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PubMed2004

Model implementation for dynamic computation of system cost for advanced life support.

Life support system designs for long-duration space missions have a multitude of requirements drivers, such as mission objectives, political considerations, cost, crew wellness, inherent mission attributes, as well as many other influences. Evaluation of requirements satisfaction can be difficult, particularly at an early stage of mission design. Because launch cost is a critical factor and relatively easy to quantify, it is a point of focus in early mission design. The method used to determine launch cost influences the accuracy of the estimate. This paper discusses the appropriateness of dynamic mission simulation in estimating the launch cost of a life support system. This paper also provides an abbreviated example of a dynamic simulation life support model and possible ways in which such a model might be utilized for design improvement.

Biomass↗
PubMed2000

Microgravity effects on water supply and substrate properties in porous matrix root support systems.

The control of water content and water movement in granular substrate-based plant root systems in microgravity is a complex problem. Improper water and oxygen delivery to plant roots has delayed studies of the effects of microgravity on plant development and the use of plants in physical and mental life support systems. Our international effort (USA, Russia and Bulgaria) has upgraded the plant growth facilities on the Mir Orbital Station (OS) and used them to study the full life cycle of plants. The Bulgarian-Russian-developed Svet Space Greenhouse (SG) system was upgraded on the Mir OS in 1996. The US developed Gas Exchange Measurement System (GEMS) greatly extends the range of environmental parameters monitored. The Svet-GEMS complex was used to grow a fully developed wheat crop during 1996. The growth rate and development of these plants compared well with earth grown plants indicating that the root zone water and oxygen stresses that have limited plant development in previous long-duration experiments have been overcome. However, management of the root environment during this experiment involved several significant changes in control settings as the relationship between the water delivery system, water status sensors, and the substrate changed during the growth cycles.

Carbon Dioxide↗
PubMed1997

Storage stability of screwpress-extracted oils and residual meals from CELSS candidate oilseed crops.

The efficacy of using screwpress extraction for oil was studied with three Controlled Ecological Life-Support System (CELSS) candidate oilseed crops (soybean, peanut, and canola), since use of volatile organic solvents for oil extraction likely would be impractical in a closed system. Low oil yields from initial work indicated that a modification of the process is necessary to increase extraction efficiency. The extracted oil from each crop was tested for stability and sensory characteristics. When stored at 23 degrees C, canola oil and meal were least stable to oxidative rancidity, whereas peanut oil and meal were least stable to hydrolytic rancidity. When stored at 65 degrees C, soybean oil and canola meal were least stable to oxidative rancidity, whereas peanut oil and meal were least stable to hydrolytic rancidity. Sensory evaluation of the extracted oils used in bread and salad dressing indicated that flavor, odor intensity, acceptability, and overall preference may be of concern for screwpress-extracted canola oil when it is used in an unrefined form. Overall results with screwpress-extracted crude oils indicated that soybean oil may be more stable and acceptable than canola or peanut under typical storage conditions.

Arachis↗
PubMed2003

Optimized bioregenerative space diet selection with crew choice.

Previous studies on optimization of crew diets have not accounted for choice. A diet selection model with crew choice was developed. Scenario analyses were conducted to assess the feasibility and cost of certain crew preferences, such as preferences for numerous-desserts, high-salt, and high-acceptability foods. For comparison purposes, a no-choice and a random-choice scenario were considered. The model was found to be feasible in terms of food variety and overall costs. The numerous-desserts, high-acceptability, and random-choice scenarios all resulted in feasible solutions costing between 13.2 and 17.3 kg ESM/person-day. Only the high-sodium scenario yielded an infeasible solution. This occurred when the foods highest in salt content were selected for the crew-choice portion of the diet. This infeasibility can be avoided by limiting the total sodium content in the crew-choice portion of the diet. Cost savings were found by reducing food variety in scenarios where the preference bias strongly affected nutritional content.

Astronauts↗
PubMed1997

A modified CROPGRO model for simulating soybean growth in controlled environments.

The CROPGRO crop growth model is adapted in order to analyze experimental data from a soybean (cv. Hoyt) experiment conducted at elevated CO2 levels (1200 micromol mol-1) at Kennedy Space Center, FL. The following adaptations to original CROPGRO produced model agreement with gas-exchange data: the input of square-wave temperature and photosynthetically active radiation (PAR) profiles; the input of the appropriate hydroponic substrate PAR albedo; modified biomass partitioning and developmental parameters; an increased leaf area expansion rate through the fifth vegetative node; a decreased specific leaf area after the fifth vegetative node; and an increased incident diffuse PAR fraction over typical field values. The model demonstrated here suggests that with continued development, modified CROPGRO will be a useful tool in the analysis and eventual optimization of legume production in bioregenerative life support systems.

