Spin motion determination of the Envisat satellite through laser ranging measurements from a single pass measured by a single station

The Satellite Laser Ranging (SLR) technology is used to accurately determine the position of space objects equipped with so-called retro-reflectors or retro-reflector arrays (RRA). This type of measurement allows to measure the range to the spacecraft with high precision, which leads to determination of very accurate orbits for these targets. Non-active spacecraft, which are not attitude controlled any longer, tend to start to spin or tumble under influence of the external and internal torques and forces.If the return signal is measured for a non-spherical non-active rotating object, the signal in the range residuals with respect to the reference orbit is more complex. For rotating objects the return signal shows an oscillating pattern or patterns caused by the RRA moving around the satellite’s centre of mass. This behaviour is projected onto the radial component measured by the SLR.In our work, we demonstrate how the SLR ranging technique from one sensor to a satellite equipped with a RRA can be used to precisely determine its spin motion during one passage. Multiple SLR measurements of one target over time allow to accurately monitor spin motion changes which can be further used for attitude predictions. We show our solutions of the spin motion determined for the non-active ESA satellite Envisat obtained from measurements acquired during years 2013–2015 by the Zimmerwald SLR station, Switzerland. All the necessary parameters are defined for our own so-called point-like model which describes the motion of a point in space around the satellite centre of mass.     

平板及减阻沟槽表面雷诺切应力的实验研究

利用二维LDV系统对零压力梯度下光滑面和减阻沟槽面湍流边界层流场进行对比测量.着重考察了相同流动条件下光滑面、沟槽面的槽及峰上部区域雷诺切应力的分布特性,并利用象限分析法研究了沟槽面对湍流边界层相干结构的影响.研究发现:减阻沟槽面槽峰增强了雷诺切应力水平,使其上部区域下扫事件的平均强度增强;而槽部则抑制了雷诺切应力水平,削弱了其上部区域下扫事件的强度;沟槽上部区域雷诺切应力水平的降低幅度高于槽峰上的增加幅度.由此可以认为:沟槽的抑制作用抵消了沟槽峰部的增强效果,使得近壁区内动量交换水平减弱,从而,减阻沟槽面的雷诺切应力在总体上表现为减小.     

基于序列图象的三维刚体运动估计研究进展

序列图象运动估计是动态场景分析的基础,它主要研究如何从变化场景的一系列不同时刻的图象中,提取出有关场景中物体的位置、运动和结构等信息。在综述了基于序列图象运动分析的传统方法及其技术特点和存在的问题后,分析了基于序列图象的三维刚体运动估计研究的发展趋势。     

Reachable set estimation for spacecraft relative motion based on bang-bang principle

For spacecraft formation flight, the information of relative motion reachable set is very important, which can be used to predict the operating boundary of adjacent spacecraft and thus to ensure the safety of spacecraft operation. In this paper, we aim at developing a numerical method to approximate the reachable set for spacecraft relative motion. In particular, we focus on the quality of the approximation and the computational cost. Based on the bang-bang control principle, a polyhedral approximation algorithm is proposed to compute the reachable set of a relative motion spacecraft system. An inner approximation and an outer approximation of the reachable set for the system can be obtained. We prove that the approximation quality measured in Hausdorff distance can be guaranteed. The method is easy to implement and has low computational cost. Finally, the effectiveness of the algorithm is demonstrated by experimental simulation.     

Experimental investigation of shock-buffet criteria on a pitching airfoil

An experimental investigation of the shock-buffet phenomenon subject to unsteady pitching supercritical airfoil around its quarter chord has been conducted in a transonic wind tunnel. The model was equipped with pressure taps connected to the fast response pressuretransducers. Measurements were conducted at different free-stream Mach number from 0.61 to0.76. The principle goal of this investigation was to experimentally discuss the shock-buffet criterion over a SC(2)-0410 supercritical pitching ...     

基于粒子滤波算法的载机着舰甲板运动预测

舰载机在着舰过程中对甲板运动的跟踪存在相位差,需要采用预报技术将甲板的运动信息提前加入到舰载机自动着舰控制系统中：文章利用粒子滤波算法,提出了载舰甲板运动的在线预估方法,及时准确地反映出各种甲板运动形式的实质。对典型海况下甲板的俯仰运动、垂直起伏运动和偏航运动进行预报仿真,仿真结果对比表明基于粒子滤波算法得到的预估结果...     

