Polyethylene in Space
Jonathon Ball, Kirk Norasak
Goals For the Summer

Develop an irradiation setup to imitate “space”
conditions.

To test mechanical properties of UHMWPE
irradiated in “space” conditions.

To improve the Orthopod wear testing
program.

To wear test the proton irradiated PE at Earth
STP.
Questions to Address
• What are the radiation conditions in space?
• What are conditions at different points in space?
• Why is polyethylene used in space?
• What are the uses of polyethylene in space?
• What other polymers are used in space?
• Polymers Irradiated in a Vacuum vs. Air
• Ideas for system setup to imitate polyethylene in space conditions.
• Timeline for wear testing of polyethylene samples proton-irradiated
in STP of earth.
What are the radiation conditions in space?

galactic cosmic rays

solar particle events
◦Includes protons and highly charged nuclei.
◦Includes protons from Solar Flares, and large mass releases from the sun.
87% of the particles of the GCR are protons, 12% are helium nuclei and 1%
are particles heavier than helium

Characteristics of
space radiation
Characteristic
SPE
GCR
proton energy range
(MeV)
up to several 100
up to several 1000
HZE energy range
(MeV/nucleon)
no significant
contribution
up to several 1000
OVERVIEW OF NASA’S SPACE
RADIATION RESEARCH PROGRAM
Walter Schimmerling
National Aeronautics and Space
Administration, Washington, DC
What are conditions at different points in
space?
International Space Station-
(-157)C - 121C 0mbar pressure
Moon-
(-233)C - 123C
0mbar pressure
Mars-
(-153)C - 20C
7.5mbar pressure
Reentry to the atmosphere-
~8000K
Why is polyethylene used in space?
• Readily available.
• The high hydrogen content allows this polymer to block
radiation neutrons.
• Can be easily made into a composite Ex.(Boron Nitride, and
Carbon nanotubes.) to improve properties such as Young's
Modulus.
What are the uses of polyethylene in
space?
• The PE is used in the crew quarters on the
International Space Station. Provided 22%
reduction in radiation exposure while in the
space station.
•
Used in the fibers and fabrics of Space
suits.
• PE based material RXF1 was developed
to possibly build a plastic space ship to
replace the Al outer shell. 3X stronger and
2.6X lighter than Al. 50% better SPE
shielding and 15% better Cosmic ray
shielding. Increased shielding would be
necessary for a mission to Mars which is
expected to last at least 30 months.
What other polymers are used in
space?
Mylar (PET)- Has radiation resistance
Electrical insulator
Used to make Solar Sails
Kapton - Temp range -273 to 400 C
Used for wire coating
Used as an insulator in UH Vac environment
Neoprene- Insulation (Wet suits) to regulate body temperature.
PTFE (Teflon) – Outer protection on the space suit.
Polymers Irradiated in a Vacuum vs. Air
Vacuum
samples that are irradiated show improved
mechanical properties.
Under
the vacuum PTFE has shown to reduce toxic
components such as HF.
UHMWPE
in pre-irradiation vacuum removed oxygen in the
system, thus leaving more free radicals to form crosslinks.
System setup to imitate polyethylene in
space conditions.
Vacuum package the PE and immerse it into a liquid Nitrogen
storage device. After that, place the setup into the radiation
testing area.

Questions still to be answered for the setup:
◦What is the pressure of the polyethylene while vacuum packaged?
◦What is the radiation shielding coefficient of the packaging material?
◦How to quantify the temperature of the PE immersed in the LN?
◦Does the LN have a shielding effect?
◦Is the effects due to the lack of Oxygen or the pressure the Vacuum
presents?
Timeline of Pin-on-Disk wear testing for
polyethylene that was proton-irradiated at
Earth's STP

2 weeks- machining time on pins, receiving new SS buttons, new circle
programming

Begin Testing June 27
◦ 2 days per 10 km
 Every MWF begin new runs of 10km
 Run samples for 40km stopping every 10km to determine wear
ratios.
 Focus on 0Gy and 35Gy samples of 1020 PE and 1020E PE for a total
of 4 sample sets.
◦ Using the developed schedule, testing on the 4 different sets would be
completed August 3.
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