During operation the mirror will be subjected to changes in orientation with respect to gravity as shown in Figure 2. The resulting figure changes, plotted in Figure 3(a), are actively controlled by three displacement actuators and several force actuators per mirror segment. A trade study is run to determine an actuator layout which will generate less than 0.045 wave surface RMS over the entire array. Figure 3(b) shows the corrected surface with only three displacement actuators on each segment and has a best corrected figure of 0.25 wave surface RMS. With the inclusion of six force actuators for each segment the surface figure, shown in Figure 3(c), can be corrected to 0.040 wave surface RMS to meet the 0.045 wave budget.
Figure 3: A trade study shows that the deformation due to the gravity orientation change shown in (a) can be corrected to (b) 0.25 waves surface RMS with rephasing only and to (c) 0.04 waves surface RMS with rephasing and figure correction with six actuators per segment.