Hopper concepts for small body landers

The investigation of small bodies, comets and asteroids, can contribute substantially to our understanding of the formation and history of the Solar System. In situ observations by landers play an important role in this field.     

小行星星壤低速侵入过程力学响应的实验研究

为研究小行星星壤在低速侵入过程中的力学响应,利用落塔实验舱构建微重力环境,制备典型的无黏性星壤模拟物,利用恒速加载方式模拟采样器等装置侵入星壤的过程,测量了模拟物的承载强度和边界应力随沉降深度的变化,并记录了模拟物表面形貌的变化过程。实验结果表明,微重力下星壤的承载能力较地球重力环境下大大降低,其响应特性更接近于流体,且与侵入速度、星壤孔隙率、颗粒粒径级配、侵入体尺寸等因素相关联。实验结果可为小行星表面着陆和采样装置的设计与验证提供重要数据支撑。     

On two kinds of intermediate orbits for asteroid explorations

In the paper, two kinds of intermediate orbits for asteroid explorations are proposed. One is around the collinear libration points of the Sun-asteroid restricted three-body problem. The other is around the asteroid itself. The first kind of intermediate orbit is applicable to asteroids with known masses, while the second is suitable for asteroids with unknown or negligible masses. Analytical solutions of these two intermediate orbits in the simplified models are introduced first, and then numerical algorithms are used to refine them to obtain the true orbits in the real force model. At last, the problem of station-keeping is addressed. The linear optimal feedback control law is used, and numerical simulations are made to both kinds of intermediate orbits. The results show that both kinds of orbits are feasible. The cost is reasonable and mainly depends on the initial insertion error.     

从月球逃逸探测小行星的发射机会搜索

从月球逃逸探测小行星的发射机会搜索因需考虑日、地、月引力的影响而使问题变得复杂。针对该多体系统的发射机会搜索问题,提出了一种分层渐近的搜索方法。该方法首先通过分析地月系质心与小行星的几何关系,搜索从地月系质心到小行星的发射机会,进而以地月运动为研究对象,推导出了从月球轨道切向逃逸机会的判别条件,并基于此判别条件及等高线图法对逃逸机会进行了搜索。同时,为提高所得发射机会在多体模型下的轨道修正收敛性,给出了基于月心逃逸轨道参数为终端约束的日-地与日-地-月动力学模型的轨道渐近修正方法。最后,以近地小行星(3908)Nyx和(190491)2000 FJ20为例,搜索其从月球逃逸的发射机会,仿真计算表明了该方法的有效性。     

Decision program on asteroid threat mitigation

The Association of Space Explorers Committee on Near-Earth Objects (NEOs) and its Panel on Asteroid Threat Mitigation have prepared a decision program to aid the international community in organizing a coordinated response to asteroid impact threats. The program is described in the ASE's report, Asteroid Threats: A Call for Global Response, which will be considered by the United Nations Committee on the Peaceful Uses of Outer Space in its 2009 sessions. The findings and recommendations of this report are presented here as well as some of the major implications of the complex decision-making involved in developing a coordinated international response to the challenge of protecting the Earth from NEO impacts.     

航天器相对运动水滴型悬停轨道研究

对航天器相对运动的C-W方程进行了分析,提出了航天器相对运动轨道设计中的一种水滴型悬停轨道,能够实现航天器相对空间目标在一定范围内进行悬停,并且只需使用脉冲速度增量控制即可实现长时间的悬停。文章对悬停轨道的悬停周期与目标航天器轨道参数和悬停位置的关系,以及悬停控制所需的速度增量ΔV进行了分析,给出了进行悬停轨道选择及设计的工程方法,并对C-W方程的状态转移矩阵进行了推导,得到了由常规的后方伴飞轨道使用脉冲速度控制方案进入目标星正下方的悬停位置的初始速度增量、转移时间及末端速度增量。根据分析结果,水滴型悬停轨道有利于工程实现,其设计方法可以应用于航天器在轨服务、侦察、巡视等任务的轨道设计。     

Conceptual design of a hypervelocity asteroid intercept vehicle (HAIV) and its flight validation mission

An intercept mission with nuclear explosives is the most effective of the practical mitigation options against the impact threat of near-Earth objects (NEOs) with a short warning time (e.g., much less than 10 years). The existing penetrated subsurface nuclear explosion technology limits the intercept velocity to less than approximately 300 m/s. Consequently, an innovative concept of blending a hypervelocity kinetic impactor with a subsurface nuclear explosion has been developed for optimal penetration, fragmentation, and dispersion of the target NEO. A proposed hypervelocity asteroid intercept vehicle (HAIV) consists of a kinetic-impact leader spacecraft and a follower spacecraft carrying nuclear explosives. This paper describes the conceptual development and design of a baseline HAIV system and its flight validation mission architecture for three mission cost classifications (e.g., $500 M, $1 B, and $1.5 B).     

Dawn′s exploration of Vesta

On 16 July 2011, after completing nearly four years of interplanetary flight, Dawn entered orbit around (4) Vesta, the second most massive body in the main asteroid belt. Dawn used solar electric propulsion to spiral to six different orbits to accomplish its science campaign. Although the transfers to progressively lower orbits presented significant challenges, all were executed smoothly. During its nearly 14 months in orbit, Dawn spiraled down to 210 km above the surface and back up before initiating the gradual departure to travel to dwarf planet (1) Ceres for a 2015 rendezvous. Dawn′s exploration of Vesta has shown it to be geologically complex and fascinating, resembling terrestrial planets more than typical asteroids. Among the principal features is a 500-km-diameter impact basin within which is the second tallest mountain known in the solar system. This paper presents Dawn′s operations at Vesta and summarizes the principal findings.     

基于分段常值推力的水滴悬停构型控制策略

针对航天器编队飞行任务对相对运动控制的要求,研究了在分段常值推力控制下航天器受迫绕飞构型的设计与控制问题。首先,基于脉冲控制下的水滴悬停构型,提出了多段常值推力控制实现水滴悬停构型的打靶方程;将打靶方程转化为求解极值问题,采用最小二乘法来求解;分析了一段常值推力可行性。然后,以连续常值小推力控制方程为基础,推导了小邻域定理,分析了近距离相对运动条件下两段常值推力控制的可行性;针对可能出现求解精度差的问题,提出了小推力增量方程来修正精度,并证明在靠近理想解的情况下多次迭代可以趋近于理想解。最后,通过数值仿真实现常值小推力控制下的水滴悬停相对运动。数值仿真结果表明常值小推力控制策略可行,研究成果完善了航天器受迫绕飞构型设计与控制的相关理论,为工程应用提供参考。      

非合作目标追踪与相对状态保持控制技术研究

基于考虑J2摄动影响的改进Hill方程数学描述,将最优机动问题转化为标准线性规划问题,为在轨服务系统对非合作目标的接近过程进行路径规划,针对卫星跟踪以及悬停的特殊相对运动状态设计控制方法,实现近距离相对轨道的精确控制.最后通过数学仿真验证方案的正确性和有效性.