Effects of the Satellite Power System on LEO & GEO Staellites

8/6/2019 Effects of the Satellite Power System on LEO & GEO Staellites

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NTIA-Report-81-75

Effects of the Satellite PowerSystem on Low Earth Orbitand Geosynchronous Satellites

W.B. GrantE.L. MorrisonJ.R. Juroshek

u.s. DEPARTMENT OF COMMERCEMalcolm Baldrige, Sec,retaryDale N. Hatfield, Acting Assistant Secretary

for Communications and Information


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PREFACE

This report summarizes work performed for the Department of Energy, Satel l i tePower System Project Office under the direct ion of Dr. Frederick A. K oo ma no ff .The w o ~ k performed under Contract Nwnbers DE-Al06-79RLl0077 and DE-AlOl-80ERlOl60.0i s written for a wide audience, inc luding the non -techn ical as well as the technicaHence, rigorous mathematical calculations are kept to a mi ni mum.


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TABLE OF CONTENTS

PREFACELIST OF FIGURES .LIST OF TABLESABSTRACT1. INTRODUCTION

PAGEiii

viv i i

1

1GEO SATELLITES.2.12.22.3

-, 2.42.52.62.7

Uplink Antenna PatternsSignal Processing Satel l i tesGEO Satel l i te ReceiversGEO Satel l i te EffectsInterference to Geostat ionaryStation Keeping ProblemsMitigation Techniques

Satel l i tes

2020272731385050

3. LEO SATELLITES3.1 LANDSAT Satel l i te3 ~ GPS Satel l i te3.3 Space Telescope

4. SUMMARY OF POTENTIAL INTERFERENCE TO SATELLITE COMMUNICATION SYSTEMS5. CONCLUSIONS AND RECOMMENDATIONS6. REFERENCES

......--.

52536266757677


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LIST OF FIGURESPA

Plane wave shielding effect iveness of g raph it e/ epoxyaccess door specimens . 1Satel l i te geometry showing possible signal multipath s i tua t ion . 1SPS on-board t rans la tor / repeater in support ofsatel l i te- to-satel l i te communication mode. 1

1

1

11

1

1

22222223333

1

Functional diagram of a solar cel l and conditioning system.SCR intermodulat ion modes.Block diagram of possible SPS control loop configuration.A typical sa te l l i t e hemisphere coverage pattern.A typical satel l i te spot beam antenna pattern.SPATS error response - single cw in te r fe ror .Generai signal processing sa te l l i t e block diagram.Multipath modulation spectra.Functional organization of two types of sa te l l i t e receivers .SS-TDMA repeater performance characterist ic.Matr ix swi tched t ransponder response.

Figure 1. SPS r ad ia ti on pa tt er n on the ear th.Figure 2. High power klystron emission at harmonics of thefundamental frequency.

Spacetenna - F2 pat tern estimate.Spacetenna - f 3 pattern estimate.Spacetenna effect ive radiated power 90 off boresight .H-Field shielding effectiveness.Magnetic shielding e f fec tiveness of g raphi te /epoxy paneland panels joined by Hi-Loks.E-Field shielding effect iveness of g raph it e/ epoxy paneland panels joined with Hi-Loks.Plane-wave sh ie ld ing e f fec tiveness of graphite/epoxy plainpanel and panels joined with Hi-Loks (QR V).Attachment i n te r face c ros s- sec ti on of panel and access door.H-Field sh ie ld ing e f fec tiveness of graphite/epoxy accessdoor specimens .E-Field shielding effect iveness of graphite/epoxy accessdoor specimens .

Figure 3.Figure 4.Figure 5.Figure 6.Figure 7.Figure 8.Figure 9.F ig ure 10.Figure l I .Figure 12.Figure 13.

Figure 14.F igur e 15.F igure 16.Figure 17.Figure 18 .F igure 19 .Figure 20 .Figure 2l.Figure 22.Figure 23.Figure 24.Figure 25.Figure 26.


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LIST OF FIGURES (CONT.)PAG

51

4447

5455565759606465676970727374

SS-TDMA repeater error character is t ic - two cw interferor cases. 35Single conversion t ransponder response . 36TDMA/PCM error character is t ic - two signal in ter feror . 37Communication satel l i te uplink/downlink frequency trends. 39Power density from SPS as a function of distance alongt he geostat iona ry orbit . 40Global beam footprint from INTELSAT IV. 43

Sate l l i te r ta t ion keeping problem potent ial interference.LANDSAT wideband communications subsystems mechanicalconfiguration. 'LANDSAT communication l inks.

Geometry for calculating angle from SPS bores ig ht to l inejoining INTELSAT IV. 43SPS rectenna gain versus range Qf angles where possibleinterference with INTELSAT IV may occur.CONUS beam' for the advanced WESTAR.

SPS microwave beam geometry at LANDSAT orbi t alt i tude.LANDSAT functional impact modes.Image dissector s tar tracker error character is t ics .thermatic mapper tes t p lan conf igura tion .SPS microwave beam geometry a t NAVSTAR orbi t al t i tude.GPS functional impact modes.S ta r tr ac ke r - stabil ized platform al t i tude responses.Crc;>ss-sectional view of the sa te l l i t e observatory.SPS power beam geometry for space telescope EMC analysis .COD video noise spectra.CCDvideo noise spectra - SPS i l lumination.CCD array imaging characterist ic .

Figure 27 .Figure 28 .Figure 29 .Figure 30 .Figure 31-Figure 32 .Figure 33.Figure 34.Figure 35 .Figure 36 .Figure 37.Figure 38 .Figure 39 .Figure 40 .Figul:e 41-Figure 42 .Figure 43 .Figure 44.Figure 45.Figure 46.Figure 47.Figure 48.Figure 49.Figure 50.

LIST OF TABLESTable 1.Table 2.

Est imates o f the Power Coupled into a 1640 MHz Satel l i teTransponder Separated 0.1 Degrees from aSPS.TDRSS Interference Estimates.

4249


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EFFECTS OF THE SATELLITE POWER SYSTEM ON LOW EARTHORBIT AND GEOSYNCHRONOUS SATELLITES*. B. Grant, E. L. Morrison and J. R. Juroshek

The large amount of power contained in the main beam and principals idel obes o f the proposed Solar Power System (SPS) , now under study byDOE and NASA, potential ly presents an EMC problem for other sa te l l i t e .systems. This report examines selected geosynchronous orbi t (GEO)satel l i tes in adjacent slots to an SPS, GEO satel l i tes on a chordpassing an earth horizon, and l o w ~ e a r t h - o r b i t (LEO) satel l i tes whichmay pass through the SPS power beam. Potential funct ional and operat ional impacts to on-board systems are analyzed. Mitigation techniquesfor SPS effects are examined, and recommendations summarized to allowsatel l i tes to operate sa t i sfac tor i ly in an SPS environment.

1. INTRODUCT IONThe SPS concept proposes a large geostationary sa te l l i t e which converts the

sun 's energy to direct current (dc) and converts the dc to microwave energy viahigh-power klystrons. The microwave energy i s formed into a beam using a largephased-array antenna 1 km in diameter. The energy is t ransmi tt ed to earth andcollected a t a receiving antenna (rectenna) where some bi l l ion dipoles convertthe microwave ene rgy back to dc where it is summed on summing busses. Each sa te l lis capable of radiating approximately 6.85 GW of microwave power, with the designintended to provide 5 GW of elec t r ica l power for dis t r ibut ion. The current design(DOE/ER-0023, Oct. 1978) emphasizes the 2.45 GHz ISM band for satel l i te-earth powetransmission.

One principal element in the Environmental Assessment Program supporting theSPS concept definit ion phase addresses the electromagnetic compatibility (EMC) ofthe proposed system. The scope of the EMC evaluation i s in p ar t d ic ta te d by thehigh microwave power of the SPS and the wide range of suscept ibi l i ty of radiofrequency receivers and other electronic equipment. On the ear th, an exclusionarea surrounding th e r ec te nna keeps systems from operating in the high-energyportion of the power beam. However, a sa te l l i t e in low earth orbi t (LEO) may passthrough the center of an SPS beam, subjecting it to extremely high f ie ld i n te n s it ieAlso of concern with such a large sa te l l i t e in geosynchronous orbi t (GEO) and thehigh microwave powers involved i s the potential interference problems that mayexis t between SPS and other sa te l l i t es eolocated in GEO.

The spacetenna radiat ion pattern for the 10 dB taper a t the ground is shown inFigure 1. This pattern assumes no phase or amplitude d i st ri bu ti on e r ro r , with 2%

The authors are with th e U.S. Department of Commerce, National Telecommunicationsand Information Administration, Ins t i tu te for Telecommunication Sciences, Boulder


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.1

.5

1.0

.0 5

5 0 ~ \ V ~ " v < : : - ~ o , , '.;:.'- 0


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klystron f ail ur e r ate . The effect of antenna errors would be to d ec rea se power inAt the surface , the peak2the center of the rectenna, under idea l conditions, would be 23 mw/cm ,

to 1 mw/cm2 a t the edge of the rectenna, and 0.08 mw/cm2 for the f i r s tThe space tenna plane wi l l develop 22 kW/m2 a t the center , and about

the main beam while increasing power in the sidelobes.power atdroppingsidelobe.22.4 kw/m a t the edge.

At p re sent t he re are no measured data available for the SPS antenna patternsand emissions a t harmonics of the proposed 2.45 GHz frequency. To get est imatesthat would be useful fo r the EMC s tudies , data was derived from measurements ofemissions from various high-power klystrons used i n m i lit ar y radar applicat ions.No wide-band sys tems were included so as to maximize the amplifier-output f i l t e rconfiguration relevance to th e SPS. Harmonic components re la t ive to the fundamentfor high-power k ly str on s a re given in Figure 2, based upon measurement extrapolat ioand the basic characterist ics of beam bunching and accelerat ion effects in tubecavit ies ( J . R. Rowe, 1965; Scherba e t a l . , 1971).

E stima te s o f second (f 2) and thi rd ( f 3) harmonic spat ia l distr ibut ions forthe SPS were derived from weighing pattern spat ia l components and correlat ionfunctions for fa , f 2, and f 3 for the COBRA DANE and SPY-l mil i tary radar systems,deriving aperture correlat ion functions for the harmonics. The SPY-l and COBRADANE systems use large phased-array antennas. Spectrum s ignature data for theSPY-l and COBRA DANE sy stems ha s a measurement error of less than + ldB inabsolute gain. These functions were combined into a l inear relat ionship to allowextrapolat ion to the aperture-wavelength ra t io for the SPS. These SPS radarra t ios were used with r el at ed co rr el at ion functions to develop spat ia l spectraestimates, referenced to boresight.

