一种星光折射卫星自主导航系统方案设计

利用星光折射间接敏感地平的卫星自主导航方案具有导航精度高、自主性强的特点,是一种极具应用潜力的自主导航方案。在基于星光折射的自主导航方案中,折射星的准确识别与折射角的精确获取是实现高精度导航的基础。提出了一种基于双星敏感器,利用连续高度星图模拟与匹配技术实现高精度折射星识别和折射角获取的方法,并在此基础上设计了一种新颖的基于星光折射的卫星自主导航系统方案。同时,为了验证该方案的可行性,设计了相关的折射星仿真程序,以轨道高度为686km的对地观测卫星为例进行计算机仿真验证,结果表明在星敏感器精度为3″时,该导航系统平均位置误差约为145m,最大位置误差不超过400m。     

A procedure for three-dimensional angular velocity determination using a star sensor in high-rate rotation modes

This paper presents an application for modern star trackers aimed at the estimation of the spacecraft angular velocity vector on the basis of the star field images acquired during fast rotations, when star identification and tracking are not possible. Angular rates in the range 2–8°/s are considered, which strongly affect the characteristics of the acquirable images, in particular for shape and brightness. The procedure consists in the exploitation of the rigid motion equations to identify the rotation that best fits the observed star trajectories in the sensor field of view. Its coverage capability is analysed with reference to the sensitivity of state-of-the-art photodetectors. The probability of an adequate acquisition is shown to be 0.80 with random pointing and rotation axis over the celestial sphere. Firstly, the accuracy of the procedure is discussed in numerical tests. Then, end-to-end tests are reported, which have been operated by implementing the procedure in a hardware sensor model that acquires simulated star field scenes in a laboratory facility. Both the validations point out that the accuracy of 1°/s, suggested by the European Space Agency for this kind of application, has been achieved. Moreover, the rate of rotation about axes perpendicular to the boresight can be computed with accuracy one order of magnitude better.     

Determining Spacecraft Motion from Four Star Sensor Measurements

The BOKZ-M60 star sensor (a module that measures the coordinates of stars) has been designed for determining the parameters of the orientation of the intrinsic coordinate system relative to the inertial system from observations of stellar sky sections. The methods and results of processing of measurements by a set of four BOKZ-M60 sensors on the Resurs-P satellite no. 2 have been described. The time interval at which the satellite was in orbital orientation exceeds three orbital revolutions (19003 s). The joint processing of measurements by the four sensors conducted at the same time instants allowed the sensors to be associated with the universal coordinate system. With a root-mean-square error of less than 0.4′′ for each angle of rotation around its axes, this system is consistent with the model of the satellite’s rotational motion. The position of the universal system with respect to the instrumental coordinate system of the satellite was determined from the angular velocity measurements. Here, the root-mean-square errors for the values determined by the angles of rotation of the universal system around its axes were 0.044°, 0.051°, and 0.18°. The low-frequency (with frequencies less than 0.05 Hz) variations in the positions of intrinsic sensor coordinate systems relative to the universal system do not exceed 10′′. These are periodic variations with a fundamental frequency equal to the orbital frequency. The root-mean-square values of high-frequency components of these variations do not exceed 18′′.     

星载激光雷达高精高稳探测卫星系统保证技术

激光雷达探测精度高,具备全天时工作和垂直探测能力,在大气环境天基遥感领域应用广泛。基于CO_2柱线浓度激光遥感探测原理,分析了积分路径差分吸收星载激光雷达测量系统的激光波长、能量精度和稳定性及光轴指向精度等关键指标要求和功能模块配置,重点开展了星载激光雷达光机头部稳定安装、良好机热环境保障及星敏载荷一体化布局等整星层面系统设计保证,仿真结果初步表明设计方案可行。同时,提出了激光雷达波长、能量精度及稳定性实时监测、卫星对地光轴指向高精度测定和星地载荷光轴指向测量误差标定的地面试验验证要求,以确保系统设计的有效性,为激光雷达遥感卫星的研制提供了技术参考。     

Estimate of accuracy of determining the orientation of the star sensor system according to the experimental data

The BOKZ-M60 star sensor (Unit for Measuring Star Coordinates) is intended for determining the parameters of the orientation of the axes of the intrinsic coordinate system relative to the axes of the inertial system by observations of the regions of the stellar sky. It is convenient to characterize an error of the single determination of the orientation of the intrinsic coordinate system of the sensor by the vector of an infinitesimal turn of this system relative to its found position. Full-scale ground-based tests have shown that, for a resting sensor the root-mean-square values of the components of this vector along the axes of the intrinsic coordinate system lying in the plane of the sensor CCD matrix are less than 2″ and the component along the axis perpendicular to the matrix plane is characterized by the root-mean-square value of 15″. The joint processing of one-stage readings of several sensors installed on the same platform allows us to improve the indicated accuracy characteristics. In this paper, estimates of the accuracy of systems from BOKZ-M60 with two and four sensors performed from measurements carried out during the normal operation of these sensors on the Resurs-P satellite are given. Processing the measurements of the sensor system allowed us to increase the accuracy of determining the each of their orientations and to study random and systematic errors in these measurements.     

