Geostationary operational environmental satellite

GEOSTATIONARY OPERATIONAL ENVIRONMENTAL SATELLITE (GOES): A MULTIFUNCTIONAL SATELLITE Leo A. M a l l e t t e P r o j e c t Engineer Hughes A i r c r a f t Company Space and Communications Group P. 0. Box 92919 - Bldg. S41/B322 Los Angeles, CA 90009

Downloaded by AEROSPACE CORPORATION on December 15, 2016 | http://arc.aiaa.org | DOI: 10.2514/6.1982-536

Abstract The GOES s a t e l l i t e s a r e m u l t i f u n c t i o n a l s a t e l l i t e s whose p r i m a r y f u n c t i o n i s t o p r o v i d e c o n t i n uous measurements o f t h e e a r t h ' s s u r f a c e and atmoaphere fgom two g e o s t a t i o n a r y o r b i t l o c a t i o n s : 75 W and 135 W. T h i s o b j e c t i v e i s accomplished w i t h t h e V i s i b l e i n f r a r e d s p i n scan r a d i o m e t e r Atmospheric Sounder (VAS), and t h e Space Environment M o n i t o r (SEM), which i n c l u d e s t h r e e i n s t r u m e n t s : a magnetometer, s o l a r x - r a y sensor, and an e n e r g e t i c p a r t i c l e sensor, which m o n i t o r t h e near e a r t h space environment. The s a t e l l i t e ' s communication system provides several user oriented functions, including: 1) Transmission o f VAS data; 2) Transmission o f SEM data; 3) Transponder c a p a b i l i t i e s f o r a ) s t r e t c h e d VAS (SVAS) data, b ) weather f a c s i m i l e (WEFAX) data, and c ) t r i l a t e r a t i o n s i g n a l s ; 4 ) Transponder capab i l i t i e s f o r Data C o l l e c t i o n P l a t f o r m I n t e r r o g a t i o n and Data C o l l e c t i o n P l a t f o r m Reply. Introduction The GOES sate1 1 it e s a r e mu1 t i f u n c t i o n a l sate1 l i t e s whose p r i m a r y f u n c t i o n i s t o p r o v i d e c o n t i n u ous measurements o f t h e e a r t h ' s s u r f a c e and atmosphere fgom two g e o s t a t i o n a r y o r b i t l o c a t i o n s : 7 5 ' ~ T h i s o b j e c t i v e i s accomplished w i t h t h e and 135 W, V i s i b l e i n f r a r e d s p i n scan r a d i o m e t e r Atmospheric The r a d i o m e t e r p r o v i d e s two dimenSounder (VAS) s i o n a l c l o u d photographs and t h e atmospheric sounder i s a second g e n e r a t i o n f e a t u r e which w i l l add a t h i r d dimension t o t h e photographs o f t h e e a r t h seen n i g h t l y by newscast viewers. The VAS i s b e i n g launched on t h e l a t e s t s e r i e s o f GOES s a t e l l i t e s : GOES D, E and F. The s a t e l l i t e a l s o c o n t a i n s a Space Environment M o n i t o r (SEM) i n c l u d i n g t h r e e i n s t r u m e n t s : a magnetometer, a s o l a r x-ray sensor, and an e n e r g e t i c p a r t i c l e sensor, which m o n i t o r s o l a r f l a r e a c t i v i t y and t h e near e a r t h space environment. The s a t e l l i t e ' s communication system provides several user oriented functions, including:

S-Band t o UHF) and b ) Data C o l l e c t i o n P l a t f o r m Reply (DCPR: UHF t o S-Band) 5)

The S p a c e c r a f t The drawinp i n F i g u r e 1 i n d i c a t e s t h e shape and t h e l o c a t i o n o f t h e i n s t r u m e n t s . The s p a c e c r a f t has a s p i n n i n g s e c t i o n and a despun antenna assembly. The despin b e a r i n g assembly and t h e n o n - c o n t a c t i n g r o t a r y j o i n t allow the spinning section t o spin f r e e l y and m a i n t a i n mechanical and thermal s t a b i l i t y . The s p i n n i n a s e c t i o n i s a c y l i n d r i c a l s o l a r panel w i t h i n which i s c o n t a i n e d t h e communications equipment s h e l f , t h e instruments, t h e h y d r a z i n e tanks and a s s o c i a t e d t h r u s t e r s . The antenna assembly p r o v i d e s e a r t h coverage w i t h 1) a North-South l i n e a r l y p o l a r i z e d d i p o l e - p a r a b o l i c r e f l e c t o r combination f o r t h e VAS downlink, t h e S-Band u p l i n k and downlink p o r t i o n o f b o t h t h e DCP s e r v i c e and t h e m u l t i f u n c t i o n a l chann e l , and 2) an RHCP b i f i l a r he1 i x w i t h a cupped r e -

GOES SATELLITE

.

