A comparative reliability analysis of ballistic deployments on binary asteroids

• Published in: Acta astronautica 2019-03, Vol.156, p.308-316
• Main Authors: Çelik, Onur, Sánchez, Joan Pau, Karatekin, Özgür, Ritter, Birgit
• Format: Article
• Language: English
• Subjects: Asteroid missions; Asteroids; Astrodynamics; Binary asteroids; Covariance; Covariance analysis; Design; Design parameters; Equatorial regions; Lander vehicles; Landing; Landing aids; Mission planning; Navigation; Navigation systems; Reliability analysis; Reliability aspects; Target recognition; Three body problem; Touchdown; Trajectories; Trajectory design
• ISSN: 0094-5765; 1879-2030
• DOI: 10.1016/j.actaastro.2018.03.020

Small body missions can significantly benefit from deploying small landing systems onto the surface of the visited object. Despite the potential benefit that they may bring, deployments of landers in small body environments may entail significant mission design challenges. This paper thus addresses the potential of ballistic landing opportunities in binary asteroid moons from a mission design perspective, particularly focusing on reliability aspects of the trajectories. Two binaries that were previously identified as target bodies in several missions/proposals, Didymos and 1996 FG3, are considered in this paper. The dynamics near them are modeled by means of the Circular Restricted Three Body Problem (CR3BP), which provides a reasonable representation of a standard binary system. Natural landing trajectories that allow both minimum-velocity local-vertical touchdown and deployment from a safe distance are investigated. Coefficient of restitution values are used as a design parameter to compute the first touchdown speeds that ensure sufficient reliability of landing trajectories. A simple reliability index, which is derived via uncertainty ellipsoid from covariance analysis, is introduced to create a global reliability map across the asteroid surfaces. Assuming 3σ deployment errors on the order of 90 m and 2 cm/s, the results show that ballistic landing operations are likely to be successful for larger binary moons if the deployments target near equatorial regions within longitude range 320o–20°. It has also been shown that the deployments to smaller binary moons may require higher accuracy in navigation and deployment systems in their mothership, and/or closer deployment distances. •Reliability of ballistic landings is investigated in 1996FG3 and Didymos.•Landing properties are computed across the surface of binary asteroids.•The effect of uncertainties are investigated in a covariance analysis.•A qualitative reliability index is defined with the area of the uncertainty ellipse.•Monte Carlo results confirms the accuracy of the reliability index.