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On the way to build the M4 Unit for the E-ELT

While the Deformable Secondary Mirror for the VLT is tested with the GRAAL adaptive system, the M4 adaptive mirror design is approaching detailed design. Although the two designs use the voice coil technology developed by Microgate and ADS, the M4 Unit requirements are more stringent. The M4 unit aims to provide adaptive correction and to cancel part of telescope wind shaking and static aberrations. The final specifications have been settled and the key performances will be demonstrated shortly on a one meter prototype. We present the main design drivers and associated requirements. We discuss what the challenges are in terms of stability and performance of the associated key technologies. We additionally describe the selected design, the current status of the project and the required schedule and work plan to manufacture the E-ELT quaternary mirror.