OT2 observing time will be allocated by the HOTAC in two different categories: priority 1 and priority 2, designated OT2p1 and OT2p2, respectively. The difference between the two can be described as follows:
OT2p1: These are observing programmes that under nominal conditions are expected to be executed fully, or close to fully.
This thus means that the OT2p1 observing programmes can be of a large variety with limited constraints, including programmes needing (near) completion of their observations in order to be viable scientifically.
OT2p2: These are observing programmes that will be used to ensure efficient scheduling. This means that on average the completion percentage will be low, but can be expected to be strongly varying between programmes depending on a large number of unpredictable parameters.
This thus means that the OT2p2 observing programmes will be much more constrained:
In particular they need to be very robust with respect to partial completion. In effect the observations individually need to be viable scientifically.
They must not be fixed-time observations, or have a dependency on the time of execution of another observation.
They must not be observations to be 'triggered' by an event of some sort, e.g. they cannot be 'ToO-like' observations.
Although it was failed to be communicated in the 'Policies and Procedures' document at the time, a similar scheme was also used in OT1 where observing time was awarded by the HOTAC as priority 1 and priority 2, designated OT1p1 and OT1p2, respectively.