Robert C. Morrow

Evaluation of light emitting diode characteristics for a space-based plant irradiation source.

Light emitting diodes (LEDs) are a promising irradiation source for plant growth in space. Improved semiconductor technology has yielded LED devices fabricated with gallium aluminum arsenide (GaAlAs) chips which have a high efficiency for converting electrical energy to photosynthetically active radiation. Specific GaAlAs LEDs are available that emit radiation with a peak wavelength near the spectral peak of maximum quantum action for photosynthesis. The electrical conversion efficiency of installed systems (micromole s-1 of photosynthetic photons per watt) of high output LEDs can be within 10% of that for high pressure sodium lamps. Output of individual LEDs were found to vary by as much as 55% from the average of the lot. LED ratings, in mcd (luminous intensity per solid angle), were found to be proportional to total photon output only for devices with the same dispersion angle and spectral peak. Increasing current through the LED increased output but also increased temperature with a consequent decrease in electrical conversion efficiency. A photosynthetic photon flux as high as 900 micromoles m-2 s-1 has been produced on surfaces using arrays with LEDs mounted 7.6 mm apart, operating as a current of 50 mA device-1 and at an installed density of approximately 17,200 lamps m-2 of irradiated area. Advantages of LEDs over other electric light sources for use in space systems include long life, minimal mass and volume and being a solid state device.

Astroculture™ root metabolism and cytochemical analysis

Physiology of the root system is dependent upon oxygen availability and tissue respiration. During hypoxia nutrient and water acquisition may be inhibited, thus affecting the overall biochemical and physiological status of the plant. For the Astroculture (TM) plant growth hardware, the availability of oxygen in the root zone was measured by examining the changes in alcohol dehydrogenase (ADH) activity within the root tissue. ADH activity is a sensitive biochemical indicator of hypoxic conditions in plants and was measured in both spaceflight and control roots. In addition to the biochemical enzyme assays, localization of ADH in the root tissue was examined cytochemically. The results of these analyses showed that ADH activity increased significantly as a result of spaceflight exposure. Enzyme activity increased 248% to 304% in dwarf wheat when compared with the ground controls and Brassica showed increases between 334% and 579% when compared with day zero controls. Cytochemical staining revealed no differences in ADH tissue localization in any of the dwarf wheat treatments. These results show the importance of considering root system oxygenation in designing and building nutrient delivery hardware for spaceflight plant cultivation and confirm previous reports of an ADH response associated with spaceflight exposure.

Commercial involvement in the development of space-based plant growing technology

Considerable technological progress has been made in the development of controlled environment facilities for plant growth. Although not all of the technology used for terrestrial facilities is applicable to space-based plant growth facilities, the information resident in the commercial organizations that market these facilities can provide a significant resource for the development of the plant growing component of a CELSS. In 1985, NASA initiated an effort termed the Centers for the Commercial Development of Space (CCDS). This program endeavors to develop cooperative research and technology development programs with industrial companies that capitalize on the strengths of industry-university working relationships. One of the these CCDSs, the Wisconsin Center for Space Automation and Robotics (WCSAR), deals with developing automated plant growth facilities for space, in cooperation with several industrial partners. Concepts have been developed with industrial partners for the irradiation, water and nutrient delivery, nutrient composition control and automation and robotics subsystems of plant growing units. Space flight experiments are planned for validation of the concepts in a space environment.

Utilization of white potatoes in CELSS.

Potatoes (Solanum tuberosum) have a strong potential as a useful crop species in a functioning CELSS. The cultivar Denali has produced 37.5 g m-2 d-1 when grown for 132 days with the first 40 days under a 12-h photoperiod and a light:dark temperature cycle of 20 degrees C:16 degrees C, and then 92 days under continuous irradiance and a temperature of 16 degrees C. Irradiance was at 725 micromoles m-2 s-1 PPF and carbon dioxide at 1000 micromoles mol-1. The dried tubers had 82% carbohydrates, 9% protein and 0.6% fat. Other studies have shown that carbon dioxide supplementation (1000 micromoles mol-1) is of significant benefit under 12-h irradiance but less benefit under 24 h irradiance. Irradiance cycles of 60 minutes light and 30 minutes dark caused a reduction of more than 50% in tuber weight compared to cycles of 16 h light and 8 h dark. A diurnal temperature change of 22 degrees C for the 12-h light period to 14 degrees C during the 12-h dark period gave increased yields of 30% and 10% for two separate cultivars, compared with plants grown under a constant 18 degrees C temperature. Cultivar screening under continuous irradiance and elevated temperatures (28 degrees C) for 8 weeks of growth indicated that the cvs Haig, Denali, Atlantic, Desiree and Rutt had the best potential for tolerance to these conditions. Harvesting of tubers from plants at weekly intervals, beginning at 8 weeks after planting, did not increase yield over a single final harvest. Spacing of plants on 0.055 centers produced greater yield per m2 than spacing at 0.11 or 0.22 m2. Plants maintained 0.33 meters apart (0.111 m2 per plant) in beds produced the same yields when separated by dividers in the root matrix as when no separation was made.