The procedure was tested in i t i a l ly in predict ion of the thi rd harmonicpat tern for the SPY-l radar system when steered to 12 off boresight with apat tern error distr ibut ion over the aperture extending from 0.08 on boresight to0.17 at 22 off boresight. These values were suff ic ien t ly accurate for the SPSpat tern est imates (Zaghlou1 e t a1. , 1978).

Predict ion procedures involved mapping the spat ia l f re quenci es f or the f 2 andf 3 patterns re la t ive t o phased-ar ray antenna element spacing and phase pat terns(normalizing aperture-wavelength and element-wavelength ra t ios ) , and pat ternsmoothing with a f i r s t order spat ia l f i l t e r . Using 10 dB antenna element pat tern


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o

- 30...QC- I.....V 60-J f2>W-J

Z 90 I-I ) II ) f3:Ew 120 f4150

HARMONIC EMISSION ESTIMATES

Figure 2. High-power klys tron emission a t harmonics of the fundamental frequency.


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point ra t ios , and direct aperture-wavelength rat ios for the SPS spacetenna andcomparison array spectra, the f 2 and f 3 pattern estimates were derived. These arep lotte d in Figures 3 and 4. These patterns are used with the fundamental fre-quency pattern ( fO) to develop the to ta l environments for other GEO and LEOsa te l l i t e locations. With these antenna and tube characterist ics, the effectiveradiated powers f rom a s ingle SPS sa te l l i t e a t 90 off boresight were derived(Arndt, 1980) and are given in FigureS.

The SPS space system intermodulation product emiss ions are an electromagneticenvironmental factor p rim ari ly fo r GEO satel l i tes positioned in adjacent orbi ts lots , and forwideband communications channels used by high al t i tude LEO satel l i te(al t i tudes ranging from 10;000 to 15,000 miles) . There are three sources ofintermodulationemissions from the SPS sa te l l i t e :

a. spacetenna and space vehicle structures i l luminated by the SPSfundamental and harmonic frequencies along with other t e r res t r i a land space sources (e.g . communication terminals, communicationsa te l l i t es , space radar systems, etc);

b. s ignal mixing in nonlinear ci rcui t elements in the power generationcliain; signal generators, power amplifiers, and phase and frequencycontrol circui t ry;c. s ignal mlxlng in the so lar cel l s and power conditioning circui tryon the SPS space system.

The SPS reference design indicates use of graphite epoxy composite materials forthe space vehicle structure, the solar blanket and supporting members, and thespacetenna. These materials have s ignif icant advantages in strength and weightcharacter is t ics over any metal structure for a system having the area of an SPSsa te l l i t e . Bonded joints of trusses and s t ru ts represent in termodulation sourceswhere large v ar ia tio ns i n electr ical cha.racterist ics over the bond area occur.Priori ty parameters include res i s t iv i ty , permitivity, and reluctances (bondcomposite boundaries and variat ions through the composite-bond-composite in ter facesCompared to m eta ls , composites are apparently more sensit ive to e lec t r ica l parametevariat ions induced by torsional s t ress across bonded areas .Intermodulat ion outputs from any junction are produced by multiple signali l lumination of an area having nonlinear resistance and reluctance character is t icswith the general relationships as d efin ed as fo llow s:

where a and b are even or odd in tegers. Frequencies and amplitudes depend on the


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oz- 10-- 20


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z 0-


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parameters of the nonlinear junct ion, and the effect ive aperture and currentreturn path impedances. Wide variations part icularly in the junction charact e r i s t i cs , occur because of material impuri t ies , time variant sur face cond it ion s,and the torsion stress factors.

Transmit Power =6.5 x 109 wattsa t 2.45 GHzTransmit Powerin dBmAntenna Gain at9 0 with respectto boresightEffect ive RadiatedPower

Fundamental(2.45 GHz)

128 dBm-20 dB

108 dBm

2nd Harmonic(4.96 GHz)

75 dBm+18 dB

93 dBm

3rd Harmonic(7.35 GHz)

34 dBm+18 dB

52 dBm

4th Harmo(9.80 GHz

15 dBm+18 dB

33 dBm

Figure 5. Spacetenna effect ive radiated power 9 0 off boresight.

The mil i tary services have in i t ia ted parameter measurements for variouscomposites to quan ti fy sh ie lding characterist ics and j unc tion proper ti e s relat iveto intermodulation generat ion. Exi sti ng data i s lim ite d in scope, but indicatesa t rend toward amplitudes in the range 0.3 to 0.5 re la t ive to aluminum or copper iident ical configurations (Hiebert , 1977, 1978).

For composites, the emission frequencies tend toward h ighe r o rd er frequencycomponents. This is correlatable with the higher dis t r ibuted reluctances andconduct iv i ty indicated in the prel iminary measurements. No genera li zat ions a rejus t i f ied on the basis of these data.The in teres ts of the SPS program wil l be served by continuing mil i tary R&D

in th is area. Measurements during development of bond and surface s tudies , anddepth variations of electr ica l parameters, wil l continue to provide data t ranslatable to SPS needs. This information wil l support a task being ini t iated byITS to re la te material and bond character i s t ics , i l lumination frequencies andamplitudes, and dominant emissions. The mil i tary measurements wil l also includetors ional stress variat ions to indicate bond parameter dependencies , which areuniquely important for the SPS because of the large moments caused by s ta t ion-keeping orb i t adjustments over a system operational l i fet ime.


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Because of the high radiat ion power of the SPS, careful ci rcui t coupling andconfiguration design are particular ly important to minimize inadver tent in tercoupl iof s ignals . Shielding and f i l te r ing for power amplifiers, and modulator e lementsassociated with phase or frequency control , must provide 40 to 60 dB isolat ion toassure suppression of intermodulation components into the f ina l power module bya t l eas t 80 to 100 dB. This requires increased emphasis in the shi el di ng a reabecause of reduced isolat ion due to composite structure shielding character is t ics .A representative comparison of shielding effectiveness for aluminum "thick wall"and foi l versus various composites i s shown in Figure 6. These data imply theposs ibi l i ty of dual shields for the high power modules and control of ground buscurrents through large area-low res is tance con ta ct a re as and s ingle point topology.

Various shielding character i s t ic da.ta for the 1 MHz to 1 GHz f requency rangeare presented in Figures 7 through 13 (Hiebert, 1977, 1978) for graphite epoxyforms. These data in clude sheets , and sheets w ith a cce ss areas having di f feren tbonding methods. These plots i l lus t ra te the shielding sens i t iv i ty for reduction oforbi ta l in termodulat ion sources. Genera.lly, in the f requency range of 100 MHz to1 GHz, there i s an indicated reduction in shielding effectiveness of compositesre la t ive to aluminum of 10 to 30 dB (Heibert ,1978; Wallenberg, 1980).

Another area of intermodulation generation, along with use of composites,would be the solar panel and conditioning circui t ry direc t ly coupled to groups ofsolar cel ls as these are exposed to SPS power along with exposure by othersa te l l i t e i l lumination sources. Space radars to be employed for military, ear thresource, and atmospheric monitor applicat ions and transmissions from GEO sa te l l i t ein orbi ta l posit ions adjacent to SPS represent the primary EM environment as i twould exis t today. Future space communication operations that would be impacted bySPS concern sa te l l i t e to sa te l l i t e modes, where SPS wil l be stationed betweencommunication sa te l l i t es (see Figure 14). As the f igure indicates , the large crosssect ion of the SPS sa te l l i t e ('\.,40 km2) represents a general ly unacceptable s ignalmultipath s i tuat ion as depicted by the single sa te l l i t e geometry. The SPS wil lrequire an on-board frequency t ranslator re pe ate r to support th is sa te l l i t e tosa te l l i t e communication mode, as shown in Figure 15. These addi ti ona l s ignal s wil li l luminate portions of the SPS sa te l l i t e solar panels , thus mixing with ambient SPSpower-beam fundamental and harmonic components . The large a ctiv e s ola r pan el a re arepresents a major source of sum and difference frequency products for combinationsof SPS, radar , and communication signals and increases spurious emissions and onboard EMI problems.


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0.037511. GRAPHITE

I/SII AL SHEET

A I 0.0013 AL FOIL

0.0411 GRAPH ITE ..,...LAMINATE-4PLY

o

80

60-Q"C-Z0' 40:::>zwI -

20

10 100FREQUENCY (MHZ)

1000

Figure 6. H-Field shielding effectiveness.


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100 .- o 90 ORIENTED PANEL JOINED TO GRAPHITE/EPOXY DOUBLER WITIlIII-LOKS0------ 0 ORIENTED PANEL JOINED TO GnArI/ITE/EPOXY DOU8LER WITI.IIII-LClKS /

/

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100

,PLAIN PANEL /V '

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routilti lWZw>l -UWILLLWoZ0llJ-Iti l

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Figure 7. Magnetic shielding effectiveness o f g raph it e/ epoxy pan el and panelsjoined by Hi-Loks.


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60 "-

o , ..........80 1-- - ....................~ ' ' ' , ~ -40 I- 0 90 . ORIENTED PANEL JOINED TO

GRAPHITE/EPOXY DOUBLER WITH HILOKS0------ 0 OflIENTED PANEL JOINED TO GRAPHITE/EPOXY D8UBLER WITH HI,LOKS

20 l- Cr--- PLAIN PANEL

120

100en"0u:ti lll.JZW>i=UUJLL

t- ' ILLUCJZ0-lW-IU1

+ INDICATES GREATER THAN MEASUREMENT CAPABILITYl ~ _ __- - - - . L I

.01'710

0.1 1 10FREOUENCY(MHl)

100 1,000

Figure 8. E-Field shielding effectiveness o f g raph it e/ epoxy pan el and panelsjoined with Hi-Loks.


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100 o 90. OniENTED PANEL JOINED;"fO GRAPHITE/EPOXY DOUBLER WITH HILm:S0- - - - - ---- 0 ORIENTED PANEL JOINED TO GRAPHITE/EPOXY DOUBLEFI WITH HI-LOI .. ...-0(/ J PLAIN PANEL/J " , , ~ ' " 60

... ,f= "...

u " -.LU ...L ,I. " ...UJ " -,,.Z "" ...-0 ,J 40 - '0 -__U -- --(/JJOINED PANELS

20 .-

iooI

1000FnEOUENCY l" 'lI lt)

Figure 9. Plane-wave sh ie lding ef fec t iveness of graphite/epoxy pla in panel andpanels joined with Hi-Loks (QR V).


