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Environmentally sealed or isolated life sciences experiments such as plant growth chambers or animal habitats often require active temperature and humidity control. The interaction between the temperature and humidity control system, and performance limitations are shown based on experimental data using a small spaceflight plant growth chamber. Limited availability of electric power, and the chosen control system implementation constrain the obtainable temperature and humidity setpoint combinations.

Small spaceflight life science experiments, such as plant growth chambers and animal habitats, operate in unique environments. The experiments are often sealed systems that control atmospheric constituents, temperature, and humidity. Chemical scrubbers can be an efficient and reliable way to actively remove carbon dioxide for shorter experiment durations because they do not require power or complex technologies to operate. Several commercially available scrubbers were tested in both low and high humidity environments, and at low concentration levels of carbon dioxide similar to those found in plant chamber applications, to find a scrubber that was both effective and efficient for use in small life sciences experiments.

BioServe Space Technologies has developed and flown a series of miniature habitats to house several different biological specimens and one biochemical experiment. This effort was in support of an educational program, Space Technology and Research Students (STARS), developed by SPACEHAB Inc. The STARS program gives students from around the world a chance to design and conduct their own spaceflight experiments. STARS-Bootes, the payload flown on STS-107, housed a Japanese Medaka fish experiment; a Chinese silkworm experiment; an American Harvester ant experiment; a Carpenter bee experiment from Liechtenstein, an Australian Orb Weaver spider experiment; and a biochemical crystal growth experiment from Israel. Each habitat was custom designed to suit each specimen's individual needs. The habitats provided passive humidity control, lighting, feeding areas, and containment as well as an artificial environment for the specimens to be observed in.

PGBA, a 0.08m2 / 27 liter spaceflight plant chamber payload employs two temperature-controlled liquid coolant loops to control the temperature and humidity of the sealed plant chamber independently. Cabin-air cooled thermoelectric heat pumps control the temperature of the water-alcohol coolant fluid in each loop, which is circulated by small, low-power, magnetically-coupled positive displacement gear pumps, designed to meet NASA safety requirements. Pulse-width-modulated DC current control circuits, controlled by two PI software controllers, maintain temperature and humidity accurately. The coolant loops feature bellows-based expansion vessels to accommodate thermal expansion and pressure fluctuations. Pressure sensors monitor the proper function and performance of the system. Pressure decay tests and unique fill procedures should ensure leak and air bubble-free operation.

Engineers and scientists from BioServe Space Technologies and Kennedy Space Center (KSC) are developing a flight-rated payload for the evaluation of two space-based plant nutrient delivery systems (NDS's). The hardware is comprised of BioServe's Plant Generic Bioprocessing Apparatus (PGBA) and KSC's Porous Tube Insert Module (PTIM). The PGBA, a double-middeck locker, will serve as the host carrier for the PTIM and will provide computer control of temperature, relative humidity, and carbon dioxide levels. The PTIM will insert into the PGBA's growth chamber and will facilitate the side-by-side comparison of the two NDS's: 1) the porous tube NDS, consisting of six porous tubes with seeds mounted in close proximity to the tubes, and 2) a substrate-based NDS, with three compartments each containing a porous tube embedded in a particulate substrate.

A microgravity dehumidification system for plant growth experiments requires the generation of no free-liquid condensate and the recovery of water for reuse. In membrane dehumidification, the membrane is a barrier between the humid air phase and a liquid coolant water. The coolant water temperature combined with a trans-membrane pressure differential establishes a water flux from the humid air into the coolant water. Building on the work of others, we directly compared hydrophilic and hydrophobic membranes for humidity control. Hydrophobic membranes did not meet the required operational parameters. In a direct comparison of the hydrophilic membranes, cellulose ester membranes were superior to metal and ceramic membranes in the categories of condensation flux per surface area, ease of start-up and stability. However, cellulose ester membranes were inferior to metal membranes in one significant category, longevity/durability.