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.     

Private property rights on asteroid resources: Assessing the legality of the ASTEROIDS Act

On June 10, 2014, a bill proposing to establish and protect (private) property rights on asteroid resources was introduced in the US House of Representatives.Regardless of its effective chances to become law, the presentation of the Bill raises numerous legal questions, particularly concerning the status of extraterrestrial natural resources and the consistency of what the Bill suggests with international space law.The purpose of the present viewpoint is to address and clarify the above questions.     

Optimal flights to near-Earth asteroid

The spacecraft flights to the Near-Earth asteroid in order to give an impact influence on the asteroid, correct its orbit and prevent the asteroid’s collision with the Earth are analyzed.In the first part, the impulse flights are analyzed in the Lambert approach. There are determined the optimal trajectories maximizing the asteroid deviation from the Earth.In the second part, the flights with the chemical and electric-jet engines are analyzed. The high thrust is used to launch the spacecraft from the geocentric orbit, and the low thrust is applied for the heliocentric motion. On the base of optimal impulse transfer, the optimal low thrust trajectories are determined using Pontryagin maximum principle.The numerical results are given for the flight to the asteroid Toutatis. Parameters of the spacecraft impact on the asteroid are determined. The asteroid deviation from the Earth caused by the spacecraft influence is presented.     

载人小行星探测的任务特点与实施途径探讨

介绍了载人小行星探测的发展现状,对目前美国基于"猎户座"飞船的载人小行星探测的概要方案进行了描述,包括探测器系统组成、运载火箭和飞行方案等内容。从速度增量、目标星引力等方面,分析了载人小行星探测的任务特点,并与载人火星探测、载人月球探测以及无人小行星探测的任务特点进行了比较。给出了载人小行星探测的实施途径建议,包括目标星选择、载人飞船系统设计等。讨论了其所涉及的推进、星际飞行安全保障、小行星表面行走等关键技术。研究结果可为我国开展载人深空探测提供参考。     

The Aster project: Flight to a near-Earth asteroid

The information on the project being developed in Brazil for a flight to binary or triple near-Earth asteroid is presented. The project plans to launch a spacecraft into an orbit around the asteroid and to study the asteroid and its satellite within six months. Main attention is concentrated on the analysis of trajectories of flight to asteroids with both impulsive and low thrust in the period 2013-2020. For comparison, the characteristics of flights to the (45) Eugenia triple asteroid of the Main Belt are also given.     

我国小行星探测发展思路及关键技术探讨

介绍了国外小行星探测的发展状况,指出小行星探测正从飞越和伴飞探测向表面软着陆取样返回探测发展,从无人探测向载人探测发展,向多目标探测以及与新技术验证相结合的发展趋势和特点。提出我国小行星探测应分4步走的发展规划和发展思路建议,并论述了小行星探测包括载人小行星探测需要解决的轨道设计、自主采样等关键技术。以上建议和研究可为我国制定小行星深空探测战略规划提供参考。     

Working and walking on small asteroids with circumferential ropes

The low gravity of a small asteroid would present a challenge for an astronaut attempting to work on its surface. Extravehicular activities (EVAs) of the sophistication of the Apollo Moon missions are not likely to be possible if astronauts attempt to walk freely on the asteroid, hover above its surface, or anchor locally into the regolith. Manipulating large rocks, drilling, and excavating at multiple locations is a high priority science objective, but would be difficult without a hold-down mechanism. If the asteroid has even a small rotation rate, maneuvering precisely over its surface could be cumbersome. A plausible means of conducting complex EVAs is to tie ropes entirely around the asteroid, under which the astronaut is pushed downward onto the asteroid surface by the tension in the rope. The downward force provides an artificial gravity that permits the astronaut to drill, excavate, hammer, and carefully document materials on the surface without the worry of being thrown from the asteroid. An astronaut could also use the ropes as handholds or guides to maneuver freely over the surface.     

Working and walking on small asteroids with circumferential ropes

The low gravity of a small asteroid would present a challenge for an astronaut attempting to work on its surface. Extravehicular activities (EVAs) of the sophistication of the Apollo Moon missions are not likely to be possible if astronauts attempt to walk freely on the asteroid, hover above its surface, or anchor locally into the regolith. Manipulating large rocks, drilling, and excavating at multiple locations is a high priority science objective, but would be difficult without a hold-down mechanism. If the asteroid has even a small rotation rate, maneuvering precisely over its surface could be cumbersome. A plausible means of conducting complex EVAs is to tie ropes entirely around the asteroid, under which the astronaut is pushed downward onto the asteroid surface by the tension in the rope. The downward force provides an artificial gravity that permits the astronaut to drill, excavate, hammer, and carefully document materials on the surface without the worry of being thrown from the asteroid. An astronaut could also use the ropes as handholds or guides to maneuver freely over the surface.     

