the pioneer mission to jupiter

8/8/2019 The Pioneer Mission to Jupiter

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NASA SP-268

THE PIONEERMISSIONTO JUPITER

CI09sjc9c-L (NASA CR OR TMX OR AD NUMEER) (CATEGORY)

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION


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FOREWORDi1i Jupiter is one of the most in~pressivesig11t.s in the night sky.f Ever since telescopes were iuvented, ast ronomers 11ttve st d i e d thisIi plitrlet with fnsciuittion, iwd h v e revealed it s bizarre ttnd mysterioustippei\lxnce itnd 1~11 i t v i 01* . -111 we Ibit\.e leitr~ledabout ,Jupiter IIHSenllit~wetlour curiosity itl)out this unique plttnet tl~itt ~l~;t\-esost1 neitrly like a stttr.s The l'ioneer missions to Jupi ter itre especitdly cllallenging and~.e\vtwding.To reach the orbit of Jup iter, the spacecraft must traveli farther than any mission rnttn has sent into space, nnd must survivet the unkno\vn llitzards of the itsteroid belt. The rewitrd will be de-tailed new knowledge of t i unique plitnet, second only to the Sun

L in the hierarchy of the solitr system. From t'lle explorittion of deepspace as well RS Jupiter we expect more can be discovered aboutthe processes t.hat produced it benign environment for life on thesurface of the Earth.Ke\.er before hits sudl t t broad spectrum of talents and t'ecllniquesbeen mustered for the st,udy of Jupi ter as will pnrticipate in thePioneer F/G Yrogrtm. I'iti-t I of this rno~~ogniplls ik .brief ttccountof the objectives, demands, t t ~ d otential rewards of t,his program.Part I1 is a highly condensed description of the complex scientificexperiments to be undertake.31. Piwt I11 is a-similar description ofthe spacecraft and tbe mi~ni~pementf tlle mission.

Jorm E. NAUGLEA ~ x o c k t eAdm,hht ra torOffice of Space Science a.nd Applications

For sale by the Superintendent of Documents,U.S.Government Printing Ornee, Washington, D.C. 20402Price 30 centsStockXumber 3300-0387Library of C w r e e e Catalog Card No. 74-611468


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NASA SP-268

THE PIONEER MISSIONTO JUPITER

Prepared for theOffice of Space Scienceand ~pplications

II

Scientific and Technical Inform atto : 0.flc.e 1971NATIONAL AERONAUTIC,C AND SPACE ADMINISTRATIONW a ~ k i n g t o n , .C .


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CONTENTS


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2 THE PIONEER MISSION TO JUPITERSo, too, will th e satellites, ionosphe re, an d atmosph ere of th e secondbrigh test plan et visible fro m the 1E:arthqs urfac e. S uch observrr.tionsare expected to reduce uncertainties about the str uctu re of Jupi ter-a planet that has puzzled astronomers increasingly throughout re-corded history.By this extension of studies of interplanetary space, and of boththe largest and many very small bodies that orbit the San, new in-sights may be obtained to the development of the Earth. More alsomay be learned ab out the physical requirements fo r life i n t,he solarsystem, and a trail blazed for further advances in both pure andap plie d sciences.OBJECTIVES

The diameter of the solar system is nearly 100 astronomical units(AU, the mean distance between the Earth and the Sun, is 92.950million miles). T he oute r bound aries of t,his system ar e still po orlydefined, both because they :we so distant and because the interplane-tar y medium obscures obser\.ntions of tlie outermost p lanet s fro m t heEarth. Little is known, therefore, about the interfaces of the solarsystem w ith other components of t he Milky W ay.Astaronomemwould like to know much more about the history andstatus of the universe as well as the history and status of the solarsystem. Better deductions might then h.e possible re gard ing th e uni-versality of physical laws, feasible applications of those laws to newprocesses on the E ar th , an d t he pro bability t ha t life exists elsewhere.Pioneers E and G will assist scientists in their quest for basic in-form ation an d engineers in thei r use of scientific knowledge fo r man-kind's benefit.Meternids and Astenids

Meteorites have sometimes penetrated our planet's atmosphere,producing larg e craters ; and billions of meteoric particles bombardthe E a rt h every day, producing the zodiacal ligh t visible just beforesunrise and a fte r sunset,. I n th e asteroid belt, much more such inter-planetary material orbits the Sun. Earth astronomers have identified1776 asteroids, some of w hich are hund reds of m iles in diam eter, an dhave convincing evidence of the existence of many more similarbodies in that belt,. These are ~vidnlybelieved to be debris from aplanet that disintegrated in the distant past in some unknown way.F igure 2 shows the estimo.ted quantities of small asteroidal andcometary matter between 1 and 4 A U from the Sun. A collision witha larg e asteroid, or penetrations by m any small bits of matter, could


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BASIC RESEARCH

Pinhead SizeDu s t

Based onTe lescop icObservat ionsBetween2 and 4 AU

Based onSpacecraftMeasurements. Between 1 andI .5 AU

3

Green

Pa r t i c l e Mass. GramsFIGURE.-Even submicroscopic particles can imperil spacecraft. These areestimates of the flux and mass of asteroidal and cometary material in spacewhich will be extended and improved by measurements from Pioneers Fand G of particles beyond Mars.prevent a spacecraft from completing a passage through the asteroidbelt to the orbit of Jupiter. Pioneers F and G will be attempts tosurrey meteoric material on both sides and within the asteroid beltand report on the composition, energies, and densities of ma tter there.

Beyond the asteroid belt there are much larger planets than theEarth, Mars, and Venus. The nearest and most colossal of those d is-tant g iants is Jup iter, and it is also one of the most puzzling com-ponents of the solar system (fig.3). Galileo discovered fou r satellites


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BASIC RESEARCH 5

orbiting it, and Ole Romer tliscovered the finite speed of light byobservations of those sut,ellites.Ju pite r is now known to have at least 12 satellites, In this and otherinteresting aspects, it resembles the S u n more nearly than it does theEarth. Although it is more than 1000 times as large us the Earth,it has only slightly more than 300 times the mass of the Earth. Yetthe total mass of Jupiter and its satellites perturbs the orbits ofcomets, asteroids, and other components of the solar system so gre atlythat a noted modern astronomer calls it "the dominating planet."It is so radiant tha t another writer refers to Jup ite r as "a pottedstar,"* nnrl there is ~*e:iso~lo Id ieva t l ~ tt , like the Moon, mayprove to be a "Rosetta ~ t o n e , " ~rom which much may be learnedabout the solar system's origin and development.Jupiter rotates faster than any other planet of the SML ight anddark bands cross its golden disk (fig. I ) , nd a great current sweepsaround its equator faster than other visible features rotate. Anenormous Red Spot, about which the re ar e many conflicting theories,floats in it s deep atmosphere. The planet's appearance from the E ar thconstantly changes (fig. 5), and intensive studies of it from the E ar thhave indicated the presence of hydrogen, helium, water vapor, andammonia and methane gas in th at atmosphere (fig. 6).Recent research also has suggested th at the same chemical reactionswhich are believed to have preceded the appearance of life on theE ar th a re taking place now on Ju piter.Jupiter, furthormore, seems to be radiating more energy than itreceives from the Sun. More rt~dionoise reaches the Earth fromJu pit er than from any other source except the Sun. Bursts of radionoise from this planet sometimes are equivalent in energy to severalhydrogen bombs or billions ol' simultaneous lightning flashes. Threedistinct types of radiofrequency emissions from Jupiter have beenrecognized, and analysts of that noise believe that Jupiter has radia-tion belts (fig. 7) comp,zmble to those discovered near the Earth bypredecessors of Pioneers F and G.

