Description: Inflatable pressurized habitats are envisioned as a practical way to build shelters much larger than landing craft for astronauts and their scientific operations on Mars, the moon and elsewhere. These habitats maintain their inflated shape via high-strength Vectran webbing. The piezoresistive extensometers developed through this STTR program can be directly integrated into or onto Vectran webbing and would allow the determination of webbing loads during the inflation process as well as creep during long-term deployment of the habitat. The objective of this NASA STTR program has been to develop such extensometer sensor materials based on NanoSonic's Metal Rubber materials technology that may be incorporated into the support webbing of stitched, pressurized space habitats during their production to monitor loading and creep. The electrical resistance of these sensor materials changes linearly with strain, its modulus is low enough not to interfere with the deformation of the webbing during habitat stowage, inflation and operation, and its failure strain can be made higher than one hundred percent, so much larger than that of the webbing. NanoSonic is working with faculty and students in the Electronic Textiles Laboratory at Virginia Tech, with input from inflatable habitat manufacturers at ILC Dover, to develop sewing / stitching / weaving methods for the integration of the sensor materials into layers of webbing during production. During Phase I, sensor performance was tested in response to both uniaxial loading using a computer-controlled laboratory load frame, and using dead loads on representative webbing material that experiences long-term creep. During Phase II, NanoSonic and Virginia Tech would work with ILC Dover to integrate and test webbing sensors on softgood habitat models and Bally Ribbon Mills to weave Metal Rubber extensometers directly into NASA habitat webbing materials.

Benefits: The primary NASA application focus for the Metal Rubber extensometers developed through this STTR program is the nondestructive measurement of creep in woven fabric webbings used to control and maintain the shape of space habitats. Monitoring long-term creep allows the statistical estimation of the remaining lifetime of the webbing material, and it is important that this estimate be significantly longer than the required mission lifetime of the inflatable. NanoSonic's Metal Rubber material may be formed into either sheet materials that may be dimensioned into discrete creep extensometers, or into yarn that may be directly woven into webbings during their manufacturing. For NASA, discrete creep extensometers may be applied where needed on existing habitat webbing, or built into the webbings during habitat production. Other similar NASA applications that require the measurement of strains without interfering with the performance of devices include use in 1) landing airbags such as those used on Mars rover landings, 2) atmospheric decelerators such as HIAD and SIAD, 3) high altitude atmospheric research balloons used on earth and elsewhere, 4) high altitude airships, 5) EVA space suit and glove fabrics and bladders, 6) inflatable UAVs, and 7) aerostats. In all of these cases, the measurement resolution at small strains is important. Such sensors could also be used in e-textiles to monitor astronaut motions during operations and exercise.

The developed piezoresistive sheet and yarn extensometers may also be used for measurement of the strain, creep, shape and load on non-NASA inflatable structures including 1) commercial EVA space suits such as the recently demonstrated StatEx suit manufactured by our ILC Dover partner, 2) passenger airships that display messages at sporting events, 3) heavy-lift lighter-than-air vehicles used for military transport to remote regions supported by little infrastructure, 4) inflatable devices such as ILC Dover's tunnel plug used for New York City subway flood protection, 5) military aerostats, and 6) inflatable military or hobby UAVs. Additional uses include: motion-sensing fabrics, the development, testing and use of military and commercial round, cruciform, ribbon and ram-air parachutes, the design and testing of fabrics for custom clothing, measurement of extension in large civil structures and installations, such as the large strains due to subsidence in soil and rock formations and the long-term displacements of buildings, dams, roadways and pipelines, and in sensor-instrumented webbings used for climbing, load securing, sporting goods and healthcare products.