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.