1)

Transmission o f VAS data

2)

Transmission o f SEM d a t a (as p a r t o f t h e telemetry)

Telemetry and command system f o r c o n t r o l and m o n i t o r i n g t h e h e a l t h o f t h e s p a c e c r a f t

f

s BAND BICONE OMN1 ANTENNA

S BAND HIGH GAIN ANTENNA

UHF ANTENNA

3) Transponder capabi 1i t i e s f o r a ) s t r e t c h e d VAS (SVAS) data, b ) weather f a c s i m i l e (WEFAX) data, and c ) t r i l a t e r a t i o n (TRILAT) s i g n a l s , which a r e time-shared w i t h t h e VAS data.

4)

SOLAR PANEL

'

EPS DOME

Transponder c a p a b i l i t i e s f o r a ) Data Coll e c t i o n P l a t f o r m I n t e r r o g a t i o n (DCPI :

/

541

\

i

SUN SENSORS

EPS TELESCOPE

F i g u r e 1.

-

Coovrieht @ American Institute of Aeronautics and .Astronaulics, Inc., 1982. All rights reserved.

i

GOES Sate1 1it e

f l e c t o r t o s u p p o r t t h e UHF u p l i n k s and downlinks o f t h e DCP s e r v i c e . The o m n i d i r e c t i o n a l bicone antenna i s t h e t e l e m e t r y and command antenna w h i l e on o r b i t and i t i s used f o r t e l e m e t r y and r a n g i n g d u r i n g launch, t r a n s f e r o r b i t and apogee boost motor (ABM) firing.


There a r e s e v e r a l c u t o u t p o r t i o n s o f t h e s o l a r panel used by t h e SEN and by t h e e a r t h and sun sensors. The e a r t h and sun sensors p r o v i d e p u l s e s d u r i n g e c l i p s e and d a y l i g h t c o n d i t i o n s t o t h e despin c o n t r o l e l e c t r o n i c s , which i n t u r n m a i n t a i n t h e antenna p o i n t i n g , and p r o v i d e i n t e r n a l t i m i n g t o ensure e f f i c i e n t t i m e - s h a r i n g o f t h e VAS generated data and t h e m u l t i f u n c t i o n transponder channel. A knowledge o f t h e i n s t r u m e n t s aboard t h e s p a c e c r a f t i s r e q u i r e d t o understand t h e communications subsystem. A d e s c r i p t i o n o f t h e i n s t r u m e n t s f o l l o w s .

The Instruments VAS The p r i m a r y i n s t r u m e n t on t h e s a t e l l i t e i s t h e V i s i b l e i n f r a r e d s p i n scan r a d i o m e t e r Atmospheric Sounder (VAS), a 16 i n c h r e f l e c t i n g t e l e s c o p e w i t h v i s i b l e and I R d e t e c t o r s i n t h e f o c a l p l a n e . The VAS i s l o c a t e d i n the s p i n n i n g p o r t i o n o f t h e spacec r a f t and i s mounted c o n c e n t r i c w i t h t h e s p i n a x i s o f t h e s p a c e c r a f t . D u r i n g each r e v o l u t i o n o f t h e s p a c e c r a f t , t h e VAS w i l l image a l o n g one l a t i t u d e l i n e . The scan m i r r o r i n t h e VAS w i l l s t e p t o t h e n e x t p o s i t i o n when t h e VAS i s n o t v i e w i n g t h e e a r t h . There a r e 1820 steps needed t o scan the f u l l e a r t h d i s c . The VAS uses a Ri t c h e y - C h r e t i e n r e f l e c t i n g o p t i c a l system w i t h 2 a n F7.2 l e n s and an e f f e c t i v e a p e r t u r e o f 1090 cm . The d e t e c t o r s a r e capable o f d e t e c t i n g i n t h e v i s i b l e and i n t h e I R . V i s i b l e r a d i a t i o n i s conveyed from t h e f o c a l p l a n e t o e i g h t p h o t o m u l t i p l i e r tubes v i a f i b e r o p t i c c a b l e s . The r e s o l u t i o n o f t h e v i s i b l e spectrum i s 0.9 km a t t h e s u b s a t e l l i t e p o i n t . I n f r a r e d r a d i a t i o n i s detected by any o f t h r e e p a i r s o f s o l i d s t a t e d e t e c t o r s . There i s one small p a i r and one l a r g e p a i r o f HgCdTe d e t e c t o r s and one l a r g e p a i r o f InSb d e t e c t o r s . The d e t e c t o r arrangement i s shown i n F i g u r e 2 w i t h t h e i r a n g u l a r spacings. The r e s o l u t i o n i n t h e I R spectrum i s 6.9 km a t t h e s u b s a t e l l i t e p o i n t . A two shage r a d i a t i o n c o o l e r m a i n t a i n s t h e I R d e t e c t o r s a t 95 K. A f i l t e r wheel can p o s i t i o n any one o f 12 s p e c t r a l bandpass f i l t e r s i n t h e o p t i c a l p a t h .

