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Crew time requirements for human space exploration missions is as critical as mass, energy, and volume requirements. However, it has only been sporadically recorded in past analog and space missions for plant cultivation. In this retrospective study on crew time data collected in various analog facilities and on the Veggie hardware on ISS, we propose a methodology for efficient categorizing and reporting of crew time in space plant growth systems. Crew time is difficult to capture in operational environments, and this study intends to harmonize these efforts among different locations. This article also provides a current database for required crew time in several plant growth hardware and facilities, on the ISS, and on Earth. These data could serve mission planners as a baseline to establish standardized activities and extrapolate crew time needed to operate future plant growth units. Finally, we discuss how crew time needed for plant cultivation will change in future exploration missions, based on choices made for plant species, watering systems, level of automation, and use of virtual assistants, among others. Crew time will need to be accounted for as a decisive factor to design future space greenhouse modules.

A plant production system called Veggie was launched to the International Space Station (ISS) in 2014. In late 2015, during the growth of Zinnia hybrida cv. ‘Profusion’ in the Veggie hardware, plan...

Among candidate leafy vegetable species initially considered for astronauts to pick and eat from the Veggie plant-growth unit on the International Space Station (ISS), Chinese cabbage (Brassica rapa L. cv. Tokyo Bekana) ranked high in ground-based screening studies. However, subsequent attempts to optimize growth within rigorous ISS-like growth environments on the ground were frustrated by development of leaf chlorosis, necrosis, and uneven growth. ‘Tokyo Bekana’ (‘TB’) grown on ISS during the VEG-03B and C flights developed similar stress symptoms. After lengthy troubleshooting efforts to identify causes of sub-par growth in highly controlled environments, the super-elevated CO2 concentrations that plants on ISS are exposed to continuously (average of 2,800 µmol/mol) emerged as a candidate environmental condition responsible for the observed plant-stress symptoms. Subsequent ground-based studies found continuous exposure to ISS levels of CO2 under Veggie environmental and cultural conditions to significantly inhibit growth of ‘TB’ compared to near-Earth-normal CO2 controls. The present study investigated growth and gas-exchange responses of ‘TB’ to sub-ISS but still elevated CO2 levels (900 or 1,350 µmol/mol) in combination with other potential stressors related to ISS/Veggie compared to 450 µmol/mol CO2 controls. Shoot dry mass of plants grown at 450 µmol•mol−1 CO2 for 28 days was 96% and 80% higher than that of plants grown at 900 µmol•mol−1 CO2 and 1,350 µmol•mol−1 CO2, respectively. Leaf number and leaf area of controls were significantly higher than those of plants grown at 1,350 µmol•mol−1 CO2. Photosynthetic rate measured using a leaf cuvette was significantly lower for plants grown at 900 µmol•mol−1 CO2 than for controls. The ratio of leaf internal CO2 concentration (Ci) to cuvette ambient CO2 concentration (Ca) was significantly lower for plants grown at 450 µmol•mol−1 CO2 than for plants grown at elevated CO2. Thus, continuously elevated CO2 in combination with a Veggie cultivation system decreased growth, leaf area, and photosynthetic efficiency of Chinese cabbage ‘Tokyo Bekana’. The results of this study suggest that ‘Tokyo Bekana’ is very sensitive to continuously elevated CO2 in such a growth environment, and indicate the need for improved environmental control of CO2 and possibly root-zone factors for successful crop production in the ISS spaceflight environment. Differential sensitivity of other salad crops to an ISS/Veggie growth environment also is possible, so it is important to mimic controllable ISS-like environmental conditions as precisely as possible during ground-based screening.

One of the major concerns for long-term exploration missions beyond the Earth's magnetosphere is consequences from exposures to solar particle event (SPE) protons and galactic cosmic rays (GCR). For long-term crewed Lunar and Mars explorations, the production of fresh food in space will provide both nutritional supplements and psychological benefits to the astronauts. However, the effects of space radiation on plants and plant propagules have not been sufficiently investigated and characterized. In this study, we evaluated the effect of two different compositions of charged particles-simulated GCR, and simulated SPE protons on dry and hydrated seeds of the model plant

Bioregenerative life-support systems for space have been investigated for 60 years, and plants and other photosynthetic organisms are central to this concept for their ability to produce food and O2, remove CO2, and help recycle wastewater. Many of the studies targeted larger scale systems that might be used for planetary surface missions, with estimates ranging from about 40 to 50 m2(or more) of crop growing area needed per person. But early space missions will not have these volumes available for crop growth. How can plants be used in the interim, where perhaps 2of growing area might be available? One option is to grow plants as supplemental, fresh foods. This could improve the quality and diversity of the meals on the International Space Station or on the Lunar surface, and supply important nutrients to the astronauts for missions like Mars transit, and longer duration Martian surface missions. Although plant chambers for supplemental food production would be relatively small, they could provide the bioregenerative research community with platforms for testing different crops in a space environment and serve as a stepping stone to build larger bioregenerative systems for future missions. Here we review some of NASA’s research and development (ground and spaceflight) targeting fresh food production systems for space. We encourage readers to also look into the extensive work by other space agencies and universities around the world on this same topic.

