E-ELT Prototype Segments

The National Facility operated by Glyndwr University is developing process and metrology technologies, and manufacturing prototype mirror segments, for what will be the world’s largest optical telescope project – the 39m aperture European Extremely Large Telescope (“E-ELT”).    The prototype segment project is described in several recent publications here

The invited SPIE newsroom article (April 2013) gives a good overview here

Segment  Acceptance

The first completed segment (designated SPN04) has successfully been though its pass-off tests at OpTIC, witnessed by ESO staff.  An unqualified Certificate of Acceptance was subsequently received.

Find out more about the new mirror process for the world's largest telescope

Polishing Master Sperical Segment   E-ELT segment  

Polishing the Master Spherical Segment

This 1.4m across corners, Zerodur,  hexagonal Spherical Mirror has an 84m radius of curvature. This mirror is the master reference artefact against which E-ELT prototype segments are compared.

It was polished to the required 18nm RMS (surface) on the Zeeko IRP1600 machine at the National Facility. 

It is particularly smooth, exhibiting 5.5nm RMS for spatial scales <250mm, and 4.2nm RMS for scales <100mm.


Prototype Full-size E-ELT segment

This shows one of the off-axis aspheric prototype segments on its hydrostatic support system, under inspection in the National Facility.

The segments are only 50mm thick, and require a support-system that:-

  • emulates the support-forces in the telescope (for zenith-pointing)
  • delivers low-hysteresis, so that surface metrology is reliable at the few-nm RMS level
  • withstands the process-forces in polishing