# Development of a Coupled Orbit-Attitude Propagator for Spacecraft of Arbitrary Geometry

The successful prediction of spacecraft motion is often heavily based upon assumptions used to simplify the problem without compromising solution accuracy. For many analyses, a primary assumption used is the decoupling of trajectory and attitude dynamics when calculating trajectories. In cases where spacecraft or objects have high area to mass ratios, non-conservative effects such as atmospheric drag and solar radiation pressure can greatly perturb spacecraft translational motion based on rotational state. A modular, six degree of freedom (6DOF) simulation with coupled orbit and attitude dynamics has been developed to model spacecraft and orbits of arbitrary geometries. First, the basis for the modular rotational and translational equations of motion are introduced. Next, formulations are provided for the gravity gradient torque, solar radiation pressure, aerodynamic, and non-spherical gravity potential sources of perturbations, and the Marshall Engineering Thermosphere atmospheric model used is described. A first test case is performed using the 6DOF simulation to simulate the deorbit of the spacecraft Lightsail 1, which flew in 2015. Next, predictive cases are demonstrated using the simulation for a theoretical sail-boom-rocket combination representative of a debris removal scenario, and for the Aerodynamic Deorbit Experiement, which will demonstrate a passively stable drag sail technology and characterize its effectiveness on orbit. All simulation cases have had aerodynamic perturbation formulations compared against high fidelity Direct Simulation Monte Carlo runs, and suggestions have been made for the future development of the simulation tool.