Dynamics and Control of Gravity Tractor Spacecraft for Asteroid Deflection

Abstract

Multiple gravity tractors in halo orbits and a hovering solar sail gravity tractor are proposed as an option for deflecting a certain class of near-Earth asteroids that may not require high-energy deflection techniques employing nuclear explosions or kinetic impactors. This paper presents the preliminary dynamic modeling and control analysis of such variants of the gravity tractor for examining their practical viability as applied to asteroid Apophis; however, detailed system-level tradeoffs are not treated in this paper. A system of orbiting multiple gravity tractors has many advantages over the hovering gravity tractor. They include'its larger total ΔV capability, multispacecraft redundancy, and mission design flexibility with smaller satellites equipped with lower-risk propulsion systems. A solar sail gravity tractor concept exploits the propellantless nature of solar reflectors despite its inherent drawback of requiring a particular hovering position with a 55-deg offset angle from the target asteroid's flight direction.