SAR regional all-azimuth observation orbit design for target 3D reconstruction

Three-dimensional(3D) synthetic aperture radar(SAR)extends the conventional 2D images into 3D features by several acquisitions in different aspects. Compared with 3D techniques via multiple observations in elevation, e.g. SAR interferometry(InSAR) and SAR tomography(TomoSAR), holographic SAR can retrieve 3D structure by observations in azimuth. This paper focuses on designing a novel type of orbit to achieve SAR regional all-azimuth observation(AAO) for embedded targets detection and holographic 3D reconstruction. The ground tracks of the AAO orbit separate the earth surface into grids. Target in these grids can be accessed with an azimuth angle span of360°, which is similar to the flight path of airborne circular SAR(CSAR). Inspired from the successive coverage orbits of optical sensors, several optimizations are made in the proposed method to ensure favorable grazing angles, the performance of 3D reconstruction, and long-term supervision for SAR sensors. Simulation experiments show the regional AAO can be completed within five hours. In addition, a second AAO of the same area can be duplicated in two days. Finally, an airborne SAR data process result is presented to illustrate the significance of AAO in 3D reconstruction.

Orbit Design for Twin-spacecraft Space VLBI

Space Very Long Baseline Interferometry(S-VLBI) is an aperture synthesis technique utilizing an array of radio telescopes including ground telescopes and space orbiting telescopes.It can achieve much higher spatial resolution than that from the ground-only VLBI.In this paper,a new concept of twin spacecraft S-VLBI has been proposed,which utilizes the space-space baselines formed by two satellites to obtain larger and uniform uv coverage without atmospheric influence and hence achieve high quality images with higher angular resolution.The orbit selections of the two satellites are investigated.The imaging performance and actual launch conditions are all taken into account in orbit designing of the twin spacecraft S-VLBI.Three schemes of orbit design using traditional elliptical orbits and circular orbits are presented.These design results can be used for different scientific goals.Furthermore,these designing ideas can provide useful references for the future Chinese millimeter-wave S-VLBI mission.

A Survey of Research on Service-Spacecraft Orbit Design

On-orbit service spacecraft orbit problem has been addressed for decades. The research of on-orbit service spacecraft orbit can be roughly divided into orbit design and orbit optimization. The paper mainly focuses on the orbit design problem. We simply summarize of the previous works, and point out the main content of the on-orbit service spacecraft orbit design. We classify current on-orbit service spacecraft orbit design problem into parking-orbit design, maneuvering-orbit design and servicing-orbit design. Then, we give a detail description of the three specific orbits, and put forward our own ideas on the existed achievements. The paper will provide a meaningful reference for the on-orbit service spacecraft orbital design research.

Orbit design and mission planning for global observation of Jupiter

This paper presents the method created by the National University of Defense Technology(NUDT)team in the 10th China Trajectory Optimization Competition,which entails a 3-year observation mission of 180 regions on Jupiter.The proposed method can be divided into three steps.First,a preliminary analysis and evaluation via an analytical method is undertaken to decide whether the third subtask of the mission,i.e.,exploring the Galilean moons,should be ignored.Second,a near-optimal orbit for magnetic field observation is designed by solving an analytical equation.Third,a set of observation windows and their sequence are optimized using a customized genetic algorithm.The final index obtained is 354.505,ranking second out of all teams partaking in the competition.

Free return orbit design and characteristics analysis for manned lunar mission

A circumlunar free return orbit design model that satisfies manned lunar mission constraints is established. By combining analytical method with numerical method,a serial orbit design strategy from initial value design to precision solution is proposed. A simulation example is given,and the conclusion indicates that the method has excellent convergence performance and precision. According to a great deal of simulation results solved by the method,the free return orbit characters such as accessible moon orbit parameters,return orbit parameters,transfer delta velocity,etc. are analyzed,which can supply references to constitute manned lunar mission orbit scheme.

