Pioneer F Press Kit

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PRE55KIT

NATIONAL AERONAUTICS ANDSPACE ADMINISTRATIONWashington, D. C. 20546202-755-8370

fOR RELEASE:FEBRUARY 20, 1972

PROJECT: PIONEER

contentsGENERAL RELEASE - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -MISSION PROFILE - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Instrument Turn-On - - - - - - - - - - - - - - - - - - - - - - - - ~ - - - Midcourse Correc t ions - - - - - - - - - - - - - - - - - - - - - - - - -

Astero id Traverse - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Facto rs i n P lane t Encounter - - - - - - - - - - - - - - - - - - - -Target ing - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Flyby Operat ions - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Beyond Ju p i t e r - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

1-78-169-10101111-1212-1313-1414-16

THE ASTEROIDS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 17-18COMETS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 19JUPITER - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 20-27What We Know - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 20-23Clouds, Curren t s , and Visua l Appearance - - - - - 21-22Magnetic Fie lds and Radia t ion Bel t s - - - - - - - - - 22Jovian Radio Signals - - - - - - - - - - - - - - - - - - - - - - - - 23Temperature - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 23Ju p i t e r Unknowns - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 24-27

Life - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 24-25Plane t S t ruc tu re - - - - - - ~ - - - - - - - - - - - - - - - - - - - - - 25A Hot Plane t - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 26Magnetic Fie ld - - - - - - - - - - - - - ~ - - - - - - - - - - - - - - - - 26Moons - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 26-27

THE. HELIOSPHERE - - - - - - - - - - - - - - - - - - - - - - - - - - ~ - - - - - - - - - - 28-31So l a r Wind, Magnetic Fie ld , and So l a rCosmic R a y s - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 29-30Plane ta ry I n t e r ac t i o n s and Neut ra l Hydrogen - - - - 30Galac t i c Cosmic Rays - - - - - - - - - - - - - - - - - - - - - - - - - - - 31

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CONTENTS (continued)THE SPACECRAFT - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 32-41Pioneer F Descr ip t ion - - - - - - - - - - - - - - ~ - - - - - - - - - - - 33-34

Orienta t ion and Navigat ion - - - - - - - - - ~ - - - - - - - - - - - 34-35Propuls ion and At t i tude Cont ro l - - - - - - - - - - - - - - - - 35-37Nuc lea r -E lec t r i c Power - - - - - - - - - - - - - - - - - - - - - - - - - 37-38Communications - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 38-39Command System - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 39Data Handl ing - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 39-40Temperature Cont ro l - - - - - - - - - - - - - - - - - - - - - - - - - - - - 40-41Magnetic Clean l iness - - - - - - - - - - - - - - - - - - - - - - - - - - - 41Re l i ab i l i t y - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 41

THE EXPERIMENTS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 42-52Magnetic Fie lds - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ~ - 43Magnetometer - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 43In te rp lane ta ry So la r Wind and Heliosphere - - - - - - 43-44Plasma Analyzer - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 43-44Cosmic Rays, Jup i t e r ' s Radia t ion Bel t s , and

Radio Emiss ions - - - - - - - - - - - - - - - - ~ - - - - - - - - - - - - - - 44-45Charged Pa r t i c l e Composit ion Ins t rument - - - - - 44Cosmic Ray Telescope - - - - - - - - - - - - - - - - - - - - - - - - 45Jupi ter- i s Charged Pa r t i c l e s - - - - - - - - - - - - - - - - - - - - 45-46Geiger Tube Telescope - - - - - - - - - - - - - - - - - - - - - - - 45Jovian Trapped Radia t ion Detec to r - - - - - - - - - - - 46Astero ids , Meteoroids , In te rp lane ta ry Dust - - - - - 46-48Astero id -Meteoro id Detec to r - - - - - - - - - - - - - - - - - 46-47Meteoroid Detec to r - - - - - - - - - - - - - - - - - - - - - - - - - - 47-48Ce le s t i a l Mechahics - - - - - - - - - - - - - - - - - - - - - - - - - - - - 48Ce le s t i a l Mechanics - - - - - - - - - - - - - - - - - - - - - - - - - 48In te rp lane ta ry Hydrogen, Helium, and Dust;Jup i t e r ' s Atmosphere, Tempera tures , Auroras ,

Moons - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 48-51Ul t rav io le t Photometer - - - - - - - - - - - - - - - - - - - - - - - 48 -49Imaging Photopo lar imeter - - - - - - - - - - - - - - - - - - - - 49-51Jup i t e r ' s Atmosphere, Ionosphere , Temperature - - 51-52In f ra red Radiometer - - - - - - - - - - - - - - - - - - - - - - - - - 51-52Occul ta t ion Exper iment - - - - - - - - - - - - - - - - - - - - - - 52

EXPERIMENTS AND INVESTIGATORS - - - - - - - - - - - - - - - - - - - - - - - 53-56Magnetic Fie lds Experiment - - - - - - - - - - - - - - - - - - - - - 53Plasma Analyzer Exper iment - - - - - - - - - - - - - - - - - - - - - 53Charged Pa r t i c l e Experiment - - - - - - - - - - - - - - - - - - - - 54Cosmic Ray Energy Spect ra Experiment - - - - - - - - - - - 54Jovian Charged Pa r t i c l e s Experiment - - - - - - - - - - - - 54Jovian Trapped Radia t ion Experiment - - - - - - - - - - - - 54Astero id -Meteoro id Astronomy Experiment - - - - - - - - 55Meteoroid Detec t ion Experiment - - - - - - - - - - - - - - - - - 55Ce le s t i a l Mechanics Exper iment - - - - - - - - - - - - - - - - - 55Ul t r av io l e t Photometry Experiment - - - - - - - - - - - - - - 55Imaging Photopo lar imet ry Experiment - - - - - - - - - - - - 56Jovian In f ra red Therma1 St ruc tu re Experiment - - - 56S-Band Occul ta t ion Exper iment - - - - - - - - - - - - - - - - - - 56- more -


