Monocular Vision-based Two-stage Iterative Algorithm for Relative Position and Attitude Estimation of Docking Spacecraft

Visual sensors are used to measure the relative state of the chaser spacecraft to the target spacecraft during close range rendezvous phases. This article proposes a two-stage iterative algorithm based on an inverse projection ray approach to address the relative position and attitude estimation by using feature points and monocular vision. It consists of two stages: absolute orientation and depth recovery. In the first stage, Umeyama's algorithm is used to fit the three-dimensional (3D) model set and estimate the 3D point set while in the second stage, the depths of the observed feature points are estimated. This procedure is repeated until the result converges. Moreover, the effectiveness and convergence of the proposed algorithm are verified through theoretical analysis and mathematical simulation.     

基于Rodrigues参数的视觉相对位姿确定算法

以Rodrigues参数作为姿态描述参数提出了一种视觉相对位姿确定算法。Rodrigues参 数作为一种简洁、高效的姿态描述法,适用于实时性要求高的视觉相对位姿确定,但它本身 的奇异性使其不能用于大角度的位姿确定。将视觉导航方法和无奇异姿态描述的Rodrig ues参数切换理论结合起来,推导了基于Rodrigues参数的视觉相对位姿解算模型,并给出了 这种相对位姿确定算法的流程。仿真结果表明该算法能很好地解决奇异问题,实现全姿态运 动情形下的相对位姿确定。
     

空间非合作目标惯性参数在轨辨识

在空间冗余机械臂抓捕非合作目标的惯性参数辨识问题中,已有方法大都基于系统动量已知的假设,且辨识过程未考虑基座姿态稳定。针对目标动量未知的问题,设计了具有增量形式的惯性参数分步辨识算法。首先基于线动量方程得到关于质量和质心位置的第一组估计方程,采用增量形式消除未知线动量更新估计方程。辨识结果收敛后根据估计参数计算线动量估计值,代入以转动惯量为未知参数的第二组估计方程中,利用其增量表达式完成对转动惯量的估计。辨识过程中的激励由自适应零反作用控制输入提供,算法在保证基座姿态不受干扰的同时还能对惯性参数精确辨识。仿真结果表明,在30s以内算法已收敛,误差收敛到零的同时,基座姿态角速率控制精度在10^-3以下,说明算法收敛快,精度高,同时还能实现基座姿态稳定。     

轨姿控推进系统用电磁阀性能仿真研究

轨姿控推进系统采用电磁阀控制内部流体通路的开启与断流,从而实现其重复启动和脉冲工作.在轨姿控推进系统快速稳定工作问题的研究中,电磁阀的性能对推进系统至关重要.针对轨姿控推进系统用电磁阀,基于电磁学及运动学等基本原理,建立了电磁阀动态数学模型,利用Matlab Simulink软件进行了动态仿真,得到了电磁阀动态响应特性;采用CFD软件对阀门内部流场进行数值模拟仿真,获得了精确的静态流阻特性,直观展现了电磁阀动态流场,为电磁阀的性能优化和轨姿控推进系统的性能提高提供依据.     

带VSCMGs的航天器姿态稳定及功率补偿控制

基于变速控制力矩陀螺群动力学模型建立其复合控制方程和分系统解耦约束方程,用矩阵投影方法同步设计得到航天器姿态与能量一体控制复合操纵律,利用Lyapunov方法分析了转子轴向惯量误差对姿态控制分系统的影响.根据飞轮转子轴向惯量与功率输出之间的误差关系设计出功率控制补偿器.复合操纵律中的力矩和功率两解形式相同,约束方程使得姿态与能量控制两分系统解耦,便于进行考虑执行机构特性的闭环控制系统性能分析.考虑飞轮转子轴向惯量误差时,姿态控制分系统的输出耗散特性使其能够保持稳定,而功率控制分系统输出误差与转子轴向惯量误差成比例关系,经过补偿后功率输出能满足控制要求.     

运载器末助推段非线性姿态控制器设计

根据单摆模型近似晃动质量推导晃动运动与姿态运动的动力学方程,基于状态相关黎卡提方程方法,综合动态逆控制方法设计了运载器末助推段非线性姿态控制器,由状态反馈实现姿态跟踪和晃动抑制。因实际中模拟晃动运动的单摆状态无法测量,引入输出多采样率技术,通过在一个采样周期内多次检测被控对象的输出估计状态,实现设计的状态反馈控制律。数...     

Robust Hybrid Control for Ballistic Missile Longitudinal Autopilot

This paper investigates the boost phase’s longitudinal autopilot of a ballistic missile equipped with thrust vector control. The existing longitudinal autopilot employs time-invariant passive resistor-inductor-capacitor (RLC) network compensator as a control strategy, which does not take into account the time-varying missile dynamics. This may cause the closed-loop system instability in the presence of large disturbance and dynamics uncertainty. Therefore, the existing controller should be redesigned to achieve more stable vehicle response. In this paper, based on gain-scheduling adaptive control strategy, two different types of optimal controllers are proposed. The first controller is gain-scheduled optimal tuning-proportional-integral-derivative (PID) with actuator constraints, which supplies better response but requires a priori knowledge of the system dynamics. Moreover, the controller has oscillatory response in the presence of dynamic uncertainty. Taking this into account, gain-scheduled optimal linear quadratic (LQ) in conjunction with optimal tuning-compensator offers the greatest scope for controller improvement in the presence of dynamic uncertainty and large disturbance. The latter controller is tested through various scenarios for the validated nonlinear dynamic flight model of the real ballistic missile system with autopilot exposed to external disturbances.     

CubeSail: A low cost CubeSat based solar sail demonstration mission

CubeSail is a nano-solar sail mission based on the 3U CubeSat standard, which is currently being designed and built at the Surrey Space Centre, University of Surrey. CubeSail will have a total mass of around 3 kg and will deploy a 5 × 5 m sail in low Earth orbit. The primary aim of the mission is to demonstrate the concept of solar sailing and end-of-life de-orbiting using the sail membrane as a drag-sail. The spacecraft will have a compact 3-axis stabilised attitude control system, which uses three magnetic torquers aligned with the spacecraft principle axis as well as a novel two-dimensional translation stage separating the spacecraft bus from the sail. CubeSail’s deployment mechanism consists of four novel booms and four-quadrant sail membranes. The proposed booms are made from tape-spring blades and will deploy the sail membrane from a 2U CubeSat standard structure. This paper presents a systems level overview of the CubeSat mission, focusing on the mission orbit and de-orbiting, in addition to the deployment, attitude control and the satellite bus.     

基于紫外敏感器和星敏感器的卫星自主导航

卫星利用紫外敏感器和星敏感器进行自主导航的方法中地心矢量的测量精度是影响导航精度的重要因素之一,而地心矢量的测量又受到地球扁率的影响。在考虑地球扁率的前提下,研究了地球扁率对地心矢量测量的影响,给出了基于卫星姿态的地心矢量的补偿方法。仿真结果表明该补偿方法具有较高的补偿精度,并且能有效地提高卫星自主导航精度。     

基于特征模型的挠性航天器姿态快速机动研究

刚体卫星的大角度姿态机动可以用常规的四元数反馈控制,当挠性帆板的振动和中心刚体的耦合系数很大时,大角度快速机动后姿态的稳定度较差．结合特征建模理论,设计一种卫星大角度机动的黄金分割控制算法,对三轴带挠性帆板的航天器姿态机动进行仿真,仿真结果表明,机动完成后的控制精度比四元数反馈控制方法的精度高一个数量级以上。