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SUflROUNDING STRUCTUflE PANEL {1B31

I 4TO GMIL ALUMINUM FLAME SPRAY \

MBLY (O3lS DOOR ASSETWOPIECE Ace, I _' \ _'L)

f ~ _ ~ _ ---..... j IIASTENf:flSTTACIHvlENf FEMOVA8LE

'

4 TO 6 MI L ALUMI,'JUry1 F L A ~ . l E ' S P R A Y

l'EfHv1/\NENJ ATTACHMENT FASTENEflS

Figure 10 . Attachment in terface cross-sect ion of panel and access door.


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PANEL 18-2 (FLAME SPRAYED, EDGE T R E AT E D P M J EL WITH NO CU r OU T )PANE L 1B-3 WITH DOOR 0-2 ( FLAME SPRAYED D O O f ~ M o u r H E D ON 1B2 WITH CUT-OUT)PANEL 18-3 WITH DOOFl 0-1 (UNPROTECTED DOOR MOUNTED o r 1B-2 WITH CUT-Dun

I I ,

1 ; ' 64004 ' )

1.0 10.0FFlEOUENCY. ~ . ' " z

100.0 lK 10K

Figure 11 . H-Field shielding effectiveness o f g raph it e/ epoxy acc es s door specimens.


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110

PANEL lB-2 (FLAME SPRAYED. EDGE TREATED PANEL WITH NO CUT-OUT)PANEL 1B-3 WITH DOOR D-2 (FLAME SPRAYED DOOR MOUNTED ON 1B-2 WITH CUTOUT)PANEL lB-3 WITH DOOR D- l (UNPROTECTED DOOR MOUNTED ON lB-2 WITH CUTOUT)

90

80en"0 70 .-viU)UJ2 60 .-J>I- ' I i=0- UUJ 50 . .u,u,UJo 40 .-0..JlUI 30 - 6-V)

Q--- ' - - ---20 - 0-- -- -10 -00.01 0.1

J ~

1.0 10.0FREQUENCY, MHz

100.0 lK 10K

Figure 12. E-Fie1d shielding effect iveness of graphi te /epoxy access door spec imens .


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t - - , - ID. i PANEL 113-2 (FLAME SPRAYED, EDGE TREATED PANEL WITH NO CUT-OUT)D-- - - - l PANEL 18-3 WITH DOOR 0 -2 ( F LA M E SPRAYED DOOR Mo u rn ED or'J lB-2 WITH CUTOUT)0- - - - - i PANEL 1 8-3 W I TH D O OR 0 1 (UNPROTECTED DOOR MOUNTED ON 18-2 WITH curoun

100-

90.-

80 -

CD-0~ 70 .-v,wZUJ GO 0->uWLL 50 o-ILlIJ0;:: 40 0-0--ltUI 30(j )

20 ._

10 0-

00.01 0.1 1.0 10.0

FREOUENCY, Mllz100.0 lK 10K

Figure 13 . Plane-wave shielding effectiveness of graphite/epoxy access door specimen.


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f--100

SPS

.. --------- MUlTIPATH . _____20

ORBITAL LINE - V BANDSIN "'30 dB

FADE DEPTH - 20 to 34 dB

V C~ - - - - -- : - - -

Figure 14. Satel l i te geometry shOWing Possible signal multipath situation.


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SPS

30/ " " /f------- 17

0

COMM/ /'/ TRANSLATORI ----- - - CoSAT / ' / ' REPEATER ------- - S' - -~ - - -t-'\D

Figure 15 . SPS on-board t ranslator / repeater in support of sate l l i te- to-sa te l lJ ,ecommunication mode.


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A functional diagram of the solar cel l and conditioning system is diagrannnedin Figure 16 . Thece1i is electr ical ly a diode usual ly b ia sed to maximize currentflow for a range of solar i l lumination. Cells are connected in combinations ofser ies and paral lel through voltage and current control lers. The voltage andcurrent controllers would consist of sunnning amplifiers and s i l icon controlledrec t i f ie rs (SCR). The SCRunits represent a nonlinear impedance a t the inputterminal, coupling switching frequency components into the cel l circui ts . Theintermodulation modes are described in F igure 17.

Mitigation methods include band-stop f i l t e rs in the ce l l current l ines or awire mesh around the cel l blanket. The l a t te r should be a square grid mesh with amesh dimension of less than one half the wavelength of the h ighest i llumina tingfrequency and a wire size in the AWG 26 to 32 range. This wire size preventsblockage of solar cel l i l lumination from the sun. To minimize circulat ing currenteffects in the small diameter mesh, connections to a vehicle ground bus should beprovided a t 10-30 f t . intervals (Skolnik, 1962) .

There may be some effect on the EM environment for GEO and high alt i tude LEOsatel l i tes from control loop ins tab i l i t i es for the SPS. Figure 18 shows a blockdiagram of a poss ib le con trol loop configuration. Because of the time constantsinvolved on such a long two-way path and the large spacetenna gain, aim pointcontrol i r istabi l i t ies caused by propagation anomalies and control character is t icsrepresent a serious design problem. I f there were such instabi l i t ies , as thecontrol loop worked towards stabil izat ion, the sidelobe amplitude and phase wouldvary accordingly, depending on perturbation magnitudes, time-spectrum properties,and .con tr ol l og ic configuration. This would present a changing f Lel r ' for closein satel l i tes .

Principal driving forces affecting s tabi l i ty margins are t ransient meteorological events, periods of turbulent troposphere conditions, and mechanicaloscil lat ion of the solar cell panel-spacetenna structures. C o n t ~ o l - l o o p modulationspectra in the 1 to 40 Hz range results from th es e longer term effects, with components extending to 100 Hz for t ransient events.

2. GEO STATELLITES2.1 Uplink Antenna Patterns

Antenna patterns for terrest r ia l terminals and sate l l i te r ec ei ve rs a re ofnearly equal importance in establishing orbi t separation constraints between SPS


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CELLBLANKETAC/DCCONVERT

BATTERYCHARGEDC LOAD

T "T

t tPULSEWIDTHMOD

FIREANGLEUNIT I I ~ AC IHAPER -_...AC LOAD

CELL EQUIVALENT CIRCUIT(CONSTANT ILLUMINATION)

'

RJUNe

RSERIES

RSHUNT R LOAD

FIRECONTROLLER

POWERTRACK + - LOAD V,A

Figure 16 . Functional diagram of a solar cel l and conditioning system.

-


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3042 18.6 (51 + 52) (dB)

6o l _ ~ I I I Io

18 I I I II

51 = 52+6dBen""0-...-I- 12u: J000:::0..

6H


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M1PLITUDE I I r10[JULAR& PHASE . - - - - [> . CONTROLCOMPONENT 1-----[>FREQUENCYDRIFT I- - - -[ >CORRECTIONCfI.,L ._ - - - - - -

q.I

SIGNALPROCESSOR


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and'communications sate l l i tes . The satel l i te receiver antenna pattern is theprimary mode of coupling of SPS fundamental and harmonic frequencies into atransponder signal channel. Terrestr ia l terminal patterns concern satel l i tes i g ~ l tracking stabili ty. with interfe,rence from SPS emissions.

Sate l l i te receiver antennas employ two patterns: earth or hemisphere coverageand spot'beams for small area coverage. The la t ter contributes to inc reasedfrequency usage efficiency as well as reducing intetference ,potential from other 'terrestr ia l transmissions. A typical hemisphere coverage pattern is indicated inFigut;e19, thepa't tern being approX:imately6 to 12 in angle width. An earthcoverage pattern requires a beamwidthof 25 to 30 depending on service requirem e n ~ s n e a r the horizon. Spot beam modes use a beamwidth in the 0.25 to 1 rangeto tra nsmit o r re ce ive between a sa te l l i te and a t ermina l serving a metropolitanarea, county, or multi-county area. Spot beam operations will .be concentrated innhe 12 to 14 GHz and 20 to 30 GHzbands because of satel l i te aperture considerat ionEarth and hemisphere beams presently use horn antennas. ,Spot beams employ singlearid multiple paraboloid antennas, with single and multiple feed e lements for each,reflector. Beam switching involves selection of feed unit and reflector. Since'the' beams are at leas t three t imestheaiin po.intarea, small variations in sa te l l i tatt i tude caused by dr i f t and s ta t Ion-keepdng control wil l not affect commui:lication, l ink .performance, (Gets'inger,1977).

Future sate l l i te antennas will use a single phased array for large area andspotcoveragerequire:ments. Beam coverage selection and spot beAm selection basedon channe1,usage arid message address would be controlled through a computer/processor. Array 'patterns 'a s controlled byphaser andgairi components are selectedby message addresses' fromNDRO storage. Total beam excursion would be about+30, which is with in cur rent a rr ay technology. For frequencies in the 20 to50 GHz ran.ge, spot beamwidthmay be increased by 20 to 50% to reduce the probabilityof deep fades' ('\120 to 30 dB) because o f atmosphere anomalies, (Edelson et a l . , 1978Gou1d,eta!. , 1975; Morgan. 1978;Welti, 1978).

A typical 0.5 'spot pattern is plotted in Figure 20. Effects of SPS coorbitali I1terference with th e array operation are l i s ted below. 'Coupling of SPS componentsis dependent on array patte rn s f or the available phaser..,.gain functions at the SPSfrequencies.

1. I n t e r f e r e n c ~ entry through side lobes causing transient addresserror's and stepped beam j i t t e r .2. Incorrect beam selection because of interference induced messagecomponent error. This effect is magnified with spot beam operationbecause of the limited spatial c o v e r a ~ e .


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+10 -I):!:!.z+20(9

I I I I I I I30 20 10 0 10 20 30o. -e- .

Figure 19 . A typical sa te l l i te hemisphere coverage pattern.


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\

\ 01 3

+20.--CD.sz


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3. With the minimal beamwidth spot using pi lot car r ier t racking, side10beout-of-channe1 cw interference wil l cause angular j i t t e r withat tendant e sc ala tio n i n BER. Typical error r espons es a s previouslymeasured with out -o f-band cw i nt er fe r ence into Space Data and TrackingSystem (SPATS) r ec ei ve rs a re presented in Figure 21.

