STS-50 (Columbia, 25 Jun 92 - 09 Jul 92):

Astroculture™ Fluid Delivery Development

The first subsystem of the Astroculture (ASC-GC) hardware developed was the equipment to deliver water, or a nutrient solution, to the root tray of the plant growth chamber. The root tray is a flower pot that has a depth of about 2.5 cm and a foot print of 12 cm x 10 cm. A pair of porous metal tubes run down the length, approximately halfway into the depth. The two tubes communicate with each other at one end, forming a U-shape. The other ends connect with the fluid handling system outside of the root tray.

Pilot Kenneth Bowersox works with the Astroculture hardware on board the space shuttle Columbia.

Water is not circulated within the system. Instead, the fluid lines are primed to eliminate any trapped air and then the water is held at a slight negative pressure, to prevent flooding the root tray. Water is brought to the plant roots via capillary action: water moves through the walls of the porous tubes, through the rooting material (a crushed, baked clay), and to the roots. The water loop is closed via transpiration of water from leaf surfaces and into the plant chamber atmosphere. The Astropore® humidity control subsystem then removes enough of the transpired water to maintain a constant relative humidity in the chamber, returning the collected transpired water to the reservoir.