A process-based software safety approach was implemented for CAU. In the context of a hazard analysis process, RRCAs were developed to analyze the CAU system and describe system faults that could result in top-level hazards. To ensure that the hazards were properly mitigated, IMPACT diagrams were constructed to depict system functional interactivity, including timing, concurrent processes, and dependencies. This dynamic modeling also linked system functions to requirements specifications to ensure that they were implemented for safe functioning. The IMPACT diagrams were then used to support testing and V&V activities. The result was a successfully planned and executed software safety program that will result in a safe CAU system for the Space Shuttle. This software safety approach met Software Safety NASA STD 8719.13A requirements cost effectively and responsibly, and the CAU system will meet its safety, technical and performance requirements.
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