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In the framework of nonlinear stability of elliptic equilibria in Hamiltonian systems with n degrees of freedom we provide a criterion to obtain a type of formal stability, called Lie stability. Our result generalises previous approaches, as exponential stability in the sense of Nekhoroshev (excepting a few situations) and other classical results on formal stability of equilibria. In case of Lie stable systems we bound the solutions near the equilibrium over exponentially long times. Some examples are provided to illustrate our main contributions.

The paper considers the attitude nonlinear stability analysis of the spatial satellite problem and takes it one step further. A study of the Lie (formal) stability is presented and long-time estimates related to the Lie stable cases are provided. The connection with Nekhoroshev theory is also shown. Finally, KAM tori related to Lie stable, as well as unstable equilibria, are also calculated.