基于激光雷达的卫星发动机精度测量方法

针对卫星发动机精度测量要求,文章提出了一种基于激光雷达的测量方法。首先利用多个已知位置的靶球建立卫星测量基准坐标系;之后利用高精度平面镜的隐藏点扫描测量功能获取发动机的内部轮廓点云图;最后利用Spatial Analyzer专业测量软件计算出发动机内部的关键几何中心轴线方向。测试结果表明,该测量方法具有较好的精度和重复性,可用于卫星发动机的精度测量。     

基于地球引力变轨的日冕探测器轨道设计

研究了相对黄道面有一定倾角的探测器轨道设计的问题。以金星借力轨道设计为例,分析了轨道偏心率与轨道倾角增量之间的关系。根据C3匹配原理搜索了“地球-中间天体-地球”多天体交会的发射窗口。最后,设计了与地球轨道周期相等的三次地球借力轨道,该轨道倾角可以达到黄纬30°以上。理论分析及仿真结果表明:基于地球引力设计此类轨道时,应采用多天体交会方案,才能既保证地球逃逸能量低,又保证首次飞入地球影响球前轨道偏心率较大的双重指标;同时应采用多次地球借力方案,该方案具有每次借力后轨道偏心率逐渐减小的特点,当其减小到零时,再次借力后轨道倾角不会继续增加。     

The Motion of a Material Point in a Newtonian Field under the Action of Equiangular Thrust

The problems of investigation and optimization of the motion of spacecraft are extensively discussed in the literature. Nevertheless, in many cases a large variety of qualitative characteristics of their motion and of the form of their trajectories are still unclear. In this paper we consider a plane equiangular acceleration of a spacecraft both in a Newtonian field and in its absence (at a large distance from the center of attraction). The general equation of a trajectory of plane acceleration is presented with the introduction of a new variable, an index of an exponent, which allows one to obtain convenient solutions at different values of the time-independent angle of inclination of the vector of thrust to the spacecraft's radius vector (i.e., when equiangular acceleration takes place). Asymptotic solutions are constructed and an interesting fact is revealed. Namely, it is shown that when the center of attraction exists or is absent, for all initial conditions the trajectories appearing at the above equiangular acceleration of a material point tend to the standard logarithmic spirals at a large distance from the center. Specifically, when the value of transverse (perpendicular to the radius vector) thrust is constant, there appears a logarithmic spiral with an angle of inclination to the radius vector equal to 35.264°. Different forms of the trajectory of equiangular acceleration of spacecraft at a low thrust are also studied. The results obtained can be useful for the investigation and choice of optimum space trajectories.     

Cassini Saturn-escape trajectories to Jupiter,Uranus, and Neptune

Potential encore-mission scenarios have been considered for the Cassini mission. In this paper we discuss one of the end-of-life scenarios in which the Cassini spacecraft could perform a Saturn escape via gravity assists from Titan. It is shown that such satellite-aided escape requires a small deterministic maneuver (e.g., Δv<50 m/s), but provides enough energy for the Cassini spacecraft to reach a range of targets in our Solar System, as close to the Sun as the asteroid belt or as far as the Kuiper belt. The escape sequence could be initiated from an arbitrary point during the on-going Cassini mission. Example tours are presented in which the final Titan flyby places the spacecraft into ballistic trajectories that reach Jupiter, Uranus, and Neptune. After years of heliocentric flight, the spacecraft could impact on the target gas giant or perform a flyby to escape from the Solar System (if not to another destination). The concept can be generalized to a new kind of missions, including nested-grand tours, which may involve satellite-aided captures and escapes at more than one planet.     

地月循环轨道动力学建模与计算研究

根据地月循环轨道的概念,按照生成第二类周期轨道的弧段进行分类,并讨论了其共振性与对称性在轨道设计与应用中的作用。然后归纳了三种循环轨道的动力学建模与计算方法及其轨道延拓策略,最后总结了三种方法的利弊和应用轨道类型。对地月系统循环轨道的研究和分析,能够为我国未来载人登月工程提供一种新的思路与理论支持。     

Spatial approaches to moons from resonance relative to invariant manifolds

In this study, the final approach to a moon or other body from resonance is explored and compared to the invariant manifolds of unstable periodic orbits. It is shown that the stable manifolds of planar Lyapunov orbits can act as a guide for the periods or resonances that are required for the final approach in both the planar and spatial problems. Previously developed techniques for the planar problem are expanded for use with resonances and used for comparison with trajectories approaching a moon from these resonances. A similar technique is then used for exploring the relationship of invariant manifolds to approach trajectories in the spatial problem. It is shown that the invariant manifolds of unstable periodic orbits provide insight into the trajectory design, and they can be used as a guide to the more direct approach trajectories.     

The use of solutions to problems of spacecraft trajectory optimization in impulse formulation when solving the problems of optimal control of trajectories of a spacecraft with limited thrust engine: II

As examples of application of the technique suggested in the first part of this work, the problems of optimizing the trajectories of spacecraft transfers between circular coplanar orbits are considered in this second part. During the transfer the spacecraft is controlled by the vector of thrust of a limited-thrust jet engine. The mass consumption is minimized for a limited time of transfer. Extreme trajectories with two and three powered sections (Homan-type and bi-elliptic transfer trajectories) are numerically determined. The solution of these well-studied problems allows one to compare the results of applying the suggested technique with the results of application of other previously used techniques.     

