Trajectory optimization and multiple-sliding-surface terminal guidance in the lifting atmospheric reentry

In this paper the problem of guiding a vehicle from the entry interface to the ground is addressed. The Space Shuttle Orbiter is assumed as the reference vehicle and its aerodynamics data are interpolated in order to properly simulate its dynamics. The transatmospheric guidance is based on an open-loop optimal strategy which minimizes the total heat input absorbed by the vehicle while satisfying all the constraints. Instead, the terminal phase guidance is achieved through a multiple-sliding-surface technique, able to drive the vehicle toward a specified landing point, with desired heading angle and vertical velocity at touchdown, even in the presence of nonnominal initial conditions. The time derivatives of lift coefficient and bank angle are used as control inputs, while the sliding surfaces are defined so that these two inputs are involved simultaneously in the lateral and vertical guidance. The terminal guidance strategy is successfully tested through a Monte Carlo campaign, in the presence of stochastic winds and wide dispersions on the initial conditions at the Terminal Area Energy Management, in more critical scenarios with respect to the orbiter safety criteria.