Hardware-in-the-loop simulations of GPS-based navigation and control for satellite formation flying

A relative navigation and formation control algorithm for satellite formation flying was developed, and a hardware-in-the-loop (HIL) simulation testbed was established and configured to evaluate this algorithm. The algorithm presented is a relative navigation estimation algorithm using double-difference carrier-phase and single-difference code measurements based on the extended Kalman filter (EKF). In addition, a state-dependent Riccati equation (SDRE) technique is utilized as a nonlinear controller for the formation control problem. The state-dependent coefficient (SDC) form is formulated to include nonlinearities in the relative dynamics. To evaluate the relative navigation and control algorithms developed, a closed-loop HIL testbed is configured. To demonstrate the performance of the testbed, a test formation flying scenario comprising formation acquisition and keeping in a low earth orbit (LEO) has been established. The relative navigation results from the closed-loop simulations show that a 3D RMS of 0.07 m can be achieved for position accuracy. The targeted leader–follower formation flying in the along-track separation of 100 m was maintained with a mean position error of approximately 0.2 m and a standard deviation of 0.9 m. The simulation results show that the HIL testbed is capable of successful demonstration of the GPS-based satellite autonomous formation flying mission.     

联合北斗导航与星间链路的大椭圆卫星定轨方法

传统的地面测控和GNSS均无法实现HEO卫星全弧段的跟踪观测.在分析北斗导航信号及其星间链路信号对典型HEO的观测几何及覆盖特性的基础上,利用北斗导航及其星间链路对HEO测控支持形成互补的特点,提出了一种卫星导航与星间链路相结合的自主导航方法.对HEO定轨进行分段划分并基于EKF设计了卫星导航与星间链路数据融合定轨的自主导航算法.分析结果表明,本文提出的方法能够从全弧段上改善HEO的观测几何,定轨精度比仅使用卫星导航提高了2个数量级,并且仅需较少的星间链路资源.      

空间多体系统轨道姿态及机械臂一体化控制

针对在轨服务等新型任务对航天器快速机动能力的大幅提高，研究了卫星基座和机械臂构成的空间多体系统的轨道、姿态和机械臂的一体化控制设计问题。首先，建立了空间多体系统的动力学模型；然后，基于退步控制思想，设计了卫星基座、姿态与机械臂一体化控制器，并证明了系统的稳定性，由于利用了空间多体系统的所有自由度，相比传统的基座停控或只控制基座姿态而轨道停轨的方法，极大地提高了系统的适应能力，可同时实现空间大范围的轨道转移、姿态机动，同时利用机械臂对目标进行精确操作控制。通过建立完整的空间多体系统仿真模型，对控制器进行仿真，达到了同时进行轨道、姿态及机械臂末端机动的控制目的，并验证了所提方法的有效性。      

用于长周期高精度轨道控制任务的快速半实物仿真系统

针对长周期高精度轨道控制任务的快速仿真试验需要,对传统的卫星控制系统半实物仿真系统进行了重构.提出利用动力学仿真模型程序的超实时运行驱动试验进程加速的方法,介绍系统总体设计思路及其结构、组成和工作原理,给出实时/超实时双模高精度动力学模型的开发及星地状态同步两项关键技术的具体实现,并通过应用实例证明了系统的有效性.     

北斗导航卫星姿态与轨道控制技术发展与贡献

通过总结北斗一号卫星到北斗三号卫星的发展过程，梳理了北斗导航卫星姿态与轨道控制技术的发展变化，以及在引领卫星姿轨控技术进步和星载器部件自主可控方面取得的成就.同时，根据下一代北斗卫星导航系统的论证需求，分析给出了未来导航卫星姿轨控系统需要关注与研究的关键技术.     

