Alan Drysdale

Life support approaches for Mars missions.

Life support approaches for Mars missions are evaluated using an equivalent system mass (ESM) approach, in which all significant costs are converted into mass units. The best approach, as defined by the lowest mission ESM, depends on several mission parameters, notably duration, environment and consequent infrastructure costs, and crew size, as well as the characteristics of the technologies which are available. Generally, for the missions under consideration, physicochemical regeneration is most cost effective. However, bioregeneration is likely to be of use for producing salad crops for any mission, for producing staple crops for medium duration missions, and for most food, air and water regeneration for long missions (durations of a decade). Potential applications of in situ resource utilization need to be considered further.

OCAM - A CELSS Modeling Tool: Description and Results

Controlled Ecological Life Support System (CELSS) technology is critical to the Space Exploration Initiative. NASAs Kennedy Space Center has been performing CELSS research for several years, developing data related to CELSS design. We have developed OCAM (Object-oriented CELSS Analysis and Modeling), a CELSS modeling tool, and have used this tool to evaluate CELSS concepts, using this data. In using OCAM, a CELSS is broken down into components, and each component is modeled as a combination of containers, converters, and gates which store, process, and exchange carbon, hydrogen, and oxygen on a daily basis. Multiple crops and plant types can be simulated. Resource recovery options modeled include combustion, leaching, enzyme treatment, aerobic or anaerobic digestion, and mushroom and fish growth. Results include printouts and time-history graphs of total system mass, biomass, carbon dioxide, and oxygen quantities; energy consumption; and manpower requirements. The contributions of mass, energy, and manpower to system cost have been analyzed to compare configurations and determine appropriate research directions.

CELSS engineering parameters

The most important Controlled Ecological Life Support System (CELSS) engineering parameters are, in order of decreasing importance, manpower, mass, and energy. The plant component is a significant contributor to the total system equivalent mass. In this report, a generic plant component is described and the relative equivalent mass and productivity are derived for a number of instances taken from the KSC CELSS Breadboard Project data and literature. Typical specific productivities (edible biomass produced over 10 years divided by system equivalent mass) for closed systems are of the order of 0.2.

Systems Analysis of Life Support for Long-Duration Missions

Work defining advanced life support (ALS) technologies and evaluating their applicability to various long-duration missions has continued. Time-dependent and time-invariant costs have been estimated for a variety of life support technology options, including International Space Station (ISS) environmental control and life support systems (ECLSS) technologies and improved options under development by the ALS Project. These advanced options include physicochemical (PC) and bioregenerative (BIO) technologies, and may in the future include in-situ resource utilization (ISRU) in an attempt to reduce both logistics costs and dependence on supply from Earth. PC and bioregenerative technologies both provide possibilities for reducing mission equivalent system mass (ESM). PC technologies are most advantageous for missions of up to several years in length, while bioregenerative options are most appropriate for longer missions. ISRU can be synergistic with both PC and bioregenerative options.

