SOLAR-B Mission and Optical
Telescope Assembly

Saku Tsuneta
National Astronomical Observatory of Japan1

Solar Physics from Space in Japan

Hionotori (1981-1982)

Yohkoh (1991- 2001)

SOLAR-B (2006)

With NASA and UK
With NASA and UK2

Solar-B•
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Japan-US-UK solar observation satellite
following highly successful Yohkoh(1991-2001)
Primary mission: systems approach tounderstand generation/transport andultimate dissipation of solar magnetic
fields with 3 well-coordinated advanced
telescopes.
Onboard instruments– Solar Optical Telescope (Japan, US)– X-ray Telescope (US, Japan)– EUV Imaging Spectrometer (UK, US,Japan)– Spacecraft and launch (Japan)
Versatile onboard data compression(JPGEG, and DPCM)
Post compression rate approx. 500 kbps
Launch on summer 2006 with ISAS M-V-7
Orbit: Sun synchronous, Altitude: ~ 600
km, Weight: ~ 900 Kg
ESA provides downlink service with
Norway station, resulting in substantial
increase in data rate.

Magnetic dissipation

Magnetic generation3

X-ray & EUV Telescopes aboard SOLAR-B••XRT• We chose grazing-incidence after extensive tradeoff• 1 arcsec resolution/1 arcsec pixel, >x3 better than Yohkoh• FOV: 30arcmin squares• Sensitive to 0.5MK-10MK(20MK)• Filter choice provides SXT and TRACE-like images.
• Filter-ratio: powerful tool for T- diagnostics• Visible light imaging for alignment purpose
EIS• EUV emission line spectroscopy• Two EUV bands: 170-210 Å and 250-290 Å, log T = 4.7, 5.4,
6.0 - 7.3 K• X 10 more sensitive than CDS• 1 arcsec/pixels, Field of View： 6 arcmin×8.5 arcmin• Selectable Slit & Slot: 1”, 2”, 40” and 250” width at primary
focus• Single line: Doppler motion, non-thermal width• ~ 25 km/s pixel sampling, a few km/sec sensitivity• Line pair ratio: Temperature, density diagnostics• Multiple lines: Differential emission measure4Solar-B Fields of View
N

EIS (360”x512”)

E

W
SOT: BFI(205”x102”)

SOT:NFI/SP(328”x164”)

XRT(2048”x2048”)
SOHO/EIT FeXII 195A

S5

Optical and control interface of SOT
Optical Telescope Assembly (OTA)
Top door

Side door

Heat dump hole

Image stabilization
Sub-system (CTM)

Tip-tilt mirror

Mission data processor(MDP) SOT observing tables

Optical Bench Unit
Focal Plane Package (FPP)

Image data
Jitter signal fromCorrelation tracker

Solar Optical Telescope

6Optical layout of SOT
Litrow Mirror

Polarizing BS

Spectoro-polarimeter
Dual 256 x 1024 CCD

X3 Mag lensPolarizing BS
Folding Mirrors

Folding Mirror

Shutter
Slit

Field lensGrating
Filterwheel

Preslit

Broadband Filter Instrument

Field lens

X2 Mag lensShutterilter
F
2048 x 4096 CCDtn
Filterwheel
Field Maskngeirf
Narrowband Filter Instrument
Bire
50 x 50 CCD

SecondaryTelecentric
Correlation Trackerlenses
Demag lensBeam Distributor
Reimaging Lens

Folding Mirror

Folding Mirror

Image Offset Prisms
Folding Mirror

PrimaryPolarization
Modulator
CLU
Tip Tilt Mirror

OTA
Color Coding
OTA
Common Optics
CT
NFI
BFI
SP

7

SOT Observables
Broadband
Filtergraph
Dt : 2s

wavelengths

388.3 CN molecular bandhead: chrom. network
396.8 Ca II H-line: magnetic elements in low chrom
430.5 G-band CH bandhead: magnetic elements
450.5/555.0/668.4 continuum.

