In semi-infinite wisdom Louis Scheffer answered:
"Rob Dekker" <rob@verific.com> writes:
"Louis Scheffer" <lou@cadence.com> wrote in message
news:4095e404$1@news.cadence.com...
Andrew Nowicki <andrew@nospam.com> writes:
[...] As a first guess, cover the planetary zones
of the nearest million stars or so, with beams that are on
all the time [Think of the beams as looking like a pincushion].
This is something we can do with existing technology for about
$200M, for a beam bright enough that we ourselves can detect it.
And this cost will come down further as a consequence of Moore's
law.
Lou Scheffer
How did you get to just $200M for a system which cover 1M stars;
semi-continuously ?
Here's how I got that number. Assume you build a large phased array consisting of
many small (10mw) transmitters. To be detectable by ourselves, you need about a
10^12 watt EIRP. 1M of these implies a total EIRP of 10^18 watts (it turns out with
phased arrays the total EIRP can be split up with almost no penalty). This means
you need 10^10, or 10B transmitters. We can build today a 10mw transmitter plus
antenna for about $0.20 (actually we can build a chip with 100 of these + a PC board
with 100 antennas for about $20, but for our purposes this is the same.)
10 billion transmitters?
Assuming 100 per board still gives 100 million boards.
This gives a total cost of $2B for the transmitters.
Think you'll need much more than that, power for starters. Either you'll
need DC to the boards, or you'll have to add power supplies. No doubt
for that power level small DC power supplies could be used, but you'd
need either 100 million of them or however many would be needed to
power multiple boards.
And unless I'm greatly confused, you'll need an active interface to
point the arrays. I'm not sure how these arrays are controlled, but
I'd imagine that you'd need to least a serial connection to each board
for control. And what kind of a system can direct 100 million boards,
simultaneously? I don't think anything like this even exists. Add in
development costs and perhaps a small supercomputer. Maybe you could
do the linux thing with a computer farm, but even that ain't cheap to
design and build.
We'll need lots of supporting infrastructure, and it seems to me that
that'll cost more than the antenna boards.
However, you are ordering 100 million identical PC boards and chips,
> so you should get a substantial volume discount.
I agree with you there. :-)
How much? I'm guessing a factor of 10 since it would be reasonable to
set up a dedicated production line for these volumes.
And how long will they last exposed to the elements? How about rain?
Dew? Insects? Animals? Birds? Bird droppings?
Come to think of it you'd probably need an enviornmental impact
study as well.
How much power do you need for the transmitters ?
About 200MW is required for 10^10 10mw transmitters at 50% efficiency.
Let's see, the Diablo Canyon reactor in CA can provide 1,087MW.
You'll need to be close to a high capacity power source. Given that
CA's supply is within 5% of demand at any peak (and sometimes less),
you probably won't get that much power here unless you build your
own power plant. Come to think of it, this may be true everywhere.
Have you factored in the cost of power generation?
Which cost/W do you use ?
At $0.08/kwh this is about $140M/year.
So we're up to about $240M already.
However, you could also make the array
solar powered to cut the operating expense
Solar cells are expensive however, up front costs would be huge,
regardless of operating costs. And I'm not aware of any large
solar facilities that show low operating costs. And the same issues
with exposure apply.
(though this reduces your coverage
since you cannot transmit at night, and introduces more site selection limitations).
You need about 32 watts/m^2 of low voltage DC - a great match to solar cell technology.
And how large is the antenna that you need ?
At about 3.5cm wavelength, the antennas need to be about 2.5 cm apart, or 1600 per
square meter. This yields a surface about 2.5 km on a side - big, but not that
much bigger than the proposed square kilometer array. And it's a lot lower
technology.
Maybe, but the power feeds would be interesting, 140MW total to antennas
2.5 cm apart. I expect that there would be significant cooling issues
also.
And when an element fails, how are you gonna get to any of them for
replacement? You could not walk between the rows. And just how sensitive
is the array to antenna failure(s)?
I think you are underestimating the actual costs by at least an order of
magnitude, perhaps more. YMMV.
[...]
Rich
Lou Scheffer