• Datum: 2024-01-31 14:50:17
• Firma: Institute of Astrophysics and Space Sciences
• Ansprechpartner: Mr Alexandre Cabral
• E-Mail: Alexandre.Cabral@ciencias.ulisboa.pt
• Anschrift: Departamento de Física – FCUL, Edifício C8 – 8.1.40, 1749-016 Lisbon
• Telefon: 351966638034
• Land: Portugal
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MOONS is the Multiple Object Optical and Near-infrared Spectrograph that will operate at the Nasmyth focus of the European Southern Observatorys Very Large Telescope. MOONS is an astronomical instrument designed to be a high performance and versatile survey spectrograph, with a large field of view, the size of the moon, capable of simultaneously observing 1,000 objects over the visible and near-infrared wavelength range. The instrument consists of the three sub-systems: the Rotating Front-End mounted on the VLT rotator on the Nasmyth platform, the two Triple-Arm Spectrographs and the Instrument Control.

The instrument Rotating Front End contains several modules, including a rotation cable wrap that is responsible to manage the cables and optical fibres between the Spectrograph, fixed in the telescope Nasmyth platform, and the Rotating Front End attached to the telescope that rotates during the pointing to the sky of the scientific observation. This rotation cable wrap uses a new configuration, based o a flexible solution from IGUX, the Triflex ® E-Chain Series, to guarantee that the sensible optical fibres that carry the light from the Front End to the Spectrograph do not feel any stress that could jeopardise the scientific observations.

The application is used in astronomical instrumentation, more precisely in the focus of one of the biggest telescopes in the world, located in the Paranal mountain at the Atacama Desert in Chile, where the European Southern Observatorys Very Large Telescope is located.

Although the ESO VLT Observatory is located in the Paranal mountain at an altitude of 2670 m resulting in peculiar environmental conditions, like very low humidity (sometimes of a few %HR) and high levels of ozone, the main challenge that was imposed to this project was related to the fibre cable management. As the part connected to the telescope has to rotate with the sky and the heavy spectrograph that receives the fibres with the astronomical light is fixe in a platform, a cable wrap is required to manage the cables and the fibres that connect both parts. The way the science fibres are moved is very critical as any push/pull force on them can cause a degradation of the optical signal (know as focal ratio degradation). Traditional rotation cable wraps are based on 2 dimensional cable chains that rotate only around one axis in a two ring configuration with two different radius of curvature. During the rotation of one of the rings, this difference (in radius of curvature) inevitably creates some slack that either pushes or pulls the cable, inducing an undesirable stress on the optical fibres. To overcome this challenge we implemented a new idea (in the area of astronomical instrumentation) with a rotation cable wrap based on a ring like shape concept that provides equal path to both halves during rotation of the Nasmyth adapter, using a 3 dimensional cable chain. This concept ensures that, during rotation, there is no longitudinal movement of the cable chain.

Other 3D movement

In astronomical instrumentation, and in scientific application in general, cost is not the critical issue. In this application, IGUS products were fundamental to allow us to implement the new concept guaranteeing the required robustness and reliability.

• Energy chain(s) Triflex ® E-Chain Series

Indeed the Triflex chain allowed us to implement the idea of a equal ring rotation cable wrap, the only way to guarantee no stress on the optical fibres.

Due to the environmental conditions in Paranal (namely the high ozone) the use of plastic based materials is critical. Our experience from the past on other instrument at same location with IGUS chains gave us the confidence and guarantee that the material would perform as expected. Therefore, and as we found a solution with the a particular type of chain, we did not searched for other alternatives as the time spent to validate them would have a considerable impact.

Considering that IGUS chains use sustainable materials and due to the robustness of them that guarantees an instrument lifetime of use without replacement, it ends up being a more sustainable solution than other possibilities.

IGUS Portugal supported us in the initial search for a 3D solution and in obtaining information about the material characteristics to validate its application. This support was very useful to help on the final implemented solution.

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