VLSI processors for signal detection in SETI

The objective of the Search for Extraterrestrial Intelligence (SETI) is to locate an artificially created signal coming from a distant star. This is done in two steps: (1) spectral analysis of an incoming radio frequency band, and (2) pattern detection for narrow-band signals. Both steps are computationally expensive and require the development of specially designed computer architectures. To reduce the size and cost of the SETI signal detection machine, two custom VLSI chips are under development. The first chip, the SETI DSP Engine, is used in the spectrum analyzer and is specially designed to compute Discrete Fourier Transforms (DFTs). It is a high-speed arithmetic processor that has two adders, one multiplier-accumulator, and three four-port memories. The second chip is a new type of Content-Addressable Memory. It is the heart of an associative processor that is used for pattern detection. Both chips incorporate many innovative circuits and architectural features.     

Frequency management and SETI: threats to SETI observations in the 1–3 GHz band

The nature of a SETI search makes observations uniquely vulnerable to radio frequency interference because the frequency of a possible ETI signal is unknown. Sensitive radio telescopes, sophisticated software and enhanced signal detection equipment are employed to detect faint signals in the 1–3 GHz frequency range. Frequency management at SETI occurs within a policy environment of the ITU spectrum allocation process. Increased demand by commercial satellite services for access to spectrum adjacent to bandwidth allocated to radio astronomy creates severe international and domestic pressures on SETI observations. Strategies for addressing the RFI problem at the international level will be discussed that include a contingency ITU allocation plan for exclusive use of a particular frequency range by SETI in the event a signal is detected. The lunar farside is, by international agreement, a radio quiet zone for use by radio astronomers. Protected from most human-generated emissions, a SETI radio telescope array on the lunar farside would provide reliable data with minimum interference.     

Analysis of a crossed Bragg cell acousto-optical spectrometer for SETI

The search for radio signals from extraterrestrial intelligent beings (SETI) requires the use of large instantaneous bandwidth (500 MHz) and high resolution (20 Hz) spectrometers. Digital systems with a high degree of modularity can be used to provide this capability, and this method has been widely discussed. Another technique for meeting the SETI requirement is to use a crossed Bragg cell spectrometer as described by Psaltis and Casasent. This technique makes use of the Folded Spectrum concept, introduced by Thomas. The Folded Spectrum is a 2-D Fourier Transform of a raster scanned 1-D signal. It is directly related to the long 1-D spectrum of the original signal and is ideally suited for optical signal processing. The folded spectrum technique has received little attention to date, primarily because early systems made use of photographic film which are unsuitable for the real time data analysis and voluminous data requirements of SETI. An analysis of the crossed Bragg cell spectrometer is presented as a method to achieve the spectral processing requirements for SETI. Systematic noise contributions unique to the Bragg cell system will be discussed.     

Detection of antipodal signalling and its application to wideband SETI

The SETI community is becoming increasingly interested in extending its searches to include wideband signals, such as information-bearing beacons. However, prior to discovery of a target signal, a SETI receiver has no knowledge of the signal parameters (bandwidth, carrier frequency, modulation type, etc.) and so detection can be very challenging, especially at low signal-to-noise ratios. However, this paper shows by example that there exist signal classes and corresponding detection methods that permit straightforward discovery of wideband signals of unknown structure. The example given is a form of binary antipodal signalling that utilises spread-spectrum modulation, which offers benefits to the receiver in terms of immunity to noise/interference and ease of detection. The proposed detection method is a ‘symbol-wise’ autocorrelation process that takes advantage of the cyclostationarity property of modulated signals. Detection sensitivity is suboptimal in comparison with what is possible if the target signal structure is known. However, this deficit can be overcome by processing longer timespans of signal, providing scope for detection at extremely low signal-to-noise ratios. It is postulated that antipodal signalling represents an attractive option for interstellar beacons because it is both power efficient and there exists a simple complementary detection method not requiring explicit coordination between the transmitter and receiver. This in turn suggests there is a case for extending future SETI searches to include this class of signal.     

