1 / 26

M1 Thermal Control

This document discusses the thermal control strategies employed for the M1 primary mirror, aimed at mitigating optical distortion and enhancing seeing requirements. Key experiments, including the Racine and Iye experiments, highlight the impact of thermal differential (DT) and wind flushing on the mirror's performance. The text outlines the thermal loading considerations, cooling systems, and 1D finite-difference modeling results that ensure optimal operating temperatures. The findings indicate significant improvements in performance under various conditions, emphasizing the importance of thermal management in high-precision optical systems.

rance
Télécharger la présentation

M1 Thermal Control

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. M1 Thermal Control 25 August 2003 ATST CoDR Dr. Nathan Dalrymple Air Force Research Laboratory Space Vehicles Directorate

  2. -0.69x10-6 K-1 0.28x10-6 mbar-1 Primary Mirror (M1) Thermal Control • Function: Mitigate mirror seeing seeing

  3. Requirements • Minimize mirror seeing • Racine experiment: q = 0.38 (TM - Te) 1.2 • Iye experiment: q greatly reduced by flushing • IR HB aerodynamic analysis: q = q(DT, V, l) • Bottom line: requirements on surface-air DT and wind flushing Ref: Racine, Rene, “Mirror, dome, and natural seeing at CFHT,” PASP, v. 103, p. 1020, 1991. Iye, M.; Noguchi, T.; Torii, Y.; Mikama, Y.; Ando, H. "Evaluation of Seeing on a 62-cm Mirror". PASP 103, 712, 1991

  4. Error Budgets

  5. Layer thickness Given layer thickness and DT, we can estimate q. Wavefront variance Fluctuating density Line-of-sight correlation length Gladstone-Dale parameter Surface-air temperature difference Phase variance Blur angle IR Handbook Seeing Analysis Strong/weak cutoff ~ 2 rad Ref: Gilbert, Keith G., Otten, L. John, Rose, William C., “Aerodynamic Effects” in The Infrared and Electro-Optical Systems Handbook, v. 2, Frederick G. Smith, Ed., SPIE Optical Engineering Press, 1993.

  6. Hydrodynamic term Buoyancy term IR Handbook Seeing Analysis (cont.) Layer thickness (mks units): L: upstream heated length (m) DT: average temperature difference over upstream length (˚C) V: wind speed (m/s) Assume: If DT < 0 then buoyancy term does not contribute to layer thickness.

  7. Convection Types and Loci Wind is good.

  8. Diffraction-Limited Error Budget Blue contours: rms wavefront error (nm) l = 500 nm Acceptable operating range, assuming no AO correction. AO correction will extend the “green” range.

  9. Seeing-Limited Error Budget Blue contours: 50% encircled energy (arcsec) l = 1600 nm Acceptable operating range

  10. Coronal Error Budget Blue contours: 50% encircled energy (arcsec) l = 1000 nm Acceptable operating range

  11. An Alternate View For a particular DT, V combination, read over on the vertical axis to find seeing

  12. Mirror Thermal Control • Time-dependent problem • Backside cooling • Controlled frontside temperature time lag through substrate knobs

  13. M1 Thermal Loading • Time-dependent problem; this is one snapshot

  14. Thermal Control System Concept Desiccant chamber included in cell to dry air

  15. Flow Loop Concept A: Closed cycle, liquid coolant (heats or cools)

  16. Flow Loop (cont.) Concept B: Open cycle, air coolant (only cools)

  17. 1D,t Finite-Difference Model Inputs: Ideal Day • Desired set point: 1–3 ˚C below ambient temperature

  18. 1D,t Finite-Difference Model Results: Ideal Day M1 temperature OK over most of day Fix with profile optimization

  19. Seeing Performance: Ideal Day Very good performance until positive T at end of observing day These results assume calm air.Wind helps both thermal control and seeing.

  20. 1D,t Finite-Difference Inputs: Sac Peak Te • 23 – 25 June 2001 (60 hr run) • Desired set point: 1–3 ˚C below ambient temperature t (hr)

  21. 1D,t Finite-Difference Results: Sac Peak Te Same cooling profile used for both days t (hr)

  22. Seeing Performance: Sac Peak Te day day t (hr) Good performance over both days

  23. Heat Removal Rate: Ideal Day Peaks at 3200 W • Next steps: • Fan and system curves • Heat exchanger specs • Chiller specs • Time response of fluid volume

  24. 2D,t NASTRAN Results • Response to 2002 workshop comments • Result: actuator thermal “print-through” negligible

  25. Flushing System Concept Covered in greaterdetail in Enclosureslides. 168 m2 flow area,each side 42 vent gates

  26. Flushing System Performance (Sample) Covered in greaterdetail in Enclosureslides.

More Related