Mechanical counter-pressure space suit design using active materials

Abstract

Mechanical counter-pressure (MCP) space suits have the potential to greatly improve the mobility of astronauts as they conduct planetary exploration activities; however, the underlying technologies required to provide uniform compression in an MCP garment at sucient pressures (29.6 kPa) for space exploration have not yet been demonstrated, and donning and dong of such a suit remains a signicant challenge. This research effort focuses on the novel use of active material technologies to produce a garment with controllable compression capabilities to address these problems. We the describe the modeling, development, and testing of low spring index (C = 3) nickel titanium (NiTi) shape memory alloy (SMA) coil actuators designed for use in wearable compression garments. Several actuators were manufactured, annealed, and tested to assess their de-twinning and activation characteristics. We then describe the derivation and development of a complete two-spring model to predict the performance of hybrid compression textiles combining passive elastic fabrics and integrated SMA coil actuators based on 11 design parameters. Design studies (including two specifically tailored for MCP applications) are presented using the derived model to demonstrate the range of possible garment performance outcomes based on strategically chosen SMA and material parameters. Finally, we present a novel methodology for producing modular 3D-printed SMA actuator cartridges designed for use in compression garments, and test 5 active tourniquet prototypes (made using these cartridges and commercially available fabrics) to assess the eect of SMA actuation on the tourniquet compression characteristics. Our results demonstrate that hybrid active tourniquet prototypes are highly effective, with counter-pressures increasing by an average of 81.9% when activated (taking an average of only 23.7 seconds to achieve steady state). Maximum average counter-pressures reached 34.3 kPa, achieving 115.9% of the target MCP counter-pressure. We observed signicant spatial variability in the active counter-pressure profiles, stemming from high friction, asymmetric fabric stretching, and near-field pressure spikes/voids caused by the SMA cartridge. Modifications to reduce tourniquet friction were effective at mitigating a proportion of this variability. System performance and repeatability were found to depend heavily on the passive fabric characteristics, with performance losses attributable to irrecoverable fabric strain, degradation in fabric elastic modulus, and non-linear modulus behavior. The results of this research open the door to new opportunities to advance the field of MCP spacesuit design, as well as opportunities to improve compression garments used in healthcare therapies, competitive athletics, and battlefield medicine.