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PPT for my first seminar on "polymers in space"
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PE1509
Geevarghese George
Semester 6
PSE
Embrittlement of MISSE 5 PolymersAfter 13 Months of Space Exposure
NASA STI Program
http://www.sti.nasa.gov/
Objective
To measure the embrittlement of 37 thin film polymers after LEO space
exposure
Why?
To design durable and stable spacecraft components
Materials International Space Station Experiment (MISSE)
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
Pre Flight photograph of the MISSE 5
Experiment Trays mounted on the ISS
Test for Space Induced Embrittlement
Bend Test
Strain necessary to induce surface cracking
Causes of Degradation
• Space Debris
• Space Radiation
• Atomic Oxygen Interaction
• Thermal Cycling
Space Debris
Size <1 to 30 cm
Haystack Radar
Surface of the HST before the HST Servicing mission
Space Radiation
Ionizing radiation is known to embrittle polymers
Photograph of embrittled and cracked Teflon FEP retrieved from the HST
Picture of HST
The Hubble Space Telescope
Atomic Oxygen Interaction
Thermal Cycling
MISSE 5 Experiments
Contained two active (FTSCE & PCSat-2)
and one passive (TBME) experiments
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
• 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
Ionizing Radiation
~2.75 Krads through 127 micrometerKapton
Sun Hours
165±25
Atomic Oxygen Influence
~1.8X0.10^20 atoms/cm2
Thermal Cycles
6400
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
Primary objective was to determine the Atomic Oxygen Erosion Yield (Ey) of polymers after exposure to space in
nadir position
• 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
Experiment Procedures
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
Bend Test Procedure
Strain necessary to induce surface cracking was determined by bending the samples over
mandrels
23 nos
1.253 to 0.052 cm
• 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
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
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
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
Results and Discussion
TWOsamples cracked in half while on-orbit
• Sample T-1 : PMMA, 50.8 µm
• Sample X-2 : PMP, 50.8 µm
17
These results indicate that many thin film polymers are susceptible to embrittlement in the LEO space
atmosphere, even after low solar and particle radiation
Therefore even minimal amounts of radiation exposure must not be overlooked when designing
spacecraft components based on expected mechanical properties.