Misalignment Angle Calculation Accuracy Analysis of Three-Axis Stabilized Geostationary Satellite

The most challenging problem of navigation in three-axis stabilized geostationary satellite is accurate calculation of misalignment angles, deduced by orbit measurement error, attitude measurement error, thermal elastic deformation, time synchronization error, and so on. Before the satellite is launched, the misalignment model must be established and validated. But there were no observation data, which is a non-negligible risk of yielding the greatest returns on investment. On the basis of misalignment modeling using landmarks and stars, which is not available between different organizations and is developed by ourselves, experimental data are constructed to validate the navigation processing flow as well as misalignment calculation accuracy. In the condition of using landmarks, the maximum misalignment calculation errors of roll, pitch, and yaw axis are 2, 2, and 104 micro radians, respectively, without considering the accuracy of image edge detection. While in the condition of using stars, the maximum errors of roll, pitch, and yaw axis are 1, 1, and 3 micro radians, respectively, without considering the accuracy of star center extraction. Results are rather encouraging, which pave the way for high-accuracy image navigation of three-axis stabilized geostationary satellite. The misalignment modeling as well as calculation method has been used in the new generation of geostationary meteorological satellite in China, FY-4 series, the first satellite of which was launched at the end of 2016.

Method of Time-Delay Calculating and Correcting to Control Spin-Stabilized Satellite Synchronously

The key to control Spin-Stabilized Satellites Synchronously is to determine the models for calculating and correcting of time-delay at the different situations. Based on the principle of Synchronous-Control mode, the methods of determining the models of calculating and correcting of time-delay are proposed. The methods have been proved to be effective in real satellite control engineering.

MTCR-CR Routing Strategy for Connection-Oriented Routing over Satellite Networks

The high-speed movement of satellites makes it not feasible to directly apply the mature routing scheme on the ground to the satellite network.DT-DVTR in the snapshot-based connectionoriented routing strategy is one of the representative solutions,but it still has room for improvement in terms of routing stability.In this paper,we propose an improved scheme for connection-oriented routing strategy named the Minimal Topology Change Routing based on Collaborative Rules(MTCR-CR).The MTCR-CR uses continuous time static topology snapshots based on satellite status to search for intersatellite link(ISL)construction solutions that meet the minimum number of topology changes to avoid route oscillations.The simulation results in Beidou-3 show that compared with DT-DVTR,MTCR-CR reduces the number of routing changes by about 92%,the number of path changes caused by routing changes is about38%,and the rerouting time is reduced by approximately 47%.At the same time,in order to show our algorithm more comprehensively,the same experimental index test was also carried out on the Globalstar satellite constellation.

Underactuated spacecraft angular velocity stabilization and three-axis attitude stabilization using two single gimbal control moment gyros

Angular velocity stabilization control and attitude stabilization control for an underactuated spacecraft using only two single gimbal control moment gyros （SGCMGs） as actuators is investigated. First of all, the dynamic model of the underactuated spacecraft is established and the singularity of different configurations with the two SGCMGs is analyzed. Under the assumption that the gimbal axes of the two SGCMGs are installed in any direction, and that the total system angular momentum is not zero, a state feedback control law via Lyapunov method is designed to globally asymptotically stabilize the angular velocity of spacecraft. Under the assumption that the gimbal axes of the two SGCMGs are coaxially installed along anyone of the three principal axes of spacecraft inertia, and that the total system angular momentum is zero, a discontinuous state feedback control law is designed to stabilize three-axis attitude of spacecraft with respect to the inertial frame. Furthermore, the singularity escape of SGCMGs for the above two control problems is also studied. Simulation results demonstrate the validity of the control laws.

Nonlinear dynamics of flexible tethered satellite system subject to space environment

The paper studies the nonlinear dynamics of a flexible tethered satellite system subject to space environments, such as the J2 perturbation, the air drag force, the solar pressure, the heating effect, and the orbital eccentricity. The flexible tether is modeled as a series of lumped masses and viscoelastic dampers so that a finite multi- degree-of-freedom nonlinear system is obtained. The stability of equilibrium positions of the nonlinear system is then analyzed via a simplified two-degree-freedom model in an orbital reference frame. In-plane motions of the tethered satellite system are studied numerically, taking the space environments into account. A large number of numerical simulations show that the flexible tethered satellite system displays nonlinear dynamic characteristics, such as bifurcations, quasi-periodic oscillations, and chaotic motions.

Control of chaotic oscillations of a satellite

Analytical conditions and practical methods of their realization are proposed to solve a problem of a command signal tracking for a nonlinear disturbed system. Nonlinear disturbed plants consisting of linear dynamic block and nonlinear block in feedback are considered. Nonlinear part of the plant and disturbance are unknown and bounded. The paper illustrates a possibility of applications of proposed algorithms to control libration angle of satellite.

