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The picture above shows the Qualification Model of the Gaia Wavefront Sensor.
The WFS system will be used to monitor the wave front errors of the two Gaia telescopes mounted on the Gaia satellite. Such system must have low optical aberrations itself. Gaia will operate over a broad wavelength and in cryogenic conditions (450 to 900 nm wavelength band and 130 to 200 K operation temperature). For these boundary conditions a temperature independent solution of Invar is selected, with fused silica optics, with the least number of dispersive elements in the design.
The telescope images the stars on the Focal Plane Array (FPA). The WFS picks up a small part of this field and images the telescope pupils on a Micro Lens Array (MLA) from where each micro lens images part of the pupil on the same FPA.
Monitoring the spot positions on the FPA array is the basic measurement of the wave front quality of the telescope of Gaia (for that field of view). The spot positions of a star can be compared to the spot positions of three calibration sources that are included in the WFS. This comparison is according the "Shack Hartmann" principle.
At this moment TNO is working to get the measurement system (OGSE) within specification before starting the qualification campaign of the QM model. The OGSE should have an accuracy even higher then the WFS itself.
Image courtesy of TNO/Leo Ploeg
[A larger version of this image is available in the following link]
[Pubished: 25/07/2008]
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