FPGA-based operational concept and payload data processing for the Flying Laptop satellite

Flying Laptop is the first small satellite developed by the Institute of Space Systems at the Universität Stuttgart. It is a test bed for an on-board computer with a reconfigurable, redundant and self-controlling high computational ability based on the field programmable gate arrays (FPGAs). This Technical Note presents the operational concept and the on-board payload data processing of the satellite. The designed operational concept of Flying Laptop enables the achievement of mission goals such as technical demonstration, scientific Earth observation, and the payload data processing methods. All these capabilities expand its scientific usage and enable new possibilities for real-time applications. Its hierarchical architecture of the operational modes of subsystems and modules are developed in a state-machine diagram and tested by means of MathWorks Simulink-/Stateflow Toolbox. Furthermore, the concept of the on-board payload data processing and its implementation and possible applications are described.     

小子样精度鉴定技术研究

讨论了小子样下的Bayes精度鉴定技术研究的一般方法,分析了考虑验前信息可信度时方差的检验,检验分为简单假设和复杂假设2种情况。给出了临界区域以及犯弃真和采伪两类错误的概率。仿真结果表明了方法的合理性。     

基于轨道摄动解的卫星编队飞行

用完全不同的方法推导出一种两颗卫星相对运动的表达式.首先,它描述的是一颗真实的卫星相对一颗在理想轨道上运动的虚拟卫星的运动,而这正是研究编队飞行所必须的;其次,这个表达式将真实卫星相对虚拟卫星的三维位置表示成虚拟卫星的Brouwer平根数及两卫星轨道根数之差的函数.据此便可以充分应用已有的关于轨道摄动的研究成果.作为一个基本模型,首先讨论了一颗真实卫星相对虚拟卫星形成椭圆型地面轨迹的飞行方式.基于轨道长期摄动的已有结果可以很容易地揭示这种飞行方式的长期变化,从而可以毫无困难地制定出轨道调整的策略.最后还研究了三颗卫星以同一条椭圆轨迹飞行的轨道设计和控制问题,该椭圆以虚拟卫星为中心.     

Dynamics in the Phobos environment

The dynamical environment on and about the Martian moon Phobos is explored. This planetary moon provides a unique dynamical environment in the solar system, being subject to extreme tidal forces and having a characteristically non-spherical shape. Further, it is not in a fully circular orbit, meaning that it has librations that arise from its eccentricity, contributing to a periodic forcing environment. Thus, to plan and implement missions in the vicinity of and on Phobos will require these considerations be taken into account. In this paper the latest published models of the Phobos shape and dynamics are used to characterize its dynamical environment in close proximity orbit about the body, for motion across its surface and for controlled hovering motion in its vicinity. It is found that surface motion is subject to a number of “speed limits” that can cause a moving vehicle to leave the surface and to possibly escape the moon and enter orbit about Mars. In terms of orbital stability, the existence of libration orbit families are characterized down to the surface using an exact potential, and the known stable QSO orbits are shown to be associated with families of stable quasi-periodic orbits.     

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.     

Design of an innovative multi-stage forming process for a complex aeronautical thin-walled part with very small radii

In this paper, an aeronautical thin-walled part with a complex geometry which has several sharp bends and curvatures in different directions was investigated. This kind of part is difficult to be manufactured only in one stage. Therefore, an innovative multi-stage active hydroforming process assisted by the rigid forming method was designed. In addition, an optimized blank geometry is obtained. In fact, the main focused point of this paper is to propose a new small radius rounded corner forming technique and analyze the mechanism. Two kinds of forming modes of changing a big rounded corner into a small one, which are related to different tangential positions of the die in the process of calibration, are analyzed theoretically. Meanwhile, the stress and strain states of the deformation region are compared. The relationships between the minimum relative radii of rounded corners I and II in the first stage and the hydraulic pressure are calculated by the bending theory. Finally, the influences of the tensile-bulging effect and the interface condition of the double-layer sheet on the forming quality of the specimen are investigated. The achieved results can make a foundation for utilizing the proposed method in forming of thin-walled parts with very small radii.     

飞轮姿控小卫星模糊控制方法研究

对三轴稳定飞轮姿控小卫星的模糊控制方法进行了研究。不考虑解耦运算,基于模糊控制,以姿态角偏差及偏差变化率为输入,飞轮转动角加速度为输出,在每个通道分别加入模糊控制器,实现了对小卫星滚转、俯仰和偏航通道耦合系统的有效控制。仿真结果表明:该法对干扰抑制明显、对结构参数变化不敏感,响应过程有良好的快速性和较高的稳态精度(可达1×10-4rad),可避免传统方法中对动力学方程的直接解耦操作,应用时可将模糊控制规则转化为控制表储存在星载计算机,简单高效。     

编队卫星碰撞规避方法研究

对编队卫星碰撞规避方法进行了研究。通过递推编队卫星的初始状态协方差阵,将碰撞概率密度函数在危险区域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,向卫星施加最小脉冲速度修正量Δv,在垂直于终止时刻相对速度的平面机动一定距离以降低碰撞概率。仿真结果表明:用计算的碰撞概率能较好地预测编队卫星的潜在碰撞危险,所选机动策略有效。     

基于UKF估计的卫星编队动力学建模方法

提出了一种基于估计的卫星编队动力学建模方法。以实际的经过简化建模的卫星编队动力学模型为基础,利用UKF算法对该模型与精确模型的模型差进行估计,并运用该估计结果对原有模型进行反馈补偿,以达到提高卫星编队建模精度的目的。为了验证该建模方法的有效性,对基于空间圆形编队的卫星进行了仿真实验。仿真结果表明,在忽略J2摄动力影响的情况下,基于UKF估计的建模方法大大提高了原有建模方法的性能。     

小型平板CPL实现高热流密度散热的研究

针对小型平板毛细抽吸两相流体回路(CPL)在高热流密度下的特点,分析了不同工质时系统的压力损失与毛细芯的毛细抽吸力,得出采用氨工质有着较好的传热性能和更高的毛细限,同时得出影响系统毛细限的主要因素是蒸汽联管管径和工质的蒸气密度,提出了工质传输系数作为选取工质的重要指标。建立了蒸发器多孔芯,金属壁面以及工质气、液空间区域的耦合数学模型,并运用SIMPLE算法进行求解,得出蒸发器内的温度分布及由于侧壁效应对多孔芯传热传质与传热极限的影响,同时提出小型平板CPL系统存在侧壁效应传热极限,它是影响系统最大传热量的一个重要极限,在设计小型平板CPL必须予以考虑。