宽频角振动地面模拟试验设备的研制

为了解并减小探月着陆系统之敏感器容易受到宽频角振动影响的任务风险,有必要进行宽频角振动地面模拟试验。文章首先提出了宽频角振动的振动转换结构和测量方法,在此基础上完成了试验设备的研制,之后针对探月着陆系统成像敏感器遭遇的角振动环境进行了地面模拟测试。测试结果表明:该试验设备的宽频角振动模拟频率范围为0~2000 Hz,控制精度达到±15%（2σ）,同时还可模拟包括平移和转动在内的着陆系统刚体运动。该设备已用于敏感器在角振动环境下的地面模拟试验验证。     

星敏感器光轴测量的锥面误差模型及其应用

星敏感器是卫星高精度姿态测量系统中的重要器件,根据其测量可以建立不同形式的星敏感器测量模型,准确分析测量模型中测量误差的特性是保证卫星姿态确定精度的重要条件。本文针对广泛采用的星敏感器光轴矢量测量方程,从几何角度出发,结合实际情况,提出了一种新颖的星敏感器光轴测量的锥面误差模型。在两个锥面参数分别服从一定的概率分布的条件下,对测量误差特性进行了深入分析,确定出新的测量误差协方差矩阵。上述研究能够在不增加算法计算量的前提下,从新的角度,更为直观地建立了星敏感器光轴矢量测量模型。最后在仿真实验中,将新的锥面误差测量模型应用于基于扩展卡尔曼滤波（EKF）的姿态确定方法中,结果表明了利用该测量模型进行姿态确定的有效性。     

Measurement and stability of the pointing of the BepiColombo Laser Altimeter under thermal load

The BepiColombo Laser Altimeter (BELA) has been selected to fly on ESA?s BepiColombo mission to Mercury. The instrument will be the first European laser altimeter designed for interplanetary flight. This paper describes the setup used to characterize the angular movements of BELA under the simulated environmental conditions that the instrument will encounter when orbiting Mercury. The system comprises a laser transmitter and a receiving telescope, which can move with respect to each other under thermal load. Tests performed using the Engineering Qualification Model show that the setup is accurate enough to characterize angular movements of the instrument components to an accuracy of ≈10 μrad. The qualification instrument is thermally stable to operate during all mission phases around Mercury proving that the transmitter and receiver sections will remain within the alignment requirements during its mission.     

System design and performance of the two-gyro science mode for the Hubble Space Telescope

For 15 years, the science mission of the Hubble Space Telescope (HST) required using three of the six on-board rate gyros for attitude control. Failed gyros were eventually replaced through Space Shuttle Servicing Missions. To ensure the maximum science mission life, a two-gyro science (TGS) mode has been designed and implemented with performance comparable to three-gyro operations. The excellent performance has enabled a transition to operations with 2 gyros (by intentionally turning off a running gyro to save it for later use), and allows for an even greater science mission extension. Predictions show the gain in mission life approaching two years. In TGS mode, the rate information formerly provided by the third gyro is provided by another sensor. There are three submodes, each defined by the sensor used to provide the missing rate information (magnetometers, star trackers, and fine guidance sensors). Although each sensor has limitations, when used sequentially they provide the means to transition from relatively large, post-maneuver attitude errors of up to 10, to the arcsecond errors needed to transition to fine pointing required for science observing. Only small reductions in science productivity exist in TGS mode primarily due to more difficult target scheduling necessary to satisfy constraints imposed by the use of the star trackers. Scientists see no degradation in image quality due to the very low jitters levels that are nearly equivalent to three-gyro mode.     

Development of a high-precision selenodetic coordinate system for the physical surface of the Moon based on LED beacons on its surface

The paper presents a mathematical algorithm for processing an array of angular measurements of light beacons on images of the lunar surface onboard a polar artificial lunar satellite (PALS) during the Luna–Glob mission and coordinate–time referencing of the PALS for the development of reference selenocentric coordinate systems. The algorithm makes it possible to obtain angular positions of point light beacons located on the surface of the Moon in selenocentric celestial coordinates. The operation of measurement systems that determine the position and orientation of the PALS during its active existence have been numerically simulated. Recommendations have been made for the optimal use of different types of measurements, including ground radio trajectory measurements, navigational star sensors based on the onboard star catalog, gyroscopic orientation systems, and space videos of the lunar surface.     

