Cubesat solar sail 3-axis stabilization using panel translation and magnetic torquing

A Cubesat mission with a deployable solar sail of 5 meter by 5 meter in a sun-synchronous low earth orbit is analyzed to demonstrate solar sailing using active attitude stabilization of the sail panel. The sail panel is kept parallel to the orbital plane to minimize aerodynamic drag and optimize the orbit inclination change caused by the solar pressure force normal to the sail surface. A practical control system is proposed, using a combination of small 2-dimensional translation of the sail panel and 3-axis magnetic torquing which is proved to have sufficient control authority over the gravity gradient and aerodynamic disturbance torques. Miniaturized CMOS cameras are used as sun and nadir vector attitude sensors and a robust Kalman filter is used to accurately estimate the inertially referenced body rates from only the sun vector measurements. It is shown through realistic simulation tests that the proposed control system, although inactive during eclipse, will be able to stabilize the sail panel to within ±2° in all attitude angles during the sunlit part of the orbit, when solar sailing is possible.     

航天器太阳圆面速度差/太阳视方向组合导航

针对航天器，尤其是深空探测器的自主导航问题，提出了一种新的太阳圆面速度差天文量测信息，该信息利用太阳的较差自转所造成的太阳圆面各点速度不同的特性，是探测器当前位置的函数，其几何本质是一个探测器的位置圆锥。在此基础上，基于太阳圆面速度差和太阳视方向互补的特性，提出了一种太阳圆面速度差/太阳视方向组合导航新方法，将太阳圆面速度差与太阳视方向2种量测量结合起来，实现了量测量之间的优势互补，进一步提高了导航性能。以太阳探测器为例进行了仿真，仿真结果表明相比较于单独用太阳圆面速度差或太阳视方向的导航方法，基于太阳圆面速度差/太阳视方向的组合导航方法精度分别提升了10.2%和16.0%。此外，还分析了光谱仪精度、采样周期和光谱仪数量对导航性能的影响，为深空探测自主导航提供了新的理论与方法。     

太阳风磁帆推进性能数值研究

利用考虑行星际磁场作用的磁流体动力学模型，建立了磁帆三维数值模拟方法，对计算方法的可靠性进行了验证，发现了线圈尾部的磁重联现象，研究了太阳风来流速度、等离子体离子数密度以及攻角对磁帆推进性能的影响。得出以下结论：不同速度、不同离子数密度的太阳风主要通过改变z方向电流的大小改变洛伦兹力，进而影响磁帆的推进性能：太阳风离子数密度恒定时，随着来流速度由30 km/s逐渐增大至75 km/s,z方向电流最大值由4 205 A/m²增至14 709 A/m²，磁帆所受推力由3.39 N增至13.40 N；太阳风来流速度恒定时，随着离子数密度由1.8×10¹⁹ m^-3增大至4.5×10¹⁹ m^-3,z方向电流最大值由6 039 A/m²增至10 585 A/m²，磁帆所受推力由6.62 N增至12.27 N。磁帆攻角变化，主要通过磁场构型的变化影响磁帆推进性能：攻角为0°和90°时的磁层半径分别为0.14 m和0.18 m，...     

RCD太阳帆航天器人工平动点轨道保持与控制

针对航天器平动点轨道保持问题,研究了含有反射率控制设备(RCD)的太阳帆航天器在日地系共线人工平动点处的轨道保持与控制,同时降低因频繁改变航天器姿态所带来的振动问题。首先,基于太阳帆圆型限制性三体问题,计算了RCD型太阳帆人工平动点位置,给出了太阳帆共线人工平动点三阶Halo轨道,并将其作为参考轨道;然后,将太阳帆动力学方程线性化,采用跟踪控制输出的方法对线性模型进行控制;最后,通过合理选择控制变量矩阵,将控制律代入非线性模型中进行轨道保持控制。仿真结果表明,通过控制RCD太阳帆反射率设备参数及姿态角,实现了长时间的Halo轨道保持,同时大幅减小了太阳帆姿态角的改变,从而减小了帆面振动,为太阳帆航天器长期轨道任务的实现提供了良好的理论依据。     

