Inflatable Rigidizable Isogrid Boom Development

Abstract

Ultra-lightweight inflatable rigidizable space structures have been identified as an enabling technology for many large-scale and Gossamer type spacecraft planned by NASA and DoD for future space missions. The unique benefits of this class of structure, such as low packing volume, reduced complexity, and reduced mass, enable the development of large antennas, solar sails, and sunshields that would have been otherwise unrealizable. Through the maturation of this technology, many applications such as space based radar would benefit directly, and other applications such as mechanical actuation devices would benefit indirectly but significantly from material advancements. ILC Dover, under contract to the Jet Propulsion Laboratory (JPL) and NASA Langley Research Center (LaRC), has developed an ultra-lightweight inflatable rigidizable boom structure for use on gossamer spacecraft. The wall of the boom structural component is comprised of a grid-work of equilateral triangles that provide isotropic performance properties. This type of construction is termed an isogrid boom (See Figure 1). The grid-work is encased in two tubular polymeric films that act as gas containment vessels to enable inflation for deployment of the structure, and prevent the material from adhering to itself when packed. The exterior film also provides insulation to control the thermal conditions that govern the deployment process and structural performance in space. This structural concept was selected for study because of its high structural efficiency and simplicity in design. The material used in the fabrication of the isogrid structure is a composite, which consists of graphite and a shape memory polymer (GR/SMP). This GR/SMP material acts as a thermoplastic material and is able to be repeatedly heated and cooled to alter the structural shape. This allows the gossamer structure flight hardware to be packed and deployed for evaluation several times during ground test for checkout prior to launch and deployment in space. Shape memory polymers exhibit the unique property of returning to the originally formed shape when heated in a packed condition. In the case of structures with considerable deployment loads, inflation is used in conjunction with the weak SMP restoring force for deployment. This type of material was selected for study because of its structural performance properties, ability to be deployed and rigidized several times prior to launch, and storage life. The overriding goal was to develop a structural rigidizable beam technology that was close to flight readiness. This goal was met by performing numerous materials development tests on several candidate composite materials, manufacturing and testing numerous subcomponents and tube sections in simulated space and lab environments, and performing a deployment and rigidization test of a long boom section in a simulated space environment. The summation of the data indicated that the GR/SMP Isogrid was at a NASA Technology Readiness Level TRL of 5 to 6, but further study is required before the technology can be transitioned to a flight program. INTRODUCTION AIAA-2002-1297 Figure 1. 24K Tow Inflatable Isogrid Boom without Membranes * ILC Dover, Inc., Frederica, DE † Member AIAA ‡ Associate Fellow AIAA Copyright © 2002 by ILC Dover, Inc. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.