SP-419 SETI: The Search for Extraterrestrial Intelligence

 

[211] COMPLEMENTARY DOCUMENT 11

THE SOVIET CETI REPORT

 

[212] blank page

 

[213] THE SOVIET CETI REPORT

 

Researchers in the USSR have long been interested in the detection of radio signals originating from extraterrestrial intelligence. The Soviet have named their program CETI or Communication with Extraterrestrial Intelligence. The acronym SETI (Search for Extraterrestrial Intelligence) was adopted by the Workshop and by the Ames Research Center to differentiate our own efforts from those of the Soviet Union and to emphasize the search aspects of the proposed program.

The Soviet plans for their CETI efforts have been summarized in "The CETI Program," Sov. Astron., vol. 18, no. 5, March-April 1975, which has been reprinted here, in total, with permission of the American Institute of Physics, whose cooperation is gratefully acknowledged. This article was translated from "Scientific Council on the Radio-Astronomy Problem Area, Academy of Sciences of the USSR, Astron., Zh., 51, 1125-1132 (September-October 1974)."

 

[214] The CETI program

 

Scientific Council on the Radio-Astronomy Problem Area, Academy of Sciences of the USSR Astron., Zh., 51 , 1125-1132 (September-October 1974)

 

In March 1974 the Board of the Scientific Council on the Radio Astronomy Problem Area, Academy of Sciences of the USSR, considered and approved a Research Program on the Problem of Communication with Extraterrestrial Civilizations. The Program was developed by the Search for Cosmic Signals of Artificial Origin section of the Council on Radio Astronomy, on the basis of recommendations made at the Soviet National Conference on the Problem of Communication with Extraterrestrial Civilizations held at the Byurakan Astrophysical Observatory in Armenia in May 1964, and the Soviet-American CETI conference held at Byurakan in September 1971. The projected program was reported to the 7th Soviet National Conference on Radio Astronomy, which convened at Gor'kii in 1972.

The program as outlined below is here published in detail with minor abridgments.

 

RESEARCH PROGRAM ON THE PROBLEM OF COMMUNICATION WITH EXTRATERRESTRIAL CIVILIZATIONS

 

PART 1.

INTRODUCTION

1. Formulation of the Problem

2. Principal Fields of Research on the Problem of Extraterrestrial Civilizations

3. Principles for Developing a CETI Program

4. Organizing Arrangements

 

PART II. SEARCH FOR COSMIC SIGNALS OF ARTIFICIAL ORIGIN

1. Search for Sources and Selection by Preliminary Criteria

1.1. Radio Surveys of the Sky

1.2. Selection of Sources by Angular Size and Investigation of Their Spatial Structure

1.3. Investigation of Selected Galactic and Extragalactic Objects

1.4. Search for Signals from Stars in the Immediate Solar Neighborhood

1.5. Search for Signals from Galaxies in the Local Group

1.6. Search for Signals with a Detection System Covering the Entire Sky

1.7. Search for Probes

1.8. Measurement of Cosmic Background Radiation in the Wavelength Range 20,µ-1 mm

1.9. Investigation of Absorption and Phase Transparency of the Interstellar Medium in the Range 20,µ-1 cm

1.1O. Sky Surveys in the Range 10 µ - 1 mm

1.11. Search for Infrared Excesses in Stars of Suitable Spectral Type

[215] 2. Investigation of the Radiation Structure of the Selected Objects and Methods of Analysis for Identifying Sources Suspected of Being Artificial

3. Instrumentation Projects for Seeking Radio Signals from Extraterrestrial Civilizations

 

PART III. DECODING OF SIGNALS

PART IV. CONCLUSION

 

PART I

INTRODUCTION

 

1. FORMULATION OF THE PROBLEM

Over the past few years the scientific community has begun to show increasing interest the problem of contacts with extraterrestrial civilizations.

The question of whether intelligent life exists elsewhere in the universe in some form or another has been posed in every era throughout the development of science. Yet it is only now, thanks to major advances in astronomy, biology, cybernetics, information theory, radiophysics and radio engineering, and the conquest of space, that it has become possible for the first time to progress from purely speculative arguments on this subject to systematic scientific investigation. The achievements of modern science have led to a deeper understanding of the fundamental aspects of the problem. The hope of establishing communication with extraterrestrial civilizations today rests on a scientific basis. This endeavor has come to be called the CETI problem (Communication with Extraterrestrial Intelligence).

