StarPicker, a cryogenic positioning system for pick-off mirrors

A pick-off mirror (or POM) is a small multi-purpose optical system that captures light emitted by celestial objects and redirects the beam towards specific imaging or spectrographic equipment. These small systems must be strategically positioned on the telescope's focal plane, where they are held in place by a magnet.


2006 | In the early 2000s, under the aegis of the OPTICON (Optical Infrared Co-ordination Network for Astronomy) program – launched more than two decades ago by the European Commission – CSEM, together with its partners ASTRON and the UK Astronomy Technology Centre, developed a cryogenic positioning system to accurately place and adjust these POMs on a telescope's potentially curved focal plate. One of the major challenges was the need for precision positioning. To achieve this, each POM must be placed in such a way that their optical field of view is aligned with the corresponding scientific instrument, and its position and those of adjacent mirrors must be accurately measured.

To handle the POMS, the positioning system – named StarPicker – is fitted with a gripper that can reliably and continuously grasp and release these mirrors onto the focal plane’s surface. The gripping mechanism was designed to operate without friction, based on so-called “flexible bearings” technology that enables precise, reliable movements, without wear and tear or particle emissions.