基于视线测量的卫星编队机动控制方法

采用视线测量的方法,建立一种编队卫星队形保持与机动的协同控制策略。编队中每一个卫星跟踪自己轨道前方邻近卫星,产生一个视线测量矢量,编队的第一个卫星根据高级控制层指令追踪期望轨道,产生链式编队,将编队卫星之间的视线距离作为反馈控制量来实现队形控制。通过推导J2相对摄动力的表达式,控制模型考虑了模型不确定性和摄动影响,采用滑模控制器,实现了基于视线测量的编队卫星链式跟踪协同控制。仿真算例结果表明,该方法在实现编队卫星队形保持与整体机动控制上具有可行性。     

执行器故障下无人机-无人车异构编队控制

针对存在执行器故障的无人机-无人车异构系统,研究了编队跟踪容错控制问题。首先,异构系统采用有向图的拓扑结构,且并非所有无人机/车都能接收到参考信号,故在充分考虑无人机/车运动学模型存在较大差异的前提下,设计了一种针对两类系统都通用的分布式信号估计器来获取参考信号的信息。然后,基于参考信号估计值,利用鲁棒自适应控制理论,提出了形式统一的分布式容错控制协议。该协议无需获取精准故障信息,就能有效地补偿故障对异构系统性能的影响,确保异构系统在故障情况下仍能按照预先设定的编队构型跟踪上外界参考信号。最后,通过仿真试验验证了所提算法的有效性。     

Robust attitude coordinated control for spacecraft formation with communication delays

In this paper,attitude coordinated tracking control algorithms for multiple spacecraft formation are investigated with consideration of parametric uncertainties,external disturbances,communication delays and actuator saturation.Initially,a sliding mode delay-dependent attitude coordinated controller is proposed under bounded external disturbances.However,neither inertia uncertainty nor actuator constraint has been taken into account.Then,a robust saturated delay dependent attitude coordinated control law is further derived,where uncertainties and external disturbances are handled by Chebyshev neural networks (CNN).In addition,command filter technique is introduced to facilitate the backstepping design procedure,through which actuator saturation problem is solved.Thus the spacecraft in the formation are able to track the reference attitude trajectory even in the presence of time-varying communication delays.Rigorous analysis is presented by using Lyapunov-Krasovskii approach to demonstrate the stability of the closed-loop system under both control algorithms.Finally,the numerical examples are carried out to illustrate the efficiency of the theoretical results.     

Line blanketing by iron group elements in non-LTE model atmospheres of hot stars

We report on our recent progress in modeling non-LTE atmospheres of O-stars including blanketing by lines from the iron group elements. The numerical method to account for the huge number of atomic levels and line transitions is presented. Results of exploratory model calculations examining the effects on the temperature structure, the hydrogen and helium line profiles and UV/EUV fluxes are discussed.     

在地球扁率摄动下的卫星编队飞行控制

卫星编队飞行的难点之一是在干扰力环境下控制队形。采用了一种基于线性二次调节器(LQR)的最优控制方法，对低轨道地球卫星所受的地球扁率摄动(J2力)加以模拟，并在模拟的地球低轨道J2力环境中。对几种卫星编队进行了模拟控制，从控制精度和能量消耗的角度对控制方法进行了分析，提出了卫星编队飞行中相对距离控制和绝对距离控制需要注意的问题。     

小卫星空间圆形编队飞行队形设计与比例-微分(PD)控制

以两体相对运动动力学为基础 ,对Hill方程表示的相对运动特性进行了分析。同时给出了小卫星空间圆形编队队形设计。并且以此队形为例 ,引入了比例 -微分 (PD)控制策略对小卫星编队飞行的队形控制进行了研究 ,利用最优算法确定了控制器比例微分系数。数字仿真结果表明了该控制策略的有效性     

星载聚束式SAR 精确成像处理

分析了星载聚束式合成孔径雷达(SAR)的信号特性,主要研究了多普勒中心频率、多普勒带宽以及脉冲重复频率(PRF)与斜视角的关系.基于改进的Chirp Scaling算法,处理时采用了子孔径方法.通过子孔径方法,可以有效降低数据率及雷达发射峰值功率,并可解决多普勒中心频率的时变问题.此外,分析了偏航控制对于实现精确成像的必要性,给出偏航控制规律,证明偏航控制可以有效减小距离徙动量,降低成像处理难度.最后,通过计算机仿真,验证了处理方法的有效性.     

Energy-optimal reconfiguration of satellite formation flying in the presence of uncertainties

In this study, a two-step control methodology is developed for energy-optimal reconfiguration of satellites in formation in the presence of uncertainties or external disturbances. First, based on a linear deterministic system model, an optimal control law is analytically determined such that a satellite maneuvers from an initial state to a final state relative to another satellite. The structure of this optimal solution is predetermined and simply given by a linear combination of the fundamental matrix solutions associated with the original equations of relative motion. Only the coefficients are to be determined to satisfy given initial and final conditions. In the second step, an uncertain nonlinear formation system is considered and a robust adaptive controller is designed to compensate for the effects of uncertainties or disturbances that the formation system may encounter. Although the control strategy is inspired by sliding mode control, it produces smooth control signals, thereby avoiding chattering. Also, an adaptation law is added such that the uncertainty or disturbance effects are effectively and quickly eliminated without a priori information about them. The combination of these two controllers guarantees that the satellite accurately tracks the optimal path in the unknown environment. Numerical simulations demonstrate the effectiveness and accuracy of the proposed two-step control methodology, in which a satellite formation is optimally reconfigured under unknown environmental disturbances.     

基于Leader-Follower的多无人机编队轨迹跟踪设计

针对四旋翼无人机（UAV）群在轨迹跟踪过程中易受外界干扰而引起跟踪误差的问题，设计了基于Leader-Follower的多无人机协同编队轨迹跟踪控制方法。在该系统中，首先通过积分反步法（IBS）对所建四旋翼飞行器模型设计Leader无人机的轨迹跟踪控制器。其次设计了滑模控制（SMC）器，以控制Leader与Follower无人机实现期望的编队队形并同时跟踪参考轨迹。然后通过数值仿真验证了算法的有效性，仿真结果表明，系统具有良好的控制精度。最后通过视觉定位系统进行实验，结果表明所设计的控制器能够实现多个无人机轨迹跟踪和编队控制，所设计的算法具有可行性。     

Recovery of the Earth’s gravity field from formation-flying satellites: Temporal aliasing issues

Temporal and mean gravity field models derived from the twin-satellite, leader–follower mission GRACE have provided a new type of information for Earth sciences. In this contribution, we study the potential of various alternative satellite formations for gravity field determination in the post-GRACE era in a simulation environment. In particular, the effects of spherical harmonic truncation and of temporal aliasing in the processing of gravity products from such future formations are investigated.