NORTH

t

The VAS i s capable o f o p e r a t i n g i n an atmospheric sounding mode, i n a d d i t i o n t o t h e normal two-dimens i o n a l c l o u d imaging mode. The on-board processor can be programmed by t h e ground s t a t i o n t o s e l e c t a sequence o f f i l t e r wheel p o s i t i o n s and t o d w e l l on a s i n g l e scan l i n e up t o 255 s p i n s . The s p e c t r a l ranges o f t h e f i l t e r s a r e designed t o g a i n i n f o r m a t i o n about w a t e r vapor and carbon d i o x i d e i n t h e a t mosphere, and t h e d w e l l i n g on a s i n g l e l i n e w i l l i n crease t h e SNR, hence t h e r e s o l u t i o n . The s p e c t r a l sharpness o f t h e a b s o r p t i o n l i n e s o f carbon d i o x i d e tends t o broaden w i t h i n c r e a s e d pressure (due t o i n c r e a s e d c o l l i s i o n s and r e s u l t a n t d o p p l e r s h i f t ) , from t h e t o p o f t h e atmosphere t o t h e e a r t h ' s s u r face. Thermal r a d i a t i o n f r o m t h e e a r t h and t h e atmosphere i n t h e v i c i n i t y o f t h e a b s o r p t i o n l i n e can be used, w i t h known p r o p e r t i e s o f t h e d i s t r i b u t e d gas, t o determine t h e two dimensional temperat u r e p r o f i l e a t a g i v e n h e i g h t above t h e e a r t h ' s s u r f a c e . The f i r s t demonstration o f t h e f i r s t A t mospheric Sounder i n space was h i g h l y s u c c e s f u l and i s d e s c r i b e d i n Reference 1. Primary p a r t i c i p a n t s i n t h e VAS demonstration a r e NASA (GSFC), NOAA (NESS) and t h e U n i v e r s i t y o f Wisconsin.

The Space Environment M o n i t o r performs t h r e e f u n c t i o n s w i t h t h r e e s e t s o f i n s t r u m e n t s . These i n d i v i d u a l i n s t r u m e n t s a r e i n d i c a t e d i n F i g u r e 1.

1) The magnetometer measures t h e magnetic f i e l d s t r e n g t h and d i r e c t i o n i n t h e v i c i n i t y o f t h e s p a c e c r a f t . The sensor i s a b i a x i a l f l u x g a t e magnetometer w i t h one a x i s p a r a l l e l t o t h e spacec r a f t s p i n a x i s and a t r a n s v e r s e a x i s p a r a l l e l t o t h e s p i n plane. The two c o i l s i n t h e magnetometer a r e mounted on a t h r e e f o o t boom which i s deployed a f t e r 1aunch. 2 ) The x-ray sensor m o n i t o r s s o l a r f l a r e act i v i t y i n t h e s o f t x-ray spectrum. The x - r a y r a d i a t i o n t r a v e l s a t t h e speed o f l i g h t and i s an advance warning t h a t slower moving e n e r g e t i c p a r t i c l e s may soon f o l l o w . A geared s t e p p e r motor can a d j u s t t h i s sensor t o t r a c k t h e seasonal r e l a t i v e movement o f t h e sun i n steps o f 0.125 degrees. The s t e p s i z e corresponds t o an average o f two steps p e r day. The 27 degrees. range o f t h e p o s i t i o n e r i s

+

3 ) The e n e r g e t i c p a r t i c l e sensor i s designed t o d e t e c t alpha p a r t i c l e s , protons, and e l e c t r o n s r e s u l t i n g from s o l a r f l a r e - a s s o c i a t e d p a r t i c l e i n j e c -

-

SCAN DIRECTION

VISIBLE CHANNELS

4I u

F i g u r e 2.