FOV / pix scale

218 × 109 / 0.054 arcsecNarrowband wavelengths
filtergraph
Dt : 3s~30s

FeI 525.0 Photospheric magnetograms
Mg Ib 517.3 Low chromosphere mag./dopplergrams
Fe I 557.6 Photospheric dopplergrams
Na D 589.6 Chromospheric magnetic fields
Fe I 630.2 Photospheric magnetograms
H I 656.3 H-alpha chromospheric image and Dopp

FOV / pix scale

328 × 164 / 0.08 arcsec

Polarization

IQUV, ~0.5% accuracySpectropolarimeter
Dt : 3s~1hrwavelengths

630.2 nm (high precision vector mag. Fields)

FOV / pix scale

164 x 324 (full scan) / 0.16 arcsec

Polarization

IQUV full profile, 0.1% accuracy

Correlation
tracker,580Hz

wavelengths629-634 nm

FOV

11 × 11 arcsec

8

Optical Telescope Assemblycold plate
for thermal control

HDM
2nd field stop
center section,interface to the satellite
CLU

low expansion CFRP truss
primary mirror
tip-tilt mirror

910

SOT (Solar Optical Telescope)
Optical Telescope Assembly (OTA) NAO, Japan
Focal Plane Package (FPP) Lockheed Martin/HAO/NASA with NAO
Fixed ULE 2dary mirror
Metal heat dump mirror

Observing wavelength: 388 ~ 668nmTelescope wavefront error ~ 18.2nm
PSF <0.2 arcsec in blue band
>0.2 arcsec in red band
Tip-tilt image stabilization system
Stability ~ 0.002 arcsec rms
bandwidth ~14Hz

FPP

Ultra-low CTE composite structure
Field stop
Collimated beam
afocal optical I/F

Collimator lens unit
ULE primary mirror

Polarization modulator
Focus mechanism

Tip-tilt mirror

11

Evaluation Method of Image Quality
Specification of Image Quality by Strehl ratio
Intensity
No-aberration
II0IStrehl ratio =I0

Diffraction-limited performance～0.2” (λ=388 – 670 nm)

View angle
Point spread function on focal plane

SOT target: Strehl ratio (I/I0) = 0.7 at λ=500nm
Relation between Strehl ratio and rms Wavefront error
Strehl ratio= e ( ) ≥ 0 . 7−2 πσλ2σ: rms Wavefront error
λ: Wavelength = 500 nm

Total rms Wavefront error for OTA-FPP: σ < 47.5 nm
OTA: 37.8 nm
FPP: 25.8 nm
Guidance: 12.8nm

12OTA development with budgets• There are multiple internal and external
elements that contribute to error andperformance degradation. These have been
controlled with strict budget during development.
• WFE budget• Focus budget• Pointing budget• Contamination budget• Weight budget• Power budget

13

OTA Key Components

Collimator lens unit

Secondary Mirror

Polarization modulator(Lockheed Martin/HAO)

Primary Mirror

Zero-CTE composite structure
Tip-tilt mirror

14

OTA primary secondary mirrors•ULE with protected Ag coat
•M1～11Kg•WFE for M1-M2 combination
18nm (rms)15Collimator lens unit requirements• 388-690nm• F/9• Achromatic focus shift< 35micron• WFE < 17nm (rms)• No retardance/no diattenuation• Orbital temperature
range: 20±10 degree C

16

Optical IT&T
60cm dia.
Auto-collimation
mirrorOTA

4.4m

Interferometer

ＯＴＡ assembly in theClass-10 clean tent

2.
4m

M1 alignment

M2 alignment

3.0m

Dedicated Optical Test
Tower for IT&T at NAOJ

Interferometric test17

END-TO-END WFE measurement with60cm dia. auto-collimation mirror

18

Solar-B SOT

Measured wavefront error 18.2nm•Telescope configuration for WFE
measurement: vertical (nominal andupside-down)•Telescope is deformed under 1-Gcondition. 0-G WFE is obtained byaveraging data taken with nominal
and upside-down configurations.

平面鏡
干渉計

•WFE (rms) is 0.0288 lambda at
632.8nm, and is 18.2nm(0.0182micron).
•WFE (RMS) at short-end of theobserving band (388nm) is 0.0469
lambda. Telescope is diffractionlimited (<0.071 lambda) for allobserving bands.

