A Refocusing Mechanism (REM has been designed and built for the SEVIRI instrument, the iinager in the Meteosat Second Generation MSG satellite. l'he purpose of the meclianisni is in-orbit focal adtustnienl of a mirror assembly which forms part of SEVIRI As the MSG satellite observes the earth and its atmosphere I roiii its geostationars orbit, the REM will be used to compensate for satellite structural distortions due to gravitational-, thermal and aging effects It is designed for frequent use. It enables in-orbit refocusing in 1 .4 pm steps over a range of 2 mm with irtuallv no spurious rotations and translations. The REM was designed to support a large 3.9 kg mirror module in an ARlANl rocket launch environment without the use of clamping mechanisms. Further niator design dris ers were the Iunited volume and the strict mass requirement. The REM function is realized in two modules. A guide module, based on elastic elements pros ides the required stroke ithin the strict requirements on lateral deviation and tilt. An actuator module with a motor, a planetary gearbox and a recirculating rollerscrew provides the force for translation of the mirror assembly. ('ouplnig of the t'. modules has been realized by a dedicated leverarni structure.