Highly Physical Penumbra Solar Radiation Pressure Modeling and the Earth Flyby Anomaly

Abstract

Numerous deep-space missions have used Earth flybys to gain or lose heliocentric orbital energy en-route to their destinations. During a number of these gravity assist maneuvers, beginning with the first Galileo Earth flyby in December of 1990, mission operators have observed motion which cannot be explained by their detailed force models. Numerous explanations have been unsuccessfully proposed and investigated as the source of the Earth flyby anomaly. In this paper, we investigate solar radiation pressure (SRP) modeling during penumbra transitions as a contributor to or explanation for the anomaly. We compare propagated Earth flyby trajectories generated using a detailed, highly physical penumbra SRP model to propagated trajectories generated using a simpler geometric method representative of what is typically used in orbit determination programs. Initial results suggest that penumbra SRP modeling is not responsible for or significantly contributing to the anomaly.