How smart are SETI@homers?

Louis Scheffer wrote:

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].
Modern phased array transmitters can generate this
number of beams, and keep them focused on the stars,
with little problem. And this is roughly the number of stars
for which we have adequate proper motion and distance measurements.
(You need both since the star will be in a different place when the
beam gets there.)

This is the first clear signal in this noisy thread. :-)
We need to flesh out details. If your message lasts 10
seconds and you are sending it to one million stars,
the same star receives the message about once every
3 months. If their SETI program works like our program,
they will probably miss our message.

I have a better idea: a parallel, modulated microwave
beam is made by a conventional transmitter. A microwave
hologram splits the beam into thousands of narrow beams
aimed at the stars.

Rich writes:

There's lots and lots of speculation, some small amount of it actually
based upon observation, but there are, as yet, no answers at all, much
less definitive answers. And curiously, I don't see many stating the
simple, honest truth, that we simply do not know.

All reputable researchers will agree with this part of your statement.

And there is no reason to think that better observations will change this.

This only makes sense if you are *certain* the observations will
fail. A successful observation would certainly give
us answers, if not definitive answers. And how can you be certain
observations will fail when you start your argument with "we simply do
not know?"

So on one hand you are arguing "Neither I nor anyone else knows anything
about this topic". Then you argue "Better observations are futile".
Either statement alone can be supported, but together they make no sense.

Lou Scheffer

Andrew Nowicki writes:

Louis Scheffer wrote:

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].
Modern phased array transmitters can generate this
number of beams, and keep them focused on the stars,
with little problem. And this is roughly the number of stars
for which we have adequate proper motion and distance measurements.
(You need both since the star will be in a different place when the
beam gets there.)

This is the first clear signal in this noisy thread. :-)
We need to flesh out details.

This has already been done. See Appendix B, pages 303-320, of the
book SETI 2020.

If your message lasts 10
seconds and you are sending it to one million stars,
the same star receives the message about once every
3 months. If their SETI program works like our program,
they will probably miss our message.

Perhaps I was not clear. All the beams, shining on all the stars,
are on all the time, just like your hologram proposal below.
Whenever the receiver looks, they will see it. This
is precisely to avoid the problem you just stated.

I have a better idea: a parallel, modulated microwave
beam is made by a conventional transmitter. A microwave
hologram splits the beam into thousands of narrow beams
aimed at the stars.

This is *exactly* what a phased array transmitter does,
except it generates the radiation locally at each point,
rather than by scattering coherent radiation from a central
source. The math is identical. However, the phased array
is able to cope with changes much better (as the stars move
with respect to each other, or you add more stars, you
would need to change the hologram.) With a phased array
you just update the coefficients with no physical changes.

Lou Scheffer

In sci.space.policy Jan Knutar wrote:
Lou Scheffer wrote:

Why look for a signal that no one is
motivated to send?

It's impossible to extrapolate any potential ETI's motivations based on what
motivates humans.


As things stand, there are good reasons to not delibertaely put out beacons
with the explicit intent of advertising our presence here. Such are not
hard to argue for - whetever these arguments would still hold in say 400
years is a different question. They might not. Or they might still, or
we might no longer be around or capable of posting such.

--
Sander

+++ Out of cheese error +++

In article ,
Louis Scheffer wrote:

private groups, it may be hard to prevent. For example, there is
already a company that will send a message of your choosing from a
radio telescope in Russia.

Yes. I'm aware of that. The person involved with the science
message (rather than the vanity messages) for this sometimes posts
on sci.astro.seti. Note it is run by a North American company
and, at least for the original transmissions, used a radio telescope
in the Ukraine, not in Russia. The total transmission time is
limited, precisely because of the cost of transmit tubes that
I mentioned.

This seems intuitively reasonable, but is not true. In a phased array,
replacing modules with smaller cheaper modules saves power. This is
because the EIRP goes as N^2, so for constant EIRP, the power per module

No. There is nothing magical. It scales with the area in the same way
as for a dish reflector (which is just a phased array with infinite
numbers of elements, but excited by a free space signal, not locally
at each element - think how you would compute the gain by integrating
over the surface area). This should be obvious from the reciprocity
principle and that gain scales with capture area. You can also get it
from books like the ARRL handbook, where the array gain for having too
stacked yagis, is 3dB, not 6dB (actually, in my copy, it is a throw away
line about expecting 2 to 3dB, as though it was too obvious to state).
I suspect where your confusion arises is that gain scales as the square
of the diameter, but you are talking about the scaling with area.

In fact, unless the array elements are far enough apart (outside
each others' "capture areas") the gain won't even scale as the number
of elements, but rather as the effective area covered by them).

goes down faster than the number of modules goes up.

For example, imagine a transmitter with 1M modules of 1 watt each.

Note that even for reception, the 1 square km array uses a hybrid
configuration with directional antennas at each array node. That's
because the current break even in a receive configuration occurs when
some of the gain is done by passive reflectors. Arrays are becoming more
cost effective for reception because the electronics cost is reducing,
and passive reflector costs scale more like the cube of the diamter than
as the area.

The 1 square km array is too costly to build at the moment, and
only exists as a small number of elements as proof of concept.

Incidentally, it would be more or less impossible to keep a million
element array operating on all 1 million elements; you would need
elements with enormous MTBFs.

If transmitters become cheaper, you can replace this with 10M
modules of 10mw each, for a total power savings of a factor of 10.

Based on false premise, see above.

True, but no rational SETI transmitter would use vacuum tubes any more,
since they don't last very long and represent a significant cost.

Current planetary radar uses vacuum tubes, as does the Evaptoria
transmitter for Cosmic Call. I believe that strategic defence radars
do, as I understand that Arecibo uses second hand strategic defence
radar transmit tubes.

