Subaru Telescope, where PFS will be installed, has been used for cutting-edge researches in astronomy and astrophysics since 1999 when it started its science operation. Because we will install a brand-new, state-of-the-art instrument on the more than 15-years old telescope, we sometimes run into difficulties due to “generation gap”.
Today we will talk about network connection, one of many such stories.
PFS consists of several subsystems, namely Prime Focus Instrument for collecting light from galaxies and stars and allocating fibers to them, Metrology Camera for checking the fiber position, Spectrographs for getting spectra of astronomical objects, and Fiber Cables delivering the light from PFI to Spectrographs, and each of these subsystems has a number of subcomponents. The control modules of these subsystems are located at various places: Some are on the telescope, others are in the control building, and so on, and they communicate with each other through fiber-optic communications.
The communication fiber cables on Subaru telescope have been working since the telescope was still under construction, namely when various communication devices that are very common now such as 1 Gbps optic fiber network, PCI Express, USB3.0, … did not even exist. On the other hand, we should use modern communication devices, considering the requirement to the communication speed between the PFS subsystems and the maintainability during the PFS operation over the next 10 years. Here we have a concern ― There is no guarantee that such modern devices will work with the old communication fibers immediately in a plug-and-play manner … So it should be better to try and test them.
In late January, we carried out communication tests at Subaru using real devices that have been planned to be used actually for PFS. By checking whether they show a transfer rate as similar to the maximum specified in specifications, we can confirm in advance that the devices function as expected, and can minimize any risks of troubles during integration and tests of subsystems after being delivered to Subaru.
During this test, we found one of the devices didn’t work correctly. We will find the root cause of this based on the test data, find an alternative device, and re-do the same test.
This way, we are developing the PFS instrument not only building hardware but also designing and testing the control systems so that it will work as expected in the real environment.