Flight-Path Angle Guidance for Aerogravity-Assist Maneuvers on Hyperbolic Trajectories

Abstract

This paper presents an original flight-path angle guidance algorithm using lift modulation for aerogravity-assist maneuvers on hyperbolic trajectories. The lift coefficient is tuned according to a three-stage guidance law, in which a linear flight-path angle guidance is assumed for both the ascending and descending atmospheric flight branches with a different gain coefficient in the feedback control form. The reference flight-path angle is linear with altitude and the closed-loop guidance attempts to track this reference. Between the descent and ascent phases, the guidance scheme provides a segment trajectory that is flown at a constant altitude. The developed algorithm was verified by comparing the obtained suboptimal results with data from previous studies on aerogravity-assist trajectory designs. A case study regarding a maneuver on a hyperbolic trajectory to Venus performed by a waverider, which is a spacecraft characterized by a high lift-to-drag ratio, is presented. The analysis provides the ranges of feasibility for the maneuver by varying the hyperbolic excess velocity and the periapsis altitude of the incoming orbit, as well as the angle flown at a constant altitude. The viability of the solutions in the presence of a number of thermal and dynamic constraints is also verified. The maneuver can be extremely effective in terms of the high values obtained for the angular deflection and the variation in velocity magnitude when appropriate values are selected for the input variables. The analysis indicates that the total heat load is the more stringent constraint.