Lit may be," according to Dr. Robert Wildey of the U.S. Geologi-cal Survey's Center of Astrogeology, "that Jupiter has not quitefinished 'falling together' into a rigid planet from the original inter-stellar mate rid from which it was formed so tha.t its power generationis essentially gravitational enerm conversion."'Whipple, Fred L . : Thr, Earth, .!loon and IJlanctrv (Harvard UniversityPress, 1963) .' irsoff, V. A. : Exploring t k Plancte (Sidgwick 6 Jackson, London, 1964).'Rnsool, 8. I . : In Astronautic8 and Arronauticu, Oct. 1968.' PI, Washington Poet. Dec. 1970.


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T HE P IONEER MlSS lON T O JUPIT ER

L t ~ o r l haualwrai C ur ren t or N o r m r u Br r n tn ( Cdrfenl\ North Equalortal Be l l ; I

FIGURE.-The Bri tish Astronomicol Association adopted this nomenclatureto distinguish Jupiter's features. The belts are usually gray, but tintedred and blue at times. The zones usuolly appear yellow or creamy white.

Sept 12, 192Uby Phillips ) Mar. 25,1943 (by Peek) Dcc. 21,1911 (b y Hargreaves)FIGURE.-These draw ings st d w some of many changes th at have been docu-mented in Jupiter 's h c e by earthbound observers. The great variety ofcurrents, drafts, and forms in the clouds conceals the big planet's surfacefrom optical telescopes on the Earth.TECHNICAL FRONTIER

The relative motions of Ju pi te r and the Earth make it possible forthe United States to send a probe out to the dominant planet onlydu ring a brief period of time every 1S months (fig.8).A t other times,


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THE PIONEER MISSION TO JUPITER

E ' 1 c ; r r ~ ~ .-Obserwtinns of Jupiter fro111 the Earth have suggested that itsmagnetic dipole may be tilted, as shown here. Pioneer observations mayhelp to explain how electrons are injected into the magnetosphere an daccelerated to relativistic energies near the planet.

the injection velocities required for such a venture exceed the rnaxi-mum now obtainable. Pioneer F is scheduled to be launch ed betweenFe,bruary 28 and March 16, 1972, and Pioneer G during the nextfavorable period, bet,ween A pr il 3 and 20, 197s.Although these vehicles will attain a speed of 47 000 to 48 000 feetper second, and thereby set a new record for spacecraft, it will takeeach o.le :houtf 2 years to reach Jupiter. They will not reach thensteroid belt unt,il more than 4 months after being launched into theproper trajectory (fig.9 ) . Ea ch one will then be in th at belt fo r morethan 6 months, on a course that will take it to the fa r side of the S unfrom the Ear th .Pioneer F is to be guided t o w ithin about 100 000 m iles of ,Jupiterand pass mound the: planet within the orbits of its satellites. Thespacecraft will be behind Ju pi te r fo r less tha n an hour. I t s trajectorywill the11 ca rry it 011 out of the solar system.Pioneer F's :ipproach nnd passage around .Jupiter will be close tothe planet's equator (fig. 10). P i m e w G may be sent around theptnnet alo ng approximately th e same course o r directed out. of &heecliptic at some moderate angle fo r observation^ a t n highe r latitude.Each rjpncecrnft will be close to ,Jupiter for only about 4 dtbys.


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BASIC RESEARCH 8The findings in those few days, nevertheless, may increase men'schances of successfully grasping futu re opp ortunities to explore theoutermost portions of the solar system. The r e l a h e positions of theE ar th and the planets beyond J up ite r will be such tha t ( 1 ) an outer-planets mission spacecraft launched ixi 1977 could fly past Jupiter in

1979, past Saturn in 1980, and approach Pluto, the outermost andle:w+ known planet, in 1085; and (2 ) a similar reh ic~ eaunclied fromthe Earth in 1979 could pass close by Uranus in 1985 and Neptunein 1988. Equally favorable opportunities fo r the exploration of thosedis tan t planets will not recur fo r scores of years-not un til the yea r2152 for Jupiter, Saturn, and Pluto, and not until 2155 for U ranusand Neptune.

Th ere is reason to believe that most of the large components of thesolar system were created a t about the same time as the E ar th, some5 billion years ago, but how the planets attained such different statesas we find them in now is far from clear. By further advances in

MARCH 1973 AMlL28 2 7 12a '7 ?= 27I I I I I I I20 25 1 6 11 16 211972FEBRUARY MARCH

E'IGUBE 8.-Launching dates determine the weight possible, the energy required,the trip time, and the communications distances involved in missions toJupiter. Pioneers F and 8 will exploit nominal opportunitien.


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18 l l lE PIONEER MISSION 10 JUPltER

planetary astronomy, scientists hope to gain greater knowledge offactors responsible for those differences, and thus achieve betterunderstanding of the development of the Earth as a favorable abodefor life."Life and its environment," the noted Harvard paleontologist,George Gaylord Simpson, assures us, "are interdependent and evolvet~gether."~xploration of the Moon, the interplanetary medium,and nearby planets has already yielded data helpful to life scientistsas well as to the physical scientists. Increasing knowledge also hasmade men more aware of their responsibilities as stewards of otherforms of life on Earth, and more basic information is clearly neededto meet those responsibilities intelligently, efficiently, and benignly.

Tremendous changes in the condition of the Earth unquestionablyoccurred before humau activities became appreciable factors in de-termining its future. The climate is one example. No one knows, how-'Quoted by Lorin Eisley in Thc Unexpected Ilniverue (Harcourt Brace

Jovanovitch, Inc., New York, 1989).

Fram 9.-The sidereal periods of Jupiter and the Earth dtdter, and the lineof sight between the Earth and the spacecraft will be close to the Sun beforethe encounter with Jupiter. Numbers along the trajectory show the Pioneem*approximate progrese in hundreds of days after being launched.


