[alma-config]Re: [mmaimcal]Memo 428

[Stephane Guilloteau]

Be carefull

    - we cannot (yet) simply assume the ACA will be build
    - however, we (astronomers) cannot continue dreaming to build whatever
we wish for ALMA.

We have a budget constraint, and within the current uncertainties, saving 1
M$ or so on 25 pads
would be more than welcome. I would rather re-affect that 1M$ to a better
calibration system. In that
area, we have some unfunded items which would be useful, such as an
automated FTS and its associated
software. This would be useful for most projects, while the 25 pads for an
elongated N/S compact configuration
are at best only useful for 5 % of the projects.

Using the inner "spiral" pads and some re-weighting scheme is not optimal
when considering fixed configurations, but if we add up the overhead time
and associated losses due to reconfiguring to such special configuration,
this becomes less obvious.

Given the imaging results shown by Mel Wright, I would strongly argue
AGAINST the added complexity
of the "elongated compact" configuration.

And remember: the configuration design IS URGENT.

The current feeling of most members in the ALMA Management Advisory
Committee is that we will need some descoping of the project, and these
people certainly have a lot of expertise on large projects. Having to
descope a receiver band would be disastrous. So we have to be careful in all
items which have a small influence of the overall performance of ALMA, but
result in some quantifiable cost savings..

        Stephane


----- Original Message -----
From: "Al Wootten" <awootten at NRAO.EDU>
To: <alma-config at NRAO.EDU>; <guillote at iram.fr>
Sent: Wednesday, June 26, 2002 4:49 PM
Subject: [alma-config]Re: [mmaimcal]Memo 428


> Configurees:
>
> I think that we should assume nothing about the ACA at the moment.
> We have a bilateral project, and the ACC is anxious lest the funding
> parties become confused over the bilateral nature of it.  We need a
> configuration design before we will know if the ACA will exist, an
> unfortunate fact of life.  Thus, the form of the ACA must be determined in
> such a way as to blend best into the ALMA configuration.
>
> Al
>
> John Conway writes:
>  >
>  > > The problem of the number of compact configurations is significantly
>  > > simpler than it used to be: we no longer need to worry so hard about
>  > > getting lots of short projected spacings at all declinations with the
>  > > addition of the ACA (which, by the way, is costing a bit more than
those
>  > > 25 extra pads would have cost).
>  > >
>  >
>  > This is a major issue though. Are we really assuming 100% certainty
>  > that ACA  will be built given its not in the bilateral baseline plan? I
>  > think that we have to ensure that the array of 12m dishes has
reasonable
>  > very short baseline coverage. Mark is making the argument I guess
>  > that with ACA we don't need to have many configurations for the 12m
>  > antennas so that for ALL  declinations we can observe such that in
>  > projection the antennas are just going into shadowing (so we are
sensitive
>  > to 0-3m baselines),  but surely in any case projection helps you mainly
in
>  > the filling in the  short baselines the v direction; in test uv
>  > coverages I have done as expected the shortest centre-to-centre
baseline
>  > along the u-axis  stays around the antenna collision seperation
distance
>  > of 15m. In conclusion using projection to fill in short spacings is
>  > only a partial solution at best and really to do a good job we
>  > need the ACA (..which is why this is top of our wish list)
>
> _______________________________________________
> Alma-config mailing list
> Alma-config at listmgr.cv.nrao.edu
> http://listmgr.cv.nrao.edu/mailman/listinfo/alma-config
>