Characteristics and close-range exploration methods of near- Earth asteroid 2016HO_(3)

The characteristics of asteroids are vital parameters for planning asteroid exploration missions.These characteristics have been explored in close range for some typical asteroids,and are summarized in the article.This allows estimates of the characteristics of asteroid 2016HO_(3),the target of the first Chinese asteroid exploration mission,Tianwen 2.We obtain 80 characteristic parameters in 9 categories and analyze their impacts on the mission.By comparing three close-range exploration modes,we provide advantages and disadvantages of each,and propose suitable methods for the exploration of 2016HO_(3).Owing to the weak gravity and small size of 2016HO_(3),a combination of multiple hovering positions and active orbiting is recommended for scientific exploration.

基于NEATM和WISE数据的小尺寸近地小行星物理特性研究

小行星是太阳系中广泛分布的金属或岩石天体,直径从米级跨越到几百公里.它们蕴含了太阳系早期的信息,同时也可能会与地球轨道相交且撞击地球,因此研究小行星的物理参数、物质成分和表面性质对于了解太阳系行星的形成演化和近地天体防御具有重要意义.以国际小行星中心(Minor Planet Center,MPC)获取直径D<160 m的小尺寸近地小行星共67颗作为研究对象,其中包含部分潜在威胁小行星(Potentially Hazardous Asteroids,PHA).基于NEATM(Near-Earth Asteroid Thermal Model),使用广域红外巡天望远镜(Wide-field Infrared Survey Explorer,WISE)的观测数据,利用反射光模型对太阳反射光进行了修正,使用动力学模型计算WISE观测历元的小行星轨道数据,计算了这67颗小尺寸近地小行星的直径和反照率.拟合过程采用马尔科夫链蒙特卡洛(Markov Chain Monte Carlo,MCMC)方法,与WISE的研究结果和MPC的数据进行了比较分析,给出了其分类特征.研究为小行星的观测和理论提供了有力的支持,可以更好地了解近地小行星的特征和演化.

Photometric Analysis for Asteroid(81)Terpsichore using Convex Inversion and Phase Function Fitting Methods

The shapes and rotation states(periods and pole orientations)of main-belt asteroids are important for understanding their formation and evolution.In order to obtain sufficient photometric data covering different apparitions for asteroid(81)Terpsichore,ground-based photometric observations in 2020 and 2021 were carried out.By combining published and newly obtained photometric data,we calculated the shape and spin parameters for(81)Terpsichore using the convex inversion method.With this method,we have derived a best fitted pole orientation—(22.2±_(3.1)^(3.3°),17.5±_(5.5)^(10.8°))with a spin period of 10.94±_(0.01)^(0.01)h.Based on the derived convex shape of(81)Terpsichore,we have fitted the H,G+1,G_(2)phase function using the calibrated TESS data and Gaia data after accounting for the lightcurve amplitude correction.As a result,we have derived its absolute magnitude H=8.68±_(0.19)^(0.22)mag with corresponding phase function parameters G_(1)=0.82±_(0.10)^(0.09)and G_(2)=0.02±_(0.02)^(0.03).

A Rendezvous Mission to the Second Earth Trojan Asteroid 2020 XL_5 with Low-Thrust Multi-Gravity Assist Techniques

As the second of Earth's Trojan asteroids, 2020 XL_(5) is worthy of rendezvous and even sample return missions in many aspects. In this paper, a rendezvous mission to Earth's second Trojan asteroid 2020 XL_(5) is proposed.However, due to its high inclination and large eccentricity, direct impulsive transfer requires large amounts of fuel consumption. To address this challenge, we explore the benefits of electric propulsion and multi-gravity assist techniques for interplanetary missions. These two techniques are integrated in this mission design. The design of a low-thrust gravity-assist(LTGA) trajectory in multi-body dynamics is thoroughly investigated,which is a complex process. A comprehensive framework including three steps is presented here for optimization of LTGA trajectories in multi-body dynamics. The rendezvous mission to 2020 XL_(5) is designed with this three-step approach. The most effective transfer sequence among the outcomes involves Earth–Venus–Earth–Venus-2020 XL_(5). Numerical results indicate that the combination of electric propulsion and multi-gravity assists can greatly reduce the fuel consumption, with fuel consumption of 9.03%, making it a highly favorable choice for this rendezvous mission.

