A passively deployed array of contamination-sensitive samples was mounted and flown in the cargo bay of the space shuttle Columbia during the first orbital flight test. A similar unit was mounted in a different location in the cargo bay at Dryden Flight Research Center during the postflight operations there prior to the ferry flight return of Columbia to Kennedy Space Center. The samples in both POSA arrays were subjected to a series of optical and analytical measurements prior to delivery for installation in the cargo bay and after retrieval of the flight hardware. A quick-look summary of the results of a comparison of the series of measurements is presented

Linton, R. C.

Miller, E. R.

English

NASA Technical Reports Server

  
 
 
N O T I C E 
 
THIS DOCUMENT HAS BEEN REPRODUCED FROM 
MICROFICHE. ALTHOUGH IT IS RECOGNIZED THAT 
CERTAIN PORTIONS ARE ILLEGIBLE, IT IS BEING RELEASED 
IN THE INTEREST OF MAKING AVAILABLE AS MUCH 
INFORMATION AS POSSIBLE 
https://ntrs.nasa.gov/search.jsp?R=19810015626 2020-03-21T14:01:37+00:00Z
MSFC - Form 3190 (Rev June 1971)
NASA i`ECHNICAL	 ,^^ ^^1112^a^j^
MEMORANDUM	
^q^^^cG^^^
	
N 2^^y^,y^^,
NASA TM-82421
I
PASSIVE OPTICAL SAMPLE ASSEMBLY lr OSA) FOR STS- 1--
QUICK LOOK POST-MISSION REPORT
By Roger C. Linton and Edgar R. Miller
Space Sciences Laboratory
June f, 1981
( N ASA-1N-8^421)
	 !?ASSI:VE UPTICA.L SAMF:Lk
	 Jd1-24161
ASSEMBLY (POSA) FGd $TS-1 QUICK LOOK
PU; T-MISSION RLPULT (NASA) 17 p
HC AO4/dkt A01
	 (SCL 22A
	 UI clai i
G3/16 4243 1
NASA
f
George C. Marshall space .17light Center
Marshall Space Flight Center, Alabama
0TABLE OF CONTENTS
Page
INTRODUCTION	 ...................................................... 	 1
DESCRIPTION OF HARDWARE	 ...........	 ..............I......	 1
POSA I'1SSION DETAILS ............................................... 	 3
RESULTS—OPTICAL MEASUREMENTS ................ 	 3
RESULTS@a--PARTICLE ANALYSIS ............ 	 ............... 	 ..	 9
RESULTS-- ELECTRET ANALYSIS ........................ 	 ..............	 9
CONCLUSIONS ....................................... 	 11
REFERENCE	 .................... 	 ......	 12
Ff
r
I
PRECEDING PAGE BLANK NOT FILMED
i i i
LIST OF'ILLUSTRATIONS
Fi uc rre No.	 Title	 P?2e
1	 POSA/DFI postflight ................................ 	 5
2	 POSA/FF postflight ................................. 	 G
LIST OF TABLES
Table No.	 Title	 Pale
1	 Passive Optical Sample Assembly (POSH) -
DF1 Pallet Unit .................................... 	 2
2	 Passive Optical Sample Assembly (POSA) -
Ferry Flight Unit ..................................
	
