Abstract: This paper examines the feasibility of an amateur approach to METI using cheaply available lasers and optics. We suggest a novel variation in the search methodology, concentrating on contacting any interstellar extraterrestrial probes that may be present in the solar system. Specifically, the Lunar poles and Lagrange points L4 and L5. It is assumed that such a probe incorporates advanced artificial intelligence (AI) at or beyond human level. Additionally, that it is able to communicate in all major languages and common communications protocols. The paper is written in non-technical language with sufficient information to act as a “how to” source for technically knowledgeable people.

Note: Any portion of this may be reproduced and used in any manner provided attributions “Dirk Bruere” and the

organization “Zero State” are included. Other more technical versions of this are available.

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Historical Introduction

On 16 November 1974 The radio telescope at Arecibo sent a brief

message to the M13 star cluster some 25,000 light years distant. It

comprised some 210 bytes of data sent at a bitrate of 10 bits per

second and a power of around one megawatt. The (colored) pictorial

representation is shown here. It is probably the best known attempt at

contacting extraterrestrial intelligence (ETI), even though it was not

serious, was not the first and by no means the last.

The first was a Morse code message sent from the USSR to Venus in

1962 which was even shorter. It is known in Russian as the Radio

Message “MIR, LENIN, SSSR”.

Latterly, in 2016 on 10 October 2016, at 20:00 UTC the Cebreros

(DSA2) deep-space tracking station of the European Space Agency

sent a radio signal towards Polaris, the Pole Star, which is

approximately 434 light years from Earth. The message consisted of a

single 27,653,733 byte, 866 second transmission. Again, it was not a

serious contact attempt, and was rather more a work of performance

art by Paul Quast.

A few, more serious, attempts have been made in the intervening

years i, targeted at more plausible planetary systems but none for any

sustained period of time.

So, enter METI ii or “Messaging Extra-Terrestrial Intelligence” who aim to start a serious

and comprehensive program of signaling various star systems some time in 2018 if they

can raise the estimated $1million per year needed to run the program. For once, judging

by their website, they intend to do it properly with a great deal of effort going into the

communications protocols of the messages themselves.

Laser Communication

And that is where we were until June 2017 and a paper iii written by Michael Hippke

examining the possible role of using the gravitational lensing effect of our sun to amplify

laser signals across interstellar distances. The surprising conclusion was that using optical

wavelength lasers and mirrors of only one-meter diameter, data could potentially be

transferred at a megabit per second rates using around one Watt of power over 4 light years.

This, to put it mildly, is spectacular especially since the receiving technology is potentially

within our ability, assuming we could locate a telescope some 600 astronomical units (AU)

from the sun. Unfortunately, our most distant spacecraft is Voyager 1 at about 140AU. He

also showed in a previous paper that the data rate drops to bits per second per watt using

a 39-meter receiving telescope and no lensing.

However, if we turn that around and assume that ETI has superior technology to us and

can implement suitable receivers, then to contact them we need only very modest laser

transmitters. Ones that are well within the budget of hobbyists and amateur astronomers.

The advantage of using lasers is more apparent, especially for amateurs, when we

consider beam divergence. Lasers can quite easily achieve divergences of less than one

milli-radian (mrad) which corresponds to one meter per kilometer. To achieve that with

microwaves at (say) 6GHz would necessitate a transmitter dish of approximately 65

meters diameter. A very expensive piece of radio astronomy kit. This also means that

power levels can be significantly less than would be needed for radio communication.

Nevertheless, there are serious caveats. These mostly concern the location and type of

transmitter. For example, to limit beam spread Hippke assumes a one-meter diameter

mirror and a beam spread of considerably less than a milliradian, so we are going to

assume a rather larger receiver at the ETI end in order to minimize beam requirements at

our end.

A much more serious problem is that the mirrors have to be aligned with each other.

