The National Aeronautics and Space Administration and the United States Information Agency (USIA) are currently engaged in a joint program to assess the technical and economic feasibility of direct sound broadcast satellite systems to meet USIA mission needs. The cooperative effort calls for a series of interrelated studies to provide the respective Agency managements with information on the potential role of direct broadcast satellites. Initial studies focused on HF propagation phenomena and broadcast coverage requirements. These studies served as the basis for parallel systems studies currently in progress. The systems studies are to provide a data base on various satellite configurations and systems concepts capable of supporting potential broadcast requirements ranging from a small fraction to a substantial addition to USIA requirements. Antenna concepts for LEO and GEO orbits are briefly described

Leroy, B. E.

Catalan 

NASA Technical Reports Server

ALTERNATIVES FOR SATELLITE SOUND BROADCAST SYSTEMS 
AT 
HF AND VHF 
Bruce E. LeRoy 
NASA Lewis Research Center 
C1 eve1 and, Ohi o 
Large Space Antenna Systems Technology - 1984 
December 4-6, 1984 
27 
https://ntrs.nasa.gov/search.jsp?R=19850015504 2020-03-22T19:03:58+00:00Z
NASA and t h e  Un i ted  Sta tes  I n f o r m a t i o n  Agency (USIA) a re  c u r r e n t l y  engaged 
A Memorandum o f  
i n  a j o i n t  program t o  assess t h e  t e c h n i c a l  and economic f e a s i b i l i t y  o f  d i r e c t  
sound broadcast  s a t e l l i t e  systems t o  meet U S I A  miss ion  needs. 
Agreement (MOA) i n i t i a t i n g  t h e  a c t i v i t y  was signed by t h e  Agency a d m i n i s t r a t o r s  
i n  March o f  1983. The MOA c a l l s  f o r  a s e r i e s  o f  i n t e r r e l a t e d  s t u d i e s  t o  p r o v i d e  
t h e  r e s p e c t i v e  Agency managements w i t h  i n f o r m a t i o n  on t h e  p o t e n t i a l  r o l e  o f  
d i r e c t  broadcast s a t e l l i t e s .  As shown i n  f i g u r e  1, i n i t i a l  s tud ies  focused on 
HF propagat ion phenomena and broadcast  coverage requirements.  
completed i n  e a r l y  1984, served as t h e  b a s i s  f o r  p a r a l l e l  systems s t u d i e s  
c u r r e n t l y  i n  progress.  The systems s t u d i e s  a r e  t o  p r o v i d e  a d a t a  base on 
var ious  s a t e l l i t e  c o n f i g u r a t i o n s  and systems concepts capable o f  suppor t ing  
p o t e n t i a l  broadcast requi rements r a n g i n g  f r o m  a smal l  f r a c t i o n  t o  a s u b s t a n t i a l  
a d d i t i o n  t o  U S I A  requirements.  
t r a c t s  (TRW and M a r t i n  M a r i e t t a ) ,  which w i l l  be completed i n  mid 1985. 
i s  suppor t ing  USIA/Voice o f  America i n  t h e  assessment of f u t u r e  r e c e i v e r  popula- 
t i o n s  and t h e  c o s t  e f f e c t i v e n e s s  study. 
These s t u d i e s ,  
NASA LeRC i s  managing t h e  systems s tudy  con- 
NASA LeRC 
I - 
.-b SATELLITE SYSTEMS __I DATA BASE REQUIREMENTS 
SYSTEMS STUDIES COST EFFECTIVENESS 
PRO PA GA T I O N  RECEIVER 
STUDY 
FOLLOW-ON 
PLANS 
-- HF MARGINS 
-- INTERFERENCE 
-- NUMBERS 
-- FREQUENCIES 
-- LOCATIONS 
-- COVERAGE -- ORBITS 
-- CHANNELS -- WT 
-- TIME -- POWER 
-- CONFIGURATION 
-- COSTS 
-- TECHNOLOGY 
F igure  1. Phased program approach. 
