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.

Image Credit: 
LSST/DOE

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).
The National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 to promote the progress of science. NSF supports basic research and people to create knowledge that transforms the future.   




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