Communications System Utilizing Passive Satellites

The Space Congress® Proceedings 1966 (3rd) The Challenge of Space

Mar 7th, 8:00 AM

Robert T. Hart Collins Radio Company

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Scholarly Commons Citation Hart, Robert T., "Communications System Utilizing Passive Satellites" (1966). The Space Congress® Proceedings. 5. https://commons.erau.edu/space-congress-proceedings/proceedings-1966-3rd/session-1/5

This Event is brought to you for free and open access by the Conferences at Scholarly Commons. It has been accepted for inclusion in The Space Congress® Proceedings by an authorized administrator of Scholarly Commons. For more information, please contact [email protected]. COMMUNICATIONS SYSTEMS UTILIZING PASSIVE SATELLITES Robert T. Hart Collins Radio Company Dallas, Texas

Summary Dallas, Texas. The geographical locations of the sta tions permitted mutual visibility on many passes The era of communications systems utilizing with the passive satellites was inaugurated by the launch of satellite at an orbital height of approximately 700 miles. Operational Echo I in 1960. This was followed by Echo II in 1964. frequencies in the S-band region These preliminary experiments have proven system were chosen for maximum radio reflectivity of the sat feasibility and indicated deficiencies of the satellite ellite consistent with available equipment in the ground station materials and configurations. Echo III will be launched complex. in the spring of 1966 to test the latest available A set of disappointing circumstances caused the materials. Echo II satellite to be less than a perfect radio reflec This paper outlines the history of the passive tor, primarily due to ejection of the balloon from the satellite communications experiments to date and canister. One of the two clam shells failed to open, offers solutions to the deficiencies that have been in imparting a sideways velocity to the satellite. The ma dicated. The solutions include a preview of studies terial used was similar to that in Echo I mylar plastic of new materials and satellite configurations. Com and aluminum foil. This material has the property of munications system capability utilizing the proposed becoming rigid in a vacuum after the pressurization satellites is detailed for conventional and specialized system stresses the material to the yield point. Before networks. the material had rigidized completely, the satellite lost pressurization prematurely. As a result, the sat The Echo I Satellite ellited shape is somewhat like that of a M prune n . The tumbling motion of the sphere due to improper ejection The Echo I satellite, launched in August, 1960, from the canister and the rough surface causes severe is a 90-foot-diameter sphere composed of aluminum scintillation of the reflected radio signals. The sphere foil and mylar plastic. It has been in orbit for al is made in a segmented configuration using many gores most six years without any significant changes in its with two polar caps. Several times during the test pro surface characteristics after the first few months. gram the satellite was oriented in such a manner that The inflation system produced a good sphere; however, the axis of rotation coincided with the reflecting sur after the first few months the surface of the satellite face and scintillation was reduced to almost zero. The became wrinkled, causing severe scintillation of the characteristics of the Echo satellites are illustrated reflected radio signals. in figures 1, 2, and 3. Tests on the reflective characteristics of Echo I Description of have 'been conducted throughout its lifetime to deter Experimental Stations mine the effects of the space environment. Immedi Before discussing the tests and results of the ex ately following orbital insertion and inflation, the perimental program on the Echo I and Ecfco II satellites, Collins Radio Company successfully transmitted a the ground station equipment should be described in facsimile picture between Dallas, Texas, and Cedar brief. Stepids, Iowa, via the Echo I satellite. The U. S. Naval Research Laboratory station em The Echo II Satellite ploys a 6 0-foot-diameter antenna, low-noise TWT re ceiving preamplifier, and a pfease-lock receiver utiliz The success of Echo I initiated a program for im ing special provisions to yield "analog data. Data was proved materials and, inflation techniques ; and the re taken at 2380 MHz, 2260 MHz, and 2190 MHz. Also, sultant launch of Echo II in June, 1964. In preparation a 10-kilowatt transmitter at the station was utilized in lor the launch, the Goddard Space Flight Center of the communications experiments. The NRL antenna NASA fead organized a network of ground stations to was pointed by means of a programmed track using study, during its first year in orbit, the communica predicted look angle tapes, corrected by optical sight tions capability of the Echo II satellite. The network ing when possible and by peaking the signal return consisted of the U. S. Naval Research Laboratory sta when the satellite was not optically visible. tion near Washington, D. C. ; the Ohio State University It should be noted that Research Foundation station at Columbus, Ohio; and all experiments by this net work were communications the Collins Radio Company experimental station near oriented and NASA provided

