SES-upgrade on route to a 3-arm high-res spectrograph.

For high-precision RV monitoring following the TESS and PLATO 2.0 findings, STELLA-II will receive a new 3-arm high-res spectrograph. It's core will be a a new vacuum-stabilized optical spectrograph reaching R=55000 with 35% efficiency peak. Currently it is assembled at the AIP optic's lab, where it will be tested exhaustively prior to shipment to Tenerife in early 2021. An IR-arm is to follow the same year, a Ca H&K spectrograph should follow 2022-23.