Advances in radiophysics and radio engineering have played a decisive role here. Modern radio techniques would enable signals transmitted across interstellar distances to be detected and recorded. Thus it is already feasible to plan research and experiments for detecting signals from extraterrestrial civilizations. From the very outset such investigations can and should rest on the achievements of radio astronomy, in which much experience has now been gained in identifying and analyzing sources of cosmic radio emission. Progress in infrared and optical astronomy will also make a vital contribution, in conjunction with rapidly advancing developments in laser technology. Also of great value for the practical organization of a CETI program will be the achievements of information theory and other branches of cybernetics, which offer general methods for studying problems of information transfer, as well as such areas of mathematics as game theory, the theory of tactics, and searching theory. With these disciplines as a basis a special CETI strategy can be devised. At the present time, then, the technical ways and means are available for practical steps to be taken in the CETI field.

The possibilities of radio communication with extraterrestrial civilizations were first analyzed by G. Cocconi and P. Morrison (United States, 1959), who showed that under certain conditions signals could be received from extraterrestrial civilizations with the radio technology [216] available at that time. In 1960 the first practical steps were taken in the United States to look for such signals at 21-cm wavelength (F. D. Drake, Project Ozma). At present a more comprehensive signal search program is under way at the U.S. National Radio Astronomy Observatory (Project Ozma 2), and a Project Cyclops has been studied1 by Stanford University in collaboration with the Hewlett-Packard Company; it would ultimately cost tens of billions of dollars. In the Soviet Union, work comparable to Project Ozma is being carried out at the Gor'kii Radiophysics' Institute.

These projects presuppose that extraterrestrial civilizations have a level of technological development analogous to our own. In this event one would anticipate discovery of monochromatic radiation similar to the radiation from ordinary transmitters on the earth.

In 1964 another signal search concept was put forward in the Soviet Union, whereby extraterrestrial civilizations would be expected to have a very high level of development. Several radio-astronomical criteria for an artificial source were formulated on the basis of this concept. Experiments were subsequently devised at the Shternberg Astronomical Institute of Moscow University and at the Institute for Space Research, Academy of Sciences of the USSR, for the purpose of examining a number of peculiar sources in order to see whether they might satisfy the proposed criteria.

Searches for pulsed signals from space have recently been undertaken in the Soviet Union at the Gor'kii Radiophysics Institute, the Institute for Space Research, and the Shternberg Astronomical Institute. Various aspects of the CETI problem are being studied individually not only at these institutions, but by the Council on Radio Astronomy of the Academy of Sciences of the USSR, the Moscow Power Institute, the All-Union Electrical Engineering Correspondence Institute of Communications, the Russian Language Institute, Academy of Sciences of the USSR, and elsewhere.

One other approach, entailing a search for signs of astro-engineering activity by highly developed extraterrestrial civilizations (in particular, from surveys of infrared radiation), has been suggested by F. J. Dyson (U.S.).

In 1960, R. N. Bracewell (U.S.) made the important suggestion that a search ought to be conducted for radio signals from space probes, which even now might conceivably be present in the solar system.

The U.S. National Academy of Sciences held a special conference in 1962 on the problem of communication with extraterrestrial civilizations.

Major contributions toward formulating and discussing the CETI problem have been made by the Soviet National Conference on the Problem of Communication with Extraterrestrial Civilizations2 (Byurakan, 1964) and the Soviet-American CETI conference3 (Byurakan, 1971). Topics pertaining to the CETI problem4 have been considered at various other conferences and meetings both in the Soviet Union and abroad.

[217] The present program has been developed from recommendations by the 1964 Soviet National Conference, the 1971 International Conference, and the 7th Soviet National Conference on Radio Astronomy in 1972.

