NASA's Langley Research Center has developed the SHEARLESS composite boom with a final cross-section shape that is lenticular and is flexible enough to allow elastic flattening and subsequent coiling around a cylindrical reel/drum. The torsional stiffness of the structure is also greatly increased and becomes two orders of magnitude larger than that of the individual tape-spring components alone.
The innovation enables a lightweight structure that can be stowed on a reel without appreciable shear stresses developing in its constitutive composite parts. This allows for unprecedentedly small coiling diameters for the total thickness of the structure, which can enable highly compact designs such as those required in CubeSat/small satellite applications.
The SHEARLESS composite boom has a rollable structure with a large moment of inertia per unit of stored height that does not suffer from shear-derived problems. The boom is fabricated from joining two independent tape-springs front-to-front with the use of a durable, seamless, polymer sleeve. This sleeve allows the two parts to slide past each other during the coiling/deployment process so as to minimize shear and its derived problems.
As demonstrated through specific laminate design of the two inner composite parts, the SHEARLESS composite boom can also be fabricated with a special inherent feature — bi-stability — that enables designs with minimal mechanisms and aids in deployment controllability and reliability.