GLTRS--Glenn
TITLE AND SUBTITLE:
Space Shuttle Pinhole Formation Mechanism Studies

AUTHOR(S):
Nathan S. Jacobson

REPORT DATE:
November 1998

FUNDING NUMBERS:
WU-260-10-0G-00

PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES):
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 44135-3191

PERFORMING ORGANIZATION REPORT NUMBER:
E-11351

SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES):
National Aeronautics and Space Administration
Washington, DC 20546-0001

REPORT TYPE AND DATES COVERED:
Technical Memorandum

SPONSORING/MONITORING AGENCY REPORT NUMBER:
NASA TM-1998-208659

SUPPLEMENTARY NOTES:
Responsible person, Nathan S. Jacobson, organization code 5160, (216) 433-5498.

ABSTRACT:
Pinholes have been observed to form on the wing leading edge of the space shuttle after about 10-15 flights. In this report we expand upon previous observations by Christensen (1) that these pinholes often form along cracks and are associated with a locally zinc-rich area. The zinc appears to come from weathering and peeling paint on the launch structure. Three types of experimental examinations are performed to understand this issue further: (A) Detailed microstructural examination of actual shuttle pinholes (B) Mass spectrometric studies of coupons containing actual shuttle pinholes and (C) Laboratory furnace studies of ZnO/SiC reactions and ZnO/SiC protected carbon/carbon reaction. On basis of these observations we present a detailed mechanism of pinhole formation due to formation of a corrosive ZnO-Na2O-SiO2 ternary glass, which flows into existing cracks and enlarges them.

SUBJECT TERMS:
Carbon/carbon; Shuttle; Corrosion

NUMBER OF PAGES:
45

PDF AVAILABLE FROM URL:
1998/TM-1998-208659.pdf
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