u

I

D = 2.137 rnr M A X

I n f r a r e d and V i s i b l e Channel D e t e c t o r Arrangement

t i o n events. T h i s i n s t r u m e n t has t h r e e d e t e c t o r assemblies t o cover t h e broad energy spectrum of p e n e t r a t i n q r a d i a t i o n . These u n i t s a r e : a)

Telescope. The t e l e s c o p e u t i l i z e s two s i l i c o n s u r f a c e b a r r i e r d e t e c t o r s (sSBD) t o d e t e c t low energy p r o t o n s (0.8 t o 15 MeV) and alpha p a r t i c l e s (3.2 t o 60 MeV) w i t h a h a l f angle f i e l d o f view o f 35 degrees.

b)

Dome. The dome u t i l i z e s t h r e e groups o f p a i r e d SSBDs t o d e t e c t e l e c t r o n i c s ( g r e a t e r than 2 MeV), p r o t o n s (15 t o 500 MeV) i n seven channels, and alpha p a r t i c l e s (60 t o 400 MeV) i n s i x channels w i t h i n a f i e l d o f view o f 130 degrees.


c)

High Energy P a r t i c l e D e t e c t o r . The HEPAD i s a Cerenkov c o u n t e r t e l e s c o p e combining a p h o t o m u l t i p l i e r tube and s o l i d s t a t e det e c t o r s t o d e t e c t p r o t o n s (350 t o < 850 MeV)

and alpha p a r t i c l e s (640 t o < 900 MeV/nucleon) w i t h i n a f i e l d o f view o f 68 degrees. The SEM payload p r o v i d e s c o r r e l a t i v e measurements o f t h e space environment near e a r t h . The d a t a a r e p r i m a r i l y used by environmental s c i e n t i s t s i n NOAA, NASA, t h e A i r Force and t h e Navy f o r p r e p a r i n g warni n g s and a d v i s o r i e s f o r o p e r a t i o n s a f f e c t e d by s o l a r f l a r e s and t h e i r induced e f f e c t s on e a r t h . The i n t e r a c t i o n of t h e VAS and SEM w i t h t h e communicat i o n s i s d e s c r i b e d below.

The Communications System The communications system aboard t h e GOES spacec r a f t i s i n t e n d e d t o s u p p o r t a t o t a l environmental m o n i t o r i n g system. F i g u r e s 3 and 4 d e p i c t t h e major u s e r f u n c t i o n s and t h e i n t e r a c t i o n o f t h e s a t e l l i t e w i t h those users r e s p e c t i v e l y . The s i g n i f i c a n t c h a r a c t e r i s t i c s o f t h e communications channels a r e

GEOSTATIONARY OPERATIONAL ENVIRONMENTAL SATELLITE (GOES)

GOES TAKES VISIBLE AND INFRARED MEASUREMENTS OF THE EARTH AND ATMOSPHERE, MEASURES VERTICAL TEMPERATURES. SENDS RAW D A T A T O GROUND PROCESSING CENTER.

PROCESSED HIGH RESOLUTION PICTURE DATA ARE RETURNED TO GOES FOR RE-DISTRIBUTION TO USERS STARTING EVERY 30 MINUTES.

REMOTELY LOCATED INSTRUMENTS TRANSMIT OCEAN CURRENT, RAIN, RIVER, SNOW AND SEISMOMETER DATA TO GOES FOR RELAY TO EARTH PROCESSING SITES.

SPACE ENVIRONMENT SENSORS O N GOES MEASURE SOLAR EMISSIONS AND MAGNETIC FIELDS TO PROVIDE INFORMATION FOR COMMUNICATION SYSTEMS.

F i g u r e 3.

Corrmunication Functions

543

summarized i n Table 1. The major communications f u n c t i o n s a r e e x p l a i n e d here.

performance o f t h e o n - o r b i t t e s t s c l o s e l y match o r exceed t h e pre-launch system t e s t requirements. The t y p i c a l crossover p o i n t f o r 10-6 BER i s a t an Eb/No o f 15.0 dB. The r a d i o astronomy requirement o f -237 d ~ w / m 2 / ~ z ,a t t h e e a r t h ' s surface, i s s a t i s f i e d w i t h a t l e a s t 2 dB o f margin.