Background Seed sanitization via chemical processes removes/reduces microbes from the external surfaces of the seed and thereby could have an impact on the plants’ health or productivity. To determine the impact of seed sanitization on the plants’ microbiome and pathogen persistence, sanitized and unsanitized seeds from two leafy green crops, red Romaine lettuce (Lactuca sativa cv. ‘Outredgeous’) and mizuna mustard (Brassica rapa var. japonica) were exposed to Escherichia coli and grown in controlled environment growth chambers simulating environmental conditions aboard the International Space Station. Plants were harvested at four intervals from 7 days post-germination to maturity. The bacterial communities of leaf and root were investigated using the 16S rRNA sequencing while quantitative polymerase chain reaction (qPCR) and heterotrophic plate counts were used to reveal the persistence of E. coli. Result E. coli was detectable for longer periods of time in plants from sanitized versus unsanitized seeds and was identified in root tissue more frequently than in leaf tissue. 16S rRNA sequencing showed dynamic changes in the abundance of members of the phylum Proteobacteria, Firmicutes, and Bacteroidetes in leaf and root samples of both leafy crops. We observed minimal changes in the microbial diversity of lettuce or mizuna leaf tissue with time or between sanitized and unsanitized seeds. Beta-diversity showed that time had more of an influence on all samples versus the E. coli treatment. Conclusion Our results indicated that the seed surface sanitization, a current requirement for sending seeds to space, could influence the microbiome. Insight into the changes in the crop microbiomes could lead to healthier plants and safer food supplementation.

The establishment of steady-state continuous crop production during long-term deep space missions is critical for providing consistent nutritional and psychological benefits for the crew, potentially improving their health and performance. Three technology demonstrations were completed achieving simultaneous multi-species plant growth and the concurrent use of two Veggie units on the International Space Station (ISS). Microbiological characterization using molecular and culture-based methods was performed on leaves and roots from two harvests of three leafy greens, red romaine lettuce (Lactuca sativa cv. ‘Outredgeous’); mizuna mustard, (Brassica rapa var japonica); and green leaf lettuce, (Lactuca sativa cv. Waldmann’s) and associated rooting pillow components and Veggie chamber surfaces. Culture based enumeration and pathogen screening indicated the leafy greens were safe for consumption. Surface samples of the Veggie facility and plant pillows revealed low counts of bacteria and fungi and are commonly isolated on ISS. Community analysis was completed with 16S rRNA amplicon sequencing. Comparisons between pillow components, and plant tissue types from VEG-03D, E, and F revealed higher diversity in roots and rooting substrate than the leaves and wick. This work provides valuable information for food production-related research on the ISS and the impact of the plant microbiome on this unique closed environment.

As human exploration moves beyond low Earth orbit, innovative life support and resource production systems become forerunners for human colonization. Plasma systems allow for complex chemical processes while mitigating consumable needs. Plasma technology and applications can redefine the space environment. With this, scientists at NASA are looking to close known space technology gaps and create a paradigm shift in space-based applications. NASA’s Kennedy Space Center is exploring the use of low-temperature plasma for applications in agriculture, sanitation, regolith reduction, waste gasification, water activation, and nutrient recovery techniques. Using low temperature plasmas, we report on the success criteria and experimental results for plasma applications for crewed transit and planetary habitation.

To explore lighting strategies for crop production in space, we investigated the impacts of light spectrum on morphology, biomass, and phytonutrients of red pak choi (Brassica rapa var. chinensis, ‘Rubi F1’) over a 28-day cycle. Light treatments were white light-emitting diodes (WLEDs) as a control, W + red (WR), W + green switched to red at 21 days (WG–R), W + far-red (WFR), red and blue (RB), and an LED-based artificial sunlight research module (ASRM). The photosynthetic photon flux density (PPFD) was maintained near 180 μmol m−2·s-1 for all light treatments. Our results indicated that red pak choi grown under a narrow spectrum of RB light was most suitable for leaf expansion, biomass yield, and relative anthocyanin accumulation. The various broad-spectrum WLED treatments reduced yield, leaf area, and anthocyanin content. Supplemental G and FR augmented the reduction of growth and phytonutrients, however chlorophyll and anthocyanin levels recovered to levels comparable to the control within 7 days of switching WG to WR. The ASRM was used to assess direct sunlight as an alternative lighting option for plant growth in space. ASRM increased overall yield and specific leaf weight compared to WLED and supplemental treatments, and was similar to plants grown under RB in terms of fresh/dry weight, but lower in phytonutrients. Our results suggest both narrow and broad-band light sources can be used to manipulate morphology, phytonutrients, and partitioning of biomass in red pak choi.

To optimize crop production/quality in space, we studied various “light recipes” that could be used in the Advanced Plant Habitat currently aboard the International Space Station (ISS). Lettuce (Lactuca sativa cv. ‘Outredgeous’) plants were grown for 28 days under seven treatments of white (W) LEDs (control), red (635 nm) and blue (460 nm) (RB) LEDs, W + blue (B) LEDs, W + green (520 nm) (G) LEDs, W + red (R) LEDs, W + far red (745 nm) (FR) LEDs, and RGB + FR LEDs with ratios similar to natural sunlight. Total PAR was maintained near 180 µmol m−2 s−1 with an 18 h photoperiod. Lettuce grown under RGB + FR produced the greatest leaf expansion and overall shoot biomass, while leaves from WB and RB showed the highest levels of pigmentation, secondary metabolites, and elemental nutrients. All other supplemental treatments had varying impacts on morphology that were dependent on crop age. The WG treatment increased fresh mass early in the cycle, while WR increased biomass later in the cycle. The plants grown under WFR exhibited elongation of petioles, lower nutrient content, and similar shoot biomass to the W control. The findings suggest that supplementing a broad spectrum, white light background with discrete wavelengths can be used to manipulate total yield, morphology, and levels of phytonutrients in lettuce at various times during the crop cycle.

