PLATO - TOU Thermal analyses

PLATO - TOUThermal 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 Bipods(link element)


• 12 points• metallic ring• 3 points

3 element types are used, SOLID70 and LINK33 (Ansys software)

~10000 nodes~8000 elements

PLATO - TOUBaffle height

Configuration 1&4 Configuration 2&3

Conf.1&4:Minimum possible height


Fast 1&4 2&3Baffle height [mm]

100 117 92

The height of the baffle for configuration 2&3 is set to obtain the same avarage temperature for the two configuration

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

Win

dow

L1 L2 L3 L4 L5 L6 baffl

e

tube

TRP

-140

-130

-120

-110

-100

-90

-80

Temperature

Al Ti

Win

dow


e

tube

0

5

10

15

20

25

30

35

40

45

50

Thermal gradient inside each com-ponent

Al Ti

Very close to the -90°C

(goal)


Win

dow


e

tube

-140

-130

-120

-110

-100

-90

-80

Temperature

Al baffle and coupling=0.0290 Al baffle and coupling=0.0148Al baffle and coupling=0.0074 Ti baffle and coupling=0.0293

FE Model results:Conf. 2&3Heaters OFF, no IR coating on the Window and baffle emiss.=0.94

Very close to the -90°C

(goal)

Win

dow L1 L2 L3 L4 L5 L6

baffl

e

tube

0

5

10

15

20

25

30Thermal gradient inside each com-

ponent

Al baffle and coupling=0.0290 Al baffle and coupling=0.0148

Al baffle and coupling=0.0074 Ti baffle and coupling=0.0293


Win

dow


e

tube

TRP

-140

-130

-120

-110

-100

-90

-80

Temperature

Baffle AL Baffle Ti

FE Model results:Fast TOU

Heaters OFF, no IR coating on the Window and baffle emiss.=0.94

The Titanium baffle is not necessary to

reach the goal (-90°C)

Win

dow


e

tube

0

5

10

15

20

25

30

35

40

Thermal gradient inside each com-ponent

Baffle AL Baffle Ti


FE Model results:Baffle-tube connection

Baffle-tube connection


Washers

Conductance baffle/tube

N° joining points

Joining material

Flexure size [mm] (length/height/minimum thickness)

Washer - Size [mm] (ext.diameter/int.diameter/height)

0.0074 4 Ti 23/7/0.7 Yes (ceramic) – 10/6/100.0148 6 Ti 23/10/0.7 Yes (ceramic) – 10/6/8 0.0296 12 Al 23/10/0.7 Yes (ceramic) – 8/4/120.0296 6 Ti 23/10/0.7 No2.9558 12 Al 18/10/0.7 (current

mechanical design)No

FE Model results:Last change


Heat from CCD [W] (cold case)

0.94 (normal TOUs) 1.73 (FAST)

Heat from CCD [W] (hot case)

1.46 (normal TOUs) 2.63 (FAST)

OB Temperature [°C] -63Bipod conductance

[W/K] 3*0.012=0.036Lenses emissivity 0.9Outer emissivity (tube, baffle and

CCD) 0.005Inner emissivity (tube and CCD) 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

FE Model results:termo-elastic analysesEvaluation of thermo-elastic deformations of telescopes

from 20°C to low temperature

ModelThermal analysis

Structural analysis


FE Model results:termo-elastic analyses


Vertical displacement

L1

L6

temperature~ -106°C

~ -102°C

Compression of lenses

Compression of tube & baffle

FE Model results:Thermo-elastic for conf. 1&4


Check for tilt of lenses

The presence of the baffle creates an asimmetry

window: 10.140 arcsec

L1: 0.058 arcsec

FE Model results:Thermo-elastic for conf. 1&4

The thermo-elastic model is OK

D Z [mm] Tilt [arcsec]

Window -589 10.140L1 -507 0.058L2 -450 0.029L3 -334 0.018L4 -225 0.016L5 -200 0L6 0 0

Tilt up to 25 arcsec do not influence

High dependence from the baffle material


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

PLATO - TOU Thermal analyses

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