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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.

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.

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.

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.

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.

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.