Biomass↗
PubMed1999

Multivariable empirical modeling of ALS systems using polynomials.

Multivariable polynomial regression (MPR) was used to model plant motion time-series and nutrient recovery data for Advanced Life Support (ALS). MPR has capabilities similar to neural network models in terms of ability to fit multiple-input single-output nonlinear data. It has advantages over neural networks including: reduced overfitting, produces models that are more tractable for optimization, sensitivity analysis, and prediction of confidence intervals. MPR was used to produce nonlinear polynomial time-series models predicting plant projected canopy area versus time and temperature. Temperature was found to not have a statistically significant effect. Models were developed to relate rate and extent of nutrient recovery to treatment parameters, including temperature and use of heat pretreatment or nutrient supplementation. These applications demonstrate MPR's capability to fill "gaps" in an integrated model of ALS. Fundamental models should be used whenever available. However, some components may require empirical modeling. Furthermore, even fundamental models often have empirical constituents. MPR models are proposed to satisfy these needs.

Biodegradation, Environmental↗
PubMed2000

Pythium invasion of plant-based life support systems: biological control and sources.

Invasion of plant-based life support systems by plant pathogens could cause plant disease and disruption of life support capability. Root rot caused by the fungus, Pythium, was observed during tests of prototype plant growth systems containing wheat at the Kennedy Space Center (KSC). We conducted experiments to determine if the presence of complex microbial communities in the plant root zone (rhizosphere) resisted invasion by the Pythium species isolated from the wheat root. Rhizosphere inocula of different complexity (as assayed by community-level physiological profile: CLPP) were developed using a dilution/extinction approach, followed by growth in hydroponic rhizosphere. Pythium growth on wheat roots and concomitant decreases in plant growth were inversely related to the complexity of the inocula during 20-day experiments in static hydroponic systems. Pythium was found on the seeds of several different wheat cultivars used in controlled environmental studies, but it is unclear if the seed-borne fungal strain(s) were identical to the pathogenic strain recovered from the KSC studies. Attempts to control pathogens and their effects in hydroponic life support systems should include early inoculation with complex microbial communities, which is consistent with ecological theory.

Ecological Systems, Closed↗
PubMed2000

Toward a reverse osmosis membrane system for recycling space mission wastewater.

Essential to extended human exploration and utilization of space is providing a clean supply of potable water as well as water for washing. Recycling of space mission wastewater is necessary for long-term space missions due to the limited capacity of water storage. In this study, initial measurements toward a wastewater reclamation system that provides a clean water supply using reverse osmosis (RO) membranes have been made using stirred cell filtration experiments. Low-pressure reverse osmosis (LPRO) membranes were used to obtain high flux of permeate as well as high rejection. Detergent removal was above 99%, and dissolved salt removal was above 90% in single-pass treatment, while total organic carbon (TOC) removal was nearly 80%. Most problematic is nitrogen rejection, which was 74% at best. Comparison of feed water before and after urea hydrolysis shows that the rejection of nitrogen compounds can be increased to 95% by allowing urea hydrolysis to occur. The removal efficiency for nitrogen compounds was also improved by increasing the shear rate near membrane surface. As a result, the product water in two passes could meet the hygiene water requirements for human space missions, and the product water in three passes could meet potable water regulations with overall recovery of 77%. This study also suggests that dynamic rotating membrane filtration, which can produce a high shear rate, will be useful to increase the system recovery as well as pollutant rejection. Grant numbers: NAG9-1053

Ecological Systems, Closed↗
PubMed2001

Development of a microgravity-compatible reagentless organic acid and alcohol monitor (OAAM).

The development of a microgravity-compatible analyzer capable of quantifying organic acids in water is described. The analyzer employs "reagentless" solid phase acidification to convert organic acids to the volatile form followed by membrane separation and specific conductance detection to determine organic acids at concentrations between 0.005 and 40 mg/L. In the future, this technology will be extended to the detection of alcohols, which will be oxidized to form the corresponding organic acid and then determined using the same processes. An immobilized enzyme biocatalyst, alcohol oxidase, oxidizes alcohols to form an aldehyde. Oxidation to the corresponding organic acid is then completed over a heterogeneous catalyst. The combined organic acid and alcohol monitor (OAAM) will be utilized to determine levels of both analyte classes at various points within the water recovery system (WRS) baselined for the International Space Station (ISS). These data will improve water quality through enhanced process control, while allowing early diagnosis of potential problems. Grant numbers: NAG9-1081.