同步双小行星系统共振轨道设计

研究了同步双小行星系统中共振轨道的设计方法及演化规律。首先，基于双椭球模型建立探测器运动方程，并给出共振轨道初值选取方法。然后，利用改进并行打靶法，提出一种双小行星系统平面共振轨道两步修正方法。同时结合稳定性理论及分岔理论，给出双小行星系统三维共振轨道生成和延拓方法；最后，以双小行星系统1999KW4为例，设计了共振比为1∶1,1∶2,1∶3,1∶4,2∶3的平面和空间共振轨道族，并分析了共振轨道的特性及轨道周期和轨道能量的变化规律。给出的双小行星系统中共振轨道的设计方法具有普适性，对未来双小行星系统探测任务中的轨道设计具有一定的参考意义与借鉴价值。     

System design of the Hayabusa 2—Asteroid sample return mission to 1999 JU3

The Japan Aerospace Exploration Agency is currently developing the second asteroid sample return mission, designated as Hayabusa 2. Following the successful return of Hayabusa from the asteroid “Itokawa”, Hayabusa 2 is designed as a round-trip mission to the asteroid “1999 JU3”. The 1999 JU3 is a C-type asteroid, which is believed to contain organic matter and hydrated minerals. Thus, it is expected that successful sample collection will provide additional knowledge on the origin and evolution of the planets and, in particular, the origin of water and organic matter. The current mission scenario will enable the spacecraft to reach 1999 JU3 in the middle of 2018 and perform an asteroid proximity operation for 1.5 years. Three touch downs for sampling and one 2-m-class crater generation by means of a high-speed impact operation are planned during the asteroid proximity operation. The samples are to be brought back to the Earth by a re-entry capsule. The present paper describes the system design of Hayabusa 2, some key technical challenges of the mission, and the development status.     

序列凸优化的小天体附着轨迹优化

针对小天体附着多约束轨迹优化问题，提出一种基于序列凸优化的轨迹优化方法。首先采用内球谐引力场模型对目标小天体附近的不规则引力场进行精确建模，内球谐引力场模型是对经典球谐系数法的改进，形式简单，计算量小，并且克服了经典球谐系数模型在形状不规则的小天体附近不收敛的问题。对于小天体附着多约束轨迹优化问题，通过约束松弛、线性化、离散化过程，转化为一个可以迭代求解的二阶锥规划问题（SOCP），进而采用内点法进行解算。数学仿真结果显示，优化结果符合各项约束条件，以零速度到达了目标着陆点，且符合燃耗最优的优化目标。利用序列凸优化算法进行小天体附着燃耗最优轨迹设计，推导简便，计算速度快，精度高，具有应用价值。     

一种提升近地小行星防御中拦截效率的方法

利用核爆直接炸毁小行星或改变小行星的轨道以避免其与地球相撞,是近地小行星防御最主要的手段之一。文章基于美国爱荷华州立大学的超高速小行星拦截器(HAIV)概念,提出一种将原撞击引导器改为长杆撞击器的方案,采用自主研发的欧拉型冲击动力学仿真软件NTS模拟长杆撞击器对小行星连续开坑的过程,并在仿真中加入能量源以模拟核爆装置在不同深度爆炸对小行星产生的偏转与破坏效应。研究结果表明,采用长杆撞击器并合理控制撞击速度,能够引导核爆装置进入更深的地下爆炸,从而更加高效地耦合核爆能量,提升偏转小行星或直接摧毁小行星的能力。     

不规则形状小行星引力环境建模及 球谐系数求取方法

在实施小行星探测任务之前,需要对不规则形状小行星的引力场有一个清楚的认识,以便于进行环绕或着陆小行星的轨道设计。文章提出了一种小行星引力场建模及球谐系数的求取方法。首先,由多面体模型方法重构出小行星外部的引力环境并以此作为虚拟观测量。在此基础上,根据球谐系数与引力势能间的关系,通过求解超定线性方程组得到小行星引力场的各阶次球谐系数。与传统的将小行星近似成三轴椭球体进而计算球谐系数的方法相比,该方法可大幅度提高引力场建模的精度。通过与由NEAR探测器轨道数据解算的Eros433小行星的球谐系数比较表明,其最大误差不超过6%。计算表明,该方法可以为小行星探测任务发射前的轨道设计提供更为精确的数据。     

航天器环绕小行星Ivar的运动分析

将小行星Ivar近似为三轴椭球体，给出了非球形引力势函数，建立了航天器环绕小行星Ivar的轨道动力学方程。利用Jacobi积分常数绘制了航天器在Ivar周围的零速度曲线，并分析了航天器的可能运动区域，给出了航天器不碰撞小行星Ivar的边界条件及不同偏心率下的近拱点半径。分析了小行星Ivar扁率和椭率对环绕轨道的影响，数学仿真结果表明：在一个轨道周期内，顺行轨道的开普勒能量、轨道角动量、偏心率和近拱点半径变化较大，而逆行轨道的相应参数变化较小。     