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THE PIONEER MISSION TO JUPITER

Thirteen experiments will be performed during the Pioneer mis-sions to Ju pite r. The y were chosen to exploit oppo rtunities fo r closemeasurements both while the spacecraft are on the way to Jupiterand during the brief encounters with that planet.Most of the experiments are closely related. Some are approachesto the same basic processes as others, but by distinctly differenttechniques. Sev eral are ingen ious combinations of instrumen ts. Cum u-latively, the findings are expected to provide d ata help ful t o special-ists in numerous branches of basic and applied sciences whenanalyzed and related.Wide ranges of electromagnetic phenomena will be examined, andspin-scan imaging will be attem pted fo r the first t ime from an inter-planetary vehicle. All of th e ap pa ratu s to be carried on t he spacecrafthas been designed to minimize its weight, volume, and power require-ments. Most of the instruments and techniques, nevertheless, will bequite similar to types already successfully employed in laboratorieson Earth and on spacecraft sent on shorter missions.Th e data returned from Pioneers FIG, consequently, will be readilyrelatttble to the data that scientists have been gathering for manyyears from their work in electronic laboratories, from optical andradio telescopes, and from other spacecraft. The findings during theJupiter mission will also be augmented by data that will be receivedconc urrently from ot,her probes of in terpla neta ry space in differentpa rts of t he solar system closer to the E arth .Two of the 13 experiments will require no special apparatusaboard the Pioneers, and will be described here first. The other 11will rely on reports from the spacecraft's 61.5-lb scientific payload,and will be described in the sequence in which the instruments thatwill be used are listed in table 1.Th e two meteoroid detectors listed first in t ha t table are relativelyeasy to understand, highly pertinent to further ventures into space,and will be rewarding months before either spacecraft approachesJupiter . T he next s ix experiments al l pertain to s tudies of the so lar


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S CI E NT I F I C E X P E RI M E NT S 13

TABLE.--On b o n d Pioneer Expe~4mentsTotal AverageYolunle, \reigllt, poweririches pounds required,(cent i~ne ters ) (k i lograms) wat t s

wind, radiation from outside the solar system, and concepts of themaze of charged particles in space. The last three devices, as listedin the table, will both further clarify such concepts and reduce un-certainties about Jupiter's role in the solar system.EARTH-BASED EXPERIMENTS

One of the two experiments for w hich Pioneers F an d G will notcarry any special ap pa ratu s will be an analysis of the trac king dat a(fig.11).The techniques will resemble those already used successfullywith data from Mariners on flights to Mars and Venus. The JetPropulsion Laboratory in Pasadena, Calif., developed these methods,which require the use of lar ge computers, and a new advanced contra1data-processing system will be operational in Pasade na fo r initlo1 usedurin g the Ju pi ter mission.T he other Earth-ba sed ex perimen t will be a study of celestialmechanics and an examination of t he effects of the S un and Ju pi te r


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14 THE PIONEER MISSION TO JUPITER

on radio transmissions in the S-band of frequencies (bet,ween 1.55and 5.2 gigacycles). These frequencies will be used increasingly inthe next few years. Findings in both experiments will be helpful inattacking unsolved scientific problems and further realization of thepotentialities of spacecraft as research vehicles.

3. r 3 FIELDOF VIEW

-25 HRS, 23.2 RJ

. . * . , 2-+a b .< + . -..*, .. "*.*!.~-lU.Rildta$ @

-154 MRS. 100 RJ

~ I G U S E11.-Investigators of celestial mechanics and P-brnd occultation willderive information from tracking data. This La a typical encounter withJupiter as envisioned.


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SCIENTIFIC EXPERIMENTS

Equinox)

FIGURE2-,Jupiter's slitellitestute an inner system : sevensince 1900.

Celestial Mechanics

differ in their masses and orbits. Five consti-others have been discovered in an outer system

Two Jet Propulsion Laboratory researchers, Dr. J. D. Andersonand C . W. Null, will direct an effort to determine the gravitationalforces to which the Pioneers are subjected in the course of theirflights. T hi s will be done by a com puter analysis of regular two-wayDoppler tracking data, acquired throughout the mission, augmentedby optical and radar position data.Such an analysis may enable the investigators to determine themass of Ju pi te r more accurat,ely t, h m has been possible from ob-servatories on the Earth. Uncertainties regarding t,he masses andorbits of some of Jupiter's satellites may also be reduced. The geo-centric coordinates of t he mass of .Jupiter w ill be used to colnput,e t.heheliocentric orbit of the planet more precisely, and the harmcnics of


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it s gr av ity field will be studied. ih d c r s o n :ind Nu11 hope to im provecurr ent calculations of th e n ~ as s f ,Japiter by a t least n factor of 10,an d those of t,he total mass of ,Jupiter :ind its m any satellites (fig. 2)by a t least a factor of 6.S-Band Occultation

I n ano ther computer analysis of the .Jupiter mission trac king &a,an atmospheric physicist who has long been ;mmersed in studies ofJupi ter , Dr. S. I. Rasool of th e God dard Space Fli gh t Center, will be:~ssocintedwit li :I ,Jet Propulsion Tl:d)orntoly team lie:~dedby Dr. ii.,I. Kliore. Th e Enrtll 's ionospIie~.e, he interp lane t:~ry medium, theSun's coroli:i, :ind ,Jupiter's ionosphere will a11 affect the S-bandt~ xn sn iiss ion s eceived from the P ioneers. The effects of tile E nr tli:tnd interplanetary phenomena are expected to I)e quite stable o.t thet irne of the Pione er mission, so these invest ig lto rs hope to isolxtegood nw:~surementsof the solar :~nd Jovi:m effects.All of the tracking data will be recwded on magnetic tape. Partsof it then will be processed with a computer to e xtract th e part.icularda ta sou ght in th is experiment. Th e da ta received while t,he line ofsight between the Earth and the spac.ccraft is ncar the Sun will beused to gage t he s olar effec,ts on th e ra dio communications. Sim ilarly ,th e signals received \ d d e t ,he spacecraft is nearing and emergingfrom behind J up it er m ay disclose the effects 0.f its ionosphere on t'hetransm issions from t,he vehicle.From refractive index profiles of the distant planet's ionosphereobtained when the spacecraft are occulted by it, the researchersexpect to derive profiles of the electron density around .Jupiter. Swlifindings can be combined with temperature data from other sourcesto find the ratio of helium to hydrogen in Jupiter's atmosphere.Estimating the ratio of those two simple elements is a formidabletask f or astronomers dependent on observations from afa r. Determ in-in g it would be extremely helpful t o theorists try ing to envision thehuge planet's development and struct,ure. Hence th is w ill also be a nobjective of investigators with apparatus aboard the Pioneers.METEOROID ASTRONOMY

Meteoric ma teria l has long been recognized as a significant compo-nent of th e solar system from which much may be learned fibout thewhole system's origin and history. Researchers in this branch ofastronomy have been especially handicapped thus far by the diffi-culties that are inherent in observations from gretit distances ofobjects tha t vary extremely in mass. Virtua lly all th at is now known


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SCIEWT F IC EXPERIMENTS 1@cr af t Center. Th e Pioneer flights will lie t r i d runs for t lie asteroid/meteoroid detector and its developers liope tha t it will be found u sefulalso on other satellites, both in orbitJsneitr the Enrt,ll and on m issionsto dista nt planets. Cometary material may be distinguishable fromother particles in tlie interplnnetury nieciium with tliis detector.Altfliougli inte rpla neta ry piwticles constitute only a small frac tionof tlie mass of tlie solar system, they nre it significant, diflicult-to-measure component. I3y c:itegoriz ing ctnd find ing the masses ofindividua l particles between the Ea rt,li and .Jupiter, astrono me rswill gain a better u n d e ~ t a n d i n g f tlie true nature of the system'smeteoric complex. Engin eers responsible fo r the design of fu tu reprobes of deep space will also benefit from the findings in the twoexperime nts just described. Overestim ation of the possibility ofencounters with destructive particles could iiilpose unnecessaryweight penalties on the performance of costly spacecraft in thefutu re. l'nderestimation of the li a za ri could increase the chancesof failu res because of collisions. More accurate estim ation of thepossibility ~ h o u ld e possible in the ligh t of Pioneer d ata.SOLAR-WIND STUDIES

Most of the scientific experiments requiring app ara tus on th espacecraft mill be focused mainly on phenomena that no one knewan yth ing about unti l tliis century. Men observed meteors an d cometslong before the solar wind, cosmic rays, and 'belts of radiation nearthe Earth were discovered. Studies of these thr, r! dynamic factorsin events within the solar sjstem already hdve been enlighteningto scientists, and the next six experiments to be described are ex-pected to yield additional helpful data regarding them.A stream of highly ionized, el~ctricttlly harged particles contin-ually sweeps by t lie E ar th from the Sun. I ts effects are manifestedat times in tlie performance of electrical systems on the Earth, andit is suspected of being a factor in tlie determiriation of long-termweather cycles. Pa rticle s in tliis wind are tra pp ed in rad iatio n beltsby tlie Ea rth 's m agnet,ic fiald, an d account f o r the a uro ra borealis:ind other phenomena tlint baffled scientists and engineers unt,ilthose belts were founci. Much of wh at is now kn ovr! about th e sola rwind bas been discovered by sending spacecraft out into it, and the,Jupiter mission will extend this research to more distant. maltns,

- Some of the most important advnnces in plasma physics since1060 have resulted from the work of the ,4mes Rewarch Center


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group led by Dr. J. H. 1\'0lfe.~ These spscidists will be in cluirgeof a plasnla. antdyzer on bo ~ir d lie next two Pioneers. I t will bethe heaviest a i d most bulky item in th e scientific package tha t th espacecraft will carry. I t will be used both to study the spatia l:md teniporal characteristics of interplanetary plasma and to investi-?ate tlie intertiction of the solar wind with the magnetic field ofJu pit er . FVit,ll this m onitorin g device, the Ames g ro up expects t,ofind the flow directions and flux levels at various energies in theplasma in previously unexplored portions of the solar system. Atthe farthest distances, the analyzer will be used to search for signsof the solar-galactic boundary.It will operate similarly to a cathode-ray tube, but solar plasmawill take the place of an electron gun (fig.14). Ions and electronswill enter a pair of detectors from a window in the instrumenthousing. Th roug hou t most of tlio long Pioneer flights th at windowwill face backward toward the Ezirth and Sun, and the S un will bewithin the field of view of the plasma analyzer.'Hartman, Edwin P. : Adventurea in Research, NASA SP-4302, p. 477.

Solar - Detector Analyzer Plates< / etector Analyzer P la te r

\\ \\ , r i f t Tube Grid

FIGURE4. Solar plasma will be admitted to two sets of detector plates fromthe left here, through apertures facing the Sun. Analytical apparatus willfunction like a cathode-ray tube with electrostatic deflection.


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22 THE PIONEER MISSION T O J 9 P I l E R

carried for the plasma physicists. I t s sensor will be a cell filled withheliunl and subjected to radiofrequency excitation and infraredoptical pumping. Th e changing magnetic fields throu gh which thespacecraft passes will cause modulations in the helium gas. Thesewill be noted to obtain the desired data.Weak as well as strong fields can be measured with such a sensor,and this magnetometer is expected to measure them in range fromabout 2.5 gamma to about 1.43 gauss. T o obtain good measure-ments of the weak parts of interplanetary fields, magnetic fieldsreaching the sensor from the spacecraft must not exceed 0.1 gamma.Hence the sensor for this experiment will be on the outer end of along mast protruding from the body of the spacecraft. Extreme carehad to be taken in designing and developing the next two Pioneers(described in part 111) to achieve this figure.Data about the magnetic forces that affect the solar wind will becomplementary to detailed da ta about its composition. Together,the plasma analyzer and the helium vector magnetometer can tellscientists much more about the interplanetary medium than isnow known.There are still many uncertainties in astronomers' minds aboutth at medium and all of th e planets beyond Mars. T he outer bounda-i ries of the solar system are still vague, and the interactions therei between i t and other pa rts of th e Milky W ay are still puzzling.i Although the Sun's influence extends f a r beyond Ju pi ter , studies oft,he solar wind in th at pow erful planet's orb it will be helpful toi

t theorists strivin g to envision the system as a whole. So, too, willi the next two experiments to be described here.COSMlCdAV ASTROWOMY

Along with radiation from the Sun, radiation reaches the Earthfrom sources outside of the solar system. T he particles in it aresamples of matter from other and much larger parts of the galaxy.Many of them have energies higher than can be attained yet in anyknown way on the Earth's surface. Submicroscopic charged par ti-cles in cosmic mys, traveling at nearly the speed of light, collideand shower the Earth with small secondary particles.Since the discovery of cosmic rays early in the 1900's, manyingenious and costly efforts have been made to determine theircomposition, account for their energies, and locate their sources.This research has contributed notably not only to advances inastronomy but also to discoveries in nuclear physics.

1 Two of the important experirlents performed with apparatust aboard Pioneers F and G will be extensions of manic-ray studies.


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SCIENTIFIC EXPERIMENTS 23They are expected to be helpful in interpreting the data acquired inprevious work and relt~tingcosmic radiation t.o other phenomena.Olle will be focused on the, composition of the charged particles, andin the other the energy spectra of cosmic rays will be emphasized.Ih tn olt,~inedns a function of distnnce out to the orbit of Jupiterin this pair of experiments slm~ld oth illcrease inen's knowledgeof mecl~nnismswi t lh the solar systein and broaden the basis forco~~clusionsegnrding interstellnr space.Charged Particla Detrcbn

Two of our country's leading authorities on the sources andcourses of cosmic rays are Prof. John A. Simpson of the Universityof Chicago tuld Dr. F. B. McDonald of t,he Goddard Space FlightCenter. Professor Simpson will be the principal investigator inone Pioneer study of the life history of cosmic rays in the solarsystem and Dr. MaDonald in another one.

While the spacecraft are on their way to the encounters with.Jupiter, cllarged particle detectors for Prof. Simpson's group will11ot.e how streams of particles from solar flares spread out and over-take one another several AU from the Sun. Later in the missionthe same detectors will be used to obtain data regarding the Jovianrndint,ion belts for comparison with findings regarding the Earth'sradiation belts.

In addition to a charged particle telescope having the same resolu-t ion as one now in an Earth orbit, the apparatus for this experimentwill include an electron detector, a pair of fission detectors, and aproton detector. With this set of devices, the radial and transversegradients and the anisotropy of particles in cosmic rays will bemeasured. Fields between Mars and Jupiter then can be mappedwith more certainty.

Dr. McDonald's team will include Prof. William R. Webber ofthe University of New Hampshire and Dr. K. G. McCracken of theCommonwealth S~ient~ificnd Industrial Research Organization ofAustralia. They will use instrumentation similar to that aboardan Interplanetary Explorer that was launched in the spring of1 9 X 8 It will be a coordinated set of solid-stab detector telescopesthat will be comprehensive, redundant, and selfcalibrating. Thisapparatus, carefully designed to maximize its diagnostic power,

"re Launch Mission Operation Rept. No. S-86l-71-08. Mar. 1, 1B71.


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will consist of one telescope for high-energy particles and two forlow-energy particles (fig. 16) .Table 2 shows the variety of particles and the energy rangeswith which these investigators will be concerned. They will analyzeenergy spectra, charge composition, and general flow patterns ofsolar, galactic, and Jovinn energetic particles. I n the vicinity ofJupiter, they will study the angular distribution of hydrogen,

30" ConicalF ie ld o f V iewFront LookAngle

Low Energy Telescope

Low Energy Telescope

"Con ica lId of Viewear LookAngle

High Energy TelescopeF1aT-m~16.-A set of lowenergy telescopes and a highenergy telescope will beused for cosmic-ray research.


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SCIENTIFIC EXPERIMENTS 25

TABLE.-Cosmic- R ay Telegcope 0 ectivesPartiole componente: Energy RangoGalactic cosmic-ray protons -----------------4.,5-800 MeVSolar protons ............................. -0.05-800 MeVGalactic cosmic-ray helium ------------- ---4,5500 MeV/nucleonSolar helium ----------------,,------------.0-800MeV/nucleon'He/'He, D/H -- - --------- ---------- ------4.6-60 MeV/nucleonGalactic and solar electrons - - - - - - - - - - - - - - - - -0 .0505.0 MeVLi, Be, B, C, N, 0, F, Ne, and

their isotopic composition ----,-----------AeV/nuc-200 MeV/nucleonIntegral flux ----------------- ------------- > 800MeV

helium, and electrons. From such studies and similar surveyselsewhere, more may be learned about cavities that planets maycause in solar radiation, what happens at the boundaries of suchcavities, and estimates improved of the density of cosmic rays outin interstellar space.RADIATION BELT OBSERVATIONS

The belts of charged particles near the Earth are trapped by itsmagnetic field from radiation in the interplanetary medium. Muchhas been learned about them since they were discovered slightlymore than a decade ago, but there are still questions about whathappens in those belts. It is widely believed, for example, thatdiffusion processes accelerate the energetic particles in those belts-but little progress has been made in identifying the mechanismsinvolved because the resenrchers cnimot vary the parameters.Convincing evidence has been obtained from radio telescopesthat there are also radiation belts around Jupiter. It is the solarsystem's electrically noisiest planet. Th e param eters there ar eclearly different from those near the Earth. Measurements of thesolar wind and cosmic radiation will help scientists determine thedifferences. A third pair of Pioneer F and G experiments willfurther augment information about the Jovian belts.

Prof . J. A: Van Allen's name was given to the Earth's radiationbelts fo r his role in discovering them: and he an d his grad ua testudents at the University of Iowa will conduct one of the studiesof Jovian trapped radiation. They will use seven Geiger-Mueller' aimov, Isaac : Twentieth Century Dfscoueries (Doubleday & Co., lW) ,p. 1M.


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8 TIIE PIOIEER MISSION I 0 JUPltERtubes to survey the intensities, energy spectra, and angular distribu-tions of electrons and protons along the trail that the Pioneers willopen through the magnetosphere of Jupiter.

These tubes are small cylinders containing gas that generateselectrical signals from charged particles. Three of them will bealined linearly, as shown in figure 17, and function as a multipurpose

Fie ld of Viewr r F i b e r g l a s s 7

Mg Collimator

F ie ld of

/kg CoverPb Shielding \

P l a w ~7.-The Geiger-tube telescope will contain three parallel cyllndem andwill rotate with the spacecraft. Fields of view of tubes A and B will be in anequatorial strip along the vehicle's path. Tube C will count particlea thatpenetrate the telefmpef shielding and give inveetigatom the baclyoandrate needed to correct data from A and B.


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telescope. Th ree otllers will be in IL triiiilgultw array, spaced so thatI I O straight line CHI^ ~ I S Sli~-o ugll ll three, and be used to measuret h e ~ ~ u m l ) e rf sllo\vcrs (n~ultple-part cle events) o ow rring . T his~ o ~ n l ~ i ~ l i i t i o nf it telescope and :I shower-detecting a r l ~ . ~ ?ill enablethe111 to compare p rinlary events in the Jo via n radia tion belt with

'r seco~~d:iryvents.A seventh G eiger t u l ~ ill be a low-energy electron detector withwllirll 11 geometric fwtor C : I ~ be added to the information from theother t h s . The investigators expect their findings wit11 this app a-rntus to IE enlightening regiuding the shock front and the tail ofthe tJovian magnetosphere. Pro tons Ili~ vin g nergies above 50 MeV;d lectrons with energies between 2 and 50 MeV will be countedi n the Van Allen experirnel~t.Trappd Radiation Telescope

Dr. R. W. Fillius and Prof. C. k). hfcI1wain of the 'IJniversity ofCalifornia at San Diego will be studying charged particles trappedaround Jupiter with n different kind of telescope at the same timens Pro f. Van Allen. Th eir app ara tus has been designed to covera broader range of energies-2, 5, and 11 MeV for electrons andabove 450 MeV for protons-than the spectra to which the Geigertubes will be responsive.

This apparatus aboard the Pioneers will include several kinds ofdetectors (fig. 18). One will be an unfocused Cerenkov counterthat detects particles by the light emitt,ed in a part,icular direction:a hey da rt through space. Th e others will be an electron scintil-lator, a proton scintillator, a detector for minimum ionizing par-

j ticles, and one for observing electron scatter. These five "eyes,"installed a s shown in th e figure, will make it possible f o r th e investi-gtttors to obtain basic indications of several of the fundamentalfeatures of .Jupiter's m li at io n belts-including th e sep aratio n ofspecies, rough descriptions of angular distributions and energyspectra, and measurements of absolute intensities over an extendedrange.Currently favored theories about Jupiter have been based largelyon the findings of the radio astronomers. Ju p it er is known t o bethe source of three principal types of radiofrequency noise-deca-metric, decimetric, and thermal-and the Pioneer F and G studiesof its radiation belts are expected to make better interpretations ofthose emissions possible. T hi s will he lp astronomers decide betweenconflicting hypotheses about such puzzling m atter as Ju piter's struc-ture. Fr om t he two experiments just described, electrical engineerswill also learn more about a radiation environment that may affect


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UltravioletPhabrcterTh is 1.4-11) device, the lightest scientific ap pa ra tu s ab oard thespncecraft, v i l l be used by th e physics ft~ cu lty f tile Un iversity ofSouther11 Ctd iforn ia a t Los Angeles. 130th Dr. D. 14 . .Judge, theprin cip ~l nrest igt~tor ,and Dr. Robert W. Carlson, his coinvesti-ga tor , Imve pnrtici pitecl in nlany prev ~ O U S st udies of ult rt~ vio letlight with souridirlg rockets and satellites.'I'he sensor used in this experiment will have a lithium fluorideclye 1.5 inches wide that will respond to radiation in the extreme1;1trnriolet range, between 200 and 801) angstroms. Although theplmtometer a i l 1 only observe evidence of helium in this wavelength,the findings will indicate interactions between charged particles and~ w a tal hydrogen.So m ~w he re h e supersonic solar r i n d subsides to a suljsonicbreeze. Estimates of the distance from the Sun that this happensnow range from 2 to 100 AU. While the two Pioneers are goingfm m 2 to 5 AU, the ultraviolet photometer will be used in a searchfor* he inner boundary of the transition zone.During the encounters with Jupiter, the photometer will be usedto look for evidence of an auroral oval in the radiation on the dayside of the planet, to find the rctt,io of helium to hydrogen in th eJovirtn atmosphere, and to take th e tempe rature of the ou ter portion

of that atmosphere.

