dimensional stability for satellite optical...
TRANSCRIPT
위성용 광학 탑재체의 치수안정성 연구
Dimensional stability for satellite optical payload
Smart Systems and Structures Lab Dept. of Aerospace Eng.
KAIST
Contents Table
o Introduction
o Thermal expansion measurement of composite materials
o Hygroscopic deformation measurement of composite materials
o Optical payload performance simulation
o Conclusion
o Other space related research at SSS lab
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INTRODUCTION
• Importance of dimensional stability
• Characteristic of CFRP
• Characteristic of FBG
• Optical performance payload simulation
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Introduction
o Dimensional instabilities(static deformation, jitter) in space Static deformation(de-space, tilt, de-center) – radiation, vacuum out-gassing
Dynamic jitter(LOS jitter) – RWA, cooler, flexible body
o Dimensional instabilities causes optical performance degradation[1]
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Static deformation – radiation, vacuum –
Dynamic jitter – RWA, Cooler –
Static deformation – tilt, de-center, de-space –
Image quality degradation[1]
Dynamics jitter – LOS jitter –
Introduction
o Materials for telescope structures
• Lightweight and high dimensional stability
High stiffness/density ratio is required
Low thermal expansion is required
• Characteristic of CFRP
High stiffness/density ratio (3times higher than titanium)
Low thermal expansion characteristic can be achieved via “Tailoring”
Hygroscopic deformation characteristic need to be known in advance
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Carbon fiber(CME ~ 0, CTE ~ -0.9)
Matrix(cynate/polymer, etc)
Unidirectional carbon fiber Prepreg
Laminate is designed to satisfy desired properties. Low CTE/CME property is useful in space environment for optical structure
Rule of mixture, FEM
α, β, E, vf is known
Desired properties
Carbon Fiber Reinforced Plastics(CFRP) can satisfy these requirements
o Examples of dimensional stability evaluation for CFRP (cont.)
• Precise measurement to evaluate near zero hygro-thermal expansion of CFRP
Introduction
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US’s hygroscopic deformation measurement[2] - Simulated space env. - Process for 6 days - Precise weight measurement
Japan’s CTE measurement[3] - Simulated space env. - Precise length measurement - Precise temperature control - 1ppb/℃ resolution
o FBG (Fiber Bragg Grating) sensor • Small, lightweight, high sensitivity, electro-magnetic immunity,
• No hygro-effects and easily installable onto/into host structures.
• Capable of Multiplexing and Temperature measurements
• Real time acquisition
o Working principle
• Bragg wavelength
Grating have sinusoidal refractive index
Reflected wavelength is defined as
• Change of the reflected wavelength is measured
and calculated into physical properties
Introduction
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Optical fiber
Bragg grating
B
I
I
B
I
Input spectrum
Reflected signal Transmitted signal
L 10mmIndex of
refraction of
fiber core
zz2z1
ne
Δn = 10-5 to 10-3
2B en
en
: effective refractive index
: grating period
(1 )B
e s f
B G
p T
Optical fiber
Introduction
o Optical performance simulation for aerospace optical payload[4,5]
• Structure-optical performance tool(SigFit, since late 1980‟s)
Combine CodeV + NASTRAN
Fully numerical, detailed structure and optical surfaces are needed
Image simulation is not supported
• End-to-end image simulation(PICASSO)
MTF/Image performance simulation
Do not consider structural aspect, consider illumination, angle condition etc
Performance calculation from analytic solution
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SigFit model PICASSO result
THERMAL EXPANSION MEASUREMENT
• Measurement system construction
• Thermal expansion measurement result
