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A reliable nutrient delivery system is essential for long-term cultivation of plants in space. At the Kennedy Space Center, a series of ground-based tests are being conducted to compare candidate plant nutrient delivery systems for space. To date, our major focus has concentrated on the Porous Tube Plant Nutrient Delivery System, the ASTROCULTURE™ System, and a zeoponic plant growth substrate. The merits of each system are based upon the performance of wheat supported over complete growth cycles. To varying degrees, each system supported wheat biomass production and showed distinct patterns for plant nutrient uptake and water use.

This project sought to develop a photocatalytic oxidation (PCO) based total organic carbon (TOC) analyzer for real time monitoring of air quality in spacecraft. Specific requirements for this application were to convert volatile organic contaminants (VOC) into CO2 stoichiometrically in a single pass through a small reactor with low power requirement. One of the greatest challenges of this TiO2-mediated PCO was the incomplete oxidation of some recalcitrant VOCs leading to less reactive intermediates that deactivate the catalyst over time. Dichloromethane (DCM) is one of these VOCs. The effect of some design factors (e.g. TiO2 catalyst surface area to volume ratio and UV photon flux field) as well as operating conditions of an annular reactor (e.g. VOC residence time and relative humidity) on the efficiency in converting DCM to CO2 were investigated.

Extension of human habitation into space requires that humans carry with them many of the microorganisms with which they coexist on Earth. Whether microbes are present by design as constructed communities in bioregenerative life support systems or by accident as hitchhikers attached to human, plant, and spacecraft surfaces, the microbial ecosystems of Earth will be present in space. But how may the space environment affect the interaction of microbial communities? Given the potential for rapid change in populations of microorganisms through mutation, recombination, and natural selection (processes accelerated under space conditions of variable microgravity and elevated background radiation), it will be necessary to understand both the pattern and process of community assembly and evolution in the space environment.

We report here on a series of KC-135 parabolic flight studies investigating various aspects of water distribution in plant nutrient delivery systems being developed for spaceflight applications. Several types of porous tubes were evaluated. Under microgravity conditions, fluid was observed to creep up the end walls of polycarbonate substrate compartments. Capillary mats wrapped around the porous tubes wetted up in a uniform fashion regardless of the level of gravity to which they were being exposed, and they were found to eliminate the end-wall creep wetting-up pattern. Results from observations using 1-2 mm glass beads and 1-2 mm Turface substrates are presented. The Turface’s absorption of water effectively minimized fluid redistribution as the compartment alternated between microgravity and 1-1.8g conditions.

A submerged membrane biological reactor (MBR) was evaluated for treatment of a spacecraft wastewater analog. The aerobic MBR (a modified CSTR) had a 12 L working volume, submerged 0.2 μm membrane filter, 12.6 h hydraulic retention time (simulated 2 person crew), and infinite solids retention time. Simulated graywater contained a urine analog and two surfactants: disodium cocoamphodiacetate and sodium laureth sulfate (461 ppm of active ingredient, combined). Two MBR runs of 60- and 10-day durations were completed with different conditions (startup: 16 d vs. 3 d, pH control vs. none). Influent, effluent, and mixed liquor were analyzed for COD, BOD, TSS, surfactant concentration, and microbial load and activity. BOD removal averaged ≥ 92% for each run with 100% surfactant degradation but no detectable nitrification. The food to mass (F/M) ratio decreased over time. Surfactant decomposition is feasible with a small-scale MBR, although changes are needed to promote nitrification.

The recycling of water will be critical for the successful long-term cultivation of plants in space. The capture of transpired water via humidity control systems and subsequent refilling of water reservoirs feeding into plant nutrient delivery systems is an approach that accomplishes this objective, but results in a progressive dilution of the nutrient levels initially present. As part of pre-spaceflight protocol development efforts for the Water Offset Nutrient Delivery ExpeRiment (WONDER), we have evaluated the reestablishment of reservoir nutrient concentration levels via the periodic injection of 60 and 90 mL pulses of concentrated (10x) Hoaglands nutrient solution. In space this will involve crew-facilitated injections via a quick disconnect port on the payload's front panel. A study demonstrating the efficacy of this approach is presented using wheat grown on porous tubes.