Low Pressure Greenhouse Concepts for Mars: Atmospheric Composition

The main principles of artificial atmospheric design for a Martian Greenhouse (MG) are described based on: 1. Cost-effective approach to MG realization; 2. Using in situ resources (e.g. CO2, O2, water); 3. Controlled greenhouse gas exchange by using independent pump in and pump out technologies. We show by mathematical modeling and numerical estimates based on reasonable assumptions that this approach for Martian deployable greenhouse (DG) implementation could be viable. A scenario of MG realization (in terms of plant biomass/photosynthesis, atmospheric composition, and time) is developed. A list is given of technologies (natural water collection, MG inflation, oxygen collection and storage, etc.) that are used in the design. The conclusions we reached are: 1. Initial stocks of oxygen and water probably would be required to initiate plant germination and growth; 2. Active control of MG ventilation could provide proper atmospheric composition for each period of plant growth; 3. MG operation based on simplest technological solutions could provide for oxygen accumulation for people arriving on Mars. There is a reasonable prospect of achieving cost effectiveness during a single 600-day mission. A short description of future development of a Mars Greenhouse-project is presented. INTRODUCTION: GREENHOUSE ATMOSPHERIC COMPOSITION BASED ON THE NATURAL RESOURCES OF THE PLANET Terrestrial plants need a balanced composition of atmospheric gases to be maintained within certain limits for growth (Wheeler et al., 2000). Carbon dioxide and oxygen are the basic gases used in the processes of photosynthesis and respiration: CO2 + H2O ⇔ CH2O + O2. During plant growth, carbon dioxide is used in greater amounts than oxygen, but oxygen is particularly critical during germination and for respiration at dark period. Presence of some trace organic gases in a closed volume (ethylene and etc.) is also important for plant growth regulation (Devlin, 1975; Chernigovsky, 1975; Lisovsky, 1979). The average composition of the Earth’s atmosphere compared to the atmosphere of Mars is presented in Table. 1 (APPENDIX, III). From the analysis of this table the following conclusions could be formulated: There are considerable differences in atmospheric composition between Mars and Earth; Carbon dioxide is presented in the Martian atmosphere in significant amounts; Oxygen and water are not common in the Martian atmosphere; The existing Martian atmospheric composition is probably not suitable for Earth’s plants growth; (other environmental parameters: temperatures, high UV – radiation, toxic gases and dust, etc., may also be a problem) Growing plants on Mars will require artificial growth conditions inside a closed environment. An analytical model can be used to simplify analysis of the minimal greenhouse atmosphere for plant growth and development. This minimal, most cost effective, atmosphere (Rygalov et al., 2001) should include CO2, O2, and water vapor at sufficient concentrations to support vigorous plant growth. We need to determine by experimentation the cost of maintaining particular conditions, and what effect different conditions would have on plant productivity. This atmosphere could probably be maintained by controlled gas exchange between the greenhouse and outside Martian air during all period of plants growth. However, due to the low concentration of oxygen and water vapor, other sources of these commodities might be more cost effective. The rate of gas exchange should be regulated to account for plant growth (photosynthesis rate changes). It is expected that any gas mixture dense enough to support plants will be adequate to maintain the mechanical pressure needed to keep the soft Deployable Greenhouse (DG) covering inflated. If the most cost effective pressure is found to be near Earth-normal pressure, there might be a problem in designing a cover that is both strong enough and transparent. Both composition of the atmosphere & DG mechanical design are closely connected through the desired exchange of air inside a greenhouse and with outside atmosphere. So, this becomes the task of Artificial Atmosphere Design (AAD). This design issue can be solved in different ways. The cheapest and most cost effective design approach is probably using of indigenous Martian resources (carbon dioxide, oxygen, water, etc.), and the lowest pressure that is suitable for vigorous plant growth. COMBINING ELEMENTS OF ARTIFICIAL ATMOSPHERE DESIGN The basic description of the atmospheric constituents dynamic inside enclosure could be presented as: Velocity of changes in atmospheric concentration (or partial pressure) of the gas = Initial atmosphere + Input from outside (provided by controlled pumping-in process) Losses to outside (provided by controlled pumping-out process or regulated venting, and unregulated leakage) + Influence of system’s closure (conversion or modification by plants and microbes, physical sorption, chemical