Modelling and performance analysis of a tether and sail-based trajectory control system for extra-terrestrial scientific balloon missions

摘要

Balloon systems show great promise for exploring the atmospheres of extra-terrestrial bodies in the solar system. The balloon system concept was demonstrated by the aerostats aboard the Vega 1 and 2 missions sent to Venus. Such systems glean propulsion from atmospheric winds, and at present are unable to travel in a direction perpendicular to the direction of the wind, limiting their exploration potential. A control system capable of modifying the system trajectory by traveling in a direction perpendicular to the direction of the wind is desired to increase exploration potential as well as to perform tasks such as maintaining latitude.A balloon and sail system which can use wind velocity and density gradients to produce a guiding force perpendicular to the velocity of the wind is discussed here. Such a guidance system is passive in nature and requires little power for actuation and control. It was previously demonstrated that such a control system is capable of generating guiding velocities of several meters per second within the Venusian atmosphere. Furthermore, this control system was shown to be capable of achieving sufficient control for the majority of the latitudes on Venus.This work builds on previous results and demonstrates the benefits of being able to generate guiding velocities via a sail system by viewing the trajectories taken by planetary balloon systems employing such a system. First, a description of the system model is given. Next, for the atmospheres of Venus and Titan, trajectory control is demonstrated for various sail parameters, such as sail size and mass. The benefit of such control is shown by the ability to achieve various latitudes of interest for a given flight duration. These latitudes are chosen based on geographic features, such as lakes on Titan. Finally, a PI controller is added to the model to demonstrate rudimentary control of the balloon system for maintaining and changing latitudes. A brief discussion regarding the control law of the system is also provided.