2.2 Signal Process ing Sate l l i tesA general s ignal processing sa te l l i t e configuration i s diagrammed in Figure 2

This system provides an advanced message and channel processing capabi l i ty re la t ivto cu rrent t ransponders, a l imited switching fac i l i ty , and a message buffer . Areaand spot-beam array antennas and the buffer capabi l i t ies provide time and spacemult ip lex ing operat ions for t e r res t r ia l point- '-to-point and point- to-area communi-cations modes. These modes would primarily operate in the 12 to 14 GHz and 20 to30 GHz bands for spot modes, and the 12 to 14 GHz and 6 to 4 GHz bands (Getsinger,1977)

Interference sensi t iv i t ies are l i s t ed .1. Coupling of SPS emissions into array sid e lobes causing array stepj i t t e r and message BER increase.2. Increase of message BER; synchronization uncertaint ies, address. errorswith incorrect spot beam assignments, and data errors .3. Reduced system and channel through-put because of address and beamcontrol errors.To maximize space system eff ic iency, sa te l l i t e - sa te l l i t e message t ransfer

wil l be employed to reduce uplink and downlink t ransfers for transcorttinenta1t ra f f ic . The large ref lect ion cross section ( ~ 5 . 1 0 4 m 2 a t 6 GHz, ~ 1 0 9 m 2 a t Vband) of the SPS imposes an unacceptable mu1tipath for the sa te l l i t e - sa te l l i t emode. A typical mu1tipath s pe ctra fo r East-West sa te l l i t e communications with anSPS ref lection component is indicated in Figure 23 . This spectra i s based on anSPS orb i ta l motion of +0.1 over a 24-hr period, and a communications sa te l l i t eorb i ta l movement of +0.1 over a 12-hr period. The SPS is represented as a f l a tref lec tor of 10 x 5 km with one -ha lf th e ref lectance of an iden t ical metal configuration a t the 2.45 GHz frequency. This s i tuat ion can readily be remedied witha frequency t ranslator transponder on the SPS; having a transmitted power of 100to 200 W for th is V band example wil l provide a SiN a t t he r ec ei vi ng sa te l l i t e ofabout 30 dB. No processing capabi l i t ies are required for the t ransponder.

2 .3 GEO Sate l l i te ReceiversReceivers employed for GEO communications sa te l l i t es extend from frequency

t rans la tors to systems that include switching between area and spot-beam antennas.Modulation and message modes include analog PM mult ip l ier , digi ta l PM mult ip l ier ,and spread-spectrum TDMA operat ions.


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1f9 r---- - - - -.- - - - - r-- - - - - ,

W 10-70:::0:::a0::0:::WI -m 10-6

-20101O-4L ' - - - l --L.

105/1 (dB)

Figure 21. SPATS e r r o r response - s ingle cw i n t e r f e ro r .


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CLOCK DATA SWITCH I ~ r--I SEP BUFFER MATRIX MOD A

:> ' I RCVR I I DEMOD II DECISION ADDRESS CONTROL IFILTER DECODE LOGICI I I II OTHER C H A N N E ~ S I I

IN CHANNELS

IIIIII

IIIIIII II ICOMPUTERCONTROL

IIIIII

CARRIERSOURCE

Figure 22. General signal processing sa te l l i te block diagram.


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c:::>,- - ....,... .-----r--__...,c:::>S2.

CllH+J(JQJo,UJ

c:::>p0-.-I+JCllM;:l

,,-... '"0N 0::Q S< ; ..c:+J

Cllc ,-.-I+JMc:::>...... .

C")NQJH;:l00-.-I

L- .....L.. . l . - -Jc:::>c:::>roI

30nllldV\ltt 3 1 \ I l ' V l 3 ~


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Functional organizations for these sa te l l i te receivers apdmessage processingand conversion modes are presented in Figure 24. The principal funct ions inc luder f amplification, conversion, noise l imiting,. switching, and channel separationand combining, (Bargellini, 1972}; Dicks and Brown, 197a; Morgan, 1978).

Receiver susceptibi l i ty to SPS emissions principally fnvolvesnonlinearresponses in th e tunnel diode and low noise FET input amplifiers"f.oroutofchannel interferor components, and resul tant intermodulatiyu product effects inAGC l imiter and conversion functions (Fuenzalida et al.. , 1973; Pau11ue1 e t a l . ,1973). For the repeater transponder systems (Figure 24), the p r i m a ~ y resul t i s Rdecreased SIN in th e output channels. For reductions in SIN in the 10-25 "dBrange, increased cross-talk for frequency-multiplexed analog modes exaggerateschannel noise. Typical repeater-transponder responses for out-of-bandinterferor.sat 2.45 GHz and 56 Hz are displayed in Figures 25 and 26. App.roximate "thresho14sfor cross-talk a re indi ca ted.The basic degradation chc:1racter for SS-TDMArepeatersis indicated inFigure 27, assuming the same two signal interferertces. Noise and intermodu1ationcomponents generated in the low nois e inpu t amplifiers and mixers i nc rease th eswitching matrix errors, and reduce the SIN in the subsequent. conversion andmultiplexing operations. A more gradual slope for th e channel e ~ r o r c h a r a c t e r i s ~ fis noted relat ive to the regenerative and basel ine repeaters . With a 10 t o l5 dBincrease in channel noise (input to the switch matrix), th e g race fu l degradationcharacterist ic decays to a catastrophic mode, as indicated in Figure 28 .The SIN characterist ic of th e DSCS repeater is affected by non1irtear responsein th e tunnel diode amplifiers and l imiters. Performance effects of noise andintermodulation components relate reduced channel SIN and c r o s s ~ t a l k at t h output of the diplexers and channel combiners. A represerttativechanne1 SINcharacterist ic for two s ignal inter fe rence is indicated in Figure 29.

2.4 GEO. Satel l i te EffectsSatel l i te systems deployed inc1dde civil ian and military communications

relays supporting in tercont inenta l services . Data, vQice,and entertainments erv ic es a re provided through these sa te l l i te operations. Sate l l i tes havingpotential interference degradation because of SPS operation. include:

MARlSAT 15 0 WATS 6 118 W (Variable)SATCOM 119 WCOMSTAR 95 W& 128 0 W


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WN

SINGLE CONVERSION TRANSPONDER

LNA RF> - - t MATRIX I ISWITCH

> I CONTROL I '

PA

Figure 24. Functional organiza tion of two ty pe s o f sa te l l i t e receivers .

, ,


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9-m I \ \ A- SIN'" 12 dBB. B - SIN", 3 dBz0~ 6 \ \; TIMING THRESHOLD0::(9w I \ ~ - - - D A T A THRESHOLD0-.JlL. 0

-24 -18 -12 -6 0 6CII (dB)

Figure 25. SS-TDMA repeater performance characterist ic.


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"....([) 15"D-- \ 1 - 2.45 GHz CW1 2 SN ..... 12dBw0::9w+:- W(f )o 6z

...JW 3zz$ 0u -6 -3 0 3 6 9 12sir (dB)

Figure 26 . Matr ix switched transponder response.

).-


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>-r-.-Jcomo0::0-0::o0::0::W.-JWZZIU

-810

-610 10 oS/1 (dB)

-10 -20

Figure 27. SS-TDHA r ep ea te r e rr or cha rac t e r i s t i c - two cw i n t e r f e ro r cases .


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m15"0......,1 2 \ 1 - 2A5GHz CWS/N",12 dBw0.:::9

w W0 \6z

cd 3zZ

Figure 28 . Single conversion t ransponder response .


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12

5/1 1=51I2 =6dB

3SIN (dB)

o.3

100 .......=---'-TJ---..:...- - - - - - - r r - J ) I10-2

10-6

0...Q) 1f4W--.J

Figure 29. TDMA/PCM error characterist ic - two signal in terferor.


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WESTARSBSANIK A-2, A-3LEASATBrazi l CommunicationsColumbia CommunicationsDSCS I I & I I IHughes CommunicationsRCA Alaska COMAdvanced WESTARINTELSAT

99 W & 91 W106 W & 122 W108.5 W & 114 W100 W65 W or 78 W79 WAtlant ic & Pacif ic75 W(to be assigned)103 W61. 4 E.

Communication sa te l l i t e uplink and downlink frequency trends are showni Figure 30. This trend to h igher f requenci es wi l l reduce SPS direct ouplinga t the primary frequency. Mitigat ion emphasis for commercial services wil lprimari ly re la te to harmonic and spurious emissions.

2.5 Interference to Geostationary Sate l l i t e sInterference between SPS and GEO sa te l l i tes includes adjacent orb i t and cross

orb i t geometry of the l a t t e r relat ive to the SPS communication sa te l l i t e couplingpath through an interconnecting chord passing nearly tangent to the Earth. Thismode wil l be addressed in subsequent discussions concerning SPS-INTELSAT in terferencoupling. The following discussion wil l show tha t substantia l s ig na l l ev el s canbe expected a t other orbit ing sa te l l i t e s , par t icu la r ly when they a re w ith in 0 .1degrees of orb i ta l separat ion from SPS.

The power f lux densi ty a t a distance r from SPS i s given by

(2)

where Gt i s the SPS antenna gain in the direct ion r , and Pt i s the input powerto the transmit antenna. The distance r can also be expressed in terms of d egreesof orb i ta l arc , where

r - d 57.3d i s th e d is ta nc e from the center of the ear th to the geostat ionary orb i t .SUbstituting (3 ) in to (2 ) resu l ts in

Figure 31 shows a plot of the power densi ty that can be expected for

(3)

(4)


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>-U:2 :w=>owa:

< ,

6/46Hz ->7

< ,

14/12 GHz ->7


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-30G) -

'10 (/s- I(\ J -40E< ,

" ' - "

CD -50"'0c...

-60.....(f )cQ)::))( -70Ju,Q)30 -80,

-90

1Separation, In degrees of orbitaI arc

10

Figure 31. SPS power density a t 2.45 GHz as a f un ctio n o f distancealong t he geos ta ti ona ry orbi t .


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Pt 6.85 x 109 watts,d = 4.22 x 107 m,Gt = 87 dB (boresight)

and three values of Gt , the spacetenna gain a t 90 degrees off boresight. Accuratedata for Gt a t 90 degrees off boresight (gain in the direction o f ad ja cen t geos ta tionary o rbi t) are not available a t the present time. However, i t is acknowledgethat these cal cu la ti ons a re accurate only fo r s ig na ls a t or near boresight and do noconsider quantities such as aperture phase distor t ion and control system toleranceswhich s ign i fican t ly a f fec t the r adia tion pa tt e rn 90 degrees off bor:s ight. The current technology in satel l i te antennas results in Gt values as large as -10 dBi ,(dBrelat ive to an i sot rop ic radiator ) given by the CCIR in Report 558-1 (CCIR, 1978c).This report will assume an SPS antenna gain in the direct ion of the geostationaryorbi t of Gt = -10 dBi unt i l more accurat;e estimates are avai lable.However the -10 dBi gain is applicable a t the normal v ic tim opera ting frequencywhich for MARISAT is 1640 M H ~ . A -10 dBi antenna gain a t 1640 MHz is equivalentto an effective antenna aperture of -35.7dBW/m2. The following will assume thatthe effective victim antenna aperture 90 degrees o ff b or es it e is the same a t2450 MHz as i t i s a t 1640 MHz.

