[mmaimcal]Memo 428

[Al Wootten]

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)