M2 Mirror Cell Assembly

The 3.5-meter diameter M2 Cell Assembly sitting in its test tower (approx. six meters off the ground) in the Harris test facility in Rochester, N.Y. Looking up through the convex Ultra Low Expansion (ULE) glass, you can see some of the three concentric rings of axial actuator pads which are bonded onto the concave back side of the mirror. Hence the mirror is suspended from these 72 locations and 6 pads hidden around the circumference. Previous Cell Assembly integration photos showed the aluminum surrogate mirror, which was used to test and demonstrate closed-loop control of the mirror software to ensure safe handling of the glass mirror. This milestone of glass integration marks the beginning of integrated optical testing which will measure the nanometer scale imperfections in the glass surface to be removed to deliver the correct final shape to be used in the telescope. be completed over the next year.