Specifically, the transmitter should be relatively stationary in space, and not on a rotating

planet which is in turn circling its sun. If the latter is the case, the receiver will probably

only align at fixed intervals lasting no more than a few tens of milliseconds unless very

precise aiming technology is used.

However, there is a more interesting search regime far better suited to low budget than

attempting interstellar communications.

Exploratory Scenario

This is a METI search that will be primarily focused on contact with self-replicating Von

Neumann (VN) style interstellar probes iv. There are strong arguments that over a time scale

of the order of thousands to a few million years, these are the best way of exploring the

galaxy by any intelligent technology-oriented species. Once one of these devices arrives in

a solar system it sets about creating sufficient infrastructure to both report back to its home

system (as well as possible siblings) and create a replica of itself for onward launch to

multiple other stars. Reasonably conservative capabilities are as follows:

They are very likely to outlive the species that sent them

They would almost certainly embody an artificial intelligence (AI) at or beyond

Human level capability

Human level capability They would be self-repairing and possibly have a lifetime in the tens of millions of

years, barring accidents

years, barring accidents They could exist around just about every star in the galaxy within ten million years

Using the kind of technology we might reasonably expect to appear sometime in the next

century or two, such as placing observatories at the gravitational focal point of our sun,

some 600AU out, we could view details on nearby extra-solar planets. And anyone out

there could do the same to us. As a consequence, Earth has likely been an interesting

place to view for the past 300 million years or so with its oxygen atmosphere and

vegetation. And vastly more interesting in the past 10,000 years since rectangular shapes

started appearing in the form of cities and fields. Rectangles generally do not occur

naturally. Then in the past 300 years, the atmosphere started to show signs of industrial

pollution followed 200 years later by radio and TV signals, intense radar pulses and the

unmistakable sign of nuclear bombs whose output peaked at around 1% of the total output

power of our sun.

If ETI exists, or has existed, within a few thousand light years there is a strong possibility

that their probes are already here, and have been for a considerable length of time.

This leads to a number of massively simplifying assumptions, again quite reasonable given

the scenario above. These are:

Since we are now searching within our solar system power levels can be vastly

reduced.

reduced. Message transit times, in both directions, are no more than a few hours maximum

and possible only seconds.

and possible only seconds. Any intelligent VN probe that has been examining Earth will have been monitoring

our technological development and radio/TV output. As a consequence, it will almost

certainly understand all the major languages both written and spoken as well as our

communications protocols.

We need to consider beaming our messages at likely locations within our own solar

systems. For example, where would we place intelligent probes to wait out the ages and

watch developments on Earth? Among strong possibilities are the Lunar poles, Lunar

caverns which we now know exist v and the Lagrange points vi associated with Earth’s orbit,

particularly L4 and L5, where position can be held with little expenditure of energy. We

intend to beam laser messages to these points as part of the Zero State program.

But what messages? People have given much thought to creating a communications

system that can be decoded by ETI, as mentioned above with METI. However, we contend

that the answer is simple – we use English, and code in simple ASCII.

What has been lacking from Earth is a specific invitation to communicate or visit. It is this

that forms the core of our project.

How Far Can We Be Seen?

Suppose we want to do the crudest communication system possible – a laser doing Morse

Code. To the unaided Human eye, how far away could we see the beam? This depends on

several factors:

Beam Divergence

Beam power

Wavelength

Eye sensitivity

Taking these in turn…

The power we will assume to be one Watt since this level of power is quite economical,

and the wavelength to be either 532nm or 520nm, the latter being a pure diode output, not

frequency doubled.

It is also the approximate wavelength where the eye peaks in sensitivity, and in our project

is partly chosen for this reason. We could have gone for high power infrared in the tens of

watts, or maybe towards the blue/violent end of the spectrum. However, green is not only

easier and safer to work with, being highly visible, but is quite photogenic. From a safety

point of view you seriously do not want an invisible beam of blinding intensity sweeping

about. That would also be more difficult to aim and focus.