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Thermal Expansion Measurement
o Measurement system requirements
• Definition of Coefficient of Thermal Expansion(CTE)
Average CTE
Instantaneous CTE
• Measurement system requirement
Precise length change measurement
Precise temperature change and its measurement
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0
1 L
L T
2 1 1*
2 1 1
( ) / 1m
L L L L
T T L T
Average/Instantaneous CTE method
Requirements Detail
Length measurement Measuring ~ 0ppm/℃ Not disturbed by temperature change
Minimize mechanical disturbance
Temperature control Simulate space environment Uniform around specimen
Thermal Expansion Measurement
o Optical interferometer and thermal vacuum chamber construction
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Requirements Detail Solution
Length measurement - Interferometer
Measuring < 0ppm/℃ Not disturbed by Temperature change
Minimize mechanical disturbance
Resolution < 5nm Quartz base minimize thermal distortion
Temperature control - Thermal vacuum chamber
Simulate space environment Uniform around specimen
Heater and Cooler(3~114℃) Rotary pump and diffuser pump(~ ) 510 torr
Thermal expansion measurement system
Thermal Expansion Measurement
o Optical interferometer measuring principle
• Interferometer is appropriate for the measurement of small displacement
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Measured material
Light path of interferometer
1 2
_ _
_ _
_
A
B
f horizonal polarized frequency
f vertical polarized frequency
d d specimen length
1 1 2 2
1 2 2 1 2
cos[2 ( ) ]
cos[2 (( ) 2 / 2 / )]
4 ( ) / ,( )
ref A B
mea A B
V A f f t
V B f f t nd nd
n d d
Measurement principle
Phase meter measure difference
Measure length change
Thermal Expansion Measurement
o Measurement system uncertainty evaluation and measuring process
• Refractive index change in air(~72nm) and uniformity(~68nm) are significant
• Reliable and repeatable measuring process is established
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Thermal expansion measuring process
Thermal Expansion Measurement
o Thermal expansion measurement composite table
o Thermal expansion measurement result
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시편 이름 시편 형상 정보
M55J fiber direction 두께 2mm, 길이 300mm X 3 for 3 times each
M55J transverse direction 두께 2mm, 길이 100mm X 3 for 3 times each
시편 이름 실험 조건 Average CTE
M55J fiber direction 13~23℃ thermal cycle condition -0.92 ppm/℃
M55J transverse direction 13~23℃ thermal cycle condition 38.8 ppm/℃
CFRP specimen Chamber figuration DMI and silica base
Thermal Expansion Measurement
o Thermal expansion measurement result
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M55J fiber direction
M55J transverse direction
Thermal Expansion Measurement
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o System configuration
• FBG sensors and Displacement measuring Interferometer
FBG sensors
Axial direction
Radial direction
Free FBG sensor
Thermal Expansion Measurement
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o Evaluation and monitoring of the thermal deformation
• Measurement of CTE of the Space materials
Invar36® (~1.3ⅹ10-6K-1), Gr/Ep [90]8
Gr/Ep [90]8 Invar 36
HYGROSCOPIC DEFORMATION MEASUREMENT
• Measurement system construction and verification
• Hygroscopic deformation measurement result
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Hygroscopic Deformation Measurement
o Measurement system requirements
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Requirements
Environment
Constant temperature 28±1℃[1]
Vacuum condition [1]
Precise measurement
Long time duration ~ 3 week
Minimize stress < 1% of displacement
Measurement range 0.1~100㎛
5~10 torr
/ at 58 0%, constant temperature strain L L RH
Precision
Stability
10㎛
0.1㎛
0.01㎛
1hr 1day 1week 3week
Interferometer w/o stabilizer
Interferometer with stabilizer
