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The High Efficiency Solid State Lighting with Integrated Adaptive Control (HELIAC) system was developed to independently detect the presence of green plant tissue and to direct light only to those locations. During testing of the HELIAC system, a major factor interfering with effective tissue detection was reflectance of sensed wavebands from the walls and ceiling causing false positives. Since it is desirable to have reflective surfaces to maintain higher light levels with less power, selective reflection systems that absorb some wavebands but reflected others were tested. A test device was fabricated to measure the reflection of red, green, and blue light from a variety of colored mirrors. It was observed that both pink and purple tinted mirrors reduced the reflection of green wavebands more than red and blue wavebands. This effect could also be obtained by using colored films attached to a silvered mirrored surface.

Based upon the development experience and flight heritage of the Biomass Production System, the Plant Research Unit embodies the next generation in the evolution of on-orbit plant research systems. The design focuses on providing the finest scientific instrument possible, as well as providing a sound platform to support future capabilities and enhancements. Performance advancements, modularity and robustness characterize the design. This new system will provide a field ready, highly reliable research tool.

The PESTO (Photosynthetic Experiment System Testing and Operation) experiment flew in the Biomass Production System (BPS) to International Space Station (ISS) on STS-110 (Atlantis) April 8, 2002, and returned on STS-111 (Endeavour) June 19, 2002, after 73 days in space. The ground control was conducted on a two-week delay at Kennedy Space Center in a BPS unit under environmental conditions comparable to ISS. Wheat (Triticum aestivum cv Apogee) and Brassica rapa cv Astroplant were independently grown in root modules for multiple grow-outs. On-orbit harvests, root modules exchanges and primings, seeds imbibitions, and gas and water samplings occurred at periodic intervals; all were replicated in ground controls. Many operations required crew handling and open access to individual chambers, allowing the exchange of microorganisms between the crew environment and the BPS modules.

The Plant Research Unit development effort will provide a high-performance and highly versatile, controlled environment plant growth chamber for space-based variable gravity science and biotechnology investigations on the International Space Station. Temperature, humidity, atmospheric composition, lighting, and nutrient delivery are the critical parameters to control in an automated and reliable way. Access to plant material on-orbit and maintenance of the unit with minimal crew effort are other major requirements, as is a modular design allowing easy subsystem/technology change-outs so that science capability and maintainability are maximized. The Plant Research Unit (PRU) development program is based on the results of the Biomass Production System (BPS) and many other technical developments, and uses the BPS as a risk mitigation prototype for the PRU.

A soil moisture sensor system consisting of small heat-pulse probes, a microcontroller, and software for data acquisition and signal conditioning was developed for use in space based plant growth units. The microcontroller allows the sensors to be used in a control application with minimum time demands on the control subsystem. A single digital serial link may be shared by up to 16 microcontrollers with 8 sensors each, for a total of 128 sensors. The microcontroller independently applies heat cycles to determine the current moisture level, and responds to a request from the computer with the last known value. Using the microcontroller system, repeatability testing was completed for wet 1–2 mm arcillite. The standard deviation in wet arcillite over a 16-hour period was about 3%. Software filtering can be used to reduce the standard deviation further.

The objective of the Fluid Handling and Maintenance Experiment (FHAME) is to research, test, and demonstrate liquid/gas phase control in fluid handling subsystems in microgravity. FHAME is currently being developed as a risk mitigation experiment for the upcoming verification and science investigations in plant growth systems, especially the Biomass Production System (BPS) and the Plant Research Unit (PRU). Because FHAME contains controlled fluid handling systems, a large suite of sensors, data acquisition, and visual observation capability, it is well suited for empirical research and testing of movement and to assessing the liquid/gas characteristics for a wide variety of applications. Its first application is to assess fluid priming and gas/liquid characteristics in a particulate bed. FHAME can play a major role in the development of future new nutrient delivery systems for plant growth application in addition to many fluid and gas/liquid empirical research investigations.

