Determining the Ballistic Missile Defense Shield’s Effective Reliability

The Ballistic Mis sile Defense System (BMDS) is a phased arrangement of equipment that is designed to engage a limited number of ballistic missiles launched against the United States and her allies. A phased system is one that changes its characteristics over time. Although a system does not modify its characteristics within a phase, when the system departs one phase and enters another, the system is by definition different in some significant manner. Determining the reliability of phased systems requires a rather complex aggregation of results across phases . For any realistic equipment architecture, simulation is the only technique with the capability to resolve the reliability of a phased system. The current method used by the BMDS community is to simulate numerous mission cycles of a phased mission representing a hostile launch and determine how many cycles were successfully completed without a hardware or software failure. Unfortunately, this approach only takes into consideration the traditional suitability aspects of the BMDS and disregards key effectiveness issues. For the BMDS, each phase has an additional requirement; not only must the hardware and software survive the phase, but the phase also must be completed in a specific time. The time required to complete a phase is a random variable that cannot exceed a maximum value, which is itself a random variable. Since a phase change occurs once a task is complete, these effectiveness rules impact the system’s reliability. By ignoring these effectiveness critical time issues, the traditional reliability analysis will inflate the system’s capabilities to destroy ballistic missiles. This can lead to overconfidence in the abilities of the BMDS and thus lead to a reduction in the number of ground-based interceptors launched to destroy a threat. This paper will develop a new reliability parameter, which will henceforth be known as effective reliability, to better estimate the characteristics of the BMDS. While mission reliability accounts for the suitability aspects such as hardware and software failures during a phased mission, the effective reliability parameter simultaneously accounts for both suitability and effectiveness issues that are statistically dependent. This paper will utilize Monte Carlo simulation to develop a methodology that more accurately predicts the capabilities of the BMDS by combining traditional reliability aspects with the requirement to perform phased tasks within an effective timeframe. Using realistic but non-classified data, it will be demonstrated that the BMDS community’s current reliance on the mission reliability parameter will overestimate the abilities of the system while our effective reliability parameter will yield a better estimator of the system’s true potential to negate ballistic missiles.