4MOST - 4-metre Multi-Object Spectroscopic Telescope
4-m Multi-Object Spectroscopic Telescope

AESOP integration

One of the core components of 4MOST is a fibre positioner, called AESOP (Australian-European Southern Observatory Positioner), which was designed and built by the Australian Astronomical Optics (AAO) Department of Macquarie University in Sydney in the framework of ESO’s partnership with Australia. AESOP is the first major subsystem of 4MOST to have arrived at the Leibniz Institute for Astrophysics Potsdam (AIP) for integration.

The AESOP system, which is based on innovative AAO technology, includes the positioner with its 2436 fibres, the positioner housing, the electronics and the electronics enclosures. The fibres are arranged in a hexagonally shaped grid and can be pointed very precisely to collect the light from stars and other objects in the sky. The fibres relay the light to three optical multi-object spectrographs that will measure the spectral properties of the observed objects simultaneously, and thus give clues on the chemical structures and movement of different regions of the Milky Way, among other things. The most important requirement for AESOP is that all fibres must be repositioned within 1 minute with an accuracy of 10 micrometres – about one fifth the thickness of a hair. When the fibres reach their new positions, they are back-illuminated with red light which is recorded by high-resolution cameras to check the positions of the fibre ends before starting a sky exposure. The better the accuracy and speed, the more light from an object will be caught in as little time as possible.

In August, the completed fibre positioner was delivered from AAO in Sydney to AIP in Potsdam. This is the first delivered major component for 4MOST and, once unpacked and reintegrated, it marks the start of 4MOST system integration at AIP’s integration hall. “After more than four years of design and analysis work, followed by 3 years of manufacturing and integration, it was very exciting to receive the finished AESOP for system integration,” reflects Joar Brynnel, Project Manager of 4MOST at AIP. “Test results from Sydney show excellent performance and we are very happy to start testing AESOP in Potsdam and continue the great collaboration with our partners and colleagues in Australia.”

Nominally, the plan was for the AAO team to travel to Potsdam and lead the re-integration and test of the AESOP fibre positioner. Due to COVID travel restrictions in and out of Australia, this was not possible. The situation posed difficult problems for the Potsdam engineering staff, who would normally rely on the collaboration with their Australian colleagues for the unpacking and delicate assembly of AESOP. The teams have now devised an alternative plan where the work will be carried out by staff from the European 4MOST partners under the remote supervision of AAO technical staff. This has started with the arrival of a support team from the Max Planck Institute for Astronomy and the Landessternwarte, both in Heidelberg, on 25 October.

Dr Roelof de Jong, Principal Investigator of 4MOST, emphasises the importance of this step: “It is amazing to reach the milestone of AESOP unpacking and assembly in Potsdam. The fibre positioner is at the heart of the facility and we can now start assembling and testing the full instrument around it before shipping everything to Chile.” The completion of the instrument in Europe and delivery to Chile is currently planned for May of 2023.

“AAO-Macquarie University is proud to engage and work closely with major observatories around the world to deliver innovative new instruments based on the new and emerging technologies, like AESOP, that we are creating,” said AAO-Macquarie University’s AESOP Project Manager Scott Smedley.

The text above has been reproduced (with minor modifications) from this AIP press release. See also this UWA press release and this ESO twitter thread.

The AESOP fibre positioner for 4MOST that controls 2448 fibre spines. Credit: F. Watson.

AESOP core opto-mechanical unit with spines and fibers on the crane being handled by Walter Seifert (LSW) and Carlos Rodriguez (AIP).

Four custom made cabinets with the AESOP control system ready to be integrated into the AESOP core instrument.

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