2
S	 POSA Mission Timeline Details 	 4
If
4	 POSA Results: Optica? Measurements ................. 	 8
5	 Comparison of Contamination During STS-1 Orbital
	 I
Flight and Ferry Flight ....... 	 ...................	 10
iv
NASA TECHNICAL MEMORANDUM
INTRODUCTION
A passively deployed array of contamination-sensitive samples was
mounted acrd flown in the cargo bay of theS ace Shuttle Columbia (STS -1)
during the first Orbital Flight Test (OFT -11,   April 12-14, 1981. A similar
array was mounted in a different location in the cargo bay at Dryden
Flight Research Center during the postflight operations there prior to
the "ferry flight" of Columbia back to Kenned ' I Space Center (KSC).
Designated as the Passive Optical Sample Assembly (POSA), the aerays
were flown to aid in the assessment of contamination hazards of the
Shuttle cargo bay for future missions.
The POSA unit flown on the orbital phase of the mission was mounted
on the Development Flight Instrumentation (Dry pallet in the cargo bay
of the Shuttle; it will henceforth be designated as the POSA/Dri unit.
The POSA unit mounted for just the ferry flight will be designated as
the FOSA/K. Samples in the POSA/DFI were subject to deposition of con-
taminants throughout prelaunch, ascent, orbital, descent, and ferry
flight phases of the OFT-1 mission, Inclusion of the second POSA unit,
POSA/"F, during the ferry flight phase of the mission provides a means
of identifying contamination hazards peculiar to that single phase of
the mission.
As experimental flight hardware, both POSA units are totally pas-
sive in nature. Each is a mounted array of five optical samples and
three static-charged Teflon sheets (eloctrats). Circumstances led to the
inclusion of only two electrots on the POSA/FF unit? Tables 1 and 2 pro-
vide directories of the samples contained in the POSA units. All of the
samples were subjected to a series of o p tical and analytical measurements
at the Marshall Space Flight Center (MSYC) prior to delivery for instal-
lation at KSC and Dryden Research Center. The measurements were repeated
in an identical manner at MSFC following retrieval of the flight hard-
ware. A summary of the results of a comparison of these measurements
constitutes the basis of this "quick-look" report; a more detailed analy-
sis will follow in a separate publication at a later date.
DESCRIPTION OF HARDWARE
Each POSA unit consists basically of a rectangular holder with six
cylindrical receptacies (1.09 in, wide, 0.187 in. deep) bored at equal
spacing. Smaller (0.75 in. diameter) holes in each of the sample "slots"
are counterbored completely through the holder so that effluents can
reach front and rear surfaces of the samples.
1, Also, uv-grade fused silica was substituted for the CaF 2 window
(sample D) for POSA/FF.
TABLE 1
PASSIVE OPTICAL SAMPLE ASSEMBLY (POSA)
DFI PALLET UNIT
Tray 012
Sampl a Ma teria l
A Magnesium Fluoride Overcoated Aluminum
(MgF2/Al)
B Gold Mirror
C
0
1510 A Filter
D Ca F2 Window
E Top:	 Ca F2 Window
Base;	 Electret #9
F Top:	 Electret	 #11
Base;	 Electret #10
TABLE 2
PASSIVE OPTICAL SAMPLE ASSEMBLY (POSA)
FERRY FLIGHT UNIT
Tray 05
Sample Material
A MgF21A1 Mirror
B Gold Mirror
C 1790 A Filter
D UV-Grade Fused Silica
E Ca F2 Window
F Top;	 Electret #14
Base; Electret #13
2
41
LIL.
A retainer plate with six circular "apertures" is bolted over the
sample holder, allowing maximum front- surface exposure of the samples
while holding down the outer edges, During i"ose phases of ground hand l.
inc3, transportation, and installation when exposure was not desired, a
solid, rectangular cover plate with captive screws was attached to pro-
tect the samples, The POSA hardware was machined from 300 series stain-
less steel. A more detailed description of the POSH hardware, including
assembly and handling specifications, is available in a prior publication
[1].
POSA MISSION DETAILS
The POSA/DFI unit was mounted to the starboard rail of the DFI
Pallet (Xo
	
1069) in the Shuttle cargo bay.In Shuttle coordinates,
the array was mounted in the X,Y plane, with the samples' surface normal
parallel to the Shuttle Z-axis. The cargo bay doors of the Shuttle were
opened 2 hr, 35 min after launch.
The POSH/FF unit was separately mounted, postlanding at Edwards
AFB, at a cargo bay location specified by Xo
	
