HARMONI at ELT: Reoptimization of the NGSS natural guide star sensors system for MCAO compatibility
HARMONI is the first-light, adaptive optics assisted, near-IR integral field spectrograph for the ELT. It covers a spectral range from below 800nm to 2400nm with resolving powers from 3000 to 7000 and spatial sampling of 25mas and 6mas. It can operate in three adaptive optics (AO) modes: single conjugate AO (SCAO), high-contrast AO (HCAO), and multi-conjugate AO (MCAO). The project is resuming its final design phase after a rescope design phase that has lasted two years. This paper describes the impact of the rescope on the natural guide star sensors (NGSS) system, imposing wide-ranging changes in particular to the low-order wavefront sensors (LOWFS) previously optimized for LTAO operation as well as on the external support and enclosure (ESE) whose external interfaces have changed. The high-contrast module (HCM) is also deeply affected due to the modified plate scale of the instrument, and the single-conjugate AO sensor (SCAOS) benefits from a reduced patrol field requirement. Description of the changes will be given together with the associated system analysis involving requirements flow-down, revisited functional analysis, and updated product breakdown structure. Elements of the new system management structure and work breakdown will also be included.