A NEIGHBORING OPTIMUM FEEDBACK CONTROL SCHEME BASED ON ESTIMATED TIME-TO-GO WITH APPLICATION TO RE-ENTRY FLIGHT PATHS.
HARVARD UNIV CAMBRIDGE MASS DIV OF ENGINEERING AND APPLIED PHYSICS
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A modification of the perturbation feedback control scheme given in other references is presented that greatly increases its capability to handle disturbances in cases where the final time is not specified. The modified control scheme uses a set of precalculated gains which allows in-flight estimation of the change in the final time due to perturbations from a nominal path. The time-to-go, determined from the predicted change in final time, is used to enter tables of precalculated feedback control gains. This modified guidance scheme is applied to a re-entry glider entering the atmosphere of the Earth at supercircular velocities. Beginning at the bottom of the pull-up maneuver nominal altitude 188,000 ft., nominal velocity 33,000 ft.sec. to the -1 power the glider is guided to a terminal altitude of 220,000 ft. and zero 0 flight path angle with maximum terminal velocity. For initial altitudes between 167,000 and 216,000 ft. the terminal error in altitude is less than two feet for initial velocities between 23,000 ft.sec. and 43,000 ft.sec. the terminal altitude error is less than 13 ft. In addition, the terminal velocity is very close to optimal for these initial conditions.
- Spacecraft Trajectories and Reentry