1 all satellite ephemeris data. Each station received a that expected for a perfect sphere at the predicted ianga set of weekly predictions. While the predictions were The data indicated that the satellite characteristics did adequate for the communications program, they were not change significantly with time, and that the Echo II poor in comparison to ephemeris data on other satel exhibits a cross section average of 1060 square meters lites; the limited use of Echo I and Echo II not justify as compared to the physical cross section of 1320 sq. ing expenditures for high accuracy satellite orbit pre meters. The Echo I exhibits a cross section of about diction programs. 3 db less than Echo II, which is approximately equal to the ratio of their physical cross sections. Analog re University Research Foundation The Ohio State cordings of received signal level are shown in figures dishes and parametric (OSU) station has four 30-foot 4 and 5. amplifiers feeding phase-lock receivers with phase- locked demodulators for deriving analog signal strength Time and Amplitude Distribution measurements. The station employs monopulse track of Fades of the four antennas. ing for the pointing Another item of extreme interest concerning the The Collins Radio Company (CRC) experimental reflected signal is its variability. The signal returns station employs a 60-foot and a 28-foot antenna. This are characterized by strong lobes persisting for a sec station was used primarily for transmitting to the ond or so, and short deep nulls between lobes. The other two stations on each of the three frequencies in depth of the nulls is normally about 20 db. to receive the 2380 MHz volved, but was also used As was previously indicated, the scintillations vir from NRL at each of the two antennas, for a signal tually disappeared on several occasions. We believe In the normal mode of space diversity experiment. this was due to the line-of-sight coinciding with the axis 10-kilowatt transmitter operating on a 50- operation a of rotation of the satellite. percent duty cycle was used in the 28-foot dish to il luminate the satellites. The 60-foot dish and receiver Essentially all of the power fluctuations occur at tracked the reflected signals and completed the radar frequencies below 3 or 4 cycles. By removing the var loop. Simultaneously, on one of the other two fre iations due to change in range between the satellite and quencies, a 10-kilowatt transmitter in the 60-foot dish the ground stations, it was found that the amplitude illuminated the satellites for the other stations. fades could be approximated by the Rayleigh distribu tion curve. The characteristics of the reflected signals from the Collins station and from the NRL Data are indicated in figures 6 through 10. station was reduced and processed by Collins, and the data from the OSU station was reduced and processed Bandwidth and Diversity by OSU. Measurements The data obtained from the program is unclassi An item of importance in the evaluation of a com fied and may be made available by Collins Radio Com munication medium is the coherent bandwidth of the pany with the permission of NASA to interested parties. medium. It is also of interest, if the medium produces While the complete program cannot be detailed here, scintillations, to discover what sort of spacings will some of the more interesting aspects are included. provide for satisfactory diversity operation. The co herent bandwidth in this case is defined as that band Typical Communication Experiments width over which the fading is highly correlated. Fre quency diversity measurements were first attempted by interest centered on the effective In general, the modulating the carrier with 6 MHz to produce sidebands section of the satellites (Echo I radar reflection cross with 12-MHz spacing. This was also tried at 70 and the characteristics of the scintillation of and Echo II), 190 MHz. Due to equipment limitations, the wider the effects of these two par the reflected signals, and spacings combined space and frequency diversity. From link. ameters on the communications the data it can be concluded that both Echo I and Echo II Average Cross Section have a coherent bandwidth in excess of 12 MHz; fre quency diversity operation could be successful at 190 single characteristic Perhaps the most important MHz or greater; and space diversity would not normally to communications of the Echo II satellite as it relates improve the system. The effects of diversity operation This param is its effective reflection cross section. are indicated in figures 11 and 12. eter was determined by measuring the received signal level as a function of time and comparing the level to Digital Data Experiment quality. Degradation of signal level due to the wrinkled shape of the spheres is relatively minor. Had Echo As a part of the program it was