Evaluating Extravehicular Activity Access Options for a Lunar Surface Habitat

NASA's upcoming return to the moon includes a plan for longer duration lunar missions that prioritize science and surface exploration. The current Artemis Base Camp reference proposes a Surface Habitat (SH) that will support 2 to 4 crewmembers with adequate capability for living and working for 30 days or more. An important aspect of the SH's design will be its ability to support a high frequency of Extravehicular Activities (EVAs) for scientific and operational purposes. There are multiple EVA access options that can support EVA access from the SH to the lunar surface. This paper explores three unique options for EVA access: a traditional airlock, a suitlock, and a suitport-airlock. A traditional airlock utilizes a segregated, variable pressure volume, accessed by use of internal and external hatches, to provide EVA access. The airlock volume must be depressurized and repressurized for every EVA. A suitlock is similar in operation to the airlock, utilizing a segregated volume that is depressurized and repressurized for every EVA. However, in this case the suits are donned/doffed through a suitlock interface installed in the airlock bulkhead. EVA suits in a suitport-airlock are accessed through suitport interfaces that are installed in the airlock bulkhead as well, but the suitport-airlock stays in vacuum while the suits themselves remain pressurized, and the airlock does not have to be depressurized and repressurized for each EVA. This study also evaluated the use of an airlock airsave system in conjunction with the traditional airlock and suitlock cases. This system captures a fraction of the airlock gas instead of venting all of the gas pre-EVA. The captured gas is then used to partially repressurize the airlock post-EVA. In this study, each option is evaluated based on six different areas of analysis. The metrics include overhead time for EVAs, dust mitigation, consumables for resupply mass, system mass, safety and mission assurance, and programmatic considerations. The EVA access options are evaluated and compared under each area of analysis. The baseline case assumes the SH operates at 8.2 psia.