An approach to mixed-fidelity system simulation of extravehicular activities

Abstract

The National Aeronautics and Space Administration (NASA) is currently developing the next generation of spacesuits for use in future exploration missions. This effort, referred to as the Exploration Extravehicular Mobility Unit (xEMU), has been underway since 2015 with the goal of demonstrating the new technologies during a mission to the International Space Station (ISS).Due to the complexity of the xEMU system, and particularly its portable life support system (PLSS), computer simulations are heavily relied on in the development process, from dynamic loads analysis to software verification. The models of the physical systems that are currently being used for system-level simulations are mostly empirical, where the underlying formulas are mathematical fits to test or simulation data. An advantage of this approach is the fact that these models are very performant and can be used in real-time applications such as user interface testing and operator training.The research presented in this paper describes a different approach to modeling and simulation. A simulation tool focused on life support systems for human spaceflight in general and PLSSs in particular has been under development at the Technical University of Munich (TUM) since 2006. The spacesuit specific variant of this tool is called The Virtual Spacesuit (V-SUIT) and is now being utilized in the current spacesuit development process at the NASA Johnson Space Center (JSC). In contrast to the previously mentioned empirical models, V-SUIT uses a first-principles-based, bottom up modeling approach, where basic physical, chemical or biological effects are modeled at the lowest level and the component and system models are created using these fundamental building blocks. This enables the simulation to account for effects, and especially off-nominal situations, that may not be within the range of validity of the empirical models.This paper presents the structure of and the rationale behind V-SUIT itself as well as a status report on the ongoing effort to integrate it with the existing simulation systems in use at JSC, which is based on Trick/GUNNS. As a proof of concept, a single component model from V-SUIT, that of the spacesuit water membrane evaporator (SWME), has been integrated with NASA's simulation tool.Results include comparisons of the performance of the two simulation systems and a description of challenges that were encountered during implementation. The paper closes with an outlook towards the future developments that are planned for V-SUIT within the xEMU development program.