Point return orbit design and characteristics analysis for manned lunar mission

Point return orbit(PRO) of manned lunar mission is constrained by both lunar parking orbit and reentry corridor associated with reentry position.Besides,the fuel consumption and flight time should be economy.The patched conic equations which are adaptive to PRO are derived first,the PRO is modeled with fuel and time constraints based on the design variables of orbit parameters with clear physical meaning.After that,by combining analytical method with numerical method,a serial orbit design strategy from initial value design to precision solution is proposed.Simulation example indicates that the method has excellent convergence performance and precision.According to a great deal of simulation results by the method,the PRO characteristics such as Moon centered orbit parameters,Earth centered orbit parameters,transfer velocity change,etc.are analyzed,which can supply references to the manned lunar mission orbit scheme.

Orbit design for the Laser Interferometer Space Antenna (LISA)

The Laser Interferometer Space Antenna (LISA) is a joint ESA-NASA mission for detecting low-frequency gravitational waves in the frequency range from 0.1 mHz to 1 Hz, by using accurate laser interferometry between three spacecrafts, which will be launched around 2018 and one year later reach their operational orbits around the Sun. In order to operate successfully, it is crucial for the constellation of the three spacecrafts to have extremely high stability. Based on the study of operational orbits for a 2015 launch, we design the operational orbits of beginning epoch on 2019-03-01, and introduce the method of orbit design and optimization. We design the orbits of the transfer from Earth to the operational orbits, including launch phase and separation phase; furthermore, the relationship between energy requirement and flight time of these two orbit phases is investigated. Finally, an example of the whole orbit design is presented.

Design of Geodetic SVLBI Satellite Orbit and Its Tracking Network

SVLBI (空间很长的基线干涉量度) 在测地学和地球动力学有一些重要潜在的应用，为哪个最困难的任务是精确决定一颗 SVLBI 卫星的轨道。这个工作学习将可能能决定一颗空间 VLBI 卫星的轨道的几种技术。然后，根据为测地学的学习和 GNSS 的几何学的卫星和要求的类型和特征(GPS，伽利略) 追踪空间 VLBI 卫星的卫星， SVLBI 卫星(TEST-SVLBI ) 的六个 Keplerian 元素被决定。一个程序被设计由网络，追踪的网络 ofTEST-SVLBI 与被设计的车站分析不同高度的空格的范围区域。由网络追踪 TEST-SVLBI 的效率被学习，并且结果被介绍。

Design and control of multiple spacecraft formation flying in elliptical orbits

Spacecraft formation flying is an attractive new concept in international aeronautic fields because of its powerful functions and low cost. In this paper, the formation design and PD closed-loop control of spacecraft formation flying in elliptical orbits are discussed. Based on two-body relative dynamics, the true anomaly is applied as independent variable instead of the variable of time. Since the apogee is considered as the starting point, the six integrating constants are calculated. Therefore, the algebraic solution is obtained for the relative motion in elliptical orbits. Moreover, the formation design is presented and both circular formation and line formation are provided in terms of an algebraic solution. This paper also discusses the PD-closed loop control for precise formation control in elliptical orbits. In this part, the error-type state equation is put forward and the linear quadratic regulator （LQR） method is used to calculate PD parameters. Though the gain matrix calculated from LQR is time-variable because the error-type state equation is time variable, the PD parameters are also considered as constants because of their small changes in simulation. Finally, taking circular formation as an example, the initial orbital elements are achieved for three secondary spacecraft. And the numerical simulation is analyzed under PD formation control with initial errors and J2 perturbation. The simulation results demonstrate the validity of PD closed-loop control scheme.

Demonstration on the indexes design of gravity satellite orbit parameters in the low-low satellite-to-satellite tracking mode

Combining with the exigent demand of the development of satellite gravimetry system in China, aiming at the determination of technical indexes of gravity satellite orbit parameters, on the basis of the numerical experiments and results analysis, the design indexes of gravity satellite orbit height, inter-satellite range and the orbit inclination are analyzed and calculated, and the issues towards twin gravity satellites such as coherence requirement of the orbit semi-major axes, control requirement of the pitch angle and time interval requirement to keep twin satellites formation in mobility are diseussed. Results show that the satellite orbit height is 400 km to 500 km, the inter-satellite range is about 220 km, the satellite orbit inclination is between polar orbit and sun-synchronous orbit, the semi-major axes difference of twin satellites orbit is within ± 70. 146 m, the pitch angle of twin satellites is about 0.9 degree, and the time interval to keep twin satellites formation in mobility is 7 days to 15 days.

