Near Earth Asteroid Rendezvous orbit phase trajectory design

Abstract

Trajectory design of the orbit phase of the Near Earth Asteroid Rendezvous (NEAR) mission involves proce-dures that depart significantly from those used for pre-vious missions. On previous missions, the trajectory design involved finding a flight path that satisfied a rigid set of spacecraft and mission design constraints. A precise spacecraft ephemeris was designed well in advance of arrival at the target body. For NEAR, the uncertainty in the dynamic environment does not permit a precise spacecraft ephemeris to be defined in advance of arrival at the target body Eros. The principal cause of this uncertainty is limited knowledge of the gravity field and rotational state of Eros. As a result, the concept for NEAR trajectory design is to define a number of rules for satisfying spacecraft and mission constraints and to apply these rules to various assumptions for the model of Eros. This paper describes a trajectory design that applys to the physical model of Eros as currently understood. The final design will be completed after arrival at Eros and the gravity field and rotational state are determined. Spacecraft and Mission Constraints The spacecraft constraints that apply to Eros trajectory design include limits on fuel consumption, solar panel illumination and momentum wheel management. Other constraints define the flexibility and speed with which mission operations may be conducted. Probably the most important spacecraft constraint is to perform the