 

2. PRINCIPAL FIELDS OF RESEARCH ON THE PROBLEM OF EXTRATERRESTRIAL CIVILIZATIONS

The problem of extraterrestrial civilizations comprises an intricate complex of topics in philosophy and sociology as well as natural science. Within the domain of this broad interdisciplinary problem a narrower area is to be considered: the CETI problem. This represents a separate task confronting science and technology, including theoretical and experimental work on searching for extraterrestrial civilizations, as well as modeling the basic links in the CETI system. But a successful result will depend on resolving a number of fundamental questions that form the heart of the extraterrestrial-civilization problem.

It is convenient to distinguish two groups of problems for planning the investigations.

Group A. Fundamental Problems of Extraterrestrial Civilizations Involving Communication

1. Astronomical matters Cosmogony . Discovery of planets, planetlike bodies, and congealed stars. Sky surveys conducted in various parts of the electromagnetic spectrum. Examination of some peculiar sources. Investigation of organic compounds in cosmic objects.

2. Life . A more precise definition of the concept of "life." Possible existence of nonprotein life forms. Origin of life on the earth; possible alternative origins of life on other cosmic bodies, and in interplanetary and interstellar space. Exobiology. Laws of biological evolution and their exobiological generalization.

3. Intelligence and intelligent systems . Refinement of the concept of "intelligence" or "reasoning." Models of an intelligent system. Theory of complex self-organizing systems. Information contacts in complex systems. Symbolic systems; language. Problems in the theories of knowledge and reflection; construction of models.

4. Mankind . Analysis of the laws governing the development of civilization on the earth. Special characteristics of the rise and development of different civilizations worldwide. Forecasting. Development and mastery of the space environment.

5. Information transfer . Optimum methods of communicating information.

 

These topics are being dealt with independently of the CETI problem itself and therefore are not considered in the present program (except for the sky surveys).

 

Group B. Problems Pertaining Directly to CETI

1. Aspects of the theory of cosmic civilizations.

[218] 2. Contacts between cosmic civilizations; possible types of contact and their consequences.

3. Modes of intercourse between cosmic civilizations . Linguistic media to be devised for establishing information contact between "intelligent" systems.

4. Procedures and scientific-technological basis for seeking signals from extraterrestrial civilizations. Development of signal search techniques. Influence of the cosmic medium on exchange of signals between civilizations. Choice of optimum electromagnetic wavelength range. Criteria for identifying signals from extraterrestrial civilizations. Characteristics of "call letters." Design of search instrumentation. Modeling of individual links in the CETI system. Computer modeling.

5. Searches for signals from extraterrestrial civilizations.

6. Deciphering of signals.

7. Searches for astro-engineering activity of extraterrestrial civilizations. Although the main emphasis in this program is given to efforts to find signals in the radio range and to the development of suitable techniques and equipment, a more complete program should also include planning with regard to other aspects of the CETI problem.

 

3. PRINCIPLES FOR DEVELOPING A CETI PROGRAM

The present program has been drawn up on the basis of the following initial propositions.

1. Efforts to detect extraterrestrial civilizations should proceed smoothly and systematically, and should extend over a prolonged period of time. [he program is oriented in this direction from the very outset. It would be a great mistake to build a program in contemplation of rapid and easy success.

2. Investigations should be based on a specially devised program (or group of programs) which would be revised and perfected as time passes. The program should provide every opportunity to take advantage of existing technology (radio telescopes, antenna systems and associated instrumentation), and should also envision the development of specialized techniques and equipment for coping with the CETI problems.

3. The program will recognize that astrophysical information will be acquired as a byproduct of the search for signals from extraterrestrial civilizations. When actual investigations are undertaken it will be necessary to analyze carefully the question of what astrophysical applications can be pursued during search activities.

4. In view of the uncertainty in our a priori knowledge as to the character of signals extraterrestrial civilizations, the program should entail parallel studies in several directions.

 

[219] 4. ORGANIZING ARRANGEMENTS

1. Matters relating directly to CETI (Group B) are currently being worked on in a ran fashion; such research is not being planned properly.

But the problem has now reached a state requiring more earnest organizational efforts. If the research is to proceed successfully one cannot avoid creating a number of organizations and institutions to deal with appropriate branches of the problem; these should be fully staffed and furnished with equipment and materials. The design of search instrumentation and detection systems calls for organizational enterprise on an industrial scale. Henceforth all scientific and engineering work in the field of searches for signals from extraterrestrial civilizations ought to be placed under the guidance of a pilot organization.

