Development Of The Lsst Raft Tower Modules

The science focal plane of the Large Synoptic Survey Telescope is made up of 21 modules designated "raft towers". Each raft tower module (RTM) is an autonomous, fully-testable and serviceable 144 Mpixel imager consisting of nine highly-segmented CCDs with complete readout electronics chain. To minimize noise and obscuration the RTM is housed in a compact enclosure fully contained within the camera cryostat. The RTM is required to meet strict performance goals for image plane flatness, readout speed, noise, and power dissipation. Key components include the 4K x 4K fully-depleted CCDs with 16 outputs each, ceramic CCD support structure, and ASIC electronics for video processing and clock/bias generation. In addition to CCD signal handling, the RTM electronics also includes monitoring for temperature, voltage, and current, makeup heater control, ASIC configuration and readback, powerdown modes, and specialized diagnostic outputs. Digitized data are transmitted out of the camera cryostat over a single 3Gb/s serial link.We describe the conceptual design of the CCD array, front and back end electronics, and mechanics, then discuss test system integration and present initial measurements of flatness metrology, optical, electronic, and thermal performance.