[alma-config]Re: [alma-site]Reconfiguration Times

[Stephane Guilloteau]

A few comments on Mark's message

>
>Three points:
>
>1) With 3 moves per day (which you got by adjusting some numbers)
>  we could do the canonical spiral or Y+ 3 antenna reconfiguring
>  with a single transporter, ie, if one of the transporters is
>  down for maintenance or is busted, which will occur on occasion
>  if we are reconfiguring every 2 or 3 or 4 days.
>
    That number of 3 moves per day is a good target.

>2) I am somewhat concerned about the accuracy of baseline and pointing
>   determinations from the subarray of just 3 antennas that have
>   just been reconfigured.  Has anyone done the numbers on this, or
>   thought of this?
>
    I thought a bit on that. The idea was not to use only 3 antennas, but
4-6 or so. By this way
    i) you increase S/N for pointing determination (which is more critical
than baseline)
    ii) you tie up the antenna coordinates of the recently moved antennas to
those already in place
    iii) you do not loose too much sensitivity of the main array while the
2-3 antennas which have not been moved are used for this calibration issue.
    See my earlier memo on that.


>>  However in the compact arrays from the configuration
>> point of view it may be  desirable to have significantly larger
>> move rates (i.e. 6 - 8  moves/day). The reason is that
>> the intermediate configurations between say the most compact
>> and the first N-S extended array may not be as useful as
>> for the intermediates.
>
>3) It seems that the gentle change in resolution with reconfiguring
>3-4 antennas means that, even though getting halfway to the N-S
>extended array is non-optimal for zenith observations, it isn't
>non-optimal by much.  It could be quite non-optimal for extreme
>declination observations which would result in several shadowed
>antennas until more are moved out.
>
    Agreed, but the "extreme" declination cover a small fraction of the sky,
and are always observed at (relatively) low elevation anyhow.



        Stephane