The VISTA wide field survey telescope will use the ESO Telescope Control System as used on the VLT and NTT. However the sensors for both auto-guiding and active optics are quite different and so the ESO TCS will require some significant modifications. VISTA will use large format CCDs at fixed locations in the focal plane for auto-guiding and a pair of curvature sensors, also fixed in the focal plane, for wave-front sensing. As a consequence, three reference stars are required for each science observation in contrast to the VLT which uses a single star for both auto-guiding and active optics. This paper will outline the reasons for adopting this design, review how it differs from the VLT/NTT and describe the modifications that are being made to the ESO TCS to enable it to be used for VISTA. It will describe the software that implements auto-guiding and active optics in the VLT TCS and how the design has been adapted to the different requirements of VISTA. This will show how the modular and distributed design of the ESO TCS has enabled it to be adapted to a new telescope with radically different design choices whilst maintaining the existing architecture and the bulk of the existing implementation.
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