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 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 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 camera, DES, and US data facility.
The construction of the observatory has been led since its inception (when it was known as the Large Synoptic Survey Telescope) by KIPAC Professor Steven Kahn. Other KIPAC members have taken leading roles in instrument design, construction, and commissioning, and operations.
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 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 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.