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

More documents

Recommendations

Info

TABLE 5-3 PARAMETER Wavelength Transmitter: Antenna diameter Number of elements Element diameter Antenna gain Peak or CW power Modulation Pulse duration Energy per bit Effective radiated power Beamwidth (seconds of arc) OPTICAL / \ A B 1.06_ 1.06# 22.5 cm 22.5 cm 1 I 22.5 cm 22.5 cm 4.4X 10 j _ 4.4X 101 10 _ 2 W lO s W Pulse Pulse 10 -9 sec 1 sec 103 J l0 s J 4.4×10_ 3W 4.4×10t*W 1" 1" INFRARED MICROWAVE / \ / \ A B A B 10.6u 10.6u 3 cm 3 cm 2.25 m 2.25 m 100 m 3 km* 1 1 1 900 2.25 m 2.25 m 100 m 100 m 4.4XI0 _j 4.4X 10 _' 1.1Xl0 _ 9.8X 10 t° lO s W lO s W lO s W lO s W Pulse PSK PSK PSK 1 sec 1 sec 1 sec 1 sec lO s J lO s J lO s J lO s J 4.4X 10_ 6W 4.4X10_ 6W 1.1xl0_ 3W 9.9X 101 sW 1'" 1" 64" 1'" Receiver Antenna diameter Number of elements Element diameter Atmosphere transmission Overall Quantum efficiency Solar background ratio Noise temperature Effective RF bandwidth Detection method 100 m 100 m 400 400 5m 5m .7 .7 .4 .1 1.2× 10 -3 36 13,600 ° K 13,600 ° K 1 GHz 3 MHz Photon Photon 100m 2.25 m 100m 3 km* 1975 1 1 900 2.25 m 2.25 m 100 m 100 m .5 .5 1 1 .2 .2 .9 .9 1.7X 10 -s 6XI0 -_ ..... 1360 ° K 1360 ° K 20 ° K 20 ° K 3kHz t Hz I Hz 1 Hz Sq. Law Synch. Synch. Synch. System: Range limit (1 .y.) State of the Art? All weather? 26 24 No No No 22 41 500 450,000 No Yes Yes No No Yes Yes *Array spread out to 6.4 km diameter to avoid vignetting. arise. The required frequency stability is one part in 10 t°, which is easily realized. Doppler rates would require correction but are only on the order of 1 Hz/sec before correction. This system has the same collecthtg area as the first three laser systems. System B. This system is the same as microwave A, but the antennas have been enlarged to phased arrays 6.4 km in diameter to provide I sec of arc resolution. The array elements are assumed to be spaced a little more than twice their diameter to avoid shadowing at low elevation angles, so the equivalent clear aperture diameter is 3 km. Arrays of these general dimensions are probably needed for the search phase, so their communication capabilities are of more than academic interest. This system has the same beamwidth as the laser systems. Table 5-3 summarizes the characteristics of the six systems studied. We see that all the systems, aside from practical considerations discussed below, can achieve communication over interstellar distances, but that the laser systems have more than one order of magnitude less range. The laser systems can span the distance to some 20 to 140 stars of interest, while microwave system A can reach about a quarter of a million stars of interest. Microwave system B can easily reach every star in the galaxy. I feach transmitting antenna element had a 200 kW phased transmitter, the total power of microwave B would be 180 MW and the range would be 20 million light-years. With microwaves we could communicate not merely (sic!) over interstellar distances but over intergalactic' distances. Why do the laser systems show up so poorly by comparison? Basically, of course, all laser systems suffer the disadvantage of a higher energy per photon than microwave systems: their effective noise temperature is high. This disadvantage is partly compensated by the ease of obtaining narrow beams, but once we approach 50
practical limits of narrow beamwidths in the microwave region as well, the photon energy disadvantage shows through. But there are additional specific disadvantages that are revealed by each of the laser systems studied. Optical system A suffers from too little energy per bit. If its pulse energy were equal to that of the other systems, its range would increase over 10 times. Optical system B does not adequately override star noise, so about 30 times as many signal photons must be received per pulse as for optical system A and, because of the filter loss, the received energy per pulse is only 25 times as great at the same range. Infrared system A suffers from