[Univ of Cambridge] [Dept of Engineering]

Gravity Compensation of Deployable Space Structures

Annette Fischer


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.  The deployable structure used for the present study is a model of a rigid panel type solar array that 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 optimisaiton requires an active system.  The two significant substructures of the active system are:  a deployable support mechanism that mirrors the structure, and seven suspension devices that contain force and displacement transducers and control the length of the support cables by a screw and nut actuator.  A theoretical representation of the active suspension system is established in an analogous way to that for the passive system.  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.

[Cambridge University | CUED | Structures Group | Geotechnical Group]

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