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 1.Block occulted field (OF) over approximately 82 arcmin circular to allow 2.5 Rs off-pointing 2.Pass field of view (FOV)

4. Requirements (cont.) 3.Fast limb tracking  Mode 3: occulter must block limb light while compensating for telescope shake and seeing 4.Remove irradiance load (up to 2.5 MW/m 2 )

5. Requirements (cont.) 5.Minimize self-induced seeing a.Experiments and scaling laws for small hot objects near M2 indicate insensitivity for seeing-limited observations (Beckers, Zago) b.Bottom line: surface temperature must be within some 10 ˚C of ambient air temperature Error Budget: DL: 10 nm @ 500 nm SL: 0.03 arcsec @ 1600 nm C: 0.03 arcsec @ 1000 nm Plumes not good for AO system 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) Most light reflects onto dome interior Tilt angle from gut ray: 19.5˚ Plume suction

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

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

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

10. Internal Flow Concept Coolant jets Jet exhaust tubes Reflective surface Coolant inlet Coolant outlet Fast occulter mount

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

12. Mounting Arrangement Ceramic shield Flow meters

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. Reflector Plate Thermal Performance 14.1˚ (sides of cone) 5.4˚ (bottom of cone) 33.6˚ (top of cone) NASTRAN axisymmetric model results: h = 15 kW/m 2 -K T c = T e – 10 K q˝ abs = 265 kW/m 2.

19. Detail of Heat Stop Aperture NASTRAN axisymmetric model results: h = 15 kW/m 2 -K T c = T e – 10 K q´´ abs = 265 kW/m 2. Hot spot is 17˚ hotter than coolant, 7˚ hotter than ambient Occulting edge is not the hottest spot!

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

21. Low Temperature Thermal Performance

22. Low Temperature Pump Power

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