THE COMPARISON OF DIFFERENT THERMAL ANALYSIS SOFTWARE FOR THERMAL SIMULATION OF THE SPACE TELESCOPE

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1 Remote Sensing Satellite Technology Workshop 216 Nov. 28, 216 THE COMPARISON OF DIFFERENT THERMAL ANALYSIS SOFTWARE FOR THERMAL SIMULATION OF THE SPACE TELESCOPE Cheng-En Ho, Meng-Hao Chen, Jeng-Der Huang, Chia-Ray Chen National Space Organization of National Applied Research Laboratories ABSTRACT SST and TRASYS & software can be applied in the thermal analysis of the space remote sensing system. There are differences between these two software in mesh generation, orbital heat resolution, calculation speed and post process. Both software were applied to simulate the space telescope and RSI satellite in thermal vacuum test and to predict the thermal balance temperature of the telescope and electronic unit. After model correlation, the difference between the software simulation results and thermal balance test results are less than 5. KEYWORDS:Thermal simulation software 1. INTRODUCTION Remote sensing image above the Earth is valuable for land survey, forest preservation, marine pollution monitoring and disaster rescue. A stable and suitable temperature range is important for the performance of the space optic-mechanic system. However, when the remote sensing satellite flight in the earth orbit, it suffers district environment of the temperature variation because of facing sunlight or entering eclipse. The thermal control design and the flight temperature prediction are important for the success of the mission. We use thermal simulation software to analysis and predict the temperature distribution and heat absorption of the remote sensing system in space. For checking and modifying the parameter in the simulation model, we make the thermal balance test of the remote sensing system in the vacuum chamber before the satellite lunch. The simulation prediction of the remote sensing system under the thermal balance condition was correlated with the thermal balance test data in order to reduces the simulation error and precisely predict the flight temperature. In AMOS-2 communication satellite (Sherman, 24), THERMICA software was used for the calculation of the black and gray form factors of the different satellite surfaces and the external heat loads. The information calculated by the THERMICA was embedded into /G software that was used for the temperature calculation. Most of the calculated temperatures fell within the 5 of the measurements. NASA Langley Research Center correlated the model of the Mars Reconnaissance Orbiter with the data obtained from cruise maneuvers (Amundsen, 27). Methods of correlation included comparing the model to flight temperatures, slopes, temperature deltas between sensors regards to thermal mass, conductive connections, and solar response. The heat fluxes obtained from Thermal Desktop radiation model were used in the run of the thermal model in Patran Thermal producing temperature predictions. An overall average error of the thermal modeling is as low as 5. TRASYS (Analytix Corporation, USA) and (Network Analysis Inc., USA) software have been used to simulate the thermal balance test of Formosat-5 remote sensing instrument (Ho, 215). TRASYS software was used to calculate the view factor and the radiation heat transfer between the surfaces. software was used to calculate the steady and transient temperatures of the remote sensing instrument based on the radiation exchange data generated by the TRASYS model. In this research, Space Systems Thermal (Siemens Product Lifecycle Management Software Inc., Germany) software is used to calculate space orbit environment heat and to simulate cube satellite, micro satellite, the space telescope, and remote sensing instrument compared with the TRASYS & software. These software are differences in mesh generation, orbital heat resolution, calculation speed and post process.

2 Remote Sensing Satellite Technology Workshop 216 Nov. 28, CUBE SATELLITE MODELING TRASYS and mesh established bases on nodes. The x y z position of the corner of the node in the coordinate system must be input manually into TRASYS. Figure 1 shows the cube satellite mesh of TRASYS. Each node has its thermal capacity. The thermal conductivity between each node must be typed into software. The thermal capacity value of each node and the thermal conductivity between nodes shall be calculated by user before input into. The command writing and subroutine calling in is based on FORTRAN language. The goodness of is clear for checking what we input. The shortage is time cost in setting up model. SST calculation is based on elements. The corner of each element or the center of the element edge is called node in. The element mesh could be 1~3. The 2D mesh could be triangular element or quadrilateral element. The 3D mesh is tetrahedral element. TRASYS & model is surface mesh, the node located on the center of the mesh. 2.1 Earth-pointing Orientation The wall surface of cube satellite is assumed as black body. Figure 2 shows orbital thermal environment heat flux absorbed on the each wall surface. The orbital heat flux calculation resolution is 3 position points per orbit in TRASYS. use different resolution 3, 6, 12 position points per orbit to compare with TRASYS. TRASYS automatically increase the position point at eclipse entering or exiting. s position points are distributed uniformly along the orbit. user can specify the calculation position of the orbit to give more point during the entering or exiting eclipse area. The orbital heat flux profile with 6 position points per orbit from simulation is similar as that with 3 position points per orbit from TRASYS. The temperature prediction of cube satellite with black body surface around earth-pointing orbit 72km is shown on figure 3. The temperature result of 3 position points per orbit in is similar as the result in TRASYS &. But takes 12 sec in running this case with 3 points per orbit for 3 cycles. TRASYS & totally takes 15 sec in running this simple cube satellite case. 2.2 Multiple-pointing Orientation Cube satellite with different complicate flight attitude such as normal mode or safe mode is shown in figure 4. The comparison of the calculation results of the orbit environmental heat flux and temperature prediction from TRASYS & or is shown in in figure 5, 6. Basically the heat flux profile from TRASYS and are very similar except the area in entering or exiting eclipse. has benefit in simulating the orbit transfer of spacecraft. The final temperature of the spacecraft in the first type orbit can be input as an initial condition to the next transfer orbit. Furthermore, can visualize the space craft orientation and orbit as a dynamic display for user checking. 3. MICRO SATELLITE MODELING The model description of the micro satellite is described as following: The.9m*.9m*.9m cube box has two internal components and solar panel. The first internal component dissipates 4W on the center of wall panel. The second internal component dissipates 25W only at night on the center of Z wall panel. The satellite covered with MLI except the center of the panel covered with radiator. Flight attitude is 7km with 45 o beta angle. The satellite is Z sun-pointing at day time and earth-point at night. The model made by TRASYS and by is shown in figure 7. The view factor calculation of TRASYS is a hybrid double summation / Nusselt sphere method. The view factor calculation methods of include Hemicube, Determinstic and Monte Carlo. The Determinstic method of combines Nusselt sphere method and shadowing check. The time consuming of the setting is listed on the table 1. The more element subdivision of let the sum of view factor more close to the correct value 1.. But complicated model with high accuracy will cost much time in calculation. The temperature prediction of wall panel and solar panel is shown in figure 7(c) (d). The temperature difference between and simulation

