Opening a Window of Discovery on the Dynamic Universe

Detector Design - Rafts and Towers

To create the LSST camera's focal plane array, 21 rafts, each comprising 9 CCDs, are mounted on towers containing the necessary electronics, and the towers are assembled into one unit.

The charge-coupled device (CCD) sensors that makes up the LSST camera's focal plane are mounted on 21 platforms called rafts, with each raft comprising a 3x3 square of sensors, for a total of 189 CCDs. Each CCD is built up of 4096 horizontal and 4097 vertical (4K x 4K) imaging elements, and has 16 outputs, adding up to a total of 144 channels per raft and 3024 channels across the entire focal plane array.

Each identical raft is mounted on a tower, which also holds the front-end electronics for data readout mounted in the shadow of the 3x3 sensor array to minimize gaps between sensors. High-density, flexible cables in each tower carry data from the sensors to the back-end electronics responsible for collecting the data, converting it to a digital format, and transmitting it to the data acquisition hardware and software. Cooling straps connect the sensors to cooling planes that keep the raft at about -100°C to help prevent noise in the sensors.

Each raft is an autonomous object and can function as a complete camera, individually controlled via the Observatory Control System. Rafts can also be grouped. Each raft is connected to a single timing and control module, while all rafts are synchronized across the focal plane array. Each CCD can capture eight megapixels of data per second, for a total of 3.2 gigapixels every two seconds.

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Financial support for LSST comes from the National Science Foundation (NSF) through Cooperative Agreement No. 1258333, the Department of Energy (DOE) Office of Science under Contract No. DE-AC02-76SF00515, and private funding raised by the LSST Corporation. The NSF-funded LSST Project Office for construction was established as an operating center under management of the Association of Universities for Research in Astronomy (AURA).  The DOE-funded effort to build the LSST camera is managed by the SLAC National Accelerator Laboratory (SLAC). 

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