基于θ-D方法的在轨操作相对姿轨耦合控制

针对诸如模块更换、燃料加注等在轨操作任务中的相对动力学与控制问题,建立了描述航天器间近距离相对运动的轨道姿态耦合动力学模型,结合轨道摄动和姿态干扰力矩分析了耦合项对模型的影响。考虑到基于状态相关系数形式模型的非线性和时变性,采用θ-D次优控制算法设计了相对姿轨耦合控制器。以在轨加注任务最终逼近段为背景,针对目标航天器失控旋转的情况进行了数值仿真,仿真结果表明了θ-D控制算法能够实现对相对轨道和姿态的同步控制,简化对控制器的求解并具有较高的控制精度。     

The influence of orbital maneuver on autonomous orbit determination of an extended satellite navigation constellation

The right ascension of the ascending node is unobservable if only the inter-satellite ranging is used for autonomous orbit determination (AOD) of an Earth navigation constellation. However, if an Earth-Moon libration point satellite is added to the Earth navigation constellation to construct an extended navigation constellation, all the orbital elements can be determined with only the inter-satellite ranging. Furthermore, the extended navigation constellation can provide navigation information for interplanetary probes. For such an extended navigation constellation, orbital control needs to be considered due to the instability of the libration-point satellite orbit. This study concerns the influence of satellite orbital maneuver on the AOD of the extended navigation constellation. An AOD method under orbital maneuver is proposed. A low thrust controller is designed to achieve libration point satellite autonomous orbit maintenance by using AOD results. A navigation constellation consisting of three GPS satellites and one libration point satellite are designed for simulation. The simulation results show that libration point satellites can achieve autonomous navigation and autonomous orbit maintenance by only using inter-satellite ranging information. The rotation drift error of the Earth navigation constellation is also suppressed.     

Near real-time BDS GEO satellite orbit determination and maneuver analysis with reversed point positioning

The Geostationary Earth Orbit (GEO) satellite is a crucial part of the BeiDou Navigation Satellite System (BDS) constellation. However, due to various perturbation forces acting on the GEO satellite, it drifts gradually over time. Thus, frequent orbit maneuvers are required to maintain the satellite at its designed position. During the orbit maneuver and recovery periods, the orbit quality of the maneuvered satellite computed with broadcast navigation ephemeris will be significantly degraded. Furthermore, the conventional dynamic Precise Orbit Determination (POD) approach may not work well, because of a lack of publicly available satellite information for modeling the thrust forces. In this paper, a near real-time approach free of thrust forces modeling is proposed for BDS GEO satellite orbit determination and maneuver analysis based on the Reversed Point Positioning (RPP). First, the station coordinates and receiver clock offsets are estimated by GPS/BDS combined Single Point Positioning (SPP) with single-frequency phase-smoothed pseudorange observations. Then, with the fixed station coordinates and receiver clock offsets, the RPP method can be conducted to determine the GEO satellite orbits. When no orbit maneuvers occur, the proposed method can obtain orbit accuracies of 0.92, 2.74, and 8.30?m in the radial, along-track, and cross-track directions, respectively. The average orbit-only Signal-In-Space Range Error (SISRE) is 1.23?m, which is slightly poorer than that of the broadcast navigation ephemeris. Using four days of GEO maneuvered datasets, it is further demonstrated that the derived orbits can be employed to characterize the behaviors of GEO satellite maneuvers, such as the time span of the maneuver as well as the satellite thrusting accelerations. These results prove the efficiency of the proposed method for near real-time GEO satellite orbit determination during maneuvers.     

基于GNSS的高轨卫星定位技术研究

利用全球卫星导航系统(GNSS)进行导航定位具有全球、全天候、实时和高精度的优点,应用于高地球轨道(HEO)卫星的定位,能够提供精确的轨道和姿态确定,并且可以克服目前主要利用地面测控系统对HEO卫星进行定位的设备复杂、投资高等缺点,使得自主导航成为可能.本文对利用GNSS的高轨卫星定位相关技术进行了研究,分析了单一GNSS系统和多个GNSS组合系统的卫星可见性、动态性和几何精度因子(GDOP).通过仿真分析表明,利用组合GNSS系统并通过提高GNSS接收机灵敏度的方法,可以解决GNSS进行HEO卫星定位的相关问题,并能保证HEO卫星定位精度的要求.      

