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Effects of Low Earth Orbit on Docking Seal MaterialsSpacecraft docking seals are typically made of silicone elastomers. When such seals are exposed to low Earth orbit (LEO) conditions, they can suffer damage from ultraviolet (UV) radiation and atomic oxygen (AO, or monoatomic oxygen, the predominant oxygen species in LEO). An experiment flew on the International Space Station (ISS) to measure the effects of LEO on seal materials S0383-70 and ELA-SA-401 and various mating counterface materials which included anodized aluminum. Samples flown in different orientations received different amounts of UV and AO. The hypotheses were that most of the damage would be from UV, and 10 days or more of exposure in LEO would badly damage the seals. Eighteen seals were exposed for 543 days in ram (windward), zenith (away from Earth), or wake (leeward) orientations, and 15 control samples (not flown) provided undamaged baseline leakage. To determine post-flight leak rates, each of the 33 seals were placed in an O-ring groove of a leak test fixture and pressure tested over time. Resistance temperature detectors (RTDs), pressure transducers, and LabVIEW (National Instruments) programs were used to measure and analyze the temperature and pressure and calculate leakage. Average leakage of control samples was 2.6 x 10(exp -7) lbs/day. LEO exposure did not considerably damage ELA-SA-401. The S0383-70 flight samples leaked at least 10 times more than ELA-SA-401 in all cases except one, demonstrating that ELA-SA-401 may be a more suitable sealing material in LEO. AO caused greater damage than UV; samples in ram orientation (receiving an AO fluence of 4.3 x 10(exp 21) atoms/(sq cm) and in wake (2.9x 10(exp 20) atoms/(sq cm)) leaked more than those in zenith orientation (1.58 x 10(exp 20) atoms/(sq cm)), whereas variations in UV exposure did not seem to affect the samples. Exposure to LEO did less damage to the seals than hypothesized, and the data did not support the conjecture that UV causes more damage than AO.
Document ID
20150000900
Document Type
Technical Memorandum (TM)
Authors
Imka, Emily C. (Hathaway Brown School Shaker Heights, OH, United States)
Asmar, Olivia C. (Hathaway Brown School Shaker Heights, OH, United States)
deGroh, Henry C., III (NASA Glenn Research Center Cleveland, OH United States)
Banks, Bruce A. (Science Applications International Corp. Cleveland, OH, United States)
Date Acquired
January 30, 2015
Publication Date
December 1, 2014
Subject Category
Mechanical Engineering
Space Radiation
Spacecraft Design, Testing and Performance
Report/Patent Number
GRC-E-DAA-TN18861
NASA/TM-2014-218435
E-19002
Funding Number(s)
WBS: WBS 871056.06.02.01.09.02
CONTRACT_GRANT: NNC12BA01B
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
Leakage
Silicones
Ultraviolet radiation
O ring seals
Low Earth Orbit
docking
adhesion

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