一种基于u检验的空海目标分类方法

阐述了对于机载雷达,测高精度不高,特别是对远距离目标的测高精度更差,因而利用机载雷达提供的高度信息进行空海目标分类存在很大的不确定性。为了能有效地利用目标高度信息进行空海目标分类,把空海目标分类问题看成是一个u检验问题。首先,给出了用于空海目标分类的判别函数;然后,给出了一种决策规则,并推导出决策门限的计算公式和空中目标误判为海面目标的概率的计算公式;最后,通过仿真表明该算法的简易性和有效性。     

Performance analysis of variable speed tail rotors with Gurney flaps

Gurney Flaps (GFs) are used for improving the performance of variable speed tail rotors. A validated analytical helicopter model able to predict the main and tail rotor power is utilized. The fixed height GF has substantially small influence on the tail rotor power in hover and low to medium speed forward flight, and can obtain significant power reduction in high speed flight. This ability can be enhanced by decreasing the tail rotor speed. With the deployment of GF, the collective pitch of the tail rotor decreases, and the maximum tail rotor thrust increases. The GF can compensate the reduction of the maximum thrust by the decrease in the tail rotor speed. The GF with a height of 5% of the chord length can almost remedy 50% of the thrust reduction introduced by decreasing 10% of the tail rotor speed. With the increase of GF height, the maximum thrust generated by the tail rotor increases. The GF with larger height can cause the increase in the tail rotor power in hover and low to medium speed flight. The retractable GF can obtain more power savings than the fixed height GF. However, the benefit is substantially small even in high speed flight. Considering the side effects introduced by the active GF, the fixed height GF may be more preferable. The mechanism for the retractable GF to generate more tail rotor thrust is to increase the lift in advancing side due to the higher dynamic pressure.     

Disturbance observer-based robust guidance for Mars atmospheric entry with input saturation

With low-lifting capability taken into account,a robust guidance law for Mars entry vehicles with low lift-to-drag ratios,such as Mars Science Laboratory(MSL),is presented.Consider the nonlinear term in the drag dynamic equation and bounded disturbances as a lumped disturbance,and design a linear disturbance observer(DOB)to estimate it.With the consideration of the control input saturation,an innovative sliding surface and a virtual system are introduced to design the guidance law.Analyses of disturbance observer performance and Lyapunov-based transient performance are also presented.It is shown that the drag tracking error can be adjustable by explicit choices of design parameters.Simulation results confirm the effectiveness of the proposed guidance law.     

IV: GEODESY: Remarks on the Role of Height Datum in Altimetry-Gravimetry Boundary-Value Problems

The problem of global geoid determination is usually solved using satellite altimetry data on the oceans, together with an oceanographic model of sea surface topography, and gravity anomaly data on the continents. Such data, however, enable to obtain only potential differences with respect to a reference surface whose absolute potential is unknown. This situation suggests to modify the classical mixed boundary-value problem of physical geodesy by inserting into the boundary conditions an unknown additive constant, that must be determined by imposing a suitable additional constraint. Yet, such formulation of the boundary-value problem, from the point of view of its mathematical properties, is not unconditionally well-posed, and, furthermore, does not reflect faithfully the available physical model, as the present knowledge of ocean circulation does not allow to connect along coastlines the reference surfaces defined on the oceans and on the continents. The introduction of two different unknown additive constants, one for the oceans and one for the earth, to be determined by imposing two additional constraints, gives rise to a more faithful picture of the present physical knowledge, and, at the same time, to a new well-posed formulation of the boundary-value problem. This revised version was published online in August 2006 with corrections to the Cover Date.     

地球卫星星光折射导航量测量及其性能对比

星光折射天文导航是一种重要的地球卫星自主导航方式,量测量是影响其导航精度的重要因素。在地球卫星星光折射导航中,折射视高度、星光折射角、折射星像素坐标（折射星矢量）是3种常用的量测量,结合星光折射导航的基本原理重点介绍了这3种量测量的获取方法和量测模型,通过仿真和可观性分析比较了相同条件下3种量测量的导航性能。仿真结果表明,由于折射星像素坐标可以同时反映星光折射的大小和方向可观性高,而星光折射角和折射视高度仅能反映星光折射的大小,无法反映其方向可观性低,因此折射星像素坐标的导航性能优于星光折射角和折射视高度。此外,本文也对星敏感器精度、卫星轨道高度、星敏感器安装夹角3种因素对3种方法导航性能的影响进行了分析。     

