Waste recycling issues in bioregenerative life support.

Research and technology development issues centering on the recycling of materials within a bioregenerative life support system are reviewed. The importance of recovering waste materials for subsequent use is emphasized. Such material reclamation will substantially decrease the energy penalty paid for bioregenerative life support systems, and can potentially decrease the size of the system and its power demands by a significant amount. Reclamation of fixed nitrogen and the sugars in cellulosic materials is discussed.     

Microbiological characterization of a regenerative life support system.

A Variable Pressure Plant Growth Chamber (VPGC), at the Johnson Space Center's (JSC) ground-based Regenerative Life Support Systems (RLSS) test bed, was used to produce crops of soil-grown lettuce. The crops and chamber were analyzed for microbiological diversity during lettuce growth and after harvest. Bacterial counts for the rhizosphere, spent nutrient medium, heat exchanger condensate, and atmosphere were approximately 10(11) Colony Forming Units (CFU) g-1 10(5) CFU ml-1, 10(5) CFU ml-1, and 600 CFU m-3, respectively. Pseudomonas was the predominant bacterial genus. Numbers of fungi were about 10(5) CFU g-1 in the rhizosphere, 4-200 CFU ml-1 in the spent nutrient medium, 110 CFU ml-1 in the heat exchanger condensate, and 3 CFU m-3 in the atmosphere. Fusarium and Trichoderma were the predominant fungal genera.     

Biodegradation pathway of an anionic surfactant (Igepon TC-42) during recycling waste water through plant hydroponics for advanced life support during long-duration space missions.

The degradation of an anionic surfactant (Igepon TC-42) was investigated as part of an integrated study of direct recycling of human hygiene water through hydroponic plant growth systems. Several chemical approaches were developed to characterize the degradation of Igepon and to measure the accumulation of intermediates such as fatty acids and methyl taurine. Igepon was rapidly degraded as indicated by the reduction of methylene blue active substances (MBAS) and component fatty acids. The Igepon degradation rate continued to increase over a period of several weeks following repeated daily exposure to 18 micrograms/l Igepon. The accumulation of free fatty acids and methyl taurine was also observed during decomposition of Igepon. The concentration of methyl taurine was below detection limit (0.2 nmol/ml) during the slow phase of Igepon degradation, and increased to 1-2 nmol/ml during the phase of rapid degradation. These findings support a degradation pathway involving initial hydrolysis of amide to release fatty acids and methyl taurine, and subsequent degradation of these intermediates.     

Development of life support requirements for long-term space flight.

When humans move out into the solar system to stay for long durations, the most immediate challenge will be the provision of a life-supporting environment in locations that are naturally devoid of food, air, and water. Life support systems must provide these commodities in all phases of space flight--during intravehicular activity (IVA) and during extra-vehicle activity (EVA). Systems that support human life must provide: overall reliability in the space environment, allowing maintenance and component replacement in space; reduced resupply mass of consumables and spares; for planetary surfaces, the ability to utilize local resources for increased self sufficiency; and the minimized mass power and volume requirements necessary for all space flight systems. This paper will discuss the melding of these technical requirements in such a way as to meet the human needs of space flight.     

Mass balances for a biological life support system simulation model.

Design decisions to aid the development of future space-based biological life support systems (BLSS) can be made with simulation models. Here we develop the biochemical stoichiometry for 1) protein, carbohydrate, fat, fiber, and lignin production in the edible and inedible parts of plants; 2) food consumption and production of organic solids in urine, feces, and wash water by the humans; and 3) operation of the waste processor. Flux values for all components are derived for a steady-state system with wheat as the sole food source. The large-scale dynamics of a materially-closed (BLSS) computer model is described in a companion paper. An extension of this methodology can explore multi-food systems and more complex biochemical dynamics while maintaining whole-system closure as a focus.     

Consideration in selecting crops for the human-rated life support system: a Linear Programming model.

A Linear Programming model has been constructed which aids in selecting appropriate crops for CELSS (Controlled Environment Life Support System) food production. A team of Controlled Environment Agriculture (CEA) faculty, staff, graduate students and invited experts representing more than a dozen disciplines, provided a wide range of expertise in developing the model and the crop production program. The model incorporates nutritional content and controlled-environment based production yields of carefully chosen crops into a framework where a crop mix can be constructed to suit the astronauts' needs. The crew's nutritional requirements can be adequately satisfied with only a few crops (assuming vitamin mineral supplements are provided) but this will not be satisfactory from a culinary standpoint. This model is flexible enough that taste and variety driven food choices can be built into the model.     

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.     

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.     

Carbon balance in bioregenerative life support systems: some effects of system closure, waste management, and crop harvest index.

