一种航天器天文自主定轨方法

提出用星敏感器和地平仪测量星光角距作为主要观测量,用地平仪直接测量得到地心方向矢量,用间接测得的地心距离作为补充观测量,并用推广卡尔曼滤波方法来实时确定航天器的轨道。文中对系统的构成、模型的建立、以及卡尔曼滤波的方法都作了认真的仿真研究,并获得了满意的结果。     

一种天文/加速度计的HEO卫星自主导航新方法

直接敏感地平是一种典型自主天文导航方法,该方法简单可靠,易于实现,但是由于常用卫星轨道动力学J2模型精度有限,地球敏感器精度较低,因此导航精度不高。加速度计是测量运载体线加速度的常用惯性导航设备,当卫星在轨运行时,星载加速度计能够测量航天器所受发散力。结合这两种方法的特点,提出一种将加速度计和天文相结合的自主天文导航新方法。在常用卫星轨道J2模型基础上,引入大气阻力和太阳光压系数模型作为自主导航系统状态方程的一部分,并建立近地空间环境下星载加速度计的测量模型,将其与直接敏感地平均作为导航系统观测方程。设计基于信息融合的自主导航滤波方法,通过对多种导航模式进行数值仿真及结果分析,结果表明所设计方法提高了系统定位精度74.8%和速度精度86.2%,增强了系统可靠性。     

一种基于加速度计和天文的卫星自主导航新方法

直接敏感地平是一种典型自主天文导航方法,该方法简单可靠,易于实现,但是由于常用卫星轨道动力学J2模型精度有限,地球敏感器精度较低,因此导航精度不高。加速度计是测量运载体线加速度的常用惯性导航设备,当航天器在轨运行时,星载加速度计能够测量航天器所受发散力。结合上述两种方法的特点,提出一种将加速度计和天文相结合的自主天文导航新方法。在常用卫星轨道动力学模型基础上,引入大气阻力和太阳光压系数模型作为自主导航系统状态方程的一部分,并建立近地空间环境下星载加速度计的测量模型,将其与直接敏感地平均作为导航系统观测方程。设计基于信息融合的自主导航滤波方法,通过对多种导航模式进行数值仿真及结果分析,结果表明所设计方法提高了系统定位精度62.8%和速度精度63.9%,增强了系统可靠性。     

一种针对临近空间滑跃目标的轨迹跟踪方法

针对临近空间跳跃滑翔目标运动建模困难,跟踪精度低的问题,提出了一种基于自适应衰减震荡模型的轨迹跟踪方法。首先,对临近空间滑翔跳跃目标的运动特点进行了深入分析,确定其运动具有周期性和衰减性的特点;根据这一特点,利用二阶时间自相关随机过程对加速度和飞行路径角进行建模,通过傅里叶变换推导了零均值衰减震荡模型;考虑到临空目标受气动阻力的作用,加速度小于零的情况,借鉴"当前"统计模型的思想,进一步对零均值衰减震荡模型进行改进,提出了自适应衰减震荡模型,实现了目标运动描述在周期性和衰减性上的统一。在此基础上,建立了地理坐标系下的目标运动模型,给出了基于雷达的测量模型。针对该系统非线性较强的特点,利用无迹卡尔曼滤波算法完成了跟踪滤波器的设计。仿真结果表明,所提出的算法具有更好的跟踪效果,其位置跟踪精度和速度跟踪精度较正弦波模型分别提高了17.91%和26.33%。     

星敏感器辅助的临近空间飞行器姿态匹配传递对准方法

为解决临近空间飞行器的精确、快速传递对准问题,提出了发射点惯性坐标系下基于星敏感器信息辅助的传递对准方案。根据星敏感器输出的不同形式的姿态信息,如利用TRIAD算法获得的姿态角信息或利用QUEST算法获得的姿态四元数信息,分别建立了基于平台失准角和基于加性四元数的非线性传递对准模型。针对非线性特性模型,采用UKF滤波算法进行了数学仿真。仿真结果表明,在2 s内,两种方案的姿态角误差均可以收敛到20"。仿真验证了两种算法的有效性,为临近空间飞行器的传递对准提供了参考。     

一种航天飞行器的INS/CNS自主导航方案

传统的天文导航方法由于受水平基准精度的制约,难以进一步提高定位精度。针对INS/CNS组合导航方法对水平基准依赖的问题,提出了一种新颖的基于星光折射技术的INS/CNS自主组合导航方案。将惯性系下的非线性惯导误差传播方程作为系统状态方程,将星敏感器测得姿态和星光折射信息作为量测,采用UKF滤波算法,构成全面最优的INS/CNS组合导航。仿真结果表明,星敏感器精度为3″时,导航系统的定位精度优于200 m,姿态精度优于3″,导航定位精度随所使用的折射星数目增多明显提高,且方案在系统大角度误差条件下仍然适用。     

