An Ideal Telescope Composed of Tensegrity

Some tensegrity practitioners feel that tensegrity is not a practical building method--it does not help that Kenneth Snelson, a prime inventor of tensegrity, is one of these skeptics.

Robert Skelton does not agree. Tensegrity is an ideal solution to building highly efficient structures in a resource constrained world, according to him. Over the years he has published a foot bridge design for architects in Switzerland that uses only one third the mass of traditional designs, and an airplane wing design that is 30% lighter than the best existing wing.

A recent post of his argued for tensegrity use in large telescopes, since mass plays a big role in the shape control of telescopes. Such dishes need to change position and resist the distortional effects of gravity.

Figure 1. Parabolic tensegrity rigid structure.

Figure 1 shows our latest parabolic tensegrity telescope concept. We believe this is the first tensegrity structure (other than a simple unit¹) that has no soft modes (i.e., it is stiff in all directions). By adjusting the tension of certain prestressed cables, one can maintain a parabolic shape for all positions of the telescope. We are now deriving the optimal complexity for this minimal-mass telescope.
The control of cable tensions requires feedback information such as force transducers in certain tension and compressive components of the structure. The design of the control algorithm should minimize the energy that would be required to suppress vibrations below a specified level and to keep the parabolic shape errors below optical tolerances. The grand challenge before us is to design a structure with minimal mass that also requires the smallest control energy to meet the performance requirements. This will be among the first attempts to truly integrate the design of structure and control rather than the traditional approach of designing the control only after the structure is determined. This integration of the control and structure design disciplines will certainly be required to meet the more stringent demands of future design challenges. Achieving this integrated approach is the focus of our ongoing research.

Links:
Telescope article:   Designing minimal-mass tensegrity telescopes of optimal complexity
Skelton's faculty page.