Achieving and documenting closure in plant growth facilities.

As NASA proceeds with its effort to develop a Controlled Ecological Life Support System (CELSS) that will provide life support to crews during long duration space missions, it must address the question of facility and system closure. Here we discuss the concept of closure as it pertains to CELSS and describe engineering specifications, construction problems and monitoring procedures used in the development and operation of a closed plant growth facility for the CELSS program. A plant growth facility is one of several modules required for a CELSS. A prototype of this module at Kennedy Space Center is the large (7m tall x 3.5m diameter) Biomass Production Chamber (BPC), the central facility of the CELSS Breadboard Project. The BPC is atmospherically sealed to a leak rate of approximately 5% of its total volume per 24 hours. This paper will discuss the requirements for atmospheric closure in this facility, present CO2 and trace gas data from initial tests of the BPC with and without plants, and describe how the chamber was sealed atmospherically. Implications that research conducted in this type of facility will have for the CELSS program are discussed.     

Performance and reliability of the NASA Biomass Production Chamber.

The Biomass Production Chamber (BPC) at the Kennedy Space Center is part of the Controlled Ecological Life Support System (CELSS) Breadboard Project. Plants are grown in a closed environment in an effort to quantify their contributions to the requirements for life support. Performance of this system is described. Also, in building this system, data from component and subsystem failures are being recorded. These data are used to identify problem areas in the design and implementation. The techniques used to measure the reliability will be useful in the design and construction of future CELSS. Possible methods for determining the reliability of a green plant, the primary component of a CELSS, are discussed.     

The Breadboard Project: a functioning CELSS plant growth system.

The primary objective of the Breadboard project for the next 3-4 years is to develop, integrate and operate a Controlled Ecological Life Support System (CELSS) at a one person scale. The focus of this project over the past two years has been the development of the plant growth facility, the first module of the CELSS. The other major modules, food preparation, biomass processing, and resource recovery, have been researched at the laboratory scale during the past two years and facilities are currently under construction to scale-up these modules to an operational state. This paper will outline the design requirements for the Biomass Production Chamber (BPC), the plant growth facility for the project, and the control and monitoring subsystems which operate the chamber and will present results from both engineering and biological tests of the facility. Three production evaluations of wheat, conducted in the BPC during the past year, will be described and the data generated from these tests discussed. Future plans for the BPC will be presented along with future goals for the project as the other modules become active.     

Material balance and diet in bioregenerative life support systems: connection with coefficient of closure.

Bioregenerative life support systems (BLSS) with different coefficients of closure are considered. The 66.2% coefficient of closure achieved in "BIOS-3" facility experiments has been taken as a base value. The increase in coefficient of closure up to 72.6-93.0% is planned due to use of soil-like substrate (SLS) and concentrating of urine. Food values were estimated both in a base variant ("BIOS-3"), and with increases in the coefficient of closure. It is shown that food requirements will be more fully satisfied by internal crop production with an increase in the coefficient of closure of the BLSS. Changes of massflow rates on an 'input-output' and inside BLSS are considered. Equations of synthesis and degradation of organic substances in BLSS were examined using a stoichiometric model. The paper shows that at incomplete closure of BLSS containing SLS there is a problem of nitrogen balancing. To compensate for the removal of nitrogen from the system in urine and feces, it is necessary to introduce food and a nitrogen-containing additive.     

Systematic approach to life support system analyses and integration.

This paper is devoted to the consideration of possible viewpoint on CELSS development and design. If the aim to create practically applicable CELSS is accepted then the task to optimize the process of CELSS research and development in terms of minimum cost, hours, maximum applicability, scientific contribution, etc. becomes actual. Requirements of applicability and scientific significance are synergetic since understanding of general properties of CELSS gives an ability to create CELSS for different applications. To accomplish the task three main groups of parameters have to be optimized: i) configuration and operating parameters of developing CELSS itself; ii) organizational management of research and development of CELSS; iii) features of an area where CELSS is planned to be used (space missions, terrestrial applications, or biosphere investigation) and where requirements to CELSS characteristic come from. Given paper is a brief review presented some attempts to arrange mentioned above into some set of formalized and interacting criteria, and some progression of research stages derived from these criteria.     

Methods for measurement and control of leakage in CELSS and their application and performance in the Biosphere 2 facility.

Atmospheric leakage between a CELSS and its surround is driven by the differential pressure between the two. In an earth-based CELSS, both negative and positive differential pressures of atmosphere are created as the resultant of three influences: thermal expansion/contraction, transition of water between liquid and vapor phases, and external barometric pressure variations. The resultant may typically be on the order of 5000 pascals. By providing a flexible expansion chamber, the differential pressure range can be reduced two, or even three, orders of magnitude, which correspondingly reduces the leakage. The expansion chamber itself can also be used to measure the leak rate. Independent confirmation is possible by measurement of the progressive dilution of a trace gas. These methods as employed at the Biosphere 2 facility have resulted in an estimated atmospheric leak rate of less than 10 percent per year.     

CELSS: possible contributions to earth science program and others.

