Project Cyclops, A Design... - Department of Earth and Planetary ...

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andwidth that will still give near maximum response we = _1/2 must set _" = 1/8 and find that Bmin . A more precise analysis would show that Bmin = _]/2 (18) where fl is a constant near unity that depends on the shape of the RF t'dter. For a gaussian f'dter we show in Appendix E that fl = 1.24 .... Substituting equation (18) into (12), we obtain for the reference range limit THE MAGNITUDE OF THE SEARCH We have seen that we must have a receiving system with large antenna gain and, as a result, high directivityso high that it will have on the order of 10 _0 resolvable directions. We have seen that the microwave window covers about 101° Hz. We have seen that more nearly monochromatic signals are easier to detect and that we probably need to "comb" the spectrum into channels 1 Hz wide or less. If the signal is beamed at us for only a small fraction of the time, say 1 see/day, we must search each direction and each 1 Hz channel for l0 s sec or more. If we were to search the entire sky, blindly, with a receiver having a 1 Hz bandwidth the search would take us a time T = 10t o (directions)X 101 °(channels/direction) × 10 s (sec/channel) Figure 6-5 shows Ro as a function of dr and v with Peff = 109 W, fl = 1, _k= kT and T = 20 ° K. As can be seen from the curves or from equation (16), a hundredfold reduction in u permits the same range with one tenth the antenna area. This is why monochromatic signals with high-frequency stability are desirable for beacons. tn IO 3 _°>102 1: tS
Butdoesbyourtechnology andourassessment ofthe joint search strategy permit us to make these assumptions? We think so. We believe that we can pinpoint the likely stars both as to spectral type and range with a reasonable optical search program concurrent with the radio search. We believe we can construct receivers that will display power spectra over 100 MHz of bandwidth with a resolution better than 1 Hz. Finally, we believe that leakage radiation is most likely to be detected at the low end of the microwave window, and that beacon signals are most likely to be found in a relatively narrow range at the low end of the window, for reasons that are given below. LEAKAGE SIGNALS Electromagnetically, Earth is at present a noisy planet. We radiate hundreds of megawatts and much of this power is at frequencies for which the ionosphere is quite transparent. This, of course, raises the question of whether or not we might eavesdrop on the signals another race transmits for its own purposes. There is then no need to assume the existence of intentional beacons and at first glance the probability of detection appears to be greatly increased. Our interstellar radiation became significant about 20 years ago with the advent of VHF TV broadcasting and more recently has increased with the expansion of TV allocations into the UHF band. Today we are surrounded in space with a sphere of radiation some 20 light-years in radius, and the energy density in this sphere is growing annually. How long this buildup will continue is anyone's guess. Cable TV is replacing direct reception in metropolitan areas where bad reflections and shadowing exist, and in many rural areas shadowed by mountains. However, the economics do not favor cable TV in the normal service areas of broadcast stations, where good reception exists. On this basis, one might conclude that powerful TV radiation would be an enduring phenomenon. Satellite broadcasting appears to be a greater longterm threat to our TV leakage than cable TV. A UHF transmitter in synchronous orbit using present transmission standards need only radiate a few kilowatts to cover the entire United States. A fair fraction of this power would be reflected back into space by the Earth but, because far fewer stations of lower power would be needed, the resulting leakage would be negligible compared with our present leakage. Nevertheless, it is of interest to calculate how far into space the present radiation level of Earth might be detectable. Our TV stations radiate about 50 kW. Assuming a grey field (signal amplitude halfway between black level and white level) the effective carrier power is about 20 kW. The antennas typically have 13 dB of gain as a result of vertical directivity, so the radiation is confined