750, inside access door
No. 44.
A summary of pertinent mission timeline details is provided in
Table 3; for example, from Table 3, the samples of the POSH/DFI unit
were exposed, unco , ared, in the cargo bay for nearly a month prior to
launch. Of course, during this period,, the cargo bay doors were closed,
with no access of personnel. With reference to both units, there were
9 days of exposure to the ambient cargo bay environment on the ground at
Edwards AFB.
RESULTS-OPTICAL MEASUREMENTS
The POSH units were received at MSFC on May 7, 1981. They were
photographed, as received, on May 8, and the postmission measurements
were begun soon thereafter (Figs. 1 and 2). From inspection of Figures
1 and 2, the larger particulates {and/or fibers) can be readily observed
on the reflective samples of both units; considerably greater amounts of
M
	
	 particulates of smaller size can be seen on closer inspection and in
magnified photographs. Visual inspection of the samples from both POSA
units reveals no direct evidence of a contaminant film, with the single
exception of the magnesium fluoride overcoated aluminum (MgF2/Al) mirror
of the POSA/DFI unit (sample position " A" in Figure 1). The smudge and
droplet on this sample remain of as yet undetermined origin, in both
chemical nature and point of time.
TABLE 3
POSA MISSION TIMELINE DETAILS
POSA/DFI ( q 1})
MSFC Shipment March 3
KSC Delivery March 3
Installation March 13
Cover Removed March 17
Launch April 12
Landing April 14
POSA/ FF (19001)
MSFC Shipment
	 April 13
Edwards AFB Delivery 	 April 14
Installation	 April 22
POSTLANDING PHASES ( B OTH UN ITS)
Shuttle Departure (Edwards AFB)	 April 23
Shuttle Arrival (KSC)	 April 24
Cargo Bay Doors Open (OPF/KSC)	 May 2
POSA Covers Installed /Units Removed	 May 6
MSFC Arrival	 May 7
a
Optical measurements of the POSA samples were performed on two
separate instrumentation facilities. In the wavelength range 120 to
290 nm, specular, spectral reflectance and transmittance (at near-normal
incidence) were measured in a reflectometer at the exit slit of a
Seya-Namloka-type monochromator. A hydrogen discharge lamp was utilized
4
r^
r.
a+
w
g
0d
vL
cr
1;-qm!m
v
rnl` J
as the source. The measurements were extended thoough 2,5 Um wavelength
(overlapping slightly in the near uv) by measuring the diffuse reflect.
ance and backscatter coefficient in 
a 
Beckman/Gier-Dunkle integrating
sphere facility.
With the single exception of the smudged MgF?/Al mirror from the
POSA/DFI unit, none of the samples measured In thCGier-Dunkle facility
(0,25 to 2.5 pm) indicate any significant degradation through that
spectral range.
The smudged MgF2/A1 mirror from the POSA/DFI unit indicated, by
diffuse reflectance measurements from 0,25 to 2.5 pill, a 10 percent rela-
tivo increase in mirror absorptance. Backscatter measurements on this
sample, in this range, indicated an increase more than double the origi-
nal level, although the levels (0.02 preflight, 0.07 postflight) are,
in magnitude, subject to large uncertainty.
In the range 120 to 290 nm, the measurements of specular, spectral
reflectance of the smudged MqF2/Al mirror indicate a generally uniform
9 to 10 percent relative decrease in reflectance. Measurements on the
other samples of both POSA units basically indicate minimal (if any,
significant) degradation at wavelengths longer than 200 nm, with patterns
of apparent increased degradation at shorter wavelengths. A summary of
the optical changes at selected, representative wavelengths is given 'in
Table 4, where the parameter %A refers to the percent change in reflect-
ance or transmittance at a given wavelength, computed as the difference
of the prelaunch values and the postlaunch value , , divided by the origi-
nal value and expressed as a percentage.
Percentage changes in reflectance or 'transmittance of magnitude
5 percent or less must be viewed with caution because these levels ap-
proach the limits of uncertainty for the measurements. 
In 
summary of
Table 4, it could be 'inferred that the reflecting optical samples may be
degraded by the presence of thin film contaminant layers. Since the