The lure of local SETI: Fifty years of field experiments

With the commemoration in October 2007 of the Sputnik launch, space exploration celebrated its 50th anniversary. Despite impressive technological and scientific achievements the fascination for space has weakened during the last decades. One contributing factor has been the gradual disappearance of mankind's hope of discovering extraterrestrial life within its close neighbourhood. In striking contrast and since the middle of the 20th century, a non-negligible proportion of the population have already concluded that intelligent beings from other worlds do exist and visit Earth through space vehicles popularly called Unidentified Flying Objects (UFOs). In light of the continuous public interest for the UFO enigma symbolized by the recent widely diffused media announcements on the release of French and English governmental files; and considering the approach of broadening the strategies of the “Active SETI” approach and the existence of a rich multi-disciplinary UFO documentation of potential interest for SETI; this paper describes some past scientific attempts to demonstrate the physical reality of the phenomena and potentially the presence on Earth of probes of extraterrestrial origin. Details of the different instrumented field studies deployed by scientists and organizations during the period 1950–1990 in the USA, Canada and Europe are provided. In conclusion it will be argued that while continuing the current radio/optical SETI searches, there is the necessity to maintain sustaining attention to the topic of anomalous aerospace phenomena and to develop new rigorous research approaches.     

The first SETI observations with the Allen telescope array

The Search for ExtraTerrestrial Intelligence (SETI) finally has its own full-time telescope. The Allen telescope array (ATA) in Northern California was dedicated on October 11, 2007. This array, which will eventually be composed of 350 small radio antennas, each 6.1 m in diameter, is being built as a partnership between the SETI Institute and the University of California Radio Astronomy Laboratory. Last October, Paul G. Allen (who provided the funds for the technology development and the first phase of array construction) pushed a silver button and all 42 antennas of the current ATA-42 slewed to point in the direction of the distant galaxy M81. Specialized electronic backend detectors attached to the ATA began making a radio map of that galaxy and simultaneously began SETI observations of HIP48573, a G5V star near M81 on the sky and a distance of 264 light years from Earth. The Allen telescope array will greatly improve the speed of conducting SETI searches over the next few decades, and it will allow a suite of different search strategies to be undertaken. This paper summarizes some of the earliest SETI observations from the array, and describes the search strategies currently being planned.     

Space missions for SETI.

Radio Telescopes for SETI searches are less demanding than general purpose astronomical radio telescopes. This provides an opportunity to exploit economical approaches in designing SETI systems. Radio Telescopes in low Earth orbit offer no discernible advantages to SETI; indeed, they probably would perform more poorly than a telescope in any other location. Telescopes in geosynchronous orbits would be sufficiently far from Earth to mitigate greatly the deleterious effect of human radio transmissions. Telescopes on the far side of the moon would be superb both from a radio interference standpoint, and from a civil engineering standpoint. Single-reflector telescopes as large as 50 kilometers in diameter could be constructed with conventional materials. However, their costs appear prohibitive. The asteroid belt and the outer solar system are unpromising places to place a large radio telescope. Perhaps the ultimate radio telescope would utilize the sun as a gravitational lens, focusing radiation on free-flying 10-meter class or possibly larger radio telescopes located at distances of the order of 1000 A.U. from the sun. Such a combination has an energy collecting area at 10 centimeters wavelength equivalent to that of a radio telescope about 11 kilometers in diameter, or of the order of 3000 Arecibo radio telescopes. Such a system could detect transmitters with EIRP of the order of a gigawatt at a distance of the order of the distance to the galactic center.     

Efficiency in SETI

While modern SETI experiments are often highly sensitive, reaching detection limits of 10^?25 W/m² Hz in the radio, interstellar distances imply that if extraterrestrial societies are using isotropic or broad-beamed transmitters, the power requirements for their emissions are enormous. Indeed, isotropic transmissions to the entire Galaxy, sufficiently intense to be detectable by our current searches, would consume power comparable to the stellar insolation of an Earth-size planet.In this paper we consider how knowledge can be traded for power, and how, and to what degree, astronomical accuracy can reduce the energy costs of a comprehensive transmission program by putative extraterrestrials. Indeed, an exploration of how far this trade-off might be taken suggests that extraterrestrial transmitting strategies of civilizations only modestly more advanced than our own would be, as are our SETI receiving experiments, inexpensive enough to allow multiple efforts. We explore the consequences this supposition has for our SETI listening experiments.     