3 Remote Sensing Satellite Technology Workshop 216 Nov. 28, 216 results is less than TELESCOPE MODELING Space optic-mechanical system modeling of the telescope is shown in figure 8. The telescope was put into thermal vacuum chamber to process the thermal balance test. The hot/cold thermal balance test condition of the telescope is listed in table 2. The chamber shroud is maintained at 3 for hot balance test and at 5 for cold balance test. Figure 9 illustrates the balance temperature distribution from or simulation for the hot/cold balance. has better post-process function. software integrates geometry drawing, mesh building, solver and post-process. But the result output of is txt file that need other software to plot the temperature distribution of the telescope and consumes much time in transferring data. Furthermore, can set specular reflectivity of the surface such as mirror, but TRASYS only set emissivity and absorptivity of the surface such as diffusion surface. The heat source type of radiation can be selected as collimated or diffused in. On the other hand, can show the heater duty in the output text file. can do that but also shown in the text file. The user needs to remember the element number of the thermistor location which controls the heater in order to see the heater duty results. After model correlation, the results from simulation or simulation are very close to the experiment results of the thermal balance test. The results comparison is listed on the table 3 and shown in the figure 1. The temperature difference between simulation prediction and experiment results are less than REMOTE SENSING INSTRUMENT MODELING RSI (remote sensing instrument) system includes Telescope, FPA (focal plane assembly) and two EU (electronic unit). The solar arrays were removed from the satellite during the thermal balance test. The RSI satellite model is shown in figure 11. software can read and load the 3D geometry drawing directly from the computational aided design software such as AutoCAD, SolidWorks, Pro/ENGINEER. The node or element establishing in can be according to the 3D engineering drawing, therefore the size and angle of the model can be precise as the real geometry size of the satellite. If geometry needs to be updated during design phase, the mesh can be automatically updated with geometry in. If the element density of the component needs to be modified, the work is easier in than in TRASYS & because is graphical user interface software and TRASYS & is command line interface software. In TRASYS &, the coordinate position and thermal property of nodes need to be manually updated or type during modification. The maximum number of nodes in is one hundred million and that is ten million in. The hot/cold thermal balance test condition of the RSI satellite is listed in table 4. The shroud of the chamber is maintained at -17. The final stable temperature data of the hot/cold balance are compared with the simulation results for model correlation. After model correlation, the RSI temperature from, and experiment are shown and compared in figure 12. The temperature difference between simulation prediction and experiment results are less than CONCLUSION SST and TRASYS & software can be applied in the thermal analysis of the space remote sensing system. There are differences between these two software in mesh generation, orbital heat resolution, calculation speed and post process. The orbit environment heat flux of TRASYS has better resolution in the entering or exiting eclipse area. has benefit in illustrating the temperature distribution, simulating the spacecraft orbit transfer and display the space craft orientation. software integrates geometry drawing, mesh building, solver and post-process. with graphical user interface is easier for user input the case than TRASYS & with command line interface. can read and load the 3D

