A method of autonomous orbit determination for satellite using star sensor

1 Introduction Autonomous orbit determination of satellite means that orbit determination is solely finished on board, independent of the observation of ground system. Study on autono-mous orbit determination of satellite has been very hot in the field of orbit determination currently internationally due to its significance in application. There are two common ways of autonomous orbit determination internationally. One is autonomous orbit deter-mination based on navigation system, such as on-b…     

Autonomous satellite constellation orbit determination using the star sensor and inter-satellite links data

A method of autonomous orbit determination for a satellite constellation using a star sensor combined with inter satellite links(ISLs) is studied.Two types of simulated observation data,Three-Satellite Constellation ISLs and background stellar observations by a CCD star sensor,are first produced.Based on these data,an observation equation is built for the constellation joint autonomous orbit determination,in which the simulations are run.The accuracy of this method with different orbital determination model...     

带噪声模拟仿真星图的实现

本文对星敏感器的姿态参数进行仿真计算,实现了观测星的提取及星图模拟。根据二维高斯分布模型对星点进行灰度弥散;考虑了噪声等因素的影响,实时模拟星敏感器在轨状态下拍摄星空的真实星图。实验证明,通过仿真模拟在轨运行卫星所拍摄的星图,可以为星敏感器星点提取、星图识别、姿态解算等功能算法提供验证。     

Optical testing of star sensor (I): Defocus spot measuring technique for ground-based test

We developed a technique for measuring the intensity distribution of a point image in sub-pixel resolution even after assembly of a lens and an image sensor, which is especially suitable for defocus adjustment of a star sensor used to determine the attitude of a spacecraft. The star sensor optical system is usually aligned in a defocused position to calculate the luminance centroid of a star image in sub-pixel resolution. In the measurement technique, the point image is carefully scanned around a certain pixel on the image sensor, and the intensity change of the pixel is recorded during the scanning. We applied this technique to the alignment of our star sensor’s optical system, and we were able to suppress the spot size in a range between 1.2 and 2.2 pixels at 1/e² diameter at a certain defocus position, making it appropriate for luminance centroid calculation.     

剪切波变换在星点提取中的应用

为了实现高精度和高准确性的星图识别和姿态确定,本文对星点提取算法进行了研究,将剪切波变换应用到星点提取技术中。首先,通过利用剪切波变换对星图进行分解,得到不同尺度、不同方向的系数;然后,对剪切系数进行阈值处理并重构得到去噪后的星图,再对重构星图进行顶帽变换和自适应阈值处理,完成星图滤波;最后,通过质心误差补偿法提取星点的坐标,有效地完成星点提取。实验结果表明,采用剪切波变换的星图滤波对噪声去除非常有效;质心误差补偿法的误差在0.003左右,明显优于传统的质心法,基本满足星敏感器的精度高和抗干扰能力强等要求。     

Optimization method for star tracker orientation in the sun-pointing mode

The star tracker, an optical attitude sensor with high accuracy, is widely used in satellites for attitude determination and control. However, it is susceptible to the sunlight and the earthlight for application on satellites in the sun-synchronous orbit. Therefore, the suppression of the sunlight and the earthlight is important for the star tracker. In this Letter, a vector model is proposed to describe the relationship among the Sun, the Earth, and the satellite body, and, based on the equations of the boundary curves, the vector areas free from the sunlight and the earthlight in the body coordinate system of the satellite are derived. Meanwhile, the installation orientation of the star tracker and the corresponding exclusion angle of the earthlight are optimized. The simulation results indicate that the optimization method for the installation orientation and the exclusion angle of the star tracker is accurate and effective.     

