Mechanical concept design for the 4MOST AESOP fibre positioner

AESOP is the fibre positioner unit for the 4MOST instrument planned for the 4-metre European Southern Observatories VISTA telescope in Chile. The 4MOST project, led by the Astrophysical Institute Potsdam (Germany), involves a number of European partners. The AAO component, AESOP, deploys 2400 optical fibres to required positions on the curved focal surface of the telescope. Each fibre can be deployed anywhere within a fixed patrol area. Field reconfigurations are achieved in an iterative closed-loop process with positional feedback from a metrology system. Optical fibres are connectorised at their exit from the positioner system, where they feed a fibre bundle terminated a series of optical spectrographs. The proposed design for AESOP is an evolution of the AAO’s tilting spine technology, first designed and implemented in the FMOS-Echidna instrument for the Subaru telescope.