Developing and validating thousands of executable finite state machines

In 1996, a project began at NASA's Kennedy Space Center to replace the legacy Launch Processing System with a state-of-the-art process control system called the Checkout and Launch Control System. Over 13 million lines of real time control software are being reengineered from a legacy language called Ground Operations Aerospace Language to a modern graphical programming language called ControlShell by Real Time Innovations. ControlShell combines a graphical language with a component-based design methodology. The ControlShell finite state machine component type is semantically similar to the statecharts of the Unified Modeling Language (UML). Thousands of executable finite state machines are being developed for the new launch system. The new system must deliver exceptionally reliable software to maintain safe operations and a high level of confidence by the end users. This paper discusses some of the development challenges of this project, the design approach, and the use of automated model checking for validation.