5.3. Time Estimates

In calculating the time estimates, we have used all the information available to date about the instruments and flight software performance. We expect that, barring unforeseen circumstances, these estimates will not change any further for PACS and SPIRE and, for HIFI, even in a worst case scenario, prove to be good to around one percent of the total 'AOR duration', or 'wall-clock time'.

This information has been updated as knowledge of the characterisation of the instruments and telescope has improved and we no longer expect it to show large variations during the rest of the mission, but small changes are still possible. Over the last year most changes have involved fixing small bugs that have appeared that affect certain types of observations only. Obviously, this means that the time estimates for your AORs may change if new information becomes available that requires a change in the time estimator version. Out of date time estimates are shown in red in the observations table and should be re-calculated before proposal submission or when updates are made to AORs.


Version 5.0 of HSpot incorporated in-flight information on sensitivities that, in some cases, implied important changes in observing time to reach a desired flux level. Further changes have occurred in the 5.2 version that are particularly important for some HIFI observations. There were some smaller changes in the 5.3 version, mainly limited again to certain HIFI bands. Where possible, the changes to the set-up time required for observations have been "hidden" in the slew overhead; when no slew overhead is applied (e.g. for concatenated observations) this additional set-up time will be added to observations - if the additional set-up time overflows the slew time, the excess will also, inevitably, be counted against the observation.

Version 6.0 contains some important changes in the way the HIFI time estimation is carried out. This should not impact the duration of AORs, but may have an impact on how fast time estimation is carried out for some observing modes, with a significant slowing of time estimation calculation possible. An issue was also found for some PACS spectroscopy observations that has required modifications to the way that time estimates are calculated in some modes.

HSpot reports the following when you request an observing time estimate:

  1. AOR Duration: This is the 'wall-clock' time, or total time required to execute the observation, including time on source, internal calibrations, slewing, settling, command execution, and the fixed slew overhead applied to each AOR. In otherwords: this time is your exposure time, plus all the overheads that are required to complete the observation. This is the time you must request in your proposal for this observation. If you request less time than you actually need (for example because you used an out of date time estimator version or failed to estimate all your AORs)

  2. Slew Time: The time spent on slews internal to the AOR.

  3. Observatory Overhead: A 180 second overhead applied to all AORs to account for the initial slew to source and other observatory overheads. For constrained observations the overhead applied is 600s to compensate for the increased difficulty in and inefficiency of scheduling and thus the hidden overhead implied by constrained observations.

  4. Integration Time(s): Estimated on-source integration time(s) in seconds. HSpot returns observing time estimates from the CUS server for all of the AOTs.

Time estimates are liable to change if observing methods are further optimised in flight. No guarantee can be made that some time estimates will not increase a little with even better knowledge of instrument sensitivity and observatory performance (while other AORs may give better than expected s/n in the time calculated), or changes in the way that observations are designed. The amounts of time given to each proposal by HOTAC will not change a posteriori based on changes in in-flight performance. It is expected that after approval of proposals some modification of AORs may be needed to optimise them; this process will be carried out in co-operation with the Herschel Science Centre.

If, with a new time estimator version, the total duration of your AORs exceeds the time awarded by HOTAC you will be obliged to make cuts to adjust to the time (rounded to 0.1h). If however, with a new time estimator, your programme requires less time than HOTAC awarded, you may invest the time saved in deeper integrations or (with HOTAC approval) additional targets.