一种小卫星高精度自主定轨/定姿一体化新方法

基于传统小卫星对轨道和姿态参数确定采用分别计算的复杂模式,提出了一种利用地磁场和天文信息同时确定卫星轨道和姿态参数的新方法。首先通过分析小卫星轨道动力学J2模型和卫星姿态动力学模型,建立系统状态方程。其次将三轴磁强计与地磁场模型参考值的矢量作差,分析微分差值与状态变量的数学关系,建立定位/定姿观测方程。利用星敏感器提供的高精度姿态信息,建立定姿观测方程,同时利用星敏感器间接敏感地平观测折射恒星,建立定位观测方程。最后提出基于信息融合的先进滤波算法,并通过对多种导航模式进行数值仿真及结果分析,论证所设计一体化方法提高了系统定轨/定姿的精度和可靠性。     

一种地磁/惯性深度融合导航方法

地磁/惯性融合导航是一种不依赖全球导航卫星系统的自主导航方式之一,具有很强的隐蔽性和抗干扰性能,是固体火箭的可用自主导航方式之一。基于前人在惯性/地磁融合导航研究的基础,对地磁导航、惯性导航的优缺点进行详细分析,将地磁导航在高度和纬度的确定优势和惯导在经度和纬度确定优势进行充分融合,提出了具备东向速度间接估计校正的地磁/惯性深度融合导航方法,摒弃地磁导航在经度、惯导在高度方向确定的劣势。结合实际弹道数据的导航仿真对比试验表明,所提出方法可以充分吸收两种导航的优势,相比传统的地磁/惯性融合方式,导航精度在相同条件下提升45.6%,为高精度地磁/惯性融合导航提供一种新的方法。     

一种适用于星敏感器的大角速度下星跟踪算法

传统的星敏感器预报方法是利用当前四元数和陀螺输出角速度来预测下帧姿态四元数,再通过预测的四元数计算视场内恒星的理想星像坐标,最后在这些理想坐标为中心的范围内来获取实际的星像坐标。但是,由于陀螺漂移的存在,随着时间的增加,预测的理想坐标与实际坐标偏差越来越大,获取实际星像坐标扫描的区域越来越大,星敏感器的数据更新率也随之降低。为此,本文提出了一种适用于星敏感器的大角速度下星跟踪算法。首先根据连续两帧的姿态偏差计算星敏感器的角速度,利用角速度来计算星敏感器当前时刻与最近上一帧的姿态偏差。然后以该姿态偏差来预报当前时刻的星敏感器姿态输出,这样不仅提高了数据更新率,而且满足飞行器在大角速度机动时单纯采用星敏感器进行姿态测控的要求。最后,采用2010年外场试验实际观星数据对该算法进行了仿真验证。     

一种未知环境下移动机器人自主导航方法

为提高未知环境下移动机器人自主导航性能,提出了一种未知环境下目标驱动的自主导航方法。不依赖实时更新的地图信息,移动机器人直接从激光雷达读数中构建候选目标点,并根据机器人自身位置和终点位置从候选目标点中选择最优点作为局部目标点。改进的基于深度强化学习的局部规划器从输入信息中直接输出动作信号,实现端到端的控制,使得移动机器人能够快速、安全地到达局部目标点,直至到达终点。实验表明,所提导航方法能够在未知复杂的环境下,可靠且高效地完成导航任务。与最近边界导航方法相比,平均路径长度减少了6.63%,平均运行时间缩短了19.11%,具有成功率高、路径短、速度快等优点。     

Aerodynamic map for soft and hard hypersonic level flight in near space

In this note, we design a velocity-altitude map for hypersonic level flight in near space of altitude 20-100 km. This map displays aerodynamic-related parameters associated with near space level flight, schematically or quantitatively. Various physical conditions for the near-space level flight are then characterized, including laminar or turbulent flow, rarefaction or continuous flow, aerodynamic heating, as well as conditions for sustaining level flight with and without orbital effect. This map allows one to identify conditions to have soft flight or hard flight, and this identification would be helpful for making correct planning on detailed studies of aerodynamics or making initial design of near space vehicles.     

