Effect of Gemini primary mirror position, relative to the lateral support, on mirror figure

The Gemini primary mirror support incorporates a system of hydraulic whiffletrees to carry the mirror weight and define its position. The six orthogonal kinematic degrees of freedom are controlled by six hydraulic zones -three axial, two lateral, plus a transverse lateral. By varying the fluid volumes in these hydraulic zones the mirror position can be adjusted in all six degrees of freedom. Because of the finite lengths of the linkages that connect the mirror to the lateral supports, any shift in mirror position changes the amplitudes and directions of the applied forces with a resulting effect on the static balance and mirror figure. These effects have been calculated for mirror translations and rotations in all six degrees of freedom, resulting in predictions of the changes in the axial and lateral support forces and in the mirror figure. This paper describes the modeling as well as experimental verification of the results.