M2 and Transfer Optics Thermal Control

25 August 2003 ATST CoDR Dr. Nathan Dalrymple

Air Force Research LaboratorySpace Vehicles Directorate

M2 & Transfer Optics Thermal Control

• Function: Mitigate mirror seeing

• Function:Reduce thermally-induced figure errors

seeing

Requirements

1. Minimize mirror seeing

a. Racine experiment: = 0.38 TM - Te) 1.2

b. Iye experiment: greatly reduced by flushing

c. IR HB aerodynamic analysis: = TV, d. Bottom line: requirements on surface-air T and

wind flushing

2. Minimize thermally-induced figure error

Ref: Racine, Rene, “Mirror, dome, and natural seeing at CFHT,”

PASP, v. 103, p. 1020, 1991.

Iye, M.; Noguchi, T.; Torii, Y.; Mikama, Y.; Ando, H. "Evaluation of Seeing on a 62-cm Mirror". PASP 103, 712, 1991

Error Budgets

(nm) Error budget Description

500 20 nmDiffraction-

limited

1600 0.05 arcsecSeeing-limited

1000 0.05 arcsec Coronal

Must share this allocation with M1. Most of the budget will be given to M1.

Diffraction-Limited Error Budget (10 nm rms, est.)

Blue contours: rms wavefront error (nm)

Acceptable operating range

Note: No AO correction assumedGreen range is larger with AO correction.

= 500 nm

Sign must be reversed for M2, which is inverted.

Seeing-Limited Error Budget (0.02 arcsec, est.)

Blue contours: 50% encircled energy (arcsec)

Acceptable operating range

= 1600 nm

Coronal Error Budget (0.02 arcsec, est.)

Blue contours: 50% encircled energy (arcsec)

Acceptable operating range

= 1000 nm

Thermal Loads

Mirror

Total Absorbed Flux

(watts)

Peak Irradiance (watts/m2)

Peak Absorbed Irradiance (watts/m2) Footprint (mm)

Mean Absorbed Irradiance (watts/m2)

M1 1,382.3 1,100 110 4,0004,000 110

M2 30.4 1,182 118 584596 111

M3 27.2 40,390 4,039 100140 2,474

M4 24.5 7,022 702 316314 314

M5 22.1 10,921 1,092 175178 903

M6 19.9 9,276 928 231189 580

Compare with 0.25 W on the DST tip-tilt mirror

Thermal Loads (cont.)

M2 irradiance(nearly the same as M1)

M3 irradiance (34x larger than M2)

Thermal Loads (cont.)

M4 irradiance(6x larger than M2)

M5 irradiance (9x larger than M2)

Thermal Loads (cont.)

M6 irradiance(8x larger than M2)

M2 Thermal Control System Concept

Air jets inserted in backside cells

SiC

M2 Cooling System Flow Loop

Insert diagram here

3D NASTRAN Model

3D NASTRAN Results for M2

Enhanced Cooling Temperature Profile (˚C above Ambient)Temperature Range of Approximately 0.14˚C Peak-to-Valley.

No coolant under mount point

3D NASTRAN Results for M2: Time History

24

22

20

18

16

14

12

10

Temperature (C)

121086420

Time (Hours)

Mirror Bulk Average Temperature Ambient Temperature

M2 Thermal Control System Specs

• Next steps:•Fan and system curves•Heat exchanger specs•Chiller specs•Time response of fluid volume

M3, M4, and M6 Thermal Control System Concept

High-k

Edge cooling of conductive substrate

M3, M4, and M6 Cooling System Flow Loop

Insert diagram here

M3, M4, and M6 Thermal Control System Performance

M3 M4 M6

All have surface to coolant T’s of less than 4 ˚C.Relatively easy to obtain good temperature control.

M5 (DM) Thermal Control System Concept

Force flow of air or dielectric liquid (Freon) past actuator array on the rear of the faceplate.

Must work with the DM manufacturer to integrate cooling scheme.

Q = 22.1 W q = 903 W/m2 Need: h = 90 W/m2-KT = 10 K

M5 Cooling System Flow Loop

Insert diagram here

Summary

1. With highly conductive substrates, we do not expect major difficulties controlling surface temperatures of M3, M4, or M6.

2. M2 performs well thermally with air jet array cooling.

3. Cooling flow option: use the same primary coolant for M1, M2, M3, M4, M5, and M6 (and maybe HS). Use shunts and throttling valves for each load.