Design, analysis, and performance verification of the interface region imaging spectrograph (IRIS) telescope primary mirror assembly

We discuss the details of the Interface Region Imaging Spectrograph (IRIS) telescope primary mirror assembly designcompared to its predecessor used in the Solar Dynamics Observatory Atmospheric Imaging Assembly (SDO-AIA) telescopes. Also included are details of the structural modeling and analysis, mirror optical surface modeling, vibration analysis, and a detailed description of the optical performance verification test program and results.The primary mirror assembly of the IRIS telescope was adapted from an existing design used on the SDO-AIA telescopes. The IRIS telescope was optimized for performance at 1369A and 2810A with a required 0.4 arc-second-resolution calling for a significant improvement to the mounted mirror optical surface quality over the existing SDOAIA design.To improve the optical performance, the proven bonded flexure heritage design was augmented with a novel “kinematic” mount used to secure the assembly to the telescope tube. The 200mm diameter concave mirror was fabricated from Corning ULE/RE Code 7973 EUV Premium Grade, Ultra Low Expansion Glass material and polished to better than 12ARMS surface roughness. The mirror is supported by three bonded titanium flexures fastened to a rigid titanium cell plate.A 25A RMS figure error was allocated in the error budget for the mounted, coated primary mirror. The first moderesonance for the mirror was specified to be <100 Hz while surviving an expected launch load of 30G’s. The mirrorassembly was designed to operate from +14°C to +26°C with survival limits specified at -20°C to +35°C.