2. Matters pertaining to Group A topics are being pursued independently of the CETI problem, and often quite separately from one another. In the very near future thought should be given to ways in which these studies can be coordinated and purposefully integrated into the CETI plane.

 

PART II

SEARCH FOR COSMIC SIGNALS OF ARTIFICIAL ORIGIN

 

Initial Premises

The program for seeking signals from other civilizations rests on the two assumptions mentioned above as to their level of development:

1. A level of technological development and, in particular, the technology of radio communications comparable to that on the earth.

2. A level of technological development and modes of communication far more advanced than our own.

For the first case, from considerations of power capability, signals should be sought primarily from nearby stars. The character of the signals might be analogous to the signals of transmitters on the earth; that is, narrow-band signals may be anticipated (it would then be possible to generate special call signals distributed over a wide frequency range so as to facilitate searches with respect to frequency).

In the second case the detection problem would be considerably simpler because of the much greater power capacity. However, uncertainty might arise both in the coordinates of the source (as such civilizations would not necessarily be associated with stars) and in the character of the signal. Presumably the signals of highly developed extraterrestrial civilizations would most likely be wide-band. Although this circumstance would ease the search in frequency, it would [220] require the formulation of definite criteria enabling such signals to be distinguished from wideband radiation of natural origin. Regions that might be worth searching could be located near the nuclei of our own and other galaxies, or associated with certain peculiar sources.

This program presupposes the need for parallel research at both the levels I and 2 above, with no a priori assumptions as to the character of the signals. Thus the problem of methodically searching for signals from extraterrestrial civilizations will include the following aspects: a) a search for sources of radiation with respect to direction, frequency, and time; b) an analysis of the structural properties of the radiation; c) determination of its artificial nature.

Accordingly, this program provides for the following steps in research activity:

1. Search for and selection of sources according to preliminary criteria.

2. Examination of the radiation structure of the sources selected.

3. Analysis of the results obtained, in an effort to identify artificial sources.

 

1. SEARCH FOR SOURCES AND SELECTION BY PRELIMINARY CRITERIA

This step entails both conducting sky surveys in the optimum wavelength range from the CETI standpoint followed by source selection according to preliminary criteria, and analysis of sources already known. The result should be the compilation of a catalog of objects promising from the CETI standpoint and warranting further study in more detail.

As criteria for preliminary source selection, the following may be used and are adopted in this program: small angular size. distinctive spatial structure of the source; distinctive spectrum (special behavior of the energy distribution, presence of narrow-band features. special shapes in the spectrum such as rectangular features, and so on); unusual character of time variability; distinctive polarization properties (such as a regular alternation of left- and right-circular polarization in the spectrum). As astrophysics progresses and new data emerge, this list could be refined or revised.

 

1.1. Radio Surveys of the Sky

Frequencies . Since a CETI signal might be restricted in its spectrum, in order to discriminate promising sources the surveys should fully cover the entire shortwave portion of the radio" astronomy range (frequencies of 1-100 GHz), which according to present indications is the most advantageous region for CETI purposes.

In the initial phase surveys could be made at discrete frequencies for which appropriate instrumentation is already available or is under development.

Antennas . The principal antennas for conducting surveys in the USSR could be the RATAN-600 (the periscopic part) in the wavelength range 0.8-2.1 cm, and the antenna for the millimeter range being developed at the Gor'kii Radiophysics Institute.

[221] Instrumentation . Radio receiving equipment for the surveys should include:

1. Continuum radiometers with delta f is approximately  0.1f and Tn  is approximately  100°K, equipped with facilities for magnetic-tape recording and with auxiliary output devices for the detection of information-carrying signals according to anticipated criteria.

2. Radiometric systems with as wide a band as possible (delta f is approximately  0.5f).

3. Spectral radiometers for surveys at the frequencies of individual radio lines, such as double lambda 21, 18, and 1.35 cm.