VAS Data The t r a n s m i s s i o n o f t h e VAS d a t a ( F i g u r e 3a) i s t h e major p r o d u c t o f t h e communications system. V i s i b l e , i n f r a r e d and sounding d a t a from t h e VAS i s mu1 t i p l e x e d i n t o two s e r i a l b i t streams and QPSK modulated a t 28 Mb/s. This data i s time m u l t i plexed i n t o t h e m u l t i f u n c t i o n r e p e a t e r channel, and i s t r a n s m i t t e d t o t h e Command and Data Acquis i t i o n S t a t i o n (CDAS) a t Wallops I s l a n d , Va. T h i s data i s t r a n s m i t t e d o n l y d u r i n g t h e t i m e t h a t t h e VAS i s scanning t h e e a r t h (about 20 degrees) and i s c a l l e d t h e f r o n t scan. For t h e remainder o f t h e s p i n p e r i o d , t h e back scan, t h i s channel i s used as a transponder.

The s p i n r a t e o f 100 rpm corresponds t o a s p i n p e r i o d o f 600 mS. The 28 Mb/S VAS data, w i t h i t s preamble and frame sync words ( F i g u r e 5 ) , a r e t r a n s m i t t e d f o r 37.5 mS. During t h e remaining 562.5 mS of t h e s p i n p e r i o d , t h e S-Band r e c e i v e r squelches t h e VAS p a t h and a l l o w s r e c e i v e d s i g n a l s t o be r e t r a n s m i t t e d . The S-Band r e c e i v e r can a l s o be commanded i n t o t h e r e p e a t e r ( o r m u l t i f u n c t i o n ) o n l y mode where t h e VAS data i s always squelched o f f .

The a d j a c e n t r a d i o astronomy band (1660 t o 1670 MHz) i s used by r a d i o astronomers t o m o n i t o r two l i n e emissions from t h e h y d r o x y l r a d i c a l OH. The r e s t f r e q u e n c i e s ( w i t h o u t d o p p l e r s h i f t ) o f these two l i n e s a r e 1665.402 and 1667.359 MHz. The r e q u i r e d r a d i o astronomy f i l t e r i n g a t t h e l o w e r edge o f t h e band and t h e COA t e l e m e t r y t r a n s m i s s i o n a t t h e h i g h end r e q u i r e d t h e design o f a f i l t e r which was narrower than t h e 28 MHz passband o f t h e VAS data. Every o t h e r v i s i b l e word o f VAS data i s i n v e r t e d t o d e f i n e a more random p a t t e r n . Hence, an RF spectrum approaching a PRN p a t t e r n . The e f f e c t o f f i l t e r i n g (22 MHz - 3 dB p o i n t s ) the VAS data ( 2 8 MHz - n u l l - t o - n u l l ) wi 11 i n t r o d u c e e r r o r s i n t o t h e data. The b i t e r r o r r a t e (BER)

The VAS 28 Mbps h i g h - r e s o l u t i o n d a t a when r e c e i v e d a t t h e CDA s t a t i o n i n Wallops I s l a n d , Va. i s r e f o r m a t t e d , c a l i b r a t e d , g r i d d e d f o r geographi c a l r e f e r e n c e , and subsequently r e t r a n s m i t t e d t o t h e s a t e l l i t e a t a reduced r a t e (1.75 Mbps) as " s t r e t c h e d " VAS (SVAS) data. The SVAS data, t r a n s m i t t e d f r o m t h e CDA s t a t i o n , i s r e l a y e d through t h e s p a c e c r a f t d u r i n g t h e back scan o f t h e VAS, when t h e s p a c e c r a f t i s i n t h e transponder mode ( F i g u r e 3b). Users w i t h s u i t a b l e r e c e i v i n g equipment can use t h e SVAS data. The end p r o d u c t i s a photograph o f t h e e a r t h d i s c , showing c l o u d p a t t e r n s and tempe r a t u r e p r o f i l e s , e v e r y 30 minutes, 24 hours p e r day. The users o f t h i s d a t a i n c l u d e t h e U. S. Navy F l e e t Numerical Oceanographic Center, Colorado

Mode/ Parameter

I

VAS 0 a t a Transmission

I

8 0"

8 L 8

""

b"

Transmission

I

DCPI

Mu1t i f u n c t i o n Channel

/

DCPR Cha

Uplink Ant P o l a r i z a t i o n

-

/

STON Ranqinq

I

STDN Telemetry

I

CDA Telnetryl

Comand

cteristics

Vertical linear

Vertical linear

RHCP

Vertical linear

Vertical linear

Earth Coverage Oish

Earth Coverage Oish

Earth Coverage Helix

Toroid Bicone

Toroid Bicone

*

2034.9

401.9

2034.2

-17.6

-17.6

-18.5

-36.9

1681.6

**

468.825

1694.5

2209 .O86

55.5

56.1

46.2

36.5

13.9 a t 30°

S/C A n t Type

Earth Coverage Dish

Earth Coverage Dish

Earth Coverage Helix

Earth Coverage Dish

Toroid Bicone

Toroid Bicone

Toroid Bicone

SIC A n t Polarization

Vertical Linear

Vertical Linear

RHCP

Vertical Linear

Vertical Linear

Vertical Linear

,Vertical Linear

SIC Antenna Type Freq Channel MHz GIT, d81K a t E a r t h Edge

II I

Downlink Channel F r ~ q MHz EIRP, dam a t E a r t h Edoe

*

U p l i n k frequency:

**

Downlink Frequency:

-

S t r e t c h e d VAS = 2029.1;

WEFAX = 2033;

S t r e t c h e d VAS = 1687.1:

Table 1.

T r i l a t e r a t i o n = 2026, 2030.2,

WEFAX = 1691;

Communication -

T r i l a t e r a t i o n = 1684. 1688.2,

2032.2 1690.2

Interface Characteristics

,


F i g u r e 4.

GOES M i s s i o n Communications L i n k s

S t a t e U n i v e r s i t y , U. S. A i r F o r c e G l o b a l Weather C e n t r a l , N a t i o n a l Severe Storms F o r e c a s t C e n t e r , NASA Goddard Space F l i g h t Center, and t h e N a t i o n a l E n v i r o n m e n t a l Sate1 l i t e S e r v i c e (NESS) i n S u i t l a n d , Md. T i m i n g s i g n a l s f r o m t h e e a r t h s e n s o r s and t h e d e s p i n c o n t r o l e l e c t r o n i c s p e r m i t a complementary t i m e - s h a r i n g o f t h e r e p e a t e r t o t r a n s m i t t h e VAS d a t a and r e t r a n s m i t t h e SVAS d a t a . The f u l l scan o f t h e e a r t h r e q u i r e s a b o u t 18 m i n u t e s and a n o t h e r t h r e e m i n u t e s f o r t h e p r i m a r y m i r r o r i n t h e VAS t o re,trace t o i t s s t a r t i n g p o s i t i o n . The c h a n n e l i s used a s a f u l l t i m e t r a n s p o n d e r d u r i n g t h e r e m a i n i n q p a r t of t h e t h i r t y m i n u t e VAS " p i c t u r e " p e r i o d .

I

PREAMBLE

ALL 0s

I

16 BIT DECOM SYNC

1

T h i s t i m e i s used p r i m a r i l y f o r t r a n s m i s s i o n o f w e a t h e r f a c s i m i l e (WEFAX) d a t a . 2 T h i s t i m e i s a l s o used o c c a s i o n a l l y f o r t r i l a t e r a t i o n (TRILAT) r a n g i n g w i t h T u r n Around Ranging (TAR) s t a t i o n s i n S a n t i a g o , C h i l e and H a w a i i . TRILAT i s used f o r p r e c i s e d e t e r m i n a t i o n o f o r b i t p o s i t i o n . The f r e quencies o f t h e v a r i o u s m u l t i f u n c t i o n s i g n a l s a r e g i v e n i n T a b l e 1. Data C o l l e c t i o n P l a t f o r m I n t e r r o g a t i o n and R e p l y Unmanned Data C o l l e c t i o n P l a t f o r m s (DCP) have been s e t up where r e p e a t e d e n v i r o n m e n t a l measure-

1

'I 'IT

8

22 BIT SUN SYNC COUNTER

3 1 44

E 2 0:1;

51 5 1

- -- - - -- - A 9 1 4

SYNC

2126

3338

4550

I I I RECYCLE

Figure 5.