reactions, etc.). Assumptions: an elevated pressure is required for mechanical stabilization of DG, so greenhouse ventilation is realized by forced pumping-in and pumping-out or controlled passive venting and unavoidable leakage; plants inside the greenhouse take in carbon dioxide and release oxygen; relative humidity is maintained by evapotranspiration and condensation; neutral gases go through the DG without any modification; however, they may need to be purged at intervals if they result in excessive pressure. Partial and total pressure changes are due to the following: • gas pumped in • gas removed • photosynthesis and respiration • leakage • transpiration This qualitative description is represented in the following mathematical description: dPi/dt = (F/V)*Pio + fiX/V + ((KLG)/V)*(Pis – Pi) – (KCGC/V)*(Pi – Pic) – (L/V)*(Pi – Pio) – (R/V)*Pi ; where: Pi = partial pressure of certain gas inside greenhouse; Pio = partial pressure of certain gas in outside atmosphere; Pis = saturated partial pressure of the gas at system temperature (included in water vapor dynamic description only; Rygalov et al., 2002); Pic = saturated partial pressure of the gas at cooling unit temperature (included in water vapor dynamic description only; Rygalov et al., 2002); F = outside air flow rate into greenhouse; R = inside air flow rate out from greenhouse (or in other words forced leaks); L = total free leaks flow rate; (Note: parameters F, R and L characterize the regime of greenhouse ventilation); V = total volume of greenhouse; X = plants biomass; fi = specific rate of gas conversion in photosynthetic processes (can be positive, for example for O2, or negative, for example for CO2); G = area of the gas evaporation (included in vapor dynamic description only; Rygalov et al., 2002); GC= area of gas condensation (included in vapor dynamic description only; Rygalov et al., 2002); KL = specific rate of gas evaporation (included in vapor dynamic description only; Rygalov et al., 2002); KC = specific rate of gas condensation (included in vapor dynamic description only; Rygalov et al., 2002); t = time. This mathematical description is not specified for certain physical unites. The total dynamic pressure in the system is equal to the sum of the individual dynamic pressures for all gases in the system. It is assumed in the equation presented that DG operation is developing with a constant system temperature. Any changes in temperature could be taken into account through changes of numerical values parameters of the model, but wide temperature swings are generally detrimental to plants. The mathematical model presented includes the most general processes determining gaseous dynamic of the greenhouse (Henderson et al., 1997; Johnson, 1999). Any other components of DG atmospheric composition dynamic (trace contaminants, or some specific sources and sinks of gases) could be easily introduced in further specific development of this model. For calculation of DG atmospheric composition this mathematical approach is applied to each constituent gas, including: 1. CO2; 2. O2; 3. H2O; 4. Neutral gases; 5. Ethylene and trace gases (neglected in the approach developed in the paper); 6. Total pressure. The solution of the differential equation for each atmospheric gas was obtained by standard well known methods, and is presented in the (APPENDIX, I). We are going to use the steady state part of this solution only in further consideration. EXPERIMENTAL REALIZATION Some of the equation parameters that characterize a greenhouse enclosure can be more easily measured experimentally (for example: KL, KC, F, L, R) than calculated directly. For these experimental measurements a Martian Greenhouse prototype was developed. The prototype, shown in Fig. 1, has a hemispheric Lexan cover installed on a stainless steel base. The prototype had a diameter of ~ 1 m, and a total volume of ~ 0.417 m. We envisage the top being made of soft transparent materials for operational use. Soft materials are planned to take a test in later works. The prototype includes the following internal environmental controls: a cold coil with an external chilled water source; resistance heating elements; an air circulation fan; A pump with rate ~ 5 L/min air under 101.3 kPa is provided for gas exchange between the system and the outside air of Thermotron. This system allows us to realize a closed water cycle and provides atmospheric gases from outside. Fig. 1. Martian Greenhouse Prototype (MGP). (In the center of the Dome there is system climate control tower that includes a coolant coil and a water distribution unit.) This MG prototype was designed to be installed inside another vacuum chamber that allows us to imitate Martian surface conditions. The vacuum chamber (Thermotron, Fig.2) has the following internal dimensions: 1.22 m-width, 1.22 m-height, and 1.62 mdepth. It provides environmental control that ranges from terrestrial to Martian conditions: temperature ~ -72 to +177 C: pressure ~ 0.1 kPa ( ~ 1 mm Hg)

