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The Biomass Production System (BPS) is a double middeck locker payload designed to fly on the Orbiter or Space Station. The BPS contains four plant growth chambers (PGCs) with independent control of temperature, humidity, lighting, CO2, and nutrient solution delivery, allowing for multiple experimental treatments. The BPS provides several features to support on-orbit science activities including the ability to downlink system and science data, video cameras with framegrab capability to collect images for recording plant development, access to plants to perform activities such as pollination or tissue sampling, and gas and fluid sampling ports for sampling of the plant environment. Other capabilities include the ability to conduct CO2 drawdowns, allowing photosynthetic measurements, and the ability to meter plant CO2 and water use. Several technology developments have been evaluated for possible implementation during future upgrades to enhance science capabilities.

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.

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 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 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).