CELSS technology, composed of various subsystems designed to stabilize the environment in closed space can be used to construct the Closed Ecology Experiment Facility. The Closed Ecology Experiment Facility has the character of an Environmental Time Machine. Many environmental researches of studies will, it is proposed, be conducted using this facility. The concept of Closed Ecology Experiment Facility is described, and several research items related to earth science potentially to be conducted using this facility are indicated. As an example of the application, an improved model of climate estimation is discussed.     

The biological component of the life support system for a Martian expedition.

Ground-based experiments at RF SSC-IBMP RAS (State Science Center of Russian Federation--Institute of Biomedical Problems of Russian Academia of Science) were aimed at overall studies of a human-unicellular algae-mineralization LSS (life support system) model. The system was 15 m3 in volume. It contained 45 L of algal suspension with a dry substance density of 10-12 g per liter; water volume, including the algal suspension, was 59 L. More sophisticated model systems with partial substitution of unicellular algae with higher plates (crop area of 15 m2) were tested in three experiments from 1.5 to 2 months in duration. The experiments demonstrated that LSS employing the unicellular algae play not only a macrofunction (regeneration of atmosphere and water) but also carry some other functions (purification of atmosphere, formation of microbial cenosis etc.) providing an adequate human environment. It is also important that functional reliability of the algal regenerative subsystem is secured by a huge number of cells able, in the event of death of a part of population, to recover in the shortest possible time the size of population and, hence, functionality of the LSS autotrophic component. For a long period of time a Martian crew will be detached from Earth's biosphere and for this reason LSS of their vehicle must be highly reliable, robust and redundant. One of the approaches to LSS redundancy is installation of two systems with different but equally efficient regeneration technologies, i.e. physical-chemical and biological. At best, these two systems should operate in parallel sharing the function of regeneration of the human environment. In case of failure or a sharp deterioration in performance of one system the other will, by way of redundancy, increase its throughput to make up for the loss. This LSS design will enable simultaneous handling of a number of critical problems including adequate satisfaction of human environmental needs.     

Development of a CELSS Experimental Facility

A CELSS Experimental Facility was developed two years ago. It contains a volume of about 40.0 m³ and a cultivating area of about 8.4 m²; its interior atmospheric parameters such as temperature, relative humidity, oxygen concentration, carbon dioxide concentration, total pressure, lighting intensity, photoperiod, water content in the growing-matrix, CO₂-added accumulative amount, O₂-released accumulative amount and ethylene concentration are all controlled and logged automatically and effectively; its growing system consists of two rows of racks along its left-and-right sides separately, each side holds two upper-and-lower layers, and the vertical distance of each growing bed can be adjusted automatically and independently; lighting sources consist of both red (95%) and blue (5%) light-emitting diodes (LED), and the average lighting intensity of each lamp bank at 20-cm distance position under it, reaches to 255.0 μmol m⁻² s⁻¹. After that, demonstrating tests were carried out and were finally followed by growing lettuce in the facility. The results showed that all subsystems operated well and all parameters were controlled automatically and efficiently. The lettuce plants in the system could grow much well. Successful development of this system laid a necessary foundation for future larger-scale studies on CELSS integration technique.     

An overview of Japanese CELSS research activities.

Many research activities regarding Controlled Ecological Life Support System (CELSS) have been conducted and continued all over the world since the 1960's and the concept of CELSS is now changing from Science Fiction to Scientific Reality. Development of CELSS technology is inevitable for future long duration stays of human beings in space, for lunar base construction and for manned mars flight programs. CELSS functions can be divided into two categories, Environment Control and Material Recycling. Temperature, humidity, total atmospheric pressure and partial pressure of oxygen and carbon dioxide, necessary for all living things, are to be controlled by the environment control function. This function can be performed by technologies already developed and used as the Environment Control Life Support System (ECLSS) of Space Shuttle and Space Station. As for material recycling, matured technologies have not yet been established for fully satisfying the specific metabolic requirements of each living thing including human beings. Therefore, research activities for establishing CELSS technology should be focused on material recycling technologies using biological systems such as plants and animals and physico-chemical systems, for example, a gas recycling system, a water purifying and recycling system and a waste management system. Based on these considerations, Japanese research activities have been conducted and will be continued under the tentative guideline of CELSS research activities as shown in documents /1/, /2/. The status of the over all activities are discussed in this paper.     

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.     

Survey of CELSS concepts and preliminary research in Japan

Many agricultural and other experiments relating to the development of a Controlled Ecological Life Support System (CELSS) were proposed by scientists throughout Japan in the fall of 1982. To develop concrete experimental concepts from these proposals, the engineering feasibility of each proposal was investigated by a CELLS experiment concept study group under the support of the National Aerospace Laboratory. The conclusions of the group were described in two documents, /1/, /2/. Originally, the study group did not clearly define necessary missions leading to the goal of an operational CELSS for spaceflight. Therefore, the CELSS experiment concept study group met again to clarify the goals of CELSS and to determine three phases to achieve the goals. The resulting phases, or missions, and preliminary proposals and studies needed to develop a CELLS are described herein.     

Interaction of physical-chemical and biological regeneration processes in ecological Life Support Systems.