1.2. Selection of Sources by Angular Size and Investigation of Their Spatial Structure

a. Preliminary selection of sources with an angular size smaller than the antenna beam, and investigation of their spatial structure. No specialized equipment would be required.

b. Measurement of the angular (as well as the linear) size and spatial structure of sources by the interstellar-scintillation technique. This method affords the highest angular resolution. However, for surveys at wavelengths shorter than 10 cm or in the case of very close sources (R < 10 pc) the interferometer method is best. The radio telescopes may either by ground-based or stationed in space, permitting earth-earth, earth-space, and space-space baselines.

 

1.3. Investigation of Selected Galactic and Extragalactic Objects

On the basis of astrophysical evidence presently available, studies of the following objects would be of interest from the CETI standpoint: globular clusters, representing the oldest objects in our galaxy; the galactic center, a region containing 109 stars; the galaxies of the Local Group; certain nearby radio galaxies and quasars.

The aim of such investigations would be to discover anomalies in the radio emission of t objects from the point of view of the criteria given above.

Instrumentation. Antennas with an effective area greater than 1000 m2 should be used for most of the objects. It is recommended that the size, spatial structure, and radio variability be investigated by the scintillation technique with earth-earth, earth-space, and space-space baselines, using a radio telescope in space and others on the ground. Spectroscopic and polarimetric properties could be examined with the same equipment and with the RATAN-600 radio telescope.

This type of work is closely linked with the central problems of radio astronomy and can be carried out in the course of conventional radio-astronomical research.

 

1.4. Search for Signals from Stars in the Immediate Solar Neighborhood

It is proposed that individual nonvariable stars of suitable spectral type be observed. Initially the observations may be confined to monitoring all appropriate stars to a distance of 10-100 light years from the sun; eventually out to 1000 light years.

[222] If the monitoring extends over a period of several years, then in order to inspect all suitable stars within a radius of 100 light years with a single antenna operating continuously, the total observing time for each star would be about one hour, or no more than a few hours.

Antennas . For this survey it would be desirable to use several radio telescopes with an effective area of approximately  1000 m2. Observations could begin with smaller-sized telescopes.

The primary task in the initial phase of investigation would be to detect radio emission from stars, because the intrinsic radio emission of solar-type stars is weak. As for the kind of signals to be expected, it would be advisable to begin by searching for very simple signalspulsed, monochromatic, and the like. This program will impose corresponding requirements on the instrumentation.

In the future one might hope to search for signals by sending automated space probes to the nearest stars.

 

1.5. Search for Signals from Galaxies in the Local Group

Any search for signals from galaxies would enable an enormous number of stars (roughly 1010-1011) to be covered simultaneously. The nearest galaxies are of interest to us inasmuch as we might be of interest to them.

Since the number of objects is small, a continuous monitoring service could be organized, with observations extending over several years. The optimum wavelength range for each object can be made more definite by taking its background into consideration.

Antennas . For a continuous service, weakly directional antennas would be used with a beam covering the galaxy being observed math signs, Greek letter theta is approximately 1-3 degrees In addition, it would be desirable to employ larger antennas with an effective area of approximately 1000 m2 so that parts of galaxies could be investigated and repeated surveys made of each galaxy.

Instrumentation would be similar to that used in the search for signals from stars.

Special emphasis should be given to a search for pulsed signals (if they have a low averaged power not influencing the observed flux density of the galaxy, they could still have a high peak power, ensuring that Ps/Pn > 1) as well as monochromatic signals.

In studying galaxies with the aim of detecting signals from extraterrestrial civilizations, one will no doubt acquire information of astrophysical character pertaining to those galaxies.

 

1.6. Search for Signals with a Detection System Covering the Entire Sky

The detection system would here be designed for continual monitoring of the radiation of the whole sky in the optimum anticipated wavelength range. Such a system would enable transient sporadic signals coming from any direction to be recorded.

[223] Regular monitoring of the entire sky would require a network of stations located at different points on the globe or in space.

For stations placed on the earth, the number needed is determined by the condition that objects be simultaneously visible from at least two widely spaced stations (in order to discriminate local interference), so that at least four would be required altogether.

If stations are placed in space at a large distance from the earth, just two would be sufficient. The best plan would evidently be to put these stations in orbit around the moon, because when they pass behind the moon maximum suppression of terrestrial interference would be assured. One very promising location for a space station would be the Lagrangian point in the earth-moon system located beyond the moon.

