The amount of available OT2p1 time is the amount of time between when we expect the currently available observations to have been executed and the nominal lifetime, minus a 'scheduling allowance' estimated to be about 2 months. In the amount of currently available observations all observations except the OT1p2 observations will be taken into account (see also Section 5.5, “OT1p2 programmes”).
The current best estimate as to when all existing Herschel observations (thus not counting OT1p2 observations) will be executed is end of June 2012. In order to put numbers in for illustration end of February 2013 will be used as the assumed end of mission, plus the fact that Herschel executes approximately 550 hours of HOTAC-approved science observations per month. (It should be noted that the actual mission lifetime could be both shorter and longer.)
It should also be remembered that as stated earlier it is required to 'over-allocate' by no less than 6 months beyond the end of the mission, and here the uncertainty in the predicted mission lifetime needs to be taken into account.
With the above assumptions the amount of OT2p1 observing time available for allocation becomes:
Science operations from end June 2012 to end February 2013, this is 8 months.
The 'scheduling allowance' of 2 months (to make (near) completion viable) needs to be deducted, thus 6 months remaining.
Since 550 hours can be allocated per month, a total of 3300 hours can thus be offered as OT2p1 observing time.
It should be noted that the amount of OT2p1 time, 3300 hours on the assumption of end of life by the end of February 2013, increases or decreases by 550 hours for every month of longer or shorter lifetime.
As opposed to the OT2p1 observing time, the amount of OT2p2 observing time is independent of mission lifetime. However, it is affected by the magnitude of the mission lifetime uncertainty.
With the above assumptions the amount of OT2p2 observing time available for allocation becomes:
The 'over-allocation' of no less than 6 months beyond the predicted mission lifetime need to be covered. Allocate 6-7 months.
The uncertainty in the predicted mission liftime needs to be covered (need 6 months of 'over-allocation' also in the case of the mission turning out to be longer than nominal). Allocate 1-2 months, cumulative 8 months.
The 'scheduling allowance' of 2 months (to make (near) completion viable) not allocated to OT2p1 needs to be added. Allocate 2 months, cumulative 10 months.
Almost 3 months of OT1p2 time has already been allocated, this needs to be subtracted. Thus a negative allocation of 3 months, cumulative 7 months.
Since 550 hours can be allocated per month, a total of 3850 hours can, and must, thus be offered as OT2p2 observing time. The already allocated OT1p2 observing time thus remains as part of the required 'over-allocation'.
As described in the above two subsections, with an assumed mission lifetime by the end of February 2013, with an uncertainty of plus/minus 1-2 months, the following amounts of observing time will be available for allocation by the HOTAC in the OT2 call:
3300 hours of OT2p1 time (increases or decreases by 550 hours for every month of longer or shorter lifetime), plus
3850 hours of OT2p2 time (independent of lifetime),
Although there is no maximum or minimum on the amount of observing time than can be proposed for, it is clear that the scientific motivation for an observing programme needing a large amount of observing time has to be correspondingly high and well justified.
Since more than half of the total nominally available observing time for Herschel has already been allocated to large programmes in the form of GT and OT KPs and OT1 LPs, this requirement is strongly emphasized in the current AO.