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)

GenesiaCanon

U-side: NASA (FPP) Lockheed Martin

HAOSolar-B Science Meeting, 3-5 Feb. 2003

M1

M2

CLU

CTM-TM

HDM

PMU

OTA overview: Aplanatic Gregorian Aperture 500mmφ Length 1500mm

Specification:- Strehl > 0.8 @500nm- φ400” FOV- λ380 - 700nm- φ30mm pupil image- minimum polarization- stabilized pointing- unnecessary heat rejected

Tests in the past one year

2002.3 OTA alone vibration/shock test/Optical performanceMechanical healthiness of OTA is proved. No change of mirror alignment.Non-negligible stress from the M1 support was discovered.

2002.3-4 CTM environmental test/CT-CTM combination testExcellent performance of the image stabilization was demonstrated

2002.5-6 System MTM test, acoustic/random vibration/shockMechanical environment was determinedOTA 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 testSignificant vibration of M1/M2 was excited by IRU.

2002.9 New M1 support mechanism, optical performance/vibration testSignificant improvements of the M1-surface figure was confirmed.

2002.10 System TTM testEfficiency 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 performanceExcellent optical performance. No change was found after vibrations.

2003.1-2 OTA Opto-thermal test (on going)

OTA vibration test, 2002.3

Wavefront measurement with OTA tower, 2002.4

MTM acoustic test MTM vibration test

FPPFPP

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)

EIS

XRT

interferometer

flat mirror

Solar-B in 2nd tower

OTA optical measurement sequence

A:Last measurement of OTA alignment @ 1st tower

System integration

System vibration/shock test

C:Post measurement @ 1st tower

System disassembling

B: Measurement on S/C @ 2nd tower

Interferometer measurement

Sys

tem

test

RESULTS:A:OTA only B:System C:OTA only

RMS 105nm (single path) A20=105nmRMS, Other= 6nmRMS

RMS 22.5nm(single path) A20=19nmRMS, Other =11nmRMS

- Change of distance between M1 and M2 (defocus) ~ +20 m. 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.

difference

Micro-vibration transmissivity test

x

y

z

plate scale @f10.176“/m

M1

M2

TM

CLU

plate scale @f20.0456“/m

Shift 1m Tilt 1arcsec

M1 0.176 2

M2 0.222 0.565

CLU 0.046 0

Optical response factor: Image shift (arcsec) /displacement

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

PSD of image motion due to M2-tilt excited by MW disturbance

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 (Q>>100) against the micro-disturbance…)

OTA in System-TTM test

19.9 ~ 43.2 C

1.1 ~ 16.3 C

27.8 ~ 4.6 C

1.7 ~ 25.0 C

16.0 ~ 30.0 C

26.2 ~ 45.7 C

Predicted OTA temperature in orbit

Heater control

21.5 ~ 4.4 C

21.1 ~ 67.3 C

Heater control

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

OTA Opto-thermal testing

Flat mirror reference

OTA alignment cubeLower shroud

Upper shroud

OTA

OTA Opt-thermal test configuration

flat

Autocollimator OTA pointing ax.

theodlite OTA mech.ax.

Support

Tilt/shift stage

shroud

　 OTA pointing ax.

interferometer

Theodlite OTA center of FOV

Dummy OBU

Test started 2003.1.28 – on-going

Test modes:

① In air ② Room temperature in vacuum③ 0C uniform temperature④ Temperature gradient (cold case, -50 ~ +23C)

operational heater, truss T un-isotropy, ⑤ Temperature gradient (hot case, -50 ~ +50C)

⑥ Room temperature in vacuum

today

Wavefront error ~ 0.015 rms (on-axis)0.028 rms (140” off-axis)

chromatic aberration of CLU- FM befor/ after vibration

- 50

- 40

- 30

- 20

- 10

0

10

20

350 400 450 500 550 600 650 700 750

wavelength [nm]

Bes

t Fo

cus[

μm

]

振動試験【前】

設計値

振動試験【後】

Chromatic aberration theoretical, before/after vibration

FM Optics Status: CLU-FM was completed (Dec. 2002)

Point spread function of OTA

～ 0.21” @ 500nm

OTA pupil

Goal of OTAStrehl > 0.8

Budget for the OTA image quality

CLU (FM measurement)

M1/M2 (test coating)

CTM-TM (theoretical)

NFI wavelengths

BFI wavelengths

02.08.07: after system MTM test

02.04.11: just before system MTM test, after cleaning

Particle contamination of M1 during MTM test

Cleanliness level ~ 1000

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.