Contamination analysis for UV observations
as an extension of Hinode OTA

Solar-C Science Definition Meeting
Nov. 20, 2008
F. Urayama (Space Engineering Development Co. Ltd.)R. Yamanaka, E. Miyazaki, Y. Kimoto (JAXA)

Outline
1. Molecular contamination on orbit
2. Contamination analysis for Hinode(SOLAR-B) OTA
3. Objectives of contamination analysis for
SOLAR-C Plan B
4. Analysis assumptions (Preliminary)
5. Results (Preliminary)
6. Summary21. Molecular contamination on orbit
International Space Station (ISS) asseen from Space Shuttle

Russian segment

Photo by NASA
Ref.: C. E. Soares, R. R. Mikatarian‡a, R. A. Scharf and E A. Miles: ISS Flights 1A/R-6A
External Contamination Observations and Surface Assessment, Proc. SPIE, 4774,
pp.210-221, 2002.

Mechanism of molecular contamination on orbit•

Molecular contaminants were outgassed from organic materials.

•The contaminants reached and accumulated on the surfaces.

•Solar UV light changed the contaminants to dark color.
32. Contamination analysis for Hinode OTA
Overview of OTA
Critical components¾ Primary Mirror (M1)

Shield tube
HDM cylinder¾ Collimating Lens Unit(CLU)

MLI¾ 388-688 nm (visiblelight)
Outgassing sources

Sunshade~210W
Secondarymirror

Silverizedteflon

165~185W
Center section

Side cooling plate

HDM

Primarymirror

OTA-Spacecraftinterface

2nd Field Stop

MLI

¾ CFRP¾ Adhesives etc.

OSR

M2 operational heater¾ Secondary Mirror (M2)

Observation wavelength

Sun light

CLU
OBU

Bottomcoolingplate~2.6W
Bottom cover

CTM-TM

CLU operational heater42. Contamination analysis for Hinode OTA (Cont’d)¾ Increase in solar
absorptance of mirrors.

Organic materials contains;¾ Plasticizers¾ Anti-oxidizers¾ UV absorbers¾ Monomers

Outgassinganddeposition
on optics¾ Decrease in reflectance ofmirrors.
¾ Decrease in transmittanceof lenses.

Contaminants degraded optical systems!
¾ Increase in temperature of mirrors.
In worst-case scenario;
Thermal deformation of the mirrors.
Degradation of diffraction-limited images ofOTA.
¾ Decrease in throughput at shorter wavelength.
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2. Contamination analysis for Hinode OTA (Cont’d)Mathematical models for OTA contamination analyses
1. Mass accumulation on the critical surfaces(Deposition rate)=(Outgassing rate)*(Transport factor)*(Sticking coefficient)
Outgassing

TransportDeposition

2. Optical degradation of the mirrorsρ (λ ) = ρ0 (λ ) ⋅ exp(−2α C (λ ) ⋅ χ )αc： Absorption coefficient inherent incontaminant.
ρ：Reflectance of contaminated mirror
χ：Contaminant thickness
ρ ： Reflectance of clean mirror
λ：Wavelength062. Contamination analysis for Hinode OTA (Cont’d)
SOT throughput
Observation

Numerical analysis
1.1

Throughput

1.00.9λ=668.4nm
λ=555.0nm
λ=450.4nm
λ=430.5nm
λ=396.8nm
λ=388.3nm

0.8Solar observation
wavelength, Angstrom

CCD bake-out

0.7

0.6036912

Elapsed time since OTA top door was opend / monthNote:1) Contaminated optics: CLU, M1, M2 in degradation
order.
2) Model contaminant: Tetra-methyl tetra-phenyl trisiloxane (MPS).
3) Absorption coefficient: constant with UV irradiation
7time.

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3. Objectives of contamination analysis for
SOLAR-C Plan B¾ To assess degradation of throughput
at wavelength range of solar UV light,
induced by molecular contamination.

84. Analysis assumptions (Preliminary)¾ SOLAR-C telescope is constructed of same materials and structures (outgassingsources) as OTA.
¾ Temperature of SOLAR-C telescope is same as the temperature (outgassing rate) ofOTA on orbit.
¾ The mirrors coated with Al and MgF2 are used for SOLAR-C. UV reflectance of themirrors is higher than that of OTA mirrors.
¾ Critical wavelengths of the SOLAR-C observation are 122, 155 and 280 nm.
Note) Observation wavelengths of OTA were ranged from 388 to 688 nm.

¾ Absorption coefficients of the contaminants are equal to;
average value of the absorption coefficients of several materials at wavelength of122 or 155 nm. These coefficients were derived from report No. MCR-80-637.
the absorption coefficient of photo-deposited Methyl Phenyl Siloxane (MPS) at
wavelength of 280 nm.
Note) The absorption coefficients of photo-deposited MPS at wavelength range of visible light
were used for OTA analysis.

¾ Photo-deposition of the molecular contaminants occurs on M1 and M2. Other opticalelements are not taken into account.
¾ Threshold of SOLAR-C throughput is 10% for three years.
95. Results (Preliminary)
Wavelength: 122 nm (Ly α)
λ = 122 nm

1

Throughput

0.8

Same as OTA bakeout time

0.6
Five months longer thanOTA bake-out time

0.4
0.2

17 months
00123

Elapsed yearsNote) Bake-out time of OTA CFRP structures: four months
In vacuum chamber: three months
On-orbit: one month105. Results (Preliminary) (Cont’d)Wavelength: 155 nm (CIV)
1

Throughput

Same as OTA bake-outtime

0.6

0.2

0012
Elapsed years

3

Same as OTA bake-outtime

0.4

0.2

0Five months longer thanOTA bake-out time

0.8

0.60.4

λ = 288 nm

1Five months longer thanOTA bake-out time

0.8Throughput

Wavelength: 280 nm (Mg II)

λ = 155 nm

012

3

Elapsed years

116. Summary¾ Preliminary analysis for SOLAR-C Plan B shows;
9 Throughput at wavelength of 122 nm decreases to 10%for 17 months.
9 Throughput at wavelength of 155 nm or 280 nm
maintains above 10% for three years.
¾ In order to achieve the SOLAR-C Plan B mission successby using one telescope, bake-out of the components invacuum chambers and on orbit will take a lot of time andeffort!
¾ If wavelength of 122 nm is important for SOLAR-C science,
redesign of telescope may be required. The redesign
includes preparation of a special telescope for 122 nm.
1213

Degradation of solar UV space instruments: OSO-8

OSO-8: 8th Orbiting Solar
Observatory
LPSP: multichannel high resolution
UV and visible spectrometer

Ref.) Udo Schühle: Cleanliness
and Calibration stability of UV
instruments on SOHO, 2004.

14Degradation of solar UV space instruments: UARSSUSIMUARS: NASA's Upper
Atmosphere ResearchSatellite
SUSIM: Solar Ultraviolet
Spectral Irradiance
MonitorOptical path degradation of SUSIM during 2.5 years of theUARS missionRef.) Udo Schühle: Cleanliness
and Calibration stability of UVinstruments on SOHO, 2004.

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