Hill区域内基于推广的Poincaré映射的低能逃逸/捕捉轨道

给出了Hill区域内基于推广的Poincare映射的低能逃逸轨道的计算.文中的推广的Poincare映射需要在相空间中选取两个(而非一个)与流相截的面,即将包含某个天平动点的截面通过轨道来映射到近拱点的通道面上的,在数值上通过总变差减小的Runge-Kutta方法来实现两个相面之间的映射.捕捉轨道则可由Hill三体模型的对称性直接导出.最后,关于Rhea的二维、三维的逃逸和捕捉轨道的仿真结果验证了该方法的精度和鲁棒性.     

An Artificial Neural Network That Uses Coarse Allocentric Coding of Direction to Represent Distances Between Locations in a Metric Space

An artificial neural network was trained to rate the distances between all possible pairs taken from a set of thirteen different cities on the map of Alberta. After learning to solve this problem, the internal structure of the network was analyzed. It was found that in spite of the fact that the network was trained to rate distances, the hidden units in the network were not sensitive to distance at all. Instead, it was found that each hidden unit could be located at a particular latitude and longitude on the map of Alberta, and that at this location each hidden unit was associated with a specific heading. Each hidden unit measured the bearing of each city relative to the hidden unit's heading, and when a stimulus was presented to the network, the hidden units combined the two city bearings and generated an activity level based on this combination. The output units of the network generated an accurate distance rating by combining the directional signals that were being computed by the hidden units. These results are discussed in terms of their implications for theories about cognitive maps, in particular the modularization of distance measurements from directional measurements.     

Trajectories of in-plane periodic solutions of tethered satellite system projected on van der Pol planes

In this paper, in-plane periodic solutions for a dumbbell model in elliptic orbits are searched using bifurcation, and their trajectories are projected on the van der Pol planes. The trajectories projected on the van der Pol plane will be employed as a tool to predict when the control of delayed feedback control will need to act to maintain the periodic motions.     

Venus transfer design by combining invariant manifolds and low-thrust arcs

The design of interplanetary trajectories based on patched circular restricted three body models is gradually becoming a valuable alternative to the classical patched conic approach. The main advantage offered by such a model is the possibility to exploit the manifold dynamics to move naturally far from or toward a body. Generally, propulsive maneuvers are required to match these structures. Low-thrust arcs offer the possibility to have a significant propellant mass reduction when moving from manifold to manifold. The aim of this paper is to present a methodology to design low-thrust trajectories between two planetary orbits connecting the manifolds of two circular three body systems. The approach is based on a grid search on the main parameters governing the solution to identify those trajectories moving within the manifold images on given Poincarè sections. The value of the Jacoby constant of the target libration point periodic orbit is chosen as stop condition for the thrusting phases. Ballistic arcs follow up to the proper Poincarè section intersection. A grid search for an Earth to Venus transfer is presented as test case.     

不确定条件下采用协方差描述函数法的再入轨迹鲁棒优化

Uncertainties are taken into account in reentry trajectory optimization and a robust trajectory optimization model is constructed based on the robust optimization theory. There are computational difficulties in solving this robust trajectory optimization problem due to the random variables associated with the uncertainties. To overcome these difficulties, the covariance analysis describing function technique (CADET) is employed to convert the robust trajectory optimization model into an equivalent deterministic trajectory optimization formulation, which is then solvable by using the existing pseudo spectral method. In the case study, a robust reentry trajectory optimization problem considering the uncertainties of aerodynamic parameters is solved to obtain the robust optimal trajectories. By comparing with the traditional deterministic optimal trajectories, the robust optimal trajectories are significantly less sensitive to the uncertainties of aerodynamic parameters, showing the effectiveness of the presented method.      

The Russian experience in medical care and health maintenance of the International Space Station crews

The main purpose of the medical support system aboard International Space Station (ISS) is crew health maintenance and high level of work capability assurance prior to during and after in space flights. In the present communication the Russian point of view dealing with the problems and achievements in this branch is presented. An overview on medical operations during flight and after finalization of the space missions based on Russian data of crew health and environment state monitoring, as well as data on the inflight countermeasures (prophylaxis) jointly with data on operational problems that are specific to ISS is presented. The report summarizes results of the medical examination of Russian members of the ISS and taxi crews during and after visits to the ISS.     

YES2 optimal trajectories in presence of eccentricity and aerodynamic drag

YES2 (launching 2007) aims to demonstrate a tether-assisted re-entry concept, whereby payload will be returned to Earth using momentum provided from a swinging tether. Deployment takes place in two phases: (1) deployment of 3.5 km of tether to the local vertical and hold, and (2) deployment to 30 km for a swinging cut. Optimal trajectories are determined for both phases after comparing the effect of different cost functions on the deployment dynamics. Closed-loop control is provided by linearizing the dynamics around the optimal trajectories and solving a receding horizon control problem for a set of linear feedback gains. The controllers are tested in a flexible tether model with large disturbances to the hardware model and environmental variables. Closed-loop simulations show that the system can be controlled quite well using only feedback of length and length rate.     