2D雷达组网中目标高度估计误差的Cramér-Rao限

 在由2坐标雷达组成的雷达网中,推导了目标高度估计误差的CRLB(Cram&;#225;r-Rao限),并通过不同条件下的数值计算得到了一些结论。结果表明,目标高度估计误差的CRLB既与雷达的测角误差有关,也与目标和2个雷达站形成的夹角有关系,雷达配置在不同的高度上有利于目标高度估计的收敛性。这些结论对于2坐标雷达组网以及雷达网中的传感器管理具有指导意义。     

Linkage of the ionospheric peak electron density and height deduced from the topside sounding data

Topside sounding electron density profiles are analyzed to explore interrelations of the F2 layer critical frequency and the peak height for a representative set of conditions provided by ISIS1, ISIS2, IK19 and Cosmos-1809 satellites for the period of 1969–1987. The foF2 and hmF2 are delivered with exponential extrapolation of electron density profile to zero of its 1st derivative. It is shown that the linear regression exists between foF2 and hmF2 under different conditions. The linkage between the two parameters amended to the empirical model of the peak height [Gulyaeva, T.L., Bradley, P.A., Stanislawska, I., Juchnikowski, G. Towards a new reference model of hmF2 for IRI. Adv. Space Res. 42, 666–672, doi:10.1016/j.asr.2008.02.021, 2008] results in an empirical model of the both foF2 and hmF2 expressed by superposition of functions in terms of local-time, season, geodetic longitude, modified dip latitude and solar activity. For the solar activity we use a proxy Fsp index averaged from the mean solar radio flux F10.7s for the past 81 days (3 solar rotations) and F10.7 value for 1 day prior the day of observation. Impact of geomagnetic activity is not discernible with the topside sounding data due to mixed positive and negative storm-time effects. Appreciable differences have been revealed between IRI-CCIR predictions and outcome of the new model which might be attributed to the different techniques of the peak electron density and height derivation, different epochs and different global distribution of the source data as well as the different mathematical functions involved in the maps and the model presentation.     

基于双目视觉的非合作目标逼近控制系统设计与仿真

主要研究空间非合作目标近距离逼近过程的控制系统设计与仿真问题.针对采用双目视觉敏感器实现对非合作目标的观测情况,提出一种考虑成像误差的目标位置矢量计算方法,有效保证目标位置解算的可行性.在主星视线坐标系下,分别考虑逼近过程的最大相对速度约束、控制推力和力矩约束,设计了基于非线性项解耦的递阶饱和PID形式的近距离逼近位置控制律和姿态控制律,并在逼近过程中设置停泊点以确保与目标无碰撞.最后对典型航天器非合作目标抓捕任务进行了数学仿真,仿真结果表明所提出的方法可在满足各种约束的情况下有效实现任意方向的空间非合作目标的抓捕任务.     

空间相机摆扫成像立体定位精度仿真分析

为了验证空间相机摆扫成像立体定位的可行性,考虑成像比例尺变化、摆扫角测量精度、摆扫角稳定度和摆扫角速度等影响因素,建立了以总体设计中影响定位精度的各指标为参数的空间相机摆扫成像几何模型,推导了基于误差传播理论的定位精度计算方法,并对平面定位精度和高程精度进行了仿真,提出了摆扫成像方式条件下提高定位精度的有效措施。结果表明,在成像幅宽较大时,单线阵摆扫成像线阵长度较小情况下和双线阵推扫成像线阵长度较大情况下,可达到相近的定位精度,提高摆扫角测量精度、摆扫角稳定度及时间同步精度,可提高平面定位精度。摆扫成像立体定位精度仿真方法适用于大幅宽成像遥感卫星定位精度指标分配。     

基于激光测距的飞艇净重在线计算方法研究

通过对三维建模软件CATIA中的飞艇副气囊模型进行切片分割,获得了不同副气囊高度下的对应体积值,使用最小二乘法建立了副气囊中心点高度与副气囊体积的三次曲线拟合公式,采用相位式激光测距仪对副气囊中心高度测量,使用该公式可以估算出副气囊的实时体积大小,从而推算飞艇净重大小,掌握飞艇的压力高度和起降能力。使用某次飞行试验对副气囊高度测量的数据计算出的飞艇净重值,与多次地面称重数据一致性较好,验证了使用激光测距仪对大型飞艇净重进行在线评估的可行性,并使用该方法对某飞艇某次飞行试验过程中的净重进行了分析,对飞艇的压力高度进行了核算。