Simple Strategy for Powered Swingby

The use of thrust during a close encounter with a celestial body can significantly improve the efficiency of the swingby maneuver. A parametric analysis of a powered swingby with the moon is carried out to find the optimal combined use of a gravity assist and propulsion. A single impulse, usually applied inside the satellite's sphere of influence, is minimized to achieve an assigned energy with respect to the Earth, for an assigned hyperbolic excess velocity on entering the sphere. Numerical results are presented, but emphasis is placed on the physical reasoning of the suggested strategies that are sometimes different from those found in recent literature. A longer stay on the low-energy; large-deflection hyperbola is always convenient. When geocentric energy is increased, thrust is applied after the passage at the periapsis, with a small misalignment with respect to the spacecraft velocity, to obtain a larger turn angle from the swingby. If reduction of the geocentric energy is required, the selenocentric energy is increased or reduced, depending on the magnitude of the inbound hyperbolic excess velocity, and the corresponding strategies are rather different. (Author)