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The ARC 3.5m observatory is being designed to permit rapid switching among seven standard instruments and to encourage routine use by remote observers. Remote operation of the telescope and instruments will be required over short distances on-site as well as by astronomers at their home institutions, since the control room and laboratory facilities will be located in a separate building to minimize thermal effects on seeing within the telescope enclosure. In this paper, we discuss our design goals, the proposed architecture for the system, and our progress in development of software to implement the user/telescope and user/instrument interface. Prototype software already in operation includes a multi-window, event-driven, graphically-oriented environment implemented on a Macintosh computer for operation of 32-channel photometer and spectrometer systems. Communications between the Macintosh and a Multibus based instrument control computer occur over a single serial link which can include telephone lines. Controls are implemented graphically via pull-down menus and "control panels" which can be easily tailored to accommodate requirements of different instruments. Status information and data are returned from the instrument control computer and displayed continuously in real time. Among the data display "windows" are multichannel (1-32 channel) strip chart displays and integrated spectra which include statistical errors of individual data points. The software is written in an object-oriented language based on FORTH. Using this approach, a very sophisticated, reliable user interface can be implemented by a single programmer in a short time (several weeks). A similar con-trol environment which will include both telescope and instruments will be implemented via communications between a Macintosh or similar "smart terminal" and a single observatory computer which communicates with additional telescope and instrument control computers.
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