4 Remote Sensing Satellite Technology Workshop 216 Nov. 28, 216 geometry drawing from the computational aided design software. Furthermore, can set specular reflectivity of the surface as mirror, but TRASYS only set as a diffusion surface. In the view factor calculation, the more element subdivision of can get more precise results. But the shortage of is taking longer time in solving problem. After simulation model correlation with the thermal balance test, both the simulation results of and are close to the experiment results. The temperature difference between simulation and experiment data are less than REFERENCES AC/TRASYS (Thermal Radiation Analyzer System) User s Manual 1997, ANALYTIX Corporation. Amundsen, Ruth M.; Dec, Joha A.; Gasbarre, Joseph F. 27. Thermal Model Correlation for Mars Reconnaissance Orbiter. NASA Langley Research Center, ICES-17. Ho, Cheng-En; Huang, Jeng-Der; Chen, Chia-Ray 215. Thermal Model Correlation of FORMOSAT-5 Remote Sensing Instrument. Remote Sensing Satellite Technology Workshop. 2 November, Hsinchu Space System Thermal Student Guide 213, Siemens Product Lifecycle Management Software Inc. Sherman, Zeev 24. The Thermal Balance Test of AMOS-2 Spacecraft. Proceedings of the 5th International Symposium on Environmental Testing for Space Programs June, Noordwijk, the Netherlands, pp (System Improved Numerical Differencing Analyzer) /G user s guide 1998, Network Analysis Inc. Table 1 View factor calculation method comparison Table 2 Test heater power and shroud temperature in thermal balance test of the telescope. Hot Balance Name Current Resistance Popwer (A) (Ω) (W) M2 baffle fitting Strut 1 (+Y M_U to R_D) Strut 2 (+Y M_U to R_U) Strut 3 (+Y D) Strut 4 (-Y D) Strut 5 (-Y M_U to R_U) Strut 6 (-Y M_U to R_D) Cold Balance Name Current Resistance Popwer (A) (Ω) (W) Main Plate (+Y+X) Main Plate (-Y+X) Main Plate (+Y) Main Plate (-Y) (+X) (-Y) (+Y) Table 3. Temperature results from, and experiment data in the thermal balance test of telescope Table 4 Component power and test heater power in thermal balance test of RSI satellite

5 Heat Flux (W/m 2 ) Heat Flux (W/m 2 ) Heat Flux (W/m 2 ) Remote Sensing Satellite Technology Workshop 216 Nov. 28, 216 Sun-pointing Earthpointing Sunpointing Sunpointing Earthpointing Sunpointing Spin Y 2 round/orbit Figure 1. Cube satellite model TRASYS Normal imaging mode Safe mode Figure 4. Satellite flight attitude on Earth orbit TRASYS:3p/orbit 16 :3p/orbit TRASYS: 32p/orbit TRASYS 16 : 44p/orbit Eclipse -Y +Y -Z 4 +X 2 16 : 6p/orbit (hr) 16 (sec) :12p/orbit..55 Time (hr) Sun-point Earth-point Sunpoint Earthpoint output: 1p/orbit 5 (sec) output: 3p/orbit Figure 2. Orbit environmental heat flux, TRASYS vs. with different resolution. TRASYS:3p/orbit, output:1p/circle 2 (sec) :6p/orbit, output 6p/circle (sec) 2 : 3p/orbit, output 3p/circle (sec) :1p/orbit, output 1p/circle (sec) Figure 5. Orbit environmental heat flux and temperature prediction, TRASYS & vs. in normal imaging mode orbit TRASYS: 27p/orbit Sun-point Eclipse Sun-point TRASYS..55 Time (hr) Y +Y -Z +X 16 5 : 3p/orbit (sec) (sec) (sec) Figure 3. The temperature prediction of cube satellite, vs. with different resolution (sec) Figure 6. Orbit environmental heat flux and temperature prediction, TRASYS & vs. in safe mode orbit.

6 EU-A +Y EU-A EU-B -Y EU-B FPA +Y FPA -Y FPA -Z Strut -Y Strut +Y Bipod -Y-Z Bipod +Y-Z Bipod -Y Bipod +Y FPA bracket EU-A +Y EU-A EU-B -Y EU-B FPA +Y FPA -Y FPA -Z Strut -Y Strut +Y Bipod -Y-Z Bipod +Y-Z Bipod -Y Bipod +Y FPA bracket ISM +X ISM +Y SHIELD +X SHIELD -Y M2 FITTING M2 BACK STRUT1 STRUT3 STRUT5 BIPOD -Y-Z BIPOD -Y MP MP RING RING Temperature (C) Temperature (C) ISM +X ISM +Y SHIELD +X SHIELD -Y M2 FITTING M2 BACK STRUT1 STRUT3 STRUT5 BIPOD -Y-Z BIPOD -Y MP MP RING RING Remote Sensing Satellite Technology Workshop 216 Nov. 28, (c) Time (hr) (d) Figure 7. Micro satellite model TRASYS ; (c)wall panel temperature prediction from vs. (d)solar panel temperature prediction from vs. M CFRP strut Y +Y -Z +X Spider (sec) (sec) Time (hr) T713 T714 6 T M1 baffle Exp. data simulation simulation Exp. data simulation simulation Figure 1. Telescope temperature results comparison from, and experiment data in the thermal balance test hot balance cold balance. RSI housing FPA Bipod Top panel EU Bus Top panel M1 Bipod Top panel FPA pin hole plate Figure 8. Telescope model TRASYS Figure 11. RSI satellite model TRASYS TTC TTC Figure 9. Telescope temperature prediction from or in the thermal balance test hot balance cold balance. Figure 12. RSI temperature results comparison from, and experiment data in the thermal balance test hot balance cold balance