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A long-duration lunar outpost will rely entirely upon imported or preserved foods to sustain the crew during early Lunar missions. Fresh, perishable foods (e.g. salad crops) would be consumed by the crew soon after delivery by the re-supply missions, and can provide a supplement to the diet rich in antioxidants (bioprotectants) that would serve as a countermeasure to radiation exposure. Although controlled environment research has been carried out on the growth of salad crops under a range of environmental conditions, there has been no demonstration of sustainable production in a flight-like system under conditions that might be encountered in space. Several fundamental challenges that must be overcome in order to achieve sustained salad crop production under the power, volume and mass constraints of early Lunar outposts include; growing multiple species, sustaining productivity through multiple plantings, and minimizing time for crew operations.

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.

Extended habitation of space may include the cultivation of plants for atmospheric regeneration, water purification and food production. Plants produce bioactive compounds that may be released into the atmosphere as volatile organic compounds (VOCs). VOCs are produced through a variety of plant processes and vary greatly in chemistry and quantity though a plants life cycle. These compounds include numerous biogenic species including alcohols, isoprene, monoterpines, acids, carbonyls, alkanes and alkenes. In a closed environment, VOCs may create a toxic environment for either humans or other plants. Human responses to biogenic compounds may include acute toxicity, chronic toxic toxicity, and allergenic effects. Chronic exposure to low concentrations of biogenic compounds, as might be common during extended space habitation missions, is largely unstudied and of particular interest.

A research project has begun to identify the best cultivar for strawberry production as part of an advanced life support system for space. For the cultivar trials, hydroponic systems will be used, so the plants can be grown optimally under controlled environmental conditions and without water stress. The objectives of this project were to determine changes in nutrient solution characteristics, specifically dissolved oxygen (DO), electrical conductivity (EC), hydrogen ion concentration (pH), and temperature, versus four different flow rates (0.5, 1.0, 2.0, and 3.6 L·min−1) at fixed distances in the hydroponic channel with and without media. Three media treatments were used: 1) no media, 2) arcillite, and 3) perlite. The results showed that the highest flow rate (i.e., 3.6 L min−1) exhibited the most uniform conditions of all nutrient solution characteristics and for each of the media treatments over the 7.92 m length of channel.

The candidate crops that have been considered by NASA for providing moderate quantities of supplemental food for crew's consumption during near term or long duration missions include minimally processed “salad” species. Lettuce (cv. Flandria), radish (cv. Cherry Bomb II) and green onion (cv. Kinka) plants were grown under cool-white fluorescent (CWF) lamps with light intensities of 8.6, 17.2, or 25.8 mol m−2 d−1, at air temperatures of 25 and 28 °C, 50% relative humidity, and 1200 µmol mol−1 CO2. Following 35 days growth, final edible mass yields were recorded. All three species grown at 25 °C showed an increase in edible fresh mass and growth rates as light intensity increased. When grown at 28 °C however, the edible fresh mass and crop growth rate of radish, lettuce and onion was significantly reduced at all light intensities when compared to yields at 25 °C. Overall, results indicated that all three crops were sensitive to changes in light intensity and temperature.

Radish (Raphanus sativus L.), green onion (Allium fistulosum L.), and lettuce (Lactuca sativa L.) are among several “salad” crop species suggested for use on the International Space Station (ISS) as a supplement to the crew’s diet. Among the more important factors affecting the crop yields will be the light intensity or photosynthetic photon flux (PPF) used to grow the plants. Radish (cv. Cherry Bomb), green onion (cv. Kinka), and lettuce (cv. Flandria) plants were grown for 35 days in growth chambers at 8.6, 17.2, and 26 mol m−2 d−1 (150, 300, or 450 μmol m−2 s−1 PPF, respectively) with a 16 hr photoperiod and cool-white fluorescent lamps and either 400 or 1200 μmol mol−1 CO2. Final (35-day) edible yields were taken for the treatments under ambient or supplemented CO2. Results showed a response of growth to incident PPF that indicated a strong influence of lighting on yields.

The first spaceflight opportunities for Advanced Life Support (ALS) Project testing with plants will likely occur with missions on vehicles in Low Earth Orbit, such as the International Space Station (ISS). In these settings, plant production systems would likely be small chambers with limited electrical power. Such systems are adequate for salad-type crops that provide moderate quantities of fresh, flavorful foods to supplement the crew diet. Successful operation of salad crop systems in the space environment requires extensive ground-based testing with horticultural methodologies that meet expected mission constraints. At Kennedy Space Center, cultivars of radish, onion, and lettuce are being compared for performance under these “flight-like” conditions.

The PESTO (Photosynthetic Experiment System Testing and Operation) experiment flew in the Biomass Production System (BPS) to International Space Station (ISS) on STS-110 (Atlantis) April 8, 2002, and returned on STS-111 (Endeavour) June 19, 2002, after 73 days in space. The ground control was conducted on a two-week delay at Kennedy Space Center in a BPS unit under environmental conditions comparable to ISS. Wheat (Triticum aestivum cv Apogee) and Brassica rapa cv Astroplant were independently grown in root modules for multiple grow-outs. On-orbit harvests, root modules exchanges and primings, seeds imbibitions, and gas and water samplings occurred at periodic intervals; all were replicated in ground controls. Many operations required crew handling and open access to individual chambers, allowing the exchange of microorganisms between the crew environment and the BPS modules.

The PESTO (Photosynthesis Experiment and System Testing and Operation) spaceflight experiment is designed to directly measure gas exchange of developing stands of wheat (Triticum aestivum L.) on the International Space Station (ISS). Gas exchange measurements will characterize photosynthesis and transpiration in microgravity at different stages of development. The Biomass Production System (BPS), a double middeck-sized plant growth will be the plant growth hardware used to support this experiment on-board ISS. This report presents results from a 10-day functional test of PESTO protocols in the BPS. Wheat canopy CO2 assimilation rate for 14-24 day-old plants grown in the BPS chambers was 6-7 μmol m-2 s-1 during this test. Plant responses to CO2 and photosynthetic photon flux (PPF) response curves were obtained at different stages of development by altering CO2 and light conditions.

Procedures were developed for a future experiment to measure wheat (Triticum aestivum L.) photosynthesis in microgravity. Specific attention was given to growing and maintaining vigorous wheat plants relative to the challenging conditions predicted in microgravity. These ground-based tests included comparisons of different rooting media, media, wicking materials, and nutrient delivery system pressures. To facilitate seed germination in microgravity, several clinostat tests were conducted to characterize the importance of initial seed orientation. Following establishment of a vigorous crop canopy, photosynthesis rates were measured and found to be affected by mutual plant shading within the growth chambers.

Reliability is a primary concern for designers and operators of life support systems. Measuring the reliability of advanced life support systems that use biological processes for regeneration presents a unique challenge to reliability engineers. The challenge lies in trying to define the reliability of a biological component (e.g., a green plant) and combine that with the reliability of physical components (e.g., a pump) to obtain a total system reliability. This paper presents issues to consider while trying to determine and to predict the reliability of such systems. The physiological response of a plant to its environment can be compared to the response of a physical component to its operating environment, and a measure of reliability can be determined. Furthermore, the physiological response of a plant can be estimated for most environmental conditions, and this estimation is necessary for the prediction of total system reliability.