Satellites at Work (Space in the Seventies)

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SaLf ILMITRATBONS REPROMhdONkpN BLACK A N d W H i T ?

S A T E L L I T E S A T W O R KS p a c e in th e Sevent ies

N72-13 8 6 6

Unclas

11470u.

(NASA-EP-8 4 ) SATELLITES AT WORK (SPACE IN

TH E SEVENTIES) W.R. Corliss (NASA) Jun.

1971 29 p CSCL 22B

Reproduced by

NATIONAL TECHNICALINFORMATION S E R V I C E

U S Department of CommerceSpringfield V A 22151

G3/31

JNational Aeronautics and Space Administration



S P A C E IN T H E S E V E N T I E S

M a n h as walked o n th e Moon, m a d e scientificobservations there, and brought back to Earthsamples of th e lunar surface.

Unmanned scientific spacecraft h a v e probed fo rfacts about matter, radiation and magnetism inspace, and h a v e collected data relating to th eMoon, Venus, Mars, th e Sun and some of the stars,and reported thei r findings to ground stationso n E a r t h .

Spacecraft h a v e b e e n put into orbit around th eE a r t h a s weather observation stations, ascommunications relay stations fo r a world-widetelephone and television network, a n d a s aids tonavigation.

I n addition, th e space program h a s acceleratedth e advance of technology for science and industry,contributing many n e w ideas, processes and

materials.All this took place in th e decade of th e Sixties.

What next? What may b e expected of spaceexploration in th e Seventies?

N A S A h as prepared a series of publications a n dmotion pictures to provide a look forward toS P A C E IN TH E S E V E N T I E S . Th e topics covered inthis series include: E a r t h orbital science; planetaryexploration; practical applications of satellites;technology utilization; m a n in space; andaeronautics. S P A C E IN TH E S E V E N T I E S presents

th e planned programs of N A S A fo r th e comingdecade.

June, 1971

COVER:

This photograph of th e Earth w as taken by AT S 3 from itson--station posit ion at 47 degrees w e s t longitude on th eequator over Brazil. Four continents ca n be seen; SouthAmer ica is m o s t prominent . Majo r weathe r ove r th e centralUni ted States consists o f a cold f ront moving eastward .At bot tom center , a tropical storm can be seen wi th a coldf ront extending into Argentina.



S A T E L L I T E S

A T W O R KI : i l n Communications, Meteorology, Geodesy, Navigation,

Traffic Control, and Earth Resources Technology

b y W i ll ia m R . C o r l i s s

O R I 6 1 1 A L C O I T M I

C O L O R L L U S T R A T I O N S

National Aeronautics and Space Administration, W ash ington, D . C . 2 0 5 4 6



TABLE O F CONTENTS

4 INTRODUCTION

6 A TESTING LABORATORY F O R

NE W CONCEPTS (ATS)

8 COMMUNICATION SATELLITES

1 1 TH E BALLOON WA T C H E R (CAS)

1 2 TH E INTELSAT FAMILY

1 3 TH E BRICK MOON REVISITED

1 5 LOCATING TH E CONTINENTS

1 7 WE A T H E R WATCHING V S . WE A T H E R PREDICTING

1 9 LATEST IN A LONG LINE (ITOS)

20 SEEING TH E B IG PICTURE (SMS)

22 NIMBUS, A TEST VEHICLE F O R

METEOROLOGICAL INSTRUMENTS

24 HUSBANDING TH E EARTH'S RESOURCES (ERTS)

28 A GLANCE AT TH E FUTURE



W N T R O D U C T I O N

W h a t possible practical uses could there be fo r afew pounds of contrived metal located over 10 0 milesabove th e Earth? Histor ians o f technology can vouch

t hat th e same k inds of quest ions were leveled at th ete legraph, the steam engine, an d almost every otherimportant invention. " G e t a ho rs e ! " w as acommonjeer still with in th e recollection o f millions.

Today, everyone accepts th e intercontinentalsatellite relay o f television programs an d te lephoneconversat ions, but t hese communicat ion satellitesinitially h ad to overcome th e same skept ic ism as th eautomobi le. W e also expec t to be warned of theapproach of dangerous hurr icanes an d to be toldtomor row 's weather with high reliability. W h o hasn ' t

seen a satell ite-taken picture of cloud cover? Weathersatellites an d communicat ion satellites represent justth e beginning. In th e artificial satellite, w e have apowerful tool which is already being turned to th esolut ion o f some of the w or ld ' s pressing practicalprob lems .

Offhand, it is difficult to see h ow a small ,automated machine more than 100 mi les up couldpossibly contr ibute to th is planet's down- to-Earthprob lems . Acentury ago, an Earth satellite wouldindeed have been of little use, but today w h e n w e arenearing th e l imits of our planet's raw materials an d its

capaci ty to recycle o ur wastes , Earth satellites proveto be invaluable pollut ion monitors , resource-f inders,weather -watchers , an d communicat ion relay points.As th e convent ional tools an d techniques falter int he i r struggle with terrestr ial problems, spacetechnology is coming forth with ne w ideas, ne w waysto solve prob lems . Th is is NASA's great challengeduring th e next decade: to help understand th e Earth 'secology an d develop space sys tems wh ich w ill , on th eone hand, solve o ld problems, and, on th e other , no tcreate additional ne w problems fo r mankind.

Th e first "appl icat ions satel l i te" w as conceived

abou t acentury ago b y Edward Everet t Hale, b e s tknown fo r h is story "The M an W ith o u t a Country . " In1 8 6 9 , H ale 's precocious tale , "The Brick M o o n , " w aspubl ished in th e Atlantic Monthly. Hale envisioneda large artificial satellite circling th e Earth in an orb i tover th e poles and passing along th e Greenwichmeridian. Ships at sea, h e reasoned, could takebearings on th is man-made moon an d t hus f ix the i rpositions more accurately. Th e Brick Moon , thoughonly f ict ional, w as th e f irst navigation satellite.

Th e Brick Moon h ad th e advantage o f he igh t overth e usual terrestr ial landmarks used by navigators.Like present-day sate l li tes , i t could be seen from afar.

Almost all o f th e practical benefits o f artificialsatellites stem from th is single factor-height and,consequent ly , a sweeping view o f th e Earth. Not onlycan terrestr ial eyes, including radio antennas, locatedthousands of miles apart see th e satel l i te, but, givenvision of its own , a satellite with a TV camera canscrutinize huge port ions of th e Earth 's sur face.Indeed, th e app lications sate l li te is an invaluableextension of our sense in tw o ways : (1 ) it sees muchmore terr i tory; an d (2 ) its sensors see wel l beyondth e narrow visible spectrum. Looking at th e Earthbelow through infrared sensors is l ike looking throu gh

magic glasses ; everyth ing glows according to itstemperature and chemica l makeup. F o r th is reason,infrared sensors an d those sensi t ive to other wave-lengths ca n diagnose the Earth's surface environmentfrom afar.

N A S A ' s A p p r o a c hBy th e time NASA w as created in 1 9 5 8 , various

government agencies h ad already made numerousstudies o f th e potential advantages of artificialsatellites in communicat ions and weather forecasting.Some of the e ar liest satellites launched by th e United

States were of t hese t ypes ; fo r example, Score ( 1 9 5 8 )an d Tiros 1 ( 1 9 6 0 ) . In 1 9 5 8 , one of NASA's first jobsw as obvious: develop communicat ion and weathersatellites fo r practical use on a day-to-day basis.During th e early 1 960 ' s , almost tw o dozen satelliteswere launched to tes t spacecraft techniques an dsensors. As space hardware and th e associated groundequipment were proven out, other governmentagencies an d private industry began to play moredominant roles in th e operational aspects o f satellitecommunicat ion an d meteorology. Th e Communica-t ions Satellite Corporation (COMSAT) was created byCongress in 1 9 6 2 to establish aglobal communica-

tion network employing communication satell ites.Soon after, th e Environmental Science ServicesAdministration (ESSA), no w part of the Nat ionalOceanic an d Atmospher ic Administration (NOAA),assumed responsibi l i ty fo r operating weathersatellites. NASA's role is now t hat of providing launchan d tracking services fo r COMSAT an d NOAA on are imbursable basis , and, more pertinent to th is

4



booklet, pursuing new ideas in the technology ofcomm unication and weather satell ites, for we can besure that we are just b eginning to reap the p racticalbenefits from the space prog ram.

The technological founda tion of app lications

satellites has three main parts:1. The spacecraft itself, in particular the data

hand ling and attitude c ontrol subsystems.Satellites tend to maintain the sameorientation with respect to the fixed stars asthey circle the Earth; therefore , satell ites mustbe designed deliberately to point c ontinuouslytoward the Earth and m ust be deliberatelyturne d on their axes once each o rbit.

2 . Sensors. The usefu I ness of sate 11 ites i n

forecasting the weather and in assessing theplanet's resources depends upon being ableto distinguish the many electromagnetic

subtleties of the radiation reflected andemitted from the Earth's surface andatmosphere. (Fig. 1)

3. Ground operations. One of the most co mplextasks is the deployment of ground stations toreceive satellite transmissions and relay themto central processing facil it ies, where they areconverted into forma ts su itable to the ultimateconsumer. O rdinary telephone lines are notadequate; new worldwide networks of highcapacity circuits must be built.

