High-Fidelity Semianalytical Theory for a Low Lunar Orbit

TL;DR

This paper develops a semi-analytical model for low lunar orbits considering high-order gravitational harmonics and third-body effects, determining the minimal model complexity needed for realistic mission analysis.

Contribution

It introduces a high-fidelity semi-analytical theory including a 50x50 gravitational field model for lunar orbits, emphasizing the importance of high-order harmonics in orbit prediction.

Findings

Higher-order harmonics significantly affect frozen orbit characteristics.

A 50x50 gravitational model is necessary for accurate lunar orbit analysis.

Ignoring high-order harmonics can lead to incorrect frozen orbit predictions.

Abstract

We have developed a semi-analytical theory for low-altitude lunar orbits with the aim of verifying what the minimum order of the gravitational model to be considered should be in order to produce realistic results that can be applied to the analysis and design of real missions. With that purpose, we have considered a perturbation model that comprises a 50x50 gravitational field and the third-body attraction from the Earth. Initially, the process of developing the theory is briefly described. Then, the discussion is focused on the search for frozen orbits, for which the effect of each harmonic term of the gravitational model is analyzed separately. As higher-order zonal harmonics are included, new families of frozen orbits can appear. In addition, the eccentricity and inclination values for which frozen orbits can exist change. This effect is very important and needs to be taken into consideration, because ignoring high-order harmonics can lead to predict the existence of frozen orbits at certain inclinations at which the frozen-orbit eccentricity actually falls beyond the impact limit. Consequently, it has been verified that, in agreement with other authors, a 50x50 gravitational model should be the minimum to be considered for real applications.