Research on dynamic performance of star tracker

This manuscript briefly summarizes the development trends and recent research focus of the star tracker.And the relevant technologies about dynamic performance of the star tracker are analyzed and discussed.These can provide reference for the star tracker and attitude measurement device researchers.

Systematic error analysis and compensation for high accuracy star centroid estimation of star tracker

Subpixel centroid estimation is the most important star image location method of star tracker. This paper presents a theoretical analysis of the systematic error of subpixel centroid estimation algorithm utilizing frequency domain analysis under the con-sideration of sampling frequency limitation and sampling window limitation. Explicit expression of systematic error of cen-troid estimation is obtained, and the dependence of systematic error on Gaussian width of star image, actual star centroid loca-tion and the number of sampling pixels is derived. A systematic error compensation algorithm for star centroid estimation is proposed based on the result of theoretical analysis. Simulation results show that after compensation, the residual systematic errors of 3-pixel-and 5-pixel-windows’ centroid estimation are less than 2×10-3 pixels and 2×10-4 pixels respectively.

Precession–nutation correction for star tracker attitude measurement of STECE satellite

Space Technology Experiment and Climate Exploration （STECE） is a small satellite mis- sion of China for space technology experiment and climate exploration. A new test star tracker and one ASTRO 10 star tracker have been loaded on the STECE satellite to test the new star tracker＇s measurement performance. However, there is no autonomous precession nutation correction func- tion for the test star tracker, which causes an apparent periodic deflection in the inter-boresight angle between the two star trackers with respect to each other of up to - 500 arcsec, so the preces- sion and nutation effect needs to be considered while assessing the test star tracker. This paper researches on the precession-nutation correction for the test star traeker＇s attitude measurement and presents a precession-nutation correction method based on attitude quaternion data. The peri- odic deflection of the inter-boresight angle between the two star trackers has been greatly eliminated after the precession and nutation of the test star tracker＇s attitude data have been corrected by the proposed method and the validity of the proposed algorithm has been demonstrated. The in-flight accuracy of the test star tracker has been assessed like attitude noise and low-frequency errors after the precession-nutation correction.

Low-frequency Periodic Error Identification and Compensation for Star Tracker Attitude Measurement

The low-frequency periodic error of star tracker is one of the most critical problems for high-accuracy satellite attitude determination.In this paper an approach is proposed to identify and compensate the low-frequency periodic error for star tracker in attitude measurement.The analytical expression between the estimated gyro drift and the low-frequency periodic error of star tracker is derived firstly.And then the low-frequency periodic error,which can be expressed by Fourier series,is identified by the frequency spectrum of the estimated gyro drift according to the solution of the first step.Furthermore,the compensated model of the low-frequency periodic error is established based on the identified parameters to improve the attitude determination accuracy.Finally,promising simulated experimental results demonstrate the validity and effectiveness of the proposed method.The periodic error for attitude determination is eliminated basically and the estimation precision is improved greatly.

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

The star tracker is an optical attitude sensor with extremely high accuracy, the structure of which is mainly composed of the baffle, the lens, the image detector, and the processing unit, and it has been widely used in satel- lites To realize attitude determination from the weak star captured by the image detector of the star tracker,

神舟飞船高精度星敏感器设计概述及在轨验证

给出了中国神舟系列飞船所采用的高精度星敏感器的设计方案和在轨验证结果。在镜头设计方面,采用了光阑前置结构型式,满足小型化和长寿命应用需求;在整机结构设计方面,采用了“框架组合环绕式”一体化结构,注重轻量化与稳定性;在电路设计方面,采用了抗辐照加固的APS图像传感器、处理器和ASIC,确保全寿命周期内高灵敏度探测与高可靠信息处理;在算法方面,采用了聚类提取、快速三角形识别、卷帘补偿以及曝光时间动态调整等算法,实现精度、更新率、动态和捕获等关键性能指标;此外,对整机热稳定性进行了改进,确保星敏感器性能可以良好保持。该星敏感器已成功应用于载人航天、探月及北斗三号等一系列重大工程,在轨应用数量达到200余台。

顾及温度效应改正的多星敏感器角速度重建方法

高精度卫星姿态控制是卫星重力数据预处理的重要环节。地球重力场和海洋环流探测(GOCE)卫星搭载的关键荷载星敏感器在低轨运行状态中,不可避免地受到空间环境的温度变化影响,导致星敏感器视轴夹角(IBA)存在2″~14″偏移,直接影响卫星姿态的精度。定量分析温度效应对卫星姿态的影响,精确测定卫星角速度,是卫星数据预处理流程中的重要环节,直接影响高精度重力梯度分量构建的精度。本文基于GOCE卫星任务的特性,构建了一种多星敏感器联合姿态四元数的温度效应改正方法,包括星敏感器之间的相对姿态偏移量构建为温度相关线性函数,结合星敏感器各轴的精度差异建立加权矩阵,依据最小二乘原理得到最优姿态四元数重建角速度。同时,在原始姿态数据的解算中,构建一种对数四元数Hermite超曲面内插方法进行数据优化处理。研究结果表明,改正后的星敏感器姿态四元数计算出的IBA与参考框架信息对比无明显偏移。且经过温度效应改正后,星敏感器各轴角速度噪声水平大幅下降了约两个量级,精度达到10^(-10 )rad·s^(-1),显著提高了角速度重建的精度,各轴角速度精度保持良好一致性。基于本文方法计算得到的重力梯度迹的功率谱密度,在整个频域内有较为明显的改善。