Building a system of large directional radio telescopes to cover the whole sky would be a major undertaking financially. Thus at the outset we would propose that investigations be organized with nearly omnidirectional antennas that would record only the strongest signals. Subsequently the stations would be equipped with high-efficiency antennas, and the detection capability of the system could be raised gradually.

Frequencies . In due course the entire shortwave part of the radio-astronomy range should be examined. At present the search should be limited to discrete frequencies, using equipment now available or under development.

The main effort at first should be concentrated toward searches for sporadic pulsed signals. It would be advisable to begin this program by utilizing equipment that satisfies the following requirements:

The recording system should detect pulses lasting from 1 sec to 10-8 sec (with a choice of time constants differing by decade factors).

The equipment should be provided with a system for obtaining the dispersion measure for an approximate distance estimate of a source, and for discriminating terrestrial interference.

Observations should be controlled by the Time Service to a precision adequate for these measurements. A rough determination of the direction toward a source could be made from the lag in the signals at different stations.

Restrictions on the observing station . The principal requirement is a low noise level. Such stations will generally be located in regions difficult of access. Perhaps a full suppression of interference and elimination of the effects of the earth's atmosphere, as well as a more accurate determination of positions, will demand that some of the stations (at least two) be placed in space at a large distance from the earth.

[224] 1.7. Search for Probes

The possible discovery of probes sent from extraterrestrial civilizations and now located in the solar system or even in orbit around the earth warrants particular attention. To search for these rapidly moving objects the system of constant monitoring of the whole sky should be supplemented by specially designed radio direction-finding systems. Initially it would be possible to use existing installations intended for space communications and radar observations.

1.8. Measurement of Cosmic Background radiation in the Wavelength Range 20,u - 1 mm

Such measurements are needed to identify regions of minimum intensity and establish more accurately the optimum wavelength range for CETI purposes.

1.9. Investigation of Absorption and Phase Transparency of the Interstellar Medium in the Range 20 µ-1 mm

1.10. Sky Surveys in the Range 10, u- I mm

These surveys should be made in an effort to find objects associated with the engineering activity of extraterrestrial civilizations.

It is proposed that the sky be surveyed in this wavelength range and that the spectra of any objects detected be investigated.

1.11. Search for Infrared Excesses in Stars of Suitable Spectral Type

The purpose of this search would be to detect thermal radiation inherently emanating from large-scale works of engineering that may have been constructed in circumstellar space.

Telescopes and equipment for surveys 1.10 and 1.11 . A special mountain observatory should be built (so as to diminish losses of infrared radiation due to absorption by atmospheric water vapor) with a telescope about 2.5-3 m in diameter, and a specialized satellite carrying analogous instrumentation should be launched.

The receivers would be high-sensitivity bolometers with a selection of filters.

 

2. INVESTIGATION OF THE RADIATION STRUCTURE OF THE SELECTED OBJECTS AND METHODS OF ANALYSIS FOR IDENTIFYING SOURCES SUSPECTED OF BEING ARTIFICIAL

 

Each of the objects selected by the preliminary criteria will be investigated more carefully, and the research program will be modified in each instance depending on the results of the measurements obtained during the preliminary selection process.

[225] It would be desirable to conduct the analysis of cosmic radio waves along the following lines: examination of the shape of the radio spectrum as a whole for envelopes and carrier waves; inspection of the fine structure of the spectrum; recordings of rapid variability of the carrier and envelope spectra; establishment of the carrier and envelope distribution functions; determination of how the polarization (especially circular polarization) depends on the carrier frequency and on time; investigation of recordings obtained by analog and digital detection of carriers and envelopes at different frequencies and bands for both.

The data obtained in this manner would be used to identify sources suspected of being artificial. The methods and criteria for identification should include an analysis of all data from the standpoint both of astrophysics (comparison with known and possible natural astrophysical objects) and cybernetics and information theory (comparison of the statistical properties and structure of the signal with known or anticipated types of communication).

 

3. INSTRUMENTATION PROJECTS FOR SEEKING RADIO SIGNALS FROM EXTRATERRESTRIAL CIVILIZATIONS

To ensure that the avenues of research described above will be carried out, two instrumentation projects, CETI I and CETI 2, are proposed, as follows.