固体运载火箭发射轨道一种快速生成方法

通过采用牛顿迭代法快速优化发射方位角,克服了发射方位角初值偏差过大的缺陷,极大缩短了优化时间。通过采用基于特征参数网格化的程序角优化设计技术,建立了程序角设计参数数据库,在机动发射的情况下能够快速进行参数插值,避免了大量优化计算过程,有力地支持了机动发射情况下发射轨道的快速生成。最后通过仿真证明设计算法的有效性和正确性。

基于参数识别应用Backstepping design控制Lü′s混沌吸引子

混沌控制在最近十几年的研究中已经取得了长足的进展,形成了许多比较成熟而且有效的控制技术和方法,如:OGY控制、线性状态空间反馈等 但对于带有未知参数的系统,前面提到的方法常常无法达到预期的控制 通过构造识别函数识别L櫣′s混沌系统的未知参数,然后应用Backsteppingdesign控制L櫣′s混沌吸引子,将L櫣′s混沌吸引子控制到一个稳定的周期轨道。

长期拟周期近直线晕轨道高效设计方法

面向未来近月空间站部署需求,提出了一种三级修正的长期拟周期近直线晕轨道(NRHO)设计方法。首先,设计了新的离散点选取策略,降低了对参数敏感区域的打靶需求,提高了多点打靶法计算多圈次拟周期NRHO的收敛性能。然后,基于NRHO的对称特性,给出了初始拟周期NRHO圈次延续方法和滚动时域长期拟周期NRHO生成方法,根据拟周期NRHO近月点半径设计了修正策略。使用不同的NRHO进行仿真实验,生成了维持500圈约10年的长期拟周期NRHO。仿真结果表明本方法提高了收敛效率,且能有效生成地月空间长期拟周期NRHO。

面向高轨空间的北斗导航性能增强星座选型研究

由于高轨空间超出北斗卫星导航系统的正常服务区域,导航信号微弱、可见性差,难以实现高轨飞行器全程稳定可靠的导航定位服务。提出了以空间卫星为时空基准传递平台,向高轨空间区域发射导航信号,从而提高高轨飞行器导航性能的方法,并展开面向高轨空间的北斗导航性能增强星座选型研究。基于卫星可见性、精度衰减因子(DOP)、信号接收门限和所需增强卫星数目等评估指标,仿真分析了基于LEO星座、MEO星座和HEO星座的北斗导航增强性能。

空间引力波探测无拖曳技术现状与趋势

航天器无拖曳控制是实现引力波空间探测科学平台超静超稳运行的核心关键技术之一。目前,国内外各研究机构对航天器系统的动力学与控制进行了深入研究,并针对不同的探测频段需求提出了不同的探测任务。根据探测任务进行了航天器编队设计与控制的详细介绍和分析,对涉及的无拖曳与姿态控制、高精度惯性传感器与执行机构等原理和理论方法进行了深入的剖析。针对现已开展的空间引力波探测无拖曳航天器在轨飞行的演示验证整体情况进行详述和分析。在此基础上,提出后续开展相关研究中亟待解决的关键问题,指出未来无拖曳航天器系统动力学与控制的研究热点和趋势。

“巴遥一号”卫星双相机热设计及验证

针对“巴遥一号”卫星相机主体全寿命周期内温度应保持较高稳定性和均匀性的任务要求。通过建立热阻网络模型,分析热控设计的重点和难点,并提出有效管理热量传递和合理设计控温方式的方法;利用结构热控一体化设计解决双相机焦面电路高功率密度热量排散问题,采用直接与间接相结合的控温方式提高主光学结构温度稳定性。通过热仿真分析和热平衡试验验证热设计的准确性。相机入轨4年后1个月内的在轨温度变化显示,相机各部分温度水平和温度稳定性满足设计指标要求,镜头的温度波动范围在0.09~0.17℃,CCD的温度波动范围在0.93~4.30℃,表明相机热控设计合理有效。以上设计实践可为双相机一体化热控设计提供借鉴。