双星定位系统/SINS深组合导航系统研究

以卫星模拟器为基础，介绍了一种双星定位系统定姿的基本原理，解决了双星定位系统存在的位置滞后即定位实时性较差的缺陷，把双星定位系统的位置与姿态信息和捷联惯导系统的位置、姿态信息进行组合后，可有效地提高系统的精度．     

基于脉冲星和紫外敏感器的自主定轨定姿授时研究

为提高深空探测器的自主导航能力, 利用脉冲星导航的脉冲到达时间和脉冲星 角位置测量值、紫外敏感器中心天体质心相对于探测器的方向矢量和距离测量 值以及紫外敏感器输出的航天器姿态角, 以探测器在惯性坐标系下的位置和速度、 探测器本体坐标系相对于惯性坐标系的姿态角、星载时钟钟差为系统状态变量, 通过联邦扩展卡尔曼滤波器估计组合导航系统的系统状态, 并利用火星环绕段 轨道数据进行仿真实验. 仿真结果表明, 该组合导航方法能够使火星轨道器 在环绕段飞行中同时进行定轨、定姿和授时, 且具有较高的导航精度和授时能力.      

MEO导航卫星在轨放气产生的干扰力矩研究

摘要： 针对多颗MEO导航卫星太阳翼展开后产生比较明显的干扰力矩，对卫星稳定控制产生了一定影响的现象，本文根据动力学模型、姿态、角速度和飞轮转速变化，给出了干扰力矩计算方法，并结合多颗卫星在轨遥测数据进行计算，得出放气期间产生的干扰力矩.通过使用此干扰力矩进行仿真得出，卫星模拟器结果和在轨表现基本一致.此研究有助于优化卫星飞控流程，并指导卫星放气孔设计.     

利用摆动地球敏感器两个探测器输出的姿态确定

摆动地球敏感器是地球同步通信卫星控制系统的重要部件。这种敏感器主要用于卫星的姿态测量,测量量作为控制系统的输入信号计算控制输出量。摆动地球敏感器有4个探测器,目前在轨卫星的基本使用方法均为至少使用3个探测器的测量信息进行姿态确定。本文给出了使用2个探测器测量确定卫星姿态的计算方法,并结合实际情况给出了使用策略。这种姿态确定方法大大拓宽了地球敏感器的使用范围,增加了地球敏感器的冗余性,延长了部件的使用寿命。     

Impact of the orbital eccentricity on the attitude performance before and after the deorbiting phase for Alsat-1

Due to the presence of periodic forcing terms in the gravity gradient torque, orbit eccentricity may produce large response for the roll, yaw and pitch angles. This paper investigates the influence of the orbit eccentricity on the performance of the attitude determination and control subsystem (ADCS) pointing of passive Low Earth Orbit (LEO) satellites stabilized by a gravity gradient boom or having long appendages before and after the deorbiting operation. The contribution of this work is twofold. First, the satellite attitude dynamics and kinematics are modeled by introducing the orbit eccentricity in the equations of motion of a LEO satellite in order to provide the best scenario in which satellite operators can keep the nominal functionality of LEO satellites with a gravity gradient boom after the deorbiting operation. Second, a Quaternion-based Extended Kalman Filter (EKF) is analyzed when the orbit eccentricity is considered in order to determine the influence of this disturbance on the convergence and stability of the filter. The simulations in this work are based on the true parameters of Alsat-1 which is a typical LEO satellite stabilized by a gravity gradient boom. The results show that the orbit eccentricity has a big influence on the pointing system accuracy causing micro-vibrations that affect the geocentric pointing particularly after the deorbiting phase. In this case, satellites have no orbital correction option. The Quaternion-based Extended Kalman Filter analyzed in this paper, achieved satisfactory results for eccentricity values less than 0.4 with respect to pointing system accuracy. However, singularities were observed for eccentricity values greater than 0.4.     