A strategic “viewfinder” for SETI research

One of the most important reasons why unsuccessful results have been obtained so far by the SETI Project is due to the fact that no sure targets to aim at have been available up-to the present state of research. All-sky surveys, even if very accurate and complete, might result to be time-consuming. SETI needs at least one effective “viewfinder” in order that a true targeted research is carried out with a possible success. The best foundation to get this can be identified with the search for the evidence of extraterrestrial astro-engineering activity in form of the Dyson spheres predicted by theory. The existence of such stellar objects can be ascertained by finding the evidence of two main signatures in stars of solar spectral type: infrared excess and anomalous light curves due to transiting artificial objects. These are probably the most powerful viewfinders in order to allow SETI techniques for intelligent signal search to be aimed at more appropriate targets. This paper is not intended to be a research paper but rather a review paper whose goal is not to present calculations and/or operational research but rather to be a research proposal for a more focused research in SETI just using Dyson Spheres as crucial markers.     

A search for optical beacons: implications of null results

Over the past few years a series of searches for interstellar radio beacons have taken place using the Parkes radio telescope. Here we report hitherto unpublished results from a search for optical beacons from 60 solar-type stars using the Perth-Lowell telescope. We discuss the significance of the null results from these searches, all of which were based on the interstellar contact channel hypothesis. While the null results of all searches to date can be explained simply by the nonexistence of electromagnetically communicating life elsewhere in the Milky Way, four other possible explanations that do not preclude its existence are proposed: (1) Extraterrestrial civilizations desiring to make contact through the use of electromagnetic beacons have a very low density in the Milky Way. (2) The interstellar contact channel hypothesis is incorrect, and beacons exist at frequencies that have not yet been searched. (3) The search has been incomplete in terms of sensitivity and/or target directions: Beacons exist, but more sensitive equipment and/or more searching is needed to achieve success. (4) The search has occurred before beacon signals can be expected to have arrived at the Earth, and beacon signals may be expected in the future. Based on consideration of the technology required for extraterrestrial civilizations to identify target planets, we argue that the fourth possibility is likely to be valid and that powerful, easily detectable beacons could be received in coming centuries.     

The transcension hypothesis: Sufficiently advanced civilizations invariably leave our universe,and implications for METI and SETI

The emerging science of evolutionary developmental (“evo devo”) biology can aid us in thinking about our universe as both an evolutionary system, where most processes are unpredictable and creative, and a developmental system, where a special few processes are predictable and constrained to produce far-future-specific emergent order, just as we see in the common developmental processes in two stars of an identical population type, or in two genetically identical twins in biology. The transcension hypothesis proposes that a universal process of evolutionary development guides all sufficiently advanced civilizations into what may be called "inner space," a computationally optimal domain of increasingly dense, productive, miniaturized, and efficient scales of space, time, energy, and matter, and eventually, to a black-hole-like destination. Transcension as a developmental destiny might also contribute to the solution to the Fermi paradox, the question of why we have not seen evidence of or received beacons from intelligent civilizations. A few potential evolutionary, developmental, and information theoretic reasons, mechanisms, and models for constrained transcension of advanced intelligence are briefly considered. In particular, we introduce arguments that black holes may be a developmental destiny and standard attractor for all higher intelligence, as they appear to some to be ideal computing, learning, forward time travel, energy harvesting, civilization merger, natural selection, and universe replication devices. In the transcension hypothesis, simpler civilizations that succeed in resisting transcension by staying in outer (normal) space would be developmental failures, which are statistically very rare late in the life cycle of any biological developing system. If transcension is a developmental process, we may expect brief broadcasts or subtle forms of galactic engineering to occur in small portions of a few galaxies, the handiwork of young and immature civilizations, but constrained transcension should be by far the norm for all mature civilizations.The transcension hypothesis has significant and testable implications for our current and future METI and SETI agendas. If all universal intelligence eventually transcends to black-hole-like environments, after which some form of merger and selection occurs, and if two-way messaging (a send–receive cycle) is severely limited by the great distances between neighboring and rapidly transcending civilizations, then sending one-way METI or probes prior to transcension becomes the only real communication option. But one-way messaging or probes may provably reduce the evolutionary diversity in all civilizations receiving the message, as they would then arrive at their local transcensions in a much more homogenous fashion. If true, an ethical injunction against one-way messaging or probes might emerge in the morality and sustainability systems of all sufficiently advanced civilizations, an argument known as the Zoo hypothesis in Fermi paradox literature, if all higher intelligences are subject to an evolutionary attractor to maximize their local diversity, and a developmental attractor to merge and advance universal intelligence. In any such environment, the evolutionary value of sending any interstellar message or probe may simply not be worth the cost, if transcension is an inevitable, accelerative, and testable developmental process, one that eventually will be discovered and quantitatively described by future physics. Fortunately, transcension processes may be measurable today even without good physical theory, and radio and optical SETI may each provide empirical tests. If transcension is a universal developmental constraint, then without exception all early and low-power electromagnetic leakage signals (radar, radio, television), and later, optical evidence of the exoplanets and their atmospheres should reliably cease as each civilization enters its own technological singularities (emergence of postbiological intelligence and life forms) and recognizes that they are on an optimal and accelerating path to a black-hole-like environment. Furthermore, optical SETI may soon allow us to map an expanding area of the galactic habitable zone we may call the galactic transcension zone, an inner ring that contains older transcended civilizations, and a missing planets problem as we discover that planets with life signatures occur at a much lower frequencies in this inner ring than in the remainder of the habitable zone.     