This instrument will be flown to Jupiter for some of the sameCalifornia Institute of Technology scientists who were responsiblefor infra red observations of Ma rs: D r. Guido Munch, a noted astro-physicist from Mexico, Dr. Gerry Neugebauer, and their colleag~es.~~In their radiometer, a %inch Cassegrain telescope will illuminatet!lermopiles to measure the irradiance in t,wo ranges of th erm al wave-lengths, between 14 and 25 microns and between 19 and 56 microns.It is ;L con~p aratively imp:e device of t he same type th at was placedaboard tx o Mars Mariners, but measurements made with i t fromthe Pioneers will be more accurate and have better spatial resolu-tion than any that can be made from the Earth.Data returned from it can help to dissipate many mysteriesa b u t Jup iter, and theories based on observations of the shadowsthat Jupiter's satellites cast on the planet's rapidly rotating atmos-phere may be substantiated, clarified, or discredited. The investi-

lo Aiarfner Mars 1868: A Prelfm fnaw Report, NASA 8P-226,p. 148.


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ludng Pb,trptlarim,tar'I'he inforwntion from all of t l w 1 1 stllisil~g ievices a lm trd the~le xt, wo Pioneers w i l l be t r n l ~ ~ l ~ ~ i t t e do the Etirtll digitdly.V ir tud ly 1111 of it. is expectcd t o lw sipl~ific ant o scientists, but onlythe imaging l)l~otopol:irin~eter i l l prodwe data intended to behighly pictorial. Pro f. ton^ G el ~re ls f the U niversity of Arizona's1,unar nnd I'ltlnettiry I,d)~r:itory~ ( 1ix colleagues will direct theuse of th is 13.1-1b :tpp tlrntus, in \vl~iclli11 in~iiging evice is combinedwith rr pohrimeter nntl R photonleter.For their resenrcll, t t p i n t able 1 i n d l iiperture telescope (fig. 19)will p rotrud e from th e side of the spiicecr:iftqs instrum ent housing.It will sweep out. n cone while the spwecrr1ft spins, and datc~willbe ob tdn ed in the form of sct~ ns long the viewing cone. Th e ligh tt , l ~a the telescope collects will be nl~nlyzed or co;t r and polerization21 the foctd poin t, t111il filtered before it ren cl~ esphotoelectric de-tectors. Those detectols will provide dig ital dntn far. transmissionto the E ar th t l ~ tan be corrected to reducc distortions of the spin-scan process, nnd used to co l~s truc t mages of Ju pit er.I3efore the encounter with the big planet, the imaging rhoto-

polarimeter will be utilized to study zodiactd ligh t as pa rt a!: effortsto assess the q uw tit y m d distributio ~l of purticulttte matter inspace and identify the nature of the piwticles. Periodic a ~ i p s illbe obtained of the brightness and polarity of ligh t outside + .h e pace-crilft over a wide range of scntte ring angles dur in g tile 1 sng flight.When the P ioneers approi1ch J up ite r, th is telescope may be pointedat one or more of t' l~ u t lanet's large snrellites to search ,'o r evidenceof a n atmosphere. I t s findings the11 may h elp to red,..cebewilder-ment a b u t the origins iuld structures of Jupiter 's moc.1s. The solarsystem's dominntil~gplanet will be scanned, too, of course, forpho tomet r ic and ~~l io topo la r iz i~ t io~~tudies.The investigators e spect to obtain t wo-color images wiiL a resolu-tion of 200 kilometers, in both the red and blue spectral bands, ofJupiter's surface (fig.20). Those. are likely to be the best picturesever taken of a planet beyond the asteroid belt.Thousands of amateur astronomers, science teachers, and journal-ists will be intensely interested in seeing those pictures, and pro-fessional astronomers will be awaiting them even more eagerly.With such pictures in hand, features of the planet that scientigtshave observed, studied intensely, nnd wondered about for centuriesmay be seen more clearly.


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SPACECRAFT AND SUPPORT

SPACECRAFT AND SUPPORTPioneers F and G will be new versions of a probe that NASA

has used to explore the solar system for 12 years. Th ree earlyPioneers did not reach the orbits that they were expected to, but thehe listed in t,able 3 have added immensely to scientific informa-

tion about the Earth's surroundings and still were transmittingdata in 1971. By then Pioneer 6, which was launched in 1965,and Pioneer 8, launched 2 years later, were at distant points 100million miles apa rt. Th eir alinement then m ade it, possible tomeasure the solar wind's density between them more accurately thanthis ever could be done previously.For journeys to Jupiter the spacecraft and some of the equip-ment have been modified in significant ways (fig. 21). Thescient.ific instrum ents, of course, also have been especially designedto meet the rigors that are foreseen, but nc major alterations inlaunching facilities and communications networks developed forother flights will be necessary.

TABLE.--Succe~f U Z Predecemors of SpacecraftSamePioneer 1Pioneer 2Pioneer 3Pioneer 4Pioneer 5Pioneer 6Pioneer 7Pioneer 8Pioneer 9

Launched AchievementsFound extent of Earth's radiation bands.Improved data on dux and energy levels of particles.Discovered second radiation belt near Earth.Extended measurements to within 37300 miles ofthe Moon.Obtained solar flare and wind data.Continued to report data after traveling 3.3 billionmiles.Reported data during solar cycle from widely sepa-rated points within 1.125 A U of the Sun.Reported data during solar cycle from widely sepa-rated points within 1.09 A U of the Sun.First spacecraft to transmit at 3 frequencies throughthe solar corona to measure the electron concen-tration.


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SPACECRAFT AND SUPPORT

PRE Cf' ON AND H I G H G A I N MEDIWWINV E LO L I i THRU STERS A NT EN NA F E E 0 1 ANTEN NA

\ ,--L A W A NA LY ZE RSPIN CONTROL

REFLECTOR PRECESSION AND'r tLOClTY THRUSTERS

LAUNCH VEHICLE /ADAPTOR / \ W&~ W E T O M E T E R

ASTEROlDlMETEOROIODETECTOR MI ANTENNAh E P LO Y E D M C N E T O M T E RSENSOR

S C I E N T I F I C I N S T RU P E N T B A Y

METEOROID DETECTORSTHERML CONTROL LOUVER

ANTENNA REFLECTOR

PRECESSION AN0VELOCITY THRUSTE9S

PRECESSIOW ANDVELOCITY THRUSTERS

E'IOUBE B.-Placement of many of the components of Pioneer F and G men-tioned in this monograph can be seen here. The instruments labeled aredescribed in part I1 of this monograph.