Fig. 1 Earth satell i te s carry a wide var iety of infra red ,microwave, and v is ib le l ight sensors for meteoro log ica l andEar th resource s tudies. The Nim bus sensor r ing is shownhere.

NASA's efforts are directed p rimarily tow ard thedevelopment of new spacecraft and sensors, whilethe major operating agencies (NOAA and theCOMSAT Corporation) are concerned more withground ope rations and the p ractical applications ofthe data a cquired by the s atell ites. Of course, NASA

works closely with these agencies to insure that thesate llites and sensors it develops meet the o bjectivesof the groups using the data.

For conven ience, NASA divides its app licationssatell ite programs into two groups: (1) the Communications Programs, and (2) the Earth ObservationPrograms. Na turally, there is considerable transferof technology fro m one program area to the other.The Communications Programs include NASA's workon advanced com mun ications satell ites, geodeticsatellites, and the Applications Technology Satellite(ATS). The ATS also provides valuable technology for

the Earth Observation Programs, which include thedevelopment of advanced meteorological satellitesand the Earth Resources Technology Sa tellite (ERTS)Program.



Each of th e program areas wil l be covered in moredetail in th e subsequent pages. Table 1 ists th especif ic satellites under development in each areaan d th e launch sch edules.

A T E S T I N G L A B O R A T O R Y F O R N E W CONCEPTS( A T S )

Aircraft manufacturers have long used flying "testbeds " to tes t ou t ne w ideas fo r improving th e species .Th e Applications Technology Satellites (ATSs) werebuilt in accordance with th is ph i losophy . A majordifference, of course, is t ha t an ATS must be operatedby remote control from th e Earth an d no opportuni tyexists fo r actual phys ica l examination of th e equip-ment under tes t once it is in orbit.

Th e ATS is a pro ject of NASA's Goddard SpaceFlight Center. Th e first five s pacecraf t in th e AT Sseries have been launched. Th e intention w as to placeall five in synchronous or geostationary orb i ts , inwhich the satel l i tes ' per iods of rotation abou t th eEarth are th e same as th e Earth 's per iod o f rotationabout its spin axis. Geostat ionary satellites orb i t overth e Equator at alti tudes of about 2 2 , 3 0 0 miles and,to an observer on th e Earth below, appear to remainin th e same spot in th e sky . The first five ATSsattempted to solve s uch technological problems asspin stabilization at geostationary alt i tudes an d th eaccurate pointing of antenna beams an d sensorpatterns at th e Earth . Several communicat ionexperiments an d tests o f cameras an d other sensors

were successfu l ly concluded during t hese f l ights.

Th e designations an d launch dates o f t hese space-craft are given below:

Prelaunch PostlaunchDesignation Designation Launch Date

AT S A AT S 1 Dec. 7 , 1 9 6 6

Remarks

First photo show ingnearly entire Earthdisc ; o v e r 2 5 0 0pho tos returned.

AT S B AT S 2 Apr. 6, 1967 Did no t attaingeostat ionary orb i tdue to launch-vehic le fai lure.

AT S C AT S 3 Nov . 5 , 1 9 6 7 Per fo rmed nineexperiments .

AT S D AT S 4 Aug. 1 0 , 1 9 6 8

ATS E AT S 5 Aug. 1 2 , 1 96 9

Did no t attaingeostationary orb i tdu e to launch-veh ic le fa ilure .

Spacecraft nutationdamp er fa i led .Part ia l s u c c e s s .

AT S Fan d G epresent a ne w generation ofspacecraft . Th e basic spacecraf t design, wh ich isdominated b y a30-foot umbrella-like antenna, will beunique among th e hundreds o f manmade craft no win orb i t around th e Earth . (Fig. 2 ) Th e unusua lgeometry is dictated by th e prime object ives of th eAT S F/G miss ion:

* Demonstrate th e feasibility of deploy ing acollapsible paraboloidal antenna 30 feet indiameter an d which h as good radio-frequency

T A B L E 1 . N A S A L a u n c h S c h e d u l e F o r App l i c a t i on s Sate l l i tes *

Satellite 7 0 7 1 7 2 7 3 7 4 75

ATS F G

CAS A Communica t ions Programs

Inte lsat IV-1IV-2

G e o s C

ITOS

N i m b u s

SM S

AkNOAA-I)

B D,C

E

A

F

B

G

FEarth Observa t ionPrograms

ERTS A B

*The letters refer to specif ic satell i te veh i c les . W h e n satell i tes ar e launched successfu l l y , numbers ar e ass igned.

6



Fig. 2 Conceptual draw ing of the ATS spacecraf t .

per fo rman ce up t o 60 00 M Hz . * (The ma jo r

techn ica l d i f f icu l ty here l ies in the fac t that the

antenna mu st be fo lde d up to f i t wi th in th e

launch vehic le fa i r ing. )

• De mon st rate prec is ion po in t ing of the space

craf t and i ts f ixed antenna to wi th in 0 .1° a nd

the capab i l i ty o f s lewing ( t u rn ing ) t he an tenna

17 .5° in 30 m inute s . The space craf t has to do

this i f i t is to provide serv ice to di f ferent areas

of the Ear th be low.

The other charac ter is t ics o f the ATS F/G spacecraf tare descr ibed in Table 2 .

Every operat iona l sa te l l i te is on ly a par t o f a largermach ine wh ich inc ludes g round equ ipm ent connec ted

by rad io l inks to the sa te l l i te and the people who usethe in fo rma t ion t rans m i t t ed by t he sa te l l it e . TheATS F and G spacec raf t wi l l be suppo r ted by NA SA's

Space Track ing and Da ta Acqu is i t i on Ne twork(STADAN) and f ou r spec ia l ATS g round s ta t ions wh ich

wi l l take par t in severa l o f the communicat ionexpe r imen ts . Two of the ATS s tat ions wi l l be at f ixed

locat ions—Rosman, N. C. , and Bars tow, Cal i f . , both

o f wh ich a re pe rmane n t NASA t rac k in g s ta t i on s i t es .The two other gro und s ta t ion s wi l l be the Mo bi leTerm ina l and t he Transpor tab le Ground S ta t ion .These wi l l be re located as the exper im ents de ma nd .

The f i rs t satel l i te (ATS F) wi l l f i rs t be placed in a

geos tat ionary o rb i t over the equ ator whe re i t can see

and be seen f ro m a lmo st one th i rd o f the Ear th 's

area. The spacecraf t ca n, however , be moved f ro m

*A M egaHer tz (M Hz) is one mi l l ion cyc les per second . It is auni t o f f requency.

one spot to another by i ts rocket motor as theexper iments requi re . These pos i t ions must a lways be

over the equator. For example, Fig. 3 shows an ATSlocated jus t west o f the South Amer ican coast , 22 ,300

mi les over the Equator . The antenna beam pat tern s inthe C Band and U l t rah igh Frequency (UHF) Band

" i l l um ina te " t he sou theas te rn U.S . w i t h rad io energyas shown by the contou rs?Th e a im ing po in t is

NASA's Rosman , N. C , t rack ing s ta t i on .

One objec t ive of the ATS F and G expe r imen ts is

t he improvement o f commun ica t ions be tweenterres t r ia l terminals v ia sate l l i te re lay . In 1944, the

noted sc ience f ic t ion wr i ter , Ar thur C. Clarke,propos ed sa te l l i te rad io re lays ; so the idea itse l f isabou t 30 years o ld . The new ATS sate l l i tes wi l l ca r ry

Clarke 's idea severa l s teps fur ther wi th exper imentsin educat ional TV broadcast ing, sate l l i te- to-sate l l i te

re lay , and a i r - t ra f f ic cont ro l . The p lannedexper iments are descr ibed on pages 9 and 10. Not

a l l ATS exper imen ts dea l w i t h commu n ica t ions . To

i l lus t ra te , a l l ATS sate l l i tes carry some sc ient i f icins t ru me nta t ion because no sc ien t i f ic sate l l i tespresent ly operate in geostat ionary orb i ts . The ATSs,the re fo re , p rov ide a un ique oppo r tun i t y t o pos i t i on

sc ien t i f ic sensors at spec i f ic spots over the Ear th 'sequa to r a t f ixed a l t i t udes .

*C-Band and UHF refer to por t ions of the e lect romagnet icf requency spec t rum ; spec if i ca l l y, 3900 -6200 MHz and300-3000 MHz.

Fig. 3 ATS F, located over the equato r jus t west of theSouth Amer ican coast , can concent rate i ts radio beams inthe regions ind icated.



T A B L E 2. D e s i g n F e a t u r e s a n d Vita l S t a t i s t i c s , A T S F a n d G*

S p a c e c r a f t F u n c t i o n s

Communica t ions

P o w e r supp ly

Att i tude con t ro l

Propu l s ion

T h e rm a l con t ro l

Guidance and cont ro l

Structure

Launch veh i c le

Track ing an d dataacquisi t ion ne twork

Design Features

A versat i le transpondert capable o f receiv ing an d replying to ter restr ia l t ransmissions atvar ious f requencies. Pulse-code modulated ( P C M ) te lemetry sends da ta on spacec ra f t s tatusto Ear th. 30 - foo t parabolo idal d ish.

Th e AT S uses deployable , flat solar-cel l panels. Th e average power level wil l be a b o u t 5 0 0wat ts , initially. Nickel -cadmium bat ter ies .