the inefficient array utilization because of incoherent addition and the spontaneous emission noise associated with each receiver. Finally, infrared system B suffers from the small size of receiving antenna possible in a coherent system at 10.6/a. Except possibly for infrared system B, all the laser systems would appear to be far more expensive than microwave A. Certainly to provide two acres worth of optical collecting area in the form of precisely steerable 2- to 5-m telescopes would cost much more than a single l O0-m dish. All the systems require cooled detectors. Optical B requires costly precision narrow band filters at each antenna. Infrared A requires precision local lasers and mixers at each of 1975 antennas, while the precision needed for the local oscilla{or of infrared B may be beyond the capabilities of even the most advanced technology. The mechanical stability and precision problems of the laser systems have their counterpart in the precision of electrical control needed to compensate for Doppler drifts. The drift due to Earth diurnal Doppler could be as great as 3 kHz/sec at 10.6/,( for stars near tile meridian and a station near the equator. Locking infrared system B onto such a rapidly drifting signal would be a nightmare. The total interstellar Doppler shift is about _+10-3 so the filters in the optical systems would require tunability over a +-300 GHz range while the infrared systems would need a -+30 GHz tuning range. Finally, laser systems suffer from atmospheric absorption even in clear weather and are unusable in cloudy weather. Sky light does not materially affect the performance of any of the systems, except for optical system B. In the daytime, the background count from the sky would reduce the range of this system from 24 to about 20 light-years. Thus all systems would be usable in clear daytime hours as well as at night, but the microwave systems are the only all-weather systems. In summary 1. The sole advantage of lasers is that they permit narrow beamwidths to be realized with small transmitting mirrors, but this advantage turns into a disadvantage at the receiver where we need a large collecting area. 2. The collecting surface is much cheaper and more durable in the microwave region, because the tolerances are much greater and polished surfaces are not needed. 3. Microwave systems offer substantially more range for the same power, even with wider beamwidths. 4. Because of the wider beams, automatic positioning and tracking are feasible at microwaves on a dead reckoning basis. 5. Doppler shifts and drift rates are orders of magnitude less at microwave frequencies and can easily be compensated. 6. Microwave systems are all-weather systems. We have gone to some length to compare microwaves and lasers because the ease of obtaining sharp beams has led many people to propose laser systems (ref. 3). We have made the comparison for point-to-point communication links where the transmitting directivity of the laser is used. When we come to consider the search problem in the next chapter we will see that transmitter directivity is not an asset, and lasers lose out completely. In fact, we believe that if lasers had been known for the last hundred years and microwaves had only recently been discovered, microwaves would be hailed as the long sought for answer to interstellar communication. COMMUNICATION RATE OF A MICROWAVE LINK At the range limits given, the links compared in the last section are all 1 bit/sec systems with a bit error rate of 0.07865. As long as the received energy per bit is held constant, the error rate will not change. Thus the connnunication rate varies inversely as the square of the _, ,ookw7s,_o-_ / / / gi/ .-ry F 2ookw2._,,o -2 / / /._'/.-"/7 Lmlk I I01 10 2 10 3 10 4 I0 5 CLEAR APERTURE DIAMETER, m FigureS-8. Information rates of microwave links; X = 3 cm. 51
Page 1 and 2:
(NASA-CR- 11_5) PROJECT CYCLOPS: A
Page 3 and 4:
CR 114445 Available to the public A
Page 6 and 7:
At this very minute, with almost ab
Page 8 and 9:
ACKNOWLEDGMENTS The Cyclops study w
Page 10 and 11:
COMMUNICATION BY ELECTROMAGNETIC WA
Page 12 and 13: APPENDIX A - Astronomical Data ....
Page 14 and 15: t _ 2
Page 16 and 17: of the living beings evolved by the
Page 18 and 19: 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 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 70 and 71: andwidth that will still give near
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
Page 121 and 122:
o-------------o_ _ o o o o ing of t
Page 123 and 124:
addedto theother IF channel. The tw
Page 125 and 126:
INPUT MHZ _PF 500 MHZ i : 575 T1 92
Page 127 and 128:
azimuth _) has a delay (2a/c)sin 0
Page 129 and 130:
stripline. For 2 _< k _< 6, appropr
Page 131 and 132:
mation are common to all antennas i
Page 133 and 134:
A cable pair costs about 20 cents/m
Page 135 and 136:
11. SIGNAL PROCESSING The Cyclops s
Page 137 and 138:
1.0 T t t I I r .9 -8 asynchronousl
Page 139 and 140:
collimated coherent light. A simple
Page 141 and 142:
power of the film and associated op
Page 143 and 144:
samples simultaneously onto the sam
Page 145 and 146:
outputs is assumed. COMPOSITE SIGNA
Page 147 and 148:
SPECTRUM I n LINES M n LINES U SPEC
Page 149 and 150:
signal andyet have a tolerable fals
Page 151 and 152:
i --_- i i i i large values of n. T
Page 153 and 154:
plottedin Figure11-15for various va
Page 155 and 156:
All the1Fsignalswillarrivein phasei
Page 157 and 158:
x:(1 +x) x 2 - _ -- (53) If we wish
Page 159 and 160:
3's = unitcostof signal planelectro
Page 161 and 162:
where0ma x is the maximum value of
Page 163 and 164:
Roughestimates of the costs of buil
Page 165 and 166:
12. CYCLOPS AS A BEACON Although th
Page 167 and 168:
13. SEARCH STRATEGY The high direct
Page 169 and 170:
distantgalaxies (oraninertialrefere
Page 171 and 172:
wouldfollowtheuppermost linein Figu
Page 173 and 174:
persquaredegreeof fieldwouldberequi
Page 175 and 176:
starsfrom/'18 to G5 could support a
Page 177 and 178:
14. CYCLOPS AS A RESEARCH TOOL Thro
Page 179 and 180:
Only a few such galaxies have been
Page 181 and 182:
15. CONCLUSIONS AND RECOMMENDATIONS
Page 183 and 184:
perhapsdecadesand possiblycenturies
Page 185 and 186:
APPENDIX A ASTRONOMICAL DATA DISTAN
Page 187 and 188:
PLANETARY Planet ORBITS Semimajor S
Page 189 and 190:
APPENDIX B SUPERCIVILIZATIONS AND C
Page 191 and 192:
ABIOLOGICAL CIVILIZATIONS Many writ
Page 193 and 194:
182
Page 195 and 196:
tqOT APPENDIX C OPTIMUM DETECTION A
Page 197 and 198:
to rmsnoise.Wenotethatthematchedfil
Page 199 and 200:
APPENDIX D SQUARE LAW DETECTION THE
Page 201 and 202:
If the output filter is very wide c
Page 203 and 204:
if B/2 > T we can start instead wit
Page 205 and 206:
Let us now introduce the normalized
Page 207 and 208:
where h-- = expectation count of si
Page 209 and 210:
APPENDIXE RESPONSE OF A GAUSSIAN FI
Page 211 and 212:
APPENDIXF BASE STRUCTURES AZ-EL BAS
Page 213 and 214:
ack,it shouldnotbenecessary to prov
Page 215 and 216:
204
Page 217 and 218:
206 i
Page 219 and 220:
PAGE BLANK NOT APPENDIX H POLARIZAT
Page 221 and 222:
APPENDIX I CASSEGRAINIAN GEOMETRY C
Page 223 and 224:
APPENDIXJ PHASINGOFTHE LOCALOSCILLA
Page 225 and 226:
APPENDIXK EFFECTOF DISPERSION IN CO
Page 227 and 228:
APPENDIX L TUNNEL AND CABLE LENGTHS
Page 229 and 230:
where r = "Ym/'rs- If we let o-_--o
Page 231 and 232:
L-4 we see that the length of IF ca
Page 233 and 234:
APPENDIX M PHASING AND TIME DELAY A
Page 235 and 236:
andobtain V = 2 (Ps [! + _(Ar)] +Pn
Page 237 and 238:
L" D 226
Page 239 and 240:
APPENDIX N SYSTEM CALIBRATION The p
Page 241 and 242:
APPENDIXO THE OPTICAL SPECTRUM ANAL
Page 243 and 244:
232
Page 245 and 246:
APPENDIX P LUMPED CONSTANT DELAY LI
Page 247 and 248:
Thevalueofthefinalcoilonthelineis =
Page 249 and 250:
APPENDIXQ CURVES OF DETECTION STATI
Page 251 and 252:
I I I I LE :E oo
Page 253 and 254:
APPENDIX R RADIO VISIBILITY OF NORM
Page 255:
io 3 - l rlrllll I I I ]l+,ll_ I _f
show all

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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?