FY-4 Meteorological Satellite

FY-4 is the second generation of Chinese geostationary satellite for quantitative remote sensing meteorological application. The detection efficiency, spectral bands, spatial and time resolution have been greatly improved with respect to those of first generation, as well as the radiometric calibration and sensitivity. The combination of multichannel detection and vertical sounding was first realized on FY-4, because both the Advanced Geostationary Radiation Imager(AGRI) and Geostationary Interferometric Infrared Sounder(GIIRS) are on the same spacecraft. The main performance of the payloads including AGRI, GIIRS and Lightning Mapping Imager, and the spacecraft bus are presented, the performance being equivalent to the level of the third generation meteorological satellites in Europe and USA. The acquiring methods of remote sensing data including multichannel and high precision quantitative observing, imaging collection of the ground and cloud, vertical observation of atmospheric temperature and moisture, lightning imaging observation and space environment detection are shown. Several innovative technologies including high accuracy rotation angle detection and scanning control, high precision calibration, micro vibration suppression, unified reference of platform and payload and on-orbit measurement, real-time image navigation and registration on-orbit were applied in FY-4.

Cloud Detection and Centroid Extraction of Laser Footprint Image of GF-7 Satellite Laser Altimetry

The laser altimeter loaded on the GaoFen-7(GF-7)satellite is designed to record the full waveform data and footprint image,which can obtain high-precision elevation control points for stereo image.The footprint camera equipped on the GF-7 laser altimetry system can capture the energy distribution at the time of laser emission and the image of the ground object where the laser falls,which can be used to judge whether the laser is affected by the cloud.At the same time,the centroid of laser spot on the footprint image can be extracted to monitor the change of laser pointing stability.In this manuscript,a data quality analysis scheme of laser altimetry based on footprint image is presented.Firstly,the cloud detection of footprint image is realized based on deep learning.The fusion result of the model is about 5%better than that of the traditional cloud detection algorithm,which can quickly and accurately determine whether the laser spot is affected by cloud.Secondly,according to the characteristics of footprint image,a threshold constrained ellipse fitting method for extracting the centroid of laser spot is proposed to monitor the pointing stability of long-period lasers.Based on the above method,the change of laser spot centroid since GF-7 satellite was put into operation is analyzed,and the conclusions obtained have certain reference significance for the quality control of satellite laser altimetry data and the analysis of pointing angle stability.

Relative Equilibria of a Satellite Moving in an Elliptic Orbit Subjected to Gravitational and Aerodynamic Torques

Here we consider the attitude motion of a satellite, subjected to gravitational and aerodynamic torques in an elliptic orbit. The determination of orientation of equilibrium points has been discussed. It is found that they coincide with those for the circular case as studied by Sarychev and others in the works [1]-[3] and besides we have aimed at the sufficient condition for stability in the sense of Lyapunov.

Stability of the coplanar planetary four-body system

We consider the coplanar planetary four-body problem,where three planets orbit a large star without the cross of their orbits.The system is stable if there is no exchange or cross of orbits.Starting from the Sundman inequality,the equation of the kinematical boundaries is derived.We discuss a reasonable situation,where two planets with known orbits are more massive than the third one.The boundaries of possible motions are controlled by the parameter c^2E.If the actual value of c^2E is less than or equal to a critical value(c^2 E)cr,then the regions of possible motions are bounded and therefore the system is stable.The criteria obtained in special cases are applied to the Solar System and the currently known extrasolar planetary systems.Our results are checked using N-body integrator.

卫星指向式双通道遥感相机设计与验证

提出一种指向式双通道卫星遥感相机设计,将大范围指向镜和双通道焦面组件相结合,可实现可视范围超1000 km的多光谱成像功能。指向镜的镜头采用大口径高轻量化设计,具备良好的成像稳定性和抗力学性能。机构部分采用高精度驱动单元和精密测角装置,能保证视轴在大范围转动过程中的精确指向。焦面组件采用双通道楔板分光设计,实现9个谱段的高精度配准,保证相机图像融合的质量;光机结构优化设计实现相机的高稳定性。地面环境试验表明:相机具有较高的指向精度、良好的稳定性和环境适应性。

Capture Efficiency Analysis in the Circular Restricted Three-body Problem

Temporary capture efficiency is studied in the framework of the circular restricted three-body problem in two steps.First, a non-uniform distribution of test particles around the secondary's orbit is obtained by fully accounting the secondary's gravitational influence. Second, the capture efficiency is computed based on the non-uniform distribution. Several factors influencing the result are discussed. By studying the capture efficiency in the circular restricted three-body problem of different mass ratios, a power-law relation between the capture efficiency(p) and the mass ratio(μ) is established, which is given by p ≈ 0.27 × μ^(0.53), within the range of 3.0035 ×10^(-6)≤ μ ≤ 3.0034 × 10^(-5). Taking the Sun–Earth system as an example, the influence from the orbit eccentricity of the secondary on the non-uniform distribution and the capture efficiency is studied. Our studies find that the secondary's orbit eccentricity has a negative influence on the capture efficiency.