Inert ia (or mom entum) w h e e l s and th e propuls ion unit desc r i bed be low .

One concept employs acontrol lable hydrazine rocke t engine. An ammonia resisto jet (a nelectr ically heated rocke t ) h as been proposed in th e o t h e r concept .

P ass ive coatings an d insulat ions. Heat pipes used in places to he lp distribute heat .Thermal louvers (bl inds) used in crit ical sec t ions .

Sun and Earth senso rs , inertial reference fo r attitude determinat ion. 5 1 2 pulse commands ;32 digital commands . Experimental rad io in ter ferometer wi l l be tested as an att itude sensor .

Deployab le 30 - foo t antenna an d solar panels . Earth-v iewing an d Aft -v iewing EquipmentModules . Tubu la r struts su p p o r t al l components in configuration shown in Fig. 2.W eigh t : a b o u t 2 0 5 0 pounds .

Titan 3.

Space Track ing and Data Acquisi t ion Network (STADAN) and four spec ial AT S groundstat ions.

*As th e des ign o f t he spacec ra f t con t inues , some o f the deta i ls presented wi l l change.

tA radio t ranspo nder au tom at ica l ly responds to t ransmiss ions from stat ions knowing th e prope r code o r f requency .

C O M M U N I C A T I O N S A T E L L I T E S

If o ne drew all of the Ear th ' s electroniccommunication links on a globe ( in th e same w ayairline rou tes are d r a wn ) , t h e following featuresw o u ld emerge :

1. Th e technically advanced nat ions are virtually

c o v e r e d wi th te lephone l ines , unde rg roundca b l e s , m i c r o w a v e links, and va r io u s o t h e relectronic nerve f ibers .

2 . T h e l ess -deve loped nat ions are compara t i ve l ybare of t h e se commun ica t ion l i nes , w i th thed e n s e s t coverage noted around a fe w cities.

3. The planet's wide oceans and v a s t expanses ofAfrica, Asia , Austra l ia , and South Americab o a s t fe w if any commun ica t ion terminals.

4. Th e continents are connec ted primarily byundersea cab les and-in recent years-bysatellite radio l inks .

Th e first commerc ia l commun ica t ion satellites, th egeostat ionary In te lsats , h a v e b e e n j o c k e y e d intopositions be tween th e continents w h e r e t h e y relayvo ice conve rsa t ions , TV p r o g r a m s , and data from oneb u s y commun ica t ion terminal to a n o th e r , m u c h asundersea cab les do. Point-to-point relay of signals ,h o w e v e r , do e s no t bring a ll t he be nef it s of goodcommun ica t ions to eve ryone . For e x a m p le , the ATSF /G educa t iona l television relay e x p e r i m e n t will

d e m o n s t ra t e t h e feasibility of broadcas t ing educa-tional p rograms to wide a reas in th e l ess -deve lopedcountries w h e r e ground -based transmitters are rare.

8



PRACTICAL E X PE R I M E N T S O N A T S F /G

T h e Laser E x p e r i m e n tTh e l ight emitted b y lasers can carry much more

information than radio waves. Because th e world 'sdemarid fo r more communicat ion may outstr ip th ecapacity o f radio sys tems , NASA is laying th egroundwork fo r laser communicat ion links between

satellites an d Earth stations an d from satellite tosatellite. (Laser exper iment on ATS Gonly.)

VISIBLE LASERW A V E S

X - R A Y S U L TRA V I OL E T K M I N F R A R E D

I0.0005 mm

M I L L I M E T E RW A V E S

r, A M I C R O W A V E S ,r /////z /zz'

I I1 10

mm mm

T he Mi l l imeter W a v e E x p e r i m e n tIn addition to e xplor ing

optical wavelengths withth e laser descr ibed above, AT S F /G wil l help expandth e useful radio spectrum into th e mill imeter regiono f th e spectrum (1 0 mm is equivalent to 3 0 , 0 0 0MHz) . Th e major objective is th e precise definitionof communicat ion channels at these high frequencies.

T he R a d io Dispers ion E x p e r i m e n tW h e n radio signals pass th rough th e Earth 's

atmosphere an d ionosphere, frequencies are changedslightly an d so are th e time relat ionsh ips betweensignals. Called f requency an d t ime dispers ion,respect ively , these phenomena cause t rouble in th e

transmission of digital data-as from one computerto another. This exper iment is aimed at understand-ing dispe rsion better an d finding ways to c i rcumventit .

n T I M E

LL1JL~TIME

TIME DISPERSI6N OF SIGNALS

T h e R a d io Frequency In ter ference E x p e r i m e n tAt th e frequencies used fo r th e microwave relay

of conversations an d business data ( 6 0 0 0 M H z ) ,there is significant interference from th e radio noisecreated by l ightning an d other atmospher icphenomena. A T S F/G wil l carry aspecial receiver torecord th is noise and help us understand an dovercome it.

R a d io B e a c o n E xp e r ime n tBy directing radio signals at severa l frequencies

toward th e Earth , this AT S exper iment wil l enablescientists to measure th e effects o f ionized particleson propagation paths beyond th e atmosphere.

T h e Very High Res ol ut i on Rad i om et erE x p e r i m e n t ( V H RRE)

In a later section on meteorology there is adiscussion of the impor tance o f c loud-cover pictures ,taken day and night, fo r better weather forecasting.Th e VHRRE consists o f a te lescope with detectorssensitive to both visible an d infrared radiation.Because clouds emit less infrared radiation than th eground, th e infrared detector can help make pictureso f t hem even at night. Th e fl ight qualification o f th isins trument is important to th e development of theSynchronous Meteorological Satellite (SMS). (Seelater.)

47TS

C

W A R M t'ADI'U

1e..5._

T he I o n Engine E xp e r ime n tSmall t h rus ts can be generated wi thou t th e

expenditure o f much propellant b y electricallyaccelerating cesium ions to high velocit ies. If th eexper imental ion engine on AT S is successfu l , futuresynchronous satellites may use ion engines to helpthem maintain t he i r stations over specif ic spots onth e Equator.

GRID

IO N +

SURFACE +

C E S I U MIONS

+

9

i

I cAln



Indian Educational Television Test

ATS F and G wi l l b roadcas t educa t iona l TVprograms to v i l lages and rura l areas in a jo in t

expe r imen t wi th Ind ia . See tex t and Fig . 4 .

Integrated Scientific ExperimentsMost sc ient i f ic sate l l i tes orb i t wel l be low the

22 ,300 m i le geos ta t ionary o rb i t s . Consequen t l y ,

ther e is com para t ive ly l i t t le data on the charg ed-par t ic le env i ronment a t ATS a l t i tudes . Because

com mun ica t ion and f u tu re m eteoro log ica l sa te l l it eswi l l operate in th is reg ion , it is impe rat ive tounders tand t h i s en v i ronme nt be t t e r . Tha t i s t he

purpose o f t h i s exper imen t .

Other ATS Experiments

In another ATS exper iment , the sate l l i te wi l l be

used as a com mun ica t ion re lay du r ing Apo l lo Moon

f l ights . An a i r t ra f f ic con t ro l exp er ime nt is a lso

planned. The f ina l exper iment wi l l invo lve an at tempt

to cont ro l the or ientat ion of ATS F/G us ing

measurements made f rom the Ea r th .

(F ig . 4) Point - to-po in t re lay and broadcast ing f romsate l l i tes ac tua l ly represent on ly ear ly s teps in theevo lu t ion of i ns tan t wor ldwide comm un ica t ion f o r

everyone. Ideal ly , i t wo uld be poss ib le to con tac t anydes i red comb ina t ion o f peop le and /o r mach ines f romany spo t on Ear th w i t h a m in imu m o f equ ipm ent andat low cost . Such serv ice is avai lable today only within

the bo undar ies o f t he t echno log ica l l y advanced

coun t r ies . Comm un ica t ion sa te l l it es can he lp expandth is k ind of serv ice to o ther cou nt r ies an d to those

desolate reg ions where wi res and large communicat ion terminals do not ex is t .

I n fo rmat ion ne two rk ing i s a concep t wheresate l l i tes can a lso he lp . I t m ight be des i rab le , by wayof i l lus t ra t ion, to l ink together a l l medica l fac i l i t ies onthe g lobe. (Fig . 5) A l l recorded knowledge could, in

pr in c ip le , be pooled and m ade avai lab le a t theterminals o f such a network . Wi th severa l geos tat ionary sate l l i tes p laced where they can be seen f rom a l l

par ts o f the p lanet , such a concept becomes poss ib le .

Ano ther concep t i s t he "mu l t i - acc es s " com mun ica t i on sa te l l i t e where in many sma l l t e rm ina ls— yourhom e, for examp le—can ca l l upon the serv ices of any

com mu n ica t ion sa te l l i te w i t h in view s imu l t aneous ly .I nd iv idua ls o r unman ned ins t rum ent s ta t ions inremote areas wi th a modest rad io t ransceiver couldbecome part of a global network at the f l ick of a

swi tch. Sensor f ie lds , such as wide ly d ispe rsed

Fig. 4 The Uni ted States- India educat iona l te lev is ion expe r iment wi lf requency s ignals can be focused onto speci f ic c i t ies.

employ ATS F for broad cast ing. High

ATS-FANTENNA COVERAGEFROM 20 ° E. LONG .

10



HOSPITAL

Fig. 5 Operat ional sche ma tic of a possible med ical info rm atio n network .

