Shape Control of Membrane Reflectors (SCMeRe)

Lead Research Organisation: University of Cambridge
Department Name: Engineering

Abstract

Large space telescopes are constrained by system mass and by the space available in the stowed configuration. With the use of gossamer structures, made of reflecting membranes or thin shells, ultra large, light-weight telescopes can be envisioned, with an areal mass that is only a fraction of a kilogram per square meter and hence orders of magnitude less than current, monolithic passive mirrors. This collaborative project between the University of Cambridge and the Universite' Libre de Bruxelles, the Universite' de Nantes, and the Centre Spatial de Liege will address the following scientific and technological challenges to the realization of large space reflectors: prediction of wrinkling in membranes and its alleviation by passive and boundary control; nonlinear analysis of piezoelectric membranes subjected to buckling (wrinkling); solution of the inverse problem of finding the strain distribution which compensates for a given shape error; numerical methods for nonlinear piezoelectric problems; coupling between optical and structural mechanics software; reflector metrology to evaluate the surface figure error, with special attention to the high spatial frequency waviness of this type of reflector; active shape control of distributed piezoelectric shells and membranes. The research consortium consists of four groups with complementary expertise in the active control of piezoelectric structures, deployable space structures and membrane wrinkling, numerical methods for highly nonlinear structures, and optics and reflector metrology. The project will lead to numerical demonstrators of the control strategy and experimental demonstrators of wrinkling alleviation and of the metrology system.The control problem addressed in this project is challenging by its size, by the complexity of the physical phenomena involved, and by the strict surface figure accuracy requirements on the reflecting surface. Because of this, it is expected that the outcome of this project will be of interest to the scientific community far beyond the specific problem of gossamer telescopes.

Publications

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Bonin Arnaud Stephane (2012) Wrinkling in polygonal membranes

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Keith Alexander Seffen (2009) Small-Diameter Membrane Reflector Wrinkling

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Keith Seffen (2009) mall-Diameter Membrane Reflector Structures

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Keith Seffen (2009) Shape Control of Wrinkled Membranes

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Santer M (2016) Optical space telescope structures: The state of the art and future directions in The Aeronautical Journal

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Schulze B (2014) When is a symmetric body-hinge structure isostatic? in International Journal of Solids and Structures

 
Description We have been interested in the shape of very thin membranes used as optical reflectors in space - their thinness broaches inevitable problems of wrinkling and creasing when supported on their edges, and we have been interested in understanding them, and eliminating them.

In particular, we are able to predict the shape of wrinkled membranes using compact theoretical models when virtually all work by other is performed computationally: we have devised a scheme for mitigating wrinkles by passive means, without resorting to complex control methods: we have provided an award-winning review of the state-of-the-art technology. Overall, this project has produced a PhD thesis (successfully examined, 2012); 3 international conference papers; 1 journal paper (given an international silver award), and 2 further journal papers are in preparation, with a view to submitting by the summer of 2012.
Exploitation Route Membranes are used everywhere terrestrially: from umbrellas to fabric roofs, from clothing to delicate medical devices. Fundamentally, their function is dictated by their shape, and this research has allowed us to better understand the susceptibility of shape to imperfections and errors and to correct for them, so the correct shape is achieved. At the heart of research, we have always sought a simplicity of description without sacrificing accuracy, for this allows us to capture the essential physics of behaviour; so the results of our work have general implications for the modelling of membrane behaviour, generally. This research informs upon the design of very thin but large structures for use in space, for the communications and observation industries. The cost of launching a satellite is prohibitive, and savings are achieved by reducing its mass and size; thin membrane structures provide an efficient solution because they are light and can be folded. But, they have to be deployed and "tensioned" into the correct shape, and this shape has to be maintained throughout its operational life. This research has explored all features associated with shape, its potential for becoming unstable, and how this might be corrected using a straightforward scheme that does not add complexity or cost.
Sectors Aerospace/ Defence and Marine
 
Description DeployTech 
Organisation Surrey Satellite Technology Ltd
Country United Kingdom 
Sector Private 
PI Contribution We were part of European Framework 7 package (RG64205), tasked with reviewing and designing new deployable booms for de-orbiting satellite technology.
Collaborator Contribution They coordinated the project overall; and they were responsible for the complete design of a deorbiting satellite.
Impact We produced a review and design paper for deployable booms, which combines Structural, Mechanical and Aerospace Engineering topics: Schenk M, Viquerat A D, Seffen K A and Guest S D (2014), "Review of Inflatable Booms for Deployable Structures: Packing and Rigidization", Journal of Spacecraft and Rockets, Vol 51(3), pp.762-778. Two co-authors, Mark Schenk and Andrew Viquerat, who initially worked as research associates, gained positions elsewhere: Mark, at Surry then Bristol University; Andrew, as project coordinator, at Surrey on this very project.
Start Year 2012