[mmaimcal] Re: [alma-sw-ssr] Band switching times revisited...

[Mark Holdaway]

I think this is quite bad.

My understanding is that there are two hot frequency bands at any time
(though the wording at one place stated "two standby frequency bands"),
and one of them is usually 90 GHz as it is required for pointing and
fast switching phase calibration.

If my understanding is correct, this is clearly bad for scheduling,
dynamic or otherwise.

If you are doing a project at 230 GHz and you then need to change to 650
GHz  (ie, if the wether gets good, or if you have just scheduled it that
way), you have something like 15 minutes while 650 is warming up and 230
is powered down, so in this 15 minutes of 650 GHz weather your only
choice is to observe at 90 GHz, clearly a waste of 650-GHz-quality time.

I think this overhead will put strong limitations on how often ALMA
changes frequencies and will eat away some part of the efficiency gains
which are made with dynamic scheduling, which seeks to be very agile.
Furthermore, it would likely impact low elevation and very demanding
observations, both of which require different atmospheric conditions
at a given frequency than the generic high elevation observations
at the same frequency, and therefore would likely be observed during
the same conditions that might be used for higher frequency generic
zenith observations.

If there is a current observing band plus two others as standbys,
I think we can live with that.  I assume these specifications are
well ossified?


	-Mark