NATIONAL LIBRARYOF MEDICINE

weather mo nitors, could be integrated bygeostationary satellites which have the sensors inview at all t imes. It is this kind of ap plication th athas led to the joint Franco-American CooperativeApplication S atell ite (CAS) program .

THE BALLOON WATCHER (CAS)

In 1971, the Government of France, throug h itsCentre National d'Etudes Spatiales (CNES),willrelease 500 instrum ented balloons between thesouthern latitudes 25° and 55°. Floating between39 ,00 0 and 45,0 00 feet, the balloons will measuretempera ture and pressures along the layer of constantdensity air in which they float. When interrogated bythe C ooperative Applications Satell ite (CAS), theballoons will radio back their scientif ic m easurements. In addition, Doppler trac king eq uipmen t on

the spacecraft wil l p inpoint the range and radialvelocity of each interrogated balloon to determ inelarge-scale m ovements of the atmosphe re. Orb iting atabout 56 0 miles at an inclination of 50 °, the CAS wil lbe able to interrogate each balloon twice each day.(Fig. 6) Collectively, the satellite and balloon sensorfield constitute France's Eole Project. Eole isdoubtless the forerunner of many other large-area,sensor-field experiments now made possible bycommunication satell ites.

The satell ite itself and the balloons are being builtby France. NASA will pro vide a Scout launch vehicleand its launch fac il ities a t Wallops Island, Virginia .NASA may also support the m ission with trac king anddata acqu isition services, althoug h the CAS wil lincorporate a tape recorder, ena bling it to recorddata from the interrogated b alloons for retransm ission to French data a cquisition stations when thesatell ite swings over them in its orb it. Thearrangement between the United States and France issimilar to tha t made when the first French satell ite,the FR-1, was launched from W allops Island in 196 5.

The CAS will be an octagona l cylinder 28 inches indiameter, weigh ing about 206 pound s. As il lustrate din F ig. 6, a skirt o f solar cell panels opens peta l-likearound the upper rim of the spacecraft. The long rodextending upw ards along the spacecraft axis is agravity-gradient stabil ization boom that helps keep

the top of the sa tell ite pointed at the Earth. A spiralantenna painted on the conical projection on the

11



Fig. 6 Art is t 's conc ept of CAS ope rat ion, showing bal loon-b orne sensor f ie ld

and relay of stored data to groun d stat ion s.

spacecraft top sends directional signals thatinterrogate the balloons about 550 miles below. Thesame antenna receives the ir replies.

The first CAS launch is scheduled for late 1971. Inaddition to launch services, the United States willhelp interpret the data telemetered from the balloons.The National Center for A tmosph eric Research andthe U niversity of California at Los Angeles w illparticipate in this analysis.

THE INTELSAT FAMILY

The Intelsat communication satellites are nowstationed in geostationary orbits above the Atlantic,Pacific, and Indian Oceans, providing thousands ofnew intercontinental radio links. (Fig. 7) Together,the Intelsats form th e Global Satellite System of theInternational Telecommunications SatelliteConsortium, which consists of more than 70 member

countries. Represented by the CommunicationsSatellite Corporation, the United States builds someof the Intelsats and operates some of the groundstations. NASA's responsibilities include launchservices and consu lting on a reimbursab le basis.

Based on technical developments made duringNASA's Syncom Program in the early 1960's, theIntelsats are all geostationary spacecraft ca rryingsma ll rocket engines that move them to and keepthem at selected spots over the Equator. There are

now four generations of Intelsats, and they allbear fam ily trait s. Intelsat I, also called Early Bird,was launched in 196 5 and was the founder of thefamily. Additional "birds" flew in 1966 and 1967with fou r spacecraft in the lnte lsat-ll gene ration. Asindicated in Table 3, the trend has been towa rd biggerand better satellites with each new gene ration.

All of the Intelsats are cylind rical in shape, withthe curved sides covered with solar cells. Weights,dimen sions, and circuit ca pacities have risen

12



marke dly in less than a decade. (Table 3 ) TheIntelsat-IV generation consists of satellites 17.6 feethigh (Fig. 8) and 93.5 inches in diame ter. TheIntelsat-IV's are so large tha t NASA had to s witch tothe more powerful Atlas-Centaur launch vehicle. Inkeeping with the trend toward more versatile worldwide comm unica tion, the new Intelsats providemu ltiple access capabilit ies. Compared to the 19 65

Early Bird, which was not much biggerthan a wastebasket, the Intelsat-IVs represent an importantadvance in terre strial c omm unications. This advancewas pioneered by NASA's Syncoms and thecomm unication expe riments aboard the ATSspacecraft.

THE BRICK MOON REVISITED

Rather than the brick of Hale's fictional satell ite,the first navigational s atell ite was fabricated mainlyfrom lightweight metals. Transit 1A was launched bythe U.S. Navy in the fall of 19 59 to h elp guide its

submarines. More Transits followed bu t there havebeen no satellites sp ecifically des igned to helpcomm ercial ships and aircraft locate themselves inareas where conventional navigational aids do notexist, especially over the oceans. With the d ensity ofhigh-speed, transoceanic air traffic rising rapidly,better schemes for locating and com mu nicating w ithaircraft are urgently needed. Fig. 8 Intelsat-IV: 17.6 feet high, 93.5 inches in diameter.

(Communicat ions Sate l l i te Corporat ion)

Fig. 7 The g loba l system of com mun icat ion sate l l ites and ground sta t ions.

13



TABLE 3. The Intelsat Family

Generation

Intelsat 1

Intelsat I I

Intelsat II I

Intelsat IV

Successful Launches

Early Bird (1965)

F-2 (1969), F-3 (1967), F-4 (1967)

F-2 (1968), F-3 (1969), F-4 (1969)

F-6 (1970), F-7 (1970)

COMSAT has contracted for eight INTELSAT IVsatel l i tes (F-l through F-8). F-2 was launchedJan . 25 , 1971 .

Circuits «

2 4 0

2 4 0

1,200

12,000

Weight at Launch

150 lbs

3 5 7

64 7

3 0 8 0

Launch Vehicle

Delta

Delta

Delta

Atlas-Centaur

"Va rious opera t ing modes are possible in whic h circu i ts can be com bined to provide for TV channe lsand other types of wide-band channels.

The classical con cept of a navigation satellite

depends upon accurately knowing the satell ite'sposition and then find ing one's position relative to it.In other w ords, the s atellite becomes a known landmark; the only one visible on the broad oceans. Thestars, of course, play the same role in stellarnavigation, but they are not always visible and stellarfixes are too slow and diff icult for airc raft f lying nearthe speed of sound. Navigation satellites have theadvantage that the signals can be received automatically and analyzed by com puters, giving p ilots the irpositions rapidly and con tinuously.

Although NASA is not bu ilding a navigation satelliteat the mom ent, it is condu cting pertinent experimentswith its ATS and Nimbus spacecraft. To il lustrate , theATS 3 was used in the Omega P osition LocationExperiment, which allowed coo perating ships andaircra ft to fix their po sitions w ithin 3 and 5 miles,respectively. In another experime nt, a jet aircraftlocated its position to within 4 miles by making radioranging measurements on ATS 1 and 3 simultaneously. (Fig. 9) The positions of the ATSs are, ofcourse, well known an d, being in geostationary o rbits,they are visible from much of the w orld's su rface.Experiments of these kinds are continu ing.

A

14

Fig. 9 Sche matic show ing ATS 1 and ATS 3 in a dual

ranging experiment with a jet aircraft . The jet was located towi th in four mi les.



Th e Director General of the European SpaceResearch Organization (ESRO) h as requested tha tNASA an d E S R O jointly explore th e possibi l i ty ofcooperative air traffic contro l experiments onsatell ites. Technical meetings have already begun.Air traffic control differs from navigation in t ha t itinvolves the centralized control of aircraft positionsrelative to one another rather than the determination

of thei r absolute geographical positions. A ir trafficcontrol is , therefore , very much a communicat ionproblem, especially over th e oceans wh ere conven-t ional communication techniques falter. Th epotential value of communication satellites in airtraffic contro l w as f irst demonstrated in November1964 , wh e n a P a n Ame rican W orld Airways planeused Syncom 3, then in ageostationary orb i t overthe Pacif ic , fo r air-ground communication across th eocean. Th e realization of practical , satell ite-aided,air traffic contro l has been hampered b y technicalproblems as well as th e $ 2 0 0 million price ta g on th e

satellite system. NASA an dE S R O

are conduct ingfur ther exper iments with th e ATSs an d other satellitesto determine th e best comm unication technique fo r apermanent international air traffic contro l system.

LOCATING TH E C O N TI N EN TS

Despite th e recent conclusion tha t th e Earth'scontinents do indeed drift a ew centimeters eachyear , one would expect t he i r positions to b e wel lknown after all t hese centuries o f mapmaking.However , wh e n geodetic satellites arrived on th escene, the continents were discovered to be located

accurately in terms of latitude an d longitude b ut no tso wel l on a relative basis; tha t is , th e distancesbetween th e continents were no t known to with inseveral miles. Some oceanic specks of land werefound to be dozens of miles from where maps saidthey should have been. To fix accurately the relativepositions of land masses, a landmark visible simul-taneously from ocean-separated islands an d conti-nents is needed. I n this sense, geodetic satellites ar ereally navigation satellites fo r th e "floating"continents. I n addition, geodetic satellites also helpdetermine the true shape of th e E a r t h - a planet w ithmany idiosyncrasies in shape.

