基于遗传算法的挠性航天器大角度机动的变结构控制

为改善带挠性梁航天器大角度机动的变结构控制精度，在建立挠性系统动力学模型的基础上，基于喷气一飞轮执行机构工作模式，设计了简单易行的滑模变结构控制策略，并采用遗传算法(GA)优化了滑动平面和边界层厚度。仿真结果表明，优化后的控制器能对航天器的大角度机动进行有效控制。     

Resonant motion, ballistic escape, and their applications in astrodynamics

A special set of solutions governing the motion of a particle, subject to the gravitational attractions of the Earth, the Moon, and, eventually, the Sun, is discussed in this paper. These solutions, called resonant orbits, correspond to a special motion where the particle is in resonance with the Moon. For a restricted set of initial conditions the particle performs a resonance transition in the vicinity of the Moon. In this paper, the nature of the resonance transition is investigated under the perspective of the dynamical system theory and the energy approach. In particular, using a new definition of weak stability boundary, we show that the resonance transition mechanism is strictly related to the concept of weak capture. This is shown through a carefully computed set of Poincaré surfaces, at different energy levels, on which both the weak stability boundary and the resonant orbits are represented. It is numerically demonstrated that resonance transitioning orbits pass through the weak stability boundaries. In the second part of the paper the solar perturbation is taken into account, and the motion of the resonant orbits is studied within a four-body dynamics. We show that, for a wide class of initial conditions, the particle escapes from the Earth–Moon system and targets an heliocentric orbit. This is a free ejection called a ballistic escape. Astrodynamical applications are discussed.     

Energisation of O+ and O+ 2 Ions at Mars: An Analysis of a 3-D Quasi-Neutral Hybrid Model Simulation

We have studied the loss of O⁺ and O⁺ ₂ ions at Mars with a numerical model. In our quasi-neutral hybrid model ions (H⁺, He⁺⁺, O⁺, O⁺ ₂) are treated as particles while electrons form a massless charge-neutralising fluid. The employed model version does not include the Martian magnetic field resulting from the crustal magnetic anomalies. In this study we focus the Martian nightside where the ASPERA instrument on the Phobos-2 spacecraft and recently the ASPERA-3 instruments on the Mars Express spacecraft have measured the proprieties of escaping atomic and molecular ions, in particular O⁺ and O⁺ ₂ ions. We study the ion velocity distribution and how the escaping planetary ions are distributed in the tail. We also create similar types of energy-spectrograms from the simulation as were obtained from ASPERA-3 ion measurements. We found that the properties of the simulated escaping planetary ions have many qualitative and quantitative similarities with the observations made by ASPERA instruments. The general agreement with the observations suggest that acceleration of the planetary ions by the convective electric field associated with the flowing plasma is the key acceleration mechanism for the escaping ions observed at Mars.     

Planetary Magnetic Dynamo Effect on Atmospheric Protection of Early Earth and Mars

In light of assessing the habitability of Mars, we examine the impact of the magnetic field on the atmosphere. When there is a magnetic field, the atmosphere is protected from erosion by solar wind. The magnetic field ensures the maintenance of a dense atmosphere, necessary for liquid water to exist on the surface of Mars. We also examine the impact of the rotation of Mars on the magnetic field. When the magnetic field of Mars ceased to exist (about 4 Gyr ago), atmospheric escape induced by solar wind began. We consider scenarios which could ultimately lead to a decrease of atmospheric pressure to the presently observed value of 7 mbar: a much weaker early martian magnetic field, a late onset of the dynamo, and high erosion rates of a denser early atmosphere.     

