The third fiber cable was installed on Subaru Telescope

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Time flies: it has been a few months since the last article. In the last a few months, the integration of the PFS Spectrograph Modules (SMs) and cameras has been proceeding at LAM and JHU. At Subaru Telescope, the second SM (SM3) experienced the first light in the engineering run in November 2022 just after shipping. However, the two successive engineering runs were cancelled due to the bad weather. Meanwhile, ASIAA visited Subaru Telescope and modified Prime Focus Instrument and Metrology Camera.

We have various stories as above, and among them one of the big stories is the installation of the third fiber cable unit on the telescope.

The optical fiber cable of the PFS instrument is about 60 m long in total. The fiber cable consists of three sections to deal with instrument exchange and to enable the development of the systems more efficiently. The main and the longest cable is about 55 m long, and delivers the light from celestial objects caught on the prime focal plane of the Subaru telescope to the Spectrograph Modules on the 4th floor in the dome building.

PFS developed 4 fiber cable units, among which the first and the second cables were installed on the telescope in 2021 and 2022, respectively.

The third cable was installed in February 2023.

Since the fiber cable is 55 m long, it is quite tough to unpack it from the shipping crate and to route on the floor. Several staffs started installation work with removing the cable coiled up on the drum in the crate, laying down on the floor as loosely as possible, and testing the performance before installation.

Winter bad weather prevented us from starting installation on the originally scheduled day, but thanks to great efforts of DayCrews and PFS team, installation was completed in two-day period.

We have been monitoring the performance by measuring the value called “FRD” () to see whether the fiber cables has got stressed during installation.

※ FRD: Focal Ratio Degradation.
FRD is a phenomenon where output light gets enlarged compared to input light when the fiber gets stressed. If FRD gets worse and/or changes while telescope is moving, observed spectra will be affected.