Department o f Defense, an d th e Department ofCommerce. Three satellites have already beenlaunched under th e so-called Geos program:

P r e la u n c h Pos t launchDesignation Designations

G e o s A

Pageos

G e o s B

G e o s 1o r Explorer 29

Pageos

L a u n c h D a t e

N o v . 6, 1 96 5

Jun . 2 3, 1 9 6 6

G e o s 2 o r Exp lo re r 36 . Jan. 11 , 1 9 6 8

Another satel l i te, Geos C , may be scheduled fo rlaunch in 1 9 7 3 . NASA bui lds the spacecraf t , providesth e launch an d t racking serv ices , an d supplies someof the exper iments. Th e agencies cooperate in th eanalysis o f th e data.

Th e principal object ives o f the Geos-C satellite areto :

1 . Establish asingle, common, wor ldwide datum( i .e., geodetic reference system) an d improve

global maps to an accuracy of about 1 0 meters.2 . Improve th e positional accuracy of geode ticcontrol stations an d spacecraft trackingstations. -

3. Define better the s tructure of th e Earth'sgravitational field.

4. Correlate an d compare the results obtainedfrom all spacecraft geodetic instrumentation.

Th e Geos satellites are essentially orbit inginstrument platforms similar to scientific satell ites.Geos is very sim ilar to th e C A S satellite. Both aregravity-gradient stabil ized by means of a long, axial

boom, with t he i r spiral antennas pointing downwardstoward th e Earth. (Fig. 1 0 ) I n th is orientation,geodetic stations can simultaneously observe an dinterrogate th e satellite. Details on th e Geosequipment an d geodetic instrumentation ar epresented in Table 4 an d on page 16.

Almost all satellites can be used fo r geodesy,provid ing they can be seen with optical or electronicinstruments from widely separated points. Th e f irstsatellite to b e launched solely fo r geodetic purposesw as ANNA lB, in 1 9 6 2 , by th e U.S. Army, Navy ,NASA, an d Air Force. (ANNA is an acronym fo r Army,Navy , NASA, Air Force.) Th e Army's Secor(Sequential Collation of Range) satell ites followed.C urrently , the U.S. National Geodetic SatelliteProgram involves th e joint efforts o f NASA, th e

15



Fig. 10 The Geos spac ecraft .

TABLE 4 . Design Features and VitalStatistics, GEOS C

Spacecraft Functions

Commun ica t i ons

Power supply

At t i tude contro l

Thermal cont ro l

Guidance and contro l

St ructure

Launch vehicle

Tracking and dataacquisi t ion network

Design Features

Sends housekeeping te lemetryon ly; comm and rece iver . Conica l,spira l , and turnst i le antennas

Solar cel ls and battery: averagepower about 40 wat ts

Spin-stabi l ized. Long boom forgravi ty-grad ient stab i l i za t ion

Passive

Solar-aspect sensors andmagnetometers to determine

at t i tudeOctagonal a luminum f rame about49 inches between the sides.Weight : about 465 pounds

Delta

Space Tracking and DataAcquisi t ion Network (STADAN)for rout ine t racking andacquisi t ion o f sta tus te lemetry.

Fig. 11 The Geos B set up for a vibra t ion test.

PRACTICAL EXPERIMENTS ON GEOS

The Tracking AidsGeos must be readily "seen" by terrestrial tracking

stations if it is to achieve the objectives listed onpage 15 . The refore, m ounted on Geos are severalreflectors that mirror laser and radar beams reachingthe sa tell ite fro m Earth. The satell ite is also madehighly visible by optical and radio beacons. Geos willalso carry a radar transpo nder, a trac king a id whichresponds to a pulse of radar energy by e mitting areturn signal m uch stronger than possible by simplereflection.

Satellite-to-Satellite TrackingIn this experimen t, Geos will be used in conjunc tion

with ATS F to determine whether a satell ite w ith aprecisely known orbit (Geos) can help ground-based

16



track ing stations improve the accuracy with whichthey track another sa tell ite (ATS).

The Radar Altimeter ExperimentBy directing radar waves downward from Geos to

the sea's surface, sea level will be measured towithin 10 cm . This is scientif ically im porta nt becausethe sea's surface is not perfectly sph erical. The

Earth's varying gravitational field makes broad h il lsand depressions that Geos will m ap.

RADARWAVES

WEATHER WATCHING VS. WEATHER PREDICTING

In August of 19 69, the greatest storm to h it N orthAmerica in recorded history cut a swath from the GulfCoast to the Caro linas. A hund red years a,go,Hurricane Camille would have swept in from the Gulfunannounced, but in 19 69 weather satell ites helpedgive ample warning . (Fig. 12) It has been estimatedthat the timely w arnings saved 50,0 00 lives. Early

Photographic coverage ofCamil le, one of the deadl iesthurr icanes in recent history,begins with a picture of thestorm's in fancy on 11August 1969. Camil le waschr istened a t rop ica l stormon 14 August and reachedhurr icane st rength thefol lowing day. I t then sweptthrough the southeasternU.S. and back into theAtlant ic where i t is shownin the last photo withhurr icane Debbie .

16 AUG

;3 K * 1 13r ' -^1

'*\,Spl RP 4t

-*y8&i|3ayB

ifo^r

8*r[^hl^«*iW

18 AUG

20 AUG

17 AUG

19 AUG

21 AUG

Fig. 12 Satel l i te photos of Hurrican e Cam il le, August 1969,shown just before she moved inland from the Gulf of Mexico.(ESSA)

17



warn ings o f dangerous s torm s have been an ear lypayoff o f weather sa te l l i tes . Indeed , th is prac t ica laspect of space meteorology has already repaid forthe rockets and spacecra f t many t im es over in te rm sof l ives and property saved.

I t became apparent on ly a few mon ths a f te r W or ldWar I I , when capture d German V-2 rockets carr ie d

cameras to h igh a l t i tudes , tha t c lou d cover p ic tu reswould be of g reat va lue to m eteoro lo g is ts . Many ear lysate l l i tes , such as Vang uard 2 , 195 8, and Exp lorer 7 ,1 9 5 9 , inc luded meteoro log ica l inst ruments in the i rpay loads. Today, thous ands o f p ic ture s o f the Earth 'ssp i ra l ing c loud system s are taken every day. Thesepictures help forecast weather two or three days inadvance and a lso g ive meteoro log is ts th e b ig p ic tureso they can bet te r under stand the fa i r and fo u lweather systems that whee l across the p lane t 'ssur face.

Meteoro log is ts are not sa t is f ied wi th thes e

accompl ishments; they wou ld l ike to fo recast weather

two weeks in advance and compre hend a l l theintr icacies of the great a ir masses. These goalsrequ i re more than the s imple watch ing o f c louds f romorb i t . Rather, accura te models o f weather systemsmust be con st ruc ted. Such ma them at ica l m ode lsrequ i re deta i led knowledge o f the temperature ,pressure , water-vapor content , and the o ther factorsthat descr ibe the a tmosphere and i ts c i rcu la t ion . I t is

imp ortan t to know how these factors vary wi th he ightabove the Earth 's surface as wel l as geographicallocat ion. This requ i rem ent means tha t meteoro log ica lsa te l l i tes mu st be ab le to m ake ver t ica l andho r izon ta l measu remen ts f rom g rea t d is tances .

The forego ing thoughts may be summarized in

terms o f th ree ob ject ives:

1. Obta in g loba l c loud cover p ic tures (a

geog raph ic ob jec t i ve ) .

2 . Observe the ent i re a tmosphere cont inuously

(a tempo ra l o b jec t i ve ) .

3 . Measure a tm osph er ic var iab les quan t i ta t ive ly ,

ver t ica l ly and hor izonta l ly .

Fig. 13 Schematic showing different amounts of infrared radiation em itted by different surfaces.ITOS sa tellite is shown overhead.

18



Th e National Oceanic an d Atmospher ic Admin-istration (NOAA)* is responsible fo r th e day-to-day operation of weather satel l i tes, b ut NASA h asbeen assigned th e task of developing an d procuringne w spacecraft an d meteorological sensors as wel l asproviding launch an d tracking services. NASA no wh as three active weather satellite programs plus th eATS effort, under wh ich ne w cameras an d o the r

sensors are tested in space. There are three specif icsatellite programs:1 . Th e Improved Tiros Operational Satellite (ITOS)

Program, involving th e development ,procurement , testing, an d launch of a ne wgeneration of operational meteorologicalsatellites fo r NOAA on a reimbursable basis.

2. Th e Nimbus Program, in which ne w techniquesan d sensors are developed using t he Nimbusspacecraft as a es t vehic le.

3. Th e Synchronous Meteorological Satellite(SMS) Program, under wh ich a ne wgeostationary weather satellite is beingdesigned to sa tisfy th e requirements of NOAA'sNational Operational Meteorological SatelliteSystem (NOMSS).