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38 THE PIONEER MISSION 1 0 JUPITERThe launching requirements, the range of environments in whichPioneers F and G must operate, and the exacting demands for 11different kinds of accurate scientific measurements, have imposed

serious constraints on the designers of these vehicles. Hence themission mill be a test of th e state of numerous engine ering arts.There are novel as well as familiar features throughout the space-craft-in its structu re, in its electrical power system, and in itscommunic&ion appa ratus. New facilities fo r receiving and process-ing data from spacecraft will also be available for initial use insuch a program.STRUCTURAL CHALLENGES

Xeither Pioneer F nor G should weigh more than 560 lb. Eachmust be stowed for launching within a cylindrical envelope only 9feet in diameter and 8 feet long, but deploynble appurtenanceswill more than double the vehicle's width throughout most of themission. Radioisotopes will provide the heat fo r the electrical gen-erators on board the spacecraft, and also will be used to warm thefuel for thrustors required to adjust the vehicle's attitude andvelocity from time to time.The basic structural component of the vehicle will be a hexagonalhub (figs. 22 and 23). I t will have an aluminum sandwich floor, analuminum frame, and sides made of aluminum honeycomb coveredby nn insulating blanket of many layers of aluminized Mylar. Dur-ing the launching it will rest on rt separation ring and support al lother pa rts of the spacecraft. Above it there will be a 9-foot-widedish to serve as the reflector fo r a high-g ain antenna. Comm unica-tion and other operational equipment will be in the hexagonal body.Scientific instruments will be isolated from such equipment in asepa rate com partmen t on one side of th e hexagon. W ith in both ofthese two main compartments, the range of temperature must bekept very small relative to that of the environment outside.Magnetic CIeaolim

Apertures in the sides of the compartment containing the scien-tific instrum ents will a dm it light to the sensing systems, and a 15.8-foot-long mast will protrude out from that compartment for mag-netic-field measurements. Any electrical current flowing within aspacecraft can produce a. magnetic field sufficient to distort measure-men ts of weak interplaneta ry fields." T h e sensor fo r th e effort toNaugle, John E. : Unmanned Bpace Flight (Holt, Rinehart & Winston, Inc.,

1965), p. 37.


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SPACECRAFT AND SUPPORT 37

measure those fields from Pioneers F and G will therefore be placedus f a r 11s possible fro m all such c urren ts. T he designers of the vehiclesalso lmve striven to make thenl as magnetically clean as possible,iiot only by ca reful testiug a i d selection of materials fo r allconlpoilents but also by the pli~cel~elitf all neeesstwy electrical11pparatus.'l'lie electrical gene rato rs will be on the o ute r ends of tw o 5.7-foot-long trusses that will be deployed from the body of the spt~cecraftaf te r it has been separated from the launcli vehicle. At the sametime tlie mast fo r the helium vector magnetometer's sensor will bedeployecl in a different direction. I t will be pointed aw ay from thetwo trusses that support the generators at a 120' angle to each oft h e m Consequently the magnetic fields from sources within a nditttaclled to the spacecraft itre expected to be less tlml 0.1 gammaa t tlie point w here th e natur:d interp laneta ry fields are observed,thu s faci lita tin g measurements of very weak portions of tliose fields.Thermal Contnl

A second major problem for the designers \\.as liow to maintainreasonable tempera tures with in th e body of t he sp ac ec ~x ft lwoug1:h-out all phases of t he Ju p it er journey. When tlie spnccraft isIaunchecl, it will be warmed both by th e rocket engines an d the radio-isotopes stored within its shroud. The flight trajectory will take itfarther and farther from the Sun, month after month, and subjectit to greate r coldness th an any of NAS A's previous probes of chesolar system. Yet the ambient temperature must not prevent o p r a -Lion of its control and communication systems or the performanceof scientific experiments.Temperatures in the immediate vicinity of the scientists' instru-ments will be kept between 0" and 90' F. This will be done partlyby using special surface finishes, boots, wraps, and multilayeredblanltets made of M ylar and ICapton. Th e spacecraft also will havelouvers facing away from the Sun that will be opened and closedby the different,ial expansion of bimetallic spr ings.Attitude CwW

W hen th e spacecraft leaves the final stage of th e laun chin g vehiclebehind, i t will be spinn ing rapidly. Before the structures to supp ortits electric generators and the magnetometer sensor are deployed,the spin r ate will have to be reduced from about 60 to about 30 rpm.Those appurtenances will then lower that rate to 4 or 5 rpm.Further changes in the spin rate and in the spacecraft 's attitudeor velocity will be needed to keep it on course, to point scientific


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38 THE PIONEER MISSIBN TO JUPITERsensors at the desired targets, and to maintain communication be-tween the Pioneers and the Eurtll. Those adjustm ents will be madeby clusters of small thrustors. There will be two of them, onopposite sides of the sp acecraft near its outer perimeter. One nozzlein each cluster will face forward, another to the rear, and a th i rdnozzle will be alined tangentially to the spin axis of the spacecraft.Pulses will be released from them to control the precession and velo-city of the vehicle.Gas for expansion through the thrustor nozzles will be producedby the decomposition of llydrazine in a catalyst bed. Th e hydrazin ewill be in n spherical, pressurized bladder in the equipment com-partment. Hyd razine freezes a t about 35' F, and both electricaland small radioisotope heaters will be used to keep it l iquid andready for use.The timing of the pulses from the thru stor nozzles will be deter-mined by signals from the Sun or star sensors and ground calcula-tions. Th e Pioneers will be able to home on radio signals from t heEarth, to heed commands from the Earth, and to store such com-mands for execution latet, !: I the sequence and at the times thatcalculations indicate are necessary.ELECTRICAL REQUIREMENTS

To provide sufficient, reliable, electrical power for a spacecraftheaded for Jupiter, the electrical engineers faced problems asunprecedented as those of the m echanical engineers responsible fo rthe structure of the vehicle. Batteries would be exhausted if notrecharged. I f so lar cells mere used, as on the M ariner M ars missions,enormous numbers of them would be required to generate enocghpower 5 AU from the Sun. Radioisotope thermoelectric gen erators(RTG's) were chosen, therefore, for Pioneers F and G. Isotopesidea se much more energy per pound than chemical fuels. T he U.S.Navy first tried this new kind of generator on navigation satellites.WASA has since used it on its Nimbus weather satellite and placedRTG's nn the Moon, but this will be the first use of an RTG on aninterplanetary spacecraft.The unit chosen for the next two Pioneers will be an advancedSNA4P-19 (SNAP is an acronym for System Nuclear AuxiliaryPower) that was developed jointly by the Atomic Energy Com-mission and NASA (fig. 24). Pioneers F and G will eachhave fo ur of these units. Ea ch unit will be enclosed in a smallcylinder and weigh about 30 lb. Two of the cylinders will bemounted on the outer end of each of the two booms that are to bedeployed from the hexagonal body of the vehicle.


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will each be citpttble of providing nearly 40 watts of power duringthe early part of the nlission and about 90 watts of power 5 yearslater. Th ree sucli gen erators should suffice to meet the requiremen tsfor experiments and con~niunicationat the time of the Pioneer en-counters with Jupiter, but each spacecraft will hnve four of theunits to reduce the possibility of a power shortage at a crucial.moment.The output from each RTG will go to n separate inverter, whichwill be paralleled with the other three inverters to form an alternat-ing cl~ rre nt ac ) bus. Most of the RC power will be rectified andfiltered to supply a main 28-volt dc bus, from which the instrumentswill receive power. Most of the othe r dema nds aboard the spac ecraftwill be met from a central transformer rectifier that will receivepower from the ac bus and deliver various dc voltages. A batterywill be recharged automatically when enough power is available,and used to meet any temporary overloads.THE COMMUNICATION SYSTEM

Men have never controlled and received readings from scientificinstruments so far away as the next two Pioneers will go fromthe Ear th. Despite the long distances, streams of da ta must bet ransmitted from and to the E ar th throughout much of the Jup itermission. T his will be possible tllanks to such developm ents as atraveling-wave-tube amplifier that weighs only 3.85 lb and takesup only 150 cu in. of space, yet has an rf output of 8 watts in theS-band,12Each Pioneer will have a high-gain antenna (fig. 25) for com-~nunications t maximum data rates and extreme distsnces, and apair of medium- and low-gain antennas for broad-angle com-munications a t intermediate and close ranges. T he parabolic re-flector fo r tthe high-gain anten na mill be an aluminum honeycombsandwich, as wide as ca n be accommodated within t he shroud of th elaunch vehicle. T he medium- and low-gain system will have twoelements, a horn facing forward and a spiml pointed to the rear.Each antenna will always be connected to a receiver in the space-craft, and the receivers will be interchangeable when commandedfrom the ground or automatically aft er a certain period of inactivity.By 1973, when the Deep Space Pu'etwork of ground stations willbe needed to communicate with these Pioneers, it will have three210-foot-diameter antennas, spaced equidistantly around the world,in addition to a network of 85-foot antennas. Bo th sizes of an ten nas* CommunCcatfone Deciger's Digest, Nov.-Dec. 1970, pp. 26-27.