航空天文组合导航技术发展研究

阐述了航空机载天文/惯性组合导航的原理,突出了天文导航技术在远程长航时航空平台导航应用的优势。首先,介绍了机载天文/惯性组合导航技术的发展研究现状,并比较了国内外发展状态;其次,分析了机载天文组合导航技术的平台需求特点,总结了当前的技术挑战,探讨了未来的技术攻关方向和发展趋势。

Alignment calibration and performance study of the STAR PXL detector

We report in this paper the alignment calibration of the STAR pixel detector(PXL) prototype for the RHIC2013 run and performance study of the full PXL detector installed and commissioned in the RHIC 2014 run. PXL detector is the innermost two silicon layers of the STAR heavy flavor tracker aiming at high-precision reconstruction of secondary decay vertex of heavy flavor particles. To achieve the physics goals, the calibration work was done on the detector with high precision. A histogram-based method was successfully applied for the alignment calibration, and the detector efficiency after alignment was studied using both p t p collision data and cosmic ray data.

Design and error analysis of a high accurate star simulator based on optical splicing technology

Dynamic tar simulator has been widely used in calibration and validation for star trackers.To achieve both high accuracy and large view field,a dynamic star simulatorbased on optical splicing technology with 2 1920 × 1080- LCDs and a half-transmission and half- reflection prisms was proposed in this paper.The physical principal and error model due to the splicing structure has been discussed and analyzed in detail.Based on the Tsinghua Micro star tracker,the error effect and system accuracy has been carefully tested and calibrated.The result showed that this simulator can get the accuracy of 10.4 "(3sigma) within a field of view of,which can meet the simulating requirement of modern star tracker,whose accuracy can reach 3"(3sigma) 。

A star identification algorithm for rolling shutter exposure based on Hough transform

The star identification algorithm usually identifies stars by angular distance matching.However,under high dynamic conditions,the rolling shutter effect distorts the angular distances between the measured and true star positions,leading to plethoric false matches and requiring complex and time-consuming verification for star identification.Low identification rate hinders the application of low-noise and cost-effective rolling shutter image sensors.In this work,we first study a rolling shutter distortion model of angular distances between stars,and then propose a novel three-stage star identification algorithm to identify distorted star images captured by the rolling shutter star sensor.The first stage uses a modified grid algorithm with adaptive error tolerance and an expanded pattern database to efficiently eliminate spurious matches.The second stage performs angular velocity estimation based on Hough transform to verify the matches that follow the same distortion pattern.The third stage applies a rolling shutter error correction method for further verification.Both the simulation and night sky image test demonstrate the effectiveness and efficiency of our algorithm under high dynamic conditions.The accuracy of angular velocity estimation method by Hough transform is evaluated and the root mean square error is below 0.5(°)/s.Our algorithm achieves a 95.7% identification rate at an angular velocity of 10(°)/s,which is much higher than traditional algorithms.

事件星敏感器自适应积分时间曲面算法

针对传统星敏感器在高动态环境下恒星成像模糊而造成的姿态跟踪失效的问题,提出了一种事件星敏感器自适应积分时间曲面算法,以获得高动态环境下清晰的星点成像。首先,基于事件流噪声特性,构建时空滤波器去除噪声。其次,设计了基于椭圆函数特征参数拟合方法,对虚拟帧内星点进行特征拟合,根据星点的几何形状特征进行积分时间的在线调节。最后,设计了多种动态环境实验。实验结果表明,所提算法可以构建出清晰的星点图像,在高动态环境下消除星点运动模糊。在角速度20°/s、线速度400 mm/s高动态环境下,与常用事件流积分方法相比,星对角距误差分别降低了77.9%和70.7%。

干涉星敏感器测角精度影响因素的研究

为了提高传统星敏感器的姿态测量精度,可将干涉测角技术与传统星敏感器相结合,即在传统星敏感器质心定位技术的基础上,利用星像点的光强信息进一步进行细分,从而突破了质心定位的精度限制,形成具有大视场高精度的干涉星敏感器。本文对制约干涉星敏感器测角精度的因素进行深入研究,重点研究干涉条纹的分割误差对测角精度的影响机理。通过研究分析,得出以下结论:光锲阵列不等分误差不是影响干涉星敏感器测角精度的主要因素;莫尔条纹周期与光楔阵列整体通光尺寸不匹配误差小于1%时,可保证单因素测角误差小于0.01";对于莫尔条纹取向与光楔阵列排布方向不正交误差,条纹旋转角度应当小于0.1°,可保证单因素测角误差小于0.01"。所以,应在实际加工与装调过程中抑制上述两个主要误差,从而使干涉星敏感器的实际测角精度接近高精度理论值。

