Choosing a control system for CCAT

The Cornell Caltech Atacama Telescope1 is a 25m aperture sub-millimeter wavelength telescope to be built in northern Chile at an altitude of 5600m. Like any modern telescope, CCAT will require a powerful and comprehensive control system; writing one from scratch is not affordable, so the CCAT TCS must be based, at least in part, on existing software. This paper describes how the search for a suitable system (or systems) was carried out, looks at the criteria used to judge the feasibility of various approaches to developing the new system, and suggests the further studies needed to validate the choices. Although the purpose of the study was to find a control system for a specific telescope with its own particular technical requirements, many of the factors considered, such as maintainability, the ability to adapt to new requirements in the future and so on, are of concern to all telescopes. Consequently, the processes used to select the system for CCAT are relevant to other projects faced with the same decision, even if the conclusions turn out to be different.