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A canopy of plants may become a vital component of advanced controlled ecological life support systems (CELSS). The interactions of the canopy with its environment need to be modeled so that designers can properly assess alternate configurations and operating strategies. Collective behavior of an entire canopy can sometimes be more expeditiously modeled than microscopic processes while preserving the robustness of the model for analysis of a CELSS. Water transpiration is a particularly important canopy process for which it is possible to link underlying microscopic processes and arrive at a description of canopy-level aggregated behavior. The underlying fundamental processes driving transpiration are relatively well understood. Unfortunately, the usual characterization of transpiration relies on parameters such as stomatal and boundary layer conductivities that are not directly measurable in typical CELSS designs.

Steady advancement over the past several decades in the optimization of controlled ecological life support systems (CELSS) design and performance has resulted in the development of a variety of approaches to CELSS control. This paper reflects this evolution by surveying the approaches used in controlling plant growth chambers currently in use in academia, industry, and government agencies. A table is presented summarizing the control system hardware and software used and the corresponding control laws implemented by these systems. The advantages seen by the science and engineering groups operating several plant growth systems are discussed. Troublesome or cumbersome properties of the control systems of some plant growth systems are also discussed as well as some of the solutions which have been derived or envisioned.