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The Gravitational-wave Optical Transient Observer (GOTO) is a wide-field telescope project focused on detecting optical counterparts to gravitational-wave sources. The GOTO Telescope Control System (G-TeCS) is a custom robotic control system written to control all aspects of GOTO’s nightly operations completely autonomously. The core of the system are the hardware control daemons, which each operate a class of hardware (dome, mount, cameras etc.). Other daemon programs monitor the on-site weather conditions, listen to incoming transient alerts, and decide which target the system should be observing. These daemons are supervised and monitored by the “pilot” master control program, which supervises observatory observations and also identifies and attempts to fix any issues that arise during the night. Observations are decided by the scheduler, which instructs the pilot what to observe using a “just-in-time” system. We present an update on work carried out on the GOTO Telescope Control System since the initial commissioning of the prototype instrument on La Palma. Efforts have been focused on developing the alert processing and scheduling systems, which allow GOTO to receive and process transient alerts, then schedule and carry out observations all without the need for human involvement. Under normal conditions GOTO will observe an all-sky survey, but when a gravitational-wave or other transient alert is received target pointings are automatically calculated by mapping the localisation region onto the survey grid. The scheduler then determines which target is the highest priority to observe, based on a variety of parameters which are set depending on a pre-defined follow-up strategy for the class of alert. A second GOTO mount is due to be constructed on La Palma in 2020. This mount will operate as an independent instrument with its own pilot, but a single scheduling system for both mounts will determine the optimal target for each. Having two independent mounts will enable more advanced follow-up scheduling opportunities, which the control system will need to determine for each incoming alert. As well a second mount on La Palma, a southern GOTO node with two additional mounts is planned to be constructed in Australia. When complete both sites will be linked to form a single multi-site observatory, requiring more advanced scheduling systems to best optimise survey and follow-up observations. GOTO is operated at the La Palma observing facilities of the University of Warwick on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory and Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth and the Instituto de Astrofisica de Canarias.
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