Acetic Acid↗
PubMed2002

Light, plants, and power for life support on Mars.

Regardless of how well other growing conditions are optimized, crop yields will be limited by the available light up to saturation irradiances. Considering the various factors of clouds on Earth, dust storms on Mars, thickness of atmosphere, and relative orbits, there is roughly 2/3 as much light averaged annually on Mars as on Earth. On Mars, however, crops must be grown under controlled conditions (greenhouse or growth rooms). Because there presently exists no material that can safely be pressurized, insulated, and resist hazards of puncture and deterioration to create life support systems on Mars while allowing for sufficient natural light penetration as well, artificial light will have to be supplied. If high irradiance is provided for long daily photoperiods, the growing area can be reduced by a factor of 3-4 relative to the most efficient irradiance for cereal crops such as wheat and rice, and perhaps for some other crops. Only a small penalty in required energy will be incurred by such optimization. To obtain maximum yields, crops must be chosen that can utilize high irradiances. Factors that increase ability to convert high light into increased productivity include canopy architecture, high-yield index (harvest index), and long-day or day-neutral flowering and tuberization responses. Prototype life support systems such as Bios-3 in Siberia or the Mars on Earth Project need to be undertaken to test and further refine systems and parameters.

Biomass↗
PubMed1997

Influence of changes in daylength and carbon dioxide on the growth of potato.

Potatoes (Solanum tuberosum L.) are highly productive in mid- to high-latitude areas where photoperiods change significantly throughout the growing season. To study the effects of changes in photoperiod on growth and tuber development of potato cv. Denali, plants were grown for 112 d with 400 micromol m-2 s-1 photosynthetic photon flux (PPF) under a 12-h photoperiod (short days, SD), a 24-h photoperiod (long days, LD), and combinations where plants were moved between the two photoperiods 28, 56, or 84 d after planting. Plants given LD throughout growth received the greatest total daily PPF and produced the greatest tuber yields. At similar levels of total PPF, plants given SD followed by LD yielded greater tuber dry mass (DM) than plants given LD followed by SD. Stem DM per plant, leaf DM, and total plant DM all increased with an increasing proportion of LD and increasing daily PPF, regardless of the daylength sequence. When studies were repeated, but at an enriched (1000 micromol mol-1) CO2 concentration, overall growth trends were similar, with high CO2 resulting in greater stem length, stem DM, leaf DM, and total plant DM; but high CO2 did not increase tuber DM.

Biomass↗
PubMedDate not supplied

Development of a gravity-independent wastewater bioprocessor for advanced life support in space.

Operation of aerobic biological reactors in space is controlled by a number of challenging constraints, mainly stemming from mass transfer limitations and phase separation. Immobilized-cell packed-bed bioreactors, specially designed to function in the absence of gravity, offer a viable solution for the treatment of gray water generated in space stations and spacecrafts. A novel gravity-independent wastewater biological processor, capable of carbon oxidation and nitrification of high-strength aqueous waste streams, is presented. The system, consisting of a fully saturated pressurized packed bed and a membrane oxygenation module attached to an external recirculation loop, operated continuously for over one year. The system attained high carbon oxidation efficiencies often exceeding 90% and ammonia oxidation reaching approximately 60%. The oxygen supply module relies on hydrophobic, nonporous, oxygen selective membranes, in a shell and tube configuration, for transferring oxygen to the packed bed, while keeping the gaseous and liquid phases separated. This reactor configuration and operating mode render the system gravity-independent and suitable for space applications.

Bacteria, Aerobic↗
PubMed2003

Work measurement for estimating food preparation time of a bioregenerative diet.

During space missions, such as the prospective Mars mission, crew labor time is a strictly limited resource. The diet for such a mission (based on crops grown in a bioregenerative life support system) will require astronauts to prepare their meals essentially from raw ingredients. Time spent on food processing and preparation is time lost for other purposes. Recipe design and diet planning for a space mission should therefore incorporate the time required to prepare the recipes as a critical factor. In this study, videotape analysis of an experienced chef was used to develop a database of recipe preparation time. The measurements were highly consistent among different measurement teams. Data analysis revealed a wide variation between the active times of different recipes, underscoring the need for optimization of diet planning. Potential uses of the database developed in this study are discussed and illustrated in this work.

Astronauts↗
PubMed1999

Engineering plants for spaceflight environments.