As human innovation continuously expands the knowledge base for life beyond Earth, the need for self-sufficient spacecraft is essential. With that, space crop production facilities are ever expanding for research and development. A current area of key interest is seed sanitation before transport from ground to the International Space Station (ISS). Sanitation practices are performed to mitigate any potential biohazard and to ensure the viability of the seed. Conventional methods involve fumigation of seeds or chemical processes but are not effective with all seed types. Therefore, plasma technology was implemented in this research to explore low-temperature plasmas as an alternative means for seed sanitation without the need for chemicals. This project investigated the viability of plasma as a means for sanitation by incorporating three different plasma types within the study. For the treatment of Cherry Belle radish seeds, the optimal system was a radio frequency (RF) sub-atmospheric plasma chamber. Treatments of 100 W for 10 min or longer with the Diener system consistently reduced microbial loads by 90% or more. While 20-min treatments caused reductions in germination rate, a treatment of 15 min with the Diener system at 100 W consistently resulted in germination rates above 80% after 1 month of seed storage. For the 5 and 10 min treatments at a pressure of 187 mTorr and power of 100 W, growth was also accelerated. Additionally, plasma provided 90% reduction of Escherichia coli and Bacillus pumilis and a 99% reduction of Fusarium ozysporum on inoculated seeds. Overall, the plasma systems show promising potential but require further exploration.

The ability to grow safe, fresh food to supplement packaged foods of astronauts in space has been an important goal for NASA. Food crops grown in space experience different environmental conditions than plants grown on Earth (e.g., reduced gravity, elevated radiation levels). To study the effects of space conditions, red romaine lettuce, Lactuca sativa cv ‘Outredgeous,’ plants were grown in Veggie plant growth chambers on the International Space Station (ISS) and compared with ground-grown plants. Multiple plantings were grown on ISS and harvested using either a single, final harvest, or sequential harvests in which several mature leaves were removed from the plants at weekly intervals. Ground controls were grown simultaneously with a 24–72 h delay using ISS environmental data. Food safety of the plants was determined by heterotrophic plate counts for bacteria and fungi, as well as isolate identification using samples taken from the leaves and roots. Molecular characterization was conducted using Next Generation Sequencing (NGS) to provide taxonomic composition and phylogenetic structure of the community. Leaves were also analyzed for elemental composition, as well as levels of phenolics, anthocyanins, and Oxygen Radical Absorbance Capacity (ORAC). Comparison of flight and ground tissues showed some differences in total counts for bacteria and yeast/molds (2.14 – 4.86 log10 CFU/g), while screening for select human pathogens yielded negative results. Bacterial and fungal isolate identification and community characterization indicated variation in the diversity of genera between leaf and root tissue with diversity being higher in root tissue, and included differences in the dominant genera. The only difference between ground and flight experiments was seen in the third experiment, VEG-03A, with significant differences in the genera from leaf tissue. Flight and ground tissue showed differences in Fe, K, Na, P, S, and Zn content and total phenolic levels, but no differences in anthocyanin and ORAC levels. This study indicated that leafy vegetable crops can produce safe, edible, fresh food to supplement to the astronauts’ diet, and provide baseline data for continual operation of the Veggie plant growth units on ISS.

Fresh produce grown in spaceflight may enhance nutrition and dietary diversity, but also may introduce a microbiological risk that requires a mitigation strategy. Cold plasma is a waterless technology that has the potential to disinfect spaceflight grown produce with only vehicle air as a resource. However, evaluation of current cold plasma devices indicated that technology and safety capabilities must be further developed and knowledge gaps in nutrition and quality must be further investigated before this technology can be adequately assessed for compatibility with spaceflight.

The first Veggie plant growth chamber was installed on the International Space Station in 2014. Crop plants can be grown in Veggie using plant pillows, small rooting packets that contain substrate, fertilizer, and germination wicks along with attached seeds. The pillows were designed to interface with the Veggie root mat reservoir watering system to provide a capillary water column to growing plants. In preparation for flight, methods of arcillite substrate washing, autoclaving, and drying were established to reduce dust and to provide a dry sterile substrate. A controlled released fertilizer mixed into arcillite substrate provides nutrition for plant growth. Methods of seed surface sterilization were tested for both germination and microbial contamination, and the optimum methods were determined for candidate flight crops. Plant pillows were prepared for flight by cutting and inserting germination wicks, filling with the substrate/fertilizer mix, and sewing closed. Following pillow filling, seeds were attached to the wicks, and the pillows were packaged for flight. Pillow preparation methods have been successfully tested in the VEG-01 hardware validation tests on the International Space Station with ‘Outredgeous’ lettuce and ‘Profusion’ zinnia, and in the VEG-03 test, using ‘Outredgeous’ lettuce and ‘Tokyo bekana’ Chinese cabbage.

