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The Flawed Project Cyclops Study

Radobs 02

 
I consider the 1971/1972 Project Cyclops study to be seriously flawed.  Not
from the general technical aspect, but from the viewpoint of the comparative
performance analysis involving the optical approach to SETI.

On page 50 of that report there is a table (Table 5-3) summarizing a
comparative analysis between the optical and microwave approaches to SETI. 
That optical analysis is seriously flawed by a complete failure of
imagination of what is, or what will be possible with optical telescopes. 
In particular, the assumed sizes of telescope mirrors causes substantial
degradation in system performance, as will shortly be illustrated.  The
Cyclops study only considered ground-based telescopes, whereas my study
assumes space-based telescopes at each end of the system, or ground-based
adaptive telescopes with deformable mirrors or phase conjugation.  The
Cyclops study assumed that optical telescope sizes were limited by
atmospheric coherence cell size.  For the near infrared wavelength of
1.06 microns (Nd:YAG) used for one of the models, the single telescope
mirror size at the transmitter was restricted to a diameter of 22.5 cm, and
the receiver was made excessively complicated and expensive by specifying
four hundred 5-meter diameter mirrors with incoherent (photon-counting)
detection receivers.

By definition (because of the relative ages of the universe and our solar
system), extraterrestrial intelligences (ETIs) will be advanced technical
civilizations (ATCs), i.e., their technology is likely to be thousands to
millions of years in advance of ours.  It could be argued, that if they are
too far advanced, they will no longer be interested in contacting us, or
they would use a technology for their own communications to which we would
be oblivious.  We are an emerging technical civilization (ETC) with very
crude technology.  It is ridiculous to restrict the ability of an ATC to
employing "toy" telescopes, or to assume that with the very narrow
beamwidths of large optical telescopes, aliens would be unable to "hit the
bull's eye".

By effectively objecting to beamwidths < 1 arcsecond because nearby star
systems are too close, so that the beam would most likely miss all the
planets in a star system, many people who oppose the optical approach would
rather cripple the optical system at the outset by specifying tiny mirrors,
particularly at the transmitter.  A 10 meter diameter transmitting telescope
will produce at visible wavelengths and a range of 10 light years, a
diffraction limited beam (beamwidth 0.014 arcseconds) that is only 0.05 A.U.
in diameter.  If there is a problem in aiming a very narrow beam into a
nearby star system, then rather degrading the long-range system performance,
simply construct the largest telescope that your technology can produce at a
cost that is bearable, and defocus (decollimate) the beam for nearby star
systems.  This could be programmed into their targeting computer.

I believe that advanced technical civilizations have the capability of
imaging the planetary bodies of nearby star systems and to determine their
orbital periods.  They will have the means to achieve "predictive
targeting", and thus aim a tight beam to strike a target planet, over what
is equivalent to the round-trip light time between the transmitter and
prospective receiver.

Possibly, these same alien civilizations have at some time visited our star
system or sent out interstellar probes, and thus would have considerable
knowledge about our planetary system.  If you subscribe to the cosmic-zoo or
non-interference directive rationale, this possibility would seem highly
plausible.  At distances of several hundred light years, even these tight
beams becomes so large, that with proper advanced aiming, the entire
targeted biosphere or planetary system would be illuminated simultaneously.

The performance of any directed (beamed) telescope system is a very
sensitive function of telescope aperture size.  This can be seen as follows
for a symmetrical telescope system (same size telescope at both ends of the
link) with mirror diameter "d":

1.   For small mirrors, the maximum usable transmitter power density is
     limited by heating not by laser technology, and is approximately
     proportional to d^2.

2.   The Effective Isotropic Radiated Power (EIRP) proportional to d^2.

3.   The received power collection efficiency is proportional to d^2.

4.   The rejection of Planckian radiation from nearby stars is proportional
     to d^2.

Thus, the performance of a visible wavelength telescope could be
proportional to a factor as high as d^8.  This means that a factor of ten
increase in the size of the mirrors could lead to an improvement in
recovered signal-to-noise ratio of between 60 and 80 dB, depending on
Planckian radiation levels and bandwidth.  Clearly, the performance of an
optical interstellar communications link, particularly one operating in the
visible region of the spectrum, is so sensitive to mirror size assumptions,
that a small change in mirror diameter produces a drastic change in system
performance.  Compared to a 10 m diameter mirror, a 10 cm diameter mirror
could reduce the system performance by 160 dB (ten thousand trillion)!