The conversion efficiency of radiation into biomass and yield has steadily increased for centuries because of continued improvement in both plant genetics and environmental control. Considerable effort has gone into improving the environment for plant growth in space, but work has only begun to engineer plants for spaceflight. Genetic manipulation offers tremendous potential to improve our ability to study gravitational effects. Genetic manipulation will also be necessary to build an efficient regenerative life support system. We cannot fully characterize plant response to the spaceflight environment without understanding and manipulating their genetic composition. Identification and selection of the existing germplasm is the first step. There are thousands of cultivars of each of our major crop plants, each specifically adapted to a unique environment on our planet. Thousands of additional lines are held in national germplasm collections to maintain genetic diversity. Spaceflight imposes the need to tap this diversity. Existing lines need to be evaluated in the environment that is characteristic of closed-system spaceflight conditions. Many of the plant growth challenges we confront in space can be better solved through genetic change than by hardware engineering. Ten thousand years of plant breeding has demonstrated the value of matching genetics with the environment. For example, providing continuous light can increase plant growth in space, but this often induces calcium deficiencies because Ca is not supplied by guttation during a dark period. This deficiency cannot be eliminated through increased root-zone and foliar Ca applications. It can be solved, in wheat, through genetic selection of lines that do not have the deficiency. Subsequent comparison of lines with and without the Ca deficiency has also helped us understand the nature of the problem.

Ecological Systems, Closed↗
PubMedDate not supplied

Interaction between exercising humans and growing plants in a Closed Ecological Life Support System.

The purpose of this study was to quantify the gas exchange between plants growing in a Closed Environmental Life Support System (CELSS) and the metabolism of human subjects undergoing various levels of physical exercise, and subsequently determine the buffer characteristics in relation to the carbon exchange established for plants in this closed loop life support system. Two men (ages 42 and 45 yr) exercised on a cycle ergometer at three different work intensities, each on a separate day. The CELSS, a 113 m3 chamber, was sized to meet the needs of one human. The plants, consisting of 20 m2 of potato, provided oxygen to the human during an artificially lighted photosynthesis phase and the human provided CO2 to the plants. The average rates of exchange for the subjects were 0.88, 1.69, and 2.47 liters O2/min and 0.77, 1.47, and 2.21 liters CO2/min at approximately 25%, 50%, and 75% of their maximal aerobic capacity, respectively. The photosynthetic rate for the CELSS was 0.95 liters/min. A balance between human CO2 production and plant utilization was noted at approximately the 50% VO2max level. The oxygen balance and changes were not within detectable limits of the CELSS instrumentation for the durations of these exercise exposures. If a CELSS environment is the methodology selected for long term spaceflight, it will be important to select plants that efficiently grow at the available light and nutrient levels while balancing the needs for the human crew at their levels of physical activity.

Adult↗
PubMed1998

Development and growth of potato tubers in microgravity.

A potato explant consisting of a leaf, its axillary bud, and a small segment of stem will develop a tuber in 10-14 days when grown on earth. The tubers develop from the axillary buds and accumulate starch derived from sugars produced through photosynthesis and/or mobilized from leaf tissue. Potato explants were harvested and maintained in the Astroculture (TM) unit, a plant growth chamber designed for spaceflight. The unit provides an environment with controlled temperature, humidity, CO2 level, light intensity, and a nutrient delivery system. The hardware was loaded onto the space shuttle Columbia 24 hours prior to the launch of the STS-73 mission. Explant leaf tissue appeared turgid and green for the first 11 days of flight, but then became chlorotic and eventually necrotic by the end of the mission. The same events occurred to ground control explants with approximately the same timing. At the end of the 16-day mission, tubers were present on each explant. The size and shape of the space-grown tubers were similar to the ground-control tubers. The arrangement of cells in the tuber interior and at the exterior in the periderm was similar in both environments. Starch and protein were present in the tubers grown in space and on the ground. The range in starch grain size was similar in tubers from both environments, but the distribution of grains into size classes differed somewhat, with the space-grown tubers having more small grains than the ground control tubers. Proteinaceous crystals were found in tubers formed in each condition.

Environment, Controlled↗
PubMed2001

Identification of complex flows in Taylor-Couette counter-rotating cavities.

The transition in confined rotating flows is a topical problem with many industrial and fundamental applications. The purpose of this study is to investigate the Taylor-Couette flow in a finite-length cavity with counter-rotating walls, for two aspect ratios L=5 or L=6. Two complex regimes of wavy vortex and spirals are emphasized for the first time via direct numerical simulation, by using a three-dimensional spectral method. The spatio-temporal behavior of the solutions is analyzed and compared to the few data actually available.

Ecological Systems, Closed↗