SETI-3: the Search for ExtraTerrestrial Intelligence. A selection of papers from 1987-1990 Symposia of the International Academy of Astronautics held during the 38th-41st Congress (Brighton, Bangalore, Malaga, Dresden) of the International Astronautical Federation

This special issue of Acta Astronautica is a compilation of selected papers presented at Review Meetings on SETI at the 1987-1990 International Academy of Astronautics Congresses. Papers are drawn from seven areas: bioastronomical context, SETI technology, SETI searches, radio frequency interferences, possibilities for newer instrumentation, interdisciplinary connections, and public relations. Two papers presented at the Pesek Lecture are included.     

Studies of radio frequency interference at Parkes Observatory

During 16 weeks of continuous SETI observing at the Parkes Observatory in New South Wales, Australia, a set of time-averaged data with 643 Hz resolution were recorded and returned to the SETI Institute for post-processing. These data are the 14 second (10 frame) average powers in each of 15,552 “subband” channels covering 10 MHz of the spectrum in both right and left circular polarizations that were used by the signal detection hardware to baseline and threshold the 1 Hz high resolution SETI spectra. The observations covered frequencies from 1.2 to 3 GHz, tracking 209 stellar targets across the sky. The data at each frequency were averaged over all directions and then interrogated to attempt to determine the prevalence of radio frequency interference (RFI). Estimates were made for the probability of encountering RFI at a particular frequency. Particular attention has been paid to those portions of the spectrum that are allocated as primary use status, or footnote protection for radioastronomy. This sixteen-week snapshot of the RFI situation at Parkes is by now out of date. Unfortunately, a year later, the situation has undoubtedly worsened.     

Is interstellar archeology possible?

Searching for signatures of cosmic-scale archeological artifacts such as Dyson spheres is an interesting alternative to conventional radio SETI. Uncovering such an artifact does not require the intentional transmission of a signal on the part of the original civilization. This type of search is called interstellar archeology or sometimes cosmic archeology. A variety of interstellar archeology signatures is discussed including non-natural planetary atmospheric constituents, stellar doping, Dyson spheres, as well as signatures of stellar, and galactic-scale engineering. The concept of a Fermi bubble due to interstellar migration is reviewed in the discussion of galactic signatures. These potential interstellar archeological signatures are classified using the Kardashev scale. A modified Drake equation is introduced. With few exceptions interstellar archeological signatures are clouded and beyond current technological capabilities. However SETI for so-called cultural transmissions and planetary atmosphere signatures are within reach.     

Project Phoenix and beyond. Pesek Lecture

Although there are no federally funded projects at this time, SETI (the search for extraterrestrial intelligence) is a vigorous exploratory science. There are currently eight observational programs on telescopes around the world, of which the Phoenix Project is the most comprehensive. Most of these projects are rooted in the conclusions of the pioneering studies of the early 1970's that are summarized in the Cyclops Report. Technology has experienced an exponential growth over the past two and a half decades. It is reasonable to reassess the Cyclops conclusions as SETI enters the next century. Listening for radio signals is still the preferred method of searching, however new technologies are making searches at other wavelengths possible and are modifying the ways in which the radio searches can and should be conducted. It may be economically feasible to undertake the construction of very large telescopes that can simultaneously provide multiple beams on the sky for use by SETI and the radioastronomy community.     

