Download - Embrittlement of Polymers in Space
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PE1509
Geevarghese George
Semester 6
PSE
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Embrittlement of MISSE 5 PolymersAfter 13 Months of Space Exposure
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NASA STI Program
http://www.sti.nasa.gov/
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Objective
To measure the embrittlement of 37 thin film polymers after LEO space
exposure
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Why?
To design durable and stable spacecraft components
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Materials International Space Station Experiment (MISSE)
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MISSE 5• Polymer samples were taken from PEACE
and were flown in a nadir-facing position for 13 months
• Samples were exposed to omni-directionalcharged particle radiation, thermal cycling, & low doses of atomic oxygen and directsolar radiation
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Pre Flight photograph of the MISSE 5
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Experiment Trays mounted on the ISS
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Test for Space Induced Embrittlement
Bend Test
Strain necessary to induce surface cracking
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Causes of Degradation
• Space Debris
• Space Radiation
• Atomic Oxygen Interaction
• Thermal Cycling
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Space Debris
Size <1 to 30 cm
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Haystack Radar
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Surface of the HST before the HST Servicing mission
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Space Radiation
Ionizing radiation is known to embrittle polymers
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Photograph of embrittled and cracked Teflon FEP retrieved from the HST
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Picture of HST
The Hubble Space Telescope
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Atomic Oxygen Interaction
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Thermal Cycling
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MISSE 5 Experiments
Contained two active (FTSCE & PCSat-2)
and one passive (TBME) experiments
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Passive Experiment
MISSE 5 Thermal Blanket Materials Experiment
• Consisted of several Individual experiments to measure the degradation of more than 200 materials in the space environments
• 49 PEACE samples were flown as a part of the Experiment
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• MISSE 5 was placed in the zenith/nadir position the P6 Trunion Pin Handrail of
the International Space Station
• And was exposed to LEO for 13 months and retrieved on September 15 2006
during the STS115 mission
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Ionizing Radiation
~2.75 Krads through 127 micrometerKapton
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Sun Hours
165±25
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Atomic Oxygen Influence
~1.8X0.10^20 atoms/cm2
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Thermal Cycles
6400
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MISSE 5 PEACE Polymers Experiment =
Thermal Blanket Materials Experiment
•MISSE 5 PEACE polymers experiment consisted of 49, 0.5X1.5in rectangular
polymer samples
•Majority of the samples were thin and flexible
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Primary objective was to determine the Atomic Oxygen Erosion Yield (Ey) of polymers after exposure to space in
nadir position
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• Thin samples were taped on to a Kaptonblanket substrate therefore making determination of Ey based on mass loss difficult
• So samples were dusted with fine salt spray particles to provide isolated locations of protectionfrom AOE so that recession depth measurements could be made post flight for Ey determination
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Experiment Procedures
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Sectioning Bend-Test Samples
• A piece measuring 0.5 X 0.2in of each sampled was sectioned for bend testing
• Small salt particles were removed from the samples prior to bend testing by:Brushing with a small horse hair water color brushRinsing with water and then gently drying the sample with pressurized Nitrogen
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Bend Test Procedure
Strain necessary to induce surface cracking was determined by bending the samples over
mandrels
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23 nos
1.253 to 0.052 cm
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• Sample was placed with the space exposed face down onto the semi guided apparatus
• Mandrel was pushed down onto the sample forcing the material against the pliable surface
• Sample was bent in a U shape where the space exposed surface was in tension and the backside was under compression
• As the diameter of the mandrel decreases, the tension on the space exposed surface increases because the sample was forced to bend more tightly around the material
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The samples where examined before and after bend testing at magnifications of
10x to 13.8xUsing an Olympus SMZ stereo zoom optical
microscope outfitted with a Canon digital camera
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Depending on the size of the samples
9 to 15Optical microscopy pictures were taken and
observed for cracks during the bend test process and were recorded
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Strain Calculations
Allows the percent strain E to be calculated based on the thickness of the sample t and
the diameter of the mandrel d
E = {t/(d+t)} * 100
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Results and Discussion
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TWOsamples cracked in half while on-orbit
• Sample T-1 : PMMA, 50.8 µm
• Sample X-2 : PMP, 50.8 µm
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17
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These results indicate that many thin film polymers are susceptible to embrittlement in the LEO space
atmosphere, even after low solar and particle radiation
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Therefore even minimal amounts of radiation exposure must not be overlooked when designing
spacecraft components based on expected mechanical properties.