Analytical development of the lunisolar disturbing function and the critical inclination secular resonance

TL;DR

This paper provides a corrected and detailed analytical expansion of the lunisolar disturbing function, addressing previous inaccuracies, and applies it to analyze the long-term dynamics of highly elliptical, critically inclined orbits.

Contribution

It offers a self-consistent, corrected derivation of the lunisolar disturbing function expansion, clarifying previous errors and enhancing the accuracy of long-term orbital dynamics analysis.

Findings

Corrected the derivation of the lunisolar disturbing function.

Compared different expansions and identified errors in literature.

Applied the expansion to analyze Molniya orbit dynamics.

Abstract

We provide a detailed derivation of the analytical expansion of the lunar and solar disturbing functions. Although there exist several papers on this topic, many derivations contain mistakes in the final expansion or rather (just) in the proof, thereby necessitating a recasting and correction of the original derivation. In this work, we provide a self-consistent and definite form of the lunisolar expansion. We start with Kaula's expansion of the disturbing function in terms of the equatorial elements of both the perturbed and perturbing bodies. Then we give a detailed proof of Lane's expansion, in which the elements of the Moon are referred to the ecliptic plane. Using this approach the inclination of the Moon becomes nearly constant, while the argument of perihelion, the longitude of the ascending node, and the mean anomaly vary linearly with time. We make a comparison between the different expansions and we profit from such discussion to point out some mistakes in the existing literature, which might compromise the correctness of the results. As an application, we analyze the long--term motion of the highly elliptical and critically--inclined Molniya orbits subject to quadrupolar gravitational interactions. The analytical expansions presented herein are very powerful with respect to dynamical studies based on Cartesian equations, because they quickly allow for a more holistic and intuitively understandable picture of the dynamics.