无控制点场景下基于多运动目标的卫星视频稳像算法

为了解决无控制点场景下现有卫星视频稳像算法失效的问题,提出了一种基于多运动目标的卫星视频稳像算法,该算法构建了目标检测、轨迹平滑和范数优化的框架,将多目标卡尔曼滤波、rlowess轨迹平滑与L1-L2范数优化相结合,最终实现卫星视频稳像。利用海上多目标舰船观测数据集开展实验,结果表明基于多运动目标的卫星视频稳像算法在X、Y方向上的稳像误差均不超过0.3个像素,验证了该算法的有效性。本研究填补了无控制点场景下卫星视频稳像的技术空白,具有重要的工程应用价值。

利用南海水面开展我国静止气象卫星红外通道在轨辐射定标

中国遥感卫星辐射校正场以青海湖水面作为遥感卫星红外探测通道外场辐射定标的场地.我国静止气象卫星风云二号(FY-2)系列是自旋稳定卫星,其红外通道无法进行在轨时的星上绝对定标,而青海湖对于位于东经105°赤道上空的FY-2卫星来说,卫星天顶角有36°,超过了外场辐射校正测量规范要求.本文介绍了利用我国南海海面水体辐射,进行与静止气象卫星的同步测量试验,开展卫星红外通道在轨外场辐射定标处理的可行性研究.在分别对FY-2B与FY-2C的测量数据处理后,初步确定我国南海海面可以作为我国静止气象卫星在轨辐射定标的场地.

SAR卫星电源系统设计与仿真研究

根据SAR卫星有效载荷的脉冲、大功率工作等典型特点及对电源母线稳定度的较高要求,设计了单母线、不调节电源系统方案,建立了电源系统的仿真模型。针对不同负载情况,分别对SAR卫星处于光照区和地影区时,其脉冲大功率电源系统在恒功率负载、负载突减和负载突加的情况进行了仿真分析。仿真结果表明此电源系统稳定,能够满足SAR卫星有效载荷的供电要求。

卫星激光测距系统稳定性分析及提高

以典型 SLR 系统为研究平台根据测量数据的产生流程详细分析了卫星测量与系统校准时的状态差异并评估了状态差异对测量数据距离偏差的影响引出 SLR 测量数据稳定性提升的途径.研究成果用于上海天文台SLR系统后 2015 年度对地球动力学卫星(Lageos)观测数据的长期稳定性、短期稳定性和标准点精度分别由改造前的12.7mm、22.7mm和2.0mm提升到4.1mm、9.3mm和1.0mm 国内率先达到国际卫星激光测距组织(ILRS)的数据质量标准(10mm 20mm和5mm)并持续保持提升了我国在SLR领域的国际地位和观测数据权重具有良好的推广应用前景.

一种基于链路稳定性模型的LEO/MEO双层卫星网星间链路设计方法

卫星网动态拓扑、长变时延等特性及其所处的复杂空间环境带来的通信干扰是影响网络通信稳定的重要因素。综合考虑这些影响因素,提出了一种衡量星间链路稳定性的模型,并基于此模型给出了LEO/MEO双层卫星网的星间链路设计方案。结合具体的星座实例对该方案进行了仿真分析,结果表明通过适当的参数调整该模型可以适应不同的网络性能要求。

顾及像面畸变的卫星视频稳像

卫星视频每帧影像外方位元素数值存在差别,相邻帧影像间的同名点在像面位置不同,且由于每帧影像均存在几何畸变,经典的帧间的投影变换模型、仿射变换模型等视频稳像的配准模型不能精确描述帧间的同名点关系。针对该问题,本文提出顾及像面畸变的卫星视频稳像算法,基于仿真的卫星视频,验证了该算法的可行性和精度。

高分七号卫星结构尺寸稳定性设计与验证

尺寸稳定性是高分七号卫星(GF-7)结构设计的重要使命。针对GF-7结构尺寸稳定性设计需求,开展了影响因素分析,并针对分解指标给出了适用于航天器结构的尺寸稳定性设计和验证流程。首先,在整星结构构型设计的基础上,通过灵敏度分析确定了结构选材方案。随后,针对尺寸稳定性关键件一体化支架,提出了热控设计和结构设计方案。最终,通过舱段级热稳定性试验获得了结构平均热膨胀系数等结构稳定性关键参数,利用经试验结果修正后的有限元模型开展了卫星在轨热变形分析并验证了指标的可实现性。结果表明,GF-7结构设计满足载荷安装面指向变化亚角秒级的尺寸稳定性指标要求。

扫描镜运动对三轴稳定卫星姿态影响研究

推导了带扫描镜运动的星体姿态动力学方程 ,以此方程对扫描过程进行了仿真计算 ,分析了扫描镜做扫描运动时星体姿态运动的一般规律及星体与扫描镜之间惯量比对星体姿态的影响。结果表明 ,扫描镜的步进运动将引起星体滚动姿态的单调变化 ,而周期性的扫描运动将引起星体偏航和俯仰姿态的周期性运动。改变扫描镜绕步进轴的转动惯量主要影响星体滚动姿态 ,而改变扫描镜绕扫描轴的转动惯量 ,主要对星体俯仰。