Catalytic combustion of inedible biomass of plants in ecological Life Support Systems (LSS) gives rise to gaseous oxides (CO2, NO2, SO2, etc.). Some of them are toxic for plants suppressing their photosynthesis and productivity. Experiments with "Bios-3" experimental LSS demonstrate that a decrease of photosynthetic productivity in a system with straw incineration can jeopardize its steady operation. Analysis of the situation by a mathematical model taking into account absorption parameters of the system in terms of toxic elements makes it possible to formulate requirements for the structure and operation of LSS to provide for its stability. Avenues for further investigation of the problem of toxic stability of LSS are proposed.     

Evaluation of optimal configuration of hybrid Life Support System for Space.

Any comprehensive evaluation of Life Support Systems (LSS) for space applications has to be conducted taking into account not only mass of LSS components but also all relevant equipment and storage: spare parts, additional mass of space ship walls, power supply and heat rejection systems. In this paper different combinations of hybrid LSS (HLSS) components were evaluated. Three variants of power supply were under consideration--solar arrays, direct solar light transmission to plants, and nuclear power. The software based on simplex approach was used for optimizing LSS configuration with respect to its mass. It was shown that there are several LSS configuration, which are optimal for different time intervals. Optimal configurations of physical-chemical (P/C), biological and hybrid LSS for three types of power supply are presented.     

Controlled environments alter nutrient content of soybeans.

Information about compositional changes in plants grown in controlled environments is essential for developing a safe, nutritious diet for a Controlled Ecomological Life-Support System (CELSS). Information now is available for some CELSS candidate crops, but detailed information has been lacking for soybeans. To determine the effect of environment on macronutrient and mineral composition of soybeans, plants were grown both in the field and in a controlled environment where the hydroponic nutrient solution, photosynthetic flux (PPF), and CO2 level were manipulated to achieve rapid growth rates. Plants were harvested at seed maturity, separated into discrete parts, and oven dried prior to chemical analysis. Plant material was analyzed for proximate composition (moisture, protein, lipid, ash, and carbohydrate), total nitrogen (N), nonprotein N (NPN), nitrate, minerals, amino acid composition, and total dietary fiber. The effect of environment on composition varied by cultivar and plant part. Chamber-grown plants generally exhibited the following characteristics compared with field-grown plants: 1) increased total N and protein N for all plant parts, 2) increased nitrate in leaves and stems but not in seeds, 3) increased lipids in seeds, and 4) decreased Ca:P ratio for stems, pods, and leaves. These trends are consistent with data for other CELSS crops. Total N, protein N, and amino acid contents for 350 ppm CO2 and 1000 ppm CO2 were similar for seeds, but protein N and amino acid contents for leaves were higher at 350 ppm CO2 than at 1000 ppm CO2. Total dietary fiber content of soybean leaves was higher with 350 ppm CO2 than with 1000 ppm CO2. Such data will help in selecting of crop species, cultivars, and growing conditions to ensure safe, nutritious diets for CELSS.     

Processing of nutritious, safe and acceptable foods from CELSS candidate crops.

A controlled ecological life-support system (CELSS) is required to sustain life for long-duration space missions. The challenge is preparing a wide variety of tasty, familiar, and nutritious foods from CELSS candidate crops under space environmental conditions. Conventional food processing technologies will have to be modified to adapt to the space environment. Extrusion is one of the processes being examined as a means of converting raw plant biomass into familiar foods. A nutrition-improved pasta has been developed using cowpea as a replacement for a portion of the durum semolina. A freeze-drying system that simulates the space conditions has also been developed. Other technologies that would fulfill the requirements of a CELSS will also be addressed.     

CELSS transportation analysis

Regenerative life support systems based on the use of biological material have been considered for inclusion in manned spacecraft since the early days of the United States space program. These biological life support systems are currently being developed by NASA in the Controlled Ecological Life Support System (CELSS) program. Because of the progress being achieved in the CELSS program, it is time to determine which space missions may profit from use of the developing technology. This paper presents the results of a study that was conducted to estimate where potential transportation cost savings could be anticipated by using CELSS technology for selected future manned space missions.

Six representative missions were selected for study from those included in NASA planning studies. The selected missions ranged from a low Earth orbit mission to those associated with asteroids and a Mars sortie. The crew sizes considered varied from four persons to five thousand. Other study parameters included mission duration and life support closure percentages, with the latter ranging from complete resupply of consumable life support materials to 97% closure of the life support system. The paper presents the analytical study approach and describes the missions and systems considered, together with the benefits derived from CELSS when applicable.     

Approaches to resource recovery in Controlled Ecological Life Support Systems.

Recovery of resources from waste streams in a space habitat is essential to minimize the resupply burden and achieve self sufficiency. The ultimate goal of a Controlled Ecological Life Support System (CELSS) is to achieve the greatest practical level of mass recycle and provide self sufficiency and safety for humans. Several mission scenarios leading to the ultimate application could employ CELSS component technologies or subsystems with initial emphasis on recycle of the largest mass components of the waste stream. Candidate physical/chemical and biological processes for resource recovery from liquid and solid waste streams are discussed and the current fundamental recovery potentials are estimated.