Stability of the relative equilibria of a rigid body in a J2 gravity field

TL;DR

This paper analyzes the linear stability of relative equilibria of a rigid body in a J2 gravity field, considering gravitational coupling, and identifies how J2 and body size influence stability, relevant for natural satellite motion.

Contribution

It extends the classical J2 problem to include rigid body dynamics with gravitational coupling and derives stability conditions using geometric mechanics and Poisson reduction.

Findings

Both J2 and body size significantly affect stability.

The stability regions resemble Lagrange and DeBra-Delp regions.

Results are applicable to natural satellite motion studies.

Abstract

The motion of a point mass in the J2 problem is generalized to that of a rigid body in a J2 gravity field. Different with the original J2 problem, the gravitational orbit-rotation coupling of the rigid body is considered in this generalized problem. The linear stability of the classical type of relative equilibria of the rigid body, which have been obtained in our previous paper, is studied in the framework of geometric mechanics with the second-order gravitational potential. Non-canonical Hamiltonian structure of the problem, i.e., Poisson tensor, Casimir functions and equations of motion, are obtained through a Poisson reduction process by means of the symmetry of the problem. The linear system matrix at the relative equilibria is given through the multiplication of the Poisson tensor and Hessian matrix of the variational Lagrangian. Based on the characteristic equation of the linear system matrix, the conditions of linear stability of the relative equilibria are obtained. With the stability conditions obtained, the linear stability of the relative equilibria is investigated in details in a wide range of the parameters of the gravity field and the rigid body. We find that both the zonal harmonic J2 and the characteristic dimension of the rigid body have significant effects on the linear stability. Similar to the attitude stability in a central gravity field, the linear stability region is also consisted of two regions that are analogues of the Lagrange region and the DeBra-Delp region. Our results are very useful for the studies on the motion of natural satellites in our solar system.