A sister to SHEARLESS booms, the Bistable Collapsible Tubular Mast (Bi-CTM) boom offers compact storage on a cylindrical drum that deploys a composite material boom with a closed tubular cross-section that has unmatched bending and torsional stiffness for the mass of the thin-shell structure. The Bi-CTM is also scalable for long booms, given the load-carrying capacity.
The Bi-CTM’s two omega-shaped composite thin shells form a bonded closed section that can spool onto a relatively compact drum for compact launch packaging and provide unparalleled stiffness-to-mass ratio when deployed. When using the booms as beam-column structures with a primarily compressive load component, this ratio determines the structural mass efficiency of the components, making the Bi-CTM exceptional for lightweight deployable structural rigging with higher load demands. The improved dimensional and thermal stability offered by the closed-section shape and low coefficient of thermal expansion materials of the Bi-CTM enables the use of the boom technology in precision applications that require high stability in harsh environments.
Just like a kid’s “slap bracelet,” the Bi-CTM design includes a secondary, stable, low-energy state aside from the rigid deployed state. The result is that the Bi-CTM is not under high-spring stress when coiled up, which simplifies the stowage process as well as enabling a more controllable extension of the boom. The simplified stowage process enables reduced size, mass, and complexity of the storage and deployment mechanism system.
Compared to the majority of deployable thin-shell booms — which have at best a semi-open cross-section — this true closed cross-section boom is stronger while keeping the compact nature of rollable booms and is able to overcome both bend and twist buckling-related limitations. Using omega-shaped cross-sections with optionally circular, parabolic, or ellipsoidal segments — where each half of these thin-shell composite booms can use equal (symmetric boom) or different (asymmetric boom) cross-section geometry and/or composite laminates — offers a great deal of boom customization in terms of stable coiled diameter and structural properties.