The ASTROCULTURE™ (ASC) middeck flight experiment series was developed to test subsystems required to grow plants in reduced gravity, with the goal of developing a plant growth unit suitable for conducting quality biological research in microgravity. Previous Space Shuttle flights (STS-50 and STS-57) have successfully demonstrated the ability to control water movement through a particulate rooting matrix in microgravity and the ability of LED lighting systems to provide high levels of irradiance without excessive heat build-up in microgravity. The humidity and temperature control system used in the middeck flight unit is described in this paper. The system controls air flow and provides dehumidification, humidification, and condensate recovery for a plant growth chamber volume of 1450 cm3.

The ASTROCULTURE™ flight unit flown as part of the SPACEHAB-03 mission on STS-63 was a complete plant growth system providing plant lighting, temperature control, humidity control, water and nutrient delivery, a CO2 control system, nutrient control using the NASA Zeoponics system, an ethylene photocatalysis unit, a control and data acquisition system, and plant video. The objective of the ASTROCULTURE™-4 experiment was to continue technological assessment of these environmental control subsystems. Plants were included in this package for the first time. Two plant species were flown, rapid cycling ‘Wisconsin Fast Plants’ (Brassica rapa), and dwarf wheat (Triticum aestivum cv. ‘Super Dwarf’). Growth and development of both plant species on orbit appeared normal and similar to that of plants grown under terrestrial conditions.

The ECLSS (Environmentally Controlled Life Support System) project goals are to identify key requirements and guidelines for a Life Support System (LSS) for surface missions based on the Exploration Spirals, to review the various technology options and candidates to fulfill the life support functionality, and to conduct initial trades and assessments at a high level. With the completion of the first six month phase of the project, ORBITEC has generated and shown that for each Exploration Spiral, different LSS architectures are optimal, but when an entire mission model is considered, hybrid systems become more attractive. Also, we can easily show that future spiral requirements should and will influence the technologies and level of closure for earlier spiral developments to reduce overall development and implementation costs, and to increase commonality across the Constellation systems.

When overhead electric lights are used for plant growth, inefficiency occurs due to inability to accurately target light. Light falls between young plants, but as they grow, shading occurs, requiring more light to achieve acceptable productivity. We have developed an intracanopy light-emitting diode (LED)-based system that can deliver light throughout the foliar canopy of crop stands and keep pace with crop growth. LEDs having narrow red and blue emission wavebands were selected. An array of 16 “Lightsicles” was constructed, each consisting of 20, 2.5 cm2 LED “light engines” containing 80 LEDs mounted along a strip. Measurements of light level and power usage have been taken and plant-growth testing is underway.

In-situ resource utilization (ISRU) is an important part of current mission architectures for both a return to the Moon and the eventual human exploration of Mars. ORBITEC has developed and demonstrated an innovative direct energy processing approach for carbon-reduction of lunar and Martian regolith that can operate in a nearly closed-loop manner. Carbon-reduction of regolith produces oxygen and a variety of other useful products, including silicon, iron and glass ceramic materials. In addition, various ISRU propulsion technologies that utilize lunar and Martian resources have been developed and demonstrated. Work is also being conducted with the USDA on techniques to use biomass and waste materials to manufacture items such as shelters, furniture, filters and paper. Atmospheric carbon dioxide on Mars would be used to support the production of biomass in excess of life support needs to be used as the raw material to manufacture useful products on-site.

The Biomass Production System (BPS) was developed to meet science, biotechnology and commercial plant growth needs in Space. The BPS is a double middeck locker equivalent payload with four internal plant chambers. The chambers can be removed to allow manipulation or sampling of specimens, and are sealed to allow CO2 and water vapor exchange measurements. Each of the growth chambers has independent control of temperature, humidity, lighting, and carbon dioxide levels. Preliminary acceptance and performance testing has demonstrated temperature control within ±1.0°C (between 20°C and 30°C) and humidity control within ±5% (between 60% and 90% RH, depending on ambient temperature and plant load). The fluorescent lighting system provides light levels between 60 and 350 μmol m−2s−1. The CO2 control system controls to the greater of ±50 ppm or ±5% (with plants, as a scrubber is not currently available).

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.