The LSST Corporation (LSSTC) and its member institutions celebrated the completion of the LSST M1M3 telescope mirror on January 10, 2015 in Tucson, Arizona. The 8-meter monolithic primary/tertiary mirror (M1M3) was constructed and spun cast into a single piece of glass in 2008; in the more than 6 years since, the University of Arizona’s Steward Observatory Mirror Lab (SOML) meticulously polished the two separate figures. The M1M3 mirror is at the heart of the LSST telescope and the celebration marked a huge step toward making LSST a reality.

On March 5, 2015, representatives from the Institut National de Physique Nucléaire et de Physique des Particules (IN2P3), of the Centre National de la Recherche Scientifique (CNRS), a French public scientific and technological institution, the Large Synoptic Survey Telescope Corporation (LSSTC), SLAC National Accelerator Laboratory, The LSST Project Office (LSSTPO), and The National Center for

The LSST project has achieved another significant milestone. The baseline for fabrication of the 3,200 megapixel digital camera has received key “Critical Decision 2” approval from the DOE. The LSST team can now move forward with the development of the camera and prepare for the “Critical Decision 3” review process this summer, the last requirement before actual fabrication of the camera can begin.

LSST Summit Facility general contractor, Besalco, has officially taken possession of the Cerro Pachon site in order to begin the construction effort. Going forward, the LSST site now is an active construction site with all of the consequent safety rules and restrictions in effect. In particular, access to the site by project personnel now must be pre-approved by Besalco. Besalco began work in January 2015, mobilizing personnel and equipment and establishing offices and a warehouse on the summit. They are working with their subcontractor Rocterra to remove the final 20,000 cubic meters of material. Excavation for the telescope pier foundation and construction of the road to the telescope main platform are nearing completion. The platform for the calibration telescope is complete.

Testing of a subscale LSST Camera refrigeration system at SLAC has demonstrated the ability to run reliably for extended periods at consistent, acceptable temperature and power use. During study periods of typically 10 days, the system has run reliably at approximately -128 degrees Celsius with a total load of about 87.5 Watts. The subscale test began in June 2014 in order to simulate more realistic camera geometry and operations.

After beginning the tests using a non-flammable refrigeration mixture designated LSST29-19C, the team later returned to using the original mix, LSST-3N, whose higher hydrocarbon content aids in the transport of oil through the system. This provided more robust performance and improved temperature stability and overall reliability. During the week of December 8, the team tested the feedback control system, used to stabilize the cryoplate temperature. With the feedback control system turned on, cryoplate temperature stabilized at -125C to better than plus/minus 0.1 degrees Celsius, with a total load about 97.5 Watts.

The lsst.org Gallery now has a page dedicated to images from a recently reactivated webcam with a view of the LSST site on the Cerro Pachon summit. The images provide a window onto the summit facilities’ construction progress. The web page image refreshes every minute; also available are time lapse animations - one with a series of images captured at hourly intervals and one with each image captured at the one-minute interval.

In early February, a team working on the LSST Camera project at Brookhaven National Laboratory (BNL) demonstrated the first successful operation of a test camera using a “vertical slice” of the final camera sensors and electronics. The test assembly contained prototype CCDs and one 48-channel raft electronic board, all housed in a developmental model of the Commissioning Camera cryostat. The raft sensor assembly was set at -100C, and the electronics sink was set at -10C. Using a variety of optical and electronic stimuli, the team found all 48 channels reading out and meeting critical performance specifications for noise, crosstalk and linearity.