Optimal atmospheric trajectory for aero-gravity assist

Abstract

Gravity assist of a planet can be enhanced by an alternate technique called aero-gravity assist (AGA). The latter uses atmospheric maneuvering around the planet to increase the deflection angle, which leads to an increase in the velocity gain. This paper presents a realistic mathematical model for AGA. Optimal atmospheric trajectory is synthesized so as to maximize the heliocetric velocity of the spacecraft. Optimization is carried out using Pontryagin's maximum principle. The atmospheric trajectory is such that the spacecraft flies mostly at the maximum lift-to-drag ratio ( E∗) so as to minimize the loss of kinetic energy and increase the angle of rotation around the planet. The heating rates have also been calculated, which show that high lift coefficient, corresponding to E∗, results in lower heating rate.