observed absorption increases inversely proportional to wavelength in
the vacuum ultraviolet, the apparent degradation may be enhanced by
interference effects with the reflectj, ng mirror film. The results for
the vacuum ultraviolet filters (1810 A central X for POSA/DFI, 1790
for POSA/FF) indicate, at first glance, similar degradation. These
filters consist of multilayer, metallic thin film overcoats on magnesium
fluoride substrates; iwwever, the percentage changes in transmittance
are subject to greater uncertainty than the comparable changes in reflect-
ance for the mirrors simply because the filter transmittance values are
low in magnitude (0 to 20 percent).
Measurements of transmittance of the transparent samples indicate
no significant changes for samples of either the POSA/DFI unit or the
POSA/FF unit.
TA13LE 4
POSH RESULTS: OPTICAL M'r.'ASUREMCNT.'i
^" IDFI
1A 
Fr
Sampl e:
Magnesium Fluoride Over- 1300 09.4 -9.3
coated Aluminum (MgF2/Al) 1600 -9.4 -4.8
Reflectance 2400 -8.8 -518
2800 -9.0 0
Gold - Reflectance 1300 -21.9 -14.3
1600 -8.1 -15.8
2400 -13.3 -5,4
2800 -5.7 -7.1
Calcium Fluoride
	 (C,0,, , )	 - 1300 +3.7 No preflight
Transmittance measurement
available
1600 -1.3 -6.8
2400 -1.1 +2,2
2800 -1.1 +1.7
Fused Silica	 ( 5102)	 - 1600 0
Transmittance 2400 0
2800 -2,2
Calcium Fluoride (Ca F2) #2 - 1300 -3.5 0
Transmittance 1600 0 0
2400 +1.1 0
2800 -1.1 0
UV Filters - (1810 (1790
Transmittance Filter) Filter)
1700 -10.0 -15.6
1800 -4.8 +5.4
2000 0 0	 41
2100 0 0
Measurvyints of the reflecting efficiency of the "back" sides (4)
of the POSA samples in the vacuum ultraviolet were performed to assess
directionality in the flow of effluents, if any. Since the magnitude of
back-surface reflectance is very low for both the transparent samples
and the reverse side of the reflecting mirrors, the measurement uncer-
tainty is increased Q 10 percent), The data show, however, that no sig-
nificant changes In the "back" surface reflectance of POSA/FF samples
were measured, while for the " back" surface reflectance of POSA/DF1
samples, there are 20 percent relative changes in the "back"
surface reflecting efficiency, significantly pronounced abovo the back-
ground uncertainty level, This difference is probably an interference
effect. The deposition on the "back" sides of the POSA /OF1 samples is
intuitively assumed to arise from outgassed products from the ort pallet
strut to which the POSA/Dri unit was mounted; the sample back side was
exposed to the paint by a narrow gap due to the Mounting spaces of the
POSA unit,
RESULTS--PARTICLE ANALYSIS
The quantity and size distribution of particles on some of the
samples of both POSA units have been measured using a white light,
imaging, digital particle counting facility. Only partial results for
the POSA samples are available at this time; three sets of particle
counting scans have been completed. These include comparison scans of
similar samples from the POSA/DF1 unit and the POSA/FF unit. For all the
samples measured to date, the results uniformly indicate a size dis-
tribution heavily weighted toward particles less than 10 v in
diameter, with the greater number of these less than 5 p in diameter.
The preliminary results indicate, further, that the type of sample sur-
face may have a considerable influence on the number of adhering particles;
particle counts on the ultraviolet filters of both POSA units exceed
WHO for particle diameters less than 5 p, while the comparable sta-
tistics for the MgFp/Al mirrors were lower by a factor of 10 3 . Most
puzzling, at this time, are the preliminary results for the transparent
calcium fluoride ( CaF2) samples of both POSA units; these samples appear
virtually free of significant particle accuoulation. Further measure-
ments and analysis will clarify these preliminary results and will be
published at a later date,
RESULTS--ELECTRET ANALYSIS
The alectrets are made of Teflon-polytetrafluorethylene, (C2H4)n.
Electrets are dielectrics with a permanent surface charge ( approximately
10- 8 Coulombs/cm 2
 density) that gives them properties analogous to magnets
