Analyses of orbital lifetime and observation conditions of small lunar satellites

Abstract

The Moon's gravitational field shows large inhomogeneities that strongly influence the shape of an orbit and can severely influence the orbital lifetime and observation conditions of any spacecraft orbiting the Moon. Small lunar spacecrafts are especially affected by those unstable orbits because their limited mass leaves little to no fuel reserves for excessive orbit maintenance maneuvers. Therefore, it may be favorable to choose an orbit, which features not the ideal observation conditions, but requires less Δ V for orbit maintenance. These limitations have to be considered during mission design as they affect both the potential capabilities and the lifetime of the satellite. To characterize these limiting factors, simulations and analyzes based on up-to-date high degree and order gravity models were conducted with regard to the upcoming small lunar satellite Lunar Mission BW1 of the Institute of Space Systems (IRS) of the Universitaet Stuttgart. The cubical-shaped spacecraft with an edge length of 1 m and a mass of approximately 200 kg will use its own all-electrical propulsion system to reach a high-inclined low lunar orbit. Due to the limited fuel mass and operational lifetime of the thrusters, we consider the orbit maintenance capabilities of the probe to be minimal. Measures to maximize orbital lifetime with the least amount of propellant have to be taken and target orbits have to be examined carefully. This paper shows the results of simulations, which analyze ground coverage and access times, as well as simulations of orbital lifetime and changes in orbital parameters. Additionally, suitable, long lasting target orbits for small lunar spacecrafts are discussed.