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On thermal stress failure of the SNAP-19A RTG heat shieldResults of a study on thermal stress problems in an amorphous graphite heat shield that is part of the launch-abort protect system for the SNAP-19A radio-isotope thermoelectric generators (RTG) that will be used on the Viking Mars Lander are presended. The first result is from a thermal stress analysis of a full-scale RTG heat source that failed to survive a suborbital entry flight test, possibly due to thermal stress failure. It was calculated that the maximum stress in the heat shield was only 50 percent of the ultimate strength of the material. To provide information on the stress failure criterion used for this calculation, some heat shield specimens were fractured under abort entry conditions in a plasma arc facility. It was found that in regions free of stress concentrations the POCO graphite heat shield material did fracture when the local stress reached the ultimate uniaxial stress of the material.
Document ID
19740022225
Acquisition Source
Legacy CDMS
Document Type
Technical Memorandum (TM)
Authors
Pitts, W. C. (NASA Ames Research Center Moffett Field, CA, United States)
Anderson, L. A. (NASA Ames Research Center Moffett Field, CA, United States)
Date Acquired
September 3, 2013
Publication Date
July 1, 1974
Subject Category
Structural Mechanics
Report/Patent Number
A-5516
NASA-TM-X-3097
Accession Number
74N30338
Funding Number(s)
PROJECT: RTOP 502-19-31
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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