The Legacy Survey of Space and Time (LSST) is a planned 10-year survey of the southern sky that will take place at the Vera C. Rubin Observatory, currently under construction on the El Penon peak of Cerro Pachon in northern Chile. The survey data will enable researchers around the world to better evaluate a wide range of pressing questions about the attributes of dark energy and dark matter, the formation of the Milky Way, the properties of small bodies in the solar system, the trajectories of potentially hazardous asteroids and the possible existence of undiscovered explosive phenomena.
The telescope at the Rubin Observatory is the Simonyi Survey Telescope (SST) a large-aperture, wide-field, ground-based telescope that will survey half the sky every three nights in six optical bands ranging from 320 to 1050 nm. Its three large mirrors will be actively controlled to minimize distortions. The telescope mount will be a compact, still structure especially designed to reduce image motion.
Mounted on the SST will be DOE’s LSST Camera, which uses three refractive lenses to illuminate a 9.6-square degree field of view, and will be the largest digital camera ever constructed. Once operational, the camera will take a pair of 15-second exposures of each field, scanning the sky throughout the entire night.
Simulations demonstrate that the telescope and camera can deliver a uniform and deep (24.5 magnitude in r-band for one 15s exposure) 18,000 square degree survey and will produce over 5.2 million exposures in ten years. This "movie," which is sensitive to redshifts of up to z=3, will open an entirely new window on the Universe: the time domain. The Rubin Observatory will produce, on average, 15 terabytes of LSST data per night, yielding an uncompressed data set of 200 petabytes. Dedicated facilities will process the image data in near real time.
KIPAC members have leading roles in project areas, including the observatory, the camera, the LSST Dark Energy Science Collaboration (DESC), and the US Data Facility, and are also working on science preparation for a broad range of topics. SLAC is the lead lab for the LSST Camera construction and commissioning, the host lab for DESC, and one of two partners (along with NSF's NOIRLab) in the operations of Rubin Observatory, including managing and hosting the Rubin US Data Facility.
The construction of the LSST Camera has been led by KIPAC / SLAC members since its inception by KIPAC Professor Steve Kahn, and Steve has been Director of the Vera C. Rubin Observatory construction project since 2013 (when LSST stood for Large Synoptic Survey Telescope). Other KIPAC members have taken leading roles in instrument design, construction, and commissioning, and operations: Phil Marshall is Deputy Director of Rubin Operations, Richard Dubois is Rubin Operations US Data Facility Lead, and Kevin Reil is Rubin Commissioning Scientist. Rubin Observatory is much more than a dome on a mountain top: it is an end-to-end scientific data generation system, a factory for producing science-ready data products from the biggest astronomical sky survey ever undertaken.
The LSST Camera
The LSST Camera is currently under construction at SLAC National Accelerator Laboratory working with a broad multi-institutional collaboration. KIPAC professor Aaron Roodman is leading the camera's Test and Integration. The camera’s 3.2-gigapixel focal plane array comprises 189 4Kx4K CCD sensors with 10 µm pixels. The sensors are deep depletion, back-illuminated devices with a highly segmented architecture that enables the entire array to be read out in two seconds. The detectors are grouped into 3 x 3 arrays called "rafts." The rafts are identical, with each containing its own dedicated front- and back-end electronics boards which fit within the footprint of its sensors, thus serving as a 144-megapixel camera on its own. The rafts and associated electronics are mounted on a silicon carbide grid inside a cryostat vacuum, with an intricate thermal system that maintains the CCDs at an operating temperature of -100 ºC. The focal plane also contains four sets of guide sensors and wavefront sensors.
The Rubin US Data Facility
Image data from Rubin Observatory's Summit Facility will be transmitted to the Rubin US Data Facility at SLAC for near real-time processing, to generate millions of alerts per night, for filtering and analysis by scientists across the world. Each year, the survey images taken to date will be reprocessed, combined and automatically measured to yield an increasingly deep picture of the whole Southern sky, and a growing catalog of astronomical objects that captures how each one has changed over time. This annual data release processing will be run at three data facilities, in France, the UK, and at SLAC, with the final dataset assembled at SLAC and served to astronomers and physicists via the Rubin Science Platform. SLAC staff are involved in all aspects of this process, making KIPAC one of the best places in the world to do LSST science.
The LSST Dark Energy Science Collaboration (DESC)
Eight scientific collaborations are already preparing to take advantage of the publicly available LSST data. KIPAC members are deeply involved in the LSST Dark Energy Science Collaboration (DESC), which seeks to characterize dark energy, the enigmatic force thought to be responsible for accelerating the expansion of the Universe. DESC will use five different cosmological probes on LSST data, including weak and strong gravitational lensing, galaxy clustering, supernovae, and large-scale structure, to create a more accurate picture of the expansion history of the Universe. Such a picture could help cosmologists constrain the behavior of dark energy and determine which models can explain it. As host lab, SLAC is home to the DESC Operations team of scientists and computing professionals leading the development, operation and maintenance of the collaboration's cosmology analysis and simulation software pipelines. Seth Digel is the DESC Operations Manager, while Jim Chiang and Pat Burchat are the Computing and Technical Coordinators overseeing the preparations for DESC's LSST-scale analysis computations and forging the needed connections between the collaboration and the observatory as it enters commissioning prior to survey operations. KIPAC students, postdocs, staff and faculty are active and enthusiastic members of DESC, working together with hundreds of colleagues around the world to make LSST dark energy science happen. Many KIPAC members are also thinking about the breadth of science opportunities that the Rubin Observatory will enable, from exoplanet science to optical counterparts of gravitational waves and identification of a wide variety of transient objects.