In semi-infinite wisdom Louis Scheffer answered:
Andrew Nowicki writes:

[...]

If your message lasts 10
seconds and you are sending it to one million stars,
the same star receives the message about once every
3 months. If their SETI program works like our program,
they will probably miss our message.


Perhaps I was not clear. All the beams, shining on all the stars,
are on all the time,

Just where do you plan to place your transmitter so that it
will not be obstructed by a planet or it's star periodically?

just like your hologram proposal below.

I'm not quite sure I understand that proposal.

Whenever the receiver looks, they will see it. This
is precisely to avoid the problem you just stated.

Gee, that technology would come in handy on Earth. Maybe
you should develop it?

I have a better idea: a parallel, modulated microwave
beam is made by a conventional transmitter. A microwave
hologram splits the beam into thousands of narrow beams
aimed at the stars.

This is *exactly* what a phased array transmitter does,
except it generates the radiation locally at each point,
rather than by scattering coherent radiation from a central
source.

As I understand it, a phased array can only transmit or
receive in one direction at a time.

The math is identical. However, the phased array
is able to cope with changes much better (as the stars move
with respect to each other, or you add more stars, you
would need to change the hologram.) With a phased array
you just update the coefficients with no physical changes.

Have you contacted the SETI people?

Rich

Lou Scheffer

Rich wrote:

Do you expect SETI to succeed?

I assume that "succeed" in this context means to detect
signs of ET civilizations, but maybe you could tell me
what success would be to you. The phrase 'the operation
was a success but the patient died' comes to mind for
some reason. Seems that doctors have a different definition
for the success of an operation than patients (and their
families) do. Perhaps SETI insiders do as well.

I do not care if the ET has four or eight limbs.
I want to know if it has a teleology that is
attractive to intelligent creatures.

ET is silent because it has nothing to say. It
is passive because it has nothing to do except
consuming narcotics.

SETI will be a success if it proves that some
civilizations are diverse, expanding, devoid of
narcotics, and durable. It will be a failure if
it detects no ETIs, or confirms that all ETIs
commit suicide.

In article ,
"Andrew Nowicki " wrote:

Mark wrote:

At least we'll know that aliens with big non-directional
radio transmitters are rare.

We have already learned that.

Even if we did detect a signal, we couldn't tell if it was directional
at source. (We are almost at the point of being able to detect our
analogue TV carriers at interstellar distances (see the 1 sq km array
below), and those, whilst directed to try and avoid wasting power,
are not strongly directional.

What we need is a non-directional microwave receiver
on the far side of the Moon. It would be a sort of
phase-array radar in reverse -- lots of small receivers

I would consider this to be multiple directional beams,
rather than non-directional reception. As far as I know, the
1 square km array, which will be an earth based equivalent, won't
normally attempt to form as many beams as there are elements, but
rather a small number.

However, such an array is beyond the wildest dreams of even
conventional radio astronmers, let alone cash starved SETI
searchers. As well as the problems of surveying and placing
each element, the large amount of electronics involved will
result in a system that will start to lose elements quickly and
have no maintenance man to replace them.

but no directional antennas. To reduce the noise, it
would be used only during lunar night, when the surface
of the Moon is cold.

Modern receiver noise temperatures are generally a long way below
ambient. The cryogenically cooled SERENDIP (S@H) receiver was actually
replace by a non-cooled one with a lower noise. I believe the total
system noise for this receiver is about 45K, of which about 12K is
galactic noise and big bang backround, which can't be eliminated.

Whilst I argue in another thread, that a pure phased array transmitter
is future, rather than current technology, it is not that far off that
it wouldn't be reasonable to assume that an ETI would form multiple
beams to allocate the total power more effectively to likely targets.

The advantage of the non-directional receiver is that
it can detect signals coming from a broad solid angle.

But only at the cost of doing a two dimensional fourier transform,
and then doing the followup signal processing a number of times
comparable to the number of elements. Remember that processing capability
for space qualified equipment is rather moderate compared with
what is on your desk top.

Incidentally, with respect to the subject, there was concern amongst
the professionals that the general public might expect a contact from
S@H when the professionals, whilst hoping for one, thought that setting
new upper bounds was the more likely outcome. This was before it went
fully live. The concern was that there might be a backlash from the
modern instant gratification culture, that might prevent funding of
more sensitive future work.

Louis Scheffer wrote:

See Appendix B, pages 303-320, of the book SETI 2020.

I will. It is called 'Omnidirectional SETI System'.

This is *exactly* what a phased array transmitter does,
except it generates the radiation locally at each point,
rather than by scattering coherent radiation from a central
source...

It seems feasible and versatile, but more expensive than
the hologram.

PS. I have just learned from the web that in the 1960's
the Soviet Union dominated SETI, and it used nearly
omnidirectional receiver antennas. I have no idea how
these antennas were designed.

Criticism of SETI in Wikipedia:
http://en.wikipedia.org/wiki/SETI#Criticism_of_SETI

David Woolley wrote:

However, such an array is beyond the wildest dreams of even
conventional radio astronmers, let alone cash starved SETI
searchers. As well as the problems of surveying and placing
each element, the large amount of electronics involved will
result in a system that will start to lose elements quickly and
have no maintenance man to replace them.

Although I respect your technical expertise, I am not yet
convinced that this array would be expensive to make and
maintain. The array would be made of a large number of
identical, mass produced panels. Damaged panels can be
replaced with new ones. A small percentage of damaged
panels does not seriously degrade the image quality.

The main issue is how much data would have to be
processed. If the array cannot filter out obvious
noise, SETI@homers would be overwhelmed with noise.