Large axial load forces and extreme temperature ranges are typical for scientific balloon missions. Therefore, a durable, flexible, and thermally stable sensor material is needed. In this innovation, sensors have been designed to be integrated onto the load-bearing seams and/or outer balloon mesh polyethylene surface of the pressurized balloon system to measure accurately and continually axial loads under extreme environmental conditions for extended intervals (i.e. more than 100 days).
A highly flexible, low-modulus Metal Rubber (MR) material is used for strain/pressure sensors that are capable of large cyclic deformation without failure. MR is a free-standing nanocomposite material produced by the layer-by-layer combination of high-performance polymers and electrically conducting metal nanoparticles that provide durability and recoverability for sensor transduction, and a wide thermal operation range. MR can behave like a rubber band in that it can be folded/compressed for stowage, and then can be deployed and continually pressurized without failure. Also, because of the very low amount of metallic nanoclusters in the system (
The nanostructured elastomeric sensors are designed to be integrated into, or onto, the load-bearing Zylon tendons of NASA’s pressurized balloon system to measure axial loads accurately and continually. Any discrepancies in the load distribution of the tendons will be monitored in order to prevent failure in the tendons, which could cause total system failure and loss of expensive experimental payload containing important scientific data. In addition, thin nanostructured film sensors have been developed for application directly onto the polyethylene film gores of the balloon to monitor strain (from balloon pressure fluctuations). The ability to measure gore strain inflight, or during testing, will allow NASA scientists to quantify predicted or estimated balloon strain that was previously done through photogrammetric methods.
MR sensor materials have distinct advantages over traditional strain gauge, axial load, or health monitoring materials in that they are low-modulus (very similar or lower modulus than the balloon material itself and can be tailored from 1.0 MPa to 1 GPa), low mass density (less than 0.99 g/cm3 and even lower for MR mesh sensor materials), extremely durable (can withstand multiple strain cycling in excess of 1,000% elongation), and able to endure extreme environmental conditions such as UV exposure and temperature fluctuations experienced in long-duration terrestrial or planetary missions.
The MR sensors can be spatially patterned and interconnected between each seam/tendon, and multiplexed for telemetry in-flight. In addition, for shape-change, pressure fluctuating, and/or morphing inflatable structures, the integrated MR sensors would allow the ability to measure/ monitor the pressure of the balloon with spatially positioned sensors. The data acquisition instrumentation system would allow for the sensor signal to be captured using a simple two-wire interface system, and would be designed to accommodate NASA’s stringent size and weight requirements. The low-weight MR sensor in this innovation, for the ultra-long-duration scientific balloon axial load monitoring, is fabricated via electrostatic self-assembly (ESA), which is a low-cost, environmentally safe processing technique to form nanostructured conformal coatings and textile-based materials.
This work was done by Andrea Hill of NanoSonic, Inc. for Goddard Space Flight Center. GSC-16484-1