A tape-spring telescope structure: deployment modelling

Paper number

IAC-06-C2.2.02

Author

Mr. Laurent Blanchard, Thales Alenia Space, France

Coauthor

Mrs. Gwenaëlle Aridon, France

Coauthor

Dr. Didier Rémond, France

Coauthor

Pr. Régis Dufour, France

Coauthor

Dr. Frédéric Falzon, Thales Alenia Space, France

Year

2006

Abstract

To be able to face the challenges of the near future in spaceborne observation, like multi-pupil systems conceived as free flyers or extremely high resolution  systems with large dimensions and high agility requirements, the Alcatel Space Research Department is studying innovative structural concepts.
One of these is a telescope structure based on an hexapod whose legs are deployable coiled tape-springs and whose feet can be vertically moved thanks to linear actuators. This concept permits stowing the secondary mirror in a favourable mechanical configuration with high stiffness and low stability requirements for launch and to self-deploy once in orbit. The deployment deviations and long-term instabilities will be corrected thanks to the vertical displacement of the hexapod's feet and the final optical performance will be reached thanks to an adaptive optics correction stage.
The major limitations of space deployable structures are their deployment accuracy and their dynamic stability. To optimize design and performances depending on the dedicated application, the deployment and the deployment repeatability have to be mastered. This paper describes the global investigation on the structure dynamics which has been carried out by three ways focusing on the dynamic stability of the deployed configuration, the deployment kinematics and the ability to control.
The first part deals with a presentation of the hexapod design and the structural finite element modelling of the deployed configuration. Sinus vibration tests have been performed on a breadboard. Results are compared to the modal analysis.
The analysis during deployment which is more complex starts with consideration of the modal behaviour of different deployed heights of the hexapod. This leads to a better understanding of the evolution of the hexapod stability during deployment. Another way to study the deployment stage is to consider a single deployable unit and to identify the dissipation in a coiling device. Measured force-deflection loops lead to a dynamic model of friction: the generalized Dahl’s model. Then, the modelling of a multi-unit hexapod gives raise to the effect of nonlinearities induced by hysteresis during deployment at the complete structure level.
The preliminary attempt to design the capability of control of the hexapod has been performed through correction tests of the structure with different levels of actuation of the hexapod feet. It reveals a linear behaviour of the upper platform in the workspace of the hexapod.

Abstract document

IAC-06-C2.2.02.pdf

Manuscript document

IAC-06-C2.2.02.pdf (🔒 authorized access only).

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