Dilatometer
transverse
longitudinal
Thermal Moisture
SSS Lab[1]
Present
EADS[7]
US[6] ESA[8]
ZERODUR
Composite
[6] James F.Gilmore. state of the art CME measurement, SPIE Vol 2542, pp. 121-128, , 1983 [7] A.Poenninger, B.Defoort, Determination of the coefficient of moisture expansion, Proceedings of the 9th International Symposium on Materials in a Space Environment Noordwijk, The Netherlands, 16-20 June 2003 [8] ] D.Bashford, “Low Temperature Cure Cyanate Ester Prepreg Materials for Space Application”, ESA Space, 2001
Hygroscopic Deformation Measurement
o Displacement measuring sensor selection
• Long term stable, optical scale sensor[9]
• Sensor module is designed for optical scale sensor measurement
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Reader – read deformation
REF – data correction
Scale – Grating is provided
Reader generate A, B phase
Direction determined by A, B phase’s intensity order
Sensor module is designed for measurement
Hygroscopic Deformation Measurement
o Basic configuration of measurement system
• Two flexible beams support scale and deliver deformation of specimen
Preload can be given
• External disturbance is minimized
Kinematic coupling is added for mechanical isolation
All structure is made of INVAR – minimize temperature disturbance
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Sensor module for ENC(INVAR)
CFRP
Reference frame (INVAR)
CME measurement system
Measurement direction (+)
Preload direction(+)
Kinematic coupling is added
Preload direction(+)
Read head
Scale
Flexible beam
Hygroscopic Deformation Measurement
o Sensor module structure design
• FEA is used for design optimization
Flexible enough in the measurement direction (1st mode<100Hz)
Stable enough in the other disturbance directions (2nd mode>10*1st mode)
The displacement of the measurement point and the displacement of the specimen have to be the same. (The present design shows <0.01% error.)
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1st 2nd 3rd 4th Error
Sensor Module 80.404(<100) 1397.1(>10*1st) 1416.8 1826.2 <0.01%
1st mode
Measurement direction
Specification
Probe part FEA model
35mm
55mm
0.5mm 5mm
40mm
Hygroscopic Deformation Measurement
o Sensor system structure design result
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CFRP : 210.5mm ±6.5mm
Ref frame(Invar)
SUS plate
Sensor module(Invar)
Sensor reader
Kinematic coupling - 4 balls, radius 2.5mm
End clamp
1. Ref frame – specimen + sensor module fix 2. Sensor module – measurement using reader& scale 3. SUS plate – isolate external disturbance by kinematic coupling 4. End clamp – scale fix part 5. CFRP specimen – 210.5mm ±6.5mm
Hygroscopic Deformation Measurement
o Sensor system verification
• Measurement precision verification
Measurement result was compared with the result of the interferometer
Displacement was given by thermal expansion of steel
Verified displacement range: 1~300㎛
Max speed – 1.5㎛/s
Prestrain – 100㎛ is given
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Heat tape – thermal expansion
Interferometer ENC
ENC Interferometer
Hygroscopic Deformation Measurement
o Sensor system verification
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~1㎛ ~10 ㎛
~100 ㎛ ~300 ㎛
Hygroscopic Deformation Measurement
o Sensor system verification
• Long term stability verification and measurement procedure
Long term stability is verified by measuring stainless steel
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MEASUREMENT PROCEDURE
Hygroscopic Deformation Measurement
o Sensor system verification
• Long term stability verification result
stainless steel keeps 0 in 5 days
Test specimen Acryl results
235㎛(=1119ppm, roughly 1000ppm is expected by acryl reference[12])
System is long term stable and reliable
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Steel test Acryl test
Steel: disp~0±0.1㎛ Acryl: disp~235㎛
