Higher-Order Corrections for Frozen Terminator Orbit Design

Abstract

Suitable orbit options around asteroids are limited due to strong perturbations caused by solar radiation pressure (SRP), a target’s irregular gravity field, and third-body acceleration. One potential option for mission operations is a frozen terminator orbit, a near-circular polar orbit that has been extensively studied for the SRP dominant case. This paper addresses modification of the conventional initial condition for the terminator orbit to account for two distinctive features: an irregular gravity field and offset of the orbit center. When orbit size is small, the asteroid’s higher-order gravity field becomes nonnegligible, and this paper specifically focuses on the effects that and have on new frozen orbit conditions. When the orbit is large, a point mass assumption becomes valid, but strong SRP pushes the spacecraft away from the sun, resulting in a geometric offset between orbit and mass centers. The offset causes large short-period variation of orbital elements, and the resulting orbit is not frozen if initial elements are defined simply as the desired mean elements. This paper proposes an approach to define orbital elements around an offset shifted along the sun–asteroid line. Finally, a unified correction valid for a wide range of semimajor axes is discussed.