Transmission and Distribution of Photosynthetically Active Radiation (PAR) from Solar and Electric Light Sources

This paper discusses the development and initial testing of a solar plant lighting system which collects, transmits and distributes photosynthetically active radiation (PAR) for controlled environment crop production. In this system, solar light, or light from an electric lamp, is collected by refl ector optics and focused on the end of an optical wave guide cable. The light is fi ltered by the selective beam splitter to reject non-PAR (λ < 400 nm and λ > 700 nm) from the light path to minimize the introduction of heat into the plant growth chamber. The PAR (400 nm < λ < 700 nm) is transmitted to the plant growth chamber where the light is distributed uniformly over the growing area. The lighting capability of the system was evaluated for solar and electric light sources. Based on the results we conclude that the solar plant lighting system with a supplemental electric light source is a viable and effective concept for space based crop production.

Object-oriented model-driven control.

A monitoring and control subsystem architecture has been developed that capitalizes on the use of model-driven monitoring and predictive control, knowledge-based data representation, and artificial reasoning in an operator support mode. We have developed an object-oriented model of a Controlled Ecological Life Support System (CELSS). The model, based on the NASA Kennedy Space Center CELSS breadboard data, tracks carbon, hydrogen, and oxygen, carbon dioxide, and water. It estimates and tracks resource-related parameters such as mass, energy, and manpower measurements such as growing area required for balance. We are developing an interface with the breadboard systems that is compatible with artificial reasoning. Initial work is being done on use of expert systems and user interface development. This paper presents our approach to defining universally applicable CELSS monitor and control issues, and implementing appropriate monitor and control capability for a particular instance: the KSC CELSS Breadboard Facility.

Clarifying Objectives and Results of Equivalent System Mass Analyses for Advanced Life Support

This paper discusses some of the analytical decisions that an investigator must make during the course of a life support system trade study. Equivalent System Mass (ESM) is often applied to evaluate trade study options in the Advanced Life Support (ALS) Program. ESM can be used to identify which of several options that meet all requirements are most likely to have lowest cost. It can also be used to identify which of the many interacting parts of a life support system have the greatest impact and sensitivity to assumptions. This paper summarizes recommendations made in the newly developed ALS ESM Guidelines Document and expands on some of the issues relating to trade studies that involve ESM. In particular, the following three points are expounded: 1) The importance of objectives: Analysis objectives drive the approach to any trade study, including identification of assumptions, selection of characteristics to compare in the analysis, and the most appropriate techniques for reflecting those characteristics. 2) The importance of results inferprefafion: The accuracy desired in the results depends upon the analysis objectives, whereas the realized accuracy is determined by the data quality and degree of detail in analysis methods. 3) The importance of analysis documentation: Documentation of assumptions and data modifications is critical for effective peer evaluation of any trade study. ESM results are analysis-specific and should always be reported in context, rather than as solitary values. For this reason, results reporting should be done with adequate rigor to allow for verification by other researchers.

Mars base zero - : A terrestrial analog

This paper presents background information and describes operating experience with Mars Base Zero, a terrestrial analog of a Mars base situated in Fairbanks, Alaska. Mars Base Zero is the current stage in a progression from a vegetable garden to a fully closed system (Nauvik) that the International Space Exploration and Colonization Company (ISECCo) has undertaken. Mars Base Zero is an 80 m 2 greenhouse, with 18m 2 of living space attached. The primary goal is to determine the necessary size for Nauvik in order to support one to four people using current ISECCo techniques for growing food crops. In the spring of 2004 Mars Base Zero was planted, and in the fall of 2004, one subject, Ray Collins, was closed in the system for 39 days. The data from this closure indicates that, using ISECCo cropping techniques, Nauvik will need 150 m 2 of crop area to support one person. While problems were encountered, the minimum goal of 30 days closure was exceeded. The diet was vegetarian, mostly potatoes. Plant productivity, diet, water consumption, waste production and crew time were tracked. Urine and feces were sterilized and recycled, though the system was largely open to water as well as air. Pests were a minor problem, eating about 20% of the wheat and 5% of the beets (mice), and damaging lettuce, sunflowers and spinach (aphids). Other issues included minor health problems; diet palatability & quality; odors from waste sterilization; and equipment problems. Thus, while years of work remain to be done to improve closure and operating procedures, the experiment was a success.