Biomass Production System (BPS) Technology Validation Test Results

The objective of the BPS Technology Validation Test (TVT) flown on the ISS as part of Increment 4 was to verify the functionality of environmental control subsystems and to measure the ability of the BPS to support plant growth and development in microgravity. Additional TVT objectives included validation of information acquisition systems, operations and support systems, and component performance. All TVT objectives were successfully addressed. Most evaluation criteria stipulated pre-flight were met. When there were deviations from pre-mission requirements, root causes were identified and subsystem configurations modified to eliminate these problems. Results from the TVT have been applied to the Plant Research Unit development to reduce technical risks and increase reliability.

Evolution of Space-Based Plant Growth Systems from Research to Life Support

Plant growth systems for space were first flown in the 1960s. Plant chambers flown from that time until the present were developed to conduct basic plant research in reduced gravity. The use of plants for providing life-support has been tested on the ground, but has never been used on-orbit. With the New Vision for Space Exploration, emphasis has now been placed on implementing the first small steps of a bioregenerative life-support system in the guise of “vegetable production units.” As the duration and size of space missions increase, these early precursors will evolve to larger units that will eventually become the primary source of life support in remote space bases.

Plant Research Unit Lighting System Development

As part of the PRU project a new plant lighting system has been developed. System design focused on light source development, chamber optical performance improvements and electronics optimization. Central to the lighting system performance is a high density LED Light Engine, enabling increased spectral diversity, higher irradiance levels, enhanced uniformity and improved efficiency. Chamber wall surface materials were tested to minimize the vertical irradiance gradient and improve planar uniformity. Total lighting system efficiency was improved through the use of switching converter LED drive circuitry. As an alternative to the LED light source, an advanced planar fluorescent lighting source has also been developed.

VEG-01: Veggie Hardware Validation Testing on the International Space Station

Abstract 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.

The Astroculture (tm)-1 experiment on the USML-1 mission

Permanent human presence in space will require a life support system that minimizes athe need for resupply of consumables from Earth resources. Plants that convert radiant energy to chemical energy via photosynthesis are a key component of a bioregenerative life support system. Providing the proper root environment for plants in reduced gravity is an essential aspect of the development of facilities for growing plants in a space environment. The ASTROCULTURE(TM)-1 experiment, included in the USML-1 mission, successfully demonstrated the ability of the Wisconsin Center for Space Automation and Robotics porous tube water delivery system to control water movement through a rooting matrix in a microgravity environment.

Tomatosphere - Mission to Mars An Educational Outreach Project for Primary and Secondary Schools

The concept for Tomatosphere originated in late 1999 and the project held its first formal meeting on February 7, 2000. The project was formally activated when 200,000 Heinz tomato seeds went into space on November 30, 2000, with Canadian astronaut, Dr. Marc Garneau. The seeds were part of an experiment designed to test the effects of short- term space travel on seed germination and interaction with new techniques designed to enhance germination rates. An equal number of seeds stayed behind on Earth and the two lots, space-flown and Earth-bound, were further subdivided into two treatments using new Infra Red and Red light technology developed at the University of Guelph. The resulting four treatments were packaged and sent to almost 2700 classrooms across Canada, along with posters and a teachers guide matched to the Pan-Canadian Protocol for Collaboration on School Curriculum, a framework of Science Learning Outcomes developed by the Council of Ministers of Education, Canada. The emphasis for the curriculum connections was from grade 3 (plants and soil) to grade six (space). The project met with an overwhelming response from educators and students. As such, in 2003, the project expanded to involve more than 5 000 classrooms across Canada; the scope of the project was also expanded from the original grade 3 - 6 focus to include grades 8 -10. The scope of the curriculum in grades 8 - 10 allows for the incorporation of several objectives relative to the ISS mission objectives, the overall concept of humans in space, and the application of knowledge from space programs to the well-being of humankind on Earth.