If you've ever moved from a southern sunbelt state to a northern clime, you know what it's like not to be able to get tree-ripened citrus fruit in season. Or perhaps you long for a juicy, flavorful summer tomato fresh off the vine when you're faced with its pale hothouse cousin in winter. But imagine having difficulty getting any kind of fresh fruit or vegetable for months at a stretch. Astronauts living aboard the International Space Station (ISS) can look out and see Earth far away, but they can only yearn for its Sun-ripened produce. And astronauts who eventually travel on long-duration missions will not have even a distant view of Earth to connect them with the gardens back home. Fresh fruits and vegetables are the mainstay of a healthful diet and a delicious connection to Earth, but providing them to astronauts is no easy task.
Enter NASA Principal Investigator (PI) Gary Stutte. Stutte, supervisor for the plant research group of Dynamac Corporation, a life sciences contractor at Kennedy Space Center in Cape Canaveral, Florida, is researching plant growth in microgravity. He uses a plant growth facility known as the Biomass Production System (BPS), which allows plants to be grown with controlled temperature, light, humidity, carbon dioxide concentration, moisture, and nutrient delivery. The modular design of the BPS offers easy access to the growing plants for accurate assessment of their growth and functions, data and video acquisition, and a control system for integrating all diagnostics. Ultimately the BPS will lead to a larger facility for studying plant growth in space, aiding critical life support systems and allowing astronauts to enjoy some greenery in orbit or beyond. From PASTA to PESTO
Above: Expedition 4 Flight Engineer Daniel Bursch, hovering in microgravity in front of the control panel for the Biomass Production System (BPS), was instrumental in the successful completion of Principal Investigator (PI) Gary Stutte's Photosynthesis Experiment Systems Testing and Operations (PESTO) experiment aboard the ISS. Bursch was responsible for collecting samples, pollinating the dwarf wheat plants, taking photographs of their growth, and performing routine care and maintenance of both plants and hardware.
Clean air (especially fresh oxygen), pure water, and fresh food are critical for human life, and plants produce all three through their normal functions. Stutte's plant growth experiment — Photosynthesis and Assimilation System Testing and Analysis (PASTA) — was originally planned for the space shuttle but was redesigned for the ISS. "The PASTA experiment was designed to look at the effects of microgravity on the growth, photosynthesis, and reproduction of wheat," Stutte explains. "We wanted to see if we could use plants as part of a bioregenerative life support system." In other words, Stutte wanted to see if the photosynthesis could take the carbon dioxide exhaled by humans and produce oxygen. He also wanted to study the efficacy of using plant transpiration (the process of taking water in through the roots and releasing it to the atmosphere from the leaves) to purify water. Finally, he wanted to correlate the yield of the wheat plants (the amount of grain they produced) with the conditions under which they were grown.
In particular, Stutte wanted to test how microgravity affected all three plant processes. If microgravity were shown to have a negative effect on photosynthesis, transpiration, and yield, NASA would have to rethink the scale and design of advanced life support systems for long-duration spaceflight or space settlements.
"As the space station began to develop," says Stutte, "I was asked if I could adapt the PASTA experiment to a long-duration mission. Thus, the PESTO experiment was born — Photosynthesis Experiment Systems Testing and Operations." Despite the change in name and venue, the experiment's goals remained the same: measuring the effects of microgravity on fundamental life support processes at both the whole-canopy level (the green parts of the plant) and the cellular and genetic levels. PESTO was flown to the ISS in April 2002 and returned to Earth in June 2002.
Going With the Grain
The first plant Stutte selected to be grown in the BPS was dwarf wheat. Stutte chose wheat for several reasons. Dwarf varieties of the same type as those grown on the space shuttle and on the Russian space station, Mir, were readily available. Wheat germinates quickly, grows fast, and has large leaves, which gave the researchers enough leaf area in a short time to measure photosynthesis and transpiration. Also, a significant body of literature exists on ground-based advanced life support systems with wheat, so the research team could compare its spaceflight and ground control data with existing large-scale research data. Additionally, wheat is a staple crop. It is versatile and easily incorporated into a diet in products such as pasta or bread, uses that will become more important as astronauts venture beyond low Earth orbit.
Right: Dwarf wheat plants thrived in the growth chamber of the BPS. The BPS allows plants to be grown with controlled temperature, light, humidity, carbon dioxide concentration, moisture, and nutrient delivery. The growth chambers can be removed from the BPS to allow crewmembers access to the plants.
