GRC NEWS RELEASE 99-97




99-97



For Release: December 14, 1999




Pam Caswell
NASA Glenn Research Center
(Bus: 216/433-5795)



Lori J. Rachul
NASA Glenn Research Center
(Bus: 216/433-8806)


<h3>Glenn Researchers Contribute to Hubble Servicing Mission</h3> 

The Hubble Space Telescope, one of the most prolific scientific 
instruments of the century, is about to get new, more durable 
insulating skin. Researchers at NASA Glenn Research Center have added 
their knowledge and experience with space-exposed materials to the 
task.



As part of the third Hubble servicing mission, whose main task will be 
to replace nonfunctioning gyroscopes, the astronaut crew of Space 
Shuttle Discovery, scheduled to launch December 16th at 12:13 a.m. 
EST, will also repair the telescope's multilayer insulation (MLI) 
blankets. The MLI blankets, which are made up of 17 thin layers of 
metallized plastic, cover nearly 80 percent of the telescope's 
surface and protect equipment from temperature extremes as the 
telescope moves into and out of Earth's shadow.



The outermost blanket layer, or skin, is made of supple, 
127-micrometer thick, clear Teflon FEP (fluorinated ethylene 
propylene), which radiates heat. The Teflon's underside has an 
ultrathin coating of aluminum, which reflects light. Altogether, the 
MLI outer later is about the thickness of an ordinary resealable 
plastic freezer bag.



After the first servicing mission in 1993, Glenn Materials Engineer 
Kim de Groh traveled to NASA Goddard Space Flight Center, Greenbelt, 
MD, for a first look at the materials the astronauts had retrieved. 
She found, with her Goddard colleague, many tiny, barely visible 
cracks in the material.



During the second servicing mission, in 1997, the astronauts found 
over 100 cracks in the outer layer, including several long ones whose 
edges had curled back and exposed the blanket underlayer. The 
underlayer materials are shiny and reflect light well, but they do 
not radiate heat well, thus increasing the chance of overheating the 
telescope's equipment. The astronauts patched the longest cracks and 
brought back a tightly curled sample.



Shortly after that mission, Glenn materials engineers became members 
of the Goddard-lead Hubble MLI review board. In comments about the 
work of the review board, Dr. John Campbell, HST Program Manager at 
Goddard said, "The MLI review board is an excellent example of what 
NASA can achieve through intercenter cooperation. Their results, 
determining the damage mechanism and identifying a replacement 
material, were only possible with a strong, cohesive team with 
members from NASA, academia, and industry."



The returned samples were much more brittle than the original 
material. "The piece from the second servicing mission was so fragile 
that it tore into pieces, just from the handling necessary for 
retrieval," said Joyce Dever, Glenn materials engineer. Despite the 
embrittlement, the material's ability to reflect light and heat was 
nearly the same as the new material. Thus, cracked but essentially 
still-in-place material is able to thermally protect the telescope's 
equipment.



To duplicate the embrittlement here on Earth, the team had to expose 
the sample materials to the constituents of Hubble's low-Earth orbit 
environment sequentially, at several government and industry 
laboratories since no one laboratory is capable of duplicating it. 
The constituents include solar ultraviolet radiation, solar wind 
electrons and protons that are trapped along Earth&rsquo;s magnetic 
field lines (Van Allen belts), x-rays from solar flares and atomic 
oxygen from Earth's atmosphere.



Both Glenn and Goddard researchers tested the exposed materials after 
thousands of heating and cooling cycles to simulate the Sun-shadow 
temperature swings the telescope experiences. "Although we were not 
able to duplicate the full extent of the damage, tests show that 
particle radiation from electrons and protons and nearly 40,000 
thermal cycles act together to embrittle Teflon FEP," Dever said.



The review board selected 10 potential replacement materials for 
evaluation. The research team subjected the materials to space 
environmental simulation exposures roughly equal to 10 years in low 
Earth orbit, the expected remaining life of the telescope. Then the 
team tested them for their tendency to become brittle.



"Ironically, our team chose the same material as before but modified 
with a scrim, or fabric, bonded to the backside," said de Groh. 
Teflon FEP's optical properties, or its ability to reflect light and 
radiate heat, are significantly better than other materials 
considered. The scrim, with its fabric-like strands, will retard 
crack growth and help keep the outer layer in place even when it 
becomes brittle. The new outer layer should last the life of the 
telescope, until 2010.



Astronauts will bring back from the telescope fresh samples of both 
the original MLI and MLI used to repair the blankets in 1997. 
Researchers will then have samples with three, three and a half, 
seven and ten years of space exposure available for study. "We're 
really looking forward to studying the returned samples. It is very 
rare to be able to study materials that have been retrieved after 
being in the space environment for such a long time," said de Groh.



By examining these materials, researchers will learn more about the 
low Earth orbit environment and its effect on all kinds of materials. 
At Glenn, the information learned from these and other studies will 
be used to design more realistic space environment simulations for 
assessing the space-worthiness of materials.




<u>Notes to Editors</u>: Joyce Dever is one of the technical advisors 
who will support NASA mission control during the astronauts' 
extravehicular activities. She will be telecommunicating with mission 
control from her office at Glenn.



A NASA video file relating to this story will air on December 13 and 
14 at noon EDT. NASA Television is available on GE-2, transponder 9C 
at 85 degrees West longitude, with vertical polarization. Frequency 
is on 3880.0 megahertz, with audio on 6.8 megahertz. Video File 
Advisories can be found at:
ftp://ftp.hq.nasa.gov/pub/pao/tv-advisory/nasa-tv.txt



An image of a long crack taken during the second Hubble servicing 
mission is available at:
http://www.grc.nasa.gov/WWW/PAO/pressrel/images/99_96i1.jpg



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