The Veggie vegetable production system was launched to the International Space Station with three sets of test plants for an initial hardware validation test, designated VEG-01. VEG-01A and B featured the crop ‘Outredgeous’ red romaine lettuce, while VEG-01C tested ‘Profusion’ zinnia plants for longer duration growth and flowering characteristics. Irrigation of plants in all three growth studies presented a challenge, with lettuce suffering from inadequate water and zinnia suffering from excess water. Direct plant pillow watering by crew members enabled plant growth, and returned samples from the first crop, VEG-01A, indicated that food safety was acceptable. VEG-01B plants at harvest were split to allow for on-orbit crew consumption as well as science sample return. Direct-watered zinnias suffered fungal growth and other physiological stresses, but two plants survived and these produced numerous flowers. The VEG-01 series allowed a large amount of data on system performance, human factors, procedures, microbiology, and chemistry of space-grown plants to be gathered. Observations from these tests are helping to drive future hardware modifications and provide information on food crop growth and development in a microgravity environment.

Light emitting diode (LED) lighting technology for crop production is advancing at a rapid pace, both in terms of the technology itself (e.g., spectral composition and efficiency), and the research that the technological advances have enabled. The application of LED technology for crop production was first explored as a tool for improving the safety and reliability of plant-based bioregenerative life-support systems for long duration human space exploration. Developing and optimizing the lighting environment (spectral quality and quantity) for bioregenerative life-support applications and other controlled environment plant production applications, such as microgreens and sprout production, continues to be an active area of research and LED technology development. This study examines the influence of monochromatic and dichromatic red and blue light on the early development of six food crop species; Cucumis sativa, Solanum lycopersicum, Glycine max, Raphanus sativus, Pisum sativum, and Capsicum annum. Results support previous findings that light responses are often species specific. The results also support the assertion that monochromatic light can interfere with the normal interaction of various photoreceptors (co-action disruption) resulting in intermediate and sometimes unpredictable responses to a given light environment. The nature of the responses reported inform both bioregenerative life-support designs as well as light quality selection for the production of controlled environment crops.

The International Space Station (ISS) now has platforms for conducting research on horticultural plant species under LED lighting, and those capabilities continue to expand. The 'Veggie' vegetable production system was deployed to the ISS as an applied research platform for food production in space. Veggie is capable of growing a wide array of horticultural crops. It was designed for low power usage, low launch mass and stowage volume, and minimal crew time requirements. The Veggie flight hardware consists of a light cap containing red (630 nm), blue, (455 nm) and green (530 nm) LEDs. Interfacing with the light cap is an extendable bellows/baseplate for enclosing the plant canopy. A second large plant growth chamber, the Advanced Plant Habitat (APH), is will fly to the ISS in 2017. APH will be a fully controllable environment for high-quality plant physiological research. APH will control light (quality, level, and timing), temperature, CO2, relative humidity, and irrigation, while scrubbing any cabin or plant-derived ethylene and other volatile organic compounds. Additional capabilities include sensing of leaf temperature and root zone moisture, root zone temperature, and oxygen concentration. The light cap will have red (630 nm), blue (450 nm), green (525 nm), far red (730 nm) and broad spectrum white LEDs (4100K). There will be several internal cameras (visible and IR) to monitor and record plant growth and operations. Veggie and APH are available for research proposals.

Here, we present the whole-genome sequences of two Fusarium oxysporum isolates cultured from infected Zinnia hybrida plants that were grown onboard the International Space Station (ISS).

Strawberry ( Fragaria x ananassa L.) is a promising candidate crop for space life-support systems with desirable sensory quality and health attributes. Day-neutral cultivars such as ‘Seascape’ are adaptable to a range of photoperiods, including short days that would save considerable energy for crop lighting without reductions in productivity or yield. Since photoperiod and temperature interact to affect strawberry growth and development, several diurnal temperature regimes were tested under a short photoperiod of 10 h per day for effects on yield and quality attributes of ‘Seascape’ strawberry during production cycles longer than 270 days. The coolest day/night temperature regime, 16°/8 °C, tended to produce smaller numbers of larger fruit than did the intermediate temperature range of 18°/10 °C or the warmest regime, 20°/12 °C, both of which produced similar larger numbers of smaller fruit. The intermediate temperature regime produced the highest total fresh mass of berries over an entire production cycle. Independent experiments examined either organoleptic or physicochemical quality attributes. Organoleptic evaluation indicated that fruit grown under the coolest temperature regime tended to score the highest for both hedonic preference and descriptive evaluation of sensory attributes related to sweetness, texture, aftertaste, and overall approval. The physicochemical quality attributes Brix, pH, and sugar/acid ratio were highest for fruits harvested from the coolest temperature regime and lower for those from the warmer temperature regimes. The cool-regime fruits also were lowest in titratable acidity. The yield parameters fruit number and size oscillated over the course of a production cycle, with a gradual decline in fruit size under all three temperature regimes. Brix and titratable acidity both decreased over time for all three temperature treatments, but sugar/acid ratio remained highest for the cool temperature regime over the entire production period. Periodic rejuvenation or replacement of strawberry propagules may be needed to maintain both quality and quantity of strawberry yield in space.

