RTS2 uses queue to facilitate both human-in-the-loop and autonomous scheduling. Multiple queues can be created in selector, and single queue is available in executor. New targets can be added to the queue with queue or queue_at command. queue_at allows users to specify time constraints - from when to when can be the target scheduled. Each queue has variables describing either what is available in the queue or how will the queue behave. There are _mode and _skip_bellow values. Start and end variables describes specific time constraints.
The queue mode can be changed by changing _mode variable between:
FIFO (for First-In-First-Out) in this mode the first target is removed from the queue, executed and then the next one is selected. Assuming you selected FIFO mode and queue targets with IDs 1003, 1002, 1001 and 1000, then 1003 will be once observed, then 1002, then 1001, and then 1000. 1000 will remain as the last target and will be observed until observatory circumstances (weather, sun position) allow observations.
CIRCULAR in this mode targets are recycled, putting the observed one to the end of queue. So assuming you selected CIRCULAR mode and queue targets with IDs 1002 and 1003, then 1002 will be observed, then 1003, then 1002, then 1003, etc.. untill observatory circumstances allow observations.
HIGHEST in this mode the highest target is selected.
WESTEAST in this mode target are selected from west to east, so the one which set early are observed as the first.
Queue mode describes how the targets will be ordered in the queue, and what will happen if the target is observed.