Function-Based Design of a Spacecraft Power System Diagnostics Testbed

Abstract

NASA’s Ames Research center is currently designing a testbed to validate and compare potential Integrated System Health Management (ISHM) technologies. The proposed testbed represents a typical power system for a spacecraft and includes components such as a fuel cell, solar cells and redundant batteries. To fulfill design requirements, the testbed must be capable of hosting a wide variety of ISHM technologies including those developed by NASA as well as those developed in the aerospace industry abroad. An internal fault injection subsystem must be built into the system to provide a common interface for evaluating these different ISHM technologies. Additionally, to ensure robust operation of the testbed, the capability to detect and manage external faults must also be present. In order to develop a set of requirements for the internal fault injection subsystems as well as predict external faults, a comprehensive set of potential failures must be identified for all of the components of the testbed. To best aid the development of the testbed, these failures needed to be identified as early as the conceptual design phase, where little is known about the actual components that would comprise the finished system. This paper demonstrates the use a function-based failure mode identification method to identify the potential failures of the testbed during the conceptual design phase. Using this approach, designers can explore the potential failure modes at the functional design stage, before a form or solution has been determined. A function-failure database is used to associate the failures of components from previous design efforts to the testbed based on common functionality. The result is a list of potential failure modes and associated failure rates, which are used to improve the design of the testbed as well as provide a framework for the fault injection subsystem.