I 28 
The scope o f  t h e  da ta  base systems s t u d i e s  i s  q u i t e  large,  c o v e r i n g  systems 
o p e r a t i n g  a t  HF (15 - 26 MHz), VHF (60 MHz), L-band (1.5 GHz), and Ku-band 
(12 GHz). Geographical coverage ranges from s i n g l e  smal l  c o u n t r i e s  t o  n e a r l y  
worldwide. Except f o r  Ku-band, power requi rements v a r y  over  two orders  of 
magnitude, and consequently, low E a r t h  o r b i t s  (LEO) a r e  considered f o r  t h e  lower 
f requency systems where launch c o n s t r a i n t s  p r o h i b i t  g e o s t a t i o n a r y  s a t e l l i t e s .  
F igures  2 and 3 i n d i c a t e  t y p i c a l  l i n k  parameters f o r  HF and VHF geo- 
s t a t i o n a r y  s a t e l l i t e s .  
10 kW i n t o  a 270 m apper tu re  i s  r e q u i r e d  t o  produce a s i n g l e  audio channel i n  a 
30 beam a t  26 MHz. 
q u a l i t y  when r e c e i v e d  b y  a commercial grade r e c e i v e r  i n  suburban areas. 
ionospher ic  s c i n t i l l a t i o n  i s  present,  however, deep fades may occur which render  
t h e  s i g n a l  useless.  
s c i n t i l l a t i o n  i s  much l e s s  a problem. 
Under t h e  assumptions i n d i c a t e d ,  a n e t  t r a n s m i t  power o f  
Under normal c o n d i t i o n s ,  such a s i g n a l  i s  o f  "reasonable" 
If 
A t  VHF, power and antenna requi rements a r e  ha lved and 
F REGION 0 DIURNAL VARIATIONS 
0 SCLAR CYCLE VARIATICMS 
0 MAGNETIC STOEIlS OLARIZATION LOSS - 3 d B  
S I N  - 40 dB 
ABSORPTION LOSS - 2 dB 
E I R P  - 74 dBW 
LOW 
ELEVATIOY 
SOURCE 
(GEO) 
TRANSMIT POYER INTO 3' BEAn 
ANTENNA (270 rn) I S  ., 10 KW 
U 
F i g u r e  2 .  HF l i n k  a n a l y s i s  (26 MHz). 
29 
F REGION 
\ 
v 
POLARIZATION LOSS - 3 dB 
C/N - 20 dB 
ABSORPTION LOSS - 1 ilfi 
HIGH 
ELEVATION 
SOURCE 
(LEO) 
EIRP - 71 3BW 
LOW 
ELEVATION 
SOURCE 
(GEO) 
/ 
Figure 3 .  VHF l i n k  a n a l y s i s  (60 MHz). 
I 30 
For b o t h  HF and.VHF systems, LEO and GEO o r b i t s  present  d i s t i n c t  advantages 
and disadvantages. 
broadcast  area, ease of program u p l i n k ,  and manageable s o l a r  a r r a y  degradat ion,  
such o r b i t s  a l s o  r e q u i r e  ex t remely  l a r g e  antennas, may n o t  be capable o f  p r o v i d -  
i n g  a s i g n a l  t o  l a t i t u d e s  beyond + 500, and due t o  launch c o n s t r a i n t s ,  have 
v e r y  l i t t l e  capac i ty .  A l t e r n a t i v F l y ,  i n c l i n e d  low E a r t h  o r b i t s  p e r m i t  s m a l l e r  
antennas, increased channel c a p a c i t y  p e r  s a t e l l i t e ,  and can cover a l l  l a t i -  
tudes. However, t h e  use of such o r b i t s  presents  o p e r a t i o n a l  problems i n  u p l i n k -  
i n g  program m a t e r i a l ,  s t e e r i n g  broadcast  beams and s o l a r  a r rays  t o  t h e  d e s i r e d  
o r i e n t a t i o n s ,  a l l o w s  o n l y  l i m i t e d  c o n t a c t  t ime, and presents  a more-severe r a d i -  
a t i o n  environment. 