The Vegetable Production System (Veggie) is a scientific payload designed to support plant growth for food production under microgravity conditions. The configuration of Veggie consists of an LED lighting system with modular rooting pillows designed to contain substrate media and time-release fertilizer. The pillows were designed to be watered passively using capillary principles but have typically been watered manually by the astronauts in low-Earth orbit (LEO). The design of Veggie allows cabin air to be drawn through the plant enclosure for thermal and humidity control and for supplying CO2 to the plants. Since its delivery to the International Space Station (ISS) in 2014, Veggie has undergone several experimental trials by various crews. Ground unit testing of Veggie was conducted during an 8-month Mars analog study in a semi-contained environment of a simulated habitat located at approximately 8,200 feet (2,500 m) elevation on the Mauna Loa volcano on the Island of Hawaii. The Hawaii Space Exploration Analog and Simulation (HI-SEAS) offered conditions (habitat, mission, communications, etc.) intended to simulate a planetary exploration mission. This paper provides data and analyses to show the prospect for optimized use of the current Veggie design for human habitats. Lessons learned during the study may provide opportunities for updating the system design and operational parameters for current Veggie experiments being conducted onboard the ISS and for payloads on future deep space missions.

Growing plants to provide food or psychological benefits to crewmembers is a common vision for the future of human spaceflight, often represented in media and in serious concept studies. The complexity of controlled environment agriculture, and plant growth in microgravity have and continue to be the subject of dedicated scientific research. However, actually implementing these systems in a way that will be cost effective, efficient, and sustainable for future space missions is a complex, multi-disciplinary problem. Key questions exist in many areas: human medical research in nutrition and psychology, horticulture, plant physiology and microbiology, multi-phase microgravity fluid physics, hardware design and technology development, and system design, operations and mission planning. This paper describes key knowledge gaps identified by a multi-disciplinary working group within the National Aeronautics and Space Administration (NASA). It also begins to identify solutions to the simpler questions identified by the group based on work initiated in 2017. Growing plants to provide food or psychological benefits to crewmembers is a common vision for the future of human spaceflight, often represented in media and in serious concept studies. The complexity of controlled environment agriculture, and plant growth in microgravity have and continue to be the subject of dedicated scientific research. However, actually implementing these systems in a way that will be cost effective, efficient, and sustainable for future space missions is a complex, multi-disciplinary problem. Key questions exist in many areas: human medical research in nutrition and psychology, horticulture, plant physiology and microbiology, multi-phase microgravity fluid physics, hardware design and technology development, and system design, operations and mission planning. This paper describes key knowledge gaps identified by a multi-disciplinary working group within the National Aeronautics and Space Administration (NASA). It also begins to identify solutions to the simpler questions identified by the group based on work initiated in 2017.

Bioregenerative life-support systems involving photoautotrophic organisms will be necessary to sustain long-duration crewed missions at distant space destinations. Since sufficient sunlight will not always be available for plant growth at many space destinations, efficient electric-lighting solutions are greatly needed. The present study demonstrated that targeted plant lighting with light-emitting diodes (LEDs) and optimizing spectral parameters for close-canopy overhead LED lighting allowed the model crop leaf lettuce ( Lactuca sativa L. cv. ‘Waldmann's Green’) to be grown using significantly less electrical energy than using traditional electric-lighting sources. Lettuce stands were grown hydroponically in a growth chamber controlling temperature, relative humidity, and CO 2 level. Several red:blue ratios were tested for growth rate during the lag phase of lettuce growth. In addition, start of the exponential growth phase was evaluated. Following establishment of a 95% red + 5% blue spectral balance giving the best growth response, the energy efficiency of a targeted lighting system was compared with that of two total coverage (untargeted) LED lighting systems throughout a crop-production cycle, one using the same proportion of red and blue LEDs and the other using white LEDs. At the end of each cropping cycle, whole-plant fresh and dry mass and leaf area were measured and correlated with the amount of electrical energy (kWh) consumed for crop lighting. Lettuce crops grown with targeted red + blue LED lighting used 50% less energy per unit dry biomass accumulated, and the total coverage white LEDs used 32% less energy per unit dry biomass accumulated than did the total coverage red + blue LEDs. An energy-conversion efficiency of less than 1 kWh/g dry biomass is possible using targeted close-canopy LED lighting with spectral optimization. This project was supported by NASA grant NNX09AL99G.

A semi-dwarf breeding line of maize ( Zea mays L., PI 587154) was grown from seed to seed in a growth chamber either at 26.7 °C days/18.3 °C nights (control treatment) or at 15.6 °C for the first 2 h of each photoperiod before being returned to standard control temperature for the rest of the photoperiod (DIP treatment). Half of the plants in each 120-day production experiment were grown in 3-L containers and half in 9-L containers, both groupings at equivalent plant-to-plant spacing. Stalks of DIP-treated plants elongated 9–10% less than controls during seed-production cycles in both pot sizes. DIP reduced vegetative dry biomass of stalks 29% relative to controls when using small pots, and 19% for plants grown in medium pots. Root dry weight was reduced 22–25% by DIP in the two container sizes, but stalk/root ratios were not altered significantly by DIP treatment or pot size. Stalk diameter also was reduced 8–9% by DIP for both pot sizes. Neither seed number nor seed weight were affected significantly by temperature treatment or pot size. DIP slowed and prolonged stalk elongation but not differentiation of nodes for both pot sizes. Timing of tassel development and pollen shed were unaffected by temperature or pot size, but timing of silk development was delayed by DIP, slightly more for plants growing in small than in medium pots. Nevertheless, primary ears developed to complete seed fill, suggesting adequate time-window overlap between pollen shed and silk receptivity for effective pollination and fertilization to occur. Controlled-environment production of maize in restricted-height growth facilities or where adequate separation distance is required between the tops of crop stands and overhead high-intensity discharge light sources may be accommodated economically by use of DIP temperature treatments without compromising grain yield. Use of medium-volume containers stabilizes the mature maize stalks bearing grain-filled ears.

