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Some considerations - Osservatorio Astrofisico di Catania

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Some considerations - Osservatorio Astrofisico di Catania
PLATO - TOU
Thermal analyses
Summary of previous thermal analyses
performed in 2010-2011
S.Basso – F. Borsa
(I.N.A.F. – Osservatorio Astronomico di Brera)
Catania, 11/Jun./2014
S.Basso - INAF OABrera
FE Model description:
elements description

3 element types are used, SOLID70 and LINK33 (Ansys software)
•
•
•
12 points
metallic ring
3 points
~10000 nodes
~8000 elements
3 Bipods
(link element)
Catania, 11/Jun./2014
S.Basso - INAF OABrera
PLATO - TOU
Baffle height
Configuration 1&4
Configuration 2&3
The height of the baffle for
configuration 2&3 is set to obtain
the same avarage temperature
for the two configuration
Conf.1&4:
Minimum possible
height
Baffle height
[mm]
Catania, 11/Jun./2014
Fast
1&4
2&3
100
117
92
S.Basso - INAF OABrera
FE Model results:
Conf. 1&4
Heaters OFF, insulating links Baffle/tube (0.0296 W/K) , no IR coating on the Window and baffle emiss.=0.94
-80
tube
baffle
L6
L5
L4
L3
L2
L1
Window
TRP
tube
baffle
Thermal gradient inside each component
L6
L5
L4
L3
L2
L1
Window
Temperature
50
45
-90
40
35
-100
30
-110
-120
25
Very close to the -90°C
(goal)
20
15
10
-130
5
-140
0
Al
Catania, 11/Jun./2014
Ti
Al
Ti
S.Basso - INAF OABrera
FE Model results:
Conf. 2&3
tube
baffle
L6
L5
L4
L3
L2
Temperature
L1
Window
Heaters OFF, no IR coating on the Window and baffle emiss.=0.94
Thermal gradient inside each component
30
-80
25
-90
20
-100
15
-110
Very close to the -90°C
(goal)
10
-120
5
-130
Al baffle and coupling=0.0290
Al baffle and coupling=0.0148
Al baffle and coupling=0.0074
Ti baffle and coupling=0.0293
Catania, 11/Jun./2014
Al baffle and coupling=0.0290
Al baffle and coupling=0.0148
Al baffle and coupling=0.0074
Ti baffle and coupling=0.0293
tube
L6
L5
L4
L3
L2
baffle
-140
L1
Window
0
S.Basso - INAF OABrera
FE Model results:
Fast TOU
Heaters OFF, no IR coating on the Window and baffle emiss.=0.94
tube
baffle
L6
L5
L4
L3
L2
Window
TRP
tube
baffle
L6
L5
L4
L3
L2
L1
Window
-80
L1
Thermal gradient inside each component
Temperature
40
35
-90
30
-100
-110
-120
25
The Titanium baffle is not
necessary to reach the
goal (-90°C)
20
15
10
-130
5
-140
0
Baffle AL
Catania, 11/Jun./2014
Baffle Ti
Baffle AL
Baffle Ti
S.Basso - INAF OABrera
FE Model results:
Baffle-tube connection
Conductance
baffle/tube
N° joining
points
Joining
material
0.0074
0.0148
0.0296
0.0296
2.9558
4
6
12
6
12
Ti
Ti
Al
Ti
Al
Catania, 11/Jun./2014
Flexure size [mm]
(length/height/minimu
m thickness)
23/7/0.7
23/10/0.7
23/10/0.7
23/10/0.7
18/10/0.7 (current
mechanical design)
Washer - Size [mm]
(ext.diameter/int.diameter
/height)
Yes (ceramic) – 10/6/10
Yes (ceramic) – 10/6/8
Yes (ceramic) – 8/4/12
No
No
Baffle-tube connection
Washers
S.Basso - INAF OABrera
FE Model results:
Last change
Heat from CCD [W]
(cold case)
Heat from CCD [W]
(hot case)
0.94 (normal TOUs) 1.73
(FAST)
1.46 (normal TOUs) 2.63
(FAST)
OB Temperature [°C]
-63
Bipod conductance [W/K]
3*0.012=0.036
Lenses emissivity
Outer emissivity
(tube, baffle and CCD)
Inner emissivity
(tube and CCD)
0.9
0.005
0.94
The intermediate value of 0.0071 W/K per bipod corresponds to
the value computed with the mechanical design proposed in
PLATO.LAM.SYS.SPE.1065 - Issue 2
Catania, 11/Jun./2014
S.Basso - INAF OABrera
FE Model results:
termo-elastic analyses
Evaluation of thermo-elastic deformations of telescopes
Model
Thermal
analysis
Structural
analysis
from 20°C to low temperature
Catania, 11/Jun./2014
S.Basso - INAF OABrera
FE Model results:
termo-elastic analyses
Compression
of lenses
L1
Compression of
tube & baffle
~ -106°C
temperature
~ -102°C
Vertical
displacement
L6
Catania, 11/Jun./2014
S.Basso - INAF OABrera
FE Model results:
Thermo-elastic for conf. 1&4
The presence of the baffle
creates an asimmetry
window: 10.140 arcsec
L1: 0.058 arcsec
Check for tilt of lenses
Catania, 11/Jun./2014
S.Basso - INAF OABrera
FE Model results:
Thermo-elastic for conf. 1&4

The thermo-elastic model is OK
D Z [mm]
Tilt [arcsec]
Window
-589
10.140
L1
-507
0.058
L2
-450
0.029
L3
-334
0.018
L4
-225
0.016
L5
-200
0
L6
0
0
Catania, 11/Jun./2014
Tilt up to 25 arcsec
do not influence
High dependence from
the baffle material
S.Basso - INAF OABrera
FE Model results:
Conclusion
The new analyses show that the latest change in the I/F parameter move away from the
goal to reach -90°C in the TRP (Temperature Reference Point) with the heaters off. The
greater effect is the decrease of the CSS temperature from -10°C to -63°C.
In order to increase again the TRP Temperature to the goal the possibility are:
1. Increase the heaters power adding 1W for the normal TOU and 0.2W for the fast
TOU. That means that the total heater power would increase of 32*1+2*0.2= 32.4W
2. Reducing the decoupling between the Camera I/F plane building bipods more
conductive. This solution would increase the uncertainty in the mean temperature of
the telescopes because the temperature of the Camera I/F plane is less known.
3. Adopt not conventional approaches like:
•
titanium baffle,
•
thermal filters
•
coating or layer on the internal surface of the baffle to reduce the internal
emissivity
Catania, 11/Jun./2014
S.Basso - INAF OABrera
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