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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 Requirements 1. Block occulted field (OF) over approximately 82 arcmin circular to allow 2.5 Rs off-pointing 2. Pass field of view (FOV) Mode Mode1:2:On-disc Corona Mode 3: Near-limb corona 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/m2) 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 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) Concept: Tilted Flat Plate Flat plate heat stop (reflective) Tilt angle from gut ray: 19.5˚ Plume suction Most light reflects onto dome interior 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) Heat Stop Detail Tilted flat plate Mount plate (SS) Exit manifold (SS) Fast occulter insert Mount (steel) Jet plate/intake manifold (SS) Reflector (GlidCop) Parts are furnace-brazed together Heat Stop, Exploded Fast occulter insert Exit manifold (SS) Tilted flat plate Reflector (GlidCop) Mount (steel) Mount plate (SS) Jet plate/intake manifold (SS) Parts are furnace-brazed together Internal Flow Concept Reflective surface Coolant jets Fast occulter mount Coolant outlet Jet exhaust tubes Coolant inlet External Flow Concept Coolant exit Main coolant inlet Inlet manifold Sector coolant inlets •Flowmeters •Thermometers •Pressure gauges Mounting Arrangement Flow meters Ceramic shield Crossflow Directors Plumbing and Ductwork Interface With OSS Flow Loop . Q is approximately 1700 W (peak) Not shown: accumulator, safety valves, etc. Safety Systems • • • • Passive-closing mirror covers Accumulators hold emergency coolant reserve Pressure-relief valves Instrumentation Surface temperature Flowrate Coolant temperature Coolant pressure Reflector Plate Thermal Performance 5.4˚ (bottom of cone) 14.1˚ (sides of cone) 33.6˚ (top of cone) NASTRAN axisymmetric model results: h = 15 kW/m2-K Tc = Te – 10 K . q˝abs = 265 kW/m2 Detail of Heat Stop Aperture Occulting edge is not the hottest spot! NASTRAN axisymmetric model results: h = 15 kW/m2-K Tc = Te – 10 K . q´´abs = 265 kW/m2 Hot spot is 17˚ hotter than coolant, 7˚ hotter than ambient Thermal Performance of Flow System VFR for h = 15 kW/m^2 K Volume Flow Rate (gpm) 120.00 100.00 80.00 VFR (gpm) 50% VFR (gpm) 40% 60.00 40.00 20.00 0.00 245 Ethylene glycol/ water solutions 265 285 Temperature (K) 305 325 Low Temperature Thermal Performance Heat Transfer Coefficient, 253 K 16000.00 14000.00 h (W/m^2 K) 12000.00 Syltherm HF Syltherm XLT 10000.00 8000.00 Dowtherm 4000 40% 6000.00 Dowtherm 4000 50% Dowtherm J 4000.00 2000.00 0.00 0 50 100 Volume Flow Rate (gpm) 150 Low Temperature Pump Power Power Curve (2,3 in), Dynalene 20 HC, 253 K 4.50 4.00 Power (hp) 3.50 3.00 P 2 in tot (hp) P 3 in tot (hp) P 1.5 in tot (hp) 2.50 2.00 1.50 1.00 0.50 0.00 0 50 100 Volume Flow Rate (gpm) 150 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