1. Oliver, Bernard M.; and Billingham, John: Project Cyclops, A Design Study of a System for Detecting Extraterrestrial Intelligent Life. NASA CR 114445, 1972.

Two parabolic reflector antennas, forming the research and development site of NASA's worldwide Deep Space Network, stand out vividly against the primitive beauty of Southern California's Mojave Desert. The bowl-shaped location provides natural protection from man-made radio interference. Both antennas are equipped with Cassegrain feed systems and are steerable from horizon to horizon. The dish diameters are 26 m (85 ft) and 9 m (30 ft). The larger uses a low noise maser preamplifier to achieve a very high sensitivity for an antenna of this size. Antennas such as these can be used for sky and frequency SETI surveys. Depending on frequency, such antennas can perform all-sky surveys over plausible microwave regions with several orders of magnitude better sensitivity than has been generally achieved. The Deep Space Network is managed and technically directed for NASA by the Jet Propulsion Laboratory of the California Institute of Technology at Pasadena, California.

4. STELLAR CENSUS

Operation of a target-search strategy requires a target list. Even if we knew precisely what types of stars were accompanied by planetary systems believed likely to provide favorable life sites, we would not know where to look for the bulk of these stars in the neighborhood of the Sun, that is, within a range of 103 light years (ly). Present catalogs out to 103 ly are probably incomplete for F, G, and K dwarf stars by a factor of 103. For early M dwarf stars, the situation is worse. As long as we favor planets orbiting stable stars as the probable sites for intelligent life, so long will we be in essential need of a Whole Sky Catalog, or stellar census of stars down to the 14th or 15th magnitudes. Even then the catalog would be seriously incomplete for M dwarf stars.

A suitable stellar census should have the following properties:

1. A high degree of completeness out to at least 1000 ly. Because planets orbiting early M dwarf stars (MO-M4) are generally not excluded as possible life sites, the census should extend down to at least the 15th apparent visual magnitude. As a consequence, 25X106 or more stars must be identified.

2. In the main, each star should have its MK classification established to a satisfactory degree. Where feasible, more refined classification is highly desirable. In particular, it is desirable to provide estimates of stellar age.

3. Stellar position and radial distances of each star should be determined to the greatest precision consistent with completing the first edition of the census in about a decade.

4. The census should be cross referenced to previously existing catalogs.

5. Where known, additional information such as parallax, proper motions, duplicity, variability, etc., should be included. In fact, the initial census should, to the degree possible, be considered both as a summation of current stellar information and as first epoch observations for a massive improvement in our knowledge of the stars in our neighborhood. In the process, of course, similar information on an enormous number of stars at much greater distances will also be obtained.

It is the contention here, though yet unsubstantiated by thorough study, that such a census can be achieved at modest cost in about a decade following funding. The approach we suggest has the following major ingredients:

1. Digitize about 400 standard MK spectra. If necessary, take additional spectra at suitable dispersion.

2. Carry out a multivariate (or multifactor) analysis seeking the optimum achievable color systems using precision photographic photometry. Assess the error contributions as well as the capabilities of the system.

3. Design a completely automated photographic photometric system, telescope to tape data bank. The design should avoid manual operations other than transporting developed plates or, preferably, sheet film, in proper containers, from the observatory to the automatic plate reading machines. Automatic standardization and calibration procedures should be provided. Separate small telescopes should be used to obtain extinction information. Moderate field telescopes of the order of 60 in. should be adequate. Above all, the design of the telescope, its controls, the auxiliaries, the photometric apparatus, and the domes should be considered to be a single integrated system design problem.

4. Install identical systems at optimum sites, one in the Northern Hemisphere and one in the Southern Hemisphere.

5. Let all photographic data be measured by computer controlled machines. The same computer can correlate, classify, and store the data, and assess the results in real time. That is, completion of the catalog should about coincide with completion of the necessary observations.

Such a stellar census would have much value to general astronomy. Discussions with some photometric and spectroscopic specialists have strongly supported the belief that such a system is feasible. In any event, laboratory trials at an early stage of the design study will surely clarify the situation.

Should photographic methods prove unsatisfactory, it will be necessary to develop an appropriate photoelectric sensor system. This is clearly possible, and should be explored as a technology requiring a special development effort.

5. SUMMARY OF POSSIBLE USES OF AN INTERSTELLAR

SEARCH SYSTEM FOR RADIO ASTRONOMY

INTRODUCTION

Radio astronomical investigations of great scientific interest can be carried out with the wide range of SETI antenna systems presently under discussion. This range includes both the SETI programs planned for the near future with existing antennas, and larger ground-based or spaceborne antenna systems that might be built in the future.

The effect of SETI technology on radio astronomy can be broadly broken down into two classes. In the first class we have the extension or improvement of existing microwave technology:

1. Receiver design: A class of receivers to be developed for SETI is characterized by near optimum noise figures (~10 K at a room temperature waveguide flange), broad instantaneous bandwidth (300 MHz), and octave bandwidth tuning ranges. This technology will probably be rapidly adopted by radio observatories so that the possession of such receivers will not make SETI systems unique, but would be a SETI spin-off.

2. Collecting area: Eventually, a SETI receiving system may vastly surpass radio astronomy facilities, existing or projected, in collecting area. (Compare the VLA at twenty-seven 25-m antennas to even two 100-m antennas.)

In the second class of SETI impact we have the development of a new generation of signal processing facilities:

3. Data Processing Hardware: On the basis of SETI requirements, it is possible to predict the general properties of such hardware. To make a microwave search tractable, it will be necessary to utilize fully the entire receiver bandwidth (300 MHz) while retaining high spectral resolution: a processor of 106 channels. An integrating spectrometer with such characteristics is an impressive scaling-up of present radio astronomy technology, but a significant development is called for when we admit that we have no a priori knowledge of the nature of SETI signals. Then, we require a fully flexible data processing system that can measure all properties of a signal (e.g., frequency distribution, time structure, polarization) continuously in real time. The ability to fully characterize radio signals offers hope for recognizing and rejecting various kinds of interference. If the processor is eventually to be used with an antenna array, the ability to operate several array subsets or several array beams simultaneously would be very useful.

4. Data Acquisition Management: The management of a 106 channel signal processor and the extraction and sorting out of various kinds of scientific data in real time represents another breakthrough area. The following kinds of data are some that need to be managed, preferably simultaneously: