High-precision inspection for the European Extremely Large Telescope (E-ELT).

The race is on for who will manufacture 1,000 mirrors for the European Extremely Large Telescope (E-ELT). Cranfield University in the UK has begun work on producing seven of the mirror segments for ‘the world’s biggest eye on the sky’ with the aid of high accuracy measurement systems from Hexagon Metrology.

Built by the European Southern Observatory (ESO) the E-ELT, a ground-based telescope, will be 42m in diameter and made up of 1,000 hexagonal segments, each 1.5m wide and just 5cm thick. The E-ELT is four to five times larger and will gather 15 times more light than the largest optical telescopes operating today.

The production and measurement challenges for this project are significant. Cranfield University is the only organisation in the UK with the capability to undertake various stages of machining the mirror segments to the accuracy required. Cranfield’s BoX (Big OptiX), a specialised grinding and measurement system, was developed at Cranfield specifically for realising these mirrors.

Located in Cranfield’s Loxham Precision laboratory, which is sponsored by Hexagon Metrology, is a Leitz PMM-F 30.20.10 CMM. This Ultra High Accuracy (UHA) measuring system is used to verify the performance of the Cranfield BoX grinding machine and measures the mirror segments.

Professor Paul Shore, Head of the Cranfield University Precision Engineering, says, “What we’ve got in our BoX machine is an ultra precision grinding and metrology system made at Cranfield that grinds the part and performs some in-process measurement. The Leitz PMM-F is then used to . . . . .