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Pointing stability of SOT against the microvibration

Pointing stability of SOT against the microvibration. K.Ichimoto and Solar-B Team SOT#17 2006.4.17-20. FPP. IRU. -. B. MW. IRU-A. . Disturbance sources in the spacecraft. OTA. Momentum wheel x 4 IRU-A (4 gyros) & B (2 gyros)

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Pointing stability of SOT against the microvibration

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  1. Pointing stability of SOT against the microvibration K.Ichimoto and Solar-B Team SOT#17 2006.4.17-20

  2. FPP IRU - B MW IRU-A . Disturbance sources in the spacecraft OTA • Momentum wheel x 4 • IRU-A (4 gyros) & B (2 gyros) • Moving mechanisms (many!) in mission instruments (SOT/XRT/EIS) Experimental evaluations of the OTA pointing error due to the micro-disturbances have been performed using the S/C-Mechanical Test Model (MTM) and the Flight Model (FM). Vibration (shift/tilt) of M1 and M2 of OTA is the dominant cause for the pointing error.

  3. Test configurations S/C installed on a dolly in the tower theodolite PSD dolly Optical end-to-end measurement of SOT pointing error using PSD and FPP/CT. More environmental noise. Two complimentary configurations were adopted. S/C hanged up by springs 630nm tunable laser Transmissibility of microvib. is measured with accelerometers on M1/M2 of OTA. Less environmental noise.

  4. Microvibration transmissibility measurement with accelerometers on OTA • sAccelerometers on M1/M2 to detect shift and tilt. • Sinusoidal force and torque injected at the locations of MW and IRU’s in MTM, and the response of OTA pointing was measured as a function of frequency at each location. • Net pointing error (f>20Hz) are calculated by using the component disturbance data. • MW and IRU are run in FM test to evaluate the SOT pointing error.

  5. Pointing error measurement with optical sensors Optical layout FPP FG-CCD CT-CCD 180oBS Insertion pipe Acc. sensors Image plane PSD Data logger Pointing error is measured by position sensitive detector (PSD, 3kHz) and FPP/CT camera (580Hz) (only in FM).

  6. Test history Components disturbance measurement (IRU/MW/PMU) Transmissibility test w/ MTM (2002) (dummy mass for IRU etc.+ shaker) (accelerometers on OTA) Transmissibility test w/ MTM (2003) Transmissibility test w/ OTA in vacuum chamber (2003) (accelerometers on OTA)  confirm that damping by air is not significant Pointing error measurement in 1st integration of FM (2004) (flight components & flight optics) (accelerometers on OTA)  confirm the consistency of two test configurations Pointing error measurements in 2nd integration of FM (2005-2006) (no accelerometers on OTA)  monitor trend before/after Vib. test, after TV test Evaluation of SOT pointing error and feedback to the flight hardware

  7. Example of microvibration transmissibility spectrum from IRU-A to M1 (red) and M2 (blue) tilt. FEM prediction (dots) fails to reproduce the transmissibility…

  8. SOT requirement on image stability = 0.09” (3s) = 0.042” (0-p) (sinusoidal jitter) (requirement) Strehl degradation due to optical error Strehl degradation due to image jitter psf with sinusoidal jitter, l = 390nm 0.09” (3s)

  9. Momentum wheels Example of data: power spectrum density of M2 tilt against MW-A spin rate

  10. Momentum wheels Suitable windows of spin rate of MW were identified. X Hanged up config. Acc. data Requirement = 0.03arcsec (rms) Y Operational spin range of MWs is decided to be 2800+100rpm so that disturbance of MW will not be a significant cause of SOT pointing error.

  11. IRU-A Optical measurement in FM PSD-X PSD-Y

  12. IRU-B Optical measurement in FM PSD-X PSD-Y

  13. IRU-A and B Total pointing error integrated for f >20Hz. For IRU-A, the observed disturbance level is much smaller (<1/30) than the prediction based on past experiments. The reason of this discrepancy is understood as the anti-resonance between IRU-A internal structure and the panel of bus module (but not conclusive). Trend of the disturbance level is being monitored during the final test period.

  14. FPP wheels NFI filter wheel BFI filter wheel

  15. XRT wheels XRT filter wheel-1 XRT filter wheel-2

  16. XRT VLS EIS coarse mirror Since operation of EIS coarse mirror mechanism is very rare, we do not care..

  17. Record of OTA pointing error induced by mission mechanisms. (by the PSD sensor from continuous rotation measurement, unit=arcsec rms) requirement = 0.03” (1s) = 0.014” (0-p)

  18. 60 < f < 200Hz Pointing disturbance caused by XRT-VLS shutter (requirement) Strehl degradation due to image jitter Strehl degradation due to optical error Disturbance level of XRT-VLS  Final Strehl ~ 0.59 Final Strehl will be ~ 0.42 @390nm.

  19. Point spread function under the sinusoidal jitter For sinusoidal jitter 009” (3s) is equivalent to 0.042” (0-p) XRT VLS ~ 0.1 (0-p)” requirement

  20. Summary: • After extensive experiments, we expect that the • requirement of SOT pointing stability is to be satisfied. • Issues to be addressed after launch: • What is the real disturbance level of the XRT-VLS in orbit? • How frequently we need the visible image of XRT for data co-alignment? • Shall we stop the IRU-B (which is redundant) during the nominal operation with IRU-A?

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