Accelerating Asteroidal Period and Pole Inversion from Multiple Lightcurves Using Parallel Differential Evolution and Cellinoid Shape Model

Determining asteroid properties provides valuable physical insights but inverting them from photometric lightcurves remains computationally intensive.This paper presents a new approach that combines a simplified Cellinoid shape model with the Parallel Differential Evolution(PDE)algorithm to accelerate inversion.The PDE algorithm is more efficient than the Differential Evolution algorithm,achieving an extraordinary speedup of 37.983 with 64 workers on multicore CPUs.The PDE algorithm accurately derives period and pole values from simulated data.The analysis of real asteroid lightcurves validates the method’s reliability:in comparison with results published elsewhere,the PDE algorithm accurately recovers the rotational periods and,given adequate viewing geometries,closely matches the pole orientations.The PDE approach converges to solutions within 20,000 iterations and under one hour,demonstrating its potential for large-scale data analysis.This work provides a promising new tool for unveiling asteroid physical properties by overcoming key computational bottlenecks.

Optimal design of near-Earth asteroid sample-return trajectories in the Sun–Earth–Moon system

In the 6th edition of the Chinese Space Trajectory Design Competition held in 2014, a near-Earth asteroid sample-return trajectory design problem was released, in which the motion of the spacecraft is modeled in multi-body dynamics, considering the gravitational forces of the Sun, Earth, and Moon. It is proposed that an electric-propulsion spacecraft initially parking in a circular 200-kin-altitude low Earth orbit is expected to rendezvous with an asteroid and carry as much sample as possible back to the Earth in a 10-year time frame. The team from the Technology and Engineering Center for Space Utilization, Chinese Academy of Sciences has reported a solution with an asteroid sample mass of 328 tons, which is ranked first in the competition. In this article, we will present our design and optimization methods, primarily including overall analysis, target selection, escape from and capture by the Earth-Moon system, and optimization of impulsive and low-thrust trajectories that are modeled in multi-body dynamics. The orbital resonance concept and lunar gravity assists are considered key techniques employed for trajectory design. The reported solution, preliminarily revealing the feasibility of returning a hundreds-of-tons asteroid or asteroid sample, envisions future space missions relating to near-Earth asteroid exploration.

Near-Earth asteroid flyby trajectories from the Sun-Earth L2 for Chang’e-2’s extended flight

Driven by curiosity about possible flight options for the Chang＇e-2 spacecraft after it remains at the Sun-Earth L2 point, effective approaches were developed for designing preliminary fuel-optimal near-Earth asteroid flyby trajectories. The approaches include the use of modified unstable manifolds, grid search of the manifolds＇ parameters, and a two-impulse maneuver for orbital phase matching and z-axis bias change, and are demonstrated to be effective in asteroid target screening and trajectory optimization. Asteroid flybys are expected to be within a distance of 2 × 10^7 km from the Earth owing to the constrained Earth-spacecraft communication range. In this case, the spacecraft＇s orbital motion is significantly affected by the gravities of both the Sun and the Earth, and therefore, the concept of the ＂he- liocentric oscillating-Kepler orbit＂ is proposed, because the classical orbital elements of the flyby trajectories referenced in the heliocentric inertial frame oscillate significantly with respect to time. The analysis and results presented in this study show that, among the asteroids whose orbits are the most accurately predicted, ＂Toutatis＂, ＂2005 NZ6＂, or ＂2010 CL19＂ might be encountered by Chang＇e-2 in late 2012 or 2013 with total impulses less than 100 rn/s.

A method for classifying orbits near asteroids

A method for classifying orbits near asteroids under a polyhedral gravitational field is presented, and may serve as a valuable reference for spacecraft orbit design for asteroid exploration. The orbital dynamics near aster- oids are very complex. According to the variation in orbit characteristics after being affected by gravitational perturbation during the periapsis passage, orbits near an as- teroid can be classified into 9 categories： （1） surrounding- to-surrounding, （2） surrounding-to-surface, （3） surrounding- to-infinity, （4） infinity-to-infinity, （5） infinity-to-surface, （6） infinity-to-surrounding, （7） surface-to-surface, （8） surface- to-surrounding, and （9） surface-to- infinity. Assume that the orbital elements are constant near the periapsis, the gravitation potential is expanded into a harmonic series. Then, the influence of the gravitational perturbation on the orbit is studied analytically. The styles of orbits are dependent on the argument of periapsis, the periapsis radius, and the periapsis velocity. Given the argument of periapsis, the orbital energy before and after perturbation can be derived according to the periapsis radius and the periapsis velocity. Simulations have been performed for orbits in the gravitational field of 216 Kleopatra. The numerical results are well consistent with analytic predictions.

Using Chebyshev polynomial interpolation to improve the computational efficiency of gravity models near an irregularly-shaped asteroid

In asteroid rendezvous missions, the dynamical environment near an asteroid’s surface should be made clear prior to launch of the mission. However, most asteroids have irregular shapes,which lower the efficiency of calculating their gravitational field by adopting the traditional polyhedral method. In this work, we propose a method to partition the space near an asteroid adaptively along three spherical coordinates and use Chebyshev polynomial interpolation to represent the gravitational acceleration in each cell. Moreover, we compare four different interpolation schemes to obtain the best precision with identical initial parameters. An error-adaptive octree division is combined to improve the interpolation precision near the surface. As an example, we take the typical irregularly-shaped nearEarth asteroid 4179 Toutatis to demonstrate the advantage of this method; as a result, we show that the efficiency can be increased by hundreds to thousands of times with our method. Our results indicate that this method can be applicable to other irregularly-shaped asteroids and can greatly improve the evaluation efficiency.

