The deployment of a spinning solar sail

[摘要] ENGLISH ABSTRACT: In recent years, interest in solar sailing has grown greatly, and significant research andresources are being contributed to its development and the development of similar and supportingtechnologies. Sailcraft utilise large deployable membrane structures to exchangemomentum with photons in order to generate thrust from Solar Radiation Pressure. Manysmall solar sailing satellites make use of three-axis stabilisation and semi-rigid booms, howeverthis design places limits on the sizes of sails possible due to the physical properties ofthese booms and the size of the deployment mechanisms required. Larger sails are desiredin order to achieve greater solar thrust. The use of a spinning solar sailcraft with flexiblebooms makes it possible to deploy significantly larger sails, as the centrifugal force actsto deploy the sail and maintain the deployment thereof, eliminating the limits enforced byavailable semi-rigid boom technologies. The low cost and small size of CubeSats may beused to further develop spinning solar sail technology. This thesis focuses on the deploymentof a spinning solar sail on a CubeSat platform.The dynamic equations which describe the behaviour of a spinning solar sailing satellitewith flexible booms during- and post- deployment are developed. These equations, whichdescribe the system, are used to investigate the behavioural trends in the deployment undervarious deployment strategies. Particular focus is given to the passive deployment of thesail booms. No direct active control is placed on the boom deployment in this case; thedeployment rate is instead indirectly controlled through the spin rate of the satellite. Thisis achieved by the application of rotational damping to the pulley on which the booms arestowed and where from they are deployed. Passive deployment cases are investigated wherecontrol is based on strategies including free spin, centrifugal force-based control and constantspin rate control. The dynamics of active deployment, where the deployment rate is directlycontrolled, are also investigated.An experimental deployment mechanism is designed in order to validate the trends seenin the cases of passive deployment. This experimental deployment mechanism makes useof 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 areconfirmed where possible. A control algorithm is developed, which is capable of detecting thedeployment state of the booms based on the control input supplied to the motor driving themechanism spin. Based on the deployment state detected, the spin rate of the mechanismcan be appropriately adjusted.Based on the practical experience and insights gained from experimentation, the designs ofthree deployment mechanisms are presented. Two of the mechanisms designed make useof rotary dampers in different configurations in order to achieve passive deployment. Thethird mechanism is intended for actively controlled deployment and possess an actuator tocontrol the deployment rate directly. The design takes advantage of centrifugal force, whichallows the actuating motor and the mechanism as a whole to be very small in size.

[发布机构] Stellenbosch University