The European ELT: Detailed Design Phase
The detailed design phase
Following ESO Council approval of the Baseline Reference Design, the 57 M€ Detailed Design Phase for the whole facility started in December 2006. While this landmark decision solely covers this 3-year period, it paves the way for starting construction early 2010, provided adequate funding is secured. Hopefully, this giant facility will be ready for operation around 2017.
The baseline is the 5-mirror approach, with a 3-mirror Cassegrain (similar to TMT) as a backup. The telescope features a 42m F/1 segmented primary mirror and for maintenance purposes is able to go to horizon. Advanced optical coatings are being explored to get better optical efficiency and lower IR emissivity than with standard evaporated Aluminium. The baseline presently assumes the worst case of a site with occasional heavy snowfall and strong earthquakes.
View of the 3-D model of the baseline E-ELT developed to optimise performance during observing conditions. Total rotating mass is 5500 tonnes. The two platforms on each side of the structure hold each a number of large instruments which can be quickly put on-line. The 42m primary mirror is composed of 906 segments, each 1.45m wide, while the secondary mirror is 6m in diameter. A tertiary mirror, 4.2m in diameter, relays the light to the adaptive optics system, composed of two mirrors: a 2.5m mirror supported by 5000 or more actuators able to distort its shape a thousand times per second, and one 2.7m in diameter that gives accurate image stabilisation. Image quality is extremely good, with no significant aberrations in the almost plane 10' diameter field of view.
Development of a specific set of prime science cases - a so-called Design Reference Mission (DRM) - is ongoing with the Community. It will serve in particular to assess by mid-2007 the quantitative impact of the telescope diameter on its science value. It will also be an essential tool for formal decision on the best site by end 2008. In parallel, the Community is strongly involved in the definition of an instrument set, including their advanced post-focal adaptive optics systems. The FP6 ELT-DS technology development programme has also been carefully steered to fulfil the needs of the project.
A full review of the project was conducted beginning March 2008. Further aspects of the project were presented at the SPIE Conference in Marseille (Astronomical Telescopes and Instrumentation) in June 2008.
The next major milestone is another full review of the project in November 2008, with in particular consolidated cost and schedule estimates.