Advanced Life Support Systems in Lunar and Martian Environments Utilizing a Higher Plant Based Engineering Paradigm

<div class="htmlview paragraph">The purpose of dynamic modeling and simulation of Advanced Life Support (ALS) systems is to help design them. Static steady state systems analysis provides basic information and is necessary to guide dynamic modeling, but static analysis is not sufficient to design and compare systems. ALS systems must respond to external input variations and internal off-nominal behavior. Buffer sizing, resupply scheduling, failure response, and control system design are aspects of dynamic system design. We develop two dynamic mass flow models and use them in simulations to evaluate systems issues, optimize designs, and make system design trades. One model is of nitrogen leakage in the space station, the other is of a waste processor failure in a regenerative life support system.</div> <div class="htmlview paragraph">Most systems analyses are concerned with optimizing the cost/benefit of a system at its nominal steady-state operating point. ALS analysis must go beyond the static steady state to include dynamic system design. All life support systems exhibit behavior that varies over time. ALS systems must respond to equipment operating cycles, repair schedules, and occasional off-nominal behavior or malfunctions. Biological components, such as bioreactors, composters, and food plant growth chambers, usually have operating cycles or other complex time behavior. Buffer sizes, material stocks, and resupply rates determine dynamic system behavior and directly affect system mass and cost. Dynamic simulation is needed to avoid the extremes of costly over-design of buffers and material reserves or system failure due to insufficient buffers and lack of stored material.</div>

<div class="htmlview paragraph">System failures, dynamics, and nonlinearities can cause unacceptable performance and damaging instability in Advanced Life Support (ALS) systems. Much current ALS modeling assumes that ALS systems are linear, static, and failure-free. But in reality most ALS hardware is subject to failure, real ALS systems are dynamic, and many ALS processors are nonlinear beyond a limited operating range. Modeling and simulation are needed to study the stability and time behavior of nonlinear dynamic ALS systems with failures and to develop appropriate controls.</div> <div class="htmlview paragraph">The nonlinear dynamics of ALS systems has many interesting potential consequences. Different equilibrium points may be reached for different initial conditions. The system stability can depend on the exact system inputs and initial conditions. The system may oscillate or even in rare cases behave chaotically. Temporary internal hardware failures or external perturbations can lead to dynamic instability and total ALS system failure. Appropriate control techniques can restore reliable operation and minimize the effects of dynamic instabilities due to anomalies or perturbations.</div>

<div class="htmlview paragraph">A successful CELSS (Controlled Ecological Life Support System) design must accommodate the potential mismatch between the crew's relatively constant CO<sub>2</sub> production and the widely varying crop CO<sub>2</sub> consumption over the plant growth cycle. Any additional changes in material flows, processor characteristics or other system characteristics may have deleterious effects which propagate throughout the CELSS. Important transient conditions which the system design and planting regimen must allow for are described, including:</div> <div class="htmlview paragraph"><ul class="list disc"> <li class="list-item"> <div class="htmlview paragraph">Crop startup.</div> </li> <li class="list-item"> <div class="htmlview paragraph">Crop failures.</div> </li> <li class="list-item"> <div class="htmlview paragraph">Changes in number of humans supported.</div> </li> </ul> </div> <div class="htmlview paragraph">A general-purpose life support system simulator was used to evaluate several CELSS design and operation approaches. The simulator was used to investigate CO<sub>2</sub> generation and removal interactions occurring between the CELSS food production subsystem and the rest of the system. These interactions were selected because they are major drivers of the system design and operation.</div>