In Advanced Life Support (ALS) systems with bioregenerative components, plant photosynthesis would be used to produce O2 and food, while removing CO2. Much of the plant biomass would be inedible and hence must be considered in waste management. This waste could be oxidized (e.g., incinerated or aerobically digested) to resupply CO2 to the plants, but this would not be needed unless the system were highly closed with regard to food. For example, in a partially closed system where some of the food is grown and some is imported, CO2 from oxidized waste when combined with crew and microbial respiration could exceed the CO2 removal capability of the plants. Moreover, it would consume some O2 produced from photosynthesis that could have been used by the crew. For partially closed systems it would be more appropriate to store or find other uses for the inedible biomass and excess carbon, such as generating soils or growing woody plants (e.g., dwarf fruit trees). Regardless of system closure, high harvest crops (i.e., crops with a high edible to total biomass ratio) would increase food production per unit area and O2 yields for systems where waste biomass is oxidized to recycle CO2. Such interlinking effects between the plants and waste treatment strategies point out the importance of oxidizing only that amount of waste needed to optimize system performance.     

Earth life support for aquatic organisms, system and technical aspects.

The importance of the research on Bioregenerative Life Support has increased dramatically in the last decade not only with regard to possible space flight application but also as a way to obtain a better understanding of our Earth's ecology. A major goal was to reach long-term stability of artificial model systems. Preliminary data are presented on the development of an improved aquatic system, currently dedicated for ground-based research. Closed aquatic ecosystems require reliability of the key parameters of pH, O2 and CO2 concentration and stability of sensors for monitoring. Besides the integration of an artificial lung (holofiber system and air pump with valves, allowing controlled oxygen uptake of air), in parallel to the oxygen producing water plants. Our new approach is to implement opto-chemical sensors, for such environmental monitoring. One major advantage of the new sensor technique is their better long-term reliability as compared to the electrochemical sensors. Our experiment with the new sensor technique has demonstrated satisfactory performance in closed aquatic ecosystems.     

Crop productivities and radiation use efficiencies for bioregenerative life support

NASA’s Biomass Production Chamber (BPC) at Kennedy Space Center was decommissioned in 1998, but several crop tests were conducted that have not been reported in the open literature. These include several monoculture studies with wheat, soybean, potato, lettuce, and tomato. For all of these studies, either 10 or 20 m² of plants were grown in an atmospherically closed chamber (113 m³ vol.) using a hydroponic nutrient film technique along with elevated CO₂ (1000 or 1200 μmol mol⁻¹). Canopy light (PAR) levels ranged from 17 to 85 mol m⁻² d⁻¹ depending on the species and photoperiod. Total biomass (DM) productivities reached 39.6 g m⁻² d⁻¹ for wheat, 27.2 g m⁻² d⁻¹ for potato, 19.6 g m⁻² d⁻¹ for tomato, 15.7 g m⁻² d⁻¹ for soybean, and 7.7 g m⁻² d⁻¹ for lettuce. Edible biomass (DM) productivities reached 18.4 g m⁻² d⁻¹ for potato, 11.3 g m⁻² d⁻¹ for wheat, 9.8 g m⁻² d⁻¹ for tomato, 7.1 g m⁻² d⁻¹ for lettuce, and 6.0 g m⁻² d⁻¹ for soybean. The corresponding radiation (light) use efficiencies for total biomass were 0.64 g mol⁻¹ PAR for potato, 0.59 g DM mol⁻¹ for wheat, 0.51 g mol⁻¹ for tomato, 0.46 g mol⁻¹ for lettuce, and 0.43 g mol⁻¹ for soybean. Radiation use efficiencies for edible biomass were 0.44 g mol⁻¹ for potato, 0.42 g mol⁻¹ for lettuce, 0.25 g mol⁻¹ for tomato, 0.17 g DM mol⁻¹ for wheat, and 0.16 g mol⁻¹ for soybean. By initially growing seedlings at a dense spacing and then transplanting them to the final production area could have saved about 12 d in each production cycle, and hence improved edible biomass productivities and radiation use efficiencies by 66% for lettuce (to 11.8 g m⁻² d⁻¹ and 0.70 g mol⁻¹), 16% for tomato (to 11.4 g m⁻² d⁻¹and 0.29 g mol⁻¹), 13% for soybean (to 6.9 g m⁻² d⁻¹ and 0.19 g mol⁻¹), and 13% for potato (to 20.8 g m⁻² d⁻¹ and 0.50 g mol⁻¹). Since wheat was grown at higher densities, transplanting seedlings would not have improved yields. Tests with wheat resulted in a relatively low harvest index of 29%, which may have been caused by ethylene or other organic volatile compounds (VOCs) accumulating in the chamber. Assuming a higher harvest index of 40% could be achieved by scrubbing VOCs, productivity of wheat seed could have been improved nearly 40% to 15.8 g m⁻² d⁻¹ and edible biomass radiation use efficiency to 0.30 g mol⁻¹.     

