The Dynamical Environment About Asteroid 25143 Itokawa: Target of the Hayabusa Mission D.J. Scheeres ∗ S. Broschart † , S.J. Ostro and L.A. Benner ‡ This paper explores the dynamical environment about Asteroid 25143 Itokawa, using the shape and rotation state model recently estimated from radar imaging data by Ostro et al. (2004). In 2005 the Japanese spacecraft Hayabusa will reach Itokawa and begin a period of vicinity operations about that body. The existence of this model can be used to prepare for the Hayabusa spacecraft rendezvous with that asteroid, enabling a more rapid transition from arrival to the start of intensive science and sampling operations. The Hayabusa mission also yields a unique opportunity to validate the shape inversion procedures from radar data described in Hudson (1993). We find that there are stable orbiting options for the Hayabusa spacecraft about Itokawa. I. The Hayabusa Mission and Itokawa In 2005 the Japanese Space Agency’s (JAXA) Hayabusa spacecraft will rendezvous with Asteroid 25143 Itokawa. In its subsequent mission it will descend to the asteroid surface several times to acquire samples, and return them back to the Earth. Motivated by this rendezvous, a radar-based shape model and rotation state has been estimated for Itokawa by Ostro et al. (2004). The existence of this model allows the dynamical environment about this asteroid to be explored prior to rendezvous, potentially enabling a more rapid transition from arrival at the asteroid to the start of intensive science and sampling operations. The Hayabusa mission also yields a unique opportunity to validate the shape inversion procedures from radar data described in Hudson (1993). This paper will first discuss the general geometric properties of the Itokawa shape model and its constant density gravity field. Following this, a detailed discussion of the dynamical environment about this body will be given, using the Hayabusa spacecraft as a motivational example. In particular, we will compute the surface environment, the dynamics environment close to the body, the dynamics environment far from the body, incorporating solar radiation pressure, and the predicted orbit stability of a Hayabusa-like spacecraft. We find that it is feasible for the Hayabusa spacecraft to orbit this asteroid, assuming a density of 2.5 g/cm 3 and some specific mass and area values for the spacecraft. Stable orbit geometries, however, are limited to lie in the sun terminator plane. In June 2004, additional observations of Itokawa were made by Ostro and Benner. While not completely processed as of yet, they do indicate additional surface structure on the asteroid not seen (due to viewing ge- ometry) during the previous observations. When these new observations are finalized, the analysis contained in this paper will be revised and should be available in advance of the 2005 rendezvous. II. Computed properties from the shape Given the detailed polyhedral shape of Itokawa we can compute a variety of quantities associated with that body. For all our discussions we assume a body-fixed coordinate frame with origin at the body center of mass and aligned with the principal axes of inertia of the asteroid (all computed assuming a uniform density throughout). We use the usual convention that the x axis is along the smallest moment of inertia (longest axis), the z axis is along the largest moment of inertia (shortest axis), and that the y axis lies along ∗ Associate Professor, The University of Michigan, Department of Aerospace Engineering, Ann Arbor, MI 48109-2140 USA, 1-734-615-3282 (tel), 1-734-763-0578 (fax), scheeres@umich.edu † PhD. Candidate, The University of Michigan ‡ Jet Propulsion Laboratory, California Institute of Technology 1 of 12 American Institute of Aeronautics and Astronautics AIAA/AAS Astrodynamics Specialist Conference and Exhibit 16 - 19 August 2004, Providence, Rhode Island AIAA 2004-4864 Copyright © 2004 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.