VARIABLE-LIFT RE-ENTRY AT SUPERORBITAL AND ORBITAL SPEEDS
Analytical solutions have been obtained for a type of variable-lift modulation applicable to a lifting body entering the atmosphere from superorbital and orbital speeds. The variablelift modulation analyzed here results in nonoscillatory trajectories and achieves a smooth transition into a nominal glide phase such as constant flight path angle, constant altitude, constant dynamic pressure, or any other glide desired. Simple closed-form formulas were derived which permit quick estimation of 1) the peak deceleration and the altitude where it occurs, and 2) the required lift modulation necessary for any set of prescribed transition conditions. These approximate formulas show the explicit dependence of trajectory quantities in terms of re-entry conditions, vehicle aerodynamic characteristics, and parameters defining the lift modulation. It can be shown that the analytical solutions obtained in this report include the constant lift-drag solutions obtained by Lees, Hartwig, and Cohen in the orbital case and by Ting and Wang in the superorbital case. Furthermore, in the case of variable lift, this report deals with a continuous lift modulation program instead of a stepwise change of lift-drag considered by Lees, Hartwig, and Cohen.