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Single Event Effect Criticality Analysis

INTRODUCTION
Our goal in generating this document is to aid the individuals in project management, systems
engineering, radiation effects, and reliability engineering who carry the responsibilities for
successful deployment of NASA systems in orbital particle environments. Traditionally, in a
manner which may differ from NASA center to NASA center, this effort has involved many
iterative passes through system and subsystem designs with involvement of engineers
representing the above disciplines. These efforts began in the 1970s when one or two low level
integration device types were identified to be susceptible to single event upset (SEU). Since then,
with advances in technology, the arena has expanded to include many types of single event
effects (SEES) in many technologies. The necessary advent of SEE hardened device technologies
has alleviated some of the worries, but simultaneously added another dimension to the already
complex trade space involved in SEE system design and analysis. Indeed, it is the combination
of the universal nature of the concern across NASA centers, coupled with the complexities of the
issues, which has prompted this study. Our aim is not to prescribe approaches to SEE immune
system design, but rather to examine the analysis process and suggest streamlined approaches to
the related design problems. In short, we seek to codify the successful elements which, in many
cases, already exist for assessing SEE risk and suggest a timeline and procedure for
implementing SEE risk analysis with respect to the system design effort.
A combination of factors have converged to impact the growing importance of the traditionally
informal single event effects criticality analysis (SEECA). Among these are:
l) The increased functionality of satellite systems which impacts the number and
complexity of various types of microcircuits,
2) The increased device SEE sensitivity commensurate with the smaller feature sizes and
advanced technologies (e. g. GaAs signal processors) required to field these systems,
3) The difficulty in acquiring space-qualified and SEE tolerant parts and the cost forces
driving the use of commercial-off-the-shelf (COTS) parts, and
4) The overall complexity of a typical orbital platform which relies on the successful
execution of an ever-growing number of instructions.
In short, it is often neither possible nor cost effective to construct systems using SEE immune
hardware, and the systems engineer must necessarily make decisions within a trade space
including availability, performance, schedule, and cost risk associated with single event effects.
Throughout these discussions we recognize that SEECA covers a highly specialized set of
concerns which in many ways parallels conventional reliability analysis. While reliability
analysis is by no means simple, the concepts and tools employed by the systems engineering
teams and project managers are familiar, and methods exist for both the estimation and
quantification of risk. Unfortunately, there seems to be no plausible approach to direct
application of these tools to single event analyses. This situation is further complicated by the
nature of the complex interplay between the environments, mechanisms, effects, and mitigation
approaches. This has led to ad hoc treatments of single event analyses. On one side, systems
engineers have a sometimes incomplete understanding of the exact nature of the risk.