NASA's In Situ Contamination Effects Facility, Marshall Space Flight Center, has been used to test several candidate materials for use upon Space Station Freedom. Optical measurements were made in the vacuum ultraviolet (VUV) as test mirrors were contaminated by materials in a space-like environment. This was done to determine the effects of the contamination and subsequent exposure to VUV radiation upon optical components that will be used upon the space station

Johnson, R. Barry

English

NASA Technical Reports Server

Final Report
Contamination Analysis of SSF Candidate Materials
Contract No. NASS-36955, D. O. 79
Acount No. 5-32391
Submitted to:
NASA
Marshall Space Flight Center, AL 35812
Submitted by:
Robert Connatser for R. Barry Johnson
University of Alabama in Huntsville
Center for Applied Optics
Huntsville, Alabama 35899
August 1991
https://ntrs.nasa.gov/search.jsp?R=19930003706 2020-03-17T10:33:17+00:00Z
Table of Contents
Page
Preface 1
Abstract 2
Introduction 3
Test Materials and Results 5
Tests 6
Conclusion 13
L r
RSIRi-Optical Data
-Temperatures
-TQCM Data
RSiR3-Optical Data
-Temperatures
-TQCM Data
RS2RI-Optical Data
-Temperature Data
-TQCM Change
RS2R3-Optical Data
-Temperature Data
-TQCM Change
RS3RI-Optical Data
-Temperature Data
-TQCM Change
Table of Graphs
RS2R2-Optical Data
-Temperatures
-TQCM Data
RSlR4-Optical Data
-Temperature Data
-TQCM Change
RS2R2-Temperature Data
-TQCM Change
RS2R4-Optical Data
-Temperature Data
-TQCM Change
RS4RiA-Optical Data
-% Reflectance Change
-Temperature Data
-TQCM Change
RS4RiB-Optical Data
-% Reflectance Change
-Temperature Data
-TQCM Change
RS5RI-Optical Data
-Temperature Data
Preface
The research reported herein was conducted by personnel at the
University of Alabama in Huntsville's Center for Applied Optics,
under contract titled "Contamination Study". The testing of
materials portion of the task was completed at the Materials and
Processes Laboratory at NASA's Marshall Space Flight Center. The
author would like to express his appreciation to Mr. Roger Linton,
Ms. Whitney Hubbs, and Mr. Don Burch for their help and suggestions
during this period.
2Abstract
NASA's In Situ Contamination Effects Facility, Marshall Space
Flight Center, has been used to test several candidate materials
for use upon Space Station Freedom. Optical measurements were made
in the vacuum ultraviolet (VUV) as test mirrors were contaminated
by materials in a space-like environment. This was done to
determine the effects of the contamination and subsequent exposure
to VUV radiation upon optical components that will be used upon the
space station.
3Introduction
The object of the contract is to help determine which
materials are suitable for use upon the space station near optical
surfaces. Through testing and analysis, it is possible to reach
conclusions about the materials and their possible effects. To aid
in the understanding of the information and research performed, an
overview of the testing and analysis procedures is necessary.
The major portion of the testing is done in the In Situ
Contamination chamber. The chamber is cylindrical, 4 feet long
with a radius of 1 foot. It is a vacuum chamber, pumped by a
mechanical roughing pump and a turbomolecular pump. The VUV source
is a microwave powered Krypton discharge lamp that emits primarily
at 1600 and 1236 Angstroms. The data gathering instruments inside
the chamber are the three photomultiplier tubes, a TQCM, and three
thermocouples.
The candidate material is mounted across from the test mirror
on a heating plate. The mirror is mounted to a plate that is also
temperature controlled. The temperature range for the material
heating plate is from 23 to >200 Celsius, and for the mirror mount
is -i0 to 50 Celsius. Under a good vacuum, the material and mirror
are heated and/or cooled to the proper temperatures. This causes
any contamination effects to occur. A direct reflectance
4measurement is taken off of the mirror, to note any specular change
in the material during the test.
After the test is completed, an analysis of the contamination
and its effect is started. This analysis includes microscope
examination, reflectometry, FTIR spectroscopy, and a florescence
check. Further testing is also done. The contaminated mirror is
sometimes exposed to UV and VUV radiation, to determine whether or
not the contamination will photolyze. In the future, mirrors will
also be exposed to atomic oxygen. After these exposures, the full
range of analysis is redone, and compared with the original
analysis.
Test Materials and Results
From January 1991 to July 1991, the following materials were
tested in the In Situ Facility.
Z-306
This material is a polyurethane binder, and is also known as
chemglaze. It is used as a thermo-control coating, with two
primary (space environment) uses. First, this material uses carbon
black as an absorber and is thereby used to keep objects warm. It
is also used as a diffuse black absorber, to keep down stray
reflected and scattered light. Z-306 is also highly atomic oxygen
sensitive and requires extensive vacuum bakeout for outgassing
purposes.
Currently, Z-306 is coated on the inside of the Hubble Space
Telescope. One of the questions that the testing was to answer is
if it would be safe to turn the telescope so that it faced closer
to the sun. Such a move would cause the overall temperature of the
telescope to rise to around 155 Celsius. The tests done here show
that there is a second level of outgassing done in at about 155
Celsius in the presence of VUV radiation, which would contaminate
the optics of the space telescope. Therefore it would be unsafe to
turn the telescope to that position.
6Silicone, Viton, and EPR
These three materials are candidates for window and docking
seals on the space station. The object was to find out which
material best fitted the requirements of low outgassing in the
space environment.
Silicone is known to be a fairly good seal material, and is
useable over a large temperature range. Viton is the best seal
material, but is not useable in a large temperature range. EPR is
a seal material that was used as a comparison to the other two.
