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Growing plants in space: controlled environment technologies.

There is "growing interest" in utilizing space for the development of plant materials, not only to support long-term human space exploration but to produce advanced commercial products on earth as well. Conduct of research to assess the impact of the space environment on plant development requires an enclosed, environmentally controlled plant growth chamber that provides the level of environmental conditions normally available in terrestrial research facilities. However, operational constraints of a space vehicle including limited resources of volume, power, mass, and crew time, have greatly hindered application of terrestrial research facilities for use in space. In addition, plants are sensitive to atmospheric contaminants that may significantly alter development. Thus, growing plants in an enclosed environment to isolate chamber atmosphere from the space vehicle atmosphere is highly desirable.

Since 1990, the Wisconsin Center for Space Automation and Robotics (WCSAR) at the University of Wisconsin-Madison has developed a series of technologies and plant growth chambers. These technologies and chambers have been tested and validated 10 times on the space shuttle, once on Russia's MIR Station, and three times on the International Space Station.

WCSAR's plant growth chambers include the Astroculture[TM]. It provides controlled parameters of temperature, relative humidity, light intensity and schedule, fluid nutrient delivery, carbon dioxide (C[O.sub.2]), and ethylene ([C.sub.2][H.sub.4]). State-of-the-art control software combined with fault tolerance and recovery algorithm increases overall system robustness and efficiency. Tele-science features allow engineers and scientists to remotely monitor, diagnose, and reconfigure an on-going experiment.

Temperature and humidity are controlled using the WCSAR-patented Astropore[TM] system, which integrates temperature control, humidification, dehumidification, and condensation recovery into one unit. Temperature control is achieved by cooling or heating a heat sink using the thermal electric coolers, which corresponds to extracting or injecting the thermal energy into the chamber. Humidity control is achieved by using the hydrophilic membrane to transfer water. The surface temperature of the membrane is controlled such that if the temperature is lower than the dew point of the chamber air, condensation will be formed on the membrane surface and the air will be dehumidified. If the membrane surface temperature is higher than the dew point, water will evaporate from the wetted membrane surface and air will be humidified.

Light emitting diodes (LEDs) are used to provide photons in the red and blue regions of the spectrum. Monolithic LED chips are mounted on the surface of a heat sink, which dissipates the heat generated by the LEDs. The high-output red LEDs have emissions in a range of 600 to 700 nanometers wavelengths with a peak of 670 nanometers, which coincides with the red absorption peak of chlorophyll. The high-output blue LEDs have emissions in a range of 400 to 500 nanometers wavelengths with a peak of 470 nanometers, which provides a photon level exceeding levels necessary to meet photomorphogenic requirements. The intensity of red and blue LEDs are controlled by adjusting the desired current delivered to the LED current drivers.

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Fluid nutrient delivery is accomplished through porous tubes buried in the solid substrate growth media or the rooting material. Fluid is confined within the porous tubes with a slightly negative pressure such that water is supplied to plants by capillary transfer through the pores into the rooting material. The moisture level in the rooting material is manipulated by regulating pressure of water inside the porous tube. When there is inadequate moisture in the rooting material, a pressure difference due to capillary action causes net water transfer from inside to outside the tube, which is absorbed by the rooting material. When there is an excess of moisture, water is drawn into the porous tube by the same capillary action.

Removal of ethylene is accomplished by using WCSAR-developed scrubber technology, which uses the titanium dioxide (Ti[O.sub.2]) coated thin-film as photocatalyst. When operating in the presence of ultraviolet irradiation, the catalyst exhibits significant increases in the photo-oxidization rate. The UV wavelengths involved are between 300 to 400 nanometers and will not produce any significant amount of ozone. The scrubber is most effective against unsaturated hydrocarbons, but may be effective against saturated or cyclic hydrocarbons. The scrubber fully oxidizes the hydrocarbons to C[O.sub.2] and water. The active material, Ti[O.sub.2], is not consumed during the oxidization process because it is a catalyst.

Weijia Zhou is director of the Wisconsin Center for Space Automation and Robotics, University of Wisconsin-Madison, 545 Science Drive, Madison WI 53711 USA; 608-262-5526, fax 608-262-9458, wzhou@engr.wisc.edu.
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Author:Zhou, Weijia
Publication:Resource: Engineering & Technology for a Sustainable World
Date:Mar 1, 2004
Words:752
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