Impacts of System Decisions at the Life Support, EVA, and Habitability Interfaces 2005-01-2907
Technology developers understand the need to optimize technologies for human missions beyond Earth. Greater benefits are achievable when systems that share common interfaces are optimized as an integrated unit, including taking advantage of possible synergies or removing counterproductive efforts at the mission level. Life support, extravehicular activity (EVA), and habitability are three systems that have significant interfaces with the crew, and thus share many common interfaces with each other.
Technologies and architectures developed for these systems need to account for the effect that design decisions will have on each of the other systems. Many of these impacts stem from the use of water by the crew and the way that the life support system provides and processes that water. Other resources, especially air-related, can have significant impacts as well. Mission and system designers should be aware of the effects that requirements and subsystem decisions at all levels can have on the total mission.
One example of an important decision is the way resources are provided to an EVA portable life support system (PLSS) from the life support system. Another example is the impact of including or neglecting waste recovery from a PLSS system on resupply requirements of the life support system. Important habitability decisions include hygiene systems, such as showers, sponge baths, or pre-hydrated wipes, and clothing options including resupply, advanced materials, and laundry options, and the water recovery architecture best suited to these choices. The method of providing food can make demands on resupply to the life support system, but significant variations occur depending on dehydration levels and cooking methods.
Each of these decisions also needs to be considered within the framework of spiral development as espoused by the NASA Exploration Systems Mission Directorate (ESMD). In spiral development, “a desired capability is identified, but the end-state requirements are not known at program initiation. Requirements are refined through demonstration, risk management and continuous user feedback.” (6) For example, ESMD Spiral 2 missions have a manned surface duration of 4 to 7 days, but a requirement (ESS0120) that states “The Exploration System of Systems shall demonstrate the capabilities necessary to prepare for long-duration human exploration of the moon.” (10) Within this additional layer of integrating system decisions between missions, the best selection may not be one that is optimized for the current mission, but rather one that has potential for testing and technology development or demonstration for future missions and requirements.