Coast-arc orbit stability during spiral-down trajectories about irregularly shaped bodies

The orbit stability for a spacecraft while in a minimum propellant, optimal low-thrust transfer from a high-altitude orbit to low-altitude orbit around an irregularly shaped body is addressed. To ensure the spacecraft's safety, it is necessary to know that if the spacecraft's main engines safe during the period of orbit transfer, then the resulting coast orbit is stable or unstable with low-probability of the spacecraft colliding with the body or escaping from orbit To answer this question, a Monte Carlo simulation, developed in FORTRAN 90, was developed to analyze a sufficiently large set of coast orbits under the influence of a high-fidelity gravitational model. The perturbations arising from the nonspherical harmonics were derived using Hotine's partially nonsingular geopotential formulation. This method was chosen because of the higher efficiency of Hotine's method when compared with using a spherical harmonic analysis. The simulation examines the orbital radius to determine the danger of spacecraft crash or escape.