Rubin Observatory secondary mirror installed

The Vera C. Rubin Observatory's 3.5-meter secondary mirror has been successfully installed on the Simonyi Survey Telescope at Cerro Pachón in Chile. This significant milestone marks the integration of the first permanent component of the telescope's cutting-edge, wide-field optical system, contributing to advancing our understanding of the Universe.

NSF–DOE Rubin Observatory secondary mirror installed

The NSF–DOE Vera C. Rubin Observatory team in Chile achieved this milestone by installing the 3.5-meter glass secondary mirror assembly on the Simonyi Survey Telescope. This accomplishment is part of a larger optical system, which includes an 8.4-meter primary/tertiary mirror and the world's largest digital camera, the LSST Camera. Funded by the U.S. National Science Foundation and the U.S. Department of Energy's Office of Science, the Rubin Observatory is set to begin the 10-year Legacy Survey of Space and Time (LSST) in 2025, ushering in a new era in astronomy and astrophysics.

The installation of the complete mirror assembly is the result of years of meticulous planning and hard work by teams in the U.S. and Chile. Following fabrication and polishing, the glass blank and mirror cell assembly components were shipped to Chile in 2018 and stored at the observatory. In 2019, the secondary mirror was coated with protected silver and integrated with the mirror cell in early July 2024 before being installed on the telescope.

“Working with the mirror again after five years is extremely exciting because it really feels like we’re in the home stretch,” said Sandrine Thomas, Deputy Director for Rubin Observatory Construction. “Now we have glass on the telescope, which brings us a thrilling step closer to revolutionary science with Rubin.”

Rubin's secondary mirror, at just under four meters in diameter, is one of the largest convex mirrors ever made. The 10-centimeter-thick monolithic mirror blank was manufactured by Corning Advanced Optics in Canton, New York, using Corning® ULE® Glass (Ultra-Low Expansion Glass).

“Corning is proud of our nearly 20-year collaboration with the Rubin Observatory team,” said Claude Echahamian, VP & GM Corning Advanced Optics. “As a result, Corning’s cutting-edge ULE mirror blank for the Simonyi Survey Telescope will help to enable crystal clear views of deep space, revealing millions of previously unknown Solar System objects with more detail than ever before.”

Preparing the secondary mirror for installation

The 3.5-meter glass mirror has been lifted onto Rubin Observatory’s Simonyi Survey Telescope

After delivery in 2009, the mirror blank was stored at Harvard University before being polished and finished at L3Harris Technologies in Rochester, New York. L3Harris employed novel measurement techniques to polish the large precision convex surface and designed and built the secondary mirror cell assembly. This assembly includes a stiff steel mounting plate, 72 axial and six tangent actuators to support and control the mirror's shape, the mirror cell electronics and sensors, a thermal control system, and the mirror control system.

“Our 55-year legacy of designing and constructing high-end optical systems for space and ground continues with the world’s largest active secondary mirror system built for Rubin Observatory,” said Charles Clarkson, Vice President and General Manager, Imaging Systems, Space and Airborne Systems, L3Harris. “With this milestone, we are closer to pushing scientific frontiers and charting the Universe like never before, and we look forward to the science that will be discovered.”

To install the mirror assembly onto the telescope mount, the Rubin summit team used a specialized cart to rotate the mirror assembly to a vertical position. They then lifted the assembly onto the telescope mount while maintaining active system control to prevent stress on the glass. After securing the secondary mirror assembly, the team connected the mirror cell to the electronics cabinet on the telescope mount and reactivated the mirror’s software control system.

In the coming weeks, the Rubin team will reinstall the Commissioning Camera, a smaller version of the LSST Camera, to conduct various test campaigns on the optical system. The team will also prepare the primary mirror assembly for telescope integration in August and the LSST Camera for installation later this year.

The Rubin Observatory is a program of NSF NOIRLab and will be jointly operated by DOE’s SLAC National Accelerator Laboratory.

Preparing the secondary mirror for installation - 2 

Rubin Observatory's secondary mirror is installed onto the telescope