Constituents of VIS. Top: The VIS focal plane showing (from left to right) the array of 36 close-butted CCDs within their SiC structure, as integrated on the PLM; a ‘slice’ of six CCDs with a pair of ROEs to control them and digitise the signals; and the integrated focal plane with a protective cover for the CCDs (six power supplies for each ROE can be seen on the left of the structure with the other six out of view behind it). Bottom: From left to right: the CU used for providing a flat illumination of the focal plane at six different wavelengths; the shutter; the Control and Data Processing Unit, which controls the instrument, sequences the 144 channels of data from the 36 CCDs, compresses the image, and communicates with the spacecraft; and the Power and Mechanism Control Unit, which drives the shutter and the CU. All of these have redundant halves except for the multiplexers on the CDPU to the 12 ROEs.