felt desirable to II achieved the proper orbit without tumbling, obtain an indication as to the quality of transmission there would be essentially no fading. of digital data over the Echo II path. The experiment was performed by transmitting an audio frequency Proposed Satellites square wave, or a string of alternate ones and zeros. Appropriate equipment was constructed to drive a Bearing in mind the background already presented, standard counter when a bit was missing and the sub consider now the future aspects of passive satellite com sequent recordings indicated that an average of one munications systems. For a number of years Goodyear bit was lost for each thousand transmitted. As might Aerospace Corporation has conducted extensive research be expected with Rayleigh fading, the bit errors are on new materials and techniques that could be applied to by no means uniformly distributed in time. As a re passive satellites, which coupled with the advances in sult, the word error rate would be considerably better the rocket program enhances the bright future in this than would be calculated if uniform bit error distribu field. tion were assumed. The results of the digital data New materials have been developed which offer experiment are indicated in figures 13 and 14. larger-diameter spheres for a given weight, with a sub Facsimile Experiment sequent effective satellite gain. In addition, a photolyz- able film bonded to a wire grid has been developed. As was previously stated, a facsimile picture was The film would be utilized to shape the wire grid to proper transmitted between Dallas, Texas, and Cedar Rapids, form in space and then evaporate due to solar radiation. Iowa, following the launch of Echo I in 1960. In 1964, The remaining wire grid would then become a stable a picture was transmitted between Dallas, Texas, and satellite, unaffected in its orbit by solar pressures Stumpneck, Maryland. In the Echo II experiment, the as are Echo I and Echo II. The wire grid would be small facsimile signals were recorded on magnetic tape and enouth to be a good reflector at microwave frequencies. then played into the Collins transmitter at four times Meteor impact would penetrate the screen without dis the recording speed. The transmission utilized fre turbing the overall shape. Many other materials quency modulation onto the carrier and the reception with unique properties are also being investigated. was with a standard frequency discriminator. Repro ductions of the facsimile tests are shown in figures In conjunction with the new material developments, 15 and 16. new satellite shapes are being investigated. One of the more promising Audio Transmission is called a lenticular satellite (figure 17). Notice on the illustration that only that portion of A number of audio tests were made on both satel a sphere visible to ground stations serves a useful pur lites and, as a graphic illustration of the transmission pose. The remainder of the sphere may be removed path utilizing passive satellites, we offer for your con without loss in effective radar cross section. Thus, sideration a portion of one transmission made from the effective cross section may be increased by using the Collins station to the NRL station. We hope you the same material to form a lens. The curvature of will notice that while there are occasional bursts of the lens would be dictated by satellite height and re noise during deep fading, in between these bursts the quired coverage. Typically, for a synchronous orbit transmission is clear and virtually free of noise, and at 21,500 nautical miles, a weight reduction of almost at no time is selective fading evident. The results of 1000:1 can be achieved with a lens, compared to a similar tests utilizing Echo I are comparable. By re sphere. The deployment of the lens is illustrated in ducing the transmitter power 10 db on the Echo n figure 18. Notice that the lens is surrounded by a torus path, good communications were still obtainable. to insure circularity. The lens itself is caused to take the proper shape by inflating the volume contained Experimental Program Summary by the lens and an associated membrane. The satellite Each of the tests mentioned was designed as a must be earth oriented to achieve usefulness and this foundation for passive satellite communications sys may be done simply by attaching a mass at the apex of tems. We feel that the knowledge gained will be ap booms under the satellite. Similar booms on top of the plicable to future satellite systems. Please note that satellite are attached to a mass through a helical spring. in each test the scintillation characteristics of the re The spring and mass constants are chosen to damp the flected signal are the governing factors for transmission system during the initial orbits of the satellite and to maintain gravity gradient