between a plane tangent to the Earth and a cone whose elements have an elevation angle of about 6° . As the earth rotates at 15°/hour this sheet of radiation sweeps across the celestial sphere. For a station at latitude 0 the beam would take a time (6/15) sec 0 hours to scan a given star on the celestial equator. Thus 20 min is a reasonable average time. Using a receiver with a 20 ° K total noise temperature, an antenna 5 km in diameter, a bandwidth of 0.1 HzJand integrating for 1200 sec, we find from equation (11) that the range limit is 50 light-years. Actually, this is a somewhat pessimistic figure since many stations, and often several on each channel, could be received at the same time and proper data processing could make use of the total power. We conclude that if we keep on broadcasting TV for another century, Earth will be visible out to something on the order of 100 light-years, which could announce our existence to beings on any of the 1000 or more likely stellar systems within that range. To beings that detected us, there would not be doubt for very long that the signal was the work of man, not nature. They would observe that the signals (1) had highly monochromatic components, (2)were distributed systematically in slots across the spectrum, (3) appeared and disappeared with great regularity (in particular, a 24-hour cycle would stand out) and (4) exhibited a sinusoidal frequency modulation whose period was proper for the annual motion of a minor planet, and whose fractional frequency variation Af/f was the same for all signals. The annual Doppler and daily periodicity would identify the signals as being of planetary origin while the monochromaticity and regularity of spacing would identify them as artificial in origin. We conclude that leakage signals are a possible means for the detection of other life. However, the longevity of their emission is very uncertain, and their low power compared with an intentional beacon restricts their detection BEACONS range significantly. One can imagine several reasons why an intelligent race might construct a beacon (or even many beacons) but perhaps the strongest reason is to facilitate the 'The Doppler shift would be less than 0.01 Hz during the observing period, but the frequency instability of the source might cause larger drifts. 59
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(NASA-CR- 11_5) PROJECT CYCLOPS: A
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CR 114445 Available to the public A
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At this very minute, with almost ab
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ACKNOWLEDGMENTS The Cyclops study w
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COMMUNICATION BY ELECTROMAGNETIC WA
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APPENDIX A - Astronomical Data ....
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t _ 2
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of the living beings evolved by the
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Figure2-1. M3I,the great galaxy in
Page 20 and 21: self.Thus,wecaninterpretFigure2-2as
Page 22 and 23: magnitude (low brightness) end, the
Page 24 and 25: Red Giant. The transition from main
Page 26 and 27: tion, as the central part of the cl
Page 28 and 29: TABLE 2-4 SELECTED NEARBY STARS WIT
Page 30 and 31: tideraisingforcesasr--_ where ,v =
Page 32 and 33: 3. Is it possible that living syste
Page 34 and 35: lawsof natural selection, more like
Page 36 and 37: starsthroughout the Galaxyhave also
Page 38 and 39: if the longevity of that life is ty
Page 40 and 41: The imaginative reader will have no
Page 42 and 43: Lookingfar ahead,supposewe aresucce
Page 44 and 45: usuallyterritorial expansion by the
Page 46 and 47: IOO IO 1 [ [ J [ J I J i [ i I i I
Page 48 and 49: order with what Morrison has descri
Page 50 and 51: The quantity gtPt is often called t
Page 52 and 53: which might result from synchronous
Page 54 and 55: 1. Wewillnothavenough resolving pow
Page 56 and 57: normalwith the meanat o x/--2. When
Page 58 and 59: Chapter11 in analyzingthe dataproce
Page 60 and 61: Therangelimitisthenfoundbyequating_
Page 62 and 63: TABLE 5-3 PARAMETER Wavelength Tran
Page 64 and 65: angeanddirectlyasthesquareof antenn
Page 66 and 67: "_ i i i i i p = STELLAR DENSITY AT
Page 68 and 69: I-- g u. O >- I--- .d tit (]O 0 0.