L A T E S T IN A L O N G LINE ( I T O S )

As th e decade of th e 1 9 7 0 s began, NASA an dE S S A (now NOAA) were able to look back on tw o longan d highly successful series of meteorologicalsatell ites. Between 1 960 an d 1 9 6 5 , NASA h adorbited te n Tiros satellites w i t h o u t asingle failure.To i l lustrate th e productivity of the se spacecraft,

Tiros 8 operated fo r 3 1 / 2 years , sending back over1 0 0 , 0 0 0 cloud cover photographs. Th e first E S S Asatellite series (also called Tiros OperationalSatellites or TOS) began in 1 966 an d ended with th elaunch of E S S A 9 in 1 9 6 9 . Like th e Tiros satel l i tes,th e E S S A s were primari ly c loud photographers . Fo r

*S u c c e sso r to th e Envi ronmental Science ServicesAdministra t ion (ESSA).

Fig. 1 4 Diagram o f th e ITOS satell i te. Meteoro logicalsensors ar e moun ted on th e bot tom, w h i c h is a lways pointedat th e Ear th.

F L A T - P L A T ERADIOMETER(FPR)

S C A N N I N G

R A D I O M E T E R

( S R )

a better understanding of weather processes an dlonger forecasts , something better w as needed.

Th e Improved Tiros Operational Satellite (ITOS)represents a major step forward in tha t it ca n takec loud-cover pictures at night with a scanning infraredradiometer .* Th e infrared radiation emitted by th eEarth depends upon th e temperature an d character of

th e radiating surface. Rivers an d lakes, fo r exampleare cooler than farmland. (Fig. 1 3) Clouds stand outvividly at night in infrared pictures. ITOS, therefore ,offers 24 -h o u r coverage of the Earth. I n contrast , t he .Tiros/ESSA spacecraft cameras were sensit ive toonly th e sunl i t portions of th e Earth . Th e I T O S craftwill t ransmit t he i r T V an d infrared pictures to usersaround th e wor ld either directly from th e satellites orth rough th e NOAA center at Suitland, Maryland.

Th e I T O S spacecraft are substantial ly differentfrom those in th e Tiros an d E S S A series. Tiros/ESSA

satellites were relatively small, cylindrical, spin-stabil ized vehic les . I n contrast , I T O S is boxl ike , withan active atti tude control system t hat keeps itsinstruments continually pointed at th e Earth . (Fig. 14)I n terms of size, ITOS weighs more than tw ice th enominal Tiros-ESSA craft; 67 8 against 30 0 pounds.Th e extra spacecraft sophist icat ion pays dividends interms of more complete photographic coverage onboth th e day an d night sides of th e Earth. Otherspacecraf t features an d th e ins trument complementare given in Table 5 an d on page 2 1 .

I T O S 1 , which w as called Tiros M before launch,

w as orbited b y aDelta rocket on January 2 3, 1 9 7 0 .Tiros Mwas in actuality an I T O S prototype, b u t itreceived th e family name anyway. I T O S A w aslaunched December 11 , 1 9 7 0 an d designatedNOAA- 1.

Th e nominal I T O S orb i t is "Sun-synchronous"with an altitude 7 9 0 miles an d an inclination of 78° .This type of orb i t w as found to be extremely useful byth e later Ti ros satellites because th e l ighting of th escene below w as consistent fo r all photographs ateach latitude. I n such an orbi t , th e satellite passes

over th e Equator - indeed , each latitude-at th e samet ime each day. Nor thbound , an I T O S should cross th eEquator twelve t imes a day at 3 P.M. , local t ime, wh i leth e southbound passage should occur at 3 A.M. Th eorbi ta l plane also precesses (rotates) approximately1 each day, keeping pace with th e seasons; t ha t is ,th e satellite's orbital plane always intersects th e Sun.

*A rad iometer measures radiation wi th in a specif ic band ofwave leng ths . Th e infrared port ion o f th e spec t rum beginsat th e long wavelength end o f the v i s ib le spec t rum. Th einfrared spectrum emitted b y a surface depends upon th esurface 's tempera tu re an d compos i t ion .

19



Fig. 15 Global cloud coverp icture made up f rom swaths 1taken from an ESSA AdvancedVid icon Camera System.

In add ition, the Earth rotates beneath the s atellitejust enough so that slightly overlapping bands ofpictures can be snapped during each revolution.

(Fig. 15 )

SEEING THE BIG PICTURE (SMS)

The view of the wo rld's weather fro m a few hun dredmiles up is spectacular. In just two hours, an ITOSphotographs a strip of clouds about 1700 miles wideand 25,000 miles long. One sees vividly the greatconvection cells ma rching across the oceans andcontin ents. However, ITOS w ill not be back to

photograph the same area for a whole day. This delaymay be critic al in the case of rapidly developingstorms. Neither can meteorologists watch less

dangerous atm osph eric phenomena develop on acontinuo us basis. Since one of the major goals ofspace meteorology is the continuou s surve illance ofthe whole globe, it appears that a geostationary orsynchronous satellite poised 22,300 miles out overthe equator might help us achieve this end . (Fig. 16)

Goddard Space Flight Center and its industrialcontractors have been studying geostationaryweather satellites since the mid-1960s. Pictures takenfrom 22 ,300 miles by TV cameras aboard some of theATSs reinforced me teoro logists' desire for geostationary weather satellites. NASA approved the fabrication,

test, and launch of the Synchronous MeteorologicalSatellite (SMS) in 1969. The program is still in itsearly stages, and a contra ctor to build the spacecraftwas selected only in mid -19 70. N evertheless, someofthe satellite's major features have been defined inthe G oddard studies, and some of these are firmenough to present below.

First, we should examine the requirem ents leviedon the SMS by the ultim ate user, NOAA. Manifestly,the ca pabilities of the SMS will go far beyond the earlyTiros/ESSA spacecraft.

1. In the visible portion of the spe ctrum , SMScameras s hould be able to resolve details towithin two miles. The ultimate goal (not arequirem ent) is a resolution of 0.5 m ile in thevisible and 4.0 miles in the infrared (neededfor nigh ttime cloud-cover pictures).

2. Sate llite electron ics sh ould be able to time -stretch picture d ata; that is, transm it it more

Fig. 16 ATS cloud cover p icture f rom about 22 ,300 mi les.

20



T A B L E 5 . D e s i g n Features a n d Vital St at is t ics ,I T O S


Communica t ions

P o w e r supp l y

Att i tude contro l

The rmal contro l

Guidance an d contro l

Structure

Launch vehic le

Tracking and dataacquisitionnetwork

Design Features

250 -mi l l iwa t t phase -modu la tedlink for beacon an d te lemetry at136 .77 M H z . Real-t ime v ideo linka t 1 37 . 5 o r 137 .62 M H z ; 5 w

f requency modulated. Playbackv ideo link at 1 6 9 7 . 5 M H z , 2 w.C o m m a n d receiver a t 1 48 M H z .

1 0 , 2 6 0 n- p 2 x 2 - c m solar cells ont h ree deployable panels plusnicke l -cadmium batter ies .Average p o w e r level : 7 0 w.

Three-axis stabi l izat ion usinginertia w h e e l and magnetic coi ls .Nutat ion damper . Points to w i t h in1 ° o f vertical .

P ass ive paints an d insulat ion plust he rma l louvers .

Horizon senso rs , Su n sensors . Re -sponds to tone c o m m a n d s f romth e Earth .

Rectangular box , 40 x 40 x.48.6inches . Th ree so la r panels 65 in -c h e s long. W eigh t : a bo u t 67 8pounds .

Delta

Space Track ing and Data Acquisi-t ion Network (STADAN). NOAAalso emp loys severa l stat ions toreceive pictures and o t h e r data.Pic tures ca n also be picked up byAutomatic Pic ture Transmiss ion(APT) stat ions built b y anyone us -ing NASA plans.

The A u t o m a t i c Picture T r a n sm i ss i on (APT) C a m e r aTh e cloud-cover pictures taken b y th e AP T camera

ca n be received by local governments and individualsall over th e wor ld. Th e pictures are transmittedcontinuously an d can be recorded with s imple,inexpensive equipment. Tw o one-inch vidicons arecarried b y I T O S fo r purposes o f reliability.

Heat I n p u t / O u t p u t M eas ur em ent sAnother radiometer measures th e heat reflected

an d reradiated b y t h e Earth. By compar ingth is withth e total heat received from th e Sun, meteorologistscan determine wh e re energy is being added toatmospher ic circulation patterns.

Ni g h t t i m e Cloud-Cover Pictures

From ITOS, a radiometer with amoving mirrorscans th e Earth below. Sensitive to both visible an dinfrared l ight, th e instrument extends weathersatellite coverage to 2 4 hours a day.

O P E R A T I O N A L I N S T R U M E N T S O N I T O S

T V C a m e r aTh e I T O S T V camera takes 1700-mile-square

pictures of th e Earth with 5 0 % overlap. NOAA usest hese pictures directly in th e preparation of weatherforecasts. Th e camera is a one-inch vidicon with 8 0 0

scan l ines.

Sol ar Proton M o n i t o rITOS also carries s ix sol id-state radiation detectors

to monitor solar protons and electrons near th e Earth.

slowly than it generates it to enable " s l o w "ground stations to pick up th e t ransmiss ionssuccessful ly .

3. Like th e Cooperative Applications Satellite(CAS) d iscussed earl ier, th e SM S m us t becapable o f collecting data from hundreds ofsmall , remotely located terrestr ial stations an dt ransmit t hem to a central location.

