Distributed, Embedded Control for Life Support Development

This paper describes the re-engineering of the hardware and software organization of an autonomous control system for advanced water recovery technology development. The hardware changes from large standing racks of VERSAModuleEurocard (VME) computers and I/O cards to a set of small, modular controllers embedded in the hardware of the controlled systems. Additionally, the paper describes the redesign of an existing intelligent control architecture, known as 3T, that since 1995 has provided autonomous 24/7 controls to several long-duration life-support systems in ground tests at JSC. The software is recast from a vertical, message-passing architecture to a distributed system which can populate the embedded hardware controllers in many alternative arrangements. Additional controllers allow for automatically migrating control codes when the original controllers fail. The resulting hardware and software architecture dramatically decreases the downtime of life support systems due to component failure, and improves safety and operational efficiency by supporting reconfiguration of the life support hardware or the control system with a minimum of deactivation or shutdown of the systems being controlled. In this paper we describe the design and implementation of the hardware, using industry standard PC104 controllers, the allocation of subsystem responsibilities to the controllers, the transformation of the intermodule software communication from message-passing to CORBA and the operation of the new design controlling a 5-stage cascade distillation system (CDS) in an 18 month technology readiness test at JSC. Based on previous tests with the old design we will detail the functional and operational benefits of the new design, as well as discuss new issues arising from such a design, and how they affected our testing of the CDS.