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From 1997 to 2001, the author worked with a team of engineers at JSC to develop the requirements and basic design for the advanced life support system testbed known as the Bioregenerative Planetary Life Support Systems Test Complex, or BIO-Plex. In addition to the testing of advanced life support equipment, the testbed was also capable of treating the control system itself as a test article. The intent was to provide, in addition to the system and equipment-level data acquisition and control, the capability of evaluating approaches to autonomy and other forms of advanced control, and eventually to evaluate them in the context of mission operations. This paper will describe the requirements and design trades we made to develop the architecture of an advanced control system that could support the flexibility and complexity of the BIO-Plex.

Technologies that facilitate the design and control of complex, hybrid, and resource-constrained systems are examined. This paper focuses on design methodologies, and system architectures, not on specific control methods that may be applied to life support subsystems. It has been estimated that 60–80% of the effort in developing complex control systems is software development, and only 20–40% is control system development [1]. It has also been shown that large software projects have failure rates of as high as 50–65% [2,3]. Concepts discussed include the Unified Modeling Language (UML) and design patterns with the goal of creating a self-improving, self-documenting system design process. Successful architectures for control must not only facilitate hardware to software integration, but must also reconcile continuously changing software with much less frequently changing hardware [4]. These architectures rely on software modules or components to facilitate change.

Industrial process control has been dominated by closed architectures and proprietary protocols for the last three decades. In the late 1990’s, the advent of open fieldbus and middleware standards has greatly changed the process control arena. Fieldbus has pushed control closer and closer to the process itself. Middleware standards have exposed real-time process data to higher level software applications. Control systems can now be designed to minimize the reconfiguration costs associated with design changes. How can Advanced Life Support (ALS) benefit from these technologies? We consider designing the control system for the BIO-Plex and evaluate how complex it will be, the effort it will require, and how much it will it cost. Various fieldbus technologies were compared and Foundation Fieldbus was chosen for detailed evaluation. This new fieldbus was integrated with an existing ALS system.

From 1997 to 2001, the third author worked with a team of engineers at JSC to develop the requirements and basic design for the Bioregenerative Planetary Life Support Systems Test Complex, or BIO-Plex. Under the Advanced Integration Matrix (AIM) Project, this earlier effort is extended to an investigation of methods and approaches for Advanced Systems Integration and Control. The intent is to understand and validate the use of software as an integrating function for complex heterogeneous systems, particularly for Advanced Life Support (ALS), in the context of support of mission operations. Preliminary investigations undertaken in the summer of 2004 indicate that integration of controls for the type of dynamic, non-linear, closed-loop biological systems under investigation for ALS systems require a different systems engineering approach than that required for traditional avionics systems.

Advanced life support and habitat functions for exploration missions will require the autonomous control of many interdependent subsystems. A controls evaluation was envisioned to help define the questions necessary to develop an architecture capable of this degree of autonomy. To conduct this evaluation, a biological test bed that consists of a pair of interdependent subsystems was developed. The biological test bed represents an analog of a life support subsystem necessary for long-duration, human-rated exploration missions. The test bed consists of a packed bed anoxic bioreactor for the removal of organic carbon, coupled with an aerobic nitrifier that converts ammonia to nitrogen.

The Advanced Integration Matrix (AIM) project at the Johnson Space Center (JSC) was chartered to study and solve systems-level integration issues for exploration missions. One of the first issues identified was an inability to conduct trade studies on control system architectures due to the absence of mature evaluation criteria. Such architectures are necessary to enable integration of regenerative life support systems. A team was formed to address issues concerning software and hardware architectures and system controls.. The team has investigated what is required to integrate controls for the types of non-linear dynamic systems encountered in advanced life support. To this end, a water processing bioreactor testbed is being developed which will enable prototyping and testing of integration strategies and technologies.