4. Th e satellite should also have th e ability torelay wea the r maps an d other meteorologicaldata of general interest. (Obviously , weather

21



DELTA S H R O U D

Fig. 1 7 Conceptua l drawing o f th e SM S s h o w n wi t h in Delta launch vehic le s h ro u d .

satellites are also partly communicat ionsatellites.)

5 . Because solar activity is important to weatherforecasting, the SM S m us t be able to measuresolar protons, solar X-ray f lux, and th e localmagnetic field.

Goddard Space Flight Center based its SM S designstudies upon th e well-proven AT S an d Intelsat-Il ldesigns. Th e SM S wil l weigh ab o u t 10 0 0 pounds. Itwil l probably be acyl inder ab o u t 5 6 inches indiameter and 65 inches long, as dictated b y th eDelta launch veh ic le 's aerodynamic shroud. (Fig. 1 7 )A hydraz ine propulsion system wil l be included to easethe space craft into geos tationary orbi t , keep it there ,and move it to new positions over th e Equator w hennecessary. Th e technology employed here originatedin th e A T S program. Th e hydrazine jets wil l also be

used fo r attitude control. Th e communicat ionsubsys tem h as no t been delineated yet. Power wil lcome from solar cells and batteries. This is averyc rude sketch . Th e details wil l be filled in b y t h e newlyselected spacecraft contractor.

Th e minimum NOAA picture requirements can bemet with th e spin-scan camera system already provenin th e A T S program. Tw o o f these cameras wil l berequired on each SM S to meet reliability object ives.

The more ambi t ious goals (0 .5 and 4.0 miles visiblean d infrared resolutions) wi l l require ane winstrument. Th e Visible-Infrared Spin-ScanRadiometer (VISSR) has been proposed as a possiblesolution. This ins trume nt consis ts o f a classicalCassegrain te lescope an d a scanning mirror that

sweeps th e telescopic image in severa l visible andinfrared wavelength bands or channels. In this way,pictures o f th e Earth ca n be taken in several regionso f th e visible- infrared portion of the spectrum.

SMS-A wil l be launched in late 1 9 7 2 , possib ly early1 973 . Because considerable design an d developmentwork remain, th e above descr ipt ion should beregarded as preliminary in nature.

N I M B U S , A TEST VEHICLE F O R M E T E O R O L O G I C A LINS T RUME NT S

Tw o object ives define the N imbus program:1 . Develop and flight tes t advanced sensors and

technology basic to meteorological research ,the atmospher ic sc iences, and th e orbitalsurvey of Earth resources.

2 . Provide fo r th e global collection an ddistr ibution o f meteorological data from allsources.

Nimbus is a large, sophis t icated spacecraft. It w asconceived in 1 9 5 9 a t Goddard about the same time

22



that NASA's b ig o b se r va to r y - c la ss sp a c e c r a ft w e r ebe ing ske tched ou t . N im b u s w as cons ide red to bea generat ion beyond t he T i ros spacec ra ft . W h e n itbecame apparen t that smal le r , less expens ivespacecra f t w o u l d m e e t NOAA's opera t i ona l requ ire -ments , N im b u s w as given th e task of testing andp rov ing o u t senso rs used for Earth obse rva t ion . Th ete s t - bed idea is essentially th e same as th e ATS

c o n c e p t , e x c e p t that N i m b u s ' fully stabilized, Ear t h -pointing capability m a k e it idea l for deve lop ingmeteoro logical and Earth resource sensors .

Th e N im b u s spacecra f t h as already p roven itself

operat ional ly . Four N im b u s satellites are now inorbit, and a fifth w as lost due to a launch veh ic lefailure, as ind icated b e l o w :

P r e la u n c h P o s t la u n c hD e s i g n a t i o n D e s i g n a t i o n

Nimbus A

N i m b u s C

N i m b u s 1

Nimbus 2

N i m b u s B --

N i m b u s B -2 N i m b u s 3

N i m b u s D N i m b u s 4

L a u n c h Date

Aug. 2 8 , 1 9 6 4

M a y 1 5 , 1 9 6 6

M ay 1 8 , 1 9 6 8 T h o r -A g e n a fai lure

Apr. 14, 1 96 9

Apr . 8 , 1 9 7 0

waIUr-

h

VERTICALT E M P E R A T U R EPROFILE

T E M P E R A T U R E

AM i c r o w a v e View o f t h e E a r t hTw o N i m b u s - E instruments will m ap the Earth in

the mic rowave portion o f th e rad io s pec t rum.M ic r o w a ve s , w h i c h are m u c h longer than infraredwaves , a re also emi t ted by wate r - vapo r mo lecu les ,vegetation, and th e ground itself-in short, just a b o u tevery th ing . Th e t w o N im b u s - E mic rowave instruments

will measure th e following meteo ro log ica l factors:vertical profiles of tempera tu re and w a t e r - va p o ra b u n d a n c e , c l o u d - co v e r w a t e r content, a m o u n t s ofprecipitation, land tempera tu re ( w h e r e c louds blockinfrared w a ve - l e n g t h s ) , th e intensities of s t o r m s ands to rm fronts, th e w a t e r content of th e soil, ice c o ve r ,and even the quantity of vegetat ion b e l o w .

Sensors being tested on N i m b u s are mounted inth e s e n s o r r ing at the bot tom of the spacecra f t ,w h i c h is k e p t pointed at th e Ear t h by th e attitude

con t ro l s u b s y s t e m . (Fig. 1 ) A con ica l truss structure

connec ts th e s e n s o r ring to t he u p p e r h o u s in g

containing th e attitude con t ro l s u b s y s t e m , th ec o m m u n ic a t i o n su b sy s t e m , and o the r spacecra f tequ ipment . Tw o wing- l i ke so la r pane ls , wh ich areautomatically po in ted tow ard th e Sun, p rov ide p o w e rto t he spacec ra ft and th e instruments. N i m b u sdetai ls ar e presen ted in Tab le 6.

P R A C T IC A L E X P E R I M E N T S O N N I M B U S E

A t m o s p h e r i c P r o f il e sRadiometers can measu re h ow th e temperature

and wate r - vapor conten t of th e atmosphe re va r ieswi th altitude b y determining h ow much infraredrad iat ion t h e a tm o sp h e r e emits at var ious w a v e -l engths . W a te r- vapor molecu les , for example , emit

in frared rad iat ion w h e n t h e y rotate. Ver t icaltempera tu re and w a t e r - va p o r profiles are important

factors in w e a t h e r prediction. N i m b u s E will carry tw oinfrared rad iometers for measu r ing vertical profilesand ano the r to he lp m a k e w o r ld w id e humidity m a p s ,

T r a c k i n g a n d Data R e l a y E x p e r i m e n tTh e communication par t o f this e x p e r im e n t will

test th e feasibility of re lay ing data f rom a low-a l t i tudesatellite (Nimbus) v ia a geostat ionary satellite (ATSF/G) to a ground rece iv ing s ta t ion . An attempt will

also b e made to track N i m b u s Ewith high p rec is ionf rom ATS F / G .

M a p p i n g th e C o m p o s i t i o n o f t h e E a r t h ' s S u r f a c eTh e infrared radiation emi t ted b y the Ear th ' s

sur face d e p e n d s upon compos i t i on as we l l astempera tu re . To illustrate, the in f rared spec t ra ofvarious mine ra ls va r y m a r ke d l y , m a k in g a satellite-bo rne infrared sp e c t r o m e t e r a potent ia l mineral-prospecting instrument. Th e Nimbus -E instrumentwill also m a k e t h e r m a l maps o f the so i l and th eocean sur face .

ROTATION OF W A T ER M O L E C U L E SGENER A T ES MICROWAVES

23



D e s i g n Features

Wideband s to red da ta , 1707 .5an d 1 7 0 2 . 5 MHz , P u lse -code -modulated te lemetry at 136.5

M H z . Command receiver at1 49 . 5 2 M H z .

Tw o movab le solar panels plusnicke l -cadmium bat ter ies .Prov ides an average o f 2 60 wat ts .

Inertia w h e e l s plus cold-gasreaction engines in equ ipmenthous ing. Keeps space craft po intedto wi th in 1° o f th e local ver t ica l .

Thermal louvers located aroundth e rim of the senso r ring,supp lemented by t he rma l coatingsan d insulat ion.

Su n sensor , ho r izon sensors ,gy roscopes .

Four major e lements :senso r ring, providing 18 squarefeet for mounting Earth sensors ;e qu i p m e n t housing; so larpaddles , an d t r uss s t ruc tu re .Overal l dimensions: 9 .5 feet highb y 9 . 5 feet wide with so lar panelsextended. Overa l l weight : a bo u t1 6 9 0 pounds .

Thor-Agena

Space Track ing an d Data

Acquisi t ion Network (STADAN)

H U S B A N D I N G E A R T H ' S R E S O U R C E S ( E R T S )

Only a few years ago man could modify th econditions on Earth with little t hough t about th eenv i ronment an d the cascading consequences o f h isacts. W ith th e Earth more crowded an d some ofou r easily garnered non-renewable naturalresources near ly depleted, one hears moreand more th e phrase "spacesh ip Ear t h , " implying th eincreasing interde pend ence of all man's activities-

h is farms, h is industr ies , h is mines, his wasteproducts , and, as h as become obv ious , h is veryexistence.

