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.

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.

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.

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.

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。

BDS/GPS新型铷原子钟长期特性分析

铷原子钟具有体积小、功耗低等显著优势,被广泛应用于导航卫星。基于星载铷钟技术发展迅速、BDS和GPS新型铷钟性能尚未得到全面分析的研究现状,对两大系统自2017年后发射的16颗星的铷钟进行了长期特性分析。以GFZ中心提供的BDS精密钟差和IGS中心的GPS最终钟差产品为数据基础,根据卫星钟工作原理确定了各表征部分的分析方法。系统特性方面,通过最小二乘拟合计算了卫星钟的短中期漂移率与频率准确度;随机特性方面,对逐日拟合残差序列进行了计算与长期变化趋势分析,通过重叠Hadamard偏差计算了卫星钟稳定度,分析了不同时段的主导噪声类型;周期特性方面,利用频谱分析方法计算了卫星钟长期表征的主周期项,综合轨道误差和运行等因素分析了周期项可能原因。结果表明:BDS/GPS新型铷原子钟的频率准确度达到10-12量级,秒漂和日漂分别达到10^(-19)和10^(-14)量级,万秒稳定度介于1.82×10^(-14)~2.98×10^(-14)之间,天稳定度普遍达到10^(-15)量级,逐日拟合残差精度达到0.1 ns~0.2 ns;所有卫星钟差序列周期特性显著,前三个主周期近似为卫星轨道周期的1倍、2倍和3倍左右。

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.

基于不同轨道和星钟类型的BDS-3星载钟特性评估

星载原子钟性能的研究对于卫星钟差估计与预报、卫星导航系统的建设与维护等具有重要的意义。采用了德国地学研究中心(GFZ)2021-01-01—2021-12-31多星定轨联合解算的精密钟差产品,基于预处理后的钟差数据,对2021年北斗三号卫星导航系统(BDS-3)星载钟的相位、频率跳变情况进行了统计,探讨了中圆地球轨道(Medium Erth Obit,MEO)卫星铷钟与氢钟的相位、频率序列图特点。使用二次多项式模型分析了BDS-3不同轨道、不同星钟类型卫星钟的频率漂移率和模型噪声等指标的变化规律,基于哈达玛方差从不同时间尺度对BDS-3卫星钟的频率稳定度展开了分析。结果表明,BDS-3卫星钟相位和频率变化相对连续且稳定,其中仅地球静止轨道(Geostationary Orbit,GEO)卫星星钟存在调相行为,MEO卫星和GEO卫星都存在调频行为,且铷钟的调频次数明显多于氢钟。从频漂和模型噪声水平来看,MEO卫星优于其他轨道类型卫星,同铷钟相比,氢钟性能更优。BDS-3星载原子钟的稳定度保持在10^(-15)~10^(-14)量级,MEO卫星星载钟的稳定度最优,其次是倾斜地球同步轨道(Inclined Geosynchronous Orbit,IGSO)卫星,GEO卫星星载钟的稳定度最差。

面向卫星编队飞行的有线无线时隙融合调度方案研究

针对卫星编队飞行场景中星内有线和星间无线链路传输速率以及调度机制的差异性引起的时敏任务在星上转发时延不确定性的问题,该文提出一种有线无线融合的时隙调度方案。首先,分别构建星间无线链路传输速率、星间无线调度以及星内有线调度模型;其次,联合有线和无线链路传输速率以及二者时隙位置关系,建立有线无线融合调度与星上转发时延关联分析模型;最后,为确保时敏业务每次在星上传输的时延稳定性,在时延分析模型基础上以抖动最小为融合调度优化目标,并采用遗传禁忌搜索算法进行求解。仿真结果表明,相比于非融合调度方案,所提融合调度方案的抖动不高于40μs,转发时延平均降低了20%。

基于奇异谱分析的BDS卫星钟差周期项提取

在建立星座自主时间基准时,必须扣除卫星钟差的周期波动,以避免将其引入系统时间。为准确地扣除周期波动,提出一种基于奇异谱分析(SSA)的BDS卫星钟差周期项提取方法。首先,经SSA分解获得钟差信号的多个重构成分;然后,引入重标极差分析方法计算各重构成分的Hurst指数,根据Hurst指数辨识钟差的低频信号主导分量和高频信号随机分量,从而实现周期项的重建提取。对不同类型的BDS卫星钟进行了分析和研究,结果表明:所提方法能够准确提取钟差周期项,所提取周期项的频谱特征比钟差多项式拟合残差的频谱更为清晰;利用多项式拟合方法扣除周期项后,万秒稳和日稳平均分别提升4.1%和2.4%,而利用所提方法扣除周期项后,万秒稳和日稳平均分别提升20.9%和34.1%,提高了卫星钟频率稳定度,为星座自主时间基准的建立提供了基础。

柔性失效卫星能量耗散与运动演化特性研究

随着各国航天活动的不断频繁,在轨失效卫星数量不断增长,为合理规划失效卫星的抢救与维修任务,尽快恢复失效卫星功能,需分析失效卫星的运动演化规律.但目前卫星上往往携带有各类柔性附件,其弹性振动与卫星的姿轨运动存在耦合,在运动演化过程中会不断耗散卫星能量,使卫星运动演化特性与传统刚体卫星不同.本文针对携带柔性附件的失效卫星,建立了适用于长期运动演化分析的姿态-振动耦合动力学模型,研究了卫星能量耗散与运动演化趋势之间的关系,并分析了能量耗散速率的影响因素.结果表明卫星初始角速度、柔性附件的安装位置、结构与材料特性对能量耗散速率影响较大,而柔性附件的初始振动状态对能量耗散速率的影响较小.

不同GNSS在高纬度地区时间传递性能分析

全球卫星导航系统(GNSS)载波相位时间传递技术是高精度时间传递领域的主要研究方法之一,但目前关于该部分的研究主要集中在中低纬度地区,在高纬度地区并不多见。不同GNSS由于星座设计不同,在高纬度地区结构差异较大,因此需要对不同GNSS在高纬度地区的时间传递性能进行分析。实验结果表明,在高纬度地区时间传递中,Galileo稳定度最高,GPS和BDS次之,GLONASS最差。同时因在高纬度地区卫星的高度角普遍偏低,为合理平衡低高度角时可视卫星多和多路径误差大的矛盾,对不同截止高度角下获取的链路时间传递性能进行了分析。结果表明,在5°截止高度角下,高纬度地区的时间传递链路稳定性最好。

空间热环境下带大型天线卫星的最优姿态控制

针对空间热环境下带有大型天线的卫星姿态稳定问题,提出一种基于滑模面的自适应近似最优控制方法。首先考虑天线存在热应力与热振动,给姿态控制系统带来未知非匹配干扰,利用状态观测器在线估计非匹配干扰上界;以此为基础,考虑非匹配干扰影响,构建一种基于干扰估计、具有在线更新能力的性能指标函数。然后设计一种基于滑模面的单层评价神经网络逼近最优性能指标函数,解决了不确定HJB方程求解困难的问题;结合滑模控制律,进一步提高收敛速度。最后,证明了该方法的稳定性。仿真结果表明:考虑地球轨道热环境,在天线温度大幅变化下,该方法能很好地实现带大型天线卫星的姿态稳定。