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Regenerative life support is considered a key enabling technology for the human exploration of space. Without regeneration, the cost of supplying the materials necessary to sustain human life escalates so rapidly that manned space flight becomes uneconomical for all but short, near-Earth missions. One of the methods for providing regenerative life support utilizes a Controlled Ecological Life Support System, or CELSS. To accomplish this regeneration, the CELSS must incorporate technologies for food production, food processing, atmospheric revitalization, water purification, trace contaminant control, and waste processing. Many experiments have been conducted to characterize the performance of individual CELSS subsystems (e.g., plant growth, waste processing). However, very little research has been done to define the performance and operational aspects of CELSS technology at the overall system level.

Little information exists on the responses of plants to environmental conditions which combine lower than Earth-normal atmospheric pressures with changes in the partial pressures of oxygen, carbon dioxide, and nitrogen. Data collected on the growth of plants in such environments will be valuable in the development of low-pressure plant growth facilities for use on Space Station Freedom, the moon, and Mars. Such low pressure environments have been proposed previously as a means of facilitating EVA operations. Additionally, in some planetary base applications, the use of low atmospheric pressure would allow the use of lightweight plant growth structures for food production, thus reducing both the mass and the launch cost of the life support system.

NASA's Centrifuge Facility is a multi-purpose life sciences research facility to be flown on Space Station Freedom. It will provide the capability for conducting experiments with living plants and animals in the microgravity environment of space. One component of the Facility is a plant habitat which is capable of supporting a wide variety of plant species under highly controlled environmental conditions. The conditions to be controlled include temperature, humidity, lighting (photosynthetically active radiation or PAR), air velocity, trace contaminant concentrations, nutrient element concentrations, and atmospheric composition. Lockheed conducted a “rapid prototyping” exercise to develop and test a preliminary design for such a plant habitat. Concurrent with an analytical effort, breadboard fabrication and testing was performed to support the acquisition of detailed performance data for both design analysis and validation of the simulation models used in the analysis.

A closed-loop, regenerative life support system must include a method for recycling organic waste materials. With a Controlled Ecological Life Support System (CELSS), this will be accomplished by decomposing the wastes and using the effluent to formulate a nutrient solution which supports food production by plants. The waste processing technology used may be either physicochemical or biological. Although the effluents from biological processors have been extensively evaluated as fertilizers for soil-based agricultural systems, few experiments have been conducted to evaluate their suitability in hydroponic applications. This paper describes the results of a series of experiments performed to evaluate effluent from an anaerobic bacterial reactor as a nutrient source for hydroponically-grown plants. Germination and initial seedling growth were found to be suppressed by pure effluent.

This paper describes the results of a project involving an anaerobic digestion system used in treating the human and vegetative wastes from a Controlled Ecological Life Support System (CELSS). The anaerobic digester biologically breaks down the organic matter in the wastes into a mixture of methane gas and carbon dioxide, while significantly reducing the BOD(biological oxygen demand ) of the wastewater. A standard waste was formulated consisting of a mixture of swine waste (the surrogate for human feces and urine), green wastes (primarilly lettuce), and paper wastes. The equipment used for this project was a 2.7 cubic meter digester tank filled with plastic media and heated to an average temperature of 35°C. The digester was run over period of 200 days and loaded on the average of five days per week. The results over this test period showed a 94% reduction in BOD and a 98% reduction in suspended solids in the wastewater.

The Space Transportation System uses a triiodide quaternary ammonium strong base resin to prevent microbial contamination of the crew's drinking water. Current plans for Space Station Freedom use the STS resin for microbial control in drinking water. Another use for this water is in the “salad machine” to grow vegetable plants hydroponically. Our experiments demonstrate that leaf lettuce (Lactuca sativa) grown in nutrient solution treated with the triiodide resin and it's next higher homologue, pentaiodide, result in greatly reduced growth or death. The triiodide and pentaiodide treatments reduced plant fresh weights to 0.2% and 0.04% of the controls respectively. Tissue analysis by neutron activation showed an iodine concentration of 0.47% to 0.6% in the experimental plants. Nutrient solution analysis showed an average residual concentration of 38 and 65 mg/l iodine at the end of the 30 day experiments for triiodide and pentaiodide treatments respectively.

