Uncertainties and Radius Tracking in Flight-Path Angle Guidance for Aerogravity-Assist

Abstract

This paper addresses the problem regarding the influence of random dispersions related to the environment and system on a flight-path angle guidance algorithm using lift modulation for aerogravity-assist maneuvers on hyperbolic trajectories. To compensate for the effects of dispersions and uncertainties, an original radius tracking guidance model is presented, with a formulation for both the temporal domain and the true anomaly domain. This algorithm allows a vehicle to successfully track a suboptimal trajectory planned before a mission. A case study involving 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. An uncertainty and sensitivity analysis is used to evaluate the impacts of dispersions in the inputs on the main parameters and the performance characterizing the mission. The analysis provides an extensive range of cases that identify the density and thickness of the atmosphere as the most influential dispersed inputs. Adequately tuning the radius tracking guidance parameters enables the efficient attenuation and compensation of the perturbative effects of the uncertainties for obtaining trajectories that are close to the nominal trajectories, estimated before the mission in the absence of dispersions, in terms of the angular deflection and velocity magnitude variation. The presented model can be easily implemented for onboard guidance purposes.