Incredibly, the SNR penalty in the visible regime imposed by the Cyclops
analysis technique could be higher than 140 dB!  In the Cyclops study, a
2.25 meter mirror was assumed for the CO2 far-infrared system.  The total
SNR penalty in that case compared to 10 meter diameter systems (including
transmitter power limitations) would be a more modest 39 dB; almost a factor
of 10,000.  It should be noted that in the Cyclops Optical System B
operating at 1.06 microns, the transmitting mirror size was 22.5 cm and the
peak power specified was a 10^5 W pulse lasting for 1 second.  This implies
an energy density at the mirror during the pulse of 251.5 W/cm^2.

I have shown than for a symmetrical 10-meter diameter visible system at a
range of 10 light years, a Carrier-To-Noise Ratio (CNR) of 19 dB could be
obtained in a 30 MHz bandwidth if transmitter powers of 1 GW were used.  The
19 dB CNR is more than sufficient for broadcast-quality "real-time" NTSC/PAL
video signals.  The transmitter mirror energy density in this case would be
1.27 kW/cm^2.  If the Cyclops report had modelled a visible system with a
10 cm coherence cell size and a corresponding 10 cm diameter mirror, the
energy density for a transmitted power of 100 kW would have been the same.
One important assumption that Dr. Oliver did make in the Cyclops study, and
which I do believe is correct, is to make no assumption about the laser
powers that would be available to ATCs.  Thus, in the Cyclops study it is
assumed that it is just as easy to generate 100 kW at optical frequencies,
as it is at microwave frequencies.

Thus, we see that by a poor assumption about mirror sizes and beamwidths,
the viability of the Optical SETI approach is substantially skewed if not
destroyed.  It is unfortunate that the optical assumptions in Project
Cyclops have been largely unchallenged for nearly two decades, for it has
reinforced the SETI lore that Optical SETI is useless.  Possibly, alien
civilizations have been trying for years to catch our attention - if only
those dumb Earthlings would tune to the correct frequency!

Even though it is now almost 20 years on and there have been substantial
improvements in optoelectronics and optical telescope technology, it is very
difficult to understand how the optical part of the Cyclops study could have
been so compromised.  Surely, no one expected aliens to employ transmitting
telescopes that they might order out of their equivalent of "Edmunds
Scientific", "Sky & Telescope" or "Astronomy" - telescopes which are even
smaller than what many terrestrial amateur astronomers use?


Post Script:

I have recently been in communication with Dr. Bernard Oliver, who is Deputy
Chief of NASA's SETI Office.  He was the Principal Investigator and Editor
for the Cyclops study.  Bob Dixon, who also participated in the study, 
challenged me to win Dr. Oliver over to my arguments, for if I did, I would
have essentially convinced the entire SETI community that the SETI rationale
needs to be reconsidered.  Dr. Oliver responded to my very strong critique,
in which I gave the Cyclops Report an "A" for technical excellence but an
"F" for failure in imagination, and amongst other things he said that "I do
not see any point in engaging in a long polemic by mail".  This is the first
time that anyone has used that word "polemic" with respect to something I
have said or written - wow!  He also said "Please do not feel rejected by
the SETI community" - I certainly don't!

Dr. Oliver did not answer my objections as to why he crippled the near-
infrared optical transmitting telescopes in his study, save to repeat the
objection that beamwidths < 1 seconds of arc are too small.  He did not
answer my major criticism concerning his rationale for crippling the long-
range performance of transmitters belonging to ATCs.  I have decided to
leave any further arguments about Cyclops till when I get the opportunity to
meet with him in person.  He has given me a standing invitation to give his
people a presentation at Ames, though I have also suggested something more
substantial, i.e., an official one or two day Optical SETI Seminar, to which
anyone who has investigated this area would be invited to participate.


December 14, 1990
RADOBS.02
BBOARD No. 265


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 * Dr. Stuart A. Kingsley                     Copyright (c), 1990          *
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 * AMIEE, SMIEEE, The Planetary Society, SSI                               *
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