一种星敏感器主点和焦距的加权在轨标定方法

星敏感器作为卫星姿态测量装置,其在轨服役过程中,主点和焦距的标定精度是影响其姿态输出精度的主要因素。针对标定过程中含有随机测量噪声偏大的星像点,导致星敏感器主点和焦距的标定结果产生较大偏差的问题,提出了一种星敏感器主点和焦距的加权在轨标定方法。该方法首先建立了星敏感器在轨标定模型,然后引入合理的标定权值,加入到最小二乘估计主点和焦距的过程中,寻找并剔除随机测量噪声偏大的星点,最后将加权估计出的结果作为测量,采用扩展卡尔曼滤波对星图进行处理。仿真结果表明,在星点位置存在较大误差的情况下,该方法能剔除随机测量噪声偏大的坏点。星内角距统计偏差约为传统方法的1/10,与真值相比标定参数精度分别为0.219 9像素、0.148 7像素、3.38 μm。     

星敏感器光学系统弥散斑测试方法

提出了一种星敏感器光学系统弥散斑尺寸的测试方法,主要是利用平行光管、转台和CCD显微摄像系统组成弥散斑测量系统,采集图像后,采用双三次插值像元细分,提取图像中灰度值,依据瑞利判据计算弥散斑尺寸。通过实际测量和试验验证,光学系统0.8视场弥散斑测量精度可以达到0.5μm,重复测量精度可达0.2μm。     

像差对星敏感器星点定位精度的影响

光学系统星点定位精度是表征星敏感器性能的一个重要指标,像差对该精度有一定影响。分析光学系统像差对星点定位精度的影响,在计算典型中等精度星敏感器光学系统星点定位误差的基础上,提出用实际测得的星点光斑能量质心位置计算理想位置的误差补偿新方法。计算结果表明:像差对高精度(如角秒级)星敏感器姿态测量精度的影响不可忽略;采用星点定位误差补偿后,星敏感器三轴姿态测量误差RMS值分别为0.38″,0.38″,5.77″,仅为原来的1/17。     

船用星敏感器星点质心精确提取方法

从星空图像中提取星点质心是星敏感器工作的重要基础,针对船用星敏感器所获取的星空图像噪声情况复杂的特点,提出一种基于重心法的星点质心精确提取方法。通过块扫描的阈值分割和星象连续性的噪点剔除,引入灰度信息参考的星象提取以及重心法质心坐标计算等步骤,从星空图像中提取星点质心。对于30幅海上实拍星图实验,该方法能够100%提取出至少10颗星点,质心坐标提取精度达到1/20像素,并且可以实现对视频图像的实时处理,满足船用星敏感器的应用需求。     

CMOS星敏感器光学系统的设计

基于对恒星星表V/50的统计,在确保一定捕获概率的前提下,确定了星敏感器光学系统的视场角和所能探测的极限星等,在此基础上,结合所选用的STAR-250CMOS探测器的性能,在保证一定信噪比的前提下,确定了光学系统的通光孔径、焦距、工作光谱范围和中心波长、弥散元大小等主要参数。以改进双高斯型结构为初始结构,在ZE-MAX平台上实现了具有良好像质的大孔径(F/1.198)、大视场(22.6°)、宽光谱范围(0.5μm~0.8μm)的光学系统的设计,满足了对弥散斑、能量集中度等的特殊要求。     

小型化宽谱段星敏感器光学系统设计

星敏感器是航天飞行器实现姿态自主导航的关键测量设备,传统星敏感器由于体积与质量较大,难以满足微纳卫星的应用需求,光学系统是星敏感器小型化的核心及瓶颈技术。分析了实现全天恒星识别的星敏感器光学系统参数需求,完成一种基于全球面透镜的微小型宽谱段透射式光学系统设计,实现了光学系统焦距40 mm,视场角26.4°,相对孔径F/2.8,光谱范围为450 nm～1 000 nm,光学系统体积与质量大幅降低,可应用于微纳卫星星敏感器。     

Laboratory calibration of star sensor with installation error using a nonlinear distortion model

The high-precise star sensor calibration method requires high-accurate turntable, collimator, star point plate or other high-precision devices that are very expensive. We present a simple and available method to calibrate the principal point, focal length, radial distortion, tangential distortion and installation error of star sensor in laboratory, and without having high accurate or expensive devices. The calibration model takes the ordinary camera calibration methods and installation error into account. The installation error is modeled by combination of three typical effects: the installation of pan-tilt-zoom (PTZ) initial status, PTZ and charge-coupled device, which result in six parameters. The proposed procedure consists of a closed-form solution, followed by a nonlinear refining based on maximum likelihood criterion. Our calibration method is validated through simulation and real data that shows the superiority with respect to the traditional methods and has the same level as the state-of-the-art methods. The accuracy of our calibration method is 0.015° in the root of mean square distances between testing points and projected ones.     

