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Independent Orbiter Assessment (IOA): Analysis of the auxiliary power unitThe results of the Independent Orbiter Assessment (IOA) of the Failure Modes and Effects Analysis (FMEA) and Critical Items List (CIL) are presented. The IOA approach features a top-down analysis of the hardware to determine failure modes, criticality, and potential critical items. To preserve independence, this analysis was accomplished without reliance upon the results contained within the NASA FMEA/CIL documentation. This report documents the independent analysis results corresponding to the Orbiter Auxiliary Power Unit (APU). The APUs are required to provide power to the Orbiter hydraulics systems during ascent and entry flight phases for aerosurface actuation, main engine gimballing, landing gear extension, and other vital functions. For analysis purposes, the APU system was broken down into ten functional subsystems. Each level of hardware was evaluated and analyzed for possible failure modes and effects. Criticality was assigned based upon the severity of the effect for each failure mode. A preponderance of 1/1 criticality items were related to failures that allowed the hydrazine fuel to escape into the Orbiter aft compartment, creating a severe fire hazard, and failures that caused loss of the gas generator injector cooling system.
Document ID
19900001615
Acquisition Source
Legacy CDMS
Document Type
Contractor Report (CR)
Authors
Barnes, J. E. (McDonnell-Douglas Astronautics Co. Houston, TX, United States)
Date Acquired
September 6, 2013
Publication Date
December 12, 1986
Subject Category
Space Transportation
Report/Patent Number
REPT-1.0-WP-VA86001-14
NAS 1.26:185568
NASA-CR-185568
Accession Number
90N10931
Funding Number(s)
CONTRACT_GRANT: NAS9-17650
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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