 

CETI 1 Project (1975-1985)

1. A ground-based system continuously monitoring the entire sky, comprising eight stations with nondirectional antennas supported by detection equipment capable of covering the whole optimum wavelength range.

2. A satellite system continuously monitoring the entire sky, comprising two space stations with nondirectional antennas and fully covering the optimum wavelength range.

3. A system of low-directivity antennas of 1-3° beamwidth for a continuous survey of nearby galaxies (subsection 1.5). These antennas might conveniently be located at the same stations where the sky is continuously monitored by nondirectional antennas.

 

CETI 2 Project (1980-1990)

1. A satellite system continuously monitoring the entire sky and equipped with antennas of large effective area.

2. A system of two widely spaced stations having large (effective area approximately1 km2) semirotatable antennas for synchronized reception, searches for signals from specific objects, and analysis of selected sources.

These instrumentation complexes could be used not only for CETI work but for a varies important astrophysical problems.

[226] In addition, individual parts of the program could be carried out with other radio telescopes in conjunction with the plans of radio-astronomy institutions (sky surveys, investigations of peculiar sources, and so on).

 

PART III

DECODING OF SIGNALS

 

One of the most important problems in need of solution for CETI purposes is to work out deciphering techniques specifically applicable to extraterrestrial communications (in the absence of any a priori information as to the language, method of encoding, and character os the signals). Within the present program a leading role should be assigned to logically formal deciphering techniques, comprising algorithms that can be implemented only by computer, and enabling a given linguistic entity to be designated according to a maximum of special "estimator" functions computed from counts made on the test being analyzed. The decoding procedure for signals from extraterrestrial civilizations that is to be developed as part of this program may be broken down into several steps.

1. Preliminary analysis of signals . In this step the alphabet of the elementary signals (messages) would be established.

2. Determination of type of text language organization . Three types of organization are presumably possible: pictorial (image transmission), linguistic (analogous to the structure of languages on the earth), and formalized (as with logical computer languages or algorithms).

3. Disclosure of grammatical system of the language . The properties of the test explained by the internal structure of the language would be ascertained at this stage, that is, the parametrization of the frames and alphabetic gradations used to express model languages. The grammar of a humanoid language would be determined, or for formalized systems, the axioms and rules of construction and derivation.

4. Disclosure of the semantics of texts under investigation .

5. Development of methods for translating the decoded language into familiar languages . This step would, in particular, encompass techniques for automatic compilation of bilingual dictionaries and structural correspondence lexicons.

The development of signal decoding techniques is closely related to research on image recognition, automatic classification and encoding (for example, some of the algorithms worked out in the decipherment analysis might be applied to study the structure of branches of the national economy), and work in the area of computer translation and automated abstracting.

 

PART IV

CONCLUSION

 

[227] Even in their initial stage investigations of the CETI problem can be of important cognitive and applied value, and can serve as a source of useful information and a stimulus in many fields of science and technology.

This working program, which includes experimental and theoretical projects of immediate concern, is provisionally directed toward the next 10-15 years. It should form part of a more complete program taking the long view, and it also offers a basis for developing specialized, detailed programs in particular areas of research that fall within the scope of the CETI problem.

Continual revision and improvement should be made in the program as data are accumulated, in all fields pertaining to CETI and as individual search programs are conducted.

 

REFERENCES

 

1 Project Cyclops: A Design Study of a System for Detecting Extraterrestrial intelligent Life (NASA-CR-114445), Stanford Univ. and NASA Ames Res. Cen., Moffett Field, Calif. (1972).

2 G. M. Tovmasyan, ed., Extraterrestrial Civilizations (Proc. Byurkan conf., May 1964), Armenian Acad. Sci. Press (1965) [Israel Program Sci. Transl., No. 1823 (1967)].

3 C. Sagan, ed., Communication with Extraterrestrial Intelligence (CETI) (Proc. Byurakan conf., Sept . 1971), MIT Press (1973).

4 S. A. Kaplan, ea., Extraterrestrial Civilizations: Problems of Interstellar Communication, Nauka, Moscow (1969) [NASA TT F-631 (1971)] .