Spaceship Earth wil l suppor t only a few billionhuman beings unless its resources are managedcareful ly. As fo r all management systems, information

must be ava ilable to make resource managementwork : abundant information, on acont inuous basis,from all parts of th e globe. Satellites by virtue of thei rfavorable positions high above th e Earth are inparticularly advantageous spots to collect some ofth e needed environmental information.

The key to obtaining information on Earthresources from severa l hu ndred miles out in spacelies in the analysis of sunl ight reflected from theEarth an d radiation emitted f rom the Earth by vir tueof its tempe rature. Flying across th e United States byplane, one sees f ields, forests , drainage patterns,geological formations, an d t he works of man, to givea partial list. If th e same plane carried an aerialcamera with a elescopic lens, photographic analysiswould reveal soil t ypes , crop identi ties, major mineraldepos i ts , etc. Taking the same fl ight once more b utwith a u ll complement o f instruments t hat " s e e " inth e infrared, ultraviolet , an d microwave regions of

the spectrum, th e panorama enlarges tremendously.(Figs. 18 and 19) By recording the scenes belowan d s tudy ingthem in l ight outside th e visible range,w e can discern forest an d crop bl ights , soil moisturecontents, p lant species , ice th i ckness , an d th e manyothe r factors summarized on page 2 5 . By collectingan d correlating th is kind of information, w e can,so to speak, take th e Earth's pulse continuously ,assessing on one hand its suitabil i ty as a habitat fo rman an d on the o the r searching fo r ways to improvethe environment.

Th e stakes in th is venture are so high t ha t

attaching a dollar sign to Earth resource informationseems superf luous. However , est imates o f money thatcould be saved annually in th e United States aloneru n over a billion dollars. Knowledge about storms,insect infestations an d more efficient pollutionsurveys is worth money.

Many other uses of Earth observat ion satelliteshave been proposed. Some of the more promising aredescr ibed on page 2 5 .

It is easy to ge t carr ied away and promise to o

much . Although ph otographs taken from aircraft andmanned spacecraf t are most promising, th e who lefield is sti l l in an embryonic state. Furthermore, someEarth resources data wil l be gathered by aircraft andground-based surveys. Th e most effective mix ofsensor carriers h as no t been establ ished yet . On eth ing is certain, though , an d tha t is t hat informationacquisit ion, t ransmiss ion an d processing wil l b e amajor part of the undertaking. To i l lustrate, aninfrared radiometer reading means little to anagriculturist making a crop survey . Data must beconver ted into terms understandable to th e user an d

24

T A B L E 6. D e s i g n Features and Vital Sta t i s t i cs ,N i m b u s E


Communica t ions

P o w e r supp l y

Att i tude control

T h e rm a l con t ro l

Guidance and con t ro l

Structure

Launch veh i c le

Track ing and data

acquisi t ion



PRACTICAL APPLICATIONS O F E R T S I N S T R U M E N T S

Ag r i c u l tu r e a n d Forest ry

Construct ion of better topographicmaps an d farm planning

Estimations of crop t ypes , densit ies,and expected yields

Calculation of th e damage from dis-ease an d insect infestations

Identification of insect infestationand disease patterns an d "earlywarnings"

Census of l ivestockEstimation of soil moisture contentan d irrigation requirements

Census of forest t ree types an d esti-mation of logging yield

Early warnings of fire, disease, an dinsect infestation in forests

O c e a n o g ra p h y

Forecasts of s e a state and ice hazardsfo r sh ipping

Location of high biological activityfrom surface temperature fo r f ishingfleets. Large schools of surface-feed-ing fish may also be pinpointed

Location of drifting o il s l icks

Survey of coastal geography, includ-ing detailed shorel ine topography ,identification of stream erosion pat-terns, an d mapping o f shal low areas

Collection of such scientific data asth e location of areas of biolumines-cence, estimation of plankton density ,an d th e pinpointing of red t ides , fishschools , an d algae concentrations

A P P L I C A B L EI N S T R U M E N T A T I O N

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H ydr o l ogy an d Wa t e r Res o u r ce

P l ann i ng

Inventory of water in regional basinsby measurement of lake levels, r iverflow rates, irrigation patterns, an ddrainage patterns

Control an d early warning o f f loodsby monitoring' rainfall, weather pre-diction, an d drainage basin surveys

Identification of water pollutants an dpolluters from maps of thermal dis-charges an d the spectral "signa-

t u res " of specif ic pollutantsEstimation of water resources th roughsnow an d frozen water surveys an dth e location of seepage an d othergroundwater sources

Geology a n d M i n i n g

Detection o f minerals ( including oil)f rom topography, drainage patterns,magnetic f ields, an d direct identifica-tion of minerals

Prediction of earthquakes fromsl ight

temperature differences, soil mois-ture content , an d topographical dis-tr ibution.

Prediction of volcanic activi ty fromtemperature changes

Prediction of landslides from soilmoisture an d slope of terrain

Location of geothermal power sourcesfrom surface temperature measure-ments

T r a n spor ta t i on , N av i ga t i on , a n dUrban P l ann i ng

Construct ion of detailed maps of ruralan d urban areas to help plan trafficarteries, terminals

Estimation of air, road, an d sea traffic

Surveys of urban areas, indicatinghous ing an d population densit ies,park areas, industrial development ,an d types of sett lement fo r purposesof planning renewal an d ne w building

programs

APPLIC ABLEINSTRUMENTATION

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4. To develop hand ling and processing techniquesfor Earth resources survey data.

Much of the ea rly ERTS work concen trated on thesensors because this was the area w ith the mostunknowns. F lights with m anned air- and sp acecrafthave already shown the probable usefulness ofvarious types of infrare d, ultraviolet, and microwaveinstrum ents. The next step consists of f lying theseinstruments on an unmanned spacecraft.

The ERTS spacecraft (Fig. 20) and the sup por tingterre strial data system are sti l l in the design and

HARVESTED

MATURING21 MAY 1969

Fig. 20 Conc eptual draw ing of an ERTS basedon Nimbus technology.

27



development phase , with th e first fl ight scheduled in1 9 7 2 . Never theless , some spacecraf t featureshave already been specif ied. For example, th e sensorend o f th e craft m us t point at th e Earth cont inuously ;an d three-axis stabil ization will be essential. Solarp o we r wil l be used. The attitude control system wil lincorporate inertia wheels ( f l ywheel , fo r storing

angular momentum) cold-gas je ts , hor izon sensors ,an d gyroscopes. Because o f th e spacecraf t size-abou t 2 1 0 0 p o u n d s - a n active thermal contro lsystem employing louvers w as chosen . There wil l bete lemetry channels at 1 36 an d 2 2 8 7 M H z an dcommand l inks at 1 48 an d 2 1 0 6 MHz. The technologydeveloped in NASA's Nimbus program wil l meet th eE R T S requirements with minimum additionaldevelopment .

Tw o ins truments ( rather sophist icated ones) arescheduled to fly on ERTS A n 1 9 7 2 . Th e first is aspecial TV camera sys tem, consisting of three returnbeam vid icon cameras. These wil l take pictures ofareas 1 0 0 x 1 0 0 nautical miles from th e nominalsatellite altitude of 49 2 nautical miles. Each camerais sensitive to a different part o f th e visible an dnear infrared spectrum. Th e second ins trumentis called a mult ispectral scanner. It wil l scanswaths o f th e Earth's surface 1 0 0 nautical mileswide as it moves along its orbi ta l t rack. Again, th epictures wi l l be taken in different parts of thevisible and near infrared spectrum.

A G L A N C E A T T H E FUTURE

In space technology, we have a ool, wh ic h , as wehave seen, h as already laid the foundations fo r bettercommunicat ions, better weather forecasting, an d th ef irst comprehensive assessments o f the planet'sresources. Th e full implications of th is tool w e do no t

yet know. C ertainly , there w i ll be better spacecraftan d better sensors and ways to wring out more of the i rmeanings. So, at th e very least, w e can foresee near-instant communicat ion among men and machineseverywhere on Earth . Weathermen wil l give uspreviews tw o weeks ahead of t ime. But communicationan d weather are only parts of a bigger picture.Spaceship Earth is a complex craft an d alreadycrowded with human i t y -and there is no escapehatch . P oss ib ly th e ultimate contr ibution of spacetechnology is in our better unders tanding o f th eEarth and h ow it affects an d is affected by its humanpassengers.

Th e E R T S orb i t wil l be Sun synchronous . Itwil l be a polar orb i t with a period o f about 1 0 3minutes an d altitude of 49 2 nautical miles. Orbitprecession wil l be such that o rb i tal swa ths wil lbe repeated every 1 8 days.

Th e E R T S program provides a fitting end to th isbook le t fo r it uses technology developed in NASA'sapplications programs to extend th e value intone w areas. Th e spacecraf t i tself wil l be based onth e Nimbus design, an d th e ERTS sensors ow emuch to th e A T S an d weather satellite programs.From the co mmu nication satellites come th e

technology fo r handl ing th e flood of data f rom th esensors an d t he i r subsequent convers ion into form atsconvenient to th e user .

* U. S. GOVERNMENT PRINTING OFFICE: 1971 O - 444- 660

28



A d d i t i o n a lRe a d ing

For titles of books and teach ing aids related to th esubjects discussed in th is booklet , see NASA's

educational publication EP-48 , AerospaceBibliography.

Produced b y th e Office of Publ i c AffairsNational Aeronaut ics an d Space Administra t ion



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Satellites at Work (Space in the Seventies)

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