一种IRST双机协同被动探测机动目标定位新方法

针对红外搜索跟踪系统（IRST）双机协同被动探测定位作战使用中，机动目标建模与实际运动失配造成定位误差偏大的问题，研究了一种基于曲线模型的自适应滤波新方法。该方法改进了传统方法根据方向角估计转弯率以及基于帧间插分线加速度估计切向加速度的思路，将转弯率及线加速度联合作为状态变量进行了状态扩维，并推导了扩维后的过程噪声协方差表达式，在缓解传统两层滤波结构带来的计算量大问题外，也提高了切向加速度的估计精度。另外基于反正切函数的值域，结合方向角在四象限间的转移关系，优化了方向角的设计。通过IRST双机协同仿真实例，验证了所提方法对机动目标的适应性更强、目标定位精度更高。     

基于数值微分计算的SERF原子自旋惯性测量动态仿真

基于量子调控技术的SERF原子自旋惯性测量仪表与传统惯性测量仪表相比,具有精度高、无活动部件、对加速度不敏感等优点,被公认是下一代高精度惯性测量的发展方向。分析了SERF原子自旋惯性装置Bloch微分方程组模型下磁场、激光、角速度输入对碱金属电子极化率和惰性气体核子极化率的影响。针对实验条件下原子系综Bloch微分方程组难以解析求解的问题,基于可变阶次数值微分计算,建立了相应的Simulink模型对实验条件下的原子系综进行数值求解,并分析了极化率对光场、磁场、角速度输入的瞬态响应与稳态响应。仿真结果与理论计算结果相吻合,验证了Bloch方程数值求解的可行性与准确性。该方法可得到惯性测量系统的动态响应,可用于模拟复杂输入下的SERF原子自旋惯性测量系统的输出响应。     

混合小推力航天器日心悬浮轨道保持控制

针对太阳帆、太阳电混合推进航天器日心悬浮轨道保持控制问题进行了研究。为解决基于局部线性化模型设计轨道保持控制器时存在的控制精度不高、模型精确性过度依赖等问题,应用自抗扰控制(ADRC)技术设计了轨道保持控制器。首先,采用圆形限制性三体问题(CRTBP)模型推导了混合小推力航天器日心悬浮轨道动力学方程;然后,考虑系统模型不确定性和外部扰动,提出了一种基于扰动估计和补偿的轨道保持控制方法;最后,数值仿真表明存在系统模型不确定性、初始入轨误差及地球轨道偏心率扰动等因素的情况下,所设计的控制器仅需很小的速度增量即可实现高精度的日心悬浮轨道保持控制。     

磁强计数据辨识卫星自旋状态

针对近地低轨三轴稳定卫星在轨管理后期,除磁强计外其他姿态敏感器都无效情况下的姿态异常问题,分析了三轴稳定卫星失去姿态基准后,星体自旋状态下三轴磁强计测量数据的特点,提出了使用磁强计测量数据的矢量信息,以找到能够获取卫星状态的方法,从而建立了磁强计测量矢量与卫星自旋轴的几何关系,给出了处于自旋状态下的卫星自旋轴确定方法。通过此种辨识方法,获得了某气象卫星姿态异常翻转状态下的自旋矢量方向和自旋角速度,从而证明了该辨识方法快速、有效,可以作为姿态异常卫星自旋状态的辨识手段,为恢复卫星姿态提供了重要信息,具有一定的工程应用价值。     

皮卫星姿态估计及粗太阳敏感器标定算法研究

粗太阳敏感器是一种由多个光电池片配置组成的模拟式太阳敏感器,它结构简单、资源要求少,在皮卫星平台应用较为广泛。光电池光伏输出特性是粗太阳敏感器测量的基础,使用余弦关系近似等效会引入很大的误差。通过实际测试和深入分析,建立了更高精度的粗太阳敏感器输出特性等效数值模型,并以此为基础,推导了卫星姿态估计及粗太阳敏感器标定的联合在轨实时算法。算法采用多级耦合结构,由1个扩展卡尔曼滤波器(EKF)和6个卡尔曼滤波器组成,同时估计卫星姿态、卫星角速度以及卫星6个面共30个标定参数。仿真表明,和常规的EKF姿态估计算法相比,联合算法的运算量只增加了一半,而估计精度却提高了一个量级。     

