The Integration and Verification Testing of the Large Synoptic Survey Telescope (LSST) Camera is described. The LSST Camera will be the largest astronomical camera ever constructed, featuring a 3.2 giga-pixel focal plane mosaic of 189 CCDs with in-vacuum controllers and readout, dedicated guider and wavefront CCDs, a three element corrector with a 1.6-meter diameter initial optic, six optical filters covering wavelengths from 320 to 1000 nm with a novel filter exchange mechanism, and camera-control and data acquisition capable of digitizing each image in two seconds. In this paper, we describe the integration processes under way to assemble the Camera and the associated verification testing program. The Camera assembly proceeds along two parallel paths: one for the focal plane and cryostat and the other for the Camera structure itself. A range of verification tests will be performed interspersed with assembly to verify design requirements with a test-as-you-build methodology. Ultimately, the cryostat will be installed into the Camera structure as the two assembly paths merge, and a suite of final Camera system tests performed. The LSST Camera is scheduled for completion and delivery to the LSST observatory in 2020.
The science focal plane of the LSST camera is made up of 21 fully autonomous 144 Mpixel imager units designated raft tower modules (RTM). These imagers incorporate nine 4K x 4K fully-depleted CCDs and 144 channels of readout electronics, including a dedicated CMOS video processing ASIC and components that provide CCD biasing and clocking, video digitization, thermal stabilization, and a high degree of monitoring and telemetry. The RTM achieves its performance goals for readout speed, read noise, linearity, and crosstalk with a power budget of less than 400mW/channel. Series production is underway on the first units and the production will run until 2018. We present the RTM final design, tests of the integrated signal chain, and performance results for the fully-integrated module with pre-production CCDs.
We present two lines of ASICs dedicated to the control and readout of CCD sensors. The CABAC (Clocks And Biases ASIC for CCDs) provides all required bias voltages and clocks. The ASPIC (Analog Signal Processing Integrated Circuit) processes 8 CCD output channels: amplification, Correlated Double Sampling, conversion to differential signal. Both chips are highly configurable in order to fulfill a wide range of astronomical CCD readout needs, from fast readout of wide-field imaging arrays to slower speeds and higher gains for spectroscopy. Their sizes and temperature ranges allow to integrate them in-cryostat, close to the sensors, and they offer diagnostic capabilities to assist the integration. In addition to extensive stand-alone tests, these chips are integrated in the LSST REB (Raft Electronics Board), and have been tested driving the E2V prototype CCD for the LSST focal plane.
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 × 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 present the first results of the SuperNova Direct Illumination Calibration Experiment (SNDICE), installed
in January 2008 at the Canada France Hawaii Telescope. SNDICE is designed for the absolute calibration of
the instrumental response of a telescope in general, and for the control of systematic errors in the SuperNova
Legacy Survey (SNLS) on Megacam in particular. Since photometric calibration will a critical ingredient for
the cosmological results of future experiments involving instruments with large focal planes (like SNAP, LSST
and DUNE), SNDICE functions also as a real-size demonstrator for such a system of instrumental calibration.
SNDICE includes a calibrated source of 24 LEDs, chosen for their stability, spectral coverage, and their power,
sufficient for a flux of at least 100 electron/s/pixel on the camera. It includes also Cooled Large Area Photodiode
modules (CLAPs), which give a redundant measurement of the flux near the camera focal plane. Before installing
SNDICE on CFHT, we completed a full calibration of both subsystems, including a spectral relative calibration
and a 3D mapping of the beam emitted by each LED. At CFHT, SNDICE can be operated both to obtain a
complete one-shot absolute calibration of telescope transmission in all wavelengths for all filters with several
incident angles, and to monitor variations on different time scales.