Electric supplemental lighting can account for a significant proportion of total greenhouse energy costs. Thus, the objectives of this study were to compare high-wire tomato (Solanum lycopersicum) production with and without supplemental lighting and to evaluate two different lighting positions + light sources [traditional high-pressure sodium (HPS) overhead lighting (OHL) lamps vs. light-emitting diode (LED) intracanopy lighting (ICL) towers] on several production and energy-consumption parameters for two commercial tomato cultivars. Results indicated that regardless of the lighting position + source, supplemental lighting induced early fruit production and increased node number, fruit number (FN), and total fruit fresh weight (FW) for both cultivars compared with unsupplemented controls for a winter-to-summer production period. Furthermore, no productivity differences were measured between the two supplemental lighting treatments. The energy-consumption metrics indicated that the electrical conversion efficiency for light-emitting intracanopy lighting (LED-ICL) into fruit biomass was 75% higher than that for HPS-OHL. Thus, the lighting cost per average fruit grown under the HPS-OHL lamps was 403% more than that of using LED-ICL towers. Although no increase in yield was measured using LED-ICL, significant energy savings for lighting occurred without compromising fruit yield.

Sweetpotato (Ipomea batatas L.) ‘Whatley–Loretan’ was developed for space life support by researchers at Tuskegee University for its highly productive, nutritious storage roots. This promising candidate space life-support crop has a sprawling habit and aggressive growth rate in favorable environments that demands substantial growing area. Shoot pruning is not a viable option for vine control because removal of the main shoot apex drastically inhibits storage-root initiation and development, and chemical growth retardants typically are not cleared for use with food crops. As part of a large effort by the NASA Specialized Center of Research and Training in Advanced Life Support to reduce equivalent system mass (ESM) for food production in space, the dilemma of vine management for sweetpotato was addressed in effort to conserve growth area without compromising root yield. Root yields from unbranched vines trained spirally around wire frames configured either in the shapes of cones or cylinders were similar to those from vines trained horizontally along the bench, but occupying only a small fraction of the bench area. This finding indicates that sweetpotato is highly adaptable to a variety of vine-training architectures. Planting a second plant in the growth container and training the two vines in opposite directions around frames enhanced root yield and number, but had little effect on average length of each vine or bench area occupied. Once again, root yields were similar for both configurations of wire support frames. The 3–4-month crop-production cycles for sweetpotato in the greenhouse spanned all seasons of multiple years during the course of the study, and although electric lighting was used for photoperiod control and to supplement photosynthetic light during low-light seasons, there still were differences in total light available across seasons. Light variations and other environmental differences among experiments in the greenhouse had more effects on vine length than on root yield. Average vine length correlated positively with total hours of daylight received across seasons, and responses for one plant per container were higher above a threshold duration of solar exposure, suggesting that the vines of two plants per container compete for available light. In addition to the adaptability of sweetpotato to various vine-training architectures and across seasons in terms of maintaining root productivity, the open, interior volumes of the support frames tested in this study will provide future opportunity to enhance sweetpotato root yield in space by adding novel interior lighting, such as from intracanopy arrays of light-emitting diodes. This work was sponsored by NASA grant NAG 5 1286.

A variety of crops and their production systems have been proposed as platforms for plant-made pharmaceuticals (PMPs) and plant-made industrial compounds (PMICs), each with their own advantages and challenges. Maize grown in isolated, confined environments avoids several challenging issues associated with future production of PMPs/PMICs. When grown under optimizing conditions of temperature, nutrition, and water status, however, maize tends to elongate excessively, which contributes to lodging and interferes with delivery of sufficient overhead electric lighting to the inner foliar canopy where ears develop. Suppression of extensive stem elongation without compromising grain yield would help in delivering overhead light into the foliar canopy for efficient grain production. The plant-growth retardant uniconazole (UCZ) was tested for its effects on maize height and grain yield. UCZ reduced plant height effectively, but dosages that strongly suppressed stem elongation also decreased grain yield, ear length, and cob weight. Duration of growth suppression was prolonged at high UCZ concentrations. UCZ also induced branching of maize, which was enhanced as concentrations increased. A range of ear types occurred on branches, with some conversion of ears to tassels at high UCZ concentrations. Minimum stem diameter declined with increasing UCZ concentration. Plant height was reduced from 306 cm to 232 cm (−25%) using a concentration of 1.0 mg/L UCZ without affecting grain yield of 180–200 g per plant. This low UCZ concentration caused 1–2 basal branches to form that would not affect planting density in a cropping situation.

