Herschel observing will be conducted autonomously without real-time interaction. This means that observers are not expected to be present at the HSC while their observations are carried out.

All observations have to be specified in full detail by the proposers using HSpot well in advance to the time when the observations will actually be executed. For a variety of reasons including efficiency, sky coverage and instrument operation constraints, Herschel mission planning will distribute the available observing time among accepted proposals on a 'per observation' (AOR) basis. This is the way other space-based facilities like the Spitzer Space Telescope and the Hubble Space Telescope operate, and it was also the case of Herschel's precursor, the Infrared Space Observatory (ISO).

Similarly, it must be emphasised here that - for operational reasons - no guarantees can be given that any particular observation (AOR in the case of Herschel) within an accepted proposal will, in fact, be executed, although every attempt will be made to achieve this objective. Note that no grades are assigned to individual AORs accepted for execution. This means that the final scheduling sequence will be based solely on maximising the telescope observing efficiency.

In addition to the top priority of producing efficient schedules, observations belonging to an earlier AO have also a higher priority over observations from a later AO (except in the case of fixed time observations and of priority 2 observations, see below). This is true also within an AO, the GT observations have priority over OT observations in the same AO (but not over OT from an earlier AO). Thus, as examples, the KPs have priority over GT1/OT1, GT1 over OT1, and OT1p1 has priority over GT2 as well as over the (yet to come) OT2p1 proposals, while the already approved OT1p2 proposals and the new OT2p2 proposals that will be approved in this AO will have the lowest priority, and as such, they will be considered only as schedule fillers at any moment.

Slew times between observations are charged over all AORs as a flat 3 minutes overhead. This overhead time is automatically applied to all non-time constrained observations entered through HSpot.

However, time constrained observations can also be defined using HSpot. These are:

Time constrained AORs reduce the flexibility of scheduling and the overall observing efficiency. For this reason they are further penalised, in terms of overhead charges, with a 10 minutes slew overhead in HSpot, instead of the 3 minutes applicable to non-constrained AORs. Programmes with heavily constrained AORs will need to be accompanied by a compelling justification.

Concatenated observations are charged 3 minutes overhead per AOR, unless observing the same target (no slew, see also below), then only 3 minutes overhead for the entire chain is charged.

If a concatenated chain is time constrained, then the overhead charge is 10 minutes for the first AOR, and 3 minutes for each following AOR, unless observing the same target, then only 10 minutes for the entire chain is charged.

Concatenation between 2 AORs is permitted:

In order to preserve the overall science efficiency of the observatory, duplicate observations will in general not be permitted. Checks for potential duplications (see the Herschel Duplication Policies document) between your planned observations and already approved AORs contained in the so-called 'Reserved Observation List' will be made by the HSC during the technical review of submitted proposals.

The 'Reserved Observation List', available in the HSC web page, contains all observations of the GT and OT Key Programmes and of the GT1, OT1, and GT2 proposals previously approved by the HOTAC that cannot be duplicated by any OT2 programme (except for OT1p2 observations, see Section 5.5, “OT1p2 programmes”). The list can be inspected by OT2 proposers using the Herschel Reserved Observations Search Tool (HROST).

HROST enables you to search all the AORs included in the current Reserved Observations List in a simple fashion through a java-based web interface (requires Java 1.6 or higher). Once you start the application you can make queries by entering a position in the sky and a search radius as input and the tool will return as output a summary description of all AORs in the database overlapping your search area. Potential duplications found using this tool can be further investigated in detail using HSpot. You can access and download those AORs of your interest by using the option 'View accepted proposals' under the 'File' menu in HSpot.

Additionally, for the OT2 call the Herschel Duplication Checker (HDC) is provided. It is a standalone web-based tool that identifies all AORs in your proposal that potentially duplicate other approved science observations which are part of the ROL.

The HOTAC will be informed of the existing duplications in each round of submissions. Duplicating AORs found in the newly submitted proposals will be removed if the duplication is with observations already approved in previous calls as they always take priority (with the exception of OT1p2 observations, see Section 5.5). In the case of duplications among the newly submitted proposals, priority will be given to those observations in the proposal which received the highest grade in the review process. The higher ranked proposal will be allowed to keep the observations while the other(s) will have to remove the duplicated AOR(s). The results of this duplication analysis will be communicated to the users by the HSC and the time allocation reduced accordingly.

The AORs belonging to OT1p2 proposals will not be blocked for OT2 proposers. Conceivably, they could be part of a proposal submitted in AO-2. If such a proposal is awarded priority 1 time, the successful proposer will have to share the data with the original OT1p2 proposer (see more details in Section 5.5. and in the Herschel Duplication Policies document).