火箭喷管极性自动化测试系统的改进设计研究

使用计算机视觉方法进行的发动机极性自动化测试是火箭地面测试中重要的测试环节，该环节存在进一步改进和提升的空间。将递归全对场变换（Recurrent All-pairs Field Transforms, RAFT）光流算法替代传统光流法检测技术用于发动机喷管实时运动监测，并根据现场测试场景对光流算法进行了优化，提升了运动检测速度与测量精确度，使自动测试系统具备了摆角的估测能力；在软件系统设计层面，引入差异图像直方图法监听法辅助喷管动作识别，避免了光流法对于未处在监测流程中的摄像头的冗余监听资源消耗，降低了系统硬件设备的负载，同时实现了一种可视化在线判读软件的设计。提出的软件与算法方面的改进在当前已投入使用的极性自动化测试系统上实现了进一步的优化。     

A homogenization-planning-tracking method to solve cooperative autonomous motion control for heterogeneous carrier dispatch systems

Taxiing aircraft and towed aircraft with drawbar are two typical dispatch modes on the flight deck of aircraft carriers. In this paper, a novel hierarchical solution strategy, named as the Homogenization-Planning-Tracking (HPT) method, to solve cooperative autonomous motion control for heterogeneous carrier dispatch systems is developed. In the homogenization layer, any towed aircraft system involved in the sortie task is abstracted into a virtual taxiing aircraft. This layer transforms the heterogeneous systems into a homogeneous configuration. Then in the planning layer, a centralized optimal control problem is formulated for the homogeneous system. Compared with conducting the path planning directly with the original heterogeneous system, the homogenization layer contributes to reduce the dimension and nonlinearity of the formulated optimal control problem in the planning layer and consequently improves the robustness and efficiency of the solution process. Finally, in the tracking layer, a receding horizon controller is developed to track the reference trajectory obtained in the planning layer. To improve the tracking performance, multi-objective optimization techniques are implemented offline in advance to determine optimal weight parameters used in the tracking layer. Simulations demonstrate that smooth and collision-free cooperative trajectory can be generated efficiently in the planning phase. And robust trajectory tracking can be realized in the presence of external disturbances in the tracking phase. The developed HPT method provides a promising solution to the autonomous deck dispatch for unmanned carrier aircraft in the future.     

一种星载伞天线展开机构研究

天线展开机构使用动力绳实现天线展开和收拢过程中易出现动力绳松弛、脱槽现象。以星载高精度伞状天线展开机构为研究对象，分析天线展开机构的工作原理；利用解析法获得展开机构的运动方程，结合天线展开机构运动部件结构参数，得到天线展开过程中展开机构动力绳的松弛规律；建立以展开机构结构参数为设计变量，以动力绳松弛量最小为目标的展开机构结构优化模型，通过模拟退火法进行求解，得到优化的展开机构结构参数，通过优化前后的展开机构展开、收扰功能试验，测试了机构工作时动力绳的松弛量，验证了展开机构优化的正确性。结果表明：优化后的展开机构动力绳松弛量较优化前降低了90%，优化效果显著。     

Close relative motion on distant retrograde orbits

Distant Retrograde Orbits (DROs) in the Earth-Moon system have great potential to support varieties of missions due to the favorable stability and orbital positions. Thus, the close relative motion on DROs should be analyzed to design formations to assist or extend the DRO missions. However, as the reference DROs are obtained through numerical methods, the close relative motions on DROs are non-analytical, which severely limits the design of relative trajectories. In this paper, a novel approach is proposed to construct the analytical solution of bounded close relative motion on DROs. The linear dynamics of relative motion on DRO is established at first. The preliminary forms of the general solutions are obtained based on the Floquet theory. And the general solutions are classified as different modes depending on their periodic components. A new parameterization is applied to each mode, which allows us to explore the geometries of quasi-periodic modes in detail. In each mode, the solutions are integrated as a uniform expression and their periodic components are expanded as truncated Fourier series. In this way, the analytical bounded relative motion on DRO is obtained. Based on the analytical expression, the characteristics of different modes are comprehensively analyzed. The natural periodic mode is always located on the single side of the target spacecraft on DRO and is appropriate to be the parking orbits of the rendezvous and docking. On the basis of quasi-periodic modes, quasi-elliptical fly-around relative trajectories are designed with the assistance of only two impulses per period. The fly-around formation can support observations to targets on DRO from multiple viewing angles. And the fly-around formation is validated in a more practical ephemeris model.