Download 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
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