xEMU spacesuit simulator

Earth-based EVA simulation has always been the subject of study by space agencies aimed at reproducing the most accurate experience for astronauts. Challenges and limitations are many and not limited to the natural Laws; the space suit system, integral part of the successful EVA, must present the same conditions to the user as it would in the environment of operation. NASA is the most prominent example of a long tradition for a faithful simulation of the outer space in which astronauts operate during EVAs: the Neutral Buoyancy Lab at Johnson Space Center in Houston still represents the standard when it comes to providing astronauts with a realistic experience. However, such infrastructures can be difficult to access, considering the renewed interest in space, this time advocated by new private players, who are looking into LEO access in the short to medium term. Virtual Reality (VR) provides the users with new, flexible and relatively inexpensive ways of simulating the space environment during an EVA, without the need to build large scale pools and mock-ups of vehicles. In this paper, it’ll be shown how the Sasakawa International Center for Space Architecture (SICSA) at the University of Houston is working to provide students and researchers with a VR-based infrastructure to simulate EVAs and Space Architectures, which are also designed in-situ. As essential component to achieve realism of experience is the design and construction, done entirely in-house, of a mock-up of the latest NASA Artemis xEMU space suit, to recreate the physical constraints that such a garment imposes to astronauts, and which cannot be entirely simulated with VR. It’ll be shown how this space suit replica substantially enhances the accuracy of the experience, by replicating the mechanisms of the xEMU suit, complementing the virtual experience provided at the same time.

The xEMUs are part of this suite of Mock-ups that needed to be developed to prepare the current and future testing campaigns. NASA is designing the new generation of spacesuits for maximum modularity across different environments (Moon, Mars, Microgravity). To match this capability, the xEMU mockup needed to account for the different features that each of these very different environments would require, and include them into the Mock-up design.

For the purpose of fulfilling the project’s objectives, the suits have been designed following a right-first-time approach based on the available manufacturing technologies and types of machinery. The suits are part of a suite of mock-ups that will be used to test a variety of multigravity scenarios, The fundamental rationale behind the suit’s construction is to reproduce as much as possible the physical limitations that are introduced while astronauts perform EVA. Those include limb movement restrictions due to the pressurization and the presence of rigid components in the arms and leg assembly. But also the limitations in the Field-Of-View (FOV) and the decoupling of the rotational axis between the human and the suit joints. The introduction of those physical limitations is fundamental to enhancing immersivity levels of XR simulations and enabling a shorter path from hardware and operations design to implementation.
Given the critical nature of the accurate simulation level that was required by the IDVS, the project mandated that a couple of space suit mock-ups were to be built. The combination mock-up-VR system has proven instrumental in reducing the requested level of accuracy of the mock-ups, enabling a simplified design which is supposed to extend the capabilities of the Virtual Reality system; this aspect, which can be extended to any mock-up within the IDVS infrastructure, is of great importance when considering the competitiveness of the IDVS system compared to other solutions. For what it pertains the suit, a set of requirements was laid out to guide the design process:

• Realism: the suit mock-up was meant to reproduce the bulk of the NASA xEMU space suit and its kinematic features\cite{fineman_objective_2018}, therefore analog structure and mechanisms had to be reproduced;
• Affordability: the mock-up was designed to be built within the faculty’s workshop and laboratories, with available tools;
• Low-Fidelity Mock-Up: the uniqueness of the IDVS system, enabling a pairing of the mock-ups with VR, enables the creation of low-fidelity mock-ups that can be paired with their digital twin with relative ease, meaning that the tangible half of the simulation can be simplified down to its most rugged and basic structure and function;
• Timely Schedule: The mock-ups of the space suit were assigned for about four months to be designed and built, based on the available design used as a reference and the University’s own schedule.

The first part to be replicated was the rigid torso shell of the space suit, which design also encompasses the helmet and backpack attachments, the latter being the entrance hatch of the suit, both in reality and for our mock-up. Geometry tracing of the 3D Model of the torso shell resulted in a wooden structure, made with MDF pieces which were laser-cut to shape for a more accurate and clean result.

The creation of the shell then proceeded with the covering of the wooden ribbed structure with a layer of spandex elastic fabric. This fabric, given its properties, can easily be stretched around the wooden structure and secured with staples. The spandex fabric serves two purposes, the first of which is to be the substrate of the fiberglass that is going over it to make the structure of the shell and secondly, once the fiber glass and resin would have settled, to protect the user from casual splinters that the fiberglass can produce with this construction method, by offering a smooth and clear inner lining of the shell. A first layer of resin is applied before the fiberglass to provide some initial strength to the spandex and make it rigid, leaving this first layer to set and dry, then layers of fiberglass are applied to still wet resin, up to a thickness of 2-3 mm. Empirical findings show that this thickness is the ideal compromise between weight and resistance requirements, yielding a rigid shell with appreciable durability. Once the resin has settled, the inner wooden rib structure is carefully fragmented and removed, leaving the shell to be cleaned from residues on the inside and to be finished on the outside.

Fiberglass filler is used to make the outer surface smooth, with several iteration steps of filler application, filler drying and then sanding with finer grained sand paper. Some layers of primer and then paint are applied with a final layer of clear coat to protect the shell from small bumps. On the front, a 3D printed mock-up of the xEMU instrumentation, obtained from the CAD Model, is mounted to provide further dimensional realism to the suit. The space suit arms were replicated by 3D CAD Modeling from the reference literature, to fulfill the requirement of motion realism of the suit and constraint reproduction, to enable a fully realistic experience. The arms have been designed to house lazy-susan-type bearing rings at the shoulder and arm levels, to enable the full range of motion of the arm as the real suit would offer.
All the mechanical parts have been 3D printed and paired with heavy duty, waterproof nylon fabric, with parts specifically designed to mimic the real suit and then sewed together with high-strength seams. Inside the space suit, a modified harness has been installed, to enhance comfort and keeping the suit mock-up lifted from the user’s shoulders. The user enters the space suit mock-up from the back life the real he/she would for the xEMU, and then a mock-up of the backpack, built with laser-cut and then assembled MDF sheets, is installed on the back portion of the suit. Because of installation issues of the backpack, the system was designed without hinges, to avoid possible incidents due to an erroneous positioning of the backpack during the donning/undressing procedure. When operating within the IDVS infrastructure, the space suit can be used in conjunction with the crane by having the analog astronaut donning a second set of harnesses, to be worn under the space suit one, mimicking the NASA Active Response Gravity Offload System, and integrating XR in the process.