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Telescope Sensor Raft/Tower Model

Scientists and engineers at Brookhaven National Laboratory (BNL) are responsible for the design of sensor raft towers used in a new Large Synoptic Survey Telescope (LSST).   The sensor raft towers consist of CCD sensors precisely mounted on a raft, which in turn is loosely connected to an electronics cooling tower that maintains the sensors at approximately -110 degrees C. To maintain image quality, the sensors must remain flat and coplanar to within a few microns, even at these very low operating temperatures.

LSST Sensor Raft Tower

Initial finite element analyses performed at BNL with ANSYS Workbench showed fairly significant distortion in the sensors, raising suspicion that incorrect methods and inputs may have been used.  CAE Associates was asked to review the models and make modifications to assure correct modeling procedures and inputs. They closely reviewed both the heat transfer and nonlinear structural parts of the analysis; specifically assessing the mesh, thermal loads, structural loads and constraints, material properties, contact connections, pin preloads, and solution controls.   CAE Associates discovered several potential problems with the model and made the appropriate changes and corrections.  The updated model yielded a more realistic temperature distribution and the deflections in the sensors were well within the allowable distortion limits. 

The detailed model evaluation and corrections provided by CAE Associates yielded significantly more confidence in the model. In addition, the work was performed in close collaboration with BNL, allowing modeling efforts to proceed in parallel and providing an improved knowledge base for future model development.

Mr. Stephen Plate, the project engineer at BNL describes the contributions of CAE Associates as follows:

"After weeks of experiencing difficulties in getting a complicated thermal and mechanical Workbench model to solve properly, I decided to contract with CAE Associates for some help.  This decision paid off well. Via exchanged phone calls and emails, the model was analyzed in detail by CAE Associates, the problem areas were identified by them, and improvements were made that provided realistic results and enhanced run time. Equally important, through working with them my knowledge base was increased so that I am better equipped for future analyses.  It was a very positive experience."