Light-emitting diodes (LEDs) represent an innovative artificial lighting source with several appealing features specific for supporting plants, whether on space-based transit vehicles or planetary life support systems. Appropriate combinations of red and blue LEDs have great potential for use as a light source to drive photosynthesis due to the ability to tailor irradiance output near the peak absorption regions of chlorophyll. This paper describes the importance of far-red radiation and blue light associated with narrow-spectrum LED light emission. In instances where plants were grown under lighting sources in which the ratio of blue light (400–500 nm) relative to far-red light (700–800 nm) was low, there was a distinct leaf stretching or broadening response. This photomorphogenic response sanctioned those canopies as a whole to reach earlier critical leaf area indexes (LAI) as opposed to plants grown under lighting regimes with higher blue:far-red ratios.

In controlled environment plant growth chambers, electric lamps provide photons necessary to drive photosynthesis. In order to determine the most productive, energy efficient, and safest way of providing light to plants for a given application, new lighting technologies are being evaluated by various researchers. Light-emitting diodes (LEDs) represent an innovative lighting source with several appealing features specific for supporting plants whether on space-based transit vehicles or planetary life support systems. For this study, there was specific interest in Swiss chard (Beta vulgaris L. cv. ‘Ruby Red Rhubarb') because these plants are among “salad-type” species chosen for early mission testing on Space Station. Of particular interest, were the growth dynamics and gas exchange characteristics of Swiss chard grown under red LEDs at narrow wavebands, which give different ratios of blue quanta to far-red photons.

A study was conducted evaluating the Temperature and Moisture Acquisition System (TMAS; Orbital Technologies, Madison, WI) and the Specific Heat Sensor (Thermal Logic, Pullman, WA) for root zone moisture level monitoring. Each design used a heat pulse and measured the transient temperature response to determine soil moisture changes. The sensors were placed in a polycarbonate compartment filled with oven-dried 1-2 mm Turface. Data was collected from the dry media, then the media was saturated with water and evaporation was monitored using the sensors and a digital balance. Generally, the TMAS sensors tended to over-estimate, while the Thermal Logic sensors under-estimated changes in soil moisture.

Microbiological sampling and analysis was performed on the wet waste returned from the STS-105 and STS-108 shuttle missions servicing the International Space Station (ISS). Samples were collected from a variety of materials including plate waste and associated food packaging (which composed the majority of the collected waste), sanitary waste, and loose liquid inside the waste container. Analyses of the microbial loads cultured on both selective and non-selective media and through total bacterial counts by acridine orange direct count (AODC) methods showed high microbial densities in the waste container liquid. Isolates identified included Klebsiella pneumoniae, Serratia marcescens, Bacillus spp., Salmonella spp., and Escherichia coli (E.coli). Dry and ash weights were collected for each sample to determine water and organic content of the materials.

A series of experiments was initiated to characterize plant growth at the elevated temperatures typically observed in the space shuttle and the International Space Station (ISS) to allow for subsequent isolation of temperature effects from those of microgravity. Plants were grown in temperatures ranging from 18-30°C in anticipated flight conditions of light intensity, photoperiod, and CO2 concentration. The effects of these environmental variables on leaf development and anatomy were examined. Results indicate that leaf anatomy is significantly effected by elevated temperature. Leaf thickness decreased with increasing temperature and showed an equal reduction in the thickness of the palisade and spongy mesophyll. Shoot fresh and dry weight/unit leaf area increased with increasing temperature and chlorophyll content was reduced. These results indicate that increased temperature lead to a reduction in intercellular air spaces within the leaf.