stabilization. Initial studies seriously considered for synchronous orbit altitudes, have indicated that this simple arrangement can main because the associated communication system suffers a tain lenticular satellite orientation to the local earth fourth power transmission loss with respect to path dis vertical with a nominal accuracy of 3 degrees and all tance to the satellite. the turning motion. This would essen but eliminate However, for a fixed-weight lenticular satellite, the tially eliminate any scintillation, should the lens take effective overall system path loss reduces in effect to an irregular shape. Hence, any deformation would that of approximately the square of the distance to the result in loss of gain but would not degrade communi satellite. This is because the satellite T s lenticular angle cations quality. is selected to illuminate only the region near the earth An additional stabilization force may be derived rather than reflecting isotropically like a complete sphere. by a loop of wire through the booms carrying a current This fact can also be deduced by noting that the equiva derived from solar cells. This system would essen lent reflected power is independent of orbital altitude if tially remove the turning component by aligning the the lens angle is varied as a function of height. satellite with respect to the earth T s magnetic field. Synchronous orbit passive communication satellite The torque produced by this "compass" effect has been systems will be considered to show the potential of this investigated by other satellite systems. concept. In the case of either active or passive satel The station-keeping facilities for the satellites to lites in synchronous orbit, only three satellites are re maintain their position over a given point above the quired for world coverage. equator are being investigated. Feasibility studies Communication System for have indicated that a technique called "solar sailing" Passive Satellites in may be used. Special coating on portions of the satel Synchronous Orbit lite to absorb or reflect solar energy could produce the required torque vectors to maintain a given position Several system configurations which may be used relative to earth as the earth and satellite rotate with are indicated in figure 19. Note that if a Saturn C-5 respect to the sun. rocket were utilized to place a lenticular satellite in synchronous orbit, presently available materials would The development of the Saturn C-5 launch vehicle allow the satellite to have an effective diameter of 6400 has given us the capability to place a 25,000-pound feet (3200 feet radius of curvature). The gain of the satellite in synchronous orbit. Using the lenticular satellite is plotted as a function of frequency, relative concept with materials already available, a satellite to a one-square-meter reflector. Path loss is also in with a diameter of 1120 feet could be placed in orbit. dicated as a function of frequency for synchronous alti - At synchronous altitude the radius of curvature could tude. be 3200 feet, or an effective diameter of 6400 feet, to correspond to an included angle of 20° for horizon-to- The other two curves indicate the relative size of horizon coverage. Based on the radar equation, the antennas required to communicate for a given transmit satellite would exhibit a gain of ter power. In the case of voice transmissions, assuming a 6 kHz bandwidth and a transmitter power of 1 kw, 34- 2 2 antennas would be required at 10 GHz. A G = 4?r P 47T2 (3200) 2 foot-diameter s X X" 10 MHz bandwidth would be available with antennas less than 100 feet in diameter if 50 kw transmitters were with X expressed in feet. For the weight expressed utilized. This represents a system capability of approxi and the diameter indicated, the material utilized has a mately 10 db below that of an active satellite. This ratio weight of less than 0. 02 pounds per square foot. The could be reduced considerably as newer materials are actual material available has exhibited a weight reduc introduced or through the use of larger launch vehicles. tion of approximately 100:1 compared to that used on the Echo I and Echo II satellites. One of the outstanding assets of the passive satellite is the unlimited bandwidth and access to all users. As Typical Proposed Communications an example, if the 1000-foot-diameter antenna atArecibo, Systems Puerto Rico, and associated 150-kw, 400 MHz trans mitter were used to illuminate the satellite, voice broad General cast reception could be achieved via a receiving antenna Isotropically reflecting passive communication with only 15 db gain. This would correspond to a 6-foot satellites, such as Echo I and Echo II, have not been dish. Since the 6-foot dish would have a beamwidth of 30 degrees, it could be permanently mounted. altitude and, after assembly, be injected