Potential Applications of Modularity to Enable a Deep Space Habitation Capability for Future Human Exploration Beyond Low-Earth Orbit

NASA Marshall Space Flight Center, United States, david.smitherman@nasa.gov Evaluating preliminary concepts of a Deep Space Habitat (DSH) enabling long duration crewed exploration of asteroids, the Moon, and Mars is a technically challenging problem. Sufficient habitat volumes and equipment, necessary to ensure crew health and functionality, increase propellant requirements and decrease launch flexibility to deliver multiple elements on a single launch vehicle; both of which increase overall mission cost. Applying modularity in the design of the habitat structures and subsystems can alleviate these difficulties by spreading the build-up of the overall habitation capability across several smaller parts. This allows for a more flexible habitation approach that accommodates various crew mission durations and levels of functionality. This paper provides a technical analysis of how various modular habitation approaches can impact the parametric design of a DSH with potential benefits in mass, packaging volume, and architectural flexibility. This includes a description of the desired long duration habitation capability, the definition of a baseline model for comparison, a small trade study to investigate alternatives, and commentary on potentially advantageous configurations to enable different levels of habitability. The approaches investigated include modular pressure vessel strategies, modular subsystems, and modular manufacturing approaches to habitat structure. The paper also comments upon the possibility of an integrated habitation strategy using modular components to create all short and long duration habitation elements required in the current exploration architectures. INTRODUCTION Habitats are the vehicles in which crew live and work during long duration missions in space. They must provide a pressurized environment and a complement of subsystems which deliver the functionality necessary to keep astronauts healthy and productive. In the context of habitat design, modularity is the buildup of a habitat with a complete set of required functionality through the assembly or recombination of multiple habitat modules or modular subsystems within the habitats. There are several potential benefits of these approaches over a “monolithic” habitat design which contains all subsystems necessary to support crew during the mission. First, multiple, smaller elements increase launch flexibility to alleviate launch vehicle mass or payload shroud dimensional constraints. Second, having multiple, separable pressurized modules or modular subsystems with common components can improve the safety of a spacecraft through increased redundancy and reduced spares requirements. Third, modularizing habitat approaches enables customization of the launched habitat size to mission duration and requirements, which can improve in-space propulsive performance and the overall cost of the mission. These and other improvements come at the potential cost of increased complexity and/or increased mass through excessive redundancy, additional structure and additional docking ports. Two things drive a designer to the consideration of modularity in habitat design. First, assembly of a large habitat which exceeds available launch vehicle volume or mass requires a modular approach with in-space assembly. The primary example of this is the International Space Station (ISS) which was assembled over many years and launches. The added desire of reconfigurability and the eventual replacement of hardware also resulted in the use of a somewhat modular subsystem design on ISS and the International Standard Payload Rack (ISPR). As the destination of such a habitat is located further away from Earth or as cost constraints limit the selection of available launch vehicles to smaller options, modularity becomes more of a driver. For example, the use of commercially available expendable launch vehicles such as the Delta IV-H for the delivery of a large long-duration habitat beyond Low-Earth Orbit (LEO) would require a modular habitation strategy (or an advanced propulsion