空间多目标掠飞观测接近轨道设计方法

针对当前的天基空间观测任务中存在的观测效率低、燃料不足等问题,基于粒子群算法与空间多目标观测模型提出一种空间多目标掠飞观测的接近轨道设计方法以实现观测器在不变轨道的情况下实现对特定多目标的近距离掠飞观测。结合两轨道卫星的距离计算与天光地影条件建立空间多目标观测模型。利用粒子群算法对观测器轨道六根数优化,得到对特定多目标的综合最近距离观测的最优轨道,以轨道高度差产生的周期差抵消目标与交线处位置的相位差,以消耗时间为代价得到了最省燃料的方式。利用仿真说明了该轨道设计方法的有效性。

载人航天器可更换舱外载荷接口通用设计与应用

为了充分利用空间暴露资源,载人航天器往往设计支持少量或大规模暴露试验的开展,暴露试验项目包括专用舱外载荷和可更换舱外载荷。载人航天器可更换舱外载荷是在航天员或机械臂照料下通过舱外载荷接口设备实现在轨安装和更换。针对不同可更换舱外载荷的接口需求不尽相同、不同载人航天器之间或同一载人航天器不同舱段之间的舱外载荷接口设备不同、载人航天器暴露试验平台在地面阶段无法与全部可更换舱外载荷进行接口匹配等技术难点,文章提出一种载人航天器可更换舱外载荷接口模块化、标准化的通用设计方法。舱外载荷接口按照安装接口、供电接口、信息接口、热接口等功能分类进行模块化设计,各功能模块相互独立;各功能模块对外接口采用标准化设计,同一类型接口的形式及定义均相同。经过在轨飞行应用,表明载人航天器可更换舱外载荷接口通用设计方法可行、正确,为载人航天器滚动开展较大规模的空间科学实验与技术试验提供了有力支撑。

多层星座网络仿真教研系统设计与实现

随着6G架构的逐渐清晰与天空地海一体化需求的明确,非静止轨道卫星星座的发展进入了空前繁荣的阶段,美国STARLINK、Kuiper、英国OneWeb、中国卫星互联网星座等系统处于建设与部署的关键阶段。其中,多层星座网络的设计是解决全球无缝覆盖与随需接入的重要研究对象。然而,受限于卫星通信系统建设成本高、系统复杂、正式系统运行受国家管控等,真实系统难以直接应用于高等院校的实验教学工作。目前卫星通信相关课内实验及综合实验主要以机房参观、实验箱分组实验等方式进行,既缺乏直观的系统认识,且参与度较低。针对上述需求,该文设计了一套基于“轨道建模+系统分析+动态显示”的仿真系统,并利用快照仿真的思想实现了非静止轨道卫星星座的高动态性分析过程。实验结果表明,该系统能够较好地完成大规模多层星座网络的覆盖分析、同频干扰分析等功能,可支撑卫星通信、无线通信、通信综合实验等课程的实践需求。

NEW METHOD OF FORMATION DESIGN FOR BOTH GMTI AND INSAR USING DISTRIBUTED SATELLITES

This letter proposes a method for designing a specific formation of satellites where the flying motion only exists in a circle orbit plane of the reference satellite, which means that the orbit eccen- tricity is zero. This method combines the Hill equation, the Kepler equation, and the geometrical meaning of orbit elements. It creates the redundancy condition to simplify the deducing process, utilizes multiple conditions to solve the orbit elements for the satellite formation, and obtains the analytical relationship of the orbit elements for the formation satellites with the formation parameters and the orbit elements of the reference satellite. Using these formulations, the orbit elements and formation parameters for the formation satellites can be solved for the given orbit elements of the reference satellite. The letter describes the proposed double-ellipse formation for both GMTI and InSAR, and the validity of the formation is demonstrated via simulation.