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The Heat Stop

The Heat Stop. 25 August 2003 ATST CoDR. Dr. Nathan Dalrymple Air Force Research Laboratory Space Vehicles Directorate. Heat Stop. Function: first field stop, blocks most light from proceeding to M2 and subsequent optics Location: prime focus. Mode 1: On-disc. Mode 2: Corona.

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The Heat Stop

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  1. The Heat Stop 25 August 2003 ATST CoDR Dr. Nathan Dalrymple Air Force Research Laboratory Space Vehicles Directorate

  2. Heat Stop • Function: first field stop, blocks most light from proceeding to M2 and subsequent optics • Location: prime focus

  3. Mode 1: On-disc Mode 2: Corona Mode 3: Near-limb corona Requirements • Block occulted field (OF) over approximately 82 arcmin circular to allow 2.5 Rs off-pointing • Pass field of view (FOV)

  4. Requirements (cont.) • Fast limb tracking Mode 3: occulter must block limb light while compensating for telescope shake and seeing • Remove irradiance load (up to 2.5 MW/m2)

  5. Requirements (cont.) • Minimize self-induced seeing • Experiments and scaling laws for small hot objects near M2 indicate insensitivity for seeing-limited observations (Beckers, Zago) • Bottom line: surface temperature must be within some 10 ˚C of ambient air temperature Plumes not good for AO system Error Budget: DL: 10 nm @ 500 nm SL: 0.03 arcsec @ 1600 nm C: 0.03 arcsec @ 1000 nm Refs: Beckers, J. M. and Melnick, J. "Effects of heat sources in the telescope beam on astronomical image quality". Proc. SPIE 2199, 478-480 (1994) Zago, L. "Engineering handbook for local and dome seeing". Proc. SPIE 2871, 726-736 (1997)

  6. Concept: Tilted Flat Plate Flat plate heat stop(reflective) Tilt angle fromgut ray: 19.5˚ Plume suction Most light reflectsonto dome interior

  7. Concept Detail 1 Normal startup: 1. Point to Sun (put Sun somewhere in OF) 2. Open mirror covers Air and liquid coolant lines Heat stop face Ceramic periphery shield Air crossflow directors (blower and getter)

  8. Mount plate (SS) Exit manifold (SS) Fast occulter insert Mount (steel) Jet plate/intakemanifold (SS) Reflector (GlidCop) Heat Stop Detail Tilted flatplate Parts are furnace-brazed together

  9. Heat Stop, Exploded Fast occulter insert Tiltedflatplate Exit manifold (SS) Reflector (GlidCop) Mount (steel) Mount plate (SS) Jet plate/intakemanifold (SS) Parts are furnace-brazed together

  10. Internal Flow Concept Reflectivesurface Coolant jets Fast occultermount Coolant outlet Jet exhaust tubes Coolant inlet

  11. External Flow Concept Main coolant inlet Coolant exit Inlet manifold • Sector coolant inlets • Flowmeters • Thermometers • Pressure gauges

  12. Mounting Arrangement Flow meters Ceramic shield

  13. Crossflow Directors

  14. Plumbing and Ductwork

  15. Interface With OSS

  16. Flow Loop . Q is approximately 1700 W (peak) Not shown: accumulator, safety valves, etc.

  17. Safety Systems • Passive-closing mirror covers • Accumulators hold emergency coolant reserve • Pressure-relief valves • Instrumentation • Surface temperature • Flowrate • Coolant temperature • Coolant pressure

  18. 5.4˚ (bottom of cone) 14.1˚ (sides of cone) 33.6˚ (top of cone) Reflector Plate Thermal Performance NASTRAN axisymmetric model results: h = 15 kW/m2-K Tc = Te – 10 K q˝abs = 265 kW/m2 .

  19. Detail of Heat Stop Aperture NASTRAN axisymmetric model results: h = 15 kW/m2-K Tc = Te – 10 K q´´abs = 265 kW/m2 . Occulting edge is not the hottest spot! Hot spot is 17˚ hotter than coolant, 7˚ hotter than ambient

  20. Thermal Performance of Flow System Ethylene glycol/water solutions

  21. Low Temperature Thermal Performance

  22. Low Temperature Pump Power

  23. Survival Reflector will last about 30 sec with no cooling • Next Steps: • Reflector lifetime with partial cooling (boiling) • Normal operating stresses • NASTRAN structural modeling • Full-scale test at NREL

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