STS-60 (Discovery, 03 Feb 94 - 11 Feb 94):

Astroculture™ Temperature/Humidity Control System

The third subsystem of the Astroculture (ASC-GC) hardware to be developed was the temperature/humidity control system (THCS). Air temperature in the plant chamber is maintained via solid state thermoelectric coolers (TECs). While the TECs may either remove heat or provide heat to the plant chamber, in practice they act to remove waste heat coming from the light cap and other sources.

The temperature and humidity control unit was tested in ASC-3 on STS-60.

Relative humidity in the Astroculture plant chamber is maintained via the unique Astropore® subsystem. This system makes use of porous nubs that are filled with water and maintained at a constant, controllable temperature via a separate set of TECs. If the water in the nubs is at a temperature above the dewpoint of the chamber air, humidification occurs; if the temperature is below the dewpoint, dehumidification occurs. To prevent "weeping", the water in the nubs is held under a slightly negative pressure. Thus, any water which condenses on the nub surface during dehumidification is sucked into the nub and sent to a reservoir. While the Astropore® subsystem provides for both humidification and dehumidification, in practice the subsystem is used to remove moisture which has been transpired into the chamber air. The Astropore® methodology is covered under U.S. Patent No. 5,368,786. 

The STS-60 activity demonstrated the effectiveness of the THCS design. Temperature was controlled, even in the absence of natural convection and with a potentially demanding load of reject heat. Relative humidity was closely controlled without the need for bulky condensation equipment or refrigerants.

STS-50 - STS-57 - STS-60 - STS-63 - STS-73 - STS-95 - STS-101 - STS-107  /  STS-89/91 - Inc 2 - Inc 4 - Inc 5