Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) for SUNRISE-3: Opto-mechanical analysis and design

The Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) is a near-IR spectro-polarimeter instrument newly designed for Sunrise III, a balloon-borne solar observatory with a 1-m diameter telescope. In order to achieve the strict requirements the SCIP wavefront error, it is necessary to quantify the errors due to environmen- tal effects such as gravity and temperature variation under the observation conditions. We therefore conducted an integrated opto-mechanical analysis incorporating mechanical and thermal disturbances into a finite element model of the entire SCIP structure to acquire the nodal displacements of each optical element, then fed them back to the optical analysis software in the form of rigid body motion and surface deformation fitted by polynomials. This method allowed us to determine the error factors having a significant influence on optical performance. For example, no significant wavefront degradation was associated with the structural mountings because the optical element mounts were well designed based on quasi-kinematic constraints. In contrast, we found that the main factor affecting wavefront degradation was the rigid body motions of the optical elements, which must be mini- mized within the allowable level. Based on these results, we constructed the optical bench using a sandwich panel as the optical bench consisting of an aluminum-honeycomb core and carbon fiber reinforced plastic skins with a high stiffness and low coefficient of thermal expansion. We then confirmed that the new opto-mechanical model achieved the wavefront error requirement. In this paper, we report the details of this integrated opto-mechanical analysis, including the wavefront error budgeting and the design of the opto-mechanics.