American Institute of Aeronautics and Astronautics 1 Modeling and Simulation of Vehicle Dynamics on the Surface of Phobos Marco B. Quadrelli 1 , J. (Bob) Balaram 2 , Abhinandan Jain 3 , Jonathan Cameron 4 , Steven Myint 5 , Avinash Devalla 6 Jet Propulsion Laboratory, California Institute of Technology 4800 Oak Grove Drive, Pasadena, CA 91109-8099 In this paper we analyze the dynamics of a spacecraft in proximity of Phobos by developing the equations of motion of a test mass in the Phobos rotating frame using a model based on circularly-restricted three body problem, and by analyzing the dynamics of a ATHLETE hopper vehicle interacting with the soil under different soil-interaction conditions. The main conclusion of the numerical studies is that the system response is dominated by the stiffness and damping parameters of the leg springs, with the soil characteristics having a much smaller effect. The system simulations identify ranges of parameters for which the vehicle emerges stably (relying only on the passive viscoelastic damper at each leg) or unstably (needing active attitude control) from the hop.The implication is that further experimental and possibly computational modeling work, as well as site characterization (from precursor missions) will be necessary to obtain validated performance models. Nomenclature a J2 , a J3 , a gyro , a 3rd = acceleration vectors G=shear strength V rel = relative tangential velocity at the point of contact R 0 = vector of the position of the test mass with respect to the origin of the Phobos-centric frame F n = normal force F t = tangential force S = contact area c = soil cohesion parameter j = tangential penetration K, k c and k φ =soil parameters from [Zhou] ρ = soil density ν = soil Poisson’s ratio μ Phobos = Phobos gravitational parameter μ Mars = Mars gravitational parameter ω = angular velocity of the rotating frame δ =soil penetration depth μ = Coulomb friction coefficient σ = normal stress τ =tangential stress φ = soil angle of friction 1 Corresponding author, Research Technologist, Mobility and Robotic Systems Section, Mail Stop 198-219, AIAA Associate Fellow. 2 Mobility and Robotic Systems Section, Mail Stop 198-219. 3 Mobility and Robotic Systems Section, Mail Stop 198-219. 4 Mobility and Robotic Systems Section, Mail Stop 198-219. 5 Mobility and Robotic Systems Section, Mail Stop 198-219. 6 Graduate Student, University of Michigan. Downloaded by JET PROPULSION LABORATORY on September 16, 2015 | http://arc.aiaa.org | DOI: 10.2514/6.2015-4632 AIAA SPACE 2015 Conference and Exposition 31 Aug-2 Sep 2015, Pasadena, California AIAA 2015-4632 Copyright © 2015 by the American Institute of Aeronautics and Astronautics, Inc. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental purposes. SPACE Conferences & Exposition