Towards a Martian mechanical counter pressure spacesuit: material properties, modelling and pressure application
Creators: name: Rudakov, Abby
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 330315
subject: Textile and fashion design
classificationCode: 401413
subject: Textile technology

description: Specialised wearable suits have a well-established role in protecting astronauts against the hostile environment of space and are gaining prominence as countermeasures for preventing adverse health conditions commonly experienced during and after space flight. 

Extra-vehicular activity (EVA) spacesuits are worn to protect astronauts from the vacuum or near-vacuum of space, radiation, micrometeoroids, and temperature extremes, as well as provide vital oxygen, nutrition and drinking liquid. To date, all EVA suits worn in space have been pressurised by gas, which fills the suit to exert the required force on the wearer’s skin. The suit is much like a balloon, and the internal pressure required makes the suit difficult to manipulate, which is metabolically exhausting for the wearer and results in a high rate of injury to astronauts. As we look to head back to the Moon and further on to Mars, the approach taken to pressurise and protect the body needs to shift from the anthropomorphic spacecraft to a garment designed to protect and enhance the properties of the body. To meet the intensive EVA schedules proposed for Martian surface exploration, EVA suits will need to be lighter, safer, and more mobile. Current gas pressure (GP) spacesuits are excessively heavy, lack mobility and dexterity, subject astronauts to a high rate of injury due to stiffness and fit, and possess inadequate durability. These limitations necessitate the investigation of solutions to enable future astronauts to explore the Martian environment safely and effectively. Several suit architectures have been proposed utilising (at least in part) mechanical counter pressure (MCP). MCP is the application of pressure directly to the body, typically using a skin-tight, elastic garment. MCP is an approach that may address the weight, comfort, function, mobility, and safety issues of current GP EVA suits and is already being utilised for countermeasure applications in space. 

Considerable research effort has been put into the concept of a full MCP EVA suit and numerous proposals for hybrid suits have been made. These hybrid suits incorporate a combination of GP and MCP in different configurations (layered and segmented). No systematic assessment had been made to determine which of these proposed architectures may be best suited for Martian surface exploration. Whilst MCP concepts show great promise, there are still issues that need to be resolved for MCP EVA suits to be fully realised and to improve upon current countermeasure garments. Pressure needs to be delivered evenly over the complex geometry of the body, and pressures must be accurately measured when wearing these garments to confirm correct pressure. Fabrics used for MCP garments require accurate characterisation and observation of time-dependant changes to ensure the resulting MCP garments will consistently deliver pressure with continued wear. 

A trade study was conducted to explore both MCP (full and augmented) and GP-MCP hybrid architectures as alternatives to full GP suits to determine the most promising pressure garment architecture that best serves Martian EVA requirements. The MCP and GP-MCP hybrid architectures were assessed for their suitability to meet Martian EVA requirements (custom capability scale) and to evaluate their maturity using NASA’s TRL system. Overall feasibility was defined as the product of normalised capability and maturity scores. Results of the trade study indicated GP suits are the most mature technology (TRL), while augmented MCP and 60% segmented hybrid architectures are best suited to meet Martian EVA capabilities (capability assessment). Overall, the augmented MCP and 60% segmented hybrids were found to be the most feasible architectures for effective Martian EVA. The findings of the trade study aim to highlight key areas of future research which may help orientate development and funding. 

To investigate MCP materials, a tensile testing method and process was defined for characterising fabrics. Two example compression fabrics were characterised to test the process and recommendations to improve the process for future testing were made. Evaluation of changes to pressure delivery over time was also conducted. 

3D body scanning technology and MATLAB were used to develop a computer model to determine accurate dimensions for compression leg sleeves. Local pressure variations around the body segment were estimated using local curvature differences by applying Laplace’s law and displayed visually with a heatmap. Visualisation of rounding and scaling of the limb segment are also modelled to improve understanding of changes to pressure delivery over time as result of the body shape changes typically experienced whilst in space. 

To understand how well the computer model and tensile testing can be used to estimate delivered pressures, validation of the model was conducting with empirical pressure testing. Compression sleeves were produced and applied to a custom shaped legform to determine the actual pressures being delivered and these were compared to pressures calculated using Laplace’s law. 

Local pressures were found to follow Laplace’s law when expressed as a relative difference, though not always within the confidence interval of the measured pressures. Results indicated that it is important to take local curvatures into consideration when determining pressure regimes for MCP garments. For body sites with large variations in local curvature, pressure determined by using the average radius is not a good indicator of actual local pressures. Two key factors were found to influence how well the measured and calculated results correlated; the Young’s modulus used and the composition of the fabrics.

To see MCP technology employed in a Martian EVA suit architecture, research funding and effort must be put towards improving the technical maturity of MCP technologies and fabric development for MCP applications. This focused effort can bring MCP from concept prototype stage into reality to enable Martian astronauts to explore the planet safely, comfortably, and effectively.