Modular Inflatable Composites for Giant Space Telescopes

There is an every-growing need to construct large space telescopes and structures for observation of exo-planets, main-belt asteroids and NEOs. Space observation capabilities can significant enhanced by large-aperture structures. Structures extending to several meters in size could potentially revolutionize observation enabling technologies. These include star-shades for imaging distant objects such as exo-planets and high-resolution large aperture telescopes. In addition to size, such structures require controllable precision surfaces and high packing efficiencies. A promising approach to achieving high compaction for large surface areas is by incorporating compliant materials or gossamers. Gossamer structures on their own do not meet stiffness requirements for controlled deployment. Supporting stiffening mechanisms are required to fully realize their structural potential. The accuracy of the ‘active’ surface constructed out of a gossamer additionally also depends on the load bearing structure that supports it. This paper investigates structural assemblies constructed from modular inflatable membranes stiffened pneumatically using inflation gas. These units assembled into composites can yield desirable characteristics.

They present the design of large assemblies of these modular elements. The work focuses on separate assembly strategies optimized for two broad applications. The first class of structures require efficient load bearing and distribution. Such structures do not need high precision surfaces but the ability to efficiently and reliably transmit large loads. This can be achieved using a hierarchical assembly of inflatable units. They also need to be stiffer as a collective assembly as compared to their constituent modules.

Preferential placement of varying modular units leads to local stiffness modulation. This in-turn helps modify load transmission characteristics. Applications of such structure also extend to deployable drag-chutes or aero-breaking devices for atmospheric maneuvering. The second are structures with precision surfaces for optical imaging and high-gain communication apertures. They demonstrate over-constrained modular assemblies exhibiting elastic averaging when assembled with a very large number of modules. Averaging effects are amplified with the number of sub-units approaching required surface precision with a large enough number. Their work includes fundamental structural studies to evolve feasible sizing schemes for both classes of structures. A structural analysis strategy using discrete finite elements has been developed to simulate the assembled behavior of modular units. The structural model of each inflatable unit has been extended from previous work to approximate each unit as a 3-dimensional truss system. Analysis results are compared with full scale simulations on commercial analysis package LS-Dyna. Analysis leads to an understanding of the extent to which inflatables can be scaled up effectively. Critical geometric design considerations are identified for stowed and deployed states of each structure. Their proposed design of compliant hinges between structure to assemble even large units. Further work includes prototype development and deployment force measurement to validate the structural model.

Arxiv – Modular Inflatable Composites for Space Telescopes

(H/T Adam Crowl)

By Brian Wang,