in a synchro nous orbit. To reiterate, I would like to point out that Notice that the received signal is a direct function presently available rockets and materials can inject of transmitter power. Many types of ground stations into synchronous orbits passive satellites that would could simultaneously use the satellite for special pur allow communications systems to be established with pose network requirements as they are conceived overall system gains approximately 10 db below that of either prior to or following orbital insertion. The present active satellites. This difference can be easily satellite concept discussed is expected to have a life achieved through an increase in transmitter power in time on the order of tens of years. the ground terminals. One further possible system Communications System for configuration may be explored. For a given satellite Low Orbit Passive Satellites weight using the lenticular concept, the ratio of the effective diameter, that is, the curvature of the lens The lenticular satellite concept is not restricted and increased diameter, is proportional to the square to any given orbital height. For a given height the of the intercept angle. As an example, consider a curvature of the lens may be set for horizon-to- synchronous satellite for hemispherical coverage with horizon coverage. As an example, if we utilize the an effective radius of curvature of 3200 feet and an lens at an altitude of 2000 nautical miles, the effective intercept angle of 20 degrees. The same weight may diameter would be 1296 feet and a single Saturn C-5 be utilized for a satellite with an intercept angle of 3 rocket could orbit 40 satellites. To give an effective degrees and an effective radius of curvature of 120, 000 continuous coverage, two vehicles would be required feet. This narrow beamwidth would be adequate to with the satellites launched in two planes. completely illuminate the United States. If the 1000- Based on an effective diameter of 1296 feet, fig foot-diameter antenna at Aricebe, Puerto Rico, utilized ure 20 indicates the required antenna sizes for a single a 150-kw transmitter at 400 MHz to illuminate the sat voice channel and for television. Note that for the ellite, nation-wide television reception would be avail same transmitter power the antennas on the ground able to every home owner using conventional television have been reduced in size by a ratio of approximately antennas and inexpensive frequency converters. This 2:3 for the smaller satellites in a 2000-mile orbit, as would put stringent requirements on the stabilization opposed to the large satellite in a synchronous orbit. system, as well as requiring accurate position keeping; Also, only two Saturn rockets would be required to but the concept does warrant serious consideration. orbit all the low orbit satellites as opposed to three rockets required for synchronous orbit. Although the Conclusions ground stations would require an antenna that would The proposed systems shown in this paper are be capable of following the satellites through their within the realm of possibility using available materi orbits, the required velocity of the antenna motion als, techniques, and presently available launch vehi would be small. cles. Experience gained from the Echo I and Echo II In effect, the communication system improve satellites has verified communication system param ment is approximately 6 db when using the low orbit eters and the pending trials on new satellites will veri satellites as opposed to the synchronous orbit, al fy the new material concepts. though smaller satellites are used. The lower orbit Passive communication satellites show great satellites also restrict communications range due to promise and present research may enhance the tech a lesser horizon for mutual visibility between two nology in the areas of proving and implementing satel stations . lite system capabilities. All of the research is directed Again, multiple access to the passive satellites is to providing economical communications systems. available throughout the frequency range of 0.1 GHz Lenticular gravity-gradient satellites, because of to 10 GHz for special applications and satellite life their inherent long life, capability to provide broad time is on the order of tens of years. communications bandwidths, and ability to operate with Specialized Systems an unlimited number of users, offer the promise of providing passive satellite communications systems With the advent of the Manned Orbiting Labora for global coverage. tories, it is conceivable that very large passive sat ellites could be assembled in space at a medium In conclusion, I would like to express my appre ciation to Mr. John Ford of Collins Radio Company and Mr. Charles Kelly of Goodyear Aerospace Cor poration for their assistance in the preparation of this paper.

