2nd On-Telescope Test of Metrology Camera System


Last year Metrology Camera System (MCS) was shipped to Subaru Telescope of National Astronomical Observatory of Japan, in Hawaii. After onsite integration and test, we installed MCS to the telescope and carried out optical alignment and on-telescope performance tests in June and October 2018. (See this for details)

Metrology Camera System at the Cassegrain focus of the Subaru Telescope

 MCS is installed to the Cassegrain focus at the bottom of the telescope and takes images of the fibers on Prime Focus Instrument (PFI) at the top of the telescope for measurements of the fiber positions. The performance test last year showed that the image shape changed when we moved the telescope, which prevented us from calculating the image centroids accurately and stably. We discussed this problem within the team and concluded that the MCS mirror support structure should be upgraded. Besides, we decided to improve the software for robust centroid calculations even if image shape changes.

 After we manufactured all the required parts and completed the software improvement, we installed MCS to the telescope again, replaced the primary support structure, and carried out the on-telescope performance test in August 2019. This time, the image was found to be stable against the change of telescope attitude, and the upgraded software always succeeded in spot detection and centroid calculation.  

Apart from the upgrades explained above, we had another goal at this on-telescope test: Demonstrating that the software modules work as expected for fiber configuration process. MCS and PFI cooperate (from both hardware and software points of view) to calculate how far the current fibers potions are from their targets, and drive the actuators to move fibers accordingly. Since we don’t have PFI yet at the telescope, we couldn’t move fibers, but we successfully ran the software modules and confirmed the command sequence and data flow up to one step before that. From now on the team at ASIAA will focus on the integration and test of PFI by using the software modules validated during this test so that, after PFI is delivered to the Subaru Telescope, we can test PFI and MCS on the telescope smoothly.

One scene in the control room during the on-telescope test: Checking the images from MCS.

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