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A set of contained environment chambers have been designed to study the effects of Volatile Organic Compounds (VOCs) on plant growth and development. The Volatile Organic Compound Analysis (VOCA) system consists of six Lexan chambers, each with independent VOC monitoring and control capacities. The VOC exposure chambers are located within a larger controlled environment chamber (CEC) which provides a common air temperature, photoperiod, and light control. Relative humidity, CO2 concentration, and VOC concentration of the atmosphere are independently controlled in each VOCA exposure chambers. CO2, air temperature, relative humidity and PPF are continuously monitored with software developed using IOControl™ and IODisplay™.

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.

Plant growth conditions must be optimized for use in advanced life support systems during space flight. Wheat cv. Apogee was grown in a nutrient delivery system (NDS) using porous tubes held at three levels of applied water pressure (Pw), or suction: −0.5 kPa, −0.3 kPa, and −0.1 kPa for 24 days. Measurements of leaf area and dry mass were made at 5, 9, 14, 18 and 24 DAP and used to determine the leaf area index (LAI), net assimilation rate (NAR), and crop growth rate (CGR). Pw did not have a significant effect on plant development until after 9 DAP, at which time growth at different treatments began to diverge. Plants grown at −0.1 kPa exhibited the largest CGR and LAI and had the greatest biomass, suggesting that −0.1 kPa was the optimal Pw. Growth analysis indicated that changes in CGR were due to changes in leaf area, rather than changes in photosynthesis.

A 24-day test of the science protocols for the PESTO (Photosynthesis Experiment System Testing and Operation) experiment was conducted in the Biomass Production System (BPS) flight hardware. One objective of these experiments was to identify the optimum times during the life cycle for characterizing canopy level evapotranspiration and photosynthesis under closed atmosphere conditions in the BPS. Carbon dioxide and light response curves were obtained at three stages of development on two dwarf wheat cultivars, Apogee and Super Dwarf. Net daily carbon assimilation rates were derived from CO2 additions to each chamber and the relative growth rate of each cultivar was determined. Evapotranspiration rates were derived from water additions to the rooting matrix through the nutrient delivery system and water vapor removal from the atmosphere though the humidity control system.

Future large-scale ALS systems may use hydroponic nutrient delivery systems (NDS) for growing staple and salad crops. Crop performance is strongly dependent on dissolved O2 concentration (DOC), pH, and nutrient content of the hydroponic solution. DOC is influenced by solution temperature and flow rate, growth rate of the crop, and the bacterial community present in the solution. Solution temperature determines the solubility of O2 in water, and may increase as solution volume is reduced to minimize overall system mass. Flow may be altered when the height of the solution bathing the root zone is reduced because of dense root mats. These factors may produce anaerobic pockets where N2 losses by denitrification occur, but without yield losses, as long as sufficient O2 to meet root respiration is supplied. Bacterial communities may compete for DOC with the plants when the NDS is used for recycling gray water streams.

A CELSS has been defined based on current or near-term technology. The CELSS was sized to support the metabolic load of four people on the Moon for ten years. A metabolic load of 14 MJ/person/day is assumed, including an average of 2.6 hr of EVA/person/day. Close to 100% closure of water, and oxygen, and 85% closure of the food loop is assumed. With 15% of the calories supplied from Earth, this should provide adequate dietary variety for the crew along with vitamin and mineral requirements. Other supply and waste removal requirements are addressed. The basic shell used is a Space Station Freedom 7.3 m (24 ft) module. This is assumed to be buried in regolith to provide protection from radiation, meteoroids, and thermal extremes. A solar dynamic power system is assumed, with a design life of 10 years delivering power at 368 kWh/kg. Initial estimates of size are that 73 m2 of plant growth area are required, giving a plant growth volume of about 73 m3.