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As part of the NASA Controlled Ecological Life Support System (CELSS) Program, a CELSS Test Facility (CTF) is being planned for installation on the Space Station. The CTF will be used to provide data on the productivity and efficiency of a variety of CELSS higher plant crops grown in the microgravity environment of the Space Station. Tight environmental control will be maintained while data on gas exchange rates and biomass accumulation rates are collected. In order to obtain an early realistic determination of the subsystem and system requirements necessary to provide the environmental conditions specified for CTF crop productivity experiments, an Engineering Development Unit (EDU) has been designed, constructed and is in the process of subsystem and system testing at NASA Ames Research Center.

Actuator equal effort level and dynamic control authority are defined. A procedure for eigenvalue assignment which results in each actuator contributing equal weighted effort in the assignment of each eigenvalue set is presented for four frequently encountered cases. Restrictions on applicability are identified, and an example is given. It is common knowledge that the majority of mathematically rigorous control theory is applicable to those systems which are sufficiently accurately modeled as linear time invariant (LTI) and in which the model reflects all relevant system dynamics. These conditions may be applicable to some systems under development as part of the CELSS Program when they are operated within appropriate regions of the adjoined state and control effort space (ASCS), e.g., near fixed set points or some tracking command paths.

The fluid and thermal dynamics of the environment of plants in a small controlled-environment system have been modeled. The results of the simulation under two scenarios have been compared to measurements taken during tests on the actual system. The motivation for the modeling effort and the status of the modeling exercise and system scenario studies are described. An evaluation of the model and a discussion of future studies are included.

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.

The Crop Growth Research Chamber (CGRC), which is being developed under the Controlled Ecological Life Support System program at NASA Ames Research Center, will be operated to support research on the growth dynamics of crops of higher plants within a closed, precisely controlled environment. The CGRC is the first in a series of instruments which will be incorporated into bioregenerative life support systems for space habitats. The dynamic processes of the thermal and fluid portions of the CGRC are profoundly coupled with those of the plants and there is strong reason to believe that consideration of these interactions is necessary in order to design a CGRC which will support sound research. In this paper we describe the modeling system which we have developed for the thermal and fluid dynamics of the CGRC. The bases of the modeling system are symbolic representations of the individual processes which are included in the representation.