The MICADO first light imager for ELT: from hexapod to octopod instrument support structure

The MICADO instrument support structure has to fulfill two purposes, a) the positioning of the camera in a stand-alone mode with SCAO wavefront sensing at the First Light, and b) when it will be mounted at a later stage downstream of its MCAO facility MAORY. Several reasons led to a change in the instrument support structure from a hexapod into an octopod mount. The paper will address the structural design driven by the telescope and the instrument itself. Tightly linked is the solution to accommodate the bulk of electronics, pumps and cryogenic service devices, which has to corotate closely but separately from the instrument. This co-rotating platform creates issues in the cable wrap in terms of sufficient capacity and large rotation range. Performance assessment will be addressed through a prototype test set-up as well as corresponding Finite-Element-Analysis.