Global Control of a Life Support System : Flow control and optimisation

Sammanfattning: The subject of study of this degree project is the MELiSSA (Micro-Ecological Life Support System Alternative) Life SupportSystem (LSS) developed by the European Space Agency (ESA). The MELiSSA LSS aims to recycle human wastes into O2,water and food for the crew of a spacecraft. The purpose of this project is to model and study the MELiSSA LSS, in order todesign a global control system that ensures the survival of the crew while minimizing the resources needed. The MELiSSA LSSis composed of 4 biochemical reactors, called the compartments, controlled locally. A model of all the possible critical flowsexchanged by the compartments is built from a functional point of view. These flows are controlled using the Predictive FunctionalControl (PFC) method.This study confirms that the MELiSSA LSS can function properly but requires external resources. In addition, the study showsthat by using the right external resources, the MELiSSA LSS can achieve its goal. The objective of the MELiSSA LSS is toproduce 100% of the O2, 90% of the water and about 40% of the food the crew needs to survive. With an additional amountof ammonia (NH3), nitric acid (HNO3) and carbon dioxide (CO2), the LSS reaches a production of 100% of the O2, more than100% of the water and between 45 and 50% of the food the crew needs. Moreover, when its operation is optimized, it reducesthe mass to carry per astronaut per day to less than 50% of the mass needed without optimization. This is about 12% of themass needed when there is no recycling system. The model built for this study can also be used as a dimensioning model or anenvironment and contextualization model for the development and testing of the different compartments.