Hygroscopic Deformation Measurement
o Hygroscopic deformation measurement result
• Hygroscopic measurement composite table
• Hygroscopic measurement result
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시편 이름 시편 형상 정보
M55J fiber direction 두께 2mm, 길이 210mm X 2
M55J transverse direction 두께 2mm, 길이 210mm X 2
시편 이름 실험조건 Length change
M55J fiber direction 26℃, RH 59%(3 weeks) → 26℃, (3 weeks) 2.71±0.49ppm
M55J transverse direction 26℃, RH 59%(3 weeks) → 26℃, (3 weeks) -77.225±7.9ppm
16[0]
5~10 torr
5~10 torr
Measurement set up
Hygroscopic Deformation Measurement
o Hygroscopic deformation measurement result
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M55J fiber direction
M55J transverse direction
OPTICAL PAYLOAD PERFORMANCE SIMULATION
• Analytic modeling for diffraction limited system
• Image simulation using MTF
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Analytic modeling for diffraction limited system
o Design parameter setting
• GSD, Altitude, CCD size and Q factor can determine specification of telescope
• Determine factor = radius of PM(1.2m, ex), effective focal length(57.7m, ex)
Optional constant = central obstruction ratio
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CCD focal plane
Ground
CCD pixel size ~ few ㎛
Effective focal length
Altitude of satellite
GSD – Ground Sampled Distance
~ size of Airy disk(Q=1)
3
1.22
0.1 ~ 0.3,
210 ( / )
PM
cent
PMco
AltEFL CCDsize
GSD
EFLR
CCDsize
general case
Rk cycle mm
EFL
Analytic modeling for diffraction limited system
o MTF calculation of the system w/ central obstruction[2]
• General reflecting telescope has central obstruction
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Central obstruction by SM
Focal plane or other auxiliary optical part
( )( )/
i t kRik Yy Zz RA
aperture
eE e ds
R
Diffraction of light w/ far distance approximation
2( )(sin sin cos cos )/
0
2( )cos( )/
0
( )
0
sin , cos,
sin , cos
2 ( / )
ai t kRik q RA
a
ai t kRik q RA
a
ai t kR
A
a
eE e d d
R
y zds d d
Y q Z q
eE e d d
R
eE J k q R d
R
Calculation for central obstruction(R_sm=ηR_pm)
1
( )
1
2 2
* 2 41 1 1 1
( ( )) ( )
( / )2 ( )
/
( / ) ( / ) ( / ) ( / )/ 2 (0) 2
/ / / /
m m
m m
i t kRaA
a
du J u u J u
du
e J ukq RE u
R kq R
J kaq R J kaq R J kaq R J kaq RI EE I
kaq R kaq R kaq R kaq R
Light intensity = PSF
2
1( / )(0)
/
J kaq RI I
kaq R
w/o obstruction
Analytic modeling for diffraction limited system
o MTF calculation of the system w/ central obstruction[2]
• MTF is Fourier transform of PSF in spatial frequency plane
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2 2
2 41 1 1 1( / ) ( / ) ( / ) ( / )2
/ / / /
J kaq R J kaq R J kaq R J kaq RMTF Normalized FFT
kaq R kaq R kaq R kaq R
2
1 2
2 1 2
2
2 2 2 1
2( )
1
cos ( ) 1
{cos ( ) ( ) 1 ( ) }, 0
0,
1, 0
2
1 1 1{ sin (1 ) (1 ) tan [ tan ]},
2 1 2 2 2
10,
2
n
n n n
n n nn
n
n
n
n
Final form
A B CMTF k
A k k k
k k kB k
k
C k
k
k
Diffraction limited MTF performance of telescope w/ central obstruction
Analytic modeling for diffraction limited system
o De-space modeling
• De-space error depends on spherical shape, number of optical surfaces
Only approximation solution can be given
• Reference[3] describes simple spherical aberration
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2 220
1
2 2
( ) 2 2
2 2
20
2
0
20
1(1 ( ) )
22
0
1
( , ) , 1
0, 1
( )_
( )
2
1( )
4sin( { 1 })
2
4( ) cos (
n
ikw x y
p
n
n
n
iax
n
s
kn
n n
f x y e x y
x y
w coefficient of spherical aberration
EFL
f
D kMTF de
D k
a kw k
D k e dxdy
ka y dy
a
D k ak J aa
1 3 3 5
0 2 2 4 4 6
0
1
20
1 1) sin 2 ( ( ) ( )) sin 4 ( ( ) ( ))
2 4
4 1 1sin sin ( ( ) ( )) sin 3 ( ( ) ( )) sin 5 ( ( ) ( ))
3 5
1( ) (2 sin 2 )
4, cos
n
n
n n
J a J a J a J a
ak J a J a J a J a J a J aa
D k
a w k k
Spherical aberration approximation
MTF change w/ de-space
Analytic modeling for diffraction limited system
o Jitter modeling[10]