List of References 1. EAKER, Herbert L. (Goddard Space Flight Cen ter; Greenbelt, Maryland), Post Launch Analysis Final Report, Passive Communications Satellite Echo II, (Published by NASA T s Goddard Space Flight Center; Greenbelt, Maryland), September 1965. 2. FORD, John L. (Space Systems Division, Collins Radio Company; Dallas, Texas), Some Commu nications Results of Echo II Experiments» (Pub lished by Collins Radio Company; Dallas, Texas), Presented to the 17th Annual SWIEEECO, Dallas, Texas, April 1965. 3. KELLY, Charles M. (Goodyear Aerospace Cor poration; Akron, Ohio), Potential Passive Satel lite Communication System for all Nations, Pre sented to the XVth International Astronautical Congress, Warsaw, Poland, September 1964. 4. Echo II Experimental Program Final Report, (an Engineering Report Published by Collins Radio Company; Dallas, Texas), Prepared in Response to Contract MASS-3 640, July 1965.

CROSS-SECTIONS OF ECHO I AND ECHO H MATERIAL

ECHO I ECHO II

0.5 mil MYLAR MYLAR 0.35 mil

VAPOR'—"""2200A

DEPOSITED ALUMINUM AL FOIL 0.18 mil AL FOIL 0.18 mil

SAMPLE SIGNAL RETURNS-PASS 3001 - ECHO H -no -115 -120 -125 -130 o -135 UJ -140 yj^^^i'Trmn iM;i ht TTTTI PiNl n ^' ^tt'''M~!'MTl''''r'l" 1 '"l,' ! ^i 1."

iî;ii«y^, ; pfwr««:f'iM( f :i îliiliffiiflfiSI 15 20 25 30 35 40 45 ELAPSED TIME, SECONDS SAMPLE SIGNAL RETURNS - PASS 3483 - ECHO E £ -no gaditl_:i^:|±i±^Siii^^•-:•————! ' i I ;|-j --.'I'————:|. 1 I: !•: :: |::K:|: :l: I I | -I I I I I I i | | I ! I I .! I ! | I . I. S -120 V r.:LL^.|jW!l. 1-I-- -:I?J-l,LjirtplLL±Ui. ÎL 1:i .m._L !.il±i..L:.,,I.:j:.iTU 2 I -125 £° -130 a - 135 £ -140 ^-^jjfiM^fehiifjiyijj-i 5 -no W^^^^^l^l|:- -:fl1^| : .-h:f:^WB m i5-120 -115 Si -125 > Q -130 o-U -135i-ir 44 S -140 ———^

10 15 20 25 30 35 40 45 ELAPSED TIME, SECONDS

RELATIVE AMPLITUDE SPECTRUM OF RECEIVED POWER - ECHO I

NO. 2 PASS NO. 17%5 NO. 3 PASS NO. 1M54

0.1 0.03 0.10 1.0 FREQUENCY - CPS

10 RELATIVE AMPLITUDE SPECTRUM OF RECEIVED POWER - ECHO I 10 LEGEND "" NO. 1 PASS NO. 25 NO. 1 " NO. 2 PASS NO. 1197 ~? / "" NO. 3 PASS NO. 1717 ;NO. 7 - - - - NO. 4 PASS NO. 2653 \ ^ NO. 5 PASS NO. 3094 \S •NO. 6 " NO. 6 PASS NO. 4069 x NO. 7 PASS NO. 4505 ^<\ ^NO. 3 1 ^ ^-:^ / ^T"i ^^^ 1.0 1 YO. j^-NO.4 ^ s ^5-

MSSN * " ). 1 Xs I. 3 ^ , W S \S -t-h << *•" NO. 2 NO 4- 1 N 0. 6- ^ — •* NO. i ^Ss, 0.1 ^ ^ 0.03 0.10 i.o ^ 10 FREQUENCY - CPS

DENSITY HISTOGRAM - PASS #6

ECHO H PASS 16 22 1177 DATA POINTS 1/4 SEC SAMPLING PERIOD

-4 2° MEAN • 899 SQUARE METERS DATE: 640125.18 I 18 i 16

^ 14

1 12 i. u. ° 8

8 6 oc fP^ LU Q_ 4 ij

2 \sLr-U "^-^- ^-U-J-u, i r-* ——— ,_ () 500 1000 1500 2000 2500 3000 3500 4000 SQUARE METERS