Given the above assumptions, the power incident to a vict1m r eceive r aper tu recan be eva luat ed a s shown in Table 1. This table is prepared for a separationbetween SPS and victim of 0.1 degrees, and sate l l i te reference bandwidths of 4 kHzand 1 MHz. Note that the liN rat io for the 4 kHz reference bandwidth system afterfi l tering is 22.1 dB with 0.1 0 separation and 2.1 dB with 1.0 0 separation. Again,these figures should be less than zero to minimize the pot en tia l f or in te rf er en ce .These calculations show that a potential for interference exis t to satel l i tesseparated from 0.1 to 1.0 degrees from an SPS.2.5.1 INTELSAT

An example of possible interference from SPS to geostationary s at el li te s i sthe cross orbi ta l interference si tuation involving INTELSAT IV or IVA in geostationary orbi t over the Indian Ocean a t about 61.4 0 East longitude, (Bargellini,1972; Dicks , 1978) . Figure 32 shows the g lobal beam footprint as viewed fromINTELSAT IV or IVA. The global beam (NASA, 1975) for INTELSAT will have a 3 dBbeamwidth equal to the optical horizon or "limb l ine," and t he hal f- cone anglesubtended a t the satel l i te by the limb l ine is about 8.65 0 as shown in Figure 33.


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TABLE 1. Estimat es o f the Power Coupled into a l640-MHzTransponder Separated 0.1 0 and 1.0 0 from4-kHz ReferenceBandwidth

Sate l l i teSPSI-MHz ReferenceBandwiq.th lSeparation 0.1 0

SPS power density a t victim(gt = -10 dBi)Victim antenna gain indirect ion of SPSat 1640 MHzEffect ive victim antenna apertureat 1640 MHzEffective victim antenna apertureat 2450 MHzSPS power received on victim antennaVictim noise power in referencebandwidth ( t = 3000 K)l/N prior to transponder f i l t ~ r i n gEstimate o f t ransponderf i l te r ing 1640 MHz to 2450 MHzl/N a ft er f il te ri ng

-20 dBW/m2

-10 dBi2-35.7 dBm2-35.7 dBm

-55.7 dBW-157.8 dBW102.1 dB80 dB22.1 dB

-20 dBW/m2

-10 dBi-35.7 dBm2.

2-35.7 dBm-55.7 dBW-133.8 dBW78.1 dB80 dB-1. 9 dB

separation 1. 0 0SPS power density at victim(gt = -10 dBi) .Victim antenna gain indirection of SPS at 1640 MHzEffect ive victim antenna apertureat 1640 MHzEffective victim antenna aperturea t 2450 MHzSPS power received on victim antennaVictim noise power in referencebandwidth ( t = 3000 K)l/N prior to transponder f i l te r ingEstimate o f tr ansponde rf i l te r ing 1640 MHz to 2450 MHzl/N a ft er f il te ri ng

-40 dBW/m2 -40 dBW/m2

-10 dBi -10 dBi-35.7 dBm2 -35.7 dBm2

-35.7 dBm2 -35.7 dBm2

-75.7 dBW -75.7 dBW-157.8 dBW -133.8 dBW82.1 dB 58.1 dB80 dB 80 dB2.1 dB -21.9 dB


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O ' r - - - r - - - I

; .-.

60' 'IVFigure 32. Global beam footprint from INTELSAT IV .

------- .........../

// GEOLJ

II\\\\ -, -,


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The geometry for calculat ing the angle from boresight on the SPS spacetenna to al ine from the SPS spacetenna joining INTELSAT IV or IVA is shown in Figure 33.Assume the SPS antenna is oriented with i t s boresight direct ion (x-axis in Figure33) pointing toward an arbi trary aim point on th e s urfa ce of the e ar th s pe ci fi edby lat i tude, ~ and longitude A. A uni t vector from SPS to this arbi trary aimpoint on the earth; i . e . ,

e-x ( C O S A C O S ~ - S C O S A 0 2 ) + ( s i n A c o s ~ - s s i n A 0 2 ) + ~ s i n ~ (5)[1 + s2 _ 2 s c o s ~ c o s (A-A )]1/2

'r 02

where s = 6.619 earth rad ii , is the distance to geostationary orbi t from the ear thcenter , and AOI and A02 are the l ongi tude o fSPS and INTELSAT, respect ively. FromFigure 34, the angle a between boresight of SPS to INTELSAT is

cosa = (6)

80

40(I )"0

C0 0...

Q)

0CL

-40

-80

10.060.04.98.96 10.00 10.02ThetaFigure 34. SPS r ec te nn a g ain v ers us range of angles where possibleinterference with INTELSAT IV may occur.


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where a unit vector , ~ R from SPS to INTELSAT iseR e-x (7)

Assume the rotat ional orientat ion of t.he SPS antenna about i t s bor es ight axi sis such that the INTELSAT l ies in the ~ - p l a n e (or H-plane) of the SPS pattern( th is w ill correspond to a worst case in terference). Then = 0 and a = TI/2-e.If we substitute (5) and (7) into (6) using AOI = 61.4, A02 = -101.3, ( ~ . f .Figure 33) = 34, A = -101.3 (the l a t t e r lat i tude and longitude close toLubbock, Texas), we find a 10.25. In Figure 34 we p lo t, th e SPS r ec tenna gainin region around a = 10.25.

The power f lu x d en sity at any point in space is found from2W(watts/m ) e.i . r .p . /4TIr2

2G T ( 8 , ~ ) P T / 4 T I (8)where GT is the transmitting antenna gain, PT th e input power, and r the distancefrom the transmitter to the point in question. Although the gain of the receivingantenna does not enter into the calculation of power f lu x d en si ty , it needs to beaccounted for when calculating basic transmission loss. F o the INTELSAT examplewe use in (8) 9 'PT = 6.85 x 10 wattsr = 2 x 6.619 x 6.37 x 10 6 m

G(lO, 0) = .01 (envelope of sidelobe packs)yielding

W -91.15 dBW/m2 (INTELSAT) (9)The sharp drop of S from i t s value at the center of the rectenna of about.3.8 dBW/m2 to about -91.15 dBW.m2 i s a resul t of the extremely sharp ro l l -offof the sidelobes reducing the gain from 87.65 dBi a t boresight to about -10 to-20 dBi a t 10 from boresight. The increase in path length from SPS to INTEL SATover the distance from SPS to the earth corresponds to a decrease in power fluxdensity of only about 7.44 dB. At the limb, the difference would be about '6 dB.The added 1.44 dB is due to distance change from limb to sa te l l i t e subpoint. FromFigure 34, the radiated power toward the ear th ' s limb is about 80 dBW. Thisincreases to about 186 dBW at boresight .


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The uplink frequency for 1NTELSAT is in the 5.930-6.420 GHz band (NASACompendium, 1975). The third harmonic of the 2.45 GHz SPS signal a t 7.35 GHzmay cause intolerable interference with the uplink frequency band for 1NTELSATi f the edge of the modulation passband is within a distance or frequency separation from an SPS vehicle to cause an S/1 a t the input to the 1NTELSAT receiveof > 12-15 dB. This c o n s t r ~ i n t is based on t he adj ac en t channel interferenceeffects characterist ics, of FDMA transponder receivers ' interference couplingoccurring through the receiver s ignal channel. Receiver interference responsesinclude AGC suppress ton and intermoaulat ion products generated by th e d es ire dcommunication signal, th e SPS fundamental, and the SPS third harmonic. Theintermodulation sens i t iv i ty of the 1NTELSAT uplink is increased by about 9-12 dBbecause of the SPS thi rd harmonic being in the uplink channel. These separationconstraints and sens i t iv i ty i nc re as e a re based on the t e s t of an FDMA t ransponder rec eiv er o f the type used for commercial sa te l l i t e multichannel relayservice. The SHS character i s t ics assumed include the fundamental and harmonicemission and spat ia l radiat ion c h a r a c t e ~ i s t i c s previously c ited in Section 1( ref . Figures 2 t h r o ~ g h 5). The SPS oroi ta l in termodulat ion products wil l be ofno consequence in this, INTEP::AT receiver since no signif icant emissions areanticipated in the uplink bands because OL the electr ica l parameters of thes t ructure equivalent cLncud.t's and solar panel components.2.5.2 Advanced WESTAR

As a second example of poss ib le in te r fe rence caused by the SPS with acommunications sa te l l i t e , consider the planned domest ic communications sa te l l i t e"Advanced WESTAR" with a tentat ive launch date scheduled for the e ar ly 1980's .This sa te l l i t e is sponsored by Western Union Space Communications Corporation(Morgan, 1978). The Tracking and Da ta Relay Sate l l i te System (TDRSS) i s leasedby NASA (US) from the We,stern Union Space Communications Corporation for 10years. These sa te l l i t es wil l c a ~ r y both TDRSS and Advanced WESTAR equipment.The CONUS beam from WESTAR a t 1 0 3 ~ W longitude is shown in Figure 35 with 3 dBbeamwidths of 3.5 x 6.8. The fQo.print in Figure 35 i s computed using anassumed aimpoint of 35' la t i tude and 1 0 3 ~ W ' l o n g i t u d e (close to Amar il lo , Texas ).The s l igh t change from the aim point in the previous example i s used to show arelat ively uniform CONUS coverage footpr int . For th is interference example,assume the SPS sa te l l i t e in geostationary orbi t displaced 5 from Advanced


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100Figure 35. CONUS beam for the advanced WESTAR.

40A.N

WESTAR, corresponding to a separation a t geostationary orbi t of 3.68 x 103 k m The parameter values used in (9) for this example are

9PT = 6.85 x 10r 3.68 x 106 m

1.493 x 10-6 (-58.26 db from Figure 18)yielding

W -92.21 dBW/m2 (WESTAR). (10) .

Although power f lux den sity r egula tions exist for (ITU, 1977) satel l i te-ear thstat ion geometries, there are no specif ic corresponding regulations for sate11ito-satel l i te geometries.