变结构制导规律及其实现

由于变结构控制的滑动模态具有完全的自适应性,不必全面研究系统的各种摄动及外干扰,只需根据高速度大机动目标的特点,对其实现自适应,将各种干扰及偏差的影响归人有关增益系数上加以考虑。应用变结构滑膜控制理论,推导了出一种适用于拦截高速大机动目标的空间制导规律,该制导规律能将系统引向滑动面并保持在其上运动。算例仿真证明,变结构项保证了对目标机动的鲁棒性,简单易行利于工程实现。     

面向海洋机动目标跟踪监视的卫星重构组网优化与仿真

摘要： 针对海洋机动目标跟踪监视问题，提出通过卫星相位重构调整进行机动目标搜索跟踪的监视策略，构建地理坐标系下机动目标航位预测模型及基于霍曼转移的卫星调相组网方式，并采用NSGA II算法进行优化求解，对比分析卫星重构组网前后的机动目标发现概率.仿真结果表明：在卫星能量消耗允许范围内进行重构组网，能够有效提升对机动目标的发现概率，为海洋机动目标的搜索跟踪问题提供了一定的方法支持.     

利用逃逸能量的太阳帆最快交会轨迹优化

讨论了运载火箭的逃逸能量产生的初始速度增量对太阳帆最短时间交会问题的影响,将逃逸能量的影响处理为端点时刻状态方程受不等式约束的最优控制问题,利用间接法得到了对应的两点边值问题的求解模型。结果表明,利用该模型可以计算逃逸能量最佳的利用量,而最优的转移轨迹并非总是对应于最大的逃逸能量,因此合理利用逃逸能量能够有效缩短飞行时间。相对于一般的不考虑逃逸能量的太阳帆轨迹优化模型,本文中提出的模型能够有效利用末级火箭的助推能力,同时有效缩短了太阳帆的任务飞行时间,对于工程应用具有更实际的参考价值。     

CHANG'E-2 lunar escape maneuvers to the Sun–Earth L2 libration point mission

This paper addresses lunar escape maneuvers of the first Chinese Sun–Earth L2 libration point mission by the CHANG'E-2 satellite, which is also the world's first satellite to reach the L2 point from a lunar orbit. The lunar escape maneuvers are heavily constrained by the remaining propellant and the condition of telemetry, track and command, among others. First, these constraints are analyzed and summarized to design a target L2 Lissajous orbit and an initial transfer trajectory. Second, the maneuver mathematical models are studied. The multilevel maneuver schemes which consist of phasing maneuvers and a final lunar escape maneuver are designed for actual operations. Based on the scheme analysis and comparison, the 2-maneuver scheme with a 5.3-h-period phasing orbit is ultimately selected. Finally, the mission status based on the scheme is presented and the control operation results are discussed in detail. The methodology in this paper is especially beneficial and applicable to a future multi-mission instance in the deep space exploration.     

机载雷达目标跟踪与航迹信息提取

针对机动目标跟踪中航迹信息提取精度不高的问题,提出一种ECEF坐标系下基于交互多模型的多机协同跟踪算法。首先,各载机以ECEF坐标系为融合中心对目标量测进行无偏转换处理,以有效减小量测转换误差对目标跟踪的影响;然后,利用交互多模型的方法对目标进行融合跟踪,以进一步提高目标机动时的跟踪精度;最后,通过二次滤波的方法,来有效实现目标航迹信息的精确提取。仿真结果表明,该算法可较好地提高目标机动时的跟踪精度和航迹信息提取精度。     

组合体机动中可变形桁架运动规划研究

目前对空间组合体中可变形桁架（VariableGeometryTruss,VGT）运动规划问题的研究集中在各级均为单自由度或离散二状态等简单结构的情形,未解决所有可调长度杆都能够自由运动的复杂结构运动规划问题。文章根据组合体的几何关系,建立了递推位姿运动学模型,再由自由漂浮系统动量守恒,建立了微分运动学模型。给出了单级VGT变化序列与运动时间分开设计的两步运动规划方法,并在优化目标中加入能量项,给出了多级冗余VGT的运动规划方法。最后通过仿真验证了算法的有效性,在算例中优化指标为J=0.8798,该方法对以VGT作为空间操作机构的组合体研究具有一定工程指导意义。