## Analytical earth-aerocapture guidance

##### Abstract

Aerocapture is a technique of employing a single atmospheric pass to inserts a spacecraft from a hyperbolic orbit, approaching from deep space, into an elliptical (captured) orbit around its destination planet. After atmospheric flight and energy dissipation, propulsive maneuvers are needed to be performed to place the spacecraft in a target orbit. The exo-atmospheric propulsive maneuvers require much less propellant consumption compared to conventional orbit capture methods. This research aims to develop a new analytical predictor-corrector (APC) guidance method for the Earth-aerocapture problem in order to provide near-optimal performance in terms of exo-atmopheric velocity impulses required to establish the desired target orbit. The optimal aerocapture problem is analyzed using the bang-bang bank control structure. This thesis presents a bank-modulation APC guidance algorithm consisting of two phases: descent phase (lift-up) and ascent phase (lift-down) to mimic the optimal bang-bang bank angle structure. The APC guidance relies on open-loop and closed-loop bank control laws during the descent and ascent phases, respectively. Using the parameterizations of the aerodynamic acceleration effects and the flight-path angle term as a function of altitude, a closed-form expression of atmospheric exit velocity is obtained. Two separate scenarios (Fourier curve fitting and exponential curve fitting) are implemented to parameterize the aerodynamic acceleration effects, while the flight-path angle is parameterized with a single term exponential function. After the bank-switching (from open-loop to closed-loop control) is reached, the bank angle is continuously commanded in the ascent phase to track the reference flight-path angle profile and achieve desired exit conditions. A bank-reversal logic is developed to minimize the difference between the inclination of the post-atmospheric orbit and the desired target inclination. Using large dispersions in the vehicle parameters, entry state, and atmospheric density, Monte-Carlo simulations are executed to test the performance and robustness of the proposed APC guidance algorithm. The simulation results reveal that the well-developed APC guidance algorithm provides the robustness and near-optimal performance.

##### Degree

Ph. D.