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Another example of interference along the geosynchronous orbi t , is thepotent ial for interference between SPS and the TDRSS, Tracking and Data RelaySatel l i te System (Poza, 1977). This system of relay satel l i tes and earth ter-minals supplies communications support for various space research miss ions.The.sate1lites can suppo rt both wideband and narrowband communications a t Sand Kband frequencies. One of t he funct ions of TDRSS, and the subject of the followinganalysis, is to supply communications relays for space shutt le missions (Batson ea1. , 1977).

The TDRSS communications frequencies closest to SPS are the S band l ink withuplink f requenci es o f 2287.5 and 2217.5 M H z ~ Downlink assignments from TDRSSare a t 2042 and 2106 MHz. The downlink from TDRSS uses spread spectrum signaling techn iques, w ith a 11.232 Mchip/s signaling rate , to prevent interference toground based terminals. The uplink to TDRSS, however, does not require spreadspectrum signaling. I t is this narrowband mode that is the subject of discussion here.

One of the typical transmission rates in the low-data-rate mode is 96 kbps.This information stream i s encoded with a 1/3 rate , constraint length 7, convolutional code. The resulting 288 kbps coded waveform is transmitted withphase sh i f t keying of the carrier . Typical signal levels that are involvedduring aTDRSS/ space shutt le communication re lay are given in Table 2. Alsoshown in the' table are estimates of SPS i nt er fe rence leve l s that would exis twith a lO'separation between SPS and TDRSS. The reference bandwidth for TDRSShas been assumed to be 228 kHz. From Table 2, one can see that the in terferenceto-system-noise ra tio a fte r f i l ter ing is e st imat ed to be l/N = -12.1 dB. Althoughan l/N ratio less than -10 dB normally would not degrade transmission efficiency,the 2 dB margin is inadequate considering SPS pattern variabi l i t ies and smallgain fluctuations because of orbi t wander.

As a f inal example of interference that may be emitted by the SPS spacetenna,we discuss briefly the possibi l i ty that over the passband of t he Klyst rons , say+lO'MHz, th e n oise ~ o w e r may cause interference with neighboring communicationsa te l l i t es . The noise power can be calculated using

Noise power = 10 loglO (kTB) (11)and, i f we assume B = 2,x 107 Hz, k = 1.38 x 10-23, and T = 300 0K in (11), yieldsnoise power of -130.8 dBW. However, the noise generated in amplifiers and/or


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TABLE 2. TDRSS Interference EstimatesVictimSpace Shutt le EIRPPath loss , shutt le to TDRSS(R=22786 nmi, f=2287.5 MHz)Pointing and polar izat ion lossesTDRSS receive antenna gainReceive sig nal le ve lTDRSS noise tempBoltzmans constantTDRSS noi se d en si tyInformation bandwidth, 96 kbps modeRF bandwidth, 228 kbps PSK modeTDRSS noise power in RF bandwidthInterferenceSPS transmit power, 6.5 GWSPS antenna gain 90 off boresightPath loss, SPS to TDRSS,(700 km, 1 s ~ p a r a t i o n , 2450 MHz)TDRSS antenna gain to SPS s ignal 90off boresightSPS interference power a t input to TDRSSreceiverReceiver diplexer f i l te r ing attenuationto SPS s ignalSPS interference power af ter f i l te r ingSummarySignal to interference ra t io a t input tor ec ei ve r d ip lexe r prior to f i l ter ingSignal to interference ra t io af terf i l te r ing in TDRSS receiverInterference to system noise ra t io priorto f i l te r ing (-79.1 + 141.9)I nt er fe re nc e to system noise ra t io af terf i l te r ing in TDRSS diplexer

15.2 dBW-192.1 dB-1 . 0 dB36.0 dB-141. 9 dBW27.7 dBK-228.6 dBW/oK'Hz-200.9 dBW/Hz49.8 dB'Hz53.5 dB'Hz-147 dBW

98 dBW-10 dB i-157.1 dB-10 dBi-79.1 dBW-80 dB-159.1 dBW

-62.8 dB17.267.9 dB-12.J.


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osci l la tors preceding the 50 to 70 kw klystrons are unknown, and thus the exactnoise levels cannot be calculated. This could be an important problem in considerat ion of interference effects .

2.6 Stat ion Keeping ProblemsSate l l i t es in GEO are not able to stay exactly in the posi t ion assig ned to

them. The wander involved depends very much on orbi t insert ion errors related tot rack instrumentation errors and the stat ion-keeping power budgets. The SPS, forexample, wil l probably have an al t i tude wander of approximately 80 km. INTELSATIV has an apogee alt i tude of 36230.5 km and a perigree al t i tude of 35739.5 km.This gives an alt i tude wander of 491 km. Other GEO sa t e l l i t es vary in al t i tudefrom 300 km to 550 km. This poses t he que st ion of interact ion between sa te l l i t esystems in adjacent orb i t slots as the sa t e l l i t es change al t i tude with respect toone another. Figure 36 depicts an INTELSAT 0.5 degree from an SPS with theINTELSAT apogee (maximum alt i tude) with respect to the adjacent SPS. Theimplications of al t i tude variat ion be tween an SPS and adjacent communicationssa t e l l i t es are demonstrated by a single example: orbi t separat ion 0 .5 ,40 kmal t i tude difference, and uplink receiver beamwidth of 2 circular . The SPSref lect ion crOss section in the direct ion of the communications sa te l l i t e would beab out 2.82 km2 (s t ructure configurat ion of SPS reference design, graphite com-posi te material 0 _ 0.5 metal equivalent area) . Uplink s/r rat ios for the l inkwith th is multipath component would be in the range of 5 to 9 dB for this s inglegeometry. This S/I rat io is unacceptable because of normal l ink signal variat ionscaused by meteorological and ionosphere effects .

2.7 Mitigat ion TechniquesThe study reported here concludes that one would not expect interference

between SPS and other GEO sa t e l l i t es when separated by 0.5 to 1.0 degrees.However, looking a t what has been placed in GEO to date , and what is plannedbetween now and the year 2000, it would appear tha t a s lo t problem w ill e xist i f60 SPS were actual ly planned. I t would seem prof i table a t th is time to s t a r tlooking a t the u t i l i ty of multiple use space platform s. In stead of each sa te l l i t ebeing designed for a narrow range of functions and each need ing an assigned s lo tin the GEO orbi t , a space platform could serve many functions (communications,data re lays , navigat ion, etc . ) a l l from one s lo t locat ion. This would allow moresystems for the given space with less l ik el ihood for EMC problems.


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GEO. ,c' ORBIT

INTEL SAT~ 7 I \I \I \I \I II I- I II +-I II I\ I\ I\ . I\ I

050 (-=1 \ /~ ~ --I

SPS~ . ~ - - -'

Figure 36. Sa t e l l i t e s ta t ion-keeping problem p o t e n t ~ a l in ter ference.


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Communications sa te l l i t e rece lvers should be separated from an SPS by 0.5 a tGEO radi i . These receivers must have band stop f i l t e r s for the SPS fundamental anprimary harmonics (2nd through 5th) with a notc h dep th of a t least 60 dB and anotch bandwidth of 5 MHz. Such f i l t e r s a re ava il ab le with an out-of-band in -sert ion loss of


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On-board sensors ~ e n s i t i v e to SPS interference include elect ro-opt ical devices,active and passive microwave systems, and p a r ~ i c 1 e detectors .

The suscept ib i l i ty of v ario us operat ional and planned LEO sa te l l i t es havebeen examined during the course of the SPS EMC evaluation program. Functionaldegradation for the electronic systems on LANDSAT, GPS, and the space telescopei s described in re la t ion to the ampli tude o f the SPS i l lumination components.Analysis and tes ts include the modes of coupling to on-board devices and subsystems, and performance effects in re la t ion to sa te l l i t e missions.

The susceptibi l i ty evaluations for LANDSAT, GPS, and SPACE TELESCOPE indicatethe character of functional degradation for data sensors, communications, at t i tudes tabi l iza t ion, and processing or control systems for power beam encounter periods.Penetrat ion through antenna and physical apertures and modes of coupling toin ternal devices and modules are examined to suppo rt s en so r and c i r cu i t moduletes ts for degradation measurement and mitigat ion technique specif icat ion.

Mili tary sa te l l i t es have been addressed separately. These considerationshave concerned SPS i l lumination effects on scanning and s tar ing sensors (visualand IR opt ics , passive RF receivers, radiat ion and par t ic le de te ct or s) o ri en tedtowards the earth.

3.1 LANDSAT Sate l l i teThe LANDSAT sa te l l i t e program i s in ten de d to develop and demonstrate a

capabil i ty for global monitoring support to Earth Resources Management. Launch ofLANDSAT-D i s scheduled in the thi rd quarter of 1981. A subsequent launching isanticipated during 1982-83 by the Space Transportation System. An advancedsystem, LANDSAT-H, is also being planned for periods which would overlap i n i t i a lSPS operations.

The LANDSAT-D, Figure 37, wil l provide imagery from a sun synchronous ci rcu lao rb it a lt itu d e of 705.3 km with a 98.2 incl inat ion. Imagery i s derived from aMultispectral Scanner (MSS) and Thermal Mapper (TM) on the sa te l l i t e . Scanner andmapper image data and system s ta tus a re t ransmi tt ed to CONUS and foreign controlstat ions direct ly and through TDRSS. These communications l inks are diagrammed inFigure 38 .

A power density-t ime plot for the case of orb i t coincidence with the SPS mainbeam is presented in Figure 39. This s i tuat ion may occur frequently because ofthe 6 to 8 orb i t tracks over CONUS.

The SPS energy coupling into LANDSAT systems i s indicated in Figure 40.As diagrammed, the communications,sensor, power bus, and at t i tude control functio


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RF COMPARTMENT

WIDE BANDMODULE

X-BANDANTENNA

TDRSS ANTENNA

S-BAND FEEDS

KU BAND FEEDS

S-BAND DIRECTREADOUTTRANSMITTER

S-BAND SHAPED BEAMANTENNA (21

WIDEBAND COMMUNICATIONS SUBSYSTEMMECHANICAL CONFIGURATION

Figure 37. LANDSAT wideband communications subsystems mechanical configuration.


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GPS POSITIONVELOCITY

K-BAND,TM/MSSDATAS-BAND J TelEMETRY& CIC, RANGE

S-BAND TELEMETRY. : R ~ ~ B ~ ~ ~ / T M DATAGOLDSTONE

S-BAND TELEMETRY

r------L---,X-BAND MSSITM TelEMETRYIS- BAND MSS DATAL--__ ~ ~ S - B A N D CIC, RANGE

LANDSAT COMMUNICATIONS LINKSITS/3.-ACTAG

Figure 38. LANDSAT communication l i nks .


