Failure propagation in SoS: Why SoS should be loosely coupled

SoS are an ensemble of complex systems, which have the potential for an extraordinary amount of structural complexity, even temporarily, as a result of interconnections and couplings that can vary in strength. Because of this, SoS can be extremely vulnerable to very sudden catastrophic collapse as a result of small and insignificant partial functionality losses in one of the constituent systems. This is an indication that SoS has the potential to behave like a complex system, or even worse if the interactions are not managed carefully. This paper provides an analysis of the SoS response to uncertainties in the form of partial failures, which is complemented by the presentation of a measure of structural complexity for SoS. Experiments with the development of random graphs to simulate SoS show that a partial failure initiated in one system has a high possibility of leading to a collapse of another system of SoS, sometimes even before leading to total failure in the originating system.