Browsing by Author "Hibbert, Luke Thirkell"

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    The deployment of a spinning solar sail
    (Stellenbosch : Stellenbosch University, 2019-04) Hibbert, Luke Thirkell; Jordaan, H. W.; Steyn, W. H.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: In recent years, interest in solar sailing has grown greatly, and significant research and resources are being contributed to its development and the development of similar and supporting technologies. Sailcraft utilise large deployable membrane structures to exchange momentum with photons in order to generate thrust from Solar Radiation Pressure. Many small solar sailing satellites make use of three-axis stabilisation and semi-rigid booms, however this design places limits on the sizes of sails possible due to the physical properties of these booms and the size of the deployment mechanisms required. Larger sails are desired in order to achieve greater solar thrust. The use of a spinning solar sailcraft with flexible booms makes it possible to deploy significantly larger sails, as the centrifugal force acts to deploy the sail and maintain the deployment thereof, eliminating the limits enforced by available semi-rigid boom technologies. The low cost and small size of CubeSats may be used to further develop spinning solar sail technology. This thesis focuses on the deployment of a spinning solar sail on a CubeSat platform. The dynamic equations which describe the behaviour of a spinning solar sailing satellite with flexible booms during- and post- deployment are developed. These equations, which describe the system, are used to investigate the behavioural trends in the deployment under various deployment strategies. Particular focus is given to the passive deployment of the sail booms. No direct active control is placed on the boom deployment in this case; the deployment rate is instead indirectly controlled through the spin rate of the satellite. This is achieved by the application of rotational damping to the pulley on which the booms are stowed and where from they are deployed. Passive deployment cases are investigated where control is based on strategies including free spin, centrifugal force-based control and constant spin rate control. The dynamics of active deployment, where the deployment rate is directly controlled, are also investigated. An experimental deployment mechanism is designed in order to validate the trends seen in the cases of passive deployment. This experimental deployment mechanism makes use of a geared rotary damper to apply a torque to the pulley from which the booms deploy - this slows the deployment rate with no external inputs. The trends seen in simulation are confirmed where possible. A control algorithm is developed, which is capable of detecting the deployment state of the booms based on the control input supplied to the motor driving the mechanism spin. Based on the deployment state detected, the spin rate of the mechanism can be appropriately adjusted. Based on the practical experience and insights gained from experimentation, the designs of three deployment mechanisms are presented. Two of the mechanisms designed make use of rotary dampers in different configurations in order to achieve passive deployment. The third mechanism is intended for actively controlled deployment and possess an actuator to control the deployment rate directly. The design takes advantage of centrifugal force, which allows the actuating motor and the mechanism as a whole to be very small in size.