So we have an intensity of approximately one Watt per square meter at a distance of one

kilometer, with the intensity dropping off as the square of the distance. At 2 km we have

0.25W per square meter, and so on.

Finally, what is the maximum sensitivity of the dark adapted Human eye? It appears to be

about 100 photons per secondvii, but for the sake of argument we shall assume a level ten

times lower, or 1000 photons per second in a dark adapted eye whose aperture is 100

square millimeters. That gives us a minimum intensity requirement of 10^7 photons per

square meter per second. With each green photon carrying an energy of approximately

3.5e-19 Joules we get a required power density of 3.5e-12 Watts.

So, how far can our 1W green laser with a divergence of 1 mRad travel before we hit that

value? The answer is a little over 500,000km – further than the Earth-Moon separation. By

the time the beam gets there it will be illuminating a circle some 500km in diameter.

If we are looking back from the Moon via a modest telescope such a beam would appear

as a bright flickering point of monochromatic light. Even a 100mm diameter telescope

would improve visibility by more than 100 times.

If we wish to improve the numbers there are certain things we can do. If we increase the

power, it scales linearly in intensity at a given distance. If we increase the collimation to

(say) 0.5mRad the intensity quadruples, but the illuminated area decreases 75% as the

spot size halves.

Proof of Principle Equipment – Stage 1

The setup described below is an absolute minimum and has been put together simply to

illustrate how easy it can be, and how cheap.

WARNING! – The lasers described should be treated like a loaded firearms with the safety

off. Anyone around it should have eye protection goggles when it is operating or being

worked on. If it sweeps across your eyes it will cause instant permanent blindness. It can

also start fires. These are Class 4viii. You should also assume they will cause eye damage

out to 1km if the beam is not expanded.

The basic equipment list is relatively straightforward – example sources are UK but may

be obtained cheaply elsewhere:

• A computer with a USB interface

• A terminal emulator program such as Realtermix or similar

• A USB to TTL converter cable x

• A battery based stabilized power supply for the laser module

• High power laser module 1 Watt or greater xi

• A telescopic rifle sight (scope)

• A GOTO telescope

• Various Weaver rail fittings and adapters

• A low power sighting laser

• Laser safety goggles

Less straightforward is any metalwork or optical interfacing of the laser module, however,

the use of a scope with integral Weaver rails simplifies things considerably. The scope

needs an attachment to the GOTO telescope, and the rest of the equipment attaches to

the scope.

The next problem is that of holding the telescopic sight on target, which is where a

motorized equatorial mount, or GOTO mount is required. Both will compensate for the

rotation of the Earth and hold on a previously acquired target with accuracy much better

than the assumed mrad (for scale, the diameter of the full moon in the sky is about 9 mrad)

A GOTO telescope is fully computerized and will automatically move to designated targets

either by name or celestial coordinates.

The first step is to securely attach the laser module co-axially to the telescopic sight so

that you can see through the scope where the beam strikes. To do this you need a

deserted area where you can aim the beam at a target some 100 meters distant and

adjust optics and mechanical attachment so that the beam is aligned and parallel to the

cross-hairs.

At this point you can examine the beam quality. With modules such as the above it will not

be around spot. More likely it will be an image of the emission diode structure. Not ideal,

but good enough for now.

The pictures below show the scope, sighting laser and Class 4 laser complete with a DIN

rail that is used to attach all this to the telescope. In this instance, it is mounted on a

camera tripod for alignment work.



Illustration 1: Left Side of the Lasers and Optics



Illustration 2: Right Side of the Lasers and Optics

Illustration 3: Front view of the Lasers and Optics

Proof of Principle Equipment – Stage 2

So, how do we improve upon this? Well, the answer is obvious. Rather than relying on the

beam straight from the laser passing through the supplied focusing lens we use custom

optics to expand and collimate the beam. This at once gives us better control over the

divergence and by expanding the beam makes it somewhat safer by reducing areal power

density.

Next, we add a receiver to the telescope eyepiece.

