[alma-config] Cost of configurations

[Adrian Webster]

Cost of ALMA configurations.

Mark Gordon has asked for outline plans of possible configurations so that 
he can come up with preliminary cost estimates.

This is to ask whether there is support among the configuration designers
for the
reverse request: i.e. for some idea from Mark of the costs of various items
of infrastructure so that we may consider putting them into our models with
a view to minimizing the total cost while maximising electromagnetic
performance. The sorts of information needed, and rough estimates would be
more than adequate at this stage, are:

a) the typical cost of one foundation ($ per station)

b) the typical cost of roadway ($ per km)

c) the typical cost of power cable ($ per km)

d) the typical cost of fibre links ($ per km).

Not only do these costs fall into two major categories from the point of 
view of modelling, in that a) is intensive whereas the others are extensive
(proportional to a distance), but the extensive costs also fall into two
categories.
The fibres for any station run all the way to the central lab without
branching, 
whereas the roads and power cables will probably have a tree structure. It
follows that the cost per station of the latter is incremental, being the
extra cost of linking the station 
into an existing network rather than the total cost of the entire link back
to the lab.

These issues do affect the general strategy for the design. If, for example,
the
concrete foundations are relatively cheap we may as well have a lot of
different 
compact configurations in order to provide near-circular beams at any zenith
angle, 
because the length of the extensive services is very small for these
configurations.
If any or all of the extensive services is expensive per km, then the outer
configuration is not merely a cost driver but a major one and well worth
extra attention at the design stage.

At present I do not have any feel at all for these costs, even to order of
magnitude,
and it may be that the other members of the group who are generating designs
also
would welcome a little enlightenment.

Adrian

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Adrian Webster,
Institute for Astronomy,
Department of Physics and Astronomy,
University of Edinburgh,
Royal Observatory,
Blackford Hill,
Edinburgh EH9 3HJ,
Scotland.
asw at roe.ac.uk
tel: 0131-668-8391
fax: 0131-668-8416

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