星点质心亚像元定位的高精度误差补偿法

在CCD星敏感器设计过程中,星点坐标的提取精度不仅影响星图识别的正确性,也直接影响星敏感器的最终姿态输出精度。本文通过分析传统质心法亚像元提取算法误差模型,证明该模型存在系统误差和随机误差。针对系统误差,提出了用最小二乘拟合法来估计质心位置和系统误差大小的对应关系,利用这个关系对系统误差进行补偿;针对随机误差,提出用边缘阈值法和星图整体相消法来消除。本文还分析了CCD成像数学模型,星光成像的能量分布近似服从二维高斯分布,星点高斯分布弥散半径不同,用于误差补偿的曲线方程也不一样,根据不同的高斯弥散半径,设计了误差补偿模板,用于补偿质心法的系统误差。实验表明,采用误差补偿模板,可以将质心法精度从1/20pixel提高到1/200pix-el,满足了星敏感器高精度星点质心提取的要求。

高精度星敏感器星点光斑质心算法

高精度星敏感器星点光斑的质心精度是星敏感器整体精度的基础,它需要达到角秒级的量级。因此,提出了一种基于亚像元相关法的星像质心算法。这种算法是利用互相关匹配实现图像定位的原理,将星像质心定位到亚像素上来提高质心精度。它可以克服由于系统误差和图像采集所带来的误差。根据系统的光学参数设计以及星像的光谱、亮度及其在视场中的位置特征,仿真得到点列图模型,针对视场内与光轴的不同夹角仿真制作一系列亚像元理想模板,然后对星像加高斯随机噪声,把有随机噪声的星像与理想星像进行相关运算来求星像质心精度。通过仿真实验,得到相关法具有较高的星像质心精度,定位精度可以优于1/12个像素的量级。

大孔径大视场轻小型星敏感器光学系统

提出了一个大相对孔径、大视场轻小型CCD星敏感器光学系统设计方案,该星敏感器焦距为22.5 mm,F数为1.2,谱段范围470-750 nm,视场角25°。采用双高斯基本型后加一片近乎等晕的正透镜,获得了较大的相对孔径,同时选择高折射率玻璃材料增大视场并降低轴上及轴外光束入射角,高折射率玻璃材料亦能降低高级像差且使系统总长缩短。像质分析表明,此设计方案能够满足使用要求,光学系统总长仅为46.51 mm,满足实际工程轻量化需求。

星敏感器技术研究现状及发展趋势

本文综述了星敏感器技术的研究现状和未来发展趋势。首先,总结了国内外星载星敏感器的发展历程。接着,根据星敏感器工作原理,分析讨论了星点质心定位算法、星图识别算法和姿态解算算法等星敏感器关键技术的发展现状。通过讨论星点质心定位精度对星敏感器测量精度影响,分析了星点质心定位算法以及对应误差补偿的研究现状;基于星座特征、字符模式和智能行为,介绍了星图识别算法并进行了对比分析;根据确定姿态解算算法和动态姿态解算算法分析了姿态解算算法的研究现状。最后,对星敏感器的未来发展进行了展望,讨论了航空机载星敏感器、微小型星敏感器和甚高精度星敏感器的发展趋势以及未来重点研究内容。

一种星图中星的提取方法

在分析星图中的星像和小目标图像中的小目标像的共性的基础上,提出了一种将高通滤波和动态阈值相结合的星图中星的提取方法,来完成星图处理过程中较为耗时的星图提取工作.即滤波后先确定阈值,再通过高通滤波提取图像的候选点,由于虚假目标太多,需要通过动态阈值对候选点进行二次提取.仿真结果表明这种方法与矢量法相比,当不给星图加背景噪声时,两种方法提取精度相当.一旦给星图加上噪声,矢量法的提取精度迅速下降,提出的方法的提取精度远远高于矢量法,而提取时间却与矢量法相差无几.因此提出的方法表现出较强的抗噪能力.

一种改进的全天自主三角形星图识别算法

三角形算法是一种当前使用最为广泛的星图识别算法 ,但作为其识别基元的三角形的特征维数比较低 ,容易出现冗余匹配或误匹配 ,因而对测量误差比较敏感。针对这一缺点 ,从导航星的选取、星座数据库的构造和算法的实现三方面着手对传统三角形算法进行改进 ,提出了新的导航星自动选取方法和导航星座数据库构造方法 ,并在此基础上实现了改进三角形算法 ,其数据库容量和实时性都略优于传统三角形算法 。

GPS/SST/SINS组合导航系统研究

提出了卫星/捷联星光/捷联惯导组合导航系统的方案和组合结构,采用改进的集中滤波对多传感器信息进行数据融合和导航状态的最优估计.该组合导航系统将捷联星光跟踪仪的姿态信息、高动态GPS的位置、速度信息与捷联惯导进行组合滤波,全面提高导航的姿态、速度和位置精度.同时该组合导航系统以弹道导弹为应用对象,设计并实现了基于弹道导弹的GPS/SST/SINS组合导航系统实时仿真平台,仿真结果表明该组合导航系统能提高导弹的导航精度,滤波算法稳定可靠.