A neighboring optimum feedback control scheme based on estimated time-to-go with application to re-entry flight paths.

Abstract

A modification of the perturbation feedback control scheme of Refs.[l] , 1 2 1 , and [3] 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 1 I the change in the final time due to perturbations from a nominal path.time-to-go, determined from the predicted change in final time, is used to enter tables of precalculated feedback control gains. TheThis modified guidance scheme is applied to a re-entry glider entering the atmosphere of the Earth at supercircular velocities.bottom of the pull-up maneuver (nominal altitude 188,000 ft., nominal velocity 33,000 ft./sec.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.Beginning at the -1 ) the glider is guided to a terminal altitude of 220,000 ft.