大动态CMOS APS的星敏感器光学系统主要参数设计

星敏感器广泛用于空间飞行器的姿态测量,为减少飞行器飞行过程中转动对星敏感器测量精度的影响,定量分析了捷联安装的星敏感器透光孔径、曝光时间、视场、焦距、像素数目与转速之间的关系,提出了大视场、短曝光时间、较少的像素都能提高星敏感器的动态。鉴于这三者之间是相互关联的,首先,由导航星的捕获概率确定了视场大小,然后,根据恒星辐射模型和CMOS有源像素传感器的噪声计算模型,确定了透光孔径、曝光时间。     

对地观测平台恒星敏感器离焦成像折中设计分析

从对地观测平台角秒量级姿态确定需求出发,在构建星敏感器惯性系成像模型的基础上指出,恒星在成像面上的定位误差是星敏感器姿态确定误差的主要来源。同时,结合理想光学系统离焦模型,分析了星敏感器主要性能指标间的量化关系,并给出了成像面定位误差最低限。仿真结果表明,从优化系统性能考虑,成像模糊区直径为2~3个像元的配置是利用星敏感器焦平面的“轻微离焦”来实现亚像元定位的最佳方案,定位误差可达0.2个像元,能够满足星敏感器惯性姿态确定精度4″~5″的要求。理论分析和数值仿真结果可为后续星敏感器指标的提出及仪器设计提供技术参考。     

温度对星敏感器光学系统像面位移的影响研究

光学系统的温度变化会使系统产生像面位移。根据镜面材料特性公式,选用铝合金作为星敏感器的镜筒,透镜组选用ψ值大的材料,并进一步通过I-DEAS软件进行了计算验证。在此基础上根据矩阵光学理论和温度的变化推导出了含有多个光学器件的星敏感器像面位移计算公式,并运用该公式对一个特定的星敏感器光学系统的像面位移进行了计算。结果发现,光学系统从一个温度均匀分布状态变到另一个温度均匀分布状态的温差越大,像面位移量的绝对值越大。同时还发现,对此星敏感器成像精度影响最大的透镜是第4块、第5块和第6块,明显地减少了在热补偿条件下的系统像面位移。     

基于UKF的恒星相机高精度姿态确定方法

为进一步提升姿态确定的精度和稳定性,首先分析了恒星相机和陀螺联合定姿的基本原理,然后选用误差四元数作为状态变量,推导了基于无迹卡尔曼滤波的恒星相机和陀螺联合定姿的算法.针对恒星相机、陀螺敏感器精度要求高的特点,仿真了多种精度的恒星相机数据和陀螺数据进行无迹卡尔曼滤波定姿试验,并与扩展卡尔曼滤波定姿试验结果进行了比较.试验表明无迹卡尔曼滤波定姿方法有效可靠、适用性强,可以有效提高恒星相机的姿态确定精度,三轴精度较扩展卡尔曼滤波算法提高约10%到20%.     

CCD星图模拟器的设计及验证

为了方便星图识别算法和星敏感器性能的测试,设计了一种CCD星图模拟器,开发了星图模拟软件。采用高分辨率显示设备及平行光管模拟无穷远处平行光,实现了高质量星图的模拟。通过高精度QUEST算法求解姿态,对模拟的星图进行了验证。计算了3颗以上恒星的偏航角、俯仰角和滚动角,对100幅模拟星图进行了统计分析,结果显示其定位精度已达98．1％。目前,该星图模拟器已成功用于实际项目,为后续的测试星图识别算法提供了良好的依据,并缩短了开发周期。     

一种非标定的快速星图识别方法

大多数现有算法在星敏感器光学系统参数标定不准确时,识别率显著降低。针对这种情况提出了一种无需标定参数的识别算法。该算法引入比例距离作为径向特征,角度作为环向特征。这两种特征不依赖焦距、主点等任何光学系统参数,仅和图像平面上的星点位置有关。识别时首先按照特征量进行初始匹配,然后利用FOV(Field of View)约束筛选待选星进行精确匹配。为了加快速度,精确匹配时引入了快速分组方法。仿真实验表明,该方法具有较快的识别速度,在没有光学系统参数的情况下,识别率可以达到97%。