by retaining electrically active particles and ions on their surface.
Energy measurements are made in the X-ray energy range from 0.707 to
^Wr
P
9
30 keV +0.170 keV (i.e,, fluorine to silver) using an X-ray microprobe to
analyze the effluents collected on the Teflon electrets, Thus, an ele.
mental analysis and an estimate of the abundance of the elements are
obtained,
Three electrets were included in the POSA/DF1 for STS-1. One was
placed under Sample E, the calcium fluoride "window." For this electret,
the ion-attracting charged surface was oriented 180 degrees from the
direction the Ca F2 sample faced, providing a measure of the direction-
ality of effluent flow, The other two electrets w-.re placed in sample
slot ' I F" of 
the 
POSH holder (one facing "up", +Z, and the other facing	 10
"down". • Z) for directionality analysis.
Two electrets in the POSH/DFI, position E (down) and electret
#10 position F down), showed no significant evidence of contamination
present. Electret #11, also at position F but facing "up", showed a
significant increase of Si and Al after X-ray microprobe analysis, On
the ferry flight of Columbia from Edwards AFB, California, to Kennedy
Space Center, Florida, no significant amount of Si was collected, but a
significant amount of Al was measured on electrets 13 and 14 after the
energy-dispersive analysis of the electrets (Table 5).
TABLE 5
COMPARISON OF CONTAMINATION DURING STS-1 ORBITAL FLIGHT
AND FERRY FLIGHT
Relative	 Total Counts +
Electret No.	 0	 Element	 Abundance	 _^ckqjoundLe ^R_Itp_tim 	 	 a
9 Cargo bay, STS-1,
OFT	 pallet,	 posi- Al -
tion E (down) Si -
10 Cargo bay, STS-1,
DFI	 pallet,	 posi- Al -
tion F (down) Si -
11 Cargo bay, STS-1,
DFI	 pallet,	 posi- Al 7700 2.4
tion F (up) Si 900 2.3
13 Ferr,,;, flight re-
turn of Columbia
from Edwards AFB Al 8300 2.4
to KSC (down) Si
14 Ferry flight re-
turn of Columbia
from Edwards AFB Al 3830 1.7
to KSC (up) Si - -
10
CONCLUSIONS
It
The most probable cause of most of the optical degradation is par-
ticulate deposition since it is measured on both POSH units, and depos ,i-
tion of molecular films would not be expected in the ferry flight environ-
ment. However, based on reflectance data, there is indication of a
molecular film on the gold sample. Reflectance data provide the most
sensitive measurement for an absorbing molecular film because the rays
pass through the film twice. Unfortunately, because of the smudge on
the MgF2/Al sample (DFI unit), it cannot be compared directly with the
ferry flight sample for molecular deposition.
Also, a significant degradation was measured on the back side of
samples with a large view factor to the painted DFI structure,
The particulate levels were very high in the 4 5 pm range for DFI
and ferry flight mirror samples and less on other samples, indicating
variations in adherence,
It is emphasized that these results are for unprotected samples
subjected to all phases of the flight, including the ferry flight. STS-1
was subjected for many months to a relatively uncontrolled environment
during manufacturing efforts, These results should not beapplied
directly to anticipated degradation of protected optics on future Space
Shuttle missions.
-e
11'
II
i
r^
,J
REFERENCE
1.
	
	 Linton, Roger C.; The Passive Optical Sample Assembly (POSA)
on STS-1, NASA TM-82407, March 1981.
12
iE	 _.
APPROVAL
PASSIVE OPTICAL SAMPLE ASSEMBLY (POSA) FOR STS-1 --
QUICK-LOOK POSTMISSION REPORT
By Roger C. Linton and Edgar R. Miller
The information in this report has been reviewed for technical
content. Review of any information concerning Department of Defense or
nuclear energy activities or programs has been made by the MSFC Security
Classification Officer. This report, in its entirety, has been deter-
mined to be unclassified.
RUDOLF DECHER
Chief, Space Ph sits Divisio
CHARLES A. t.UNDQUIST--
Director, Space Sciences Laboratory
I
,.
* U.S. GOilERNMENTPRINTING OFFICE 1981-740 ,066/446 REGION NO.4
i
	
13


Passive Optical Sample Assembly (POSA) for STS-1 quick look post-mission report

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server