Options for Transpiration Water Removal in a Crop Growth System Under Zero Gravity Conditions

The operation of a crop growth system in micro-gravity is an important part of the National Aeronautics and Space Administration's Closed Ecological Life Support System development program. Maintaining densely arrayed plants in a closed environment imposed to induce high growth rates must be expected to result in substantial levels of water transpiration rate. Since the environmental air is recirculated, the transpiration water must be removed. In an operating CELSS, it is expected that this water will provide potable water for use of the crew. There is already considerable knowledge about water removal from crew environmental air during orbital and transfer activities, and the difference between the conditions of the described requirement and the conditions for which experience has been gained is the quantities involved and the reliability implications due to the required periods of operation. A simplified statement of this specific problem is: “Given a flow-stream of air containing water vapor in a zero gravity field, what system can this flow-stream be passed through to produce only an air flow-stream which contains a prescribed lesser water vapor content and confined liquid water having no gas/vapor spaces?” In this paper, we describe some of the available processes which can accomplish the steps required to achieve the objective, and look at some of the energy considerations.