Time critical OB execution policy

Since the introduction of observing tools that automatically take into account absolute and relative time delay when scheduling observations at the telescope, time-critical Service Mode OBs are handled more rigorously than before. The OB Ranking Algorithm identifies the most time critical OBs that will soon have time windows expiring and assigns them higher execution priority. Nevertheless, it is possible that due to too many conflicting high priority observations or unsuitable weather, some time-critical OBs cannot be executed within their assigned time window. If all time windows have already passed, the OB expires and is marked with the status F(ailed). This status cannot be changed and the OB is lost.

There are two types of time-critical OBs:

  1. OBs with absolute time constraint window

    Setting an absolute time window in an OB implies that the execution of that OB out of the specified time window(s) is not useful scientifically. Hence if the OB cannot be executed and it expires, this time is lost. Therefore, during Phase 2 submission, the time-windows should be set in the OBs only if strictly necessary and as loosely as possible.

  2. OBs with relative time constraints, that are part of a time-link container

    Relative time constraints in time-linked OBs should also be set as loosely as possible, according to the science goals. For some runs (e.g. of monitoring nature) the science case may require the completion or quasi-completion of the observing sequence. Should one or more OBs be marked with the status F(ailed), it may be possible to submit one or more new OBs to compensate for the epoch(s) that was/were missed and for which the corresponding OB(s) has/have expired, if the observing run is still active. However, this is not an automatic process and requires a scientific evaluation.

    • The PI should ask for permission to submit new OBs by clicking on 'Ask for help' in the ESO User Portal or by sending an e-mail to usd-help@eso.org. The information conveyed in this manner shall contain a short scientific justification.
    • If the submission of new OBs is approved, they will be either added to the end of the existing time-linked sequence or submitted as a new time-linked sequence. Final advice will be provided by the support astronomer.


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