Guidance and Control During Direct-Descent Parabolic Reentry

The results of studies of four reentry guidance and control techniques for the energy management of vehicles returning to the earth at escape speeds are compared in this paper. The reentry trajectories are constrained to those of direct descent, that is, where the vehicle does not leave that portion of the atmosphere where useful aerodynamic forces are available after its initial entry. The guidance techniques compared are:

1) A piloted simulator study reference trajectory techniques;

2) An automatic controller using reference trajectory techniques;

3) A predictor system employing linear prediction (perturbation) techniques; and

4) A repetitive prediction system employing rapid-time computer techniques.

The results indicate that none of the procedures provide nearly
optimum range capability when maximum down range is required. The repetitive prediction system was shown to obtain excellent control of the
initial peak deceleration and, therefore, better minimum range control.
The piloted procedure indicates that the pilot with experience and a
good display of flight information can capably perform the reentry guidance maneuvers and energy management functions. Actually, the procedure
used by the pilot illustrates the manner in which the maximum ranges can
be obtained. The other two systems, that is, the automatic reference-trajectory control and the linear prediction technique, indicate that
these procedures are applicable to control of reentry from parabolic
orbit.