What kind of food will astronauts eat and what is the best way to grow it during deep space exploration missions? A group of plant biologists is seeking the answers as it works on one of NASA’s Advanced Exploration Systems (AES) Habitation Projects at Kennedy Space Center’s Space Life Sciences Laboratory, one in a series of projects taking place at the agency to forge new approaches to rapidly develop prototype systems, demonstrate key capabilities and validate operational concepts for future human missions beyond Earth orbit.

Radish plants (above) were harvested from a plant growth chamber. The plants were grown under red and blue LED lights. This plant experiment studies the effects of different types of lighting on plants such as radishes and leaf lettuce. (Photo: NASA/ Frank Ochoa-Gonzales)
Gioia Massa, a NASA Postdoctoral Fellow in the Surface Systems group of Kennedy’s Engineering Directorate who works on this AES habitation-related project, said they looked at the responses of a red leaf lettuce called “Outredgeous” and radish plants to different light sources including broad spectrum fluorescent lighting and solid state red and blue LED lighting. LED lights, because of their durability and long life, are considered to be ideal for space missions where resupply of things from Earth is limited.”

According to Dr. Ray Wheeler, lead for advanced life support activities in the Engineering Directorate, using LED lights to grow plants was an idea that originated with NASA as far back as the late 1980s. Some of the first NASA-funded tests were done at the University of Wisconsin and at Kennedy using wheat and just red LEDs. Wheeler said the wheat plants were very leggy and almost bleached out.

Because blue LEDs weren’t very good back then, using blue fluorescent lights helped correct those problems, Wheeler explained, adding that today’s LEDs have much better efficiency.

Dr. Matthew Mickens (left), a plant biologist from North Carolina Agriculture and Technical State University, measures Cherry Bomb Hybrid II radish plants harvested from a plant growth chamber inside the Space Life Sciences Laboratory at NASA's Kennedy Space Center. (Photo: NASA/Frank Ochoa- Gonzales)
Dr. Matthew Mickens, a graduate of North Carolina Agricultural and Technical State University and recipient of the NASA-sponsored Harriett G. Jenkins Predoctoral Fellowship, followed the plants’ growth during his tenure at the center. During a recent harvest of the plants, Mickens measured the plants’ shoot length, the shoot diameter, total fresh mass or the weight of the plants at time of harvest, total dry mass of the edible plant matter accumulated during the growth cycle, and the leaf area index. He also used a chlorophyll meter to measure chlorophyll content. Then Mickens flash-froze some of the plants in liquid nitrogen and ground them to a powder in order to perform a new test, an adenosine triphosphate analysis, which measures stored energy in the plant tissue. One of the objectives of the study was to understand the effects of green light on plant growth.

For the test, Mickens compared the growth responses of the lettuce and radishes grown under a treatment of red and blue LEDs, and a treatment of broad spectrum white fluorescent lamps with green light present. What he discovered was that there were considerable physiological differences between the two treatments. According to Mickens, results showed darker red color under the red and blue LEDs, which indicates a higher concentration of anthocyanin, a powerful antioxidant that can combat some of the effects of cosmic radiation. Additional replications of the crop cycles are currently ongoing to further confirm these observations.

According to Mickens, even subtle changes in light quality can potentially increase antioxidant properties of crops such as lettuce. The nutritional quality of the vegetables meant to feed astronaut explorers can be controlled by proper selection of the lighting used to grow these crops during long range space missions beyond low Earth orbit. According to Wheeler, there is evidence that supports fresh foods, such as tomatoes, blueberries and red lettuce, are a good source of antioxidants.

Red leaf lettuce plants were also harvested from a plant growth chamber grown under red and blue LED lights. The plant experiment at Kennedy is part of the Advanced Exploration Systems, or AES, program in NASA’s Human Exploration and Operations Mission Directorate. (Photo: NASA/Frank Ochoa-Gonzales)
As the researchers learn more about different light sources, they will be better equipped to configure them to more efficiently grow plants that will produce food for the crew, recycle the atmosphere and help to recycle water. The goal, ultimately, is to develop closed-loop bioregenerative technologies that are self-sustaining.

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