The Orbital Dynamics Environment of 433 Eros: A Case Study for Future Asteroid Missions

The Near-Earth Asteroid Rendezvous (NEAR)–Shoemaker mission was a milestone in that it represented the practical navigation of a spacecraft in the most severely perturbed orbital environment (relative to the standard two-body problem) ever experienced by a spacecraft. Furthermore, all future asteroid orbital missions will encounter environments similar, in some way, to the environment encountered by NEAR at Eros. Thus, it is of interest to discuss the orbital dynamics that the NEAR-Shoemaker spacecraft was subject to at Eros. This article first provides a brief review of the measured force and model parameters of Eros. Next, an evaluation of the resulting orbital dynamics environment in the vicinity of Eros is made using these estimated values. The Eros dynamical environment is discussed in the region relatively far from the asteroid, where solar effects are the dominant perturbation, and in the region close to the asteroid, where the gravity field and rotation of Eros are most important. In particular, we give limits for stable motion about Eros and provide analytical descriptions of the dynamical environment found there. Many of the methods discussed and introduced in this article can be used for future asteroid missions as well. I. Introduction While the force environment at asteroids is unique for each separate body, the analysis and evaluation of these environments can be formulated in a general manner that can be equally applied to each new situation. Thus, in this article we consider a somewhat detailed discussion of the dynamical environment about Eros, formulated in such a fashion as to be applicable to most asteroids. Specifically, we consider the dynamical environment far from and close to an asteroid, where strong perturbation forces exist. Far from an asteroid, the perturbations arise from solar radiation pressure and solar tidal forces. Close to an asteroid, the perturbations arise from the gravity field and rotation state of the body. The one case that is not explicitly covered in the current analysis is when the solar radiation pressure and asteroid gravity-field spheres of influence overlap. This situation can lead to interesting interactions between these competing perturbations and is an area of practical interest as future missions to near-Earth asteroids likely would fall into this regime.