The research objectives and observational possibilities for fast moving near-Earth asteroids

The paper describes observations of fast-moving near-Earth asteroids(NEAs) made with the small ground-based telescopes of National Time Service Center of Chinese Academy of Science(NTSC of CAS) and Research Institute "Mykolaiv Astronomical Observatory"(RI MAO) by the rotating-drift-scan CCD(RDS CCD) technique. This technique is used to obtain the point images of both the studied objects and reference stars. The results of ongoing follow-up observations of NEAs are discussed. The residual differences(O-C) between the observed and calculated positions from JPL ephemeris were generally small for these asteroids. The standard deviations of these differences were typically ±(0.2′′-0.3′′) in both coordinates for objects with apparent velocity which substantially exceed FWHM for the given exposure time. The results of comparative statistics for such observations from the MPC database show that this is a good level of precision for NEAs. Moreover, the telescopes with the RDS CCD technique implemented can observe the NEAs that closely approach the Earth and with enough observations can improve the precision of determining their orbital elements and impact predictions.

Modeling and Analysis of the Impacts of Temporal-Spatial Variant Troposphere on Ground-Based SAR Imaging of Asteroids

The near-Earth asteroid collisions could cause catastrophic disasters to humanity and the Earth,so it is crucial to monitor asteroids.Ground-based synthetic aperture radar(SAR)is an observation technique for high resolution imaging of asteroids.The ground-based SAR requires a long integration time to achieve a large synthetic aperture,and the echo signal will be seriously affected by temporal-spatial variant troposphere.Traditional spatiotemporal freezing tropospheric models are ineffective.To cope with this,this paper models and analyses the impacts of temporal-spatial variant troposphere on ground-based SAR imaging of asteroids.For the background tropo-sphere,a temporal-spatial variant ray tracing method is proposed to trace the 4D(3D spatial+temporal)refractive index network provided by the numerical weather model,and calculate the error of the background troposphere.For the tropospheric turbulence,the Andrew power spectral model is used in conjunction with multiphase screen theory,and varying errors are obtained by tracking the changing position of the pierce point on the phase screen.Through simulation,the impact of temporal-spatial variant tropospheric errors on image quality is analyzed,and the simulation results show that the X-band echo signal is seriously affected by the troposphere and the echo signal must be compensated.

NEA低剂量研究项目的进展讨论

核能署(NEA)低剂量研究高级小组(HLG-LDR)通过全球协调正在进行的和未来的低剂量研究项目来提高研究的有效性和效率,从而支持辐射防护政策、监管和实施选择。该小组于2023年6月27日至28日在法国布洛涅-比扬古的NEA举行了第七次全体会议。HLG-LDR成立于2021年,首次线下开会,现场有20人,线上有15人参加。印度代表团应邀参加了会议。

“天问二号”任务科学目标和有效载荷配置

回顾了近30年国际上小行星探测任务的科学目标和载荷配置。在总结小行星探测主要科学问题的基础上,对中国行星探测工程“天问二号”探测任务的对象选择、科学目标和有效载荷配置进行了论述。围绕实现科学目标探测,并提出了相应的科学研究内容和有效载荷技术指标。

NEA和WANO加强合作以改善核安全

核能署(NEA)和世界核营运者协会(WANO)签署了一份新的谅解备忘录(MoU),以期进一步合作发展,以加强世界各地的核安全工作。2023年3月9日,NEA总干事William D.Magwood和WANO首席执行官Naoki Chigusa博士在WANO伦敦总部签署了两个组织之间的续签协议。根据谅解备忘录,NEA和WANO将涉及多个合作领域,包括:改善核设施运行;安全运行先进反应堆;改善培训和安全文化;解决人力、技术和组织因素。

近地小行星材料特性对激光烧蚀驱动效率的影响试验分析

基于激光驱动效果和小行星材料特性密切相关的问题,针对脉冲激光对近地小行星物质的烧蚀驱动效率开展了试验研究,选用不同材质、孔隙率的类小行星试验样品,开展了冲量耦合规律测量试验。试验结果表明:在脉冲激光烧蚀的作用下,C型小行星比S型小行星具有更高的冲量耦合效率;随着小行星孔隙率的升高,冲量耦合效率降低,激光烧蚀驱动的效率下降。此外,还对激光烧蚀类小行星物质质量变化的规律进行试验,试验结果表明存在使得小行星质量烧蚀效率最佳的激光功率密度。对于需长期预警时间的威胁小行星,在烧蚀驱动偏转其轨道的同时,以最快的速率减少其质量,可进一步提升防御效率,实现防御的目的。