Analysis on navigation accuracy of high orbit spacecraft based on BDS GEO and IGSO satellites

To make up for the insufficiency of earth-based TT&C systems, the use of GNSS technology for high-orbit spacecraft navigation and orbit determination has become a new technology. It is of great value to applying Geosynchronous Earth Orbit (GEO) and Inclined GeoStationary Orbit (IGSO) navigation satellites for supporting the navigation of high-orbit spacecraft since there are three different types of navigation satellites in BeiDou Navigation Satellite System (BDS): Medium Earth Orbit (MEO), GEO and IGSO. This paper conducts simulation experiments based on Two-Line Orbital Element (TLE) data to analyze and demonstrate the role of these satellites in the navigation of high-orbit spacecraft. Firstly, the spacecraft in GEO was used as the target satellite to conduct navigation experiments. Experiments show that for the spacecraft on the GEO orbit, after adding GEO and IGSO respectively on the basis of receiving MEO navigation satellite signals, the accuracies were improved by 7.22 % and 6.06 % respectively. When adding both GEO and IGSO navigation satellites at the same time, the accuracy can reach 16 m. In the second place, navigation and positioning experiments were carried out on three high elliptical orbit (HEO) satellites with different semimajor axis (32037.2 km, 42385.9 km, 67509.6 km). The experiments show that the number of visible satellites has been improved significantly after adding GEO and IGSO navigation satellites at the same time. The visible satellites in these three orbits were improved by 32.84 %, 41.12 % and 37.68 %, respectively compared with only observing MEO satellites.The RMS values of the navigation positioning errors of these three orbits are 25.59 m, 87.58 m and 712.48 m, respectively.     

星载GNSS确定GEO卫星轨道的积分滤波方法

采用星载全球导航卫星系统（GNSS）确定地球静止轨道（GEO）,以解决目前应用星载全球定位系统(GPS)时导航卫星可见性差的问题。以风云卫星为例,分析了未来的GNSS相对于GEO卫星的可见性,针对GEO轨道上导航接收机采样间隔较长的问题,综合轨道积分和卡尔曼滤波方法的优点,提出了确定GEO卫星轨道的积分滤波方法。并利用STK软件仿真产生所需数据,用MATLAB对提出的算法编程并进行仿真验证,结果表明,提出的方法性能优越,定轨精度较高。     

Guidepost-based autonomous orbit determination method for GEO satellite

Guidepost-based navigation system is a novel autonomous orbit determination method for the GEO satellite. The system is achieved by using the camera imaging function to obtain the guidepost images and the GNSS signal receiver to obtain the pseudoranges between the GEO and the navigation satellites. Due to the high altitude of GEO satellite and the time-varying sunlight condition in the space environment, it may be difficult to obtain object image points and the distance measurements of GNSS because of the weak visibility of the guideposts. To deal with the problem, a novel integrated orbit determination system is presented. The Earth landmarks, the in-orbit spacecraft and GNSS navigation satellites whose line-of-sights and the distance can be easily obtained are used at the same time as information for the GEO satellite navigation based on the observability conditions analysis. The observability of the GEO satellite navigation system is analyzed through the physical observability, the mathematical observability and the engineering observability through the observing geometry, the rank of observability matrix and the Cramer-Rao lower bound (CRLB) respectively. Besides, the maximum correntropy unscented Kalman filter (MCUKF) algorithm is applied to improve the estimation stability of the system in the presence of non-Gaussian noises. The simulation indicates the feasibility of the proposed scheme.     

航星座自主运行平行系统的轨道计算方法

构建一个能够与实际卫星导航系统长期保持时空一致的平行系统，可为导航星座自主运行提供一个监视与评估平台。针对建设该平行系统所需的高逼真轨道计算问题，引入平行系统理论的思想，在分析历史精密轨道的基础上，提出高精度轨道计算与预报方法。该方法以不断更新的精密轨道作为输入，利用PID增量式算法或时变加权法进行数据平滑，使得轨道计算结果始终与实际系统保持高度一致性。试验结果表明，该方法可使卫星轨道计算的结果与实际卫星轨道长期保持在分米量级。     

Instantaneous BeiDou–GPS attitude determination: A performance analysis

The advent of modernized and new global navigation satellite systems (GNSS) has enhanced the availability of satellite based positioning, navigation, and timing (PNT) solutions. Specifically, it increases redundancy and yields operational back-up or independence in case of failure or unavailability of one system. Among existing GNSS, the Chinese BeiDou system (BDS) is being developed and will consist of geostationary (GEO) satellites, inclined geosynchronous orbit (IGSO) satellites, and medium-Earth-orbit (MEO) satellites. In this contribution, a BeiDou–GPS robustness analysis is carried out for instantaneous, unaided attitude determination.