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

Bruce L. Davis* and Mark Lake*  

Abstract  

Since the pioneering days of space exploration, large deployable structures have played a n important role  in expanding satellite capability and performance.  Perhaps one of the more prominent and simplistic  building block s 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 mec hanical 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 deplo yable 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  deploy ment . 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 .      Roccor’s High Strain Composite  Boom Deployer Family    The f our unique deployer systems  discussed in this paper are identified in Figure 1. Each of these systems  was designed for a s pecific application  with a series of performance and operational requirements . A brief  description of design considerations for each system  follows below:                                                             * Roccor, Louisville, CO  

Proceedings of the 43rd Aerospace Mechanisms Symposium, NASA Ames R esearch Center, May 4-6, 2016