Strawberry is a candidate crop for space that is rich in protective antioxidants and could also have psychological benefits as a component of crew diets during long-duration space habitation. Energy for electric lighting is a major input to a controlled-environment crop-production system for space habitation. Day-neutral strawberry cultivars were evaluated at several different photoperiods to determine minimum lighting requirements without limiting yield or negatively impacting fruit quality. The cultivars ‘Tribute’, ‘Seascape’, and ‘Fern’ were grown at 14, 17, or 20 h of light per day, and fruit yield was evaluated over a 31-week production period. This amounted to a difference of 2418 kWh m−2 in energy usage between the longest and shortest photoperiods. All cultivars produced similar total fresh weight of fruit regardless of photoperiod. Volunteer tasters rated organoleptic characteristics including sweetness, tartness, texture, and overall appeal as measures of fruit quality. Generally, organoleptic attributes were not affected by photoperiod, but these attributes were somewhat dependent upon cultivar and harvest time. Cultivars under different photoperiods varied in their production of fruit over time. ‘Seascape’ was the most consistent producer, typically with the largest, most palatable fruit. ‘Seascape’ plants subsequently were grown at 10-, 12-, or 14-h photoperiods over a treatment period of 33 weeks. Photoperiod again had no significant effect on total fruit weight, although there were periodic flushes of productivity. Fruit under all photoperiods had acceptable approval ratings. A large-fruited, day-neutral strawberry cultivar such as ‘Seascape’ remains productive under shortened photoperiods, allowing reductions in energy and crew labor while maintaining flexibility for mixed-cropping scenarios in space.

Additional index words. controlled environment agriculture, light quality, light-emitting diode, edema, intracanopy lighting Abstract. Light-emitting diodes (LEDs) have tremendous potential as supplemental or sole-source lighting systems for crop production both on and off earth. Their small size, durability, long operating lifetime, wavelength specificity, relatively cool emitting surfaces, and linear photon output with electrical input current make these solid-state light sources ideal for use in plant lighting designs. Because the output waveband of LEDs (single color, nonphosphor-coated) is much narrower than that of traditional sources of electric lighting used for plant growth, one challenge in designing an optimum plant lighting system is to determine wavelengths essential for specific crops. Work at NASA's Kennedy Space Center has focused on the proportion of blue light required for normal plant growth as well as the optimum wavelength of red and the red/far-red ratio. The addition of green wavelengths for improved plant growth as well as for visual monitoring of plant status has been addressed. Like with other light sources, spectral quality of LEDs can have dramatic effects on crop anatomy and morphology as well as nutrient uptake and pathogen development. Work at Purdue University has focused on geometry of light delivery to improve energy use efficiency of a crop lighting system. Additionally, foliar intumescence developing in the absence of ultraviolet light or other less understood stimuli could become a serious limitation for some crops lighted solely by narrow-band LEDs. Ways to prevent this condition are being investigated. Potential LED benefits to the controlled environment agriculture industry are numerous and more work needs to be done to position horticulture at the forefront of this promising technology.

Plants must sense and respond to diverse stimuli to optimize the architecture of their root system for water and nutrient scavenging and anchorage. We have therefore analyzed how information from two of these stimuli, touch and gravity, are integrated to direct root growth. In Arabidopsis thaliana, touch stimulation provided by a glass barrier placed across the direction of growth caused the root to form a step-like growth habit with bends forming in the central and later the distal elongation zones. This response led to the main root axis growing parallel to, but not touching the obstacle, whilst the root cap maintained contact with the barrier. Removal of the graviperceptive columella cells of the root cap using laser ablation reduced the bending response of the distal elongation zone. Similarly, although the roots of the gravisensing impaired pgm1-1 mutant grew along the barrier at the same average angle as wild-type, this angle became more variable with time. These observations imply a constant gravitropic re-setting of the root tip response to touch stimulation from the barrier. In wild-type plants, transient touch stimulation of root cap cells, but not other regions of the root, inhibited both subsequent gravitropic growth and amyloplast sedimentation in the columella. Taken together, these results suggest that the cells of the root cap sense touch stimuli and their subsequent signaling acts on the columella cells to modulate their graviresponse. This interaction of touch and gravity signaling would then direct root growth to avoid obstacles in the soil while generally maintaining downward growth.

In preparation for future human exploration missions to space, NASA evaluates habitat concepts to assess integration issues, power requirements, crew operations, technology, and system performance. The concept of a Food Production System utilizes fresh foods, such as vegetables and small fruits, harvested on a continuous basis, to improve the crew's diet and quality of life. The system would need to fit conveniently into the habitat and not interfere with other components or operations. To test this concept, a plant growing "atrium" was designed to surround the lift between the lower and upper modules of the Deep Space Habitat and deployed at NASA Desert Research and Technology Studies (DRATS) test site in 2011 and at NASA Johnson Space Center in 2012. With this approach, no-utilized volume provided an area for vegetable growth. For the 2011 test, mizuna, lettuce, basil, radish and sweetpotato plants were grown in trays using commercially available red I blue LED light fixtures. Seedlings were transplanted into the atrium and cared for by the. crew. Plants were then harvested two weeks later following completion of the test. In 2012, mizuna, lettuce, and radish plants were grown similarly but under flat panel banks of white LEDs. In 2012, the crew went through plant harvesting, including sanitizing tlie leafy greens and radishes, which were then consumed. Each test demonstrated successful production of vegetables within a functional hab module. The round red I blue LEDs for the 2011 test lighting cast a purple light in the hab, and were less uniformly distributed over the plant trays. The white LED panels provided broad spectrum light with more uniform distribution. Post-test questionnaires showed that the crew enjoyed tending and consuming the plants and that the white LED light in 2012 provided welcome extra light for the main HAB AREA.

