Near Earth Asteroid Rendezvous (Near) Revised Orbit Phase Trajectory Design

Trajectory design of the orbit phase of the NEAR mission involves a new process that departs significantly from those procedures used for previous missions. In most cases, a precise spacecraft ephemeris is designed well in advance of arrival at the target body. For NEAR, the uncertainty in the dynamic environment around Eros does not allow the luxury of a precise spacecraft trajectory to be defined in advance. The principal cause of this uncertainty is the limited knowledge of the gravity field and rotational state of Eros. As a result, the concept for the NEAR trajectory design is to define a number of rules for satisfying spacecraft, mission, and science constraints, and then apply these rules to various assumptions for the model of Eros. Nominal, high, and low Eros mass models are used for testing the trajectory design strategy and to bracket the ranges of parameter variations that are expected upon arrival at the asteroid. The final design is completed after arrival at Eros and determination of the actual gravity field and rotational state.The application of the NEAR orbit phase trajectory design to the current best estimate of the Eros physical parameters is described in this payer. The resulting orbit is the prototype for the actual trajectory design to be performed upon arrival at Eros in February of 2000. The trajectory is described and illustrated, and some of the problems encountered in the design and their resolution are discussed.