The testing done indicates that Viton is the cleanest
material, under the test conditions. • This was the expected
conclusion, from previous testing.
7Solithane 113
This material is used for elastomeric sealing and as a potting
compound. It is a candidate material for the European Space
Agency's SOHO satellite, as well as for Space Station Freedom. The
purpose of the tests on solithane is to gather baseline
contamination information, with special concern for the effects of
any residue on optical surfaces.
The initial tests have shown that solithane does outgas, even
after a proper vacuum bakeout. This outgassing left a residue on
the test mirror that could be seen with the naked eye. Analysis of
the residue has not been completed at this time.
8Tests
Each candidate material was tested individually, and each test
is different from the others. They vary in duration and in the
temperatures that the mirror and contaminant are set at. For some
materials many tests are appropriate, while others only require one
or two tests.
Following is a list of the different tests, with descriptions
of their conditions. The tests have been labelled as the "Rob
Series," and any multiple tests are identified by the "Run" number.
For example, the first test of Z-306 has been labelled as Rob
Series i, Run i. The test mirrors used also have identifying
labels, but they have no specific ordering.
Rob Series 1
This is the series of tests made on Z-306.
conditions for the three tests were identical.
Run
The general
1 11-91 12,000 sec 488 hz -27.6%
2 9-91 10,800 sec 362 hz -5.7%
3 12-91 20,400 sec 1679 hz -56.5%
4 7-91 15,060 sec 870 hz -48.0%
Mirror Duration Total TQCM % Specular
Change Change
Rob Series 2
This is the series of tests that investigated Solithane.
Several of the tests had slightly different conditions; these
tests will be explained independently.
For Run I, there were to be three different stages. The first
was with the contaminant and the mirror at 50 and 0 Celsius
respectively. Then when the optical and TQCM outputs levelled off,
the contaminant temperature was to be raised to I00 Celsius, and
then 120 Celsius when the outputs had levelled off again. The
length of time between level stages caused the last stage of the
test to be delayed overnight.
Run 2 was set to be a TQCM test of Run I. It was done without
a mirror, but with the mirror stage taken to the same temperature
as in Run i. This test only repeated the 50 Celsius and i00
Celsius portions of Run i.
Run 3 was designed to have a steady contamination temperature,
but have different stages of mirror temperatures. The mirror was
initially taken to 0 Celsius, then lowered to -16 Celsius for the
majority of the test, then raised to 30 Celsius for last portion of
the test.
Run 4 also had different stages of mirror temperatures. The
mirror, TQCM, and contaminant were initially set to 50 Celsius.
Then the mirror and TQCM were lowered i0 degrees, and maintained
there for 30 minutes. This was repeated until the mirror and TQCM
reached -8 Celsius, which was as low as the water chiller would go.
I0
Run Mirror Duration Total TQCM % Specular
Change Change
1 S1 22,798 sec 233 hz -13.6%
2 na 22,800 sec 105 hz na
3 R2 82,200 sec 176 hz -15.4%
4 R2X 26,400 sec 188 hz -24.3%
Rob Series 3
This test was conducted using Viton as the contaminant. This
test was similar to the last run on Silicone (RS2R4). The
contaminant was taken to about 60 Celsius, and the mirror and TQCM
were lowered to about -i0 Celsius. Then the mirror and TQCM
temperatures were raised first in i0
increments, until they reached 60 Celsius.
each temperature for about a half hour.
degree then 5 degree
They were maintained at
The TQCM result seems to
indicate that there was more outgassing off of the crystals as the
temperature rose, than any accumulation from the material.
Run Mirror Duration Total TQCM % Specular
Change Change
1 R1 30,000 sec -204 hz -15.3%
ii
Lv
Rob Series 4
This test used EPR rubber as the candidate material. This
test was split into two sections, due to time considerations. The
first section had the contaminant, mirror, and TQCM raised to 50
Celsius. Then the mirror and TQCM were lowered to 40 Celsius, then
on towards 0.
The second section had the contaminant raised towards 60
Celsius, with the mirror and TQCM taken to about 30 Celsius. The
mirror and TQCM temperatures were lowered in I0 degree increments,
down to 0 Celsius. They were left at each temperature for a period
of twenty to thirty minutes.
Run Mirror Duration Total TQCM
Change
% Specular
Change
IA R3 15,000 sec 990 hz -20.1%
IB R3 22,800 sec 102 hz -90.9%
Rob Series 5
These tests will be devoted to the candidate material
Solithane 113. Only one test in this series has been completed at
this time.
The test performed on the material was different from all
others in that a secondary mirror holder was placed in the chamber
beneath the primary mirror station. This holder was externally
connected to the coolant lines (external to the lines) so as to
12
provide some measure of thermal control over them. It held two
test mirrors and two slugs, so as to provide several contaminated
samples along the same run.
The mirrors were cooled overnight, to allow for the best
temperature to be reached by the secondary mirrors, with a target
temperature of 0 Celsius. A facilities test later showed that the
secondary mirrors probably reach a temperature of approximately 5
Celsius. For the test, the contaminant was raised to 60 Celsius.
Run Mirror Duration Total TQCM % Specular
Change Change
1 R4 22,800 sec na -22.4%
13
Conclusion
The testing process used at the In Situ Contamination Facility
provides worthwhile information on the contamination effects of the
materials tested. This aids in making recommendations about which
materials are suitable for use upon Space Station Freedom. This
facility is able to help support any further research on the
effects of contamination by space materials on optics.
R. Bar ry L_-_Oh_Son
Principal Invest/gator
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Contamination analysis of SSF candidate materials

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