A successful CELSS (Controlled Ecological Life Support System) design must accommodate the potential mismatch between the crew's relatively constant CO2 production and the widely varying crop CO2 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: Crop startup. Crop failures. Changes in number of humans supported. A general-purpose life support system simulator was used to evaluate several CELSS design and operation approaches. The simulator was used to investigate CO2 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.

It is extremely likely that the amount of crew time available to operate, service, and maintain life support systems for advanced space missions will be limited. Using published data from the Soviet Bios experiments, this paper provides descriptions of operational, servicing, and maintenance tasks anticipated for a Controlled Ecological Life Support System (CELSS) which includes both higher plants and algal reactors. This data shows that the Bios higher plant culture system operations required about 6.2 crew-hours per day, the algal culture system operations required approximately 7.5 crew-hours per day, and miscellaneous domestic operations required about 7.5 crew-hours per day. By integrating Bios task descriptions with typical laboratory procedures, detailed descriptions of nominal operations and maintenance activities were constructed. Crew time requirements were then derived for each of the activities identified.

This paper describes an evolutionary method of technology integration for the development of a Lunar base life support system. The baseline is a partially-closed Regenerative Life Support System (RLSS) based upon Space Station Freedom physicochemical technology. The paper describes the stepwise evolution of this baseline system into a closed-loop, Lunar base Controlled Ecological Life Support System (LCELSS), a hybrid design which incorporates both physicochemical and bioregenerative technologies. The steps taken in the evolutionary process are derived from a rationale which addresses: 1) the incorporation of specific bioregenerative functions into the life support system, 2) the supplementation of specific physicochemical functions with bioregenerative systems, 3) the replacement of initial physicochemical technologies with more advanced technologies, and 4) the addition of new physicochemical technologies.

Past spacecraft life support systems have used open-loop technologies that were simple and sufficiently reliable to demonstrate the feasibility of crewed spaceflight. A critical technology area needing development in support of both long duration missions and the establishment of lunar or planetary bases is regenerative life support. The subject of this paper is an ongoing study for a conceptual design of a Lunar-Base Controlled Ecological Life Support System (LCELSS) to support a crew size ranging from 4 to 100. An initial description of the LCELSS subsystems is provided within the framework of the conceptual design. The system design includes both plant (algae and higher plant) and animal species as potential food sources.

One of the most frequently encountered problems in the design and development of life support systems concerns system integration and evaluation. Lockheed Missiles & Space Co. has developed a simulation modelling toolkit to assist life support system designers in conducting system design, integration and performance assessment. This work arose from a recognized need for a flexible, easily-visualized simulation tool to support aerospace life support system design. The simulator supports performance analysis and “what if” studies based on the construction of block diagrams of the systems to be simulated. Libraries of physicochemical, bioregenerative and hybrid technologies have been developed. These subroutines can be accessed for use in developing system block diagrams. The blocks specified in a particular model can be easily interchanged with other blocks which perform similar functions to assess changes in system performance.

This paper describes the results of a study to develop a conceptual design for an experimental, closed-loop fluid handling system capable of monitoring, controlling, and supplying nutrient solution to higher plants. The Plant Feeder Experiment (PFX) is designed to be flight tested in a micro-gravity (micro-g) environment and was developed under NASA's In-Space Technology Experiments Program (INSTEP). When flown, PFX will provide information on both the generic problems of micro-g fluid handling and the specific problems associated with the delivery of nutrient solution in a micro-g environment. The experimental hardware is designed to fit into two middeck lockers on the Space Shuttle, and incorporates several components that have previously been flight tested.