Reentry Terminal Guidance through Sliding Mode Control

A guidance scheme has been developed which provides for the terminal guidance of an unpowered lifting reentry vehicle during the Approach and Landing phase. The proposed approach allows for trajectories to be generated “on-line” through the use of a closed-loop control law. In scenarios where the reentry vehicle is significantly deviated from its nominal trajectory upon entry into the A&L phase, the usefulness of such an on-line method can be clearly realized. These types of scenarios are of interest since the current space shuttle guidance approach during the A&L phase involves tracking trajectories created off-line. In order to solve the A&L guidance problem, in this work a concept of Sliding Mode Terminal Guidance (SMTG) is utilized. SMTG takes advantage of the finite-time reaching phase of the sliding mode technique to ensure that any desired constraints can be fulfilled in a finite time. The effectiveness of the SMTG approach is demonstrated through a series of simulations, and it is shown that feasible trajectories can be generated which depend only on the initial and final conditions of the A&L phase. Also, since a closed-loop control law is obtained, the SMTG approach could be readily implemented in a reusable launch vehicle