Spacecraft attitude/rate estimation using vector-aided GPSobservations

A sequential filtering algorithm is presented for spacecraft attitude and attitude-rate estimation from Global Positioning System (GPS) differential carrier phase measurements. A third-order, minimal-parameter method for solving the attitude matrix kinematic equation is used to parameterize the state of the filter, which renders the resulting estimator computationally efficient. Borrowing from tracking theory concepts, the angular acceleration is modeled as an exponentially autocorrelated stochastic process, thus avoiding the use of the uncertain spacecraft dynamic model. The new formulation facilitates the use of aiding vector observations in a unified filtering algorithm, which can enhance the robustness and accuracy of the method. Numerical examples are used to demonstrate the performance of the method     

Investigation of anode shaping process during co-rotating electrochemical machining of convex structure on inner surface

A novel co-rotating electrochemical machining method is proposed for fabricating convex structures on the inner surface of a revolving part. The electrodes motion and material removal method of co-rotating electrochemical machining are different from traditional electrochemical machining. An equivalent kinematic model is established to analyze the novel electrodes motion,since the anode and cathode rotate in the same direction while the cathode simultaneously feeds along the line of centres. Acc...     

太阳帆航天器被动姿态控制研究

针对由有效载荷、太阳帆和4个控制叶片所组成的太阳帆航天器系统,从物理模型出发,利用欧拉方程建立了姿态动力学模型,并通过数值仿真对太阳帆航天器基于控制叶片的对日定向性能进行了研究。研究结果表明,在行星际飞行中太阳帆航天器可以通过使控制叶片保持偏置来保持姿态稳定。     

基于可观测性分析的旋转式惯导系统在线自标定方法的设计

本文建立了速度误差外观测量的静基座双轴旋转式惯导系统在线标定卡尔曼滤波模型,其状态向量包括地速误差、姿态失准角和惯性器件零偏、标度因数误差、安装误差,可估计旋转式惯导系统失准角与惯性器件误差参数。通过分段线性定常系统(PWCS)可观测性分析方法分析不同旋转方式下系统可观测性变化情况,得出双轴连续旋转的角运动方案可以改善卡尔曼滤波滤波的可观测性。根据基于奇异值分解的可观测度分析结果进行模型降阶,同时结合旋转式惯导系统的工程应用特性,得到12阶卡尔曼滤波参数模型。降阶系统阶数降低约55%,可以显著降低运算量,有效提高了导航计算机运算效率和实时性。仿真实验表明：降阶模型的估计精度不低于原模型,而且部分状态量的滤波收敛速度有提高。     

混合小推力航天器轨道保持高性能滑模控制

针对采用太阳帆、太阳电混合小推力推进的航天器，研究了其在日心悬浮轨道的保持控制问题。为解决已有控制方法中未综合考虑内部未建模动态和外部未知扰动的问题，以及进一步提高系统控制性能，设计了一种高性能滑模控制策略。首先，考虑模型不确定性，建立了混合小推力航天器在日心悬浮轨道柱面坐标系的动力学方程；其次，基于改进型条件积分滑模面和径向基（RBF）神经网络设计了控制律，结合自适应方法在线估计不确定参数；接着，将求取的虚拟控制量在推进剂最优条件下转换成实际控制量，即太阳帆姿态角和太阳电推进力；最后，数值仿真验证了上述设计方法提高了系统鲁棒性，减小了轨道位置超调，并且混合推进相比于单一太阳帆推进，在更短收敛时间内控制精度提高了4个数量级，相比于单一太阳电推进，一年可以节省约89.6%的推进剂。     

弯曲流道内二次流动的运动学分析和 数值可视化方法

通过运动学分析,得到了涡量与二次流之间的关系方程,介绍了弯曲流道内二次流结构的可视化方法.以截面法向涡量为基础,可求解得到与涡量对应的二次流速度场.该方法具有以下几个特点:从运动学求解得到的涡量与二次流流函数之间的方程,直接体现了二次流作为涡的特性,且作为分析流动结构的后处理方法,能够量化地求解出二次流速度以及分布情况.该方法消除了位势流的影响,使二次流显示更加真实清晰,这种方法比速度矢量图法更加准确完善.      

