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The Biomass Production System, recently flown on the ISS for 73 days, demonstrated significant advancements in functional performance over previous systems for conducting plant science in microgravity. The Biomass Production System (BPS) was the first flight of a system with multiple, independently controlled, plant growth chambers. Each of four chambers was controlled separately with respect to temperature, humidity, light level, nutrient level, and CO2, and all were housed in a double Middeck locker-sized payload. During the mission, each of the subsystems performed within specification. This paper focuses on how the performance of the BPS hardware allowed successful completion of the preflight objectives.

The Plant Research Unit (PRU) is the Space Station Biological Research Program plant growth facility being developed for the International Space Station. The plant habitat is designed for experiments in near-zero gravity or it can be rotated by the ISS Centrifuge for experiments at any gravity level from microgravity to twice Earth's gravity. Plant experimentation will be possible in multiple Plant Research Units at one time, isolating the effect of gravity on the biological specimens. The PRU will provide and control all aspects of a plant's needs in a nearly closed system. In other words, the shoot and root environments will not be open to the astronaut's environment except for experiment maintenance such as planting, harvesting and plant sampling. This also means that all lighting, temperature and humidity control, nutrient delivery, and air filtering and cleaning must be done in a very small volume, with very little mass and power usage and with minimal crew time.

The Advanced Animal Habitat (AAH) represents the next generation of Space Station based animal research facilities. Building upon previously developed flight hardware and experience, the AAH offers greatly enhanced system capabilities and performance. The design focuses upon the creation of a robust and flexible platform capable of supporting present and future experimental needs. A modular packaging and distributed control architecture leads to increased system adaptability and expandability. The baseline configuration includes group housing capability for up to six rats with automated food and water delivery as well as waste collection. Animals are continuously monitored with three cameras during both day and night cycles. The animals can be accessed while on-orbit through the Life Sciences Glovebox to perform a wide variety of experimental protocols.

The CANDS (Circulating, Aeration, and Nutrient Delivery System) Phase II SBIR is currently developing and testing methods and procedures to control moisture, oxygen, and temperature in the root zone of a particulate based micro-gravity nutrient delivery system. The completion of the first year and a half of the CANDS Phase II SBIR has shown significant engineering developments towards environmental control of the root zone. These developments include the measurement of root zone oxygen content, characterization of forced and flood-ebb aeration rates, successful control of root zone moisture using miniature heat-pulse moisture sensors, and successful control of root zone temperature via an insulating/temperature controlling water jacket. At the conclusion of the CANDS Phase II SBIR an integrated root zone environmental control system will be constructed for integration into plant growth systems to eliminate the uncertainties that exist in current plant growth data.

Unique challenges arise during the design of temperature and humidity control systems (THCS) for use in microgravity. The design of the Plant Research Unit’s (PRU) THCS builds on the experience gained during the Biomass Production System (BPS) project and extends the understanding of the critical design variables and necessary technical advancements to allow for longer on-orbit operation. Previous systems have been limited by loss of prime, clogging in the porous plates and component reliability. Design of THCSs for long-duration space flight experiments requires the mitigation of these issues as well as a complete understanding of the relevant design variables. In addition to the normal design variables (e.g. mass, power, volume), a complex and interdependent relationship exists between the THCS variables including operational temperature range, operational humidity range, required humidity condensation rate and system air flow.

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. INTRODUCTION