This consists of a bandpass optical filter centered at the wavelength of the laser

transmitter. Again, this assumes that any VN probe is quite capable of transmitting on the

received wavelength at a power level comparable to, or greater than, our own.

The necessary electronics, including a high sensitivity photodiode, is not prohibitively

expensive.

Final equipment and Message Format

The above describes a minimal setup both from a cost and capability point of view. A more

suitable laser system would be one using a far higher power, and a receiving telescope

with a mirror at least 200mm diameter (8” reflector).

The choice of lasers is wide, but if we limit the choice to minimize atmospheric absorption

and costly optics that leaves visible and near infrared (NIR).

One possibility stands out. That is a Q-switched Nd:YAG laserxii, with around a 200W continuous,

1MW pulsed, output at 1064nm normally used as an industrial cutter. The

output can if necessary be frequency doubled to 532nm green but with loss of power.

This should be able to communicate with its equivalent to a distance beyond the orbit of

Jupiter.

Such systems typically cost under $15k, although the optics, beam guides and alignment

equipment will add significantly to this price. Needless to say, such a beam in free space is

spectacularly dangerous if mishandled.

Additional requirements will include an electric generator or power source in the kilowatt

region, water cooling and a trailer if the equipment has to be moved to an open air site

before use.

All together we intend to budget around $30,000 for the hardware. Location is as yet

undecided, although a strong possibility is Provo, Utah in the USA given its clear skies and

weather. Britain is a poor second in this respect. Plus, we may locate it at the

TransHumanist Housexiii available to Zero State House Adar. However, much depends on

location and local laws.

The message format with Q-switched pulses would be somewhat different from the

existing setup. The coding would be provided by the timing between the pulses, or by the

timing between successive pulse trains. Again, data rate would be low because we are not

attempting to communicate anything complex. Just attract attention.

Zero State seeks collaboration from like-minded engineers and scientists, and sponsorship

for this project, which after initial hardware costs are met should incur very low running

costs.

Ethical Considerations

On 13 February 2015, scientists (including Geoffrey Marcy, Seth Shostak, Frank Drake,

Elon Musk and David Brin) at a convention of the American Association for the

Advancement of Science, discussed Active SETI and whether transmitting a message to

possible intelligent extraterrestrials in the Cosmos was a good idea; one result was a

statement, (which was not signed by Seth Shostak or Frank Drake), that a “worldwide

scientific, political and humanitarian discussion must occur before any message is sent” xiv

.

We believe that this is not, and should not be the case for local METI. We should issue the

invitation to communicate now. It is beyond reasonable doubt that if any ETI capable of

receiving these messages lies within our solar system or a few tens of light years, then

they already know of our existence.

References:

i https://en.wikipedia.org/wiki/List_of_interstellar_radio_messages

ii http://meti.org/mission

iii https://arxiv.org/abs/1706.05570

iv Journal of the British Interplanetary Society, Vol.33, pp. 251-264 1980

v https://en.wikipedia.org/wiki/Lunar_lava_tube

vi https://en.wikipedia.org/wiki/Lagrangian_point

vii S. Hecht, S. Schlaer and M.H. Pirenne, “Energy, Quanta and vision.” Journal of the Optical Society of America, 38, 196-208

(1942)

viii http://www.lasersafetyfacts.com/4/

ix https://sourceforge.net/projects/realterm/

x https://www.maplin.co.uk/p/usb-to-ttl-serial-cable-cable-n74de

xi http://odicforce.com/epages/05c54fb6-7778-4d36-adc0-0098b2af7c4e.sf/en_GB/?ObjectPath=/Shops/05c54fb6-

7778-4d36-adc0-0098b2af7c4e/Products/OFL365-5-TTL

xii https://en.wikipedia.org/wiki/Nd:YAG_laser

xiii https://hpluspedia.org/wiki/Transhuman_House

xiv https://en.wikipedia.org/wiki/List_of_interstellar_radio_messages