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Remote observing from the bottom up: the architecture of the WIYN telescope control system

Remote observing has many definitions, ranging from unattended batch-mode use through simple remote logins to fully faithful off-site observing centers indistinguishable from the on- site telescope control room. There are problems with each of these ideas: batch mode operation, for example, precludes remote interactive target acquisition and remote access to targets of opportunity. Simple remote login suffers from network problems such as full-duplex character latency; shipping screens instead of the underlying data can cause bandwidth problems and interferes with analyzing or archiving data. Brute-force reproduction of the control room requires expensive fiber or satellite connections. The WIYN Telescope control system was designed to be inexpensive to build and inexpensive to maintain. We emphasized the use of standard tools, portable implementations, and network friendliness. These techniques and features are precisely those that underlie a powerful remote observing capability. The WIYN Telescope control system therefore supports remote observing from the very lowest levels, and does so effectively and inexpensively using a carefully planned architecture, standard software and network tools, and innovative methods to ship large digital images over low bandwidth connections such as phone lines. Even before the construction was complete, these techniques proved their value by allowing remote access for the purposes of eavesdropping, troubleshooting, and servo tuning. This paper presents a block diagram and detailed descriptions of the WIYN Telescope control system architecture. Each aspect of the control system is discussed with respect to its contribution to the overall goal of remote observing, including multi-user access, bandwidth conservation, interoperability, and portability.