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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.