System-Theoretic Process Analysis of a Novel Airborne Laser Communication System

Abstract

As the military strives to create a more robust battle network, laser communication offers many advantages such as supporting more secure and efficient data sharing. For this reason, interest has grown in recent years in implementing lasercom as a means for intra-aircraft communication. However, many challenges unique and inherent to lasercom such as stringent line-of-sight and pointing requirements and susceptibility to atmospheric degradation lead to difficulties in implementation. Consequently, establishing and maintaining lasercom links in the dynamic environment of flight will require seamless coordination between aircraft. The complexity and novelty of such a system warrant a hazard analysis technique that can fully address the associated challenges of collaboration while the system is in an early concept phase of design. System-Theoretic Process Analysis (STPA) is a proactive hazard analysis technique rooted in Systems Theory. While more traditional hazard analysis methods evaluate the safety of system components individually, STPA provides guidance to analyze systems holistically, thus supporting the identification of emergent behaviors that arise due to component interactions. Recently, STPA has been extended to address hazards specifically associated with collaboration of multiple controllers providing shared control over a physical process. This extension known as STPA-Teaming provides a methodology to analyze unsafe combinations of control actions that may lead to system losses. The method allows for the systematic identification of causal factors related to coordination that are likely to be missed by more traditional hazard analysis techniques. Because this approach relies on abstraction and includes human operators along with software and hardware components, it is well-suited for novel, complex systems. This thesis applies STPA and its extension, STPA-Teaming, to an early concept airborne lasercom system to identify scenarios in which loss of communication may occur. As a result, it identifies scenarios related not only to individual component failures and unsafe internal control, but also related to flaws in coordination of multiple controllers. The output of the analysis is system recommendations that can support the remainder of the systems engineering process including generation of system requirements, definition of system concept of operations (ConOps) and system architecture, and system validation and verification (V&V). In this way, the results of the analysis provide a baseline level of traceability for future design decisions to manage the emergent behavior of the system and ultimately prevent mission losses.