     

非合作目标自主交会对接的椭圆蔓叶线势函数制导

针对非合作式航天器自主交会对接任务的安全性要求,提出了一种基于椭圆蔓叶线的人工势函数制导方法。首先根据视线坐标系建立了相对动力学方程与状态方程。进而应用人工势函数制导方法解决了非合作目标航天器自主交会对接与静态障碍物躲避问题,并且把势函数方法与椭圆蔓叶线函数相结合,解决了追踪航天器在接近目标航天器时运行在安全走廊中的安全性要求。应用Lyapunov稳定性理论证明了在所提出的制导方法控制下系统的稳定性。最后,用精确的数学模型进行了计算机数值仿真,验证了所提出的制导控制方法的正确性和有效性。
     

Autonomous guidance and control of Earth-orbiting formation flying spacecraft: Closing the loop

Previous work on autonomous formation flying guidance and control identified three key challenges to overcome in order to obtain a fully autonomous guidance and control loop: an accurate but simple model of relative motion about elliptical and perturbed orbits, an efficient way of performing conflicting requirements trade-off with power-limited on-board computers, and finally an optimal or near-optimal control algorithm easy to implement on a flight computer. This paper first summarizes recent developments on each of these subject that help to overcome these challenges, developments which are then used as building blocks for an autonomous formation flying guidance and control system. This system autonomously performs trade-offs between conflicting requirements, i.e. minimization of fuel cost, formation accuracy and equal repartition of the fuel expenditure within the formation. Simulation results show that a complete guidance and control loop can be established using mainly analytical results and with very few numerical optimization which facilitates on-board implementation.     

A Concept of Guidance for an Air-Launch Vehicle with Compensation of Initial Downrange and Launch Time Errors at Direct Insertion into a Rendezvous Point in the Orbit

A flying launcher (airplane carrier) can generate initial errors in position and time of launch. In order to compensate for these errors, one should have two control parameters in addition to those that provide for a spacecraft's injection into a preset orbit. We suggest the concept of controlling the trajectory of injection by choosing thrust values (within allowable regions of control) of second-stage engines or/and of a space booster of the Polyot carrier launcher. As an example, a rendezvous of the spacecraft at the end of its boost phase with the International Space Station (ISS) is considered. The methodology of the suggested approach can be extended to other mobile systems of launch to rendezvous orbits.     

基于双目视觉的相对状态自主确定

基于双目视觉系统提出了一种适于交会对接最后阶段的近距离绕飞的相对状态自主确定方法。用修正罗德里格参数(MRP)描述姿态,给出了追踪器与目标器间的相对姿态运动学与动力学方程,以及相对运动方程,根据双目视觉系统的小孔成像原理建立了双目系统的测量数学模型,由扩展卡尔曼滤波(EKF)获得两航天器的相对位姿及其变化率。仿真结果表明该法可行。