Detectability of asteroid density distribution and boulder mass from spacecraft orbital data and asteroid surface gravimetry

小行星是丰富的天体，是研究三个相关方面的重要研究对象：一)潜在的小行星撞击造成的危险；二)小行星采矿产生的经济利益；三)增进对太阳系起源的理解的知识。为了解决这些研究问题，美国国家航空航天局和欧空局目前尚未制定一些小行星飞行任务概念，分别是小行星重定向任务(ARM)和小行星影响任务(AIM)。这两次任务都涉及对小行星的访问，以调查结构、矿物成分和潜在的重新定向战略。这项拟议的研究旨在量化模拟小行星和模拟地表巨石的重力场和密度结构。NASA的小行星重定向和机器人任务(ARRM)计划从小行星表面捡起一块直径2-4米的巨石。关于巨石质量和完整性的知识对这些任务目标至关重要。该项目将确定利用两个来源的重力观测(在此模拟)：i)航天器轨道数据和ii)小行星表面重力数据，估计选定巨石的质量以及潜在小行星目标的密度结构的观测要求。轨道数据将来自航天器摄影测量数据、激光雷达和轨道确定数据(恒星跟踪器、加速计)。地面数据将从GRAPH等拟议的重力着陆器任务中获得。由GEDEX公司研制的矢量重力/加速度计(VEGA)在太空中的仪器灵敏度为~1NGAL。重力场的三个矢量分量将从着陆器上测量，该着陆器旨在通过推进跳跃来测量小行星的整个表面。我们将通过改变相关的重力观测参数，如站点密度、传感器精度、噪声水平以及轨道和表面数据的组合来进行正反向建模模拟。这将导致对各种巨石和小行星的观测灵敏度和采样要求进行可量化的估计，对飞行任务规划和传感器开发产生直接影响。

Asteroids are abundant celestial objects and represent important research targets to study three relevant aspects,i) the hazard arising from a potential asteroid impact, ii) the economic benefits originating from asteroidmining, and iii) the knowledge gain towards improved an understanding of the origin of the solar system. Inorder to address those research questions, a number of asteroid mission concepts are currently underdevelopment at NASA and ESA, namely the Asteroid Redirect Mission (ARM) and the Asteroid ImpactMission (AIM), respectively. Both missions involve asteroid visits in order to investigate structure, mineralcomposition, and potential redirection strategies. The proposed research aims at quantifying the gravity fieldand the density structure of a simulated asteroid and simulated surface boulders. NASA's Asteroid Redirect andRobotic Mission (ARRM) proposes to pick-up a boulder of 2-4 m in diameter from the asteroid surface.Knowledge of boulder mass and integrity is critical to these mission objective. This project will determine theobservation requirements for estimating the mass of selected boulders as well as the density structure ofpotential asteroid targets using gravity observations from two sources (simulated herein); i) spacecraft orbitaldata, and ii) asteroid surface gravity data. Orbital data would be available from spacecraft photogrammetricdata, LiDAR, and orbit determination data (star trackers, accelerometers). Surface data would be available froma proposed gravimetry lander mission such as GRASP. The VEctor Gravimeter/Accelerometer (VEGA) builtby GEDEX has an instrument sensitivity of ~1 nGal in space. Three vector components of the gravity field willbe measured from a lander vehicle designed to survey the entire surface of an asteroid via propulsive hopping.We will conduct forward/inverse modelling simulations by varying relevant gravity observation parameterssuch as station density, sensor accuracy, noise levels and combinations of orbital and surface data. This willlead to quantifiable estimates of observation sensitivity and sampling requirements for various boulders andasteroids with direct impact on mission planning and sensor development.