Note t h a t  f o r  cons tan t  area coverage, broadcast  power i s  a constant .  
t h a t  w h i l e  LEO o r b i t s  r e q u i r e  a s m a l l e r  antenna, t h e y  r e q u i r e  more pr ime power 
than GEO o r b i t s  due t o  r a d i a t i o n  damage e f f e c t s .  
Whi le  GEO o r b i t s  p e r m i t  cont inuous c o n t a c t  w i t h  t h e  t a r g e t  
These general  t r e n d s  are  dep ic ted  i n  f i g u r e s  4 and 5. 
Note a l s o  
m L L E N  EELT 
GEOSYNCHRONOUS 
F i g u r e  4. Impact of o r b i t  per iod .  
31 
(FOR CONSTANT AREA COVERAGE) 
I 
ANTENNA SIZE ArJD 
WEIGHT 
/ \ \  LAUNCH CAPAB I L I  TY 
ECLIPSE TIME 
ALTITUDE/ORBIT PERI OD 
(FOR CONSTANT SATELLITE ANTENNA SIZE) 
I POWER AND SPACECRAFT WE1 GHT 
/ ANTENNA 
N 
ALTITUDE/ORBIT PERI OD 
Figure 5. General trade-off trends. 
I 32 
Figure 6 below depicts the required antenna aperture sizes for constant 
area coverage as a function o f  orbit altitude. 
LEO satellites are larger than those indicated to compensate f o r  beam spreading 
as the beams are steered away from the sub-satellite point. 
In practice, apertures used by 
300 - 
ANTENNA 
D I AMETE R j 
f’iETERS 
200 - 
HF 
ORBIT ALTITUDE, KILOPETERS 
Figure 6. Antenna diameter versus a1 titude equivalent 3’ beamwidth. 
33 
Figures 7 through 11 d e p i c t  antenna concepts developed by our  c o n t r a c t o r s ,  
TRW and M a r t i n  M a r i e t t a .  
(10 - 11 dB) elements i n  a square phased a r r a y  t o  reduce o v e r a l l  a p e r t u r e  s ize .  
The TRW GEO concept ( f i g .  9 )  uses t h e i r  cable-catenary antenna. The M a r t i n  
M a r i e t t a  LEO concept ( f i g s .  10 and 11)  i s  based on t h e  box t r u s s  r i n g  s t r u c t u r e .  
A v a r i a b l e  aper tu re  approach i s  used t o  i l l u m i n a t e  var ious  t a r g e t  broadcast 
zones d i f f e r i n g  i n  apparent s i z e  a t  t h e  s a t e l l i t e .  
t r a n s m i t t e r s  t o  operate a t  var ious  power l e v e l s  as t h e  e f f e c t i v e  aper tu re  i s  
The TRW LEO concept ( f i g s .  7 and 8 )  uses h i g h  ga in  
I 
T h i s  approach r e q u i r e s  
changed. 
SOLAR ARRAY (295' L, 4 4 ' W )  
EACH WING: 13,000 FT2 
69 KW (EOL) 
SPEC1 F ICATIONS: 
OPERATING FREQUENCY 26.1 MHz 
ANTENNA APERTURE 92 M 
BEAMWIDTH 6.2 DEG 
/MESH GROUND PLANE 
PLOYABLE TRUSS 
F i g u r e  7. S a t e l l i t e  concept f o r  8 -hr  o r b i t .  
IAGONALS (WIRE1 
Figure 8. Cross-beam s t ruc ture  stowage and deployment. 
