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MILANO 14-15/Dec.2010 S. Basso (INAF - Osservatorio Astronomico di Brera)

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Tasks Milano, 14-15/Dec./2010S.Basso - INAF OABrera The goals of the thermal analysis are: Dimensioning the baffle size for the three configurations in order to dissipate the heat from the ccd to the sky and to obtain a temperature of the TRP (Temperature Reference Point) of about -90°C Understanding the temperature distribution in the TOUs (lens and structure)

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FE Model description The FEM model has been implemented according the following optical configuration (with 6lens+window) Milano, 14-15/Dec./2010S.Basso - INAF OABrera ThicknessZ quotematerialD/2Rc Window BK-7 95inf Window inf L S-FPL L inf L N-KZFS L L CaF L L S-FPL L L KZFSN L L659 BK L64492inf

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FE Model description: geometrical parameters 3 cases are analyzed, two normal TOUs and the fast TOU. The two normal TOUs have a different baffle shape and size according the position into the satellite. Hbaffle incl Milano, 14-15/Dec./2010S.Basso - INAF OABrera incl 2& & fast4030

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FE Model description: thermal parameters Emissivity of the first lens toward the sky (0.2; 0.9) Emissivity of the last lens toward the ccd (0.3; 0.9) Emissivity of the internal surface of the baffle (0.08; 0.3; 0.94) Heaters (from 0 to 2 W) Heat source from the ccd (from 1.62 to 6 W) Bipod contuctance (from 3* to 3*0.0056) Temperature of the Optical Bench (-10°C; 0°C) Temperature of the ccd (-70°; no constr.) =0.005 =0.9 =0.94 Milano, 14-15/Dec./2010S.Basso - INAF OABrera Heaters position

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FE Model description: elements description 3 Bipods (link element) Milano, 14-15/Dec./2010S.Basso - INAF OABrera 12 points metallic ring 3 points 3 element types are used, SOLID70 and LINK33 ~10000 nodes ~8000 elements

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FE Model description: results Milano, 14-15/Dec./2010S.Basso - INAF OABrera Dimensioning of the baffle (middle November) configuration Normal 1&4Normal 2&3Fast Qccd [W] bipod conductance OB/TOU [W/K] T OB [°C] -10 Heaters [W] 000 emiss (window) 0.2 emiss (lenses) 0.9 H baffle [mm] angbaffleincl [deg] Tccd [°C] -70 With 5W for the Fast TOU from the CCD it is possible to dimension the heigth of the baffle The heigth of the 2&3 TOU has been optimized to obtain the same temperature of the cases 1&4

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FE Model description: results Milano, 14-15/Dec./2010S.Basso - INAF OABrera Dimensioning of the baffle (middle November) configuration Normal 1&4Normal 2&3Fast Qccd [W] bipod conductance OB/TOU [W/K] T OB [°C] -10 Heaters [W] 000 emiss (window) 0.2 emiss (lenses) 0.9 H baffle [mm] angbaffleincl [deg] Tccd [°C] -70

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FE Model description: results Milano, 14-15/Dec./2010S.Basso - INAF OABrera The sensitivity has been performed on TOU 1&4 (middle November) parameterValue 1Value 2 T (TRP) [°C] Qccd [W] Window T OB [°C] Heaters [W] L Note that the constrain of Tccd = -70°C overstimate the radial flux from the ccd to L6: for this reason the last row can be uncorrect.

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FE Model description: results Milano, 14-15/Dec./2010S.Basso - INAF OABrera On December the values are changed (see of Helene Pasquier 2/12/10) 1&4Fast1&4Fast Qccd [W] T max (Window) bipod conductance OB/TOU [W/K] T min (Window) T OB [°C] -10 T max (L1) Heaters [W] 00T min (L1) emiss (Window) 0.9 T max (L2) emiss (last lens) 0.9 T min (L2) H baffle [mm] 11095T max (L3) angbaffle [deg] 40 T min (L3) angbaffleincl [deg] T max (L4) Tccd [°C] NA T min (L4) cond. [W/mK] 210 T max (L5) emiss baffle 0.94 T min (L5) TRP [°C] (~L2) T min (L6) Area [m 2 ] T min (baffle) ellipt. Area [m 2 ]

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FE Model description: results Milano, 14-15/Dec./2010S.Basso - INAF OABrera Temperature of 1&4 configuration with the new parameters

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FE Model description: results Milano, 14-15/Dec./2010S.Basso - INAF OABrera Temperature gradient of 1&4 configuration with the new parameters

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FE Model description: results Milano, 14-15/Dec./2010S.Basso - INAF OABrera Window (fast TOU)L1 (fast TOU)

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FE Model description: results Milano, 14-15/Dec./2010S.Basso - INAF OABrera L2 (fast TOU)L3 (fast TOU)

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FE Model description: results Milano, 14-15/Dec./2010S.Basso - INAF OABrera L4 (fast TOU)L5 (fast TOU)

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FE Model description: results Milano, 14-15/Dec./2010S.Basso - INAF OABrera L6 (fast TOU)Tube + baffle (fast TOU)

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FE Model description: results Milano, 14-15/Dec./2010S.Basso - INAF OABrera Temperature at TRP (fast TOU)

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FE Model description: results Milano, 14-15/Dec./2010S.Basso - INAF OABrera Conclusion The baffle size could be as short as possible (also for the fast TOU with the new reduced value of heat (2 W instead of 5 W) To obtain a TRP temperature of -90°C a very low value of emissivity of the baffle must be used (14°C of thermal gradient in the window!) or insulating the baffle from the tube (problem in the convergence in the FE model) The heaters increase the temperature in the TRP of 7,5°C/W (to be verified with the new value of the parameters). Their position must be on the top of the tube The difference of the mean temperature of the lenses are less than 5 °C (not for the window) Next steps Solving the problem of convergence using an insulating interface between baffle and tube Better modeling the connections between the lens, the mechanical structure and the ccd Implementing the thermo-elastic deformation to understand the optical behavior Improving the sensitivity analyses with the new parameters

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