Estimation of the determination accuracy of orbit parameters of the apophis asteroid from measurement results

An analysis of the existing astrometric and radar observations of the Apophis asteroid is performed. On the basis of this analysis, characteristics of future measurements of the asteroid orbit and limitation on their conduction are accepted. A proposed launching of a spacecraft to the asteroid in order to obtain high-accuracy measurements of its distance and radial velocity is also considered. Trajectories of the flight to the asteroid in 2012–2022 are studied. Estimates of the accuracy of the Apophis position determination at various sets of both available and planned measurements at various numbers of determined parameters are obtained. The method of estimating accuracy is similar to that used in [1] for the Vega project.     

Equilibrium attitude and stability of a spacecraft on a stationary orbit around an asteroid

The stationary orbits around an asteroid, if exist, can be used for communication and navigation purposes just as around the Earth. The equilibrium attitude and stability of a rigid spacecraft on a stationary orbit around a uniformly-rotating asteroid are studied. The linearized equations of attitude motion are obtained under the small motion assumption. Then, the equilibrium attitude is determined in both cases of a general and a symmetrical spacecraft. Due to the higher-order inertia integrals of the spacecraft, the equilibrium attitude is slightly away from zero Euler angles. Then necessary conditions of stability of this conservative system are analyzed based on the linearized equations of motion. The effects of different parameters, including the harmonic coefficients C₂₀ and C₂₂ of the asteroid and higher-order inertia integrals of the spacecraft, on the stability are assessed and compared. Due to the significantly non-spherical shape and rapid rotation of the asteroid, the effects of the harmonic coefficients C₂₀ and C₂₂ are very significant, while effects of the third- and fourth-order inertia integrals of the spacecraft can be neglected. Considering a spacecraft on a stationary orbit around an example asteroid, we show that the classical stability domain predicted by the Beletskii–DeBra–Delp method on a circular orbit in a central gravity field is modified due to the non-spherical mass distribution of the asteroid. Our results are confirmed by a numerical simulation.     

Artificial spin-up and fragmentation of sub-kilometre asteroids

The article demonstrates the feasibility of artificially increase the spin rate of asteroids about 200 m in diameter beyond the limit in which they begin to disrupt. In the proposed concept a tethered satellite of less than a few tens of kilometres length anchored to the asteroid surface is employed as a mean to exchange angular momentum with the celestial body and increase its spin rate. Simple calculations based on angular momentum and energy conservation show that a 200 m diameter asteroid can be spun-up to critical rotation speed in less than one year with current technology.The scheme can be utilized as a unique scientific tool to characterize the asteroid internal structure and composition.     

Tether assisted near earth object diversion

Potential earth impact threats posed by asteroids have motivated researchers to find effective NEO diversion techniques. Several means to perturb the motion of an asteroid have been discussed in the literature. Attaching a long tether and ballast mass to the asteroid can effectively alter its trajectory. In this paper it is shown that by cutting the tether at an appropriate time the diversion can be enhanced. The instant of cutting the tether significantly affects the final orbit of the asteroid and thus the resulting deflection from the original path.     

On coordinated approach to the problem of asteroid-comet impact hazard

A review of the current state of investigations into the complex global problem of asteroid-comet hazard (ACH) is presented. Main attention is drawn to a comprehensive analysis of prospects of developing the intra-Russia cooperation of studies on the ACH problem and initiating a working program of solving this problem on the national basis. Special space projects are briefly discussed, aimed to investigate and solve the ACH problem, in particular, the project of a mission of spacecraft with an onboard transponder to a hazardous asteroid (conventionally, asteroid Apophis is chosen as a target).     

Generalized restricted circular three-body problem as a model for dynamics of binary asteroids

Exploration of the Solar System has recently revealed the existence of a large number of asteroids with satellites, which has stimulated interest in studying the dynamics of such systems. This paper is dedicated to the analysis of the relative motion of a binary asteroid. The conditions of existence of such a system (i.e., when its components do not run away) are derived in the Introduction. Then it is assumed that the satellite has no significant effect on the motion of the main asteroid, the latter being modeled as a dumbbell-like precessing solid body. The equations of motion of this system are a two-parameter generalization of the corresponding equations of the restricted circular three-body problem. It is demonstrated that in the system under consideration there exist steady-state motions in which the small asteroid is equidistant from attracting centers at the ends of the dumbbell (an analog to triangle libration points). The conditions of existence of such motions are derived, and the positions with respect to the dumbbell are analyzed in detail. Examination of the stability of the triangle libration points is reduced to investigation of a characteristic equation of the sixth degree. The stability conditions are derived in the case when the main asteroid executes near-planar motion.