OTA Status Report

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OTA Status Report K.Ichimoto/Y.Suematsu, NAOJ
Following institutes/companies are in
collaboration. J-side ISAS (Institute of Space
and Astronautical Science) (OTA) NAOJ (National
Astronomical Observatory, Japan) MELCO
(Mitsubishi Electric Corporation) Genesia Cano
n U-side NASA (FPP) Lockheed Martin HAO
Solar-B Science Meeting, 3-5 Feb. 2003
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OTA overview Aplanatic Gregorian
Aperture 500mmf Length 1500mm Specification -
Strehl gt 0.8 _at_500nm - f400 FOV - ?380 - 700nm -
f30mm pupil image - minimum polarization -
stabilized pointing - unnecessary heat rejected
M2
HDM
M1
CLU
PMU
CTM-TM
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Tests in the past one year
2002.3 OTA alone vibration/shock test/Optical
performance Mechanical healthiness of OTA is
proved. No change of mirror alignment. Non-neglig
ible stress from the M1 support was
discovered. 2002.3-4 CTM environmental
test/CT-CTM combination test Excellent
performance of the image stabilization was
demonstrated 2002.5-6 System MTM test,
acoustic/random vibration/shock Mechanical
environment was determined OTA pointing axis and
wavefront were measured on the S/C. No change in
wavefront, 20 change of the pionting on
S/C. 2002.7 System micro-vibration
test Significant vibration of M1/M2 was excited
by IRU. 2002.9 New M1 support mechanism, optical
performance/vibration test Significant
improvements of the M1-surface figure was
confirmed. 2002.10 System TTM test Efficiency
of the OTA heat dump path was confirmed. M1/CLU
temperature was 10C lower than expected (good
news!). Accurate mathematical model of OTA was
established. 2002.12 CLU-FM vibration
test/Optical performance Excellent optical
performance. No change was found after
vibrations. 2003.1-2 OTA Opto-thermal test (on
going)
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OTA vibration test, 2002.3
Wavefront measurement with OTA tower, 2002.4
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MTM acoustic test
MTM vibration test
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SOT optical testing during the system MTM test
- OTA optical performance check (measure WFE)
- OTA-FPP alignment check with the Solar-B
tower. (2nd OTA tower)
flat mirror
XRT
EIS
interferometer
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Solar-B in 2nd tower
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OTA optical measurement sequence
Interferometer measurement
ALast measurement of OTA alignment _at_ 1st tower

• System integration

• System vibration/shock test

System test
B Measurement on S/C _at_ 2nd tower

• System disassembling

CPost measurement _at_ 1st tower
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RESULTS
AOTA only
BSystem COTA only
difference
RMS 105nm (single path) A20105nmRMS,
Other 6nmRMS
RMS 22.5nm(single path) A2019nmRMS,
Other 11nmRMS

• Change of distance between M1 and M2 (defocus)
  20 mm
• . ? probably due to temperature/humidity
  change
• Coma and other aberrations were negligibly
  small.
• Change of pointing axis (center of OTA FOV) wrt.
  OTA cube was 30 on S/C.

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Micro-vibration transmissivity test

• Sources of disturbance
• Momentum Wheel
• IRU-A B
• Mechanisms in mission instruments

Optical response factor Image shift (arcsec)
/displacement
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PSD of image motion due to M2-tilt excited by MW
disturbance
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• It was found that the disturbance of IRUs causes
  a significant pointing error of the OTA.
• The degree of pointing jitter is reduced from
  that initially expected, owing to the efforts of
  reduction of the IRU disturbance, but still NOT
  meets the SOT requirement.
• To overcome this problem,,,
• - System decided to move one of the Gyro (for
  nominal usage) from the OBU to the bus box..
• OTA will test the counter-weight mechanism to
  suppress the M2 resonance at 130Hz.
• 2nd micro-vibration testing with OTA and S/C is
  planed in March.
• Effects of the shutter or filter wheels in
  mission instruments are still unknown.
• Careful tuning for balancing the moving
  mechanisms of each instrument is highly
  appreciated! ( It was found that the dumping
  rate of the OBU structure is extremely small
  (Qgtgt100) against the micro-disturbance)

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OTA in System-TTM test
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OTA Opto-thermal testing
Predicted OTA temperature in orbit

• Aim to verify the optical performance (image
  quality) of OTA under the thermal environment in
  orbit.
• Items for evaluation
• Deformation of mirrors by stress from
• the mirror supports,
• Dimensional change of the truss
• structure,
• due to temperature change and dryout

-1.7 25.0 C
Heater control
-21.5 4.4 C
-27.8 4.6 C
21.1 67.3 C
1.1 16.3 C
19.9 43.2 C
16.0 30.0 C
26.2 45.7 C
Heater control
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OTA Opt-thermal test configuration
? OTA pointing ax.
Upper shroud
Theodlite ? OTA center of FOV
OTA
interferometer
Dummy OBU
Test started 2003.1.28 on-going
Support
theodlite ? OTA mech.ax.
Lower shroud
OTA alignment cube
flat
shroud
Flat mirror reference
Tilt/shift stage
Autocollimator ? OTA pointing ax.
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Test modes ? In air ? Room temperature in
vacuum ? 0C uniform temperature ? Temperature
gradient (cold case, -50 23C) operational
heater, truss T un-isotropy, ? Temperature
gradient (hot case, -50 50C) ? Room
temperature in vacuum
today
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FM Optics Status CLU-FM was completed (Dec. 2002)
Wavefront error 0.015l rms (on-axis) 0.028l
rms (140 off-axis)
Chromatic aberration theoretical, before/after
vibration
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Point spread function of OTA
Goal of OTA Strehl gt 0.8
0.21 _at_ 500nm
OTA pupil
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Budget for the OTA image quality
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M1/M2 (test coating)
CTM-TM (theoretical)
CLU (FM measurement)
BFI wavelengths
NFI wavelengths
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Particle contamination of M1 during MTM test
02.04.11 just before system MTM test, after
cleaning
02.08.07 after system MTM test
Cleanliness level 300?
Scattered light should be still negligible, but
we plan to make more complete bagging of OTA or
S/C during the FM test phase.
Cleanliness level 1000