<div class="htmlview paragraph">For a planetary base, a reliable life support system including food and water supply, gas generation and waste management is a condition <i>sine qua non</i>. While for a short-term period the life support system may be an open loop, i.e. water, gases and food provided from the Earth, for long-term missions the system has to become more and more regenerative. Advanced life support systems with biological regenerative processes have been studied for many years and the processes within the different compartments are rather complete and known to a certain extent. The knowledge of the associated interfaces, the management of the input and output phases: liquid, solid, gas, between compartments, has been limited. Nowadays, it is well accepted that the management of these phases induces generic problems like capture, separation, transfer, mixing, and buffering.</div> <div class="htmlview paragraph">A first ESA study on these subjects started mid 2003. This study, performed by Stork, TNO, Stirling and the University of Guelph, is limited to the main gas components, oxygen, water vapour and carbon dioxide. Ammonia was included as a contaminant component. The study has been started with the establishment of a simulation model (closed loop) to identify the critical items, which is followed by the selection of the gas capture and recovery technologies, the development of a breadboard model and is finished by a set of experiments.</div> <div class="htmlview paragraph">For the control of carbon dioxide (CO<sub>2</sub>), a dedicated activated carbon will be applied. This material, produced by Norit, is applied to control the CO<sub>2</sub> at fruit storage, and pressure swing adsorption is applied for regeneration. In the breadboard set-up, electrical swing adsorption will be applied. This rather new technique has been selected to enable the development of a compact system which can be operated within almost any range atmospheric pressure, resulting in a safe system having a low mass.</div> <div class="htmlview paragraph">This paper will report the status of these activities.</div>

CELSS transportation analysis

<div class="htmlview paragraph">This paper addresses the effect of waste processing on advanced life support (ALS) system design. Waste processing is a critical component of an advanced life support system. It must take all life support system wastes and either convert them into useful products or into a form in which they can be discarded. Waste can be treated as soon as it is produced, stored as is, or processed into an intermediate form for further treatment. The decisions made will affect the cost-effectiveness of the system. Strategies must be developed to meet waste processing requirements for specific mission scenarios.</div>

Achieving and documenting closure in plant growth facilities

Canadian advanced life support capacities and future directions

<div class="htmlview paragraph">A Breadboard-Scale Aerobic Bioreactor (B-SAB) has been designed and integrated with the Kennedy Space Center's Biomass Production Chamber (BPC). The bioreactor utilizes a mixed microbial community to biodegrade inedible plant residues, a component of a Controlled Ecological Life Support System (CELSS) waste-stream. The continuously stirred tank reactor (120 L working volume) supports nutrient recycling and secondary food production experiments, and can process an influent with a solids loading as high as 50 g L<sup>-1</sup>. The volumetric oxygen mass transfer coefficient, k<sub>L</sub>a, is 0.013 s<sup>-1</sup>. Nutrient solution for BPC lettuce and wheat crops has been produced. Currently, B-SAB is supplying 80% of the nutrients for 10 m<sup>2</sup> of potato plants in a continuous production experiment.</div>

During long-duration space missions that require recycling and regeneration of life support materials the major human wastes to be converted to usable forms are CO2, hygiene water, urine and feces. A Controlled Ecological Life Support System (CELSS) relies on the air revitalization, water purification and food production capabilities of higher plants to rejuvenate human wastes and replenish the life support materials. The key processes in such a system are photosynthesis, whereby green plants utilize light energy to produce food and oxygen while removing CO2 from the atmosphere, and transpiration, the evaporation of water from the plant. CELSS research has emphasized the food production capacity and efforts to minimize the area/volume of higher plants required to satisfy all human life support needs. Plants are a dynamic system capable of being manipulated to favour the supply of individual products as desired. The size and energy required for a CELSS that provides virtually all human needs are determined by the food production capacity. Growing conditions maximizing food production do not maximize transpiration of water; conditions favoring transpiration and scaling to recycle only water significantly reduces the area, volume, and energy inputs per person. Likewise, system size can be adjusted to satisfy the air regeneration needs. Requirements of a waste management system supplying inputs to maintain maximum plant productivity are clear. The ability of plants to play an active role in waste processing and the consequence in terms of degraded plant performance are not well characterized. Plant-based life support systems represent the only potential for self sufficiency and food production in an extra-terrestrial habitat.