SATELLITE DIMENSIONS PERTAIN 
TO MOLNIYA ORBIT SOLAR ARRAY 
PER WING: izooo F T ~  
52.5 KW (EOL) 
280'L x 43'w 
EFFECTIVE APERTURE: 114 M 
CABLE-CATENARY 
FEED ARRAY 
OPERATING FREOUENCY 68 MHz 
ANTENNA APERTURE 
Figure 9. S a t e l l i t e  concept fo r  Molniya and geostationary o rb i t s .  
35 
PHASE ARRAY USING INDIVIDUAL TRANSMITTER FOR DIPOLE RADIATING ELEMENT 
BOX TRUSS RING SUPPORTS ARRAY SURFACE 
TYPICAL 26 MHZ DESIGN (SECTION VIEW) 
O 
' 
RAD I AT I NG 
/-- SURFACE /COAX BOX TRUSS STRUCTURE / 
l- SUPPORT FOR TRANSMITTERS 
F i g u r e  10. LEO antenna concept. 
. . . . . . . . . . .  
' 1 '  . . . . . . . . .  . I .  
o DESIGNED FOR SMALLEST . . I . .  . . . . . . . .  . I . .  APPARENT ZONE 
I 
. . . . . . . . .  S q A L E R  APERTURES FOR ' " * ' ' -60 METERS . . . . . . . .  LARGER ZONES 
. I . .  
. . . . . . . . . .  . I . ;  
. . . . . . . . . . . . .  o VARIABLE TRANSMITTER L-- _ _ - -  - - _ _ _  - - ,J 
',\ POWER 
I '  
. . . . . . . . . . . . .  
DOTS REPRESENT RADIATING ELEMENT 
AND TRANSMITTER PAIRS 
F i g u r e  11. V a r i a b l e  a p e r t u r e  approach. 
36 
Obviously, t h e  s a t e l l i t e  concepts p resent  technology chal lenges, p a r t i c u -  
A t  LEO, a 
l a r l y  i n  t h e  areas o f  power generat ion,  h a n d l i n g  and d i s t r i b u t i o n ,  antenna 
system s ize ,  RF power handl ing,  and e l e c t r i c  and p h y s i c a l  c o n t r o l .  
p a r t i c u l a r  concern i s  high-power-plasma i n t e r a c t i o n .  
expensive, consuming f u l l  Shut t le-Centaur  c a p a b i l i t y .  
c u r r e n t  s t a t e  o f  t h e  a r t  i s  d e p i c t e d  i n  f i g u r e  12. 
l i m i t e d  s e r v i c e  a t  v e r y  low s i g n a l  s t r e n g t h - - b u t  may be an a p p r o p r i a t e  f i r s t -  
g e n e r a t i o n  concept. 
Most HF and VHF c o n f i g u r a t i o n s  s t u d i e d  t o  da te  have been q u i t e  l a r g e  and 
An HF concept c l o s e r  t o  
Such a s a t e l l i t e  would p rov ide  
F i n a l l y ,  n o t e  t h a t  t h e  concepts--as t e c h n i c a l l y  i n t r i g u i n g  as t h e y  are--are 
o n l y  p a r t  o f  a d a t a  base. That d a t a  base w i l l  be used a long w i t h  o t h e r  tech-  
n i c a l ,  economic, p o l i t i c a l ,  and r e g u l a t o r y  i n f o r m a t i o n  t o  address t h e  broader 
i s s u e  o f  whether, i n  f a c t ,  s a t e l l i t e s  o f f e r  t h e  U S I A  a c o s t - e f f e c t i v e  means o f  
meet ing t h e i r  m i s s i o n  needs. 
0 10 KW SOLAR ARRAY 
O 9-ELEMENT PHASED ARRAY 
0 650 W TRANSRITTERS 
0 16' BEAMWIDTH 
o 50 - 70 V/m 
O 8-HOUR O E B I T  
Figure  12. t o w - c a p a b i l i t y  f i r s t - g e n e r a t i o n  system. 
37 


Alternatives for satellite sound broadcast systems at HF and VHF

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