the heat stop
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The Heat Stop
25 August 2003 ATST CoDR Dr. Nathan Dalrymple
Air Force Research LaboratorySpace Vehicles Directorate
Heat Stop
• Function: first field stop, blocks most light from proceeding to M2 and subsequent optics
• Location: prime focus
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)
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 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)
Concept: Tilted Flat Plate
Flat plate heat stop(reflective)
Most light reflectsonto dome interior
Tilt angle fromgut ray: 19.5˚
Plume suction
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
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)
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
Internal Flow Concept
Coolant jets
Jet exhaust tubes
Reflectivesurface
Coolant inlet
Coolant outlet
Fast occultermount
External Flow Concept
Main coolant inletCoolant exit
Inlet manifold
Sector coolant inlets•Flowmeters•Thermometers•Pressure gauges
Mounting Arrangement
Ceramic shield
Flow meters
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 temperatureFlowrateCoolant temperatureCoolant pressure
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.
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!
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
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
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)
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
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