A velocity transformation method for the nonlinear dynamic simulation of railroad vehicle systems

The solution of the constrained multibody system equations of motion using the generalized coordinate partitioning method requires the identification of the dependent and independent coordinates. Using this approach, only the independent accelerations are integrated forward in time in order to determine the independent coordinates and velocities. Dependent coordinates are determined by solving the nonlinear constraint equations at the position level. If the constraint equations are highly nonlinear, numerical difficulties can be encountered or more Newton–Raphson iterations may be required in order to achieve convergence for the dependent variables. In this paper, a velocity transformation method is proposed for railroad vehicle systems in order to deal with the nonlinearity of the constraint equations when the vehicles negotiate curved tracks. In this formulation, two different sets of coordinates are simultaneously used. The first set is the absolute Cartesian coordinates which are widely used in general multibody system computer formulations. These coordinates lead to a simple form of the equations of motion which has a sparse matrix structure. The second set is the trajectory coordinates which are widely used in specialized railroad vehicle system formulations. The trajectory coordinates can be used to obtain simple formulations of the specified motion trajectory constraint equations in the case of railroad vehicle systems. While the equations of motion are formulated in terms of the absolute Cartesian coordinates, the trajectory accelerations are the ones which are integrated forward in time. The problems associated with the higher degree of differentiability required when the trajectory coordinates are used are discussed. Numerical examples are presented in order to examine the performance of the hybrid coordinate formulation proposed in this paper in the analysis of multibody railroad vehicle systems.     

Solution of Navier-Stokes equations near the trailing edge of a plate

The appearance of a local singularity in the solutions for the neighborhood of the trailing edge of a plate in a sub- or supersonic flow makes it necessary to consider the flow in the local region which is described in the first approximation by the Navier-Stokes equations for an incompressible gas. In this paper numerical solutions are obtained for such a region for both a thin plate and a plate with thickness. The streamline patterns and the distributions of the flow functions over the surface of the plate and in the wake behind it are presented. For the plate with finite thickness, a numerical solution is obtained in a wide range of variation of the local Reynolds number.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 4, pp. 173–176, July–August, 1985.     

一种星敏感器杂散光规避方法

星敏感器应用于弹道导弹、卫星等近地空间的航天器上时易受到太阳光和月亮光等杂散光的干扰,使星图的信噪比大大降低,甚至淹没星点。针对上述问题,提出了一种星敏感器杂散光规避方法。首先,以地心赤道惯性坐标系为参考坐标系,分析给出了太阳光、月亮光和地气光这三种主要的杂散光进入星敏感器视场的条件;然后,推导了能够同时规避三种杂散光的星敏感器光轴参考指向;最后,梳理提出了一种快速有效的星敏感器杂散光规避方法。利用STK软件进行仿真实验的结果表明,在卫星运行期间,根据所提方法给出的星敏感器光轴指向规避太阳光、月亮光和地气光的成功率为100%,所提方法的有效性得到了验证。     

A double vortex sheet model of the viscous flow near the trailing edge of a lifting aerofoil

Classical definitions of boundary layer mass and momentum flux deficiency thicknesses can lead to gross errors when applied to measurements near a trailing edge where the flow curvature in the free stream is appreciable. This paper presents a double vortex sheet model as a development from the single vortex sheet model of Helmholtz and others. Two bound vortex sheets define a potential function which can describe a flow with the same mass and momentum flux deficiencies as the viscous regions. The bound nature of these sheets allows the modelling of the integral properties of these regions while retaining the advantages of a potential flow. The application to the flow near the trailing edge of a lifting aerofoil is given     

Stochastic estimation of flow near the trailing edge of a NACA0012 airfoil

A stochastic estimation technique has been applied to simultaneously acquired data of velocity and surface pressure as a tool to identify the sources of wall-pressure fluctuations. The measurements have been done on a NACA0012 airfoil at a Reynolds number of Re _c  = 2 × 10⁵, based on the chord of the airfoil, where a separated laminar boundary layer was present. By performing simultaneous measurements of the surface pressure fluctuations and of the velocity field in the boundary layer and wake of the airfoil, the wall-pressure sources near the trailing edge (TE) have been studied. The mechanisms and flow structures associated with the generation of the surface pressure have been investigated. The “quasi-instantaneous” velocity field resulting from the application of the technique has led to a picture of the evolution in time of the convecting surface pressure generating flow structures and revealed information about the sources of the wall-pressure fluctuations, their nature and variability. These sources are closely related to those of the radiated noise from the TE of an airfoil and to the vibration issues encountered in ship hulls for example. The NACA0012 airfoil had a 30 cm chord and aspect ratio of 1.