TNO developed a Wave Front Sensor (WFS) instrument for the GAIA mission. This Wave Front Sensor will be used to monitor the wave front errors of the two main telescopes mounted on the GAIA satellite, which may be corrected by a 5-degree of freedom (DOF) mechanism during operation. The GAIA-WFS will operate over a broad wavelength (450 to 900 nm) and under cryogenic conditions (130 to 200 K operation temperature). The WFS uses an all reflective, a-thermal design and is of the type of Shack-Hartmann. The boundary condition for the design is that the focal plane of the WFS is the same plane as the focal plane of the GAIA telescopes. The spot pattern generated after a micro lens array ( MLA) by a star is compared to the pattern of one of the three calibration sources that is included in the WFS, allowing in flight calibration. We show the robust and lightweight opto mechanical design that is optimised for launch and cryogenic operation. Furthermore we give details on its alignment and commissioning. The WFS can measure wave front distortions in the order of lambda/1000, and determines the focal plane with an accuracy of 50 µm

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.