The second fiber cable system is now on the Subaru telescope!

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As we reported in the previous article, the second fiber cable system was standing by in Hilo, Hawaii, for its installation to the Subaru telescope. Thanks to the schedule arrangement by the observatory, we had a 2-week slot in April to install and test the second fiber cable system. We are going to report the installation and test activities in this article.

Installation and test activity were carried out by Kavli IPMU and Subaru with remote help of the fiber team led by Brazilian consortium. In the first week, we unpacked ~60m fiber cable from the crate and laid down the cable on the floor to test its performance before installation. One of the features to assess the performance is called FRD, Focal Ratio Degradation. If fibers get stressed or twisted, their FRD gets worse. At first, we confirmed FRD was as expected from the number before shipping, which means that the fibers have survived the shipping well.

In the second week, the week of 11 April, the fiber cable was installed to the telescope. Because the fiber cables connect the Prime Focus Instrument on the top of the telescope and Spectrograph Modules on the 4th floor in the dome building, the fiber route is divided to the two parts, telescope side and dome side, as shown the below figure.

Sketch of the fiber cable routing.

The fiber Installation was split to the two stages accordingly —- (1) route from the top to the bottom of the telescope side and pass the half of cable to the dome building, and (2) from the bottom to the top in the dome building. See this post for details of installation procedure. In between the two stages we monitored FRD to confirm if the installation of the telescope side is OK, and give feedback if needed.

Subaru staffs are installing the fiber cable on the telescope.

The fiber cable labeled “2” was installed this time. A test cable was attached to check the performance.
The fiber cable are under the test after installation in the clean room.

More than ten people worked on the installation. Performance test was also carried out after installation, and it was confirmed the fiber cable was not twisted or stressed during the installation. FRD is stable against the telescope movement. We are monitoring the FRD performance in longer-term to test the dependency on the temperature.

We appreciate great work of Subaru DayCrews, and great fiber cables made by the fiber team.