第十二届全国(中国)空间轨道设计竞赛:地月空间助力火星移民和近地小行星探测

本文首先简要介绍了全国(中国)空间轨道设计竞赛的发展概况和第十二届全国(中国)空间轨道设计竞赛题目的研究背景。然后介绍并解读了“可重复使用地火运输空间站火星移民”“可重复使用探测器飞越探测近地小行星”两组竞赛题目,回顾了竞赛组织历程,分析了竞赛最终提交结果。最后简要陈述了赛后交流和研讨情况以及总结和展望。此外,文中各章节对本竞赛区别于其他学科竞赛的若干特色也进行了简要陈述。

我国应对近地小行星撞击风险和动能撞击偏转研究的若干进展

近地小行星(NEA)撞击地球是人类长期面临的重大潜在威胁,基于监测预警和风险评估,实施在轨处置是防范化解NEA撞击风险的最佳途径。本文概述了国际近地小行星撞击风险应对的现状与发展趋势,介绍了2020年我国启动应对近地小行星撞击风险工作以来的主要进展。着重从实验、数值仿真和理论建模3个方面介绍了我国在动能撞击偏转在轨处置技术研究的若干进展,展望了我国即将实施的首次近地小行星动能撞击防御演示验证任务,提出了在轨处置体系能力与技术深化研究建议。

小行星样品密封设计及验证

中国计划开展探测编号为2016H03的近地小行星并采集样品返回地面,测定小行星样品的物理性质、化学成分与矿物成分,为小行星起源与演化、太阳系的形成与演化过程提供科学依据。针对中国首次近地小行星采样封装任务,设计多种样密封方案,综合考虑密封力、密封面样品颗粒污染物防护等因素,采用双弹性体径向密封方案,并开展密封方案验证工作,通过高温、低温及模拟尘埃污染漏率试验,密封漏率优于5×10^(-6)Pa·m^(3)·s^(-1),满足小行星样品密封要求。

弱引力小天体的自主捕获与相对导航方法

远距离自主捕获与近距离高精度自主相对导航是小天体探测任务中的关键问题,并且目标尺寸越小,问题越突出。首先,针对数万千米到数千千米远距离范围内的星空背景暗弱目标难以识别的问题,提出综合利用运动学和亮度的全自主捕获和识别方法,可以实现距离大范围变化的快速准确捕获,具备了3万千米以远捕获10等星暗弱目标的能力;其次,针对数千到数十千米范围交会段视线测量可观性不足的问题,提出基于视线和轨迹机动一体化设计的相对导航方法,在考虑燃料消耗的前提下有效地提高了轨迹可观性,实现了交会段优于5%精度的相对位置导航;最后,针对近距离不规则小天体表面附近的相对导航问题,提出基于图像陆标和点云特征相结合的光学导航方法,可同时适应阳照区和阴影区的探测需求,并结合基于多源数据融合的弱引力小天体重力场反演方法,进一步提高近距相对导航的精度,近距采样相对位置优于1 m,相对速度优于1 cm/s。对所提出的方法进行了数学和物理的仿真验证。提出的方法有效解决了小天体探测中的高精度相对导航问题,也能适用于数十米量级直径大小和明暗快速交替变化的小天体着陆探测任务。

超声波钻谐振控制算法设计及试验验证

为解决小天体表面引力小及温差变化大难以实现锚固的问题,提出以超声波钻作为锚固工具并采用模糊控制和恒流控制相结合的策略,实现了低钻压力和高低温环境条件下的超声波钻钻进锚固。压电驱动的超声波钻将高频电能转化为高频机械振动,驱动钻具高频破碎岩石,具有极低钻压力的显著优势,尤其适用于弱引力小天体的钻进锚固作业。针对超声波钻的驱动,对超声波钻的谐振控制算法进行研究。首先,建立超声波钻换能器的等效电路模型,在等效模型基础上研究换能器的阻抗特性、负载特性、温度特性和滞后特性。其次,根据超声波钻的工作特性研究谐振频率识别算法、谐振频率跟踪算法和恒电流控制算法,针对谐振频率跟踪算法研究了基于递归最小二乘估计的频率跟踪算法和基于模糊控制的频率跟踪算法,并对实际控制效果进行对比分析。最后,进行常温常压和高低温环境下钻进试验,试验结果表明,在不同温度环境和不同的钻进对象条件下,所设计的谐振控制算法能够实现对超声波钻的稳定驱动。研究结果表明,所提出的模糊控制和恒流控制能够有效的在低钻压力以及不同温度下实现有效钻进。