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10 2

10NE(, )


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SOLAR PANEL VOLTAGE CONTROLCIRCUITS CIRCUIT NOISE

JSPS

INCIDENTPWR

THERMAL MAPPER I (SENSOR &. VIDEO

M S SCANNERSENSOR &. VIDEO

STAR TRACKERS I - - - - .

sus S E r ~ S O R S

CONTROL &. STAB I (. CIRCUITS

CIC ANT. (S &. L BANDS) IRCVRS I 1 SIG PROCI 0

Figure 40 . LANDSAT functional impact modes.

ITS/3-ACTAG


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can be.affected. Coupling would occur through the communications antennas, at t i tudsensor optical apertures, and the opt ical apertures and thermal lo uv res o f theMultispectral Scanner and Thermatic Mapper. Energy coupling through the solar panto the power uni ts , transmitting noise to the computers and instrumentation, isnot affected bec au se of th e f i l te r ing and regulation circui t ry . Unshielded areaand scanner locations on the sa te l l i t e i n d i ~ a t e that the opt ical aperture is theprincipal coupling mode for these sensors.

Star tracker noise and angle error ranges in relat ion to microwave i l luminatiolevels are indicated in Figure 41. The LANDSAT s ta r tracker provides error datato the at t i tude control software. Attitude error would accumulate over a periodof about 4 to 5 seconds w ithin th e SPS beam. This at t i tude deviation (pointingdeviation magnitude and ra te , hemisphere orbi t distance for the error increase,and restabil ization phases) wil l be derived for SPS main beam and primary sidelobeillumination of LANDSAT orb i t passes.

Because of the locations of the Thermatic Mapper (TM) and Mult ispectral Scann(MSS) on the sa te l l i t e , the sensor responses wil l be sensi t ive to SPS orbi t posi t ioSensor performance was evaluated for the peak and average SPS power density magnituindicated in Figure 39 . As shown, the sa te l l i t e wil l be subjected to microwavef ie ld i n te n si ti es greater than 100 vim for about 1 second, in tens i t ies greater than10 vim for 3.2 seconds, and in tens i t ies greater than 1 vim for about 13 seconds a tLANDSAT velocity . Coupling of th is energy into the TM and MSS systems may occurthrough the thermal control louv ers o r direct ly through the opt ical aperture.

The performance deg rada tion o f the TM/MSS subsystems in an SPS environmenttakes the form of the following:

General increased video noise resul t ing in overal l degradationof immage. Introduce control signal j i t t e r through the multiplexer

timing electronics and introduce image l ine stagger.Reduce spat ia l frequency which effect picture edge sharpness. Reduced dynamic range which affects range of contrast .

Figure 42 shows the thermatic mapper t es t plan configuration. A t e s t wasconducted using normal tes t procedures wi th no simulated SPS i l lumination. Bartargets were scanned and recorded impulse response to a 0.2C resolution weremeasured. This gave the normal imaging performance of the system.


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, - - - - - - - - - - - - - - - - - - - - - - - - ; ] A ~ - ~ 0 . 5 - M W / C M 2 !F = 2.5 GHz - - - - 8 - 2 MW/CM2C- 10Mw/cMi

1 - SIGNAL NOISE2 - AVERAGE ANGLE ERROR

101LU(/ ,)ex:LUa:u 81:LU 82C )ex:I -2 :LUUa:LUC-

100A1

A2

C1 C2 POINT S-oURCE III3M, 8M

10 1L------------------_----'

Figure 41. Image d i s sec to r s t a r t racker er ror cha rac t e r i s t i c s .ITS/3-ACTA


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'

THERMAL _ _ - - = - . . - . ~ ICONTROL __ - -_ - -~ U V E ~ : ' -_ -= ~ . : - - -81 2AS GHz SOURCE~ ~ : ~ ~ ~ : = -----S:R TARGET

APERATURETHERMATIC MAPPER

Figure 42. Thermatic mapper te s t plan configuration.


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Identical tes ts were then conducted" using. the bar targets . recording impulser esponse, w ith the addition of a microwave: s:i:gnal illuminating the op t Lcal, apertureas i l lustra ted in Figure 42. The microwilve signal level was varied in steps frommw/cm2 unt i l complete malfunction occured at l6mw/cm2 The microwave illuminationwas then aimed direct ly into the therma"lcont ro l louvers w ith the louvers open tothe position which gave maximum coupling. The bar target tests were conducted agaa t various levels of i l lumination. A preliminary data se t indicates an increase invideo channel noise of 8%, and a decrease in modulation t ransfer function of 18 to20% which affects thesp&tia l imaging capability by approximately 20%.

The sate l l i te-ear th stat ion uplinks use an S-band channel a t 2106.4 MHz withwideband modulation modes through the TDRSS. Other sa te l l i te receiver channelsinclude a 1377.5 MHz t ra ck s igna l from TDRSS, and the 1227.6 MHz and 1575.4 MHztransmissions from GPS. For the direct earth-stat ion to sa te l l i te S-band l ink (2kbps - NRZ/PM), a bit-error-ra te (BER) in cre ase o f 70-85% would occur for SPS mainbeam exposure period of approximately 16 s e c o n d s ~ For the wide band TDRSS c h a n n e l ~the BER increase would be 20 to 40%,. th e h ighe r range caused by nonlinear r e s p o n s e in the f i r s t conversion and ampl if ie r s tages of the receiver decreasing exp,osure toSPS power densit ies of ~ mw/cm2 .

For perhaps 1 to 3 SPS operations maximally separated over CONUS, the LANDSATmission profi le could be modified to eliminate S band command/control transmissionduring th e specif ic orbi t time slots corresponding to SPS i l lumination. This i sobviously not a satisfactory mode, except for temporary operation of an operationasa te l l i te while functional modif ications are incorporated into future vehicles.These modifications should e lim inate th e BER effects for the narrowband and widebatransmissions to the sa te l l i t e , thus removing a l l mission dependencies betweenLANDSAT and SPS operations.

Mitigation techniques to be investigated include rejection f i l ters and antennmodifications. The former a re p re fe rr ed because of the relat ive simplicity, ~ n telimination of antenna control command and steering software additions. This f i l t eshould have a bandwidth of about 10 MHz, and an out-of-bandinser t ionloss of lessthan 2 dB.

For the multispectral scanner and thermatic mapper, mitigation techniques toconfirmed include circui t f i l te rs , noise extraction ( spectra l dens i ty-cor re la tionmodels) in the data ana ly si s process, and extended shielding for the detectors andcolocated video amplifiers. Additional s h i e l d i n ~ for the video channel and scan


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control circui try is recommended to eliminate j i t t e r in the l ine scans for ~ i t u a t iwhere coupl ing occurs directly into these circuits and not through internal commonconnections. For the star tracker, circui t shielding and opt ica l aperture wire mshielding is recommended. The la t ter i s applicable here since focusing opticalcomponents are used in front of the image dissector tube. Attitude control i simplemented by stored c o ~ a n d s based on sa te l l i t e ephemerii. The s tar tracker errdata updates at t i tude commands by modification of the Kalman f i l ter coeff icients ,minimizing image degradation because of att i tude t ransients. S ta r tr acke r erro r distr ibut ion spread induced by SPSnoise would propagate over approximately 30% ofthe orbi t because of the indirect control action, reducing image registrat ion andeffective reduction in spat ial resolution of about 20%. These effects could becorrected by process ing software a t the CONUS o r o th er re ceiv ing centers, butrepresent additional processing time for imagery collected over about 30% of anorbi t track aftex; SPS exposure. Effects of the sun sensors are insignif icant ,approximately 2% increase in no ise, p rimari ly because of SPS harmonics. This noisshould cause less than 29 to 5 ori en ta ti on e rr or for the solar panels over a perio 1 to 1.3 seconds of maximum SPS beam exposure, and be correc ted wi th in 2 to 5seconds after LANDSAT departs th e SPS beam. The error magnitude is l imited by thepolar panel control bandwidth and the small a p ~ r t u r e of the sun sensors. Where suacquisition by the sun sensors is occur ing during SPS main beam exposure, the solapanel tranpien,t time would be ex tended by approximately 3 to 5 seconds because ofthe signal channel noise and related angular uncertainties , the sun-SPS illuminating power rat ios also being minimal during this event.

3 .2GPS Satel l i teThe GPS is a navigation and position-fixing system being implemented by the

Department of Defense to support worldwide strategic and tact ical combat systemoperations and non-defense users through the re;duced p reci si on , s ingl e frequencymodes. The orbiting complement wil l include 18 satel l i tes by 1984. The sa te l l i t ehave a 10900, mile circular orbi t , with a 12-hr orbi t time.

This system provides a passive operational mode for users (receive only). Thsatel l i tes provide 2 frequency transmissions a t 1227.6 GHz and 1575.4 GHz in a QPSfbrmat. Signa ls inc lude time, ephemeris, ident if icat ion, data to compute propagaterrors, and user location. Users include sate l l i tes , ai rcraf t , surface vehicles,and individuals. A position measurement accuracy of + 30 to 100 f t has been verifthe variance depends on local-user mu1tipath severity and signal thresholds, andr ece iver ve loc ity in the case of low-altitude, high-speed military ai rcraf t .


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Ear th- to-sa te l l i te communications provide ephemeris update, orbit ing clockcorrect ions, and command/control data to the sa te l l i t e computer directly and througTDRSS relay. The uplink communications use S-band. Sate l l i te conical spira lreceiver antennas are located on the space and earth-point ing planes.

The GPS power density variat ions for SPS beam in teract ion a re p lo tte d inFigure 43 . Power coupling modes into the GPS sa te l l i t e are diagrammed in Figure 44This diagram indicates the coupling to sensors and communications in a mannersimilar to LANDSAT. The GPS vehicle has the addi t ional mode of di rect entry througthe thermal control louvers that control the temperature of the pr inc ipa l e l ec t ron ifunctions: clock, computer, and command/control receiver and decoder components.indicated on the coupling diagram, th is di rect penetrat ion energy would primarilycouple to the various electronic functions through cables and interface circui ts(impedances 21 through 24).Maximum and average SPS power levels reflected into the sa te l l i t e electronicsare 25 Wand 2.8 W, respect ively, considering power densi t ies about 0.1 mw/cm2 andlouver o p e n ~ n g s of 10, 30, and 45. Induced j i t t e r in the in ternal clock andmessage decoder logic is in the 10% to 65% range for SPS power in the 10 W to 25 Wrange. These i n i t i a l measurements wil l be fur ther v erifie d in future tes ts ofmodular logic components configured to r ep re se nt GPS systems/ physical arrangement.

