Generally, visits are SAA hiders during only some fraction of their schedulability. The SAA hiding times will repeat on the 56 day orbit precession period.
SPIKE can predict the orientation of the orbital plane with good accuracy and can identify on which days a given visit is likely to be an SAA hider. So we could provide a display which shows those days. The actions which an observer could do to increase the amount of time that a visit is an SAA hider are (1) reduce maximum alignment length (2) split visits into smaller numbers of orbits
Visits can be made more SAA friendly by splitting very long exposures.
None of these are things which observers would normally have a science-driven reason to do. Also, the amount of improvement which is obtained by making these changes is dependent on the orbital geometry, so some iteration would be required to optimize the SAA hiding - requiring additional work by the observer. Perhaps we would need to provide tools which would automatically adjust exposure times or split visits and re-display schedulability and SAA hiding times.
Overall efficiency is improved so there is a benefit to having users increase the number of visits which are SAA hiders and to increase the amount of time for which they are SAA hiders. However, the benefit to the individual observer is marginal, unless, e.g., substantially increasing the amount of time that a visit is a SAA hider results in quicker scheduling of the visit. Thus, there are policy issues which would need to be addressed.
One possible policy issue would be whether we want to require observers to restrict the maximum number of orbits in a single visit to e.g., 3 (except for cases where longer visits were scientifically justified). However, it is not yet clear how much of a gain in efficiency we could expect from this. Some studies would need to be done by the PC group.
Additionally, we note that it may be possible to obtain some improvements in efficiency from changes to the in-house software - TRANS, SPIKE, SPSS. Mark G. felt that more benefit would likely be achieved by such software improvements than from user input. But this topic is beyond the charter of the VP group.
At this point in time, the observers have no way of knowing whether any visit they construct is helpful in this regard, whether it can hide an SAA crossing. Given that they have no way of knowing about that, we make no attempt to ask them to provide us with SAA hiders. It is much too complicated a situation to explain to them, especially when they get no feedback as they are building a proposal.
It seems to me that the first step in all this is simply to provide them with the visibility into whether a visit can be an SAA hider. Until the system provides this feedback, there is no point in our even asking them to consider it. There is no point in worrying about policy questions or whether we would ask individual GOs to make a trade-off that does not provide them an advantage.
So, what I would like considered, and from your minutes it looks like it would be relatively easy to provide, is simply to enable the visit planner to provide display information concerning SAA hiding. This will be a big step forward from the current situation, where no information is provided either to the GO or to internal users.
Once that type of display is available, then the PCs or others could do a more expansive study on what types of steps can be taken to increase SAA hiding. We can also use it internally, in conjunction with the PIs of large programs, to see if we can selectively work on a few programs to provide us with larger pools SAA hiders. I am sure that we may discover other techniques, and consider possible policy changes, once we have a system that allows us to experiment operationally.
I think this is a pretty clear case where we want first to provide information, and then use the system and determine whether, and how best, to take advantage of it.
Thanks, Rodger
Chris O'Dea sent out the following comments which will provide seeds for the discussion.
I have spoken with Ian Jordan about SAA hiding and here are some issues.
SAA hiders are visits which can be scheduled when the SAA passage occurs during occultation. SAA friendly visits are those which can be broken up around SAA passages and so can be scheduled (but with a penalty in efficiency). The schedulers prefer to schedule visits when they hide the SAA since this improves efficiency.
Generally, visits are SAA hiders during only some fraction of their schedulability. The SAA hiding times will repeat on the 56 day orbit precession period.
SPIKE can predict the orientation of the orbital plane with good accuracy and can identify on which days a given visit is likely to be an SAA hider. So we could provide a display which shows those days. The actions which an observer could do to increase the amount of time that a visit is an SAA hider are (1) reduce maximum alignment length (2) split visits into smaller numbers of orbits
Visits can be made more SAA friendly by splitting very long exposures.
None of these are things which observers would normally have a science-driven reason to do. Also, the amount of improvement which is obtained by making these changes is dependent on the orbital geometry, so some iteration would be required to optimize the SAA hiding - requiring additional work by the observer. Perhaps we would need to provide tools which would automatically adjust exposure times or split visits and re-display schedulability and SAA hiding times.
Overall efficiency is improved so there is a benefit to having users increase the number of visits which are SAA hiders and to increase the amount of time for which they are SAA hiders. However, the benefit to the individual observer is marginal, unless, e.g., substantially increasing the amount of time that a visit is a SAA hider results in quicker scheduling of the visit.
We could have meeting to discuss these issues. We would want to invite Ian and a SPIKE developer to attend. Any comments ?