Following the ComCam On-sky Campaign that ended in mid-December (see the weekly Community posts between October and December 2024 for the details), the Rubin Observatory Team successfully executed the multi-month coordinated activity of removing ComCam from the Simonyi Telescope, installing the LSSTCam, and connecting it to all Rubin Observatory systems. Now, the engineering test phase of the Rubin Observatory with LSSTCam, the largest Camera ever built for astrophysics, has started!
On Tuesday 15 April 2025, the first on-sky engineering data taking began, with the i-band filter in the beam. Thanks to the successful ComCam on-sky campaign, the telescope optical alignments were remarkably close to optimal before even looking at the sky. In just a handful of on-sky iterations the system delivered, across the focal plane, a median image quality of about 1.8 arcsec FWHM, before any detailed tuning with the active optics system (AOS). The Data Management system successfully transported and processed the 3-gigapixel images at the US Data Facility within about a minute of acquisition.
The distributed Rubin Team was jubilant, taking a few moments to celebrate the first few data acquisitions, and then quickly got back to work. Already on the second night, sub-arcsecond FWHM image quality across most of the focal plane was achieved.
We have many months of effort and challenges ahead, but the experience during the first night of LSSTCam on-sky engineering data taking bodes well. Along with the great initial performance of the full Observatory optical system, the LSSTCam, its supporting refrigeration equipment, and the data acquisition and control systems all demonstrated smooth operation, just a few weeks after installation. For the first night of engineering data taking, 183 out of the 189 science CCDs were in operation, with the other 6 powered off in an abundance of caution due to technical issues. This has no substantial impact on commissioning activities, and work is proceeding in parallel to bring those sensors back online. The AOS tuning can now proceed with the added benefit of the wavefront sensors in LSSTCam, which was not possible with ComCam. The highest-priority nearterm activity is to commission the whole system so that it runs automatically and reliably.
As we did during the ComCam campaign, we plan to post these updates approximately weekly until further notice.