The S-band communications receiver and associated processor would experience aincrease in BER in the range of 50 to 1000 with the antennas exposed to SPSpower densi t ies of 10 mw/cm2 to 100 mw/cm2. Loss of lock because of intermodulat ionoise and sens i t iv i ty suppression occ ur s dur ing SPS main-beam and h ighe r s idelobeexposure.

Mitigation technique tes ts to be completed for the GPS communications receiverare iden t ical to those indicated for LANDSAT. Functional differences w ill re su ltfrom the increased SPS maximum power density and the broad band CPS s ignal mode.

Sun sensor control of solar panel orientat ion wil l be affected only in the sammanner as discussed for LANDSAT. The short exposure times and the low controlbandwidth l imi t the possible ro l l of the solar panels because of s ig na l n oi se . Thes ta tement regarding sun acquis i t ion when exposed to SPS i l lumination is also appl i cable to GPS.

The earth sensors on GPS are effect ively shielded from SPS exposure by thesa te l l i t e structure for a l l possible SPS-GPS geometric relat ionships over thewestern hemisphere. For geometries where GPS is over European or Asian areas but


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10 2

10N /1.35..) SEC, 1E

..

\ 10-1-n2w 10-21 / ' I ~ 4 . 9 SEC-c-- ' 10-3

3555 5 0 5 15DISTANCE FROM BORE SITE, km

2510-1 I I35 I I ! ! I 1 I I I I I I

Figure 43 . SPS microwave beam geometry at NAVSTAR o rbi t a lt it ud e . ITS-3/ACTAG


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ISOLAR PANELS I "I PWR CONTROLS

- EB'" T11 EnMA L CONTR0L CIRCUIT & CABLELOUVERS APERTURESSOLAR PAtJEL Z1 Z2 Z3 14--REFL I CLOCK l

= I I .. ' ~ R o c l oIC ANTSUN & EARTH ATTITUDE. STAB,.

CONTROLENSORS EEDCIRCUITS

II VOLTAGE. CIRCUIT PWR NOISE

SPSINCIDENT

' PWR

Figure 44. GPS functional impact modes.

ITS-3/ACTAG


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has a l ine-of-sight with an SPS sidelobe, those power densi t ies are a t leas t 103 t104 below any sa te l l i t e pointing upset threshold.

The GPS transmitters will be unaffected by SPS penetration at the levelsindicated. Power and driver amplifier circui t ry and t he physi ca l con fi gu ra ti onindicate no poss ibi l i ty of induced PM j i t t e r on the transmitted signal at t r ibutablto coupling in to t ransm it te r circui t ry . Transmitter antennas are shielded fromdirec t SPS power exposure by the body of the GPS. The 50 Q power amplifier impedance, the wideband output tuned f i l t e rs , and the output-input coupling of the p o w ~and driver stages indicate a net coupling of -40 dB to -65 dB for the SPS fundamental frequency, and values of -70 dB to -80 dB for the SPS second harmonic.

The at t i tude s tabi l iza t ion responses of a direct tracking stabil ized platformwere measured with respect to illumination of the s tar tracker sensor system withmicrowaVe energy. This track loop configuration is applicable to direc t controla t ti tude s tab i li z at ion for space systems and terrest r ia l astronomical telescopes tar tracking. Detectors inc lude image dissectors and sp l i t image photomultiplierMicrowave effects include induced detector noise and video ampli fi er no ise, whichcauses increased dynamic errors, and bias for larger i l lumination magnitudes. Theeffects are magnified when tracking higher magnitude number sources. Figure 45shows at t i tude error in arc-seconds versus time in seconds. The lower data se tshows normal set t l ing time in a single axis with no i l lumination. Here it can beseen that in less than 10 seconds the platform wil l be in a stable condition fromdisturbed condi tion. The upper data se t shows what happens i f the platform werecaged with the s tar tracker i l luminated with a 15 mwicm2, 2.6 GHzmicrowave signalInstabi l i ty is introduced, which increases with time, with ultimate loss of looplock.

However, sa te l l i t es wil l not be in the beam for more than a few seconds, asindicated in the case of LANDSAT and GPS. There may be be tween three to eight arcseconds of error i nt roduced dur ing a passage through the SPS beam, but as the lowecurve of Figure 45 shows, for systems having the tracker directly in the at t i tudecontrol loop (e .g . , GPS, Space Telescope), th is w ill set t le out in five to tenseconds af ter leaving the beam.

3.3 Space TelescopeIn 1977, the space telescope project was approved by the United States

Congress. The space telescope has major advantages over ground-based telescopesin three important areas: 1) the f i r s t and most signif icant is an order ofmagnitude improvement in angular resolution, 2) twenty-four hour per day observing


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20

10en /z0u SINGLE AXISLUen 0 TRACKER IUUM - 15 MW/CM2I ---------20'\ c:l-I-l-e::( 0

I _ ~ I_ IotTO

5 10TIME (SECONDS)

15 20

Figure 45 . S ta r t ra ck er - stabi l ized platform alt i tude responses.


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time, 3) the telescope being beyond the Earth atmosphere allows photometr ic datacollect ion over a much wider wavel ength r ange - ultraviolet , infrared, andsubmillimeter wavebands as well as the visual spectrum.

The planned schedule shows the i n i t i a l launch in the l as t quarter of 1983. Thdesign l ifetime i s f i f teen years in orbi t . The orbi t i s circular a t a 500 kmal t i tude and 28.8 inclination. A cross-sect ional view of the sa te l l i t e observatoris shown in Figure 46. The telescope consists of the primary and secondary mirrorsthe metering structure for maintaining th e re la t ive posit ions of the mirrors , thein ternal l ight baffl ing system, and the fine guidance sensors. Communications withthe satel l i te wil l be via the TDRSS. The sc ient i f ic instruments on-board are asfollows:

Wide Field/Planetary Camera - the camera contains eight chargecoupled device (CCD) detectors, each consisting of 800 x 800 elements.Faint Object Spectrograph -u s e s digicon detectors, each of whichconsists of a l inear array of 512 independent diode elements.Faint Object Camera - the design uses a three-stage image intensif ierwith an in tensif ied s i l icon t ar ge t t el ev is ion camera tube.High Resolution Spectograph - the detector is a digicon device cons is t ing of a l inear array of 512 diode elements.High Speed Photometer/Polarimeter - the device consists of a numberof image dissectors, the i r associated electronics and a focal planeaperture mask and f i l t e r plate.Fine Guidance System - Uses three independent sensors and detectorslocated in annular segments around the f ield of view in the focalplane. This system provides grea t as tromet ri c potent ial . These threehigh resolution sensors provide data for s ta r fie ld maps to support futures te l lar experiment p l a n n i n ~ . These sensors must acquire s tars a t M = 13with an accuracy of 7 x 10 arc sec.

The SPS microwave power beam geometry a t space telescope orbi t al t i tude isshown in Figure 47. Coupling of electromagnetic energy into the sa te l l i t e ins t rumentation wil l occur mainly through the te lescope 's 2.4 meter optical aperture. ThSPS peak f ield in tensi ty would be approximately 28 TrM/cm2 . This would be equivalento 12.67 kw of microwave energy on top of the telescope. About 40% of the energywould be coup led through the baffled area to the primary mirror. Some 20% of th is

)energy would then be reflected through th e m irr or system into the det ec to r a re as .There would be about a 60% penetration into the dete ct or a re as , which would beequ iv al en t t o 55 watts of 2.45 GHz energy directly into the inst rumentat ion area.

The impact of SPS radiations on the scient if ic instruments would be to increasdetector channel noise, reduce spat ial resolut ion, and reduce dynamic range. Forthe sa te l l i t e guidance sys tem and astrometry missions , there would be increased


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Scale1m' - - - - - - l

,Focal- / .I plane [Focal planeassembly shroud

Primary mirror2A m diameter

-----

OpticalteleSCOjeassembly

" Communicationsx ontenno",.

Light shield assembly Equipmentsection.. System Support Module

Combination\ ~ r ' ' ' " ' ' door-\",hOd'\J I I I I I I I h J i ; ' i i i i i i ' < ' i i , , ? 1 , l i l ~ I . 7 K n J \ II

.. 13.16 m

Figure 46 . Cross-sectional view of th e sa te l l i te observatory.


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detector channel noise and reduced spa t ia l resolu t ion , which would increase a t t i tudi ns t ab i l i t i e s for the few seconds the space telescope i s in the SPS beam.

Figure 48 shows vol tage output vs. i l luminating frequency for a 512 element CCarray a t two widely separated t emperatures g iven in degrees k elvin . Thesevideonoise spectra show the normal r esponse curve s for CCD arrays. Figure 49 shows theCCD a rr ay s pe ctr a in the presence of a 2.5 GHz 2 mW/cm2 f ie ld . Comparing Figures48 and 49 , it is seen that the frequency resolut ion has degraded considerably in thi l luminated case, par t icu lar ly above 100 her tz . This would adversely ef fec t theimaging capabil i ty of such an array.

Figure 50 shows the same CCD array being i l luminated with a normal sourcesignal and the associated resolut ion given in l ines per minute. The l i neA i s thenormal response of such an array. The l ine B shows the degradation in resolut ion ithe presence of a 2.5 GHz, 2 mW/cm2 r f f ie ld . Here it can be seen tha t it takes ahigher source i l lumination for a given resolut ion in the presence of the microwave-5 2f ie ld , p ar ti cu la rl y below 10 mW/cm.

The CCD matrices, digicon devices, image in tens i f iers , and image dissec tors wiexperience degraded capabi l i t ies in the presence of SPS energy as the sa t e l l i t eobservatory in tersects the main power beam and major sidelobes. The apertures infront of the de te ct or s a ff or d very l imited protect ion since the axia l length wil l bmuch less than A/2 for the SPS fundamental or primary harmonics . Figure 41,(page 59) shows the percent increase in noise and average angle error for animage dissec tor subjected to microwave i l lumination in a s ta r t racker configuration

Mitigation techniques would include wire mesh s hie ld in g f or image dissectors ,d ig icon devi ce s, and CCD arrays where focusing opt ics are employed. For submill imeter , infrared, or

Effects of the Satellite Power System on LEO & GEO Staellites

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