11 DENSITY HISTOGRAM - PASS #1170

ECHO H PASS 11170 22 1978 DATA POINTS 1/4 SEC SAMPLING PERIOD 20 MEAN • 1110 SQUARE METERS DATE: 640423.01

12 Pt-

4 L LjT-I.^ 2 *—— - L__ -• ——— ———«——— L. "•»—— • — • — — i i £1 500 1000 1500 2000 2500 3000 3500 4000 SQUARE METERS

DENSITY HISTOGRAM - PASS #2310

ECHO H PASS «310 22 1076 DATA POINTS 1/4 SEC SAMPLING PERIOD 20 MEAN • 1406 SQUARE METERS DATE: 640718.03 a 18

e 14 I 12 I., s, 1;

500 1000 1500 2000 2500 3000 3500 4000 SQUARE METERS

12 AMPLITUDE CORRELATION MEASUREMENT ECHO I PASS 1533

CROSS CORRELATION EXPERIMENT RESULTS

SPACING ECHO ECHO (MO II _\_ 12 0.91 0.88 0.90 0.84

70 0.63 0.50

190 0.44 0.39 0.35

13 • ' : ; : : ; i ; ? ; ! : < ' • = : : ; ; = ; • : ; i • ; • i . : •; • ; - i • • i : i': i i I 1 r • . : • • = '• \ '•• M : ; ; i • ; '= ' ; : : ' ' : ' '•' '• '• ! ' !| ' ' ''• ' ' = • • " ! 1 "f -j- - : j-Mi- '-' i .J. : ,j.._L...!.... i : 1 ! i j •; i j ] j : , : , i j ; ; • ; ; i ; ; j ; ; i i i ! jr;rT'1~rrt"1"1" i , i . ! } i • ; ii~Tl" i i i 'f-rrr' l"1 ••!••-[-•)- rl -|-rTtt"T1' T-;-"!'"'!" ITJ_ : L4...i.... ""]"" -|-j...L: ~ i i 1 i

: i ! Si i I i ! ! i Li i j -: i i . : . . ; i i MM irr'TT'TTT-iTTTTS ,!• I""!" s r < • ' ' \ • . • 0 15 30 45 60 75 90 105 120 135 BITS TRANSMITTED, THOUSANDS

' -

s~ '( - / 0 - x *x 0 ^ - > sf ' * O o <^

x°< tf^ O - x ' x DIGITAL DATA o / EXPERIMENT

o ECHO PASS 1730

0 o

0 EXPECTED ERROR RATE FOR AVERAGE SIGNAL RECEIVED ASSUMING RAYLEIGH FADING AND LINEAR DETECTION 0 EXPECTED ERROR RATE FOR AVERAGE SIGNAL . RECEIVED MINUS 3 DB 0 AC:TUAL ERR OR RATE AkVG'D OVI:R 15,000 BITS

130 180 230 280 330 380 430 480 TIME IN SECONDS

14 ill

tit

\ OH03 VIA 31IWISOVJ A9 Q3AI303d a311IIAISNVai HdVdOOlOHd HdVdOOlOHd JO AdOO dO AdOO

OF OF

ECHO ECHO

COPY COPY

RECEIVED RECEIVED

VIA VIA

PHOTOGRAPH

OF OF

vpr.

FACSIMILE

COPY COPY

BY BY

TRANSMITTED PHOTOGRAPH PHOTOGRAPH LENTICULAR SATELLITE CONCEPT

FOR HORIZON TO HORIZON COVERAGE 0=2SIN-' Ro Ro+H 6= 77 Po

ORBITAL FOR CONSTANT WEIGHT ALTITUDE 6 66 .A!. WHERE 0o = 20 DEGREES AT SYNCHRONOUS HEIGHT

17 LENTICULAR SATELLITE

18 GHZ

FREQUENCY

•

U.I.A.

4973

MAD!

CO.

E8SER

DIVISIONS

KEUFFEL

CYCLES

SEMI-LOGARITHMIC

GHZ

- -

FREQUENCY FREQUENCY

1 1

359-61 359-61

DIVISIONS

70 70

X X

CYCLES CYCLES

2 2

dl-LOGARITHMIC dl-LOGARITHMIC

90 8