Energy-efficient control of nanosatellites during distributed region formation flying

In this paper, we present an energy-efficient method for distributed region formation flying of nanosatellites. The proposed framework consists of two concurrent sub-schemes that include estimation and formation. In the estimation sub-scheme, unlike the existing methods on satellite formation flying, that assume the availability of the reference orbital elements to all followers, here, a distributed estimator is developed so that the follower nanosatellites estimate the position of the leader in its orbital slot. In the formation sub-scheme, we consider a region formation strategy which is an efficient method in dealing with the formation of a large number of nanosatellites. We propose an optimal region following formation method based on the receding horizon control (RHC) using the estimated reference orbital elements. Subsequently, an algorithm is presented to solve the proposed energy-efficient formation flying method. Finally, the simulation result is presented that illustrates the purposed method improves the power consumption for each nanosatellite with respect to the existing non-optimal region formation flying controllers.     

基于Hermite的SAR卫星轨道插值干涉测量应用研究

合成孔径雷达(Synthetic aperture radar, SAR)卫星轨道参数是干涉测量技术中影像配准、基线估算、平地相位去除等环节的重要参数,但部分SAR卫星轨道参数采样间隔较大,导致干涉测量过程中产生残余相位,发生较大的系统误差;利用MTALAB编程工具,对卫星原始轨道状态矢量进行了埃尔米特插值法拟合,等距插值计算后,发现可以缩小轨道参数采样间隔,提高干涉测量精度;以覆盖巴姆地区的Envisat卫星为例,分别获取了基于粗轨、埃尔米特插值轨道参数和代尔夫特精密轨道参数得到的干涉测量图,定性判断出埃尔米特插值法可有效提高SAR卫星轨道精度;再以覆盖陕西地区的AOLS卫星为例,插值轨道矢量采样间隔分别为10秒、5秒、2秒,发现间隔为5秒时相干性最优;结果表明：采用埃尔米特插值法可有效增加SAR卫星轨道状态矢量数量,消除系统误差,提高干涉测量精度。     

Trajectory‐keeping in satellite formation flying via robust periodic learning control

This paper proposes an iterative learning control (ILC) scheme to ensure trajectory‐keeping in satellite formation flying. Since satellites rotate the earth periodically, position‐dependent disturbances can be considered time‐periodic disturbances. This observation motivates the idea of repetitively compensating for external disturbances such as solar radiation, magnetic field, air drag, and gravity forces in an iterative, orbit‐to‐orbit manner. It is shown that robust ILC can be effectively utilized for satellite trajectory tracking, thus enabling time‐variant formation flying between the leader‐ and follower‐satellites. The validity of the results is illustrated through computational simulations. Copyright © 2009 John Wiley & Sons, Ltd.     

基于相对轨道根数计算的测绘卫星单点定位研究

传统测绘卫星定位方法无法获取轨道全面信息,且传统方法忽略了多个测绘卫星并行航行情况,导致出现定位误差的问题。因此,提出一种基于相对轨道根数计算的测绘卫星单点定位方法。采用基于J₂摄动模型的卫星轨道根数预测方法,预测卫星所在的轨道六根数,以此掌握卫星所在轨道信息;在此基础之上,通过基于相对轨道根数的卫星单点位置预测方法,预测卫星单点位置与卫星的运行速度,实现测绘卫星单点定位。实验结果验证：所提方法在多个测站位置的N、S、E三个方向的平均定位误差最大值为0.05 m。且所提方法预测近地卫星、中高度卫星、地球同步卫星所在轨道根数时,预测误差均方值均低于0.04;定位三种测绘卫星时,定位误差均方值最大值为0.02。数据表明所提方法可准确预测卫星位置信息,可作为测绘卫星定位的有效工具。     

基于T-H方程的编队卫星碰撞概率与规避策略研究

基于T-H方程,对椭圆轨道下编队卫星碰撞预测以及规避机动进行了研究。通过递推编队卫星的初始状态协方差矩阵,将碰撞概率密度在危险域内积分获得编队卫星的碰撞概率。当碰撞概率大于安全阈值时,采用瞬时校正速度的控制策略对卫星施加最小脉冲速度修正量,在所预测的碰撞点沿碰撞概率梯度产生偏移,到达安全等高线上,从而降低碰撞概率。仿真结果表明,该预测方法有效,规避策略可行。     

基于北斗系统的船载USB轴系参数标校方法

在目前跟踪精轨目标进行直接标校电轴参数方法的基础上,充分利用北斗卫星资源较多、分布均匀和包含有不同轨道周期卫星的特点,通过合理设计USB跟踪北斗卫星方案提高了USB轴系参数标校的效率。通过试验验证,该方案能够有效克服目前USB轴系参数标校受天气影响、跟踪低轨道标校星受时间限制等不利条件的影响,实现USB轴系参数的快速标校,标校结果能够满足USB测角指标的要求。     