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42 THE PIONEER MI SS IO N TO JUPITER

22 bits. Only 8 of those bits will colltain commnild information;the others will be used for routing, decoding, and verifying themessages. Tin ling and operatioliid ord ers will be transmitted both tothe various subsysten~s f t h e s p ~c c c m f t nd to the scientific instru-m en t,~ . No command will be executed until it has been correct,lyrouted and verified.Readings from the scientific instruments may be either trans-mitted instantly or stored on the spacecraft for transmission laterwide r more favorab le circumstances. Da ta can be read out fromthe system's memory a t any of eight. different bit rate s f or tran smis -sion to the Earth .Data from the scientific experiments will be handled separatelyfrom the engineering data, but both types will be received on theE ar th in a single stream. Separa te formats will be used to dis-tinguish the types of data transmitted, and redundancy will be builtinto most part s of the digi tal telemetry unit. Special form ats willenable investigators to sample data from certain instruments at ahigh rate by reducing the rate of transmission of other data. Th isfeature will be especially helpful to the scientists during the brieftime that the spacecraft will bc (!ti, '.e close to Jup iter.

I n plannin g th is mission, NASA has drawn heavily on experience,techniques, and skills acquimd in lunar exploration, in seven pre-vious planetary missions, and in its efforts to place a Mariner inorbit nround Mnrs in 1071. I n numerous respects, as indicated intable 4, the Pioneer F/G project is a much more ambitious, chtll-lenging, and complex undertaking than orbiting Mars.

Mariner 71 Pioneer F/GFlight time to accomplish objectives -,,-D month6 20montbsConimunica tion distance ,,-,,,,- - - 250X 10' km 700 X 1VLmSolar inteneity (relative to Earth)at encounter ,,,-,-,-,,,,,,,,--------..4 0.04Launch energy required ,,,,,,,,,,,,,,-,kma/sec' 90hg/dOnboard apparatua for ecietltificexperimente ,-,,,,,,,,,,,,-,,,-,---,,- 11Maximum telemetry bit rateat encounter ,--,,,,,,-,--,,--,,-------6000bite/sec 1024bits/lrecTotal information transmittedduring nominal mMon -----,--------.&I1@ 78 X 10'


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PROBRAM MANAGERK T !PROJECT MANAQERL-I

FIGITRE6.-The lmic nrgnnization of the Pioneer project ulrowu the fivekey system8 nt the bottom Irere. They correspond to those for the MarinerMnrx 1071 project.Responsibility for the management of the Pioneer F I G project

has hen entrusted to the Ames Researd! Center by the NASAOffice of Space Science and Applications. (F ig u re 26 shows theh s i c orpculizntion.) Uoth the m anagement and t.he implem entingorpt~~iiznt~ionsave h e n nnd will contiilue to be g;.?lided an d aid edhy many of the Nation's most highly regarded scientists, engineers,rind institutions. Some of th e part ici pn ting organizations a re listedin table 5.

The Atlas-Centaur combination that NASA h ~ ssed for severalyea rs will prov ide the first two stages of propu lsion when PioneersF nd G leave Pa d 36A at th e Cape Kennedy A ir Force Statiliin. TheAtlas first stage has two Rocketdyne booster engines. The Cent'aursecond s t ~ g e a s two P ra t t & Whitncy engines powered by liquidhydrogen and liquid oxygen. Th e third and final stage of propulsionwill be provided by a Thiokol solid -pro plln nt motor. This will be i tsfirst operational ilse with the Atlas-Centaur combinat.ion.The countdowns and launchings will be controlled from the Ken-nedy Space Centor. Air Force and Manned Space Flight Networkfacilities will be used for th e downrange tracking. T he launch BZI-muth will be between 90 and 110 east of north, and the powered


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W E MNE ER MISSION TO JUPITER


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Throughout the many months that each spacecraft is far fromthe Earth, the Deep Space Set\vork will be used for tracking anddata acquisition. That. network h i~ sriicked Pioneers 6 imd 9 nearly190 million miles away from the E i ~ t l l uccessfully. To followPioneers F and G at greater distances, it will use both its S5-footantenn as and three 210-foot. antenn as (fig. 27 ) . At the c1imact. i~hours of t.hc mission, the distances between those iintennus on theEarth and the spacecraft will be so great t ' l~ato query the vehicleand receivi? a reply will take 90 minutes.DATA DISTRIBUTION

Th e Deep Space Network will forwa rd d ata a s i t is received to t .heoperations fzcil i ty at the Jet Propulsion Laboratory operated forNA SA in Pasadena by th e Ca lifornia Jnst it ute of Techaology, wherea master dat a record will be kept on mag netir tape. Th at, laborato ryd l ave an advanced central da ta processor which wil l be used inconnec t ion ~ i t~11n interplanetary flight for the first time. AmesResearch Center will be connected with the operations fzcility byhigh-speed dat'a lines, and have stan db y com puting capab ility.Scientists a t the Ames Research Center an d many oth er notedlaborat'ories will reduce an d analyze th e trnnsmissions to ext'ract thescientific data fo r particular purposes from t 'he great quan tity th at ,is anticipated. These p articip ants will include t,he *Jet Prop ulsionLab ora tmy , t,he Vn iversity of Chicago, the I 'niversity of Iow a, th eUniversity of Sou thern California, t , l~ eDudley Observatory, theC a l i f ~ r n i a nst.it.ute of Technology, t,he General E lectric Co., an dNASA's Godd ard Space Flight. Center and Langley Research C enter.More interp lane tary spacecraft ha re been sent out. from Russiathan f rom the Uni ted Sta tes , but none to Jupi te r . Grea ter inter -natio nal cooperation in space is one of th e si x spec,ific objectives -enunciated March 7, 1970, by President Nixon for our country'sprogram. I n furtherance of th at objective, f indings in all of th e +experiments to be undertaken on the Pioneer mission to Jupiter will :be made availrble in appropriate ways, as promptly as possible, totheoretical and experimental scientis ts t~l~r ou ph ou the world. 4i*"The universe," one astronomw, Carl Sagan, has written, "is vastand awesome, an d fo r th e first time we a re becoming a part of it." id1T

a U. S. GOVERNMENT PRINTING OFFICE : 1971 0 - 426-917 $ 1a


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