+-

VAS Data PCM O u t p u t Format

MOTE: V2. V4. V6, V 8 ARE INVERTED


ments a r e needed, b u t where t h e l o c a t i o s a r e d i f f i c u l t , hazardous o r expensive t o acceSSSq The DCPs can m o n i t o r ocean c u r r e n t s , r a i n , snow, t i d e and r i v e r l e v e l s , seismometer readings, temperatures, atmospheric p r e s s u r e and h u m i d i t y . An i n t e r r o g a t i o n s i g n a l i s t r a n s m i t t e d from t h e CDAS t o t h e DCPs through t h e S-Band t o UHF transponder. T h i s i n t e r r o g a t i o n s i g n a l i n s t r u c t s t h e DCP t o t r a n s m i t ( r e p l y ) i t s stored o r r e a l time information t o the s a t e l l i t e . Both t h e i n t e r r o g a t i o n and r e p l y s i g n a l s a r e a t UHF. Several DCPs a r e timed o r a u t o m a t i c a l l y t r i g g e r e d ( b y weather phenomena) t o t r a n s m i t w i t h o u t b e i n g i n t e r r o g a t e d . The r e p l y from t h e DCPs i s r e t r a n s m i t t e d through t h e UHF t o S-Band transponder ( F i g u r e 3c) f o r r e c e p t i o n by users throughout t h e Western Hemisphere. As an a d d i t i o n a l user s e r v i c e , and NBS-maintained atomic c l o c k a t t h e CDAS t r a n s m i t s a t i m e code (UTC) w i t h hemispherical coverage w i t h t h e DCP i n t e r r o g a t i o n s i g n a l .4 The DCP u p l i n k f r e q u e n c i e s a r e chosen such t h a t t h e y can be channelized a c c o r d i n g t o t h e i r frequency o f f s e t from a p i l o t c a r r i e r . The DCPR channel i s l i n e a r t o minimize i n t e r m o d u l a t i o n p r o d u c t s when s e v e r a l o f t h e e v e n l y spaced DCPR c a r r i e r s occur i n a d j a c e n t frequency s l o t s .

cessor d a t a l o a d v e r i f i c a t i o n , bus c u r r e n t , command execute and sun, e a r t h and index p u l s e occurances a r e d e t e c t e d and modulated on IRIG 12 and IRIG B s u b c a r r i e r s . SEM d a t a i s processed as p a r t o f t h e PCM data and i s r e c e i v e d a t t h e NOAA Table Mountain F a c i l i t y a t Boulder, Colorado ( F i g u r e 3d). A t t h i s f a c i l i t y , t h e SEM d a t a i s s o r t e d o u t o f t h e t e l e m e t r y stream, separated a c c o r d i n g t o i n s t r u m e n t t y p e and processed i n r e a l t i m e i n t o q u a n t i t a t i v e form f o r e n t r y i n t o t h e Space Environmental L a b o r a t o r y Data A c q u i s i t i o n and D i s p l a y (SELDADS) data base.

Telemetry

The t h r e e s a t e l l i t e s under c o n t r a c t have t h e f o l l o w i n g launch dates:

The t e l emetry d a t a i s t r a n s m i t t e d by two p a i r s o f redundant t r a n s m i t t e r s as d e p i c t e d i n F i g u r e 4. The CDA and STDN t e l e m e t r y t r a n s m i t t e r s a r e i d e n t i c a l save f o r downlink frequency, EIRP and modulat i o n i n d i c e s which a r e d e l i n e a t e d i n Table 11. The baseband assemblies c o n s i s t o f two redundant C e n t r a l Telemetry U n i t s (CTU) and two p a i r s o f redundant Remote Telemetry U n i t s (RTU) which sample t h e 512 transducers t h a t m o n i t o r t h e general h e a l t h o f t h e s p a c e c r a f t . Analog, p a r a l l e l b i l e v e l d i g i t a l , and s e r i a l d i g i t a l d a t a a r e c o l l e c t e d by t h e remote u n i t s upon i n t e r r o g a t i o n from t h e CTU v i a a superv i s o r y bus. The data i s c o n d i t i o n e d , mu1 t i p l e x e d and A/D converted i n t h e RTUs and t h e d i g i t a l data stream i s t r a n s f e r r e d t o t h e CTU v i a a r e p l y bus. The d a t a i s processed, f o r m a t t e d and synchronized i n t o a p u l s e code modulated (PCM) data stream by t h e CTU. The update r a t e o f any sensor can be i n creased by commanding t h e Central Telemetry U n i t s (CTU) i n t o t h e a ) Dwell, b ) I n h i b i t o r c ) h e l l / I n h i b i t Mode. These modes and t h e e n t i r e t e l e m e t r y subsystem a r e d e s c r i b e d i n Reference 5. ~ i m u l t a n g ously, t h e r e a l t i m e d a t a concerning s p a c e c r a f t nut a t i o n , ABM f i r i n g , a x i a l t h r u s t e r f i r i n g , VAS p r o -

Command and Ranging The command and r a n g i n g s i g n a l s a r e t r a c k e d by a phase l o c k e d l o o p r e c e i v e r where t h e command sidebands a r e r o u t e d t o and processed by t h e command demodulator/decoder. The r a n g i n g s i g n a l (100, 20, 4 kHz and 4 kHz w i t h AM sidebands) i s upconverted and r e t r a n s m i t t e d . The a b s o l u t e t i m e d e l a y through t h e s p a c e c r a f t i s 4000 nanosecond.