低轨编队卫星构形保持的模糊PID控制

近地轨道上的编队卫星,大气摄动和J2项摄动是影响编队构形的主要因素,编队会造成卫星编队构形产生沿航迹方向漂移,导致队形发散,面质比差直接决定了漂移的方向和速度。因此可以通过调整面质比差消除漂移。可以相对队形绕飞中心的漂移距离为输入量,以卫星面质比差为控制量,用模糊控制和PID控制相结合设计控制器消除编队构形的航迹引起的漂移,实现PID参数的自寻优模糊控制。仿真利用MATLAB链接STK实现模糊PID控制的仿真,结果表明,对于两颗卫星构成的构形长半轴为10km的共面绕飞椭圆,相对构形沿航迹漂移距离能够控制在40m之内,实现了设计要求。     

编队星载GNSS观测数据的建模与仿真

编队星载GNSS观测数据的建模仿真是编队卫星研发任务中的关键问题之一.结合编队卫星构形设计方法、导航卫星可见性分析、几何距离生成以及观测误差的特性分析,建立了观测数据仿真模型.基于SIX的三维图形显示、精确的卫星轨道模型和数据报告等功能,以及Matlab便于数据操作和算法开发的特点,搭建了观测数据仿真平台,获取了编队星载GNSS接收机的观测数据.给出了仿真设计框架与具体流程,并通过仿真实例给出了观测数据仿真结果及其可信性验证.     

基于MapObjects的在轨卫星运行仿真

卫星轨道预报技术是与卫星通信及卫星回收的关键技术。该文将卫星轨道预报技术和计算机仿真技术相结合,提出了在GIS控件——MapObjects上建立卫星在轨运行仿真平台的设计思想。在综合卫星的轨道计算、覆盖区域推导与地图投影的基础上,设计了基于二维实时动态显示技术的卫星轨道预报仿真平台。该平台可用于卫星轨道预报的地面测试及分析,应用数据库技术进行卫星及观察站点的管理。在实时显示卫星当前的参数的同时,利用二维显示技术动态仿真演示卫星的星下点轨迹及其覆盖区域和太阳的位置及其照亮区域的变化。     

卫星运行三维场景及星下点轨迹可视化研究

应用可视化技术构造卫星运行的虚拟场景,实时显示卫星运行状态及星下点轨迹,可为卫星轨道设计、卫星运行状态监控及卫星应用提供直观的分析和指导。通过对卫星轨道计算方法、几何建模、虚拟场景装配及虚拟场景驱动方法研究,本文开发了卫星运行三维场景及星下点轨迹可视化软件。本文详细给出了地球模型、卫星模型的建模及由此模型组装卫星运行场景的方法,卫星轨道计算及星下点轨迹可视化方法。该软件可实时模拟卫星在太空中的运行场景,给出卫星的即时经纬度坐标及星下点位置坐标。该软件已在实践中得到应用。     

非太阳同步重访干涉轨道设计与摄动影响分析

为了满足合成孔径雷达(SAR)卫星大型星座任意轨道面都可保持长期重访干涉的需求,提出了一种通用的非太阳同步重访干涉参考轨道设计方法,将重访周期作为修正变量之一,采用迭代修正方法得到了高精度动力学模型下的任意轨道倾角的参考轨道。仿真分析给出了一定轨道高度范围内所有候选的参考轨道,并指出了不同轨道倾角、相同重访圈数的参考轨道高度的明显变化,为实际任务的轨道筛选提供了参考。此外,针对日、月引力摄动对轨道倾角的影响进行了详细分析,指出了中低轨道倾角的非太阳同步轨道所需轨道保持控制的代价非常小,完全可以保持长期重访干涉。     

Distributed optimal formation algorithm for multi-satellites system with time-varying performance function

ABSTRACT

This paper studies a fully distributed optimal formation flying problem for a multi-satellite system with a chief satellite and some deputy satellites, in order to seek the optimal formation via simple local information exchange. A distributed algorithm is proposed such that the satellites team performance is optimised in finite time while all of the satellites meet the formation constraint. To achieve the optimal flight, the performance functions for each deputy satellite that can describe the satellite's contribution to the task are introduced. Here, the performance functions can be time varying, which generally changes the problem from finding the fixed optimal point to tracking the optimal trajectory. Theoretical studies indicate that the proposed algorithm will optimise the satellites flight and all of the satellites can keep the desired communication distance. Finally, simulation examples are presented to show the validity of the theoretical results.     

编队飞行卫星高精度自主相对定轨研究

设计了一种应用于卫星编队的自主相对轨道确定方案,不同于目前广泛采用的C-W方程,采用了包含摄动影响的相对运动方程的解析表达式描述编队飞行。利用星间距离信息和方位信息作为观测量,设计扩展卡尔曼滤波器实现环绕卫星相对轨道的自主确定,仿真结果表明定轨精度比采用C-W方程提高一个数量级,验证了这种导航方案的有效性。     

应用控制系统设计工具箱PIMCSD求解卫星编队重构问题

利用线性时变系统终端约束最优控制方法,为椭圆轨道卫星编队的队形重构控制问题设计了均衡耗能最优控制器.由于描述椭圆轨道卫星编队相对运动的Lawden方程是时变方程,给卫星编队重构的最优控制器设计带来一定的困难.利用基于精细积分算法的控制系统设计工具箱-PIMCSD进行系统设计,求解卫星编队重构所需的时变最优反馈控制律和前馈控制律,最后给出了由三颗卫星组成的编队队形重构控制仿真计算结果.     

