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