Considerations of design for life support systems

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doi: lO.l016/SO273-1177(03)00079-6

CONSIDERATIONS OF DESIGN FOR LIFE SUPPORT SYSTEMS Akira Ashida ‘* Institutefor

Environmental

Sciences, Ienomae 1-7, Obuchi, Rokkasho-tiura, Kamikita-gun,Aomori, 039-3212 Japan

ABSTRACT (1) During the design phase for construction of artificial ecosystems, the following considerations are important. Influences on living things in the ecosystem, such as lifestyles and physiological functions caused by stresses due to The long stay in the artificial ecosystem has a possibility to lead to evolutional change in environmental changes.

the living things. (2) The system operation method in trouble, which relates to maintainability. (3) The system metamorphosis according to new technologies. (4) Route minimization of material flow that leads to an optimum system layout. 0 2003 Published by Elsevier Science Ltd on behalf of COSPAR.

INTRODUCTION Construction of an artificial experimental closed ecological system facility has been conducted, firstly, for applications to human life in space and for basic research relating to life support in closed systems. The main facilities for closed ecological experiments are: BIOS facility consisting of human habitat, higher plant module and algal cultivation module at the Institute of Biophysics in Krasnoyarsk, Russia since 1961, 2 facility simulating earth’s biosphere by Space Biosphere Ventures located in Arizona since 1984 (Alling, 1993),

Biosphere

BPC (Biomass

Production

Chamber)

in CELSS and ALS (Advanced Life Support) programs at NASA KSC

since 1985 (Jones, 2000), C.E.B.A.S. (Closed Equilibrated Biological Aquatic System) consisting of zoological component (habitat for aquatic animals), botanical component (higher aquatic plant bioreactor) and microbiological component, aiming at basic research on bioregenerative life support systems at Ruhr-University of Bochum since 1988 (Slenzka, 1999), CEEF (Closed Ecology Experiment Facilities) consisting of CPEF (Closed Plantation Experiment Facility), CAHF (Closed Animal Breeding & Habitation Experiment Facility) and CGEF (Closed Geo-Hydrosphere Experiment Facility) at IES (Institute for Environmental Sciences) in Rokkasho-mura, Japan, since 1993 (Ashida, 1995), VPGC (Variable Pressure Growth Chamber) and LSSIF (Life Support Systems Integration Facility, BIO-Plex) in LMLSTP (Lunar-Mars Life Support Test Project) at NASA JSC since 1994 (Tri and Barta, 1999), MELISSA (Micro-Ecological Life Support Alternative) for the purpose of understanding the behavior of artificial ecosystem and for the development of technology for future biological life support systems at ESA since 1994 (Lasseur; 2000).

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moved to Institute of Future Technology,

now Westron Corporation

Space Res. Vol. 31, No. 7, pp. 1805-1809.2003 8 2003 Published by Elsevier Science Ltd on behalf of COSPAR Printed in Great Britain 0273-l 177/03 $30.00 + 0.00

Adv.

Difficulties and research targets lie m the treatment ofbiospecies in an artificial environment different from the natural environment, and in the system control including material circulations in the closed system. ‘The physiological changes of the biospecies due to special environmental factors should be taken into account. long term and/or large-scaled experiments need more new design concepts based on basic research results from various experiments obtained by using the above-mentioned facilities. PHYSIOLOGICAL

CHANGE

OF BIOSPECIES

Biospecies have, in general, a physiological character acquired through evolution over a long period, with interaction between other surrounding biospecies and in various physical and chemical environmental conditions. The artificial environment differs largely from the natural environment and offers various influences on the biospecies living in the artificial environment. Most of the physiological data of biospecies are experimentally obtained in the controlled environment. The designs of artificial ecological facilities are, in general, made based on such data, partly using field data. Artificial ecological facilities need capabilities of controlling various environmental conditions and material circulations to minimize undesirable system conditions. Biospecies other than human in closed ecological systems where humans live, are in general selected for food production for humans. The plant species are selected so as to satisfy nutritive requirement for humans (Ashida, 1995). Such plant species are cultivated so as to get efficient and suitable growth by nutrients and the environmental control such as temperature, humidity, light intensity, etc.. Although the automatic cultivation will be a future problem, the maintenance and care by persons or crew are very important to get good harvest. Other necessary biospecies are introduced into the closed ecological system for special experiments, such as animal The materials in the closed system have to be processed and breeding or simulating earth’s natural environment. Especially, physiological materials that relate to nutritive and circulated to maintain the system stability. physiological functions are circulated in the closed system and enter living things in the system. On the other hand, non-physiological materials that are constituent materials of the hardware and appliances are in general harmful to living things when such materials enter the living things’ body. The artificial ecological system should be maintained to realize a suitable environment and to supply physiological materials by reasonable control of the environment and material circulation (Ashida, 1993). The physiological nature of biospecies depends on or changes according to environmental factors. Maximum biomass production and system stabilization are important operational control problems of artificial closed ecological systems. Biospecies living in the artificial ecological system experiences special environmental A change in environmental factors gives the biospecies stresses situations different from the natural environment. in some cases (Ashida, 1997) that may lead the biospecies to change physiological character. Furthermore, contact of or symbiotic relations with microorganisms and a small amount of special materials are important factors The biospecies that have continued several generations of changes in an to estimate the physiological change. The lifestyle planning for humans is important artificial closed ecological system may cause evolutional change. The diet menu is also important for for design of the closed system including the habitat and the work program. maintaining physical and mental health, and so occupies an important position in the personal lifestyle (Alling. 1993). INTERRUPTION