Page 72 and 73: acquisitionphasefor otherraces.Supp
Page 74 and 75: 1. They would transmit continuously
Page 76 and 77: and ¢-Ceti. No signals were detect
Page 79 and 80: vz .i g)mo PAGE NOr Ir[[,MZ 7. THE
Page 81 and 82: The price of incomplete sky coverag
Page 83 and 84: modest size.A largedatabaseontapeor
Page 85 and 86: THEAUXILIARYOPTICALSYSTEM Althoughn
Page 88 and 89: edetectedat 20,000light-years byCyc
Page 90 and 91: feeds must correct for spherical ab
Page 92 and 93: side of the dish and shade on the o
Page 94 and 95: TABLE 8-1 UNADJUSTED UNIT COST DATA
Page 96 and 97: 7. Using huge specially designed ji
Page 99 and 100: 9. THE RECEIVER SYSTEM The receiver
Page 101 and 102: whereP is the radiated power. Divid
Page 103 and 104: SHADOWED AREA SHADOWED AREA // // /
Page 105 and 106: Corrugatedhornssupportingbalancedhy
Page 107 and 108: o 50 ----- - _ T i 20 _,o 5 ,,,5 09
Page 109 and 110: TABLk ?- I A COMPARISON OF VARIOUS
Page 111 and 112: CENTRAL POINT STATION LSB LINE FREQ
Page 113 and 114: A02 .... + No (25) (i C 1 where No
Page 115 and 116: COAXIAL LINE DIRECTIONALCOUPLER FRE
Page 117 and 118: DeJager, J.T.:IEEETrans.onMicrowave
Page 119 and 120: pR_ING PA6E BLANK HOT FILMF_ 10. TR
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o-------------o_ _ o o o o ing of t
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addedto theother IF channel. The tw
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INPUT MHZ _PF 500 MHZ i : 575 T1 92
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azimuth _) has a delay (2a/c)sin 0
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stripline. For 2 _< k _< 6, appropr
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mation are common to all antennas i
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A cable pair costs about 20 cents/m
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11. SIGNAL PROCESSING The Cyclops s
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1.0 T t t I I r .9 -8 asynchronousl
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collimated coherent light. A simple
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power of the film and associated op
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samples simultaneously onto the sam
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outputs is assumed. COMPOSITE SIGNA
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SPECTRUM I n LINES M n LINES U SPEC
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signal andyet have a tolerable fals
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i --_- i i i i large values of n. T
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plottedin Figure11-15for various va
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All the1Fsignalswillarrivein phasei
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x:(1 +x) x 2 - _ -- (53) If we wish
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3's = unitcostof signal planelectro
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where0ma x is the maximum value of
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Roughestimates of the costs of buil
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12. CYCLOPS AS A BEACON Although th
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13. SEARCH STRATEGY The high direct
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distantgalaxies (oraninertialrefere
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wouldfollowtheuppermost linein Figu
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persquaredegreeof fieldwouldberequi
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starsfrom/'18 to G5 could support a
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14. CYCLOPS AS A RESEARCH TOOL Thro
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Only a few such galaxies have been
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15. CONCLUSIONS AND RECOMMENDATIONS
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perhapsdecadesand possiblycenturies
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APPENDIX A ASTRONOMICAL DATA DISTAN
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PLANETARY Planet ORBITS Semimajor S
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APPENDIX B SUPERCIVILIZATIONS AND C
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ABIOLOGICAL CIVILIZATIONS Many writ
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182
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tqOT APPENDIX C OPTIMUM DETECTION A
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to rmsnoise.Wenotethatthematchedfil
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APPENDIX D SQUARE LAW DETECTION THE
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If the output filter is very wide c
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if B/2 > T we can start instead wit
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Let us now introduce the normalized
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where h-- = expectation count of si
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APPENDIXE RESPONSE OF A GAUSSIAN FI
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APPENDIXF BASE STRUCTURES AZ-EL BAS
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ack,it shouldnotbenecessary to prov
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204
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206 i
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PAGE BLANK NOT APPENDIX H POLARIZAT
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APPENDIX I CASSEGRAINIAN GEOMETRY C
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APPENDIXJ PHASINGOFTHE LOCALOSCILLA
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APPENDIXK EFFECTOF DISPERSION IN CO
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APPENDIX L TUNNEL AND CABLE LENGTHS
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where r = "Ym/'rs- If we let o-_--o
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L-4 we see that the length of IF ca
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APPENDIX M PHASING AND TIME DELAY A
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andobtain V = 2 (Ps [! + _(Ar)] +Pn
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L" D 226
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APPENDIX N SYSTEM CALIBRATION The p
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APPENDIXO THE OPTICAL SPECTRUM ANAL
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232
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APPENDIX P LUMPED CONSTANT DELAY LI
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Thevalueofthefinalcoilonthelineis =
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APPENDIXQ CURVES OF DETECTION STATI
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I I I I LE :E oo
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APPENDIX R RADIO VISIBILITY OF NORM
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io 3 - l rlrllll I I I ]l+,ll_ I _f
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