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.     

New problems to be solved for establishing closed life support system.

New test bed facilities such as Bioplex and CEEF have been constructed to test the new advanced technologies for solving the various problems as follows, (1) how to develop air content stabilization technologies with gas balance between the generation and the absorption by living organisms, (2) how to solve the mismatching between the assimilation rate of autotrophic organisms and the respiration rate of heterotrophic organisms, (3) how to balance the speed of the waste decomposition with the absorption speed of nutrient components in the sequential plant cultivation, (4) how to develop new nutrient adjusting subsystems for each plant species, (5) how to compensate the denitrification during the waste decomposition and anaerobic microbes in the nutrient solution.     

Indications and counterindications for applying different versions of closed ecosystems for space and terrestrial problems of life support.

Different versions of manned closed ecosystems (CES) based on photosynthesis of unicellular and/or higher plants and chemosynthesis or bacteria are considered. Different versions of CES have been compared for applying them on Earth, Moon, Mars and Venus orbital stations, for Mars missions and planetary stations as well as to provide high-quality life in extreme conditions on the Earth. In microgravity [correction of mycrogravity] we recommend CES with unicellular organisms based on photosynthesis or chemosynthesis (depending of the availability of the light or electric energy). For the planetary stations with Moon gravity and higher CES with higher plants are recommended. Improvement of indoor air quality by CES biotechnology is considered.     

A novel signal processing approach for LEO space debris based on a fence-type space surveillance radar system

The increase in space debris can seriously threaten regular activities in the Low Earth Orbit (LEO) environment. Therefore, it is necessary to develop robust, efficient and reliable techniques to understand the potential motions of the LEO debris. In this paper, we propose a novel signal processing approach to detect and estimate the motions of LEO space debris that is based on a fence-type space surveillance radar system. Because of the sparse distribution of the orbiting debris through the fence in our observations, we formulate the signal detection and the motion parameter estimation as a sparse signal reconstruction problem with respect to an over-complete dictionary. Moreover, we propose a new scheme to reduce the size of the original over-complete dictionary without the loss of the important information. This new scheme is based on a careful analysis of the relations between the acceleration and the directions of arrival for the corresponding LEO space debris. Our simulation results show that the proposed approach can achieve extremely good performance in terms of the accuracy for detection and estimation. Furthermore, our simulation results demonstrate the robustness of the approach in scenarios with a low Signal-to-Noise Ratio (SNR) and the super-resolution properties. We hope our signal processing approach can stimulate further work on monitoring LEO space debris.     

Atmospheric dynamics and bioregenerative technologies in a soil-based ecological life support system: initial results from Biosphere 2.

Biosphere 2 is the first man-made, soil-based, bioregenerative life support system to be developed and tested. The utilization and amendment of local space resources, e.g. martian soil or lunar regolith, for agricultural and other purposes will be necessary if we are to minimize the requirement for Earth materials in the creation of long-term off-planet bases and habitations. Several of the roles soil plays in Biosphere 2 are 1) for air purification 2) as a key component in created wetland systems to recycle human and animal wastes and 3) as nutrient base for a sustainable agricultural cropping program. Initial results from the Biosphere 2 closure experiment are presented. These include the accelerated cycling rates due to small reservoir sizes, strong diurnal and seasonal fluxes in atmospheric CO2, an unexpected and continuing decline in atmospheric oxygen, overall maintenance of low levels of trace gases, recycling of waste waters through biological regeneration systems, and operation of an agriculture designed to provide diverse and nutritionally adequate diets for the crew members.     

NASA's Biomass Production Chamber: a testbed for bioregenerative life support studies.

The Biomass Production Chamber (BPC) located at Kennedy Space Center, FL, USA provides a large (20 m2 area, 113 m3 vol.), closed environment for crop growth tests for NASA's Controlled Ecological Life Support System (CELSS) program. Since the summer of 1988, the chamber has operated on a near-continuous basis (over 1200 days) without any major failures (excluding temporary power losses). During this time, five crops of wheat (64-86 days each), three crops of soybean (90 to 97 days), five crops of lettuce (28-30 days), and four crops of potato (90 to 105 days were grown, producing 481 kg of dry plant biomass, 196 kg edible biomass, 540 kg of oxygen, 94,700 kg of condensed water, and fixing 739 kg of carbon dioxide. Results indicate that total biomass yields were close to expected values for the given light input, but edible biomass yields and harvest indices were slightly lower than expected. Stand photosynthesis, respiration, transpiration, and nutrient uptake rates were monitored throughout growth and development of the different crops, along with the build-up of ethylene and other volatile organic compounds in the atmosphere. Data were also gathered on system hardware maintenance and repair, as well as person-hours required for chamber operation. Future tests will include long-term crop production studies, tests in which nutrients from waste treatment systems will be used to grow new crops, and multi-species tests.     

Potential of salt-accumulating and salt-secreting halophytic plants for recycling sodium chloride in human urine in bioregenerative life support systems

This study addresses the possibility of growing different halophytic plants on mineralized human urine as a way to recycle NaCl from human wastes in a bioregenerative life support system (BLSS). Two halophytic plant species were studied: the salt-accumulating Salicornia europaea and the salt-secreting Limonium gmelinii. During the first two weeks, plants were grown on Knop’s solution, then an average daily amount of urine produced by one human, which had been preliminarily mineralized, was gradually added to the experimental solutions. Nutrient solutions simulating urine mineral composition were gradually added to control solutions. NaCl concentrations in the stock solutions added to the experimental and control solutions were 9 g/L in the first treatment and 20 g/L in the second treatment. The mineralized human urine showed some inhibitory effects on S. europaea and L. gmelinii. The biomass yield of experimental plants was lower than that of control ones. If calculated for the same time period (120 d) and area (1 m²), the amount of sodium chloride taken up by S. europaea plants would be 11.7 times larger than the amount taken up by L. gmelinii plants (486 g/m² vs. 41 g/m²). Thus, S. europaea is the better choice of halophyte for recycling sodium chloride from human wastes in BLSS.     

Comparison of three soil-like substrate production techniques for a bioregenerative life support system

It is very important to recycle the inedible biomass of higher plants to improve the closure of bioregenerative life support system (BLSS). Processing candidate higher plant residues into the soil-like substrate (SLS) as the plant growth medium is a promising way to achieve. In this study, three different processing techniques of SLSs, using residues of wheat and rice as feedstock, were compared. As for the first traditional technique, SLS1 was obtained by successive conversion of wheat straw by oyster mushrooms and worms. In the other two methods, SLSs were produced with aerobic fermentation (SLS2) or anaerobic fermentation (SLS3) followed by worm conversion. The changes in SLS cellulose, lignin, available elements and pH were measured during the production processes. The maturity was evaluated by the value of C/N. The fertilities were compared in terms of available elements contents and lettuce productivities. The results indicated that the second technique was optimal, whose process cycle was 30 days less than that of SLS1. The total cellulose and lignin degradation of SLS2, achieved 98.6% and 93.1% during the 93-days-processing, and the lettuce productivity reached 12.0 g m⁻² day⁻¹.     

Developing a vitamin greenhouse for the life support system of the International Space Station and for future interplanetary missions.

In order to evaluate the effects of gravity on growing plants, we conducted ground based long-term experiments with dwarf wheat, cultivar Apogee and Chinese cabbage, cultivar Khibinskaya. The test crops had been grown in overhead position with HPS lamp below root module so gravity and light intensity gradients had been in opposite direction. Plants of the control crop grew in normal position under the same lamp. Both crops were grown on porous metallic membranes with stable -1 kPa matric potential on their surface. Results from these and other studies allowed us to examine the differences in growth and development of the plants as well as the root systems in relation to the value of the gravity force influence. Dry weight of the roots from test group was decreased in 2.5 times for wheat and in 6 times - at the Chinese cabbage, but shoot dry biomass was practically same for both test and control versions. A harvest index of the test plants increased substantially. The data shows, that development of the plants was essentially changed in microgravity. The experiments in the space greenhouse Svet aboard the Mir space station proved that it is possible to compensate the effects of weightlessness on higher plants by manipulating gradients of environmental parameters (i.e. photon flux, matric potential in the root zone, etc.). However, the average productivity of Svet concerning salad crops even in ground studies did not provide more than 14 g fresh biomass per day. This does not provide a sufficient level of supplemental nutrients to the crew of the ISS. A cylindrical design of a space plant growth chamber (SPGC) allows for maximal productivity in presence of very tight energy and volume limitations onboard the ISS and provides a number of operational advantages. Productivity from this type of SPGF with a 0.5 kW energy utilization when salad growing would provide approximately 100 g of edible biomass per day, which would almost satisfy requirements for a crew of two in vitamin C and carotene and partly vitamin B group as well as rough fiber.