the heat stop
DESCRIPTION
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. - PowerPoint PPT PresentationTRANSCRIPT
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The Heat Stop
25 August 2003 ATST CoDR Dr. Nathan Dalrymple
Air Force Research LaboratorySpace Vehicles Directorate
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Heat Stop
• Function: first field stop, blocks most light from proceeding to M2 and subsequent optics
• Location: prime focus
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Mode 1: On-discMode 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)
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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)
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Requirements (cont.)
5. Minimize self-induced seeinga. 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 nmSL: 0.03 arcsec @ 1600 nmC: 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)
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Concept: Tilted Flat Plate
Flat plate heat stop(reflective)
Most light reflectsonto dome interior
Tilt angle fromgut ray: 19.5˚
Plume suction
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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
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Heat Stop Detail
Tilted flat plate
Parts are furnace-brazed together
Reflector (GlidCop)
Jet plate/intakemanifold (SS)
Exit manifold (SS)Mount plate (SS)
Fast occulter insert
Mount (steel)
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Heat Stop, Exploded
Tilted flat plate
Reflector (GlidCop)
Jet plate/intakemanifold (SS)
Exit manifold (SS)
Mount plate (SS)
Parts are furnace-brazed together
Mount (steel)
Fast occulter insert
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Internal Flow Concept
Coolant jets
Jet exhaust tubes
Reflectivesurface
Coolant inlet
Coolant outlet
Fast occultermount
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External Flow Concept
Main coolant inletCoolant exit
Inlet manifold
Sector coolant inlets•Flowmeters•Thermometers•Pressure gauges
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Mounting Arrangement
Ceramic shield
Flow meters
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Crossflow Directors
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Plumbing and Ductwork
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Interface With OSS
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Flow Loop
Q is approximately 1700 W (peak)Not shown: accumulator, safety valves, etc.
.
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Safety Systems
• Passive-closing mirror covers• Accumulators hold emergency coolant reserve• Pressure-relief valves• Instrumentation
Surface temperatureFlowrateCoolant temperatureCoolant pressure
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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/m2-KTc = Te – 10 Kq˝abs = 265 kW/m2.
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Detail of Heat Stop Aperture
NASTRAN axisymmetric model results:h = 15 kW/m2-KTc = Te – 10 Kq´´abs = 265 kW/m2.
Hot spot is 17˚ hotter than coolant, 7˚ hotter than ambient
Occulting edge is not the hottest spot!
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Thermal Performance of Flow System
VFR for h = 15 kW/m^2 K
0.00
20.00
40.00
60.00
80.00
100.00
120.00
245 265 285 305 325
Temperature (K)
Volume Flow Rate (gpm)
VFR (gpm) 50%
VFR (gpm) 40%
Ethylene glycol/water solutions
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Low Temperature Thermal Performance
Heat Transfer Coefficient, 253 K
0.00
2000.00
4000.00
6000.00
8000.00
10000.00
12000.00
14000.00
16000.00
0 50 100 150
Volume Flow Rate (gpm)
h (W/m^2 K)
Syltherm HF
Syltherm XLT
Dowtherm 4000 40%
Dowtherm 4000 50%
Dowtherm J
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Low Temperature Pump Power
Power Curve (2,3 in), Dynalene 20 HC, 253 K
0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4.50
0 50 100 150
Volume Flow Rate (gpm)
Power (hp)
P 2 in tot (hp)
P 3 in tot (hp)
P 1.5 in tot (hp)
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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