AVOIDANCE

OF CLOSED

ECOLOGICAL

EXPERIMENTS

Equipment Failure Artificial Closed Ecological Systems are composed of many kinds of material processing subsystems and complex material flow piping networks. Therefore, it is difficult to realize failure-free operation. There are always equipment failures, if small-scale failures are counted. Since experiments of closed ecological systems require a long period to avoid the interruption of the experiment, some mechanisms should be introduced in the material circulation system. For instance, the reservoir volume and material process capability are increased in order to supply necessary material during repair of the failed equipment, as well as during maintenance of the system and equipment.

Improvement of System Adoption of new technology and improvement of the system or equipment are important for effective operation of the closed ecological experiment. The execution of this improvement when the system is in operation

1807

Design for Life Support Systems

is more effective especially for long-term operation. for effective experimental results.

Such improvements reduce operational loads and contribute

System Expansion In construction of a lunar or Mars base, the facility or system starts from a small scale and expands to a large scale. It is desirable that the system is expanded in operation. The expansion scenario for the material process and circulation system should be planned based on the ecological system behavior. SYSTEM METAMORPHOSIS OF CLOSED ECOLOGICAL SYSTEMS System Metamorphosis The system change of the artificial closed ecological system in operation due to repair, improvement and system expansion is called ‘system metamorphosis’. A good example of system metamorphosis is seen in the growth and activity of living things. The system of living things is characterized as below: The system always has failure portions, changes by growth and metabolism and . accomplishes its objects almost completely. ?? ??

The concept of the autonomous decentralized system has been considered based on the model of living things as shown in Figure 1. The autonomous decentralized system has been so far applied to information processing systems. Such a system with hardware is called dependable (Miyamoto and Ihara, 1983). System Feature of Material Process System in Artificial Closed Ecological Systems Good operation of the artificial closed ecological system is achieved by the circulation of necessary material to/from each subsystem at the appropriate amount. Reduction of the amount of circulation material is due to chemical change, deposition, and adhesion. It is difficult to avoid these phenomena, because it relates to selection of hardware, solubility control in fluids, and degradation of material surface characteristics including temperature dependency. Pure fluids such as fresh air and pure water, and chemically stable material are suitable material that is circulated and stored in the closed system. As solid circulating systems are always facing this difficulty, the piping route should be shortened. Some cleaning mechanism and maintenance procedures are needed for the piping route and storage tank. A fluid system containing solids, therefore, must be treated essentially as a solid system. A liquid system with dissolving solids that have low solubility or changes in solubility due to the existence of other material dissolved or temperature may cause a separation problem. Therefore, the material processes should be categorized as listed in Table 1. Table 1. Categorization of Material Processes Material Systems

Examples of Process Systems

Gas systems

Air process subsystems

Liquid systems

Liquid transport subsystems

Solid systems (Fluid systems containing solids)

Waste process subsystems Waste water process subsystem

Features

These subsystems can process at a distant place. These subsystems treat pure water/liquids and can process at a distant place. Solidification occurs at piping and storage. These subsystems process nearby generation place of wastes.