Systems for the growth of crops in closed environments are being developed and tested for potential use in space applications to provide a source of fresh food. Plant growth conditions, growth media composition and harvest methods can have an effect on the microbial population of the plant, and therefore should be considered along with the optimization of plant growth and harvest yields to ensure a safe and palatable food crop. This work examines the effect of plant cultivar, growth media, and harvest method on plant microbial populations. Twelve varieties of leafy greens and herbs were grown on a mixture of Fafard #2 and Arcillite in the pillow root containment system currently being considered for the VEGGIE plant growth unit developed by Orbitec. In addition, ,Sierra and Outredgeous lettuce varieties were grown in three different mixtures (Fafard #2, Ardllite, and Perlite/Vermiculite). The plants were analyzed for microbial density. Two harvest methods, "cut and come again" (CACA) and terminal harvest were also compared. In one set ofexpe'riments red leaf lettuce and mizuna were grown in pots in a Biomass Production System for education. Plants were harvested every two weeks by either method. Another set of experiments was performed using the rooting pillows to grow 5 varieties of leafy greens and cut harvesting at different intervals. Radishes were harvested and replanted at two-week intervals. Results indicate up to a 3 IOglO difference in microbial counts between some varieties of plants. Rooting medium resulted in an approximately 2 IOglO lower count in the lettuce grown in arscillite then those grown in the other mixtures. Harvest method and frequency had less impact on microbial counts only showing a significant increase in one variety of plant. Post harvest methods to decrease the bacterial counts on edible crops were investigated in these and other experiments. The effectiveness of PRO-SAN and UV-C radiation is compared.

In this paper, a pH control system for an experimental recirculating hydroponic growth chamber for the NASA Mars exploration program has been modeled and implemented. The resulting model has a bilinear Weiner type structure. A novel approximation approach is presented to obtain a simplified plant model controller design. Perturbation analysis validates the applicability of the approximation for the specific pH control of a closed-loop hydroponic growth chamber. A modified PI controller that takes into account on-off nature of the solenoid valve actuator was designed to control the pH level. The closed-loop system is shown to be BIBO stable with respect to the original bilinear plant model. Experimental results for reference tracking and disturbance rejection in an operational hydroponic chamber with growing plants have demonstrated the effectiveness of the proposed approach.Copyright © 2006 by ASME

Plant roots are optimized to exploit resources from the soil and as each root explores this environment it will encounter a range of biotic and abiotic stimuli to which it must respond. Therefore, each root must possess a sensory array capable of monitoring and integrating these diverse stimuli to direct the appropriate growth response. Touch and gravity represent two of the biophysical stimuli that plants must integrate. As sensing both of these signals requires mechano-transduction of biophysical forces to biochemical signaling events, it is likely that they share signal transduction elements. These common signaling components may allow for cross-talk and so integration of thigmotropic and gravitropic responses. Indeed, signal transduction events in both plant touch and gravity sensing are thought to include Ca(2+)- and pH-dependent events. Additionally, it seems clear that the systems responsible for root touch and gravity response interact to generate an integrated growth response. Thus, primary and lateral roots of Arabidopsis respond to mechanical stimuli by eliciting tropic growth that is likely part of a growth strategy employed by the root to circumvent obstacles in the soil. Also, the mechano-signaling induced by encountering an obstacle apparently down-regulates the graviperception machinery to allow this kind of avoidance response. The challenge for future research will be to define how the cellular signaling events in the root cap facilitate this signal integration and growth regulation. In addition, whether other stimuli are likewise integrated with the graviresponse via signal transduction system cross-talk is an important question that remains to be answered.

Touch and gravity are two of the many stimuli that plants must integrate to generate an appropriate growth response. Due to the mechanical nature of both of these signals, shared signal transduction elements could well form the basis of the cross-talk between these two sensory systems. However, touch stimulation must elicit signaling events across the plasma membrane whereas gravity sensing is thought to represent transformation of an internal force, amyloplast sedimentation, to signal transduction events. In addition, factors such as turgor pressure and presence of the cell wall may also place unique constraints on these plant mechanosensory systems. Even so, the candidate signal transduction elements in both plant touch and gravity sensing, changes in Ca2+, pH and membrane potential, do mirror the known ionic basis of signaling in animal mechanosensory cells. Distinct spatial and temporal signatures of Ca2+ ions may encode information about the different mechanosignaling stimuli. Signals such as Ca2+ waves or action potentials may also rapidly transfer information perceived in one cell throughout a tissue or organ leading to the systemic reactions characteristic of plant touch and gravity responses. Longer-term growth responses are likely sustained via changes in gene expression and asymmetries in compounds such as inositol-1,4,5-triphosphate (IP3) and calmodulin. Thus, it seems likely that plant mechanoperception involves both spatial and temporal encoding of information at all levels, from the cell to the whole plant. Defining this patterning will be a critical step towards understanding how plants integrate information from multiple mechanical stimuli to an appropriate growth response.