The MOMFOS fibre positioner

The Anglo-Australian Observatory has undertaken a design study for a 1000 fibre positioner for the prime focus of the Giant Segmented Mirror Telescope (GSMT) as part of the MOMFOS (Multi-Object MultiFibre Optical Spectrograph) instrument. To our knowledge this is the first design study funded for a prime focus instrument for an ELT. It offers a particularly elegant and efficient solution for wide-field multiobject spectroscopy on extremely large telescopes (>30m) for the acquisition of large scale high-redshift surveys (1<z<10) with sufficient area (25 deg), density coverage ( 2.5 million galaxies) and limiting magnitude (R 26.5). Closely based on the innovative Echidna positioner under construction for Subaru's FMOS system, the MOMFOS positioner uses piezoelectric microrobotic actuators able to position accurately all 1000 fibres simultaneously. The FMOS-Echidna design is extended to include a novel position feedback system offering radical benefits in cost and speed. We present positioning results for a design capable of a higher packing density than that developed for FMOS-Echidna, providing ~1000 fibres across the 175 mm diameter field of view (20 arcmin).