Description: For long-duration missions, one of the primary concerns is the potential for structural material failure of the inflatable softgoods restraint layer due to creep. Creep is a phenomenon where deformation occurs under sustained loading. Structural health monitoring (SHM) of the restraint layer in inflatable systems is essential to ensure the safety of crew members and the continued operation of NASA missions. To address this issue, there is a need to develop a new SHM approach to accurately and actively measure creep of the restraint layer. The current methods include adhesive foil strain gages, fiber optics, accelerometers, and acoustic sensors which all have their potential drawbacks and require extensive wiring which must survive deployment. To address this critical need, X-wave Innovations, Inc. (X-wave) proposes to develop an Adjacent Inductive Coil Sensor (AICS) system to monitor the creep of the restraint layer in multilayer systems. The proposed AICS system improves upon the current state of the art sensors by not requiring any electrical cabling or wiring to the restraint layer. The proposed sensor system is also advantageous over other types of SHM sensors such as fiber optics or other flexible materials in that the proposed sensor does not need to withstand significant elongation during deployment or while in operation. The AICS system will be an integrated sensing system that utilizes multiplexing to monitoring the restraint layer as a whole. The AICS system will use non-contact interrogation of the restraint layer from the interior of the inflatable softgoods structure, therefore interference from the thin metallic depositions of the outer layer will have no effect on the performance of the sensor system. The AICS system will include a prognostication algorithm that will predict the creep behavior of the restraint layer and notify the crew members of any anticipated failures.

Benefits: NASA has a great interest in using deployable mechanisms, expandable booms, and inflatable structures for a variety of applications. Our proposed system can provide creep monitoring of the restraint layer for programs such as NASA's NextStep Habitat program and the commercial Low Earth Orbit destinations program. In addition, existing inflatable NASA systems such as the Hypersonic Inflatable Aerodynamic Decelerator, and the Low-Earth Orbit Flight Test of an Inflatable Decelerator would benefit from the proposed system.Other government agencies, including the Department of Defense and Department of Energy, will directly benefit from this technology. The US Navy's Multi-Occupant Flexible Recompression Chamber, a recompression chamber for expeditionary environments, uses Vectan as a strength member. The DOE has developed an inflatable Resilient Tunnel Plug to prevent or limit flooding in subway tunnels.