Solar orbiter – EUS instrument mechanical design Tim Froud and Doug Griffin

Talk outline Mechanical-thermal-optical considerations for the Primary Mirror Silicon Carbide Testbed Study Structural layout

Primary mirror WFE under Solar IR Loads The Solar radiation load will introduce thermal gradients in the Primary Mirror –Thermal stresses Internal mirror temperature gradients Possibly also from CTE mismatches The thermal load will vary by roughly an order of magnitude during each orbit Goal is to meet the optical performance during the encounter and during down link phases of the orbit Mirror distortions will introduce distortions in the surface of the mirror which will reduce the spectral and spatial resolution of the instrument

Primary Mirror WFE Tolerance Estimates Calculation based on encircled energy and are to be considered provisional Given the Spectral and Spatial resolution requirements: –Derived requirement on PSF ~ 10um: Mirror rms WFE: ~ /30 i.e. 21nm rms

NI Primary Mirror Distortion Estimates Model Geometry Uniform heat load B/C 35kW/m 2 Axis of symmetry 5mm 10mm 5mm 25mm 40mm Fixed Temperature B/C

NI Primary Mirror Distortion Estimates Material Assumptions Assume that the mirror is made from homogeneous Silicon Carbide –E=249GPa –Poission ratio: 0.16 –CTE: 2.7x10-6 m/m –Thermal conductivity: 127 W/m/K –Mirror is absorbing in the IR Thermal interfaces have identical mechanical properties as Mirror –No interface stresses

NI Primary Mirror Distortion Estimates Temperature Distribution

NI Primary Mirror Distortion Estimates Thermal distortions

NI Primary Mirror Distortion Estimates Conclusions The analysis has to be considered as a preliminary estimate –Optical –Thermal –Mechanical –Layout Nonetheless: The conclusion is that the thermal control of the Primary Mirror will have to be considered in tandem with the overall instrument optical performance –It could be one of the largest challenges for the instrument design –Rastering of the instrument via the Primary mirror could be very difficult with the complexity of the thermal control

Primary Structure Material Selection Test Bed Study A study was carried out on a SiC based Optical Bench –Looked at the practical details of designing structural components in SiC –Very useful in terms of understanding: Detailed manufacturing processes Achievable tolerances Mounting and interface designs Lightweighting Non-destructive Testing – Procurement of test-bed did not proceed due to cost –Promising outcome for Flight-build

Primary Structure Material Selection Test Bed Study

Components of system

Optical bench

Primary mirror

Slit mechanism

Grating

Detectors and electronics

Enclosure and baffling