Optimization of low-energy resonant hopping transfers between planetary moons

In response to the scientific interest in Jupiter's Galilean moons, NASA and ESA have plans to send orbiting missions to Europa and Ganymede, respectively. The inter-moon transfers of the Jovian system offer obvious advantages in terms of scientific return, but are also challenging to design and optimize due in part to the large, often chaotic, sensitivities associated with repeated close encounters of the planetary moons. The approach outlined in this paper confronts this shortcoming by exploiting the multi-body dynamics with a patched three-body model to enable multiple “resonant-hopping” gravity assists. Initial conditions of unstable resonant orbits are pre-computed and provide starting points for the elusive initial guess associated with the highly nonlinear optimization problem. The core of the optimization algorithm relies on a fast and robust multiple-shooting technique to provide better controllability and reduce the sensitivities associated with the close approach trajectories. The complexity of the optimization problem is also reduced with the help of the Tisserand–Poincaré (T–P) graph that provides a simple way to target trajectories in the patched three-body problem. Preliminary numerical results of inter-moon transfers in the Jovian system are presented. For example, using only 59 m/s and 158 days, a spacecraft can transfer between a close resonant orbit of Ganymede and a close resonant orbit of Europa.     

基于轨迹成型法星际小推力转移轨道快速设计

给出了一种基于轨迹成型法星际小推力转移轨道的快速设计方法.首先介绍了基于轨迹成型法的有关内容,并通过与Hohmann变轨相对比验证了该方法描述小推力变轨的可用性.鉴于这种方法数学模型收敛性强,计算速度快的特点,以地火转移轨道为例,提出了不同推力条件下发射窗口的搜索方法.最后,利用基于轨迹成型法和真实数值仿真之间误差小、线性度好的特点,通过几次简单的线性迭代设计出小推力转移轨道.     

自由返回轨道的P平面参数快速设计方法

针对自由返回轨道求解过程中地心轨道类型变化造成的B平面参数方法计算失败问题,提出一种基于P平面参数的自由返回轨道快速设计方法。首先,基于轨道半通径参数的普适性,给出了不同轨道类型的P平面参数定义,建立了以P平面参数为求解目标量的自由返回轨道求解模型。其次,给出了基于P平面参数的自由返回轨道快速设计方法,在构建的瞬时地月惯性系下,以平面双二体自由返回轨道作为初值,实现了高精度力模型下的自由返回轨道快速求解。对8种构型自由返回轨道的设计结果表明,P平面参数具有类似于B平面参数的大收敛域,且有效解决了轨道类型变化对计算的影响,可直接应用于中国后续月球探测任务轨道设计。     

Solar Probe Mission with Multiple Gravity-Assist Maneuvers Realized with Conversion Launchers

The trajectories of solar missions that could be realized with conversion launchers are investigated. The insufficient energy resources of the rocket launchers is compensated by multiple gravity-assist maneuvers near terrestrial planets. A method based on the construction of a set of attainability for all the mission trajectories rather than on optimization of separate trajectories is presented, which makes it possible to analyze the problem more widely and to find global extremums using various criteria. Detailed features of the most rational trajectories are given.     

Hydrodynamic Approach to Modeling the Thermal Plasma Distribution around a Moving Charged Satellite

The electric field distribution around a charged satellite in a rarefied magnetospheric plasma influences greatly the densities and trajectories of particles measured by onboard instruments. The simulation of macroparameters of thermal plasma near the moving charged satellite, which is necessary for correction of experimental measurements, encounters considerable computational difficulties. In this work, two three-dimensional models of the electric field distribution around the satellite are considered under the conditions when the Debye length is comparable to the geometrical size of the spacecraft. In the first model a system of hydrodynamic equations of continuity and motion was used, which was solved jointly with the Poisson equation. In the second model the hydrodynamic equation of motion was used for analyzing the motion of large particles by means of the method of particles in a cell. The numerical algorithms and the results of calculations of the potential near the satellite, as well as the distributions of densities of electrons and ions and of volume charge, are considered. The results of test calculations for some situations in the ambient plasma are presented, and the influence of the spatial electric field distribution on the thermal plasma measurements is considered.     

Optimization of interplanetary trajectories for spacecraft with ideally regulated engines using the continuation method

The problem of optimization of interplanetary trajectories is considered for spacecraft with a small-thrust ideally regulated engine. When the maximum principle is used, determination of the optimal trajectory is reduced to solution of a two-point boundary value problem for a system of ordinary differential equations. In order to solve this boundary value problem, the method of continuation in parameter is used, and with the help of it the formal reduction of the boundary value problem to a Cauchy problem is performed. Different variants of the continuation method are considered, including the method of continuation in the gravitational parameter which allows one to find extreme trajectories with a preset angular distance. The issues of numerical realization of the continuation method are discussed, and numerical examples of its use for solving the problems of optimization of interplanetary trajectories are presented.