On the rotation vector differential equation

A direct and simple derivation of the differential equation of the rotation vector is provided. The property that the time derivative of the rotation vector and the angular velocity have equal magnitude along the direction of the rotation vector is also derived     

Pico-satellite Autonomous Navigation with Magnetometer and Sun Sensor Data

This article presents a near-Earth satellite orbit estimation method for pico-satellite applications with light-weight and low-power requirements. The method provides orbit information autonomously from magnetometer and sun sensor, with an extended Kalman filter (EKF). Real-time position/velocity parameters are estimated with attitude independently from two quantities: the measured magnitude of the Earth’s magnetic field, and the measured dot product of the magnetic field vector and the sun vector. To guarantee the filter’s effectiveness, it is recommended that the sun sensor should at least have the same level of accuracy as magnetometer. Furthermore, to reduce filter’s computation expense, simplification methods in EKF’s Jacobian calculations are introduced and testified, and a polynomial model for fast magnetic field calculation is developed. With these methods, 50% of the computation expense in dynamic model propagation and 80% of the computation burden in measurement model calculation can be reduced. Tested with simulation data and compared with original magnetometer-only methods, filter achieves faster convergence and higher accuracy by 75% and 30% respectively, and the suggested simplification methods are proved to be harmless to filter’s estimation performance.     

初始运行条件对空间飞行器飞行影响研究

某试验型微小空间飞行器用于检测空间探测技术,通过对该飞行器运动轨迹及姿态变化的研究,对比分析空间探测技术的实时响应和检测精度。针对发射过程中,扰动会改变空间飞行器自由飞行过程的初始运行条件的问题,建立计及环境因素的空间飞行器轨道动力学和基于欧拉方程的姿态动力学模型,并对飞行器在不同初始运行条件下的运动过程进行数值研究。结果表明:改变初始条件,飞行器运动过程将产生不同程度的变化;入轨初速度越大,飞行器轨道离心率和周期越大;非零发射角将引起轨道偏移和旋转,俯仰发射角主要引起俯仰角变化,偏航发射角主要影响滚转角和偏航角,并且角度越大,幅度越大;自转角速度越大,姿态角变化越小。     

Interlaced Kalman filtering of 3D angular motion based on Euler'snonlinear equations

A novel Kalman filtering technique is presented that reduces the mean-square-error (MSE) between three-dimensional (3D) actual angular velocity values and estimated ones by an order of magnitude (when compared with the MSE resulting from direct measurements) even under extremely low signal-to-noise ratio conditions. The filtering problem is nonlinear in nature because the dynamics of 3D angular motion are described by Euler's equations. This nonlinear set of differential equations state that the angular acceleration in one axis is proportional to the torque applied to that axis, and to the products of angular velocity components in the other two axes of rotation. Instead of using extended Kalman filtering techniques to solve this complex problem, the authors developed a new approach where the nonlinear Euler's model is decomposed into two pseudolinear models (primary and secondary). The first model describes the time progression of the state vector containing the linear terms, while the other characterizes the propagation of the state vector containing the nonlinearities. This makes it possible to run two interlaced discrete-linear Kalman filters simultaneously. One filter estimates the values of the state vector containing the linear terms, while the other estimates the values of the state vector containing the nonlinear terms in the system. These estimates are then recombined, solving the nonlinear estimation process without linearizing the system. Thus, the new approach takes advantage of the simplicity, computational efficiency and higher convergence speed of the linear Kalman filter form and it overcomes many of the drawbacks typical of conventional extended Kalman filtering techniques. The high performance and effectiveness of this method is demonstrated through a computer simulation case study     

Stability of Gyro in a Vehicle Spinning with Uncertain Angular Velocity

The analysis of a single-axis rate gyroscope mounted in a vehicle which is spinning with uncertain angular velocity about the spin axis of the gyro is presented. The nonlinearity in the equation of motion of the gimbal is retained. Using circle criterion, it is shown that the gimbal motion is globally asymptotically stable if Nyquist plot of the linear transfer function of the gyro lies in the interior of a certain disk. A simple analytical relation for the selection of gyro parameters for stability is derived.