Solids include minerals or trace elements that are indispensable nutrients for living things. The trace elements are Li, B, F, Si, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Sr, MO, Cd, Sn, and I. Most of the trace elements become harmful for living things when they take in such material in amounts exceeding an allowable level (Ashida, 1994). Major materials of metabolic substances are organic materials that consist of carbon, hydrogen, oxygen and nitrogen, Organic materials are finally changed to water (H,O) and air (COz, 02, Nz) at the material processing. On the other hand, non-metabolic materials, which are components of hardware, are almost solids and are harmful for living things. On earth, small amount of materials naturally and artificially produced, including the trace elements, are circulated through air and water in rivers and seas in a similar content (Ashida, 1994). In

A. Aahida

I x0x

an artificially

controlled

environment,

the amount of material circulated

in the environment

should be controlled

m

Self-Centeredness Self-Responsibility

Survival Protection (Fault Tolerant)

Self-Restoration

Controllability (Metabolism)

1 System Continuation

Entropy

Equalization

Coordinatorless

Cooperation (Growth)

Multi-peaked

Stabilization

Fig. 1. Concept of Autonomous Decentralized System suitable level, which is a new problem, although some allowance data of the special materials were established for Therefore, solid systems are the key process to maintain for artificial ecosystems the international space station. to be safe and stable. System Expansion of Artificial Closed Ecological Life Support Systems The system expansion of the artificial closed ecological life support system such as a space station and a Lunar-Mars base should be made by increasing the number of habitat systems with the support systems consisting The key to The single system expansion brings in poor system dependability. of material process subsystems. accomplish the system dependability lies in the system configuration of material processes and supply subsystems. Figure 2 shows the concept of material process configuration of the large-scale artificial closed ecological life support system. At the stage of the system expansion, a system consisting of a living organisms module and its process When a It is desirable for each system to have its own energy system. subsystem is a unit of the expansion. waste process subsystem such as wet oxidation processor of the system B has an operational problem, the Therefore, a process subsystem neighboring waste process subsystem (for example system A) covers the process. On the other hand, the air process and the liquid transport can be done has to have more than twice the capacity. When repair or improvement of the system through the pipeline by the corresponding processor at a distant place. This system configuration is considered B is performed, a similar approach to the abovementioned is performed. as an example, applied to a hardware system of the autonomous decentralized system. Material Circulation on Earth In the material circulation on Earth, air circulates widely on the earth surface, water flows through rivers to the The feature of material seas that spread over the earth surface, and solids do not generally move great distances. circulation on Earth is characterized as shown in Figure 2. In the global environmental problem, pollution of air and seawater causes worldwide problem and waste dumped in the environment makes harmful effects on the environment between nations or in a local area.

Design for Life Support Systems

1809

1

Solids

Fig. 2. Material Process Configuration

of Large Scale System

Connection between Artificial Ecological Systems Various artificial ecological systems are considered as mentioned in the Introduction in this paper. The future construction of artificial ecological systems will be carried out using various kinds of system configurations in the event of international cooperation. An artificial ecological system utilizing new technologies is a different type. The possible candidate connections among artificial ecological systems are considered as shown in Figure 2. REFERENCES Alling, A., and M. Nelson, Life Under Glass-The Inside Story of Biosphere 2, The Biosphere Press, 1993. Ashida, A., and K. Nitta, Material Circulations in a Closed System, 932289,23rd ICES, 1993. Ashida, A., Recycling of Trace Elements required for Humans in CELSS, Adv. Space Res., 14, No. 11, 177-187, 1994. Ashida, A., and K. Nitta, Construction of CEEF is Just Started, 9.51584,25th ICES, 1995. Ashida, A., Problems of Human Life in a CELSS, 972515,27th ICES, 1997. Barta, D.H., J.M. Castillo and R.E. Forston, The Biomass Production System for the Bioregenerative Planetary Life Support Systems Test Complex: Pleliminary Desighns and Considerations, 1999-Ol-2188,29th ICES, 1999. Ihara, H., and K. Mori, Autonomous Decentralized Computer Control Systems, COMUTER, pp. 57-66, Au. 1983. Jones, H., and J. Cavazzoni, Top-Level Crop Models for Advanced Life Support Analysis, 2000-01-2261, 30th ICES, 2000. Lasseur, Ch., M. Dixon, G. Dubertret, G. Dussap, F. Godia, J.B. Gros, M. Mergeay, J. Richalet and W. Verstraete, MELLISA: 10 years of Research, Results, Status and Perspectives, 2000-Ol-2378,3Oth ICES, 2000. Miyamoto, S., M. Nohmi, K. Mori and H. Ihara, Fault-Tolerant Multi-Microprocessor System Based on Autonomous Decentralization Concept, IEEE 1983 FTCS 13th Annual International Symposium Fault-Tolerant Computing, pp. 4-9, 1983. Slenzka, K., The C.E.B.A.S.-Minimodule - Development, Realization and Perspectives -, 1999-01-1988, 29th ICES, 1999. Tri, Terry O., Bioregenerative Planetary Life Support Systems Test Complex (BIO-PLEX): Test Mission Objectives and Facility Development, 1999-Ol-2186,29th ICES, 1999. E-mail address of A. Ashida

ashida@-living,ne.jp