<div class="htmlview paragraph">MELISSA (Micro Ecological Life Support System Alternative) is a research project for the development of advanced life support systems, conducted by the European Space Agency. Its basic design is based on a loop of bioreactors with the main objective of the regeneration of the wastes generated by a crew into an edible material, with concomitant regeneration of the atmosphere for human respiration.</div> <div class="htmlview paragraph">The MELISSA Pilot Plant is a European facility to study and validate advanced life support systems. It has as main objectives the ground demonstration and characterization of a closed loop concept. This includes the development of the associated technology for its successful continuous operation such as water treatment, pathogen detection, food preparation, and other related items. At present time, the main research project developed in the Pilot plant is the MELISSA project.</div> <div class="htmlview paragraph">A key point in its development is the collection of experimental data under real operating conditions in order to perform mathematical modeling. This is a key issue in the approximation followed, both for the control and simulation of the individual bioreactors and the complete loop. The state of the art of the pilot plant is discussed, and particular emphasis is made in the description of the continuous operation of the interconnected bioreactors. Also the necessary associated research, required for its successful operation, such as the development of an advanced control system or the analysis of the effect of the malfunction of one compartment, on the subsequent ones are reviewed.</div>

Performance and reliability of the NASA biomass production chamber

Effectiveness of Emergency Medical Services for Victims of Out-of-Hospital Cardiac Arrest: A Metaanalysis

<div class="section abstract"><div class="htmlview paragraph">The inclusion of bioregenerative life support elements (i.e., plant growth systems and bioreactors) will significantly increase the total abundance of microorganisms in extraterrestrial facilities. If the microbial communities associated with these systems (e.g., biofilms attached to plant roots or hardware surfaces) serve as reservoirs for potentially pathogenic human-associated bacteria, then bioregenerative systems may represent a human health risk. Research at the Kennedy Space Center during the past several years has attempted to quantify this risk by assessing the capacity of different human-associated bacteria to survive in prototype ALS systems. Preliminary, short-term studies indicated that many potentially pathogenic human-associated bacterial species identified from past space missions (<i>Pseudomonas aerugi-nosa</i>, <i>Pseudomonas cepacia</i>, <i>Escherichia coli</i>, <i>Staphylococcus aureus</i>, and <i>Streptococcus pyogenes</i>) have the capacity to grow on the roots of plants, one of the largest potential sites of microbial activity in bioregen-erative life support systems. However, only <i>P. aeruginosa</i> could persist at detectable levels when competition from typical root-associated bacteria was present. Subsequent long-term plant growth experiments have confirmed the greater capacity of <i>P. aeruginosa</i> to persist in plant growth systems, although no human-associated bacteria tested to date have proliferated in the systems. Rather, relative success is measured by the rate at which bacterial numbers decrease following introduction. Recent and current studies have focused on the influence of community richness (i.e., the number of microbial species) on the ability of introduced human-associated bacteria to persist within prototype systems. Richness may be manipulated in a bioregenerative system; a stringent decontamination approach could lead to very low richness, but specific inoculation with either defined bacterial isolates or undefined mixtures of microbial communities would increase richness.</div></div>

<div class="htmlview paragraph">Future space exploration will require advanced life support (ALS) systems capable of <i>in situ</i> resource recycling. Hypobaric, bioregenerative life support systems have been proposed to address this requirement. The need to explore the limits of plant tolerance to hypobaric conditions is clear, however, research has been limited due to the difficulties and costs associated with this field. The Controlled Environment Systems Research Facility (CESRF), at the University of Guelph, Canada, has been designed to address the issues surrounding plant production under reduced pressure conditions. The measurement of plant physiological responses to hypobaric conditions is the subject of this study. Measurements of whole plant water relations, in terms of transpiration and plant water potential, are the ultimate goal. This phase of the work includes development and testing of the variable pressure plant growth chamber, and calibration of the <i>in situ</i> stem psychrometer for measuring plant water potential.</div>