A symbiotic approach to SETI observations: use of maps from the Westerbork Synthesis Radio Telescope

High spatial resolution continuum radio maps produced by the Westerbork Synthesis Radio Telescope (WSRT) of The Netherlands at frequencies near the 21 cm HI line have been examined for anomalous sources of emmission coincident with the locations of nearby bright stars. From a total of 542 stellar positions investigated, no candidates for radio stars or ETI signals were discovered to formal limits on the minimum detectable signal ranging from 7.7 x 10(-22) W/m2 to 6.4 x 10(-24) W/m2. This preliminary study has verified that data collected by radio astronomers at large synthesis arrays can profitably be analysed for SETI signals (in a non-interfering manner) provided only that the data are available in the form of a more or less standard two dimensional map format.     

Recent progress on the lunar farside crater Saha proposal

The aim of this review, whose title might as well be “Toward a dedicated lunar farside radio observatory”, is to provide information for potential interested workers whom we invite to contribute to this multidisciplinary effort.First point: in view of the dramatic increase of radio interference due to the development of satellite-based human telecommunications, it will soon become impossible to conduct valuable high-sensitivity SETI observations from the terrestrial ground. It is why a few years ago I started an interdisciplinary and international endeavor to protect for the next 20/30 years a well specified lunar farside crater (Saha) which no Earth- or geostationary orbit-based radio emission could reach.After raising technical, programmatic, legal, astronautical, industrial, political, ethical issues at a number of conferences of international learned institutions, this enterprise is now of interest for the wider field of next generation high-sensitivity radioastronomy at large, from decametric to sub-millimetric waves.This last year, positive results were the creation of an IAA Sub-committee for “A Lunar SETI Study”, the presentation of a Resolution to the IAU for the protection of a potential lunar radio observatory site, discussions at the IAA/IISL Scientific-Legal Roundtable on SETI & Society at IAF Congress in Torino, the organization of a half-day Scientific Event at next COSPAR Assembly in Nagoya and the initiation of an IAA Cosmic Study on the subject.We shall conclude by outlining the next efforts to be initiated up to a real Moon radio observatory.     

SETI,extrasolar planets search and interstellar flight: When are they going to merge?

The SETI Permanent Study Group (abbreviated SETI PSG) of the International Academy of Astronautics (IAA), with web site: http://www.setileague.org/iaaseti/index.html, is one of the few international venues where, as of 2006, scientists with different backgrounds and from all over the world can meet and discuss recent advances in the scientific, technical and societal aspects of SETI. In particular, the Pe?ek Lecture that traditionally opens in October every year the SETI 1 Session of the International Astronautical Congress (IAC), is intended to describe the updated state-of-the-art in SETI and related fields with the accent on science and technology rather than on the societal consequences of a contact with ET. We have thus come to the conclusion that a Pe?ek Lecture devoted to the interplay between SETI and the rapidly evolving field of the Search for Extrasolar Planets (or Exoplanets) would be quite up-to-date, especially in view of the over 200 exoplanets rapidly discovered in the 11 years between 1995 and 2006. Moreover, besides SETI and Exoplanets, there is a third field of scientific investigation that, although not as mature as the former two fields in terms of experimental research, is striving ahead among many theoretical difficulties but might really change the course of human history when becoming reality: this is the theory (so far) of Interstellar Flight, that would one day enable us to travel across the vast interstellar distances initially by virtues of probes only, and later “in person”.The present Pe?ek Lecture is trying to compare the different grow rate and the (now small) overlap in between these three apparently “unrelated” fields. And even if we can hardly find any answer in these “dark ages” we live, let us at least raise the question: “When are SETI, Exoplanet Searches and Interstellar Flight going to merge in the future of Humankind?”.     

Search for high-proper motion objects with infrared excess

The possibility of interstellar migration has been theorized during the past thirty years in the form of “Dysonships” that, using non-relativistic propulsion systems, are able to colonize the Galaxy in a relatively short time compared to the age of the Galaxy and consequently penetrate inside our solar system too. Observational evidence of this can be potentially obtained using the present state of the art of telescopes and related sensors, by following aimed searches and an expanded SETI protocol. Some transient and unrepeated radio signals recorded during standard SETI observations might be due to the transit of high-proper motion artificial sources of extraterrestrial origin, which are expected to show a very weak optical emission, a strong infrared excess and occasional high-energy bursts in the X and Gamma-ray wavelength ranges. Such artificial sources might show an interest to Earth by sending probes to visit it: such a possibility can be investigated scientifically as well.