星敏感器光学系统参数的确定

光学系统是星敏感器的重要组成部分。选择合理的参数不但能确保星敏感器达到预期的性能，而且有助于降低产品的研制成本。本文介绍一种确定光学系统参数的新方法，包括通过参考比较已有星敏感器及其光学系统特性来选取新光学系统焦距、相对孔径和视场；根据所选取的参数预计星敏感器的捕获概率；采用综合恒星光谱方法确定光学系统中心波长和光谱范围。     

Modelling of the optical observations of a geosynchronous fragmentation event

A study of the evolution and optical detectability of a fragmentation debris cloud in geosynchronous orbit has been carried out. The 1998 NASA breakup model has been used to generate orbit data for 95 fragments larger than 10 cm size from a 1000 kg satellite. The orbital evolution of these fragments is studied using a precision numerical propagator, employing a high-fidelity force model. Although the fragments rapidly disperse throughout the geostationary arc, they remain localised in right ascension of ascending node and inclination, and are driven along a narrow inertial corridor by luni-solar perturbations. The ESA PROOF software is used to study the detectability of the fragments using a 1- and 0.5-m telescope design. The 1-m telescope can detect 82% of the fragments (down to 13 cm in size) whilst the 0.5-m telescope can detect 39% of the fragments (down to 30 cm size). Due to the large along-track spread of the fragments, a time limit of 1-month post-breakup can be established for a space surveillance system to catalogue the breakup fragments. After this time the angular separation is such that the fragments disperse into the background population, and are no longer distinguishable as originating from a common breakup event.     

地基光学图像中本体-帆板结构航天器姿态估计方法

提出一种利用地基光学图像估计空间目标姿态的方法。针对本体-帆板结构航天器外形结构特点，定义了一种不易遮挡的两轴结构特征，设计了地基光学图像中该特征的提取方法；根据航天器成像过程建立了特征点二三维几何投影方程，实现了航天器三维姿态的解算。利用单站序列图像，可获得航天器姿态变化角速度信息。在轨航天器的试验结果表明，本方法能有效地从地基光学图像估计出航天器姿态。     

空间多载荷高精度拼接支撑结构的优化设计

针对遥感卫星在多载荷高精度拼接扩大幅宽时需保证成像质量的要求,考虑多载荷之间的耦合,对支撑结构进行空间布局优化以及结构/热控一体化设计.应用改进的Heaviside密度滤波拓扑优化方法获取最优结构/热控的材料分布形式,结合多目标遗传算法进行详细优化设计,获取支撑结构质量、一阶固有频率和载荷安装面面形精度的Pareto前...     

激光星间链路终端指向误差标定中的误差分离研究

针对激光星间链路终端指向误差在轨标定中航天器姿态测量误差影响标定结果的问题，本文提出了基于多链路测量的航天器姿态测量误差分离方法。该方法利用了导航星座中同一航天器同时建立多条链路的特点，获取不同方向的LCT指向误差测量数据。通过同时估计航天器姿态测量误差与LCT自身指向误差参数，实现了航天器姿态测量误差与LCT自身指向误差的分离。仿真结果表明：航天器姿态测量误差对LCT指向误差标定结果有显著影响，利用本方法进行误差分离后，LCT指向误差标定结果最大偏差由分离前的64.9 μrad下降到误差分离(6条链路)后的21.1 μrad，有效降低了航天器姿态测量误差对LCT指向误差标定结果的影响。该方法的有效性取决于链路条数和链路拓扑构型。     

模糊控制在光电跟瞄平台稳定控制中的应用

机载光电跟瞄系统是一个复杂的角位置随动系统,其精确模型不易建立。利用模糊控制不要求精确模型的特点,以跟瞄平台俯仰回路的稳定控制为例,设计了基本模糊控制器和自组织模糊控制器。仿真研究表明,在模型参数摄动又有多种干扰作用时,两种控制器都能进行有效地控制,特别是自组织模糊控制的稳态误差更小,计算速度更快。     

基于修正模型的天线指向误差统计特性分析

作为评估天线性能的重要指标之一,天线指向精度直接影响着天线的跟踪观测性能。为了适应任务需求,提高天线及星地链路分析精度,本文基于指向误差修正模型对模型各分量的影响因素含义进行了系统分析,并定量研究了各个分量对指向误差的影响。基于各模型参数的分布特性,提出了一种指向误差概率分布模型,进一步完善了天线指向误差分析计算方法,最后利用天线的典型参数分析计算了天线指向误差角近似满足修正瑞利分布下的特征,可为后续星地链路统计分析提供参考依据。     

基于交叠视场亮度优选算法的导航星库构建方法

星敏感器导航星库直接影响星图识别效率和姿态解算精度。分析了参与姿态解算的星颗数和亮度对姿态精度影响,在此基础上,提出了一种基于交叠视场亮度优选算法的星敏感器导航星库构建方法。将精度较高的Hipparcos星表作为基础星表,分析了星等、双星、自行、变星等对姿态精度的影响,将星库筛选成一个备选星库,生成覆盖全天球的交叠视场。每个拥有较多星的视场,都按照亮度优先原则从视场内的扇形区域中选择导航星,从而得到分布均匀的导航星库。结果表明:该方法能有效减小星敏感器导航星库规模,实现导航星在全天球和局部天区的均匀分布。     

Multiple blur of star image and the restoration under dynamic conditions

According to the flight characteristics of vehicle under high dynamic conditions, the impact of linear, angular, and vibrational motion on star sensor imaging was researched. Then, the mathematical model of motion blur corresponding to various flight conditions was deduced, and the star centroiding accuracy affected by motion blur was analyzed subsequently. On this basis, the mechanism of multiple blur was discussed. In order to ensure the accuracy of star sensor in high dynamic environment, a restoration method was proposed to remove the multiple blur. Finally, simulations are implemented to validate the restoration method.