Epi 1ogue

GOES D ( 4 )

September 19, 1980*

GOES E ( 5 )

May 22, 1981*

GOES F ( 6 )

A p r i l 28, 1983

There have been two o n - o r b i t anomalies o f t h e communications system as o f t h i s w r i t i n g (November 1981): 1. The GOES 4 redundant S-Band t r a n s m i t t e r l o s t DC power two months a f t e r launch. I t i s bel i e v e d t h a t t h e h i g h power t r a n s i s t o r s a r e n o t a t f a u l t , b u t t h e e x a c t f a i l u r e mechanism has n o t been determined. 2. The GOES 4 p r i m a r y UHF r e c e i v e r c r e a t e d excessive n o i s e about e i g h t months a f t e r launch. T e s t i n g o f s p a c e c r a f t r e v e a l e d t h e h i g h g a i n f r o n t end o f t h e UHF r e c e i v e r would t e n d t o o s c i l l a t e when coupled t o h i g h - Q devices such as i s o l a t o r s and t h e UHF d i p l e x e r . The problem was c o r r e c t e d on t h e two successive s p a c e c r a f t . The b l o c k diaaram of t h e communications subsystem i s i n c l u d e d ds F i g u r e 6 *Actuals CDA

STDN

Downlink Freq, MHz

1694.0

2214.0

EIRP, dBm Antenna Angle

33.0 +loo -

+300 -

Transmitter --

26.0

Flodulation Type PCM IRIG 12 IRIG B M o d u l a t i o n Index, Rad PCM I R I G 12 IRIG B PCM B i t Rate, bps *PCM d a t a a r e Manchester coded Table II. Telemetry Transmi t t e r C h a r a c t e r i s t i c s

The n e x t s e r i e s of GOES sate1 l i t e s (G, H and I ) w i l l be launched beginning i n 1985. The design f o r GOES G, H and I w i l l be i d e n t i c a l except f o r Furthermore, the t e l e m e t r y and command subsystem. t h e r e have been d i s c u s s i o n s about adding a search and rescue t r a n s m i t t e r which would add another p u b l i c s e r v i c e f u n c t i o n t o t h i s a l r e a d y mu1 t i functional s a t e l l i t e .

Acknowledgement Programmatic and o p e r a t i o n a l r e s p o n s i b i l i t i e s f o r t h e system a r e e s t a b l i s h e d w i t h i n t h e Department of Commerce and managed by t h e N a t i o n a l OceanTechnoi c and Atmospheric A d m i n i s t r a t i o n (NOAA) l o g i c a l developments and advances f o r GOES a r e p r o v i d e d t o NOAA by t h e N a t i o n a l Aeronautics and Space A d m i n i s t r a t i o n a t t h e Goddard Space F l i g h t Center. The GOES 4, 5 and 6 s a t e l l i t e s a r e b e i n g b u i l t by Hughes A i r c r a f t Company, Space and Communications Group, under c o n t r a c t NAS-5-24342. My s p e c i a l thanks a r e extended t o Karen Brady, who p r o v i d e d a l l o f t h e s u p p o r t needed t o make t h i s paper p o s s i b l e .


.

References

W. L. Smith, e t a1 , 1981. F i r s t Sounding Res u l t s from VAS D, B u l l e t i n o f t h e America M e t e o r o l o g i c a l Society, Volume 62, PP 232-236 F u r t h e r i n f o r m a t i o n on compatible ground s t a t i o n s can be had from a manufacturer: ALDEN E l e c t r o n i c and Impulse Recording Equipment Co., Westboro, MA 01581 F u r t h e r i n f o r m a t i o n on compatible ground s t a t i o n s can be had from a m a n u f a c t u r e r : Synerg e t i c s I n t e r n a t i o n a l , P. 0. Box E, Boulder, Colorado 80306, (303) 530-2020 NBS Time and Frequency Di ssemination Services, S . L. Howe, E d i t o r , NBS Special P u b l i c a t i o n 432, September 1979 G e o s t a t i o n a r y Operational Environmental S a t e l l i t e , Telemetry and Communications, A p r y l l M. Nakamura and Leo A. M a l l e t t e , ITC/USA/'81 Conference Proceedings, ~ c t o b e r1981

28 M H Z TO V D M

UHF

TRANSMITTER 1

DCPR TRANSMITTER 1 16S4.6

UHF

TRANSMITTER 2

DCPR TRANSMITTER 2

96.8 M H z

IRO W I R I G 1 1 PCM l R l G W l R I G 12 PCM

I R l G V l R l G 17 PCM

IRlGlllllG 11

rcu