Each red square, or row of red squares, again indicates the location of a PRT sensor. First step in the reduction process is a calculation of the temperatures of ALL nodes in the FEA model. The present implementation uses a thermal conduction model for this purpose. Once all the temperatures are known, a consistency check is performed to flag unrealistic values. The second step is a calculation of the thermal expansion of the telescope structure using a full-blown FEA analysis.
Third step is to fit an ideal parabolid through the displaced surface nodes.
This is dramatically illustrated by the 2 figures below for a temperature change in one of the elevation drive rings. The figure on the left is the raw FEA result, requesting a large correction of the surface. The figure on the right shows the residual adjustments which are needed to tweek the telescope back into a perfect shape after a simple pointing correction in Elevation is made. After fitting the claclulated surface node displacements, the number of steps for each one of the 828 steppermotors for moving the panels is determined. Step rate is 40 Hz.