Nonlinear programming control using differential aerodynamic drag for CubeSat formation flying

Because of their volume and power limitation, it is difficult for CubeSats to configure a traditional propulsion system. Atmospheric drag is one of the space environmental forces that low-orbit satellites can use to realize orbit adjustment. This paper presents an integrated control strategy to achieve the desired in-track formation through the atmospheric drag difference, which will be used on ZJUCubeSat, the next pico-satellite of Zhejiang University and one of the participants of the international QB50 project. The primary mission of the QB50 project is to explore the near-Earth thermosphere and ionosphere at the orbital height of 90–300 km. Atmospheric drag cannot be ignored and has a major impact on both attitude and orbit of the satellite at this low orbital height. We conduct aerodynamics analysis and design a multidimensional nonlinear constraint programming (MNLP) strategy to calculate different desired area–mass ratios and corresponding hold times for orbit adjustment, taking both the semimajor axis and eccentricity into account. In addition, area–mass ratio adjustment is achieved by pitch attitude maneuver without any deployable mechanism or corresponding control. Numerical simulation based on ZJUCubeSat verifies the feasibility and advantage of this design.     

Necessary and sufficient conditions of the rendezvous between a single spacecraft and three non-coplanar Walker constellation satellites

The probability of the rendezvous between a single spacecraft and three non-coplanar constellation satellites is studied,and the necessary and sufficient conditions of the rendezvous without orbital maneuver are deduced.The rendezvous orbit design can be transformed into the patching of two spacecraft orbits,either of which can achieve the rendezvous with two satellites.Firstly,due to the precious quality of spherical geometry,the unique existence of the rendezvous orbit for two constellation satellites is ...     

基于星载GPS卫星编队可视化仿真系统

针对研究星载GPS编队卫星自主导航算法及模型对编队的影响,为实际编队提高导航定位精度,结合数据库系统编制出了关于星载GPS编队卫星仿真系统。在分析卫星编队相对导航运动规律基础上,利用OPENGL及数据库技术对星载GPS空间圆编队,车轮式编队和水平圆编队进行了三维可视化仿真,给出了设计过程。考虑到编队卫星需要接收GPS信号进行自主导航,利用GPS星座可见性分析方法,实现星载GPS编队卫星的GPS星座选择。三维可视化仿真结合STK进行了验证。仿真系统已作为编队方案设计、编队飞行相对导航仿真算法设计的基础工具,还为将来各种航天器编队飞行应用技术及航天器对接技术提供可靠的试验基础数据和技术依据。     

A distributed model predictive control (MPC) fault reconfiguration strategy for formation flying satellites

In this paper, an active distributed (also referred to as semi-decentralised) fault recovery control scheme is proposed that employs inaccurate and unreliable fault information into a model-predictive-control-based design. The objective is to compensate for the identified actuator faults that are subject to uncertainties and detection time delays, in the attitude control subsystems of formation flying satellites. The proposed distributed fault recovery scheme is developed through a two-level hierarchical framework. In the first level, or the agent level, the fault is recovered locally to maintain as much as possible the design specifications, feasibility, and tracking performance of all the agents. In the second level, or the formation level, the recovery is carried out by enhancing the entire team performance. The fault recovery performance of our proposed distributed (semi-decentralised) scheme is compared with two other alternative schemes, namely the centralised and the decentralised fault recovery schemes. It is shown that the distributed (semi-decentralised) fault recovery scheme satisfies the recovery design specifications and also imposes lower fault compensation control effort cost and communication bandwidth requirements as compared to the centralised scheme. Our proposed distributed (semi-decentralised) scheme also outperforms the achievable performance capabilities of the decentralised scheme. Simulation results corresponding to a network of four precision formation flight satellites are also provided to demonstrate and illustrate the advantages of our proposed distributed (semi-decentralised) fault recovery strategy.     

Leader–follower type relative position keeping in satellite formation flying via robust exponential stabilization

Satellite formation flying is an essential technology in both the current and the future aerospace industry. Conducting a fast and safe flying formation between satellites is always a key requirement for successful mission accomplishment. This paper addresses a leader–follower type relative position keeping in satellite formation flying via a novel robust exponential stabilization. This paper establishes an exponentially convergent relative position keeping taking account of various external disturbances that cannot be modeled into current formation dynamics, along with a set of time‐varying model parameters and measurement noises. The condition for an exponential convergence is established by decomposing the positive definite matrix used in Lyapunov function candidate into several element‐wise submatrices. Through numerical simulations, the effectiveness of the proposed method is illustrated. Copyright © 2011 John Wiley & Sons, Ltd.