New observing concepts for ESO survey telescopes

The start of operations of the VISTA survey telescope will not only offer a new facility to the ESO community, but also a new way of observing. Survey observation programs typically observe large areas of the sky and might span several years, corresponding to the execution of hundreds of observations blocks (OBs) in service mode. However, the execution time of an individual survey OB will often be rather short. We expect that up to twelve OBs may be executed per hour, as opposed to about one OB per hour on ESO's Very Large Telescope (VLT). OBs of different programs are competing for observation time and must be executed with adequate priority. For these reasons, the scheduling of survey OBs is required to be almost fully automated. Two new key concepts are introduced to address these challenges: ESO's phase 2 proposal preparation tool P2PP allows PIs of survey programs to express advanced mid-term observing strategies using scheduling containers of OBs (groups, timelinks, concatenations). Telescope operators are provided with effective short-term decision support based on ranking observable OBs. The ranking takes into account both empirical probability distributions of various constraints and the observing strategy described by the scheduling containers. We introduce the three scheduling container types and describe how survey OBs are ranked. We demonstrate how the new concepts are implemented in the preparation and observing tools and give an overview of the end-to-end workflow.