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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.

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 use of composting technology is attractive to NASA’s Bioregenerative Life Support System (BLSS) research because it offers a potential reduction in system costs when compared to other waste recycling approaches. Water-soluble leachates from 28-day composted fresh or oven-dried inedible wheat biomass were amended with reagent-grade nutrients to be inorganically equivalent to ½-strength Hoagland’s (control) replenishment solution. A portion of the fresh and oven-dried compost leachate was filtered to remove large organic particles and a majority of the microflora, and wheat plants were grown hydroponically on these amended leachates. For both the fresh and oven-dried compost leachate treatments, filtering the leachate had no effect on plant response. No significant difference was observed between the fresh compost leachate treatments and the control.

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.

A primary challenge for supporting plants in space is to provide as much photosynthetically active radiation (PAR) as possible, while conserving electrical power. Light-emitting diodes (LEDs) and microwave lamps are innovative artificial lighting technologies with several appealing features for supporting plant growth in controlled environments. Because of their rugged design, small mass and volume, and narrow spectral output, red and blue LEDs are particularly suited for outfitting plant growth hardware in spaceflight systems. The sulfur-microwave electrode-less high-intensity discharge (HID) produces a bright broad-spectrum visible light at a higher electrical conversion efficiency than conventional light sources. Experiments compared the performance and productivity of spinach (Spinacia oleracea L.) grown under conventional lighting sources (high-pressure sodium and cool-white fluorescent lamps) with microwave lamps and various wavelengths of red LEDs.

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.

Under certain nutrient solution management practices in hydroponic systems, sweetpotato [Ipomoea batatas (L.) Lam.] plants can exhibit excessive shoot growth and reduced storage root yield. An experiment was conducted which compared sweetpotato production in nutrient film technique (NFT) systems either with daily nutrient solution replenishment + real-time pH control or with nutrient solution replenishment 3-times per week + periodic pH adjustment. Results showed that replenishment of nutrient solution on a daily basis produced excessive foliage growth with very little storage root production. Nutrient solution replenishment 3-times per week produced manageable vine growth and respectable storage root yields.

Because of mass and power constraints in spacecraft, plant growth units designed for spaceflight have limited volume and low photosynthetic photon flux (PPF). Sufficient lighting and nutrient delivery are basic challenges to the success of supporting long-term plant growth in space. At the Kennedy Space Center, plant lighting and nutrient delivery hardware currently under NASA-sponsored development are being evaluated to define some of the fundamental issues associated with producing different fresh salad crops. Lettuce crops performed well under all nutrient delivery systems and lighting sources tested. Spinach and radish yields were lower in the presence of zeoponic media (using an ASTROCULTURE™ root tray) relative to plant grown in conventional NFT systems. Within each nutrient delivery system, yields of salad crops under red LEDs + blue light were similar to those crops grown under conventional white light.