PESTO's primary objective was to see how well wheat grew under a range of environmental conditions. Inside the BPS, researchers changed carbon dioxide levels, humidity, temperature, light intensities, and other environmental variables to explore optimal ranges and to see how plant growth parameters were affected by exposure to suboptimal conditions. For example, by sharply increasing the concentration of carbon dioxide, they could simulate the presence of additional people aboard a craft and could measure its effect on the wheat's oxygen production.
Growth and Validation
The wheat research isn't solely about plant growth; it is also about validating the prototype BPS hardware, according to Orlando Santos, scientific research coordinator for the Fundamental Space Biology Office at Ames Research Center, Moffett Field, California.
"Designing this kind of hardware takes a multistage approach," says Santos. "We learn from what's been done in the past." He says, "The BPS incorporated a lot of new ideas" from previous ground-based and flight research. For example, the BPS includes an ethylene scrubber, a chemical means of removing ethylene (a volatile plant hormone) from the atmosphere. Although plants naturally produce ethylene as a by-product of growth, it is toxic to them in high concentrations. The decision to add the scrubber to the BPS was based on experimental results from growth chambers without a means for purifying the atmosphere.
According to Santos, the BPS is designed to enable plants to produce seeds. Thus, the growth chambers are tall enough to accommodate adult plants so multigenerational growth can be observed. Crewmembers, however, are responsible for pollinating the plants, a function normally performed by insects on Earth. "The next unit we're building, which is in the design phase and is tentatively called the Plant Research Unit, will build on [what we learn from] the BPS unit," Santos says.
A Good Harvest
Credit: Gary Stutte
Stutte and Santos report that the BPS performed up to all expectations. The plants grown aboard the ISS last year have returned to Earth, and results so far look promising — precisely because they vary so little from the ground-based controls. The dwarf wheat plants grown on the ISS had the same photosynthesis rates as those grown on Earth. The plants also responded the same as Earth-grown plants to variations in ambient carbon dioxide levels, light intensity, and amount of water — very good news for any plans to use green plants as part of an environmental control system on spacecraft.
Above: NASA PI Gary Stutte (left) and Bill McLamb monitor the PESTO experiment during its 73-day mission aboard the ISS.
But not everything was identical; subtle differences were observed. For example, plants grown in orbit were taller than their Earth counterparts. Stutte also noted changes in the efficiency of the plants' chloroplasts (chlorophyll-containing cells) — meaning that microgravity had perceptible effects at the cellular level. Now Stutte is examining genetic data to see if corresponding changes can be identified at the genetic level.
Given the results he's obtained so far, Stutte is optimistic about the prospects for plants in space. His BPS research, combined with others' research on the dwarfing of salad crops, could lead to a space version of a fresh salad bar — with the same salad plants performing extra duty as air cleaners and water purifiers.
An unanticipated but perhaps not surprising extra result was the effect of the dwarf wheat experiment on the astronauts' psychological well-being. "It's amazing how much the astronauts enjoyed working with the BPS," Santos observes. "They used it many hours above the scheduled crew time because they simply enjoyed looking at the plants." The green growing shoots provided a little piece of home in an otherwise somewhat sterile environment.
Knowledge of plant growth and photosynthesis requirements gained in space is also relevant to controlled-environment agriculture on Earth, such as that in greenhouses, the cut-flower industry, and hydroponics (growing plants in a soil-free environment using a nutrient solution and an inert medium for plant support). Moreover, the research is highly interesting for researchers studying the use of plants to control the environment in office buildings. " [Using plants] becomes a piece of a larger effort of understanding the ecosystem a little better," says Stutte. "We have collaborated with the Canadian Space Agency and the University of Guelph in Ontario, Canada, which together have a very active biological atmospheric regeneration program. They're moving into various office buildings throughout Canada and then into the United States."
Knowledge gained from the development of growth media and water delivery systems for plants in space might even be useful in further development of subirrigation systems, water-conservation techniques for arid and semi-arid agriculture conditions that direct moisture underground where roots need it rather than spraying it on top of the ground where much evaporates before crops can use it.
"In the BPS, we optimized the conditions to maximize productivity while using the least power and volume. Lessons we've learned are directly applicable to the controlled-environment and agriculture industries. And that efficiency relates to income," Stutte concludes. "This technology can be adapted to conserving water, minimizing waste, and stretching resources between competing urban and agricultural interests."
That's a lot of progress for a little salad.
|More information on Stutte's research -- From OBPR's Research on Station Site.|