Growth Temperatures And Lighting Intensity Are Key Factors That Directly Impact The Design, Engineering, And Horticultural Practices Of Sustainable Life-Support Systems For Future Long-Term Space Missions. The Effects Of Exposure Of Lettuce (Cv. Flandria), Radish (Cv. Cherry Bomb Ii). And Green Onion (Cv. Kinka) Plants To Controlled Environment Temperatures (Constant Day/Night Temperature Of 22, 25, Or 28 °C) And Lighting Intensities (8.6, 17.2, Or 25.8 Mol M−2 D−1 Photosynthetic Photon Flux [Ppf]) At Elevated Co2 (1200 µMol Mol−1) Was Investigated To Ascertain Overall Yield Responses. Following 35 Days Growth, The Yields Of Lettuce Indicated That Increasing The Growing Temperature From 22 To 28°C Slightly Increased The Edible Fresh Mass Of Individual Plants. However, Even Though Lettuce Plants Grown Under High Ppf Had The Highest Fresh Mass, The Resultant Increase In The Incidence And Severity Of Tipburn Reduced The Overall Quality Of The Lettuce Head.

With the development of the International Space Station and the need for international collaboration for returning to the moon and developing a mission to Mars, NASA has embarked on developing international educational programs related to space exploration. In addition, with the explosion of educational technology, linking students on a global basis is more easily accomplished. This technology is bringing national and international issues into the classroom, including global environmental issues, the global marketplace, and global collaboration in space. We present the successes and lessons learned concerning international educational and public outreach programs that the Fundamental Space Biology Outreach Program staff have been involved in for NASA as well as the importance of sustaining these international peer collaborative programs for the future generations.

The Porous Tube Plant Nutrient Delivery System (PTPNDS) was designed for NASA to grow plants in microgravity of space. The system utilizes a controlled fluid loop to supply nutrients and water to plant roots growing on a ceramic surface moistened by capillary action. Utilizing remote sensing systems, spectral analyses procedures, gas-exchange, and fluorescence measurements, we examined differences in plant water status for wheat plants (Triticum aestivum, cv. Perigee). These plants were grown in a modified growth chamber during the summers of 2003 and 2004. Some differences in plant performance were detectable in the gas-exchange and fluorescence measurements. For instance, in both years the plants grown with the most available water had the lowest rates of photosynthesis and exhibited higher proportions of non-photochemical quenching, particularly under low light levels.

Radish (Raphanus sativus L.) is a salad type crop that is being evaluated for possible use on the International Space Station (ISS). The study will determine the growth and development of radish in the microgravity environment. A series of experiments were initiated to determine whether volatile organic compounds (VOC) that are commonly accumulated in closed systems of spacecraft atmosphere are biologically active. A survey of existing atmospheric samples from the space shuttle and ISS revealed over 260 compounds with potential biogenic activity of which a subset of 14 compounds have been selected for detailed evaluation. Initial screening is achieved by exposing radishes to VOC concentrations corresponding to 0.1 and 1.0 the Spacecraft Maximum Allowable Concentration (SMAC) of the contaminants. Biogenic effects of ethanol at 0.1 of the SMAC resulted in lower chlorophyll content, reduced growth rate, and lower yields.

As part of NASA’s continued interest in the feasibility of Bioregenerative Life Support Systems (BLSS), research has focused on increasing the efficiency of bioregenerative technology. To reduce the costs associated with recovery of plant nutrients from inedible crop biomass, composting combined with leaching appears to be an attractive alternative to continuously stirred tank reactors. Tests at Kennedy Space Center investigating the effects of pre-processing of inedible wheat biomass composted for 21 days prior to leaching on nutrient recovery and growth of a subsequent wheat crop have been performed. In long-term hydroponic tests, pre-processed compost leachate was amended with reagent grade nutrients to approximate half-strength Hoagland’s solution. Although reductions in growth and yield were observed for plants grown on pre-processed compost leachate compared to the control, the differences were not statistically significant.