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The demand for highly flexible manipulation of plant growth generations, modification of specific plant processes, and genetically engineered crop varieties in a controlled environment has led to the development of a Commercial Plant Biotechnology Facility (CPBF). The CPBF is a quad-middeck locker playload to be mounted in the EXPRESS Rack that will be installed in the International Space Station (ISS). The CPBF integrates proven ASTROCULTURE” technologies, state-of-the-art control software, and fault tolerance and recovery technologies together to increase overall system efficiency, reliability, robustness, flexibility, and user friendliness. The CPBF provides a large plant growing volume for the support of commercial plant biotechnology studies and/or applications for long time plant research in a reduced gravity environment.

Maintaining thermal balance in a space-based plant chamber has proven to be difficult to achieve, particularly if the air temperature in the plant chamber is desired to be below that of the atmosphere of the space vehicle. Analysis of the thermal condition of a plant chamber has identified three heat sources as major contributions to this serious problem. The first is the input of radiant energy into the chamber required to support plant growth. The second is via thermal conduction through the chamber walls. The last major thermal input is from the fans and other electronic components embedded inside the chamber. Design solutions to achieve thermal balance are further exacerbated by virtue of the limited power availability, volume and mass restrictions, and safety considerations.

The ASTROCULTURE™-1 (ASC-1) flight experiment, flown on STS-50 as part of the U.S. Microgravity Laboratory-1 mission, June 25 to July 9, 1992, successfully demonstrated the ability of the WCSAR porous tube nutrient delivery system (PTNDS) to control water movement through a particulate rooting matrix in microgravity. One critical aspect of this demonstration was to maintain the fluid circulating through the porous tubes at a slight negative pressure. Control of the fluid loop pressure allows regulation of the amount of water maintained in the rooting matrix while preventing free water from escaping the root zone in microgravity. Pressure control in the ASC-1 flight unit was achieved by using a digital microcomputer and a proportional-plus-integral-plus-derivative control algorithm to manipulate flow restrictors and pump speeds in response to changes in fluid pressure.

A system was developed which provides nutrients and water to plants while maintaining good aeration at the roots and preventing water from escaping in reduced gravity. The nutrient solution is circulated through porous tubes under negative pressure and moves through the tube wall via capillary forces into the rooting matrix, establishing a non-saturated condition in the root zone. Tests using prototypes of the porous tube water and nutrient delivery system indicate that plant productivity in this system is equivalent to standard soil and solution culture growing procedures. The system has functioned successfully in short-term microgravity during parabolic flight tests and will be flown on the space shuttle. Plants are one of the components of a bioregenerative life support system required for long duration space missions.