AESOP- the fibre positioner unit for ESO 4MOST- fully assembled

AESOP is the fibre positioner unit for the 4MOST instrument currently under construction for the 4-metre diameter VISTA telescope in Chile, which is operated by the European Southern Observatory (ESO).

The 4MOST instrument is expected to observe 75 million stars and galaxies during its lifetime, conducting research that will significantly advance our understanding of dark matter and galaxy formation, including the events that formed our own Milky Way galaxy. The Astralis AESOP team have a significant role in this pioneering instrument with the development of an innovative fibre positioner.

Images of AESOP assembly process. It took the AESOP team several years to design, develop, test, and verify all of the instrument components.

Astralis’ component, AESOP, deploys 2448 optical fibres to positions on the curved focal surface of the telescope to extremely high precision (<10 microns). Each fibre can be deployed anywhere within a fixed 11.5mm patrol area. Field reconfigurations are achieved in an iterative closed-loop process. All 2448 fibres are positioned simultaneously in <1 minute. Optical fibres are grouped and connectorised at their exit from the spine modules, where they feed 3 optical spectrographs.

The design for AESOP is an evolution of Astralis’ tilting spine technology, first designed and implemented in the FMOS-Echidna instrument for the Subaru telescope.

The AESOP instrument is fully assembled in the Astralis integration room, prior to final system testing.

The AESOP project commenced in 2012. In October 2020, the Astralis team completed a major milestone by successfully holding the Local Acceptance Review (LAR) that was attended remotely (due to COVID) by the 4MOST Project Office. AESOP is currently being disassembled and packed for it’s journey to Germany for integration with other 4MOST subsystems.

AESOP will be the first major subsystem of the 4MOST project to be delivered.

Mechanical model of the overall 4MOST instrument installed on the VISTA telescope. For reference, the diameter of the telescope main mirror is 4 metres.

Check out our AESOP Video on Twitter!