重力方向

干渉計
平面鏡

19

Gravity cancellation by overturning OTA
for WFE measurement

20Telescope IT&T

OTA&FPP
Integrated to S/C
Optical benchPreparation for
Opto-thermal-vacuum testAssembly21

-20 degree C Strong T-gradient +20degree C

Telescope assembly

System level optical test (1)Opto-thermal test for WFE&alignment measurement
in orbit environment

Uppershroud
OTA

Dummy OBU

干渉計

SupportLower
shroudOTA alignment cube

flat mirror

shroudTilt/shift stage

Flat mirror
reference

22

NAO Clean room
for space optics
190m2 ,10mHighClass 100
Class 0-10 in the boothSpace-chamber, large opticalflat, fast interferometer, large
Newport table

Heliostat to introduce natural star and sun
light: Beam size 55 cm dia.

23

Telescope assembly

System level optical test (2)Natural sun-light test
at NAO clean room

Telescope in clean room illuminatedwith 50cm sun beam24

Natural sun-light test Engineering first lightwith full flight model 2004 AugustNote•Bad seeing in Tokyo•Under 1-G

Stokes polarimeter

H-alphaG-band25

ALL DONE

26

Image stabilizer US-J interface test
Light source withnanopositioner

Tip-Tilt Mirror

Correlation tracker
Electronics BOX

Correlation tracker
CCD

27

The TeamSOLAR-B可視光望遠鏡完成
国立天文台高度環境試験棟
クリーンルーム2005年4月27日

28

OTA
OTA and FPP at NAOJ

Gregorian heat-dump window
FPP

29

OTAFPPOBU

30

Spacecraft-level testing
Micro-vibration

AssemblyLaunchVibration test

Acoustic test (telescope)

Integration to rocket

Final inspection

Thermal-vacuum（ASTRO-EII）

31

Preparation for S/C thermal vacuum
test with OTA thermal model

32

OTA WFE & alignment check as well as FPP
optical tests can be done on the spacecraft level
after each environment test

1000

OTA optical performance check (measure WFE)
OTA-FPP alignment check

XRT

FPP

~800

~4000

EIS

500

Class 10000Æ Surface Cleanliness Level ~ 250/24hr

衛星台車

33

Micro-vibration problem
resonance vibration of sensitive optical elements due tomoving parts such as gryo-scope and filter wheels

34

SOT Image stablizer performance

servo-onservo-off

サーボオン時には、20Hの制御帯域内では、1σ = 0.0002”の安定度を達成している（太陽角換算）実線：サーボオン、破線：制御オフ

35

Advantage of SOT• High resolution (0.2arcsec)• Very stable PSF– Only need seasonal focus adjust• Continuous 24 hours observations– Made possible by ESA Norway station• Both filtergraph and spectro-polarimeter• Versatile observing modes• Simultaneous X-ray/EUV observations

36

Science Topics• Continuous high resolution observations ofelemental flux tube
• Flux emergence and formation of sunspot
simultaneous with helio-seismic observations• Demography of magnetic fields with different
origins• Detection of MHD waves• Photospheric-chromospheric reconnection• Pico-flares and Lagrangian tracking of elemental
magnetic fields (The Parker concept)• Magnetic properties of hot and cool loops

37

OTA current status• OTA development completed, and integrated
to the spacecraft.
• Diffraction limited performance verified.
• Image stabilization system performance withFPP superb• On-spacecraft WFE/alignment measurementsrepeatedly done after testing milestones: nochange in performance– Final test to be done in July38

Mission Lifetime• Desires to observe the sun as close to the next
maximum as possible• Sun-synchronous orbit maintained over > 7 years• No fuel limit• Limited-lifetime Gyroscopes fully redundant• Lifetime for SOT diffraction-limited imaging– Contamination of organic materials to M1 increases the heatabsorption, resulting in higher M1 temperature.
– Current best estimate will be presented in this meeting.
– Prioritization of the science observations important.

39Schedule• 2006 End July: Spacecraft shipped to the launch
site• 2006 September 23: Launch date
• 2006 October: Spacecraft verification andcheckout phase• 2006 November: Instrument Checkout phase(first light phase) for three telescopes• 2006 December: Performance and Verification(PV) Phase– In-orbit calibration and• 2007 January Initial Observing Phase40