Search Results

Porous plate dehumidifiers (PPD) and porous tube nutrient delivery systems (PTNDS) are designed to provide a means for accurate environmental control, and also allow for two-phase flow separation in microgravity through surface tension. The technological challenges associated with these systems arise from the requirement to accurately measure and control the very small pressures that typically occur within and across the porous media. On-orbit automated priming or filling of the system in the absence of gravity may be necessary. Several porous plate dehumidifiers and porous tube nutrient delivery systems have been tested and evaluated, and experimental results for engineering design are presented.

Accurate root zone moisture control in microgravity plant growth systems is problematic. With gravity, excess water drains along a vertical gradient, and water recovery is easily accomplished. In microgravity, the distribution of water is less predictable and can easily lead to flooding, as well as anoxia. Microgravity water delivery systems range from solidified agar, water-saturated foams, soils and hydroponics soil surrogates including matrix-free porous tube delivery systems. Surface tension and wetting along the root substrate provides the means for adequate and uniform water distribution. Reliable active soil moisture sensors for an automated microgravity water delivery system currently do not exist. Surrogate parameters such as water delivery pressure have been less successful.

Spaceflight plant growth chambers require an atmosphere control system to maintain adequate levels of carbon dioxide and oxygen, as well as to limit trace gas components, for optimum or reproducible scientific performance. Recent atmosphere control anomalies of a spaceflight plant chamber, resulting in unstable CO2 control, have been analyzed. An activated carbon filter, designed to absorb trace gas contaminants, has proven detrimental to the atmosphere control system due to its large buffer capacity for CO2. The latest plant chamber redesign addresses the control anomalies and introduces a new approach to atmosphere control (low leakage rate chamber, regenerative control of CO2, O2, and ethylene).