• Telescope internal jitter – from vibration relative to SM and PM…1
• LOS(Line Of Sight) jitter – from vibration of whole body…2
Pointing error of whole body
• MTF value factor : amplitude/CCD size
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movement of CCD plane
, , f LOS error of telescope f effective focal length
0 (2 )
( / )
,
,
1,
jitter
capture jitter
capture
jitter capture
MTF J k
k spatial frequency cycle mm
F amplitude of vibration
ff f
fF
f f
LOS jitter
Internal jitter
Amp/CCD
Image simulation using MTF
o Image resampling
• High quality image degrades due to min GSD(resolution) of system
• Using average filter for times of pixel size(original pixel/system pixel)
o Spatial frequency tuning for image
• FFT of image(in MATLAB) dimension fitting for MTF is needed
• Pixel size of image is same as CCD size(few ㎛)
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Resampling image
Resampling by „average filter‟
Original size of pixel(w/ exaggeration)
2 2 1/2( )
1000img
size size
i jk
CCD image
FFT
Real spatial frequency for FFT of image
Spatial frequency x: i
Spatial frequency
y: j
Multiplied by each MTF function
i,j FFT image
Image simulation using MTF
o MTF filter for image
• Original system MTF
• De-spaced MTF
• Jittered MTF
• Final system MTF(product of all previous terms)
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Spatial frequency x: i
Spatial frequency
y: j
Multiplied by each MTF function
i,j FFT image
…are multiplied to filter the original image
Original system
Final system
De-spaced system
Jittered system
Image simulation using MTF
o MTF result comparison w/ ZEMAX and image simulation result
• De-spaced MTF and image simulation
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10㎛ 50㎛ Original system
CONCLUSION
• Conclusion
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Conclusion and Future Plan
o Precise thermal expansion measurement for composite
• Thermal expansion measurement using DMI
• DMI + vacuum chamber system construction
• Thermal expansion of highly stable composites in dimensional is measured
o Precise hygroscopic deformation measurement for composite
• Hygroscopic deformation measurement using optical scale sensor
• Mechanical dilatometer + vacuum chamber system construction
• Precision of dilatometer is verified by DMI comparison test
• Long term stability of measurement system is verified
• Hygroscopic deformation of lamina is measured
o Future plan
• Hygroscopic deformation measurement for various composite
Quasi-isotropic, cross ply specimen
• thermal expansion measurement capability is added to hygroscopic deformation measurement system
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Reference
[1] 윤재산, M.S.Thesis, “위성카메라용 복합재료의 흡습변형에 관한 연구”, 2011
[2] James F.Gilmore. "state of the art CME measurement", 1983, SPIE Vol 2542, pp. 121-128
[3] Y.Takeichi et al,High-precision(<1ppb/℃) Optical Heterodyne Interferometeric Dilatometer for Determining Absolute CTE of EUVL Materials, SPIE Vol.6151, 2006
[4] http://www.sigmadyne.com(SigFit)
[5] S.A.Cota et al, PICASSO: an end-to-end image simulation tool for space and airborne imaging systems, Journal of Applied Remote Sensing, Vol.4 (8 June 2010)
[6] James F.Gilmore. state of the art CME measurement, SPIE Vol 2542, pp. 121-128, , 1983
[7] A.Poenninger, B.Defoort, Determination of the coefficient of moisture expansion, Proceedings of the 9th International Symposium on Materials in a Space Environment Noordwijk, The Netherlands, 16-20 June 2003
[8] ] D.Bashford, “Low Temperature Cure Cyanate Ester Prepreg Materials for Space Application”, ESA Space, 2001
[9] H.Kunzmann et al, “Scales vs Laser Interferometers Performance Comparison of Two Measuring Systems”, Annals of the CIRP Vol.42, 1993
[10] Integrated Optomechanical Analysis, K. B. Doyle et al
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