Session: 01-12-01: Spacecraft Structures 1

Paper Number: 152297

152297 - Eliminating Shear in Flattenable and Rollable Booms 

Flattenable and rollable booms have seen great success as deployable structures on several spacecraft missions to unfold sails, arrays, and antennas. Historically, these booms have been restricted to relatively gossamer applications because the rolling process induces high shear loads between the top and bottom shells – the inside shell is highly compressed, while the outside shell is in tension and through the rolling transition region, these loads manifest as a shear load between the two shells. Shear load directly relates to shell thickness, driving shells to be extremely thin to minimize shear. Past boom architectures that are sensitive to rolling shear include TRAC booms and collapsible tubular masts (CTM). Living hinge booms (LHB) that employ two thin and narrow hinges along the length of the boom allowing two semi-circular shells to be connected and flattened, are also sensitive to rolling shear.

This paper will report on analysis, fabrication, and test results for a new patented (opterusrd.com/vpm) flattenable and rollable boom concept called Hybrid Inflatable Boom (HIB). The key innovation of the boom is that it eliminates shear between the top and bottom shells by allowing axially stiff structural materials in the two shells to interleave in the flattened state so that the neutral axis of each flattened shell is coincident and lies on the same plane during rolling. This allows much thicker structural materials to be used in each shell, greatly increasing the stiffness and load carrying capacity of the boom. A drawback of this approach is that as it is applied more, there is less shell thickness available to for structural materials to provide boom hoop stiffness. Booms with insufficient hoop stiffness tend to fail at lower loads in kinking or Brazier buckling modes. Reduced hoop stiffness is mitigated with an inflation pressure to maintain a circular tube cross-section. Hence, the HIB is hybrid in that it uses both inflation pressure (for hoop stiffness) and stiff materials (for axial stiffness).

Rolling and deployed finite element analyses have been used to design several LHB and HIBs. The HIB simulations demonstrate a dramatic reduction in peak stresses during rolling compared to booms with constant thickness cross sections. Boom variations have been fabricated using both high strain composite materials and materials more commonly used in inflatable structures. A variety of manufacturing methods have been investigated for the longitudinal hinges that connect the two shells. Booms have been tested for rolling performance and axial and bending stiffness and strength. Results from these analysis, design, fabrication, and testing activities will be presented.

Presenting Author: Thomas Murphey Opterus

Presenting Author Biography: Thomas Murphey received a PhD from University of Colorado in 2001. Murphey is an accomplished leader, scientist, and innovator in the space structures industry with 30 years of experience and an impressive technology commercialization record. Many of his patents and developments have been licensed and are currently used in space or are part of current space flight programs. His pioneering work serves as the foundation for the high strain composites industry through 12 patents and over 70 publications. Murphey is currently the founder and CEO of Opterus, a small business focused on 1) rapid innovation in industries requiring advanced structures and 2) the fabrication of high strain composites for folding structures.