The available Herschel observing time will be allocated in three AO cycles. In each cycle there will be GT and OT, GT is awarded first, followed by OT. The first cycle was the pre-flight Key Programmes (KP) cycle, which was conducted in 2007. The second cycle, which was the first in-flight cycle and designated AO-1, was conducted in 2010. The current cycle is the second and final in-flight cycle, designated AO-2.
The concept of Key Programmes (KPs), is an important element of the Herschel science mission, and was introduced in a dedicated pre-launch AO. The KP concept is a mechanism to ensure that large programmes, requiring a great deal of observing time (in practice in the range 100-900 hours), could be proposed, selected, and executed. These programmes are intended to exploit the unique Herschel capabilities, addressing important scientific issues in a comprehensive manner, generating well characterised data sets of high archival value and the need for follow-up observations.
The three major GT owners, the instrument PIs, were required to spend a minimum of 50% of their GT on Key Programmes, with no specified maximum, while there was no such requirement on the remaining minor GT holders. The outcome of the GT KP process is that in excess of 90% of the total available GT time has been spent in the form of Key Programmes.
Regarding the OT, the HOTAC was free to approve proposals requiring up to a maximum of 40% of the total nominally available OT in the form of Key Programmes and this was actually the amount of time eventually allocated.
In the end by coincidence 21 GT as well as 21 OT Key Programmes were awarded observing time. Altogether in the KP AO cycle approximately 11,000 hours of observing time were allocated.
In the AO-1 cycle, about 550 hours were allocated in GT1, and a further just under 6600 hours in OT1.
The GT1 time is shared between 33 observing programmes, as described in GT1 Programmes web page.
The OT1 time is shared between 241 observing programmes, as described in OT1 Programmes web page. The OT1 time was divided between OT1 priority 1 (OT1p1) time, constituting almost 5000 hours, and the remaining time designated OT1 priority 2 (OT1p2).
In the current AO-2 cycle, about 350 hours have been allocated in GT2, and the remainder of the available observing time will be offered as OT2.
The GT2 time is shared between 32 observing programmes, as described in GT2 Programmes web page.
The OT2 time allocation is addressed in Chapter 5, OT2 Time Allocation.