To enable sustainable long-duration human space flight, regenerative life support systems (RLSS) will be indispensable. Waste materials will need to be processed and transformed back into nutrients for life-supporting ecosystems. MELiSSA (Micro-Ecological Life Support System Alternative) is a well-documented and studied example of such an RLSS, developed by the European Space Agency. The system consists of five interconnected compartments: a crew compartment, an edible plant/algae compartment, and three types of bioreactors. The microorganisms in the bioreactors gradually break down the waste materials of the astronauts and provide the edible plants and algae with their necessary resources. This paper proposes a model of an agent-based system (ABM) of MELiSSA in which the five compartments and their interactions are modeled and implemented using virtual agents that represent humans, plant plots, and bioreactors. The model also includes the corresponding mass flows of chemicals. For each type of agent, its properties, behavior, life cycle, and rules of interaction are described. An 'administrator agent' implements 'top-down' rules for overall control where needed. The behavior of each biological agent is modeled according to the expected behavior and main chemical reactions within each MELiSSA compartment, as documented in publicly available sources. Rules implemented to describe the complete life cycle of the agents - e.g., growth curves and susceptibility to nourishment deficits - are also included. This 'bottom-up' approach, characteristic for ABM, allows for the emergence of patterns that provide insight into the behavior of the overall system. In addition, the mass flows are made visible as the different chemical compounds are exchanged between compartments. This agent-based system of MELiSSA is, in fact, a simulation platform with which the behavior of the cycle as a whole, down to its individual agents, enables exploration of the robustness of the system and the impact of stressors on survivability. A series of simulation experiments has been set up for this purpose. Two types of stressors are used in these experiments. First, stochastic outputs from at least one of the compartments, beginning with the crew compartment. Second, environmental stressors, more specifically cosmic radiation causing loss of metabolic functionality and particle impact causing catastrophic failure of parts of the life support system. This research is part of the E|A|S (Evolving Asteroid Starships) project by the DSTART team at Delft University of Technology. The project entails conceptual research on interstellar travel, including onboard regenerative ecosystems.

The hostile and unpredictable environment of deep space requires a new conceptual approach for interstellar flight, one that differs radically from any current design in aerospace. A design solution is proposed in which the starship is attached to a C-type asteroid and whose architecture evolves over time. The starship gradually mines resources of the asteroid, while at the same time using it as a shielding structure against frontal impacts. The extracted raw materials are used for cultivation of the onboard ecosystem and expansion of the starship's architecture, the latter of which is primarily conducted by mobile 3D printers. Within the bounds of its sensing horizon, the spacecraft can detect prospective high-energy particle collisions and radiation events along its upcoming flight path. Subsequently, the starship will adapt itself by changing its interior and exterior morphology. This constant evolution aims to minimize the spacecraft damage and loss of functionality, and handles the inherent unpredictability of the mission. The Delft University of Technology Starship Team (DSTART) simulates this concept using an array of different techniques. The ecosystem dynamics are approached using agent-based modeling, while the evolving architecture of the starship is approached with genetic algorithms. The starship simulation relies on four distinct timelines. A first timeline provides real-time updates on the state of the starship's regenerative ecosystem, with a focus on population sizes, mass fluxes, and radiation impact. ESA's MELiSSA project was used as a conceptual blueprint for the ecosystem. A second timeline deals with the growth of the starship architecture, taking into account material supplies, mining rates, 3D printing speeds and wear of existing structures. The third timeline forecasts the impact of future particle collisions and interstellar radiation as assessed within the sensing horizon. The fourth and final timeline is concerned with the evolution of the starship architecture as a response to this forecast. This is done by comparing the structural integrity and ecosystem health of different variations of the starship's morphology. The first results of this work will be presented, as well as an overview of the implications for space system design.