[alma-config]Re: Early science Configs

[Mark Holdaway]

Al,

I think it sounds reasonable to transition from "move all antennas when
reconfiguring" when we have 6, to "move 4 antennas every n days" when
we have more than m antennas.  However, we still have the problem of
"how do we configure 32 antennas on all these pads?"   One answer is 
just put them on the inner-most spiral pads, evacuate antennas from the
inside to the outside -- ie, the exact same reconfiguration strategy
used by the full 64 -- I'm sure that a somewhat better configuration
using the existing pads could be found, but at that point it might make 
only a small difference, not worth worrying about.  Reconfiguration
would certainly take longer, and the configurations would have a lower
long_baseline / shortest_baseline ratio.  A simple alternative would be to 
make "skeletal" configurations, ie, where every 2nd antenna pad in a
64-pad configuration is not filled.  Some simulations would let us know
which style made more sense.  Of course, if you do the skeletal approach, 
you need a strategy for filling in the 33rd through 63rd antennas.

However, I think the approach of having special configurations for
6, 14, 23, 32 antennas will be highly non-optimal, though it has the
advantage of being a finite problem which is solubale.

What exactly do we need this for?  For DSRP purposes, or to actually know
what to do when the 15th antenna arrives?  It seems that we want to have
a tool that can help us decide what to do when the next antenna 
comes rather than to have a full solution at this moment -- flexibility
may be required, as our presuppositions of what is required of these
configurations may not hold true as we are commissioning the antennas.

Take care,

   -Mark

> 
> Hi John and Mark
> 
> This sounds like a reasonable plan to me.  Early on, we'll probably have
> bursts of science--two weeks of science observations, then two or more
> weeks of commissioning and verification, followed by a period of science
> observations.  These science times might alternate between configuration
> sets which would be combined to obtain useful images.  Proposal calls will
> occur every six months or so in the paradigm we currently have, so the
> science array wouldn't get augmented on shorter timescales than that, at least
> for the first year or so.  
> 
> One major break point comes when 32 antennas are available.  At least then
> but perhaps before we might consider beginning an n day reconfiguration
> series, where n becomes 4 in the final stages in our current paradigm.
> The Earliest Science configuration plan would then cover the period until
> 32 antennas were available, and would consist then of perhaps four sets
> of configurations involving 6, 14, 23, 32 antennas.  Comments?
> 
> Al
> 
> John Conway writes:
>  > 
>  > Hi,
>  > 
>  >  Mark makes some good points, I agree a spatial dynamic range of 20
>  > is hard for 6 antennas. but for a fully 1D array of 6 antennas close to
>  > EW then  a baseline range of 20 could just about be achieved, but long
>  > tracks  are then of course required to get good azimuthal coverage.
>  > 
>  > Its more in line with the pad pattern and expandability of the array to
>  > full operation to have a 2D pattern of 6 antennas. For instance an outer
>  > triangle of three antennas and an inner triangle,will give azimuthally good
>  > uv covergae in 3-6hrs , but has a low spatial dynamic  range (like 3-5 maybe),
>  > however by combining two such arrays one  could get a  useful array for
>  > astronomical imaging,
>  > 
>  >       Jihn
>  > 
>  > 
>  > On Wed, 14 Jan 2004, Mark Holdaway wrote:
>  > 
>  > >
>  > > I think that these are reasonable boundary conditions (though a factor
>  > > of 20 between long and short baselines for 6 antennas seems to be
>  > > stretching it -- the VLA, with 27 antennas, has a ratio of 40), but
>  > > I think the defining concepts for this task may be:
>  > >
>  > > (1) that we usually want to use multiple configurations to get good (u,v)
>  > > coverage (this is ALMA, not OVRO).
>  > >
>  > > (2) that we want these configurations to be "expandable" in that
>  > > we will be adding antennas every month or so.  I know this was not
>  > > part of the current objective, but that is really the ultimate task.
>  > > Initially (ie, when there are 6 antennas), we may move all or almost
>  > > all between each configuration -- but at some point, more and more
>  > > antennas will NOT be moved as we change configurations.
>  > >
>  > >    -Mark
>  > >
>