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Title: Gravity compensation of deployable space structures
Author: Fischer, Annette
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2001
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Gravity compensation suspension systems are essential to support space structures during tests on Earth, but also impose constraints on the structures that have the effect of changing their behaviour. These constraints, except for those exactly offloading the self-weight, have to be minimised in order to replicate as closely as possible the zero-g conditions of space. The deployable structure that is used for the research carried out is a model of a rigid panel type solar array which is able to deploy and retract automatically. A computational and experimental study of the interaction of this structure with a manually adjustable suspension system, during quasistatic deployment tests, is presented. A methodology is established for modelling this interaction, for predicting the effects of suspension system adjustments, and for optimisation of the suspension system through these adjustments. It was found that some improvements can be achieved by manual adjustment, but further optimisation requires an active system. The two significant substructures of the active system that has been built are: a horizontally deploying support mechanism that mirrors the test structure, and seven suspension devices that contain strain gauges and displacement transducers and adjust the length of vertical suspension cables by a screw and nut actuator. A computational representation of the active suspension system is established, partly from theoretical methods and partly from measurements through which the structural properties have been identified, and the interaction between the active suspension and the solar array is investigated. Two different gravity compensation strategies, displacement control and force control, are implemented. Experiments carried out with the active suspension system are presented for these two schemes and their gravity compensation capability is evaluated and compared. It was found that gravity can be compensated by controlling the forces in the suspension elements to between 10% and 20% of g, however by controlling the displacements, the compensation is more than twice as bad. The latter strategy was, in practice, only marginally better than the passive system. Better results would have been possible with actuators having a higher positioning accuracy. This research has shown that a system with a self-deploying overhead structure, and active vertical suspension elements is a good concept for multi-point gravity compensation and should be further developed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available