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The NASA Johnson Space Center has plans to integrate a Solid Amine Water Desorbed (SAWD II) carbon dioxide removal subsystem into the Variable Pressure Growth Chamber (VPGC). The SAWD II subsystem will be used to remove any excess carbon dioxide (CO2) input into the VPGC which is not assimilated by the plants growing in the chamber. An analysis of the integrated VPGC-SAWD II system was performed using a mathematical model of the system implemented in the Computer-Aided System Engineering and Analysis (CASE/A) package. The analysis consisted of an evaluation of the SAWD II subsystem configuration within the VPGC, the planned operations for the subsystem, and the overall performance of the subsystem and other VPGC subsystems. Based on the model runs, recommendations were made concerning the SAWD II subsystem configuration and operations, and the chambers' automatic CO2 injection control subsystem.

The design and operation of hybrid physical/chemical and biological life support systems for space application is a complex and difficult process. This paper describes the approach and results of an effort to characterize wheat growth, under various environmental conditions, at the Johnson Space Center's (JSC) Ambient Pressure Growth Chamber (APGC). Using a designed experiment, a test plan was developed for varying environmental parameters during a wheat growth experiment. The test plan was developed using a Central Composite approach to experimental design. As a result of the experimental runs, an empirical model of both the transpiration process and carbon dioxide assimilation for wheat growth over specified ranges of environmental parameters has been developed. The environmental parameters include carbon dioxide concentration, ambient chamber temperature, vapor pressure deficit, and air velocity.

The development of regenerative life support systems (RLSS) to support long duration manned space exploration is of great importance. To design future chambers effectively, it is necessary to model both chamber performance and plant growth in current systems. The Johnson Space Center RLSS test bed, which consists of the Variable Pressure Growth Chamber (VPGC) and the Ambient Pressure Growth Chamber (APGC), is a facility that is being used to investigate plant growth and support hardware integration. Detailed and simplified models of the VPGC and APGC have been developed to investigate system performance and response to changes in loading as well as to study long-term plant growth under varying environmental conditions, including temperature, light level, CO2 level, dew point or relative humidity, and photoperiod. To support these studies, models of two crops, lettuce and wheat, have also been developed and integrated into the detailed and simplified simulations of each chamber.

This paper describes the approach and results of an effort to characterize plant growth under various environmental conditions at the Johnson Space Center variable pressure growth chamber. Using a field of applied mathematics and statistics known as design of experiments (DOE), we developed a test plan for varying environmental parameters during a lettuce growth experiment. The test plan was developed using a Box-Behnken approach to DOE. As a result of the experimental runs, we have developed empirical models of both the transpiration process and carbon dioxide assimilation for Waldman's Green lettuce over specified ranges of environmental parameters including carbon dioxide concentration, light intensity, dew-point temperature, and air velocity. This model also predicts transpiration and carbon dioxide assimilation for different ages of the plant canopy.

A computer simulation of the variable pressure growth chamber (VPGC) located at the NASA Johnson Space Center (JSC) has been developed using an expanded version of the Computer-Aided Systems Engineering and Analysis (CASE/A) simulation package. The VPGC is a pressure chamber that has been outfitted to support the growth of approximately 10.6 m2 of plants in an enclosed environment of approximately 27 m3 (Reference 1). CASE/A is a physical/chemical system-level simulation package originally developed to model the life support systems of Space Station Freedom. The expanded version of CASE/A extends the simulation package by including biological components, primarily plant growth algorithms. The configuration, modeling methods and verification of the CASE/A Variable Pressure Growth Chamber model are described. Performance estimates generated from the model are compared to data from recent lettuce growth experiments in the VPGC.

The use of bioregenerative components in a long-term mission closed ecological life support system (CELSS) will help lower mission costs by reducing the need for expensive resupply for oxygen, water, and food. By growing plants on a lunar base, we may be able to provide significant amounts of food and potable water while revitalizing the air supply. By processing solid wastes, we can supply growing plants with additional carbon dioxide and water. Recently, we added the capability of modeling plant growth and waste processing to the Computer-Aided System Engineering and Analysis (CASE/A) environmental control and life support system (ECLSS) modeling package. The objective of this study was to determine if a plant growth unit, embedded within a CELSS lunar base design, including a physical-chemical waste processing unit and crew, would be sufficient to handle system air revitalization requirements.