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

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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.