m2 and transfer optics thermal control 25 august 2003 atst codr dr. nathan dalrymple air force...
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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.