Characterisation and Applications of Aerodynamic Torques on Satellites

Abstract

Increasing interest in low Earth orbits as a means of reducing the operational cost of satellites demands the development of new optimised solutions. One of the main difficulties when operating at these altitudes is the atmospheric drag resulting from the collision of gas molecules with the satellite's surface. Despite this effect being observed since the very beginning of the space era, an accurate prediction of drag forces and torques is still challenging. As a consequence, engineers treat these forces and torques as a bounded but unknown perturbation to the system. In recent times, the launch of low-altitude scientific missions has renewed the interest in atmospheric and drag phenomena. Thanks to the collected data, an active research community is making progress towards a better understanding of the upper atmosphere, improving current density models and allowing a better characterisation of aerodynamic interactions. Taking advantage of these advancements, this work explores how to transform aerodynamic torques, an inconvenient perturbation to the satellite attitude, into something useful that contributes to achieving mission goals. This is accomplished by a proper characterisation of the aerodynamic properties of the spacecraft. Accordingly, a contemporary review of the satellite drag phenomena identifying current challenges, limitations, and available solutions is first presented. Then, in order to predict drag coefficients and its variations, a new satellite aerodynamic tool has been developed, which provides aerodynamic databases of satellites with complex shapes. This allows the development of novel applications of aerodynamic torques. Three studies are then conducted. First, aerostability and attitude response: from the classical rotational equations of motion including gravity gradient, the influence of aerodynamic torques is studied both in the pitch and roll-yaw axes. The study aims to link geometrical properties with attitude response, providing a way to design satellites that take into account environmental torques. Following this idea, the next application shows how a physically consistent modelling of the aerodynamic torque allows to perform reaction wheels momentum dumping using existing hardware, solar arrays. Finally, the study of optimal attitude manoeuvres in drag-dominated orbits is undertaken. Using the example of a full-electric geostationary satellite transfer orbit, it is shown how these attitude manoeuvres can be used to eliminate the mass penalties and cost associated with a perigee raising manoeuvre.In all cases, results prove the feasibility of the approach showing the value added of aerodynamic analysis. The benefits range from the reduction of attitude requirements to the development of cost-effective solutions, including propellant savings and, hence, operational life extension.

Date of Award	1 Aug 2017
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Peter Roberts (Supervisor) & Katharine Smith (Supervisor)