Development of Compact Mechanically Driven Systems for High Strain Composite Slit-Tubes

摘要

Since the pioneering days of space exploration, large deployable structures have played an important role in expanding satellite capability and performance. Perhaps one of the more prominent and simplistic building blocks of deployable structures is the rollable slit-tube boom, or a “Storable Tubular Extendible Member” [1,2]. This device functions in a mechanically similar fashion to a tape measure where a long metallic cross-section is rolled into a coil, providing a high packaging efficiency and the ability to deploy to various lengths. This technology has been commonly employed in space for 50+ years due to the simple nature of the design and the limited number of mechanical components required to deploy in orbit. Moreover, the industry has long known and applied a wealth of lessons learned from early flights of these simple devices [2]. Examples include using the slit-tube as a standalone structure to offset sensors or cameras from a spacecraft body to more fully integrated systems such as the primary drive mechanisms for telescoping booms used to deploy the sunshade on the James Webb Space Telescope. Despite the extensive use, this technology is limited when the deployable structure requires high precision or is subjected to large structural loads. For these cases a complex set of mechanisms consisting of rollers, guides, and bearings to unravel the metallic slit-tube becomes necessary in order to contain its considerable stored strain energy in the coil and properly manage its deployment. Conversely, the use of High Strain Composite (HSC) slit-tubes [3,4,5] can allow greatly increased boom strength and stability. Roccor LLC, based in Louisville, Colorado is currently developing a series of HSC slit-tube deployers that take advantage of the non-isotropic material properties HSC materials to reduce their stored energy. Specifically, Roccor is developing HSC slit-tube laminates composed of traditional space-qualified materials, which are highly structural in the extended configuration but also have a relatively low stored strain energy in the stowed configuration. As a result, the need for a complex set of rollers and constraints on the coil are eliminated and the deployment device volume is reduced. In addition, these laminates provide near zero coefficient of thermal expansion (CTE) and/or the opportunity to embed internal conductors, which can act as an RF element or to transfer power/data without a standalone harness. The Roccor team has developed a series of integrated HSC slit-tube boom deployer systems that vary in size, performance and application. In this paper, a design review of four selected systems is outlined with a focus on the mechanical components enabling deployment/retraction while also ensuring structural rigidity. In addition, the best practices for ensuring adequate boundary conditions are also identified.