A vital component in the build up to return to the moon, Gateway will serve as the living quarters and staging area for the Artemis astronauts as they conduct sorties to the lunar surface. The Habitat and Logistics Outpost (HALO) serves as the primary hub of the Gateway station and is thus responsible for maintaining a livable atmosphere for the crews throughout the habitable volume. For HALO, this task will be performed through the use of an open-loop Environmental Control and Life Support System (ECLSS), with air injection and pressure regulation being performed by the Pressure Control System (PCS). The PCS is a new design for HALO, leveraging a mix of heritage and bespoke components to meet the breathable air and habitable pressure requirements. The HALO PCS is split into two primary stages of operation, with the high-pressure (4500 psia) flow controlled by the Remote Isolation Valve (RIV), a heritage brushless DC motor-controlled valve, and the low-pressure (150 psia) flow section downstream of the newly designed two-stage Regulator, and was designed to efficiently deliver O2 and N2 to HALO and connected modules. The design includes the ability to maintain a habitable environment for crew during mission phases, provide maintainable atmospheric gas reservoir, provide atmospheric flow rate to support contingency operations, and provide capability to maintain separate N2 and O2 control bands for crew comfort. The decision to opt for an open-loop system, and the associated design choices made for the PCS, were done to ensure the necessary performance characteristics were met. Through this design process there were many lessons learned for application to future space vehicle ECLSS, both open- and closed-loop.
Dougherty et al. (Sun,) studied this question.