Overall Description

The LSST camera is a wide-field optical (0.4-1 ^m) imager designed to provide a 3.5° FOV with better than 0.2 arcsecond sampling ([1], see Fig. 1). The image surface is flat with a diameter of approximately 64 cm. The detector format will comprise a mosaic of 16 Mpixel silicon detectors providing a total of approximately 3.2 Gpixels. The camera includes a filter changing mechanism and shutter. It is positioned in the middle of the telescope where cross-section area is constrained by optical vignetting and heat dissipation must be controlled to limit thermal gradients in the optical beam. The camera must produce data of extremely high quality with minimal downtime and maintenance.

Figure 1. The LSST optical design.

The focal plane array operates at a temperature of approximately -100°C to achieve the desired detector performance. The focal plane array is contained within an evacuated cryostat, which incorporates detector frontend electronics and thermal control. The lens L3 serves as an entrance window and vacuum seal for the cryostat. Similarly, the lens L1 serves as an entrance window and gas seal for the camera housing, which is filled with a suitable gas to provide the operating environment for the shutter and filter change mechanisms. The filter carousel can accommodate 5 filters for rapid exchange without external intervention.

The camera mechanical mount (see Fig. 2) provides proper support and registration to the telescope and incorporates provisions for adjusting camera position and orientation to compensate for alignment variations with telescope elevation. In addition, the camera axial position must be adjusted to optimize focus at different filter wavelengths (the axial position of L2 is similarly adjusted). Additional camera interfaces include electrical power, thermal cooling, and fiber optic connections for control and data interfaces. The following sections describe these features in detail and discuss the considerations leading to the current design conclusions.

Figure 2. LSST camera.

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