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CONTENTS (continued)

THE PROJECT TEAM - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 57-59Office o f Space Science - - - - - - - - - - - - - - - - - - - - - - - - - 57Off ice o f Tracking and Data Acquis i t ion - - - - - - - - - 57Ames Research Cen te r , Mountain View, Ca l i f . - - - - - - 57-58Deep Space Network, JPL - - - - - - - - - - - - - - - - - - - - - - - - - 58Lewis Research Cen te r , Cleveland - - - - - - - - - - - - - - - - 58Kennedy Space Center , Flor ida - - - - - - - - - - - - - - - - - - - 58AEC Space Nuclear Systems Divis ion - - - - - - - - - - - - - - 58-59TRW Systems Group - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 59

PIONEER F CONTRACTORS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 60-61LAUNCH VEHICLE - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 62-63Launch Vehicle Charac t e r i s t i c s - - - - - - - - - - - - - - - - - - 63FLIGHT SEQUENCE - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 64-66Atlas/Centaur/TE-M-364-4 F l igh t Sequence (AC-27)- 64

Atlas Phase - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 65Centaur Phase - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 65Third Stage Phase - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 65Retromarieuver - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 66LAUNCH OPERATIONS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 67-68MISSION OPERATIONS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 69-10TRACKING AND DATA RETRIEVAL - - - - - - - - - - - - - - - - - - - - - - - - - - 71-73

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Howard Allaway(Phone: 202/755-3680)Pe te r W. Waller (Ames)(Phone: 415/961-2671)RELEASE NO: 72-25

PIONEER F MISSION TO JUPITER

NATIONAL AERONAUTICS ANDSPACE ADMINISTRATIONWashington, D. C. 20546

fOR RELEASE:FEBRUARY 20, 1972

Man w i l l reach out beyond Mars to t ake the f i r s t c loselook a t the p lane t Ju p i t e r on th e miss ion of the unmannedPioneer F spacecra f t , to be launched by the Nat iona lAeronaut ics and Space Adminis t ra t ion from Cape Kennedy, Fla . fbetween Feb. 27 and March 13, 1972.

Th e t r i p to Ju p i t e r w i l l l a s t l e ss than two yea rs , fo rmost launch da tes , with most a r r iva l t imes before Dec. 31, 1973.

Ju p i t e r i s a spec tacu la r p lane t . It appears to have i t sown i n t e rn a l energy source and i s so massive t h a t it i s a lmosta smal l s t a r . I t may have th e necessary i ng red ien t s to producel i f e . I t s volume i s 1,000 t imes t ha t of Ear th , and it has morethan twice the mass o f a l l t he o the r p l ane t s combined. St r ipedin glowing yel low-orange and blue-gray , it f loa t s in space l i kea br igh t -co lo red rubber b a l l . It has a huge red "eye" in i t ssouthern hemisphere and sp ins more than twice as f a s t as Earth .

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The miss ion inc ludes a number of othe r f i r s t s . Pioneer Fi s expected to make the f i r s t reconnaissance of the Astero idBel t between th e o rb i t s of Mars and Ju p i t e r . It i s planned tobe th e f i r s t man-made objec t t o escape the so la r system, andth e f i r s t to use the o r b i t a l ve loc i ty and powerful grav i ty ofJ u p i t e r fo r t h i s escape. It i s a lso th e f i r s t NASA spacec ra f tto draw i t s e l e c t r i c a l power e n t i r e ly from nuclear gene ra to rs ,four radio isotope thermoelec t r ic genera to rs (RTGs) developedby th e Atomic Energy Commission.

The Atlas-Centaur-TE-M-364-41aunch veh ic l e w i l l dr ivethe spacec ra f t away from th e Earth i n i t i a l l y a t 51,800 ki lometersper hour (32,000 miles per hour) - - f a s t e r than any man-madeobjec t has flown before . At t h i s t ime th e spacec ra f t w i l l benamed Pioneer 10. For the f i r s t week, it w i l l t r a v e l anaverage of 800,000 ki lometers (a ha l f -mi l l ion miles) a day.I t w i l l pass the Moon's o r b i t in about 11 hours .

Pionee r ' s 13 sc i en t i f i c exper iments are expected to providenew knowledge about Ju p i t e r and many aspec t s of the oute r s o l a rsystem and our galaxy. I t w i l l r e tu rn th e f i r s t close-upimages of Ju p i t e r , and w i l l make the f i r s t measurements ofJ u p i t e r ' s tw i l i g h t s i d e , never seen from the Ear th .

The miss ion opens the e ra of explora t ion of the o u t e rp lan e t s , s ince it i s in tended in p a r t to develop technologyfo r o ther oute r p l a n e t miss ions .

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The spacec ra f t w i l l t e s t out the haza rds o f cosmic d eb r i sin th e Astero id Bel t . It w i l l probe J u p i t e r ' s r ad i a t i o n b e l t s ,which could c r i p p l e or des t roy a spacec ra f t approaching tooc l o s e l y . The b e l t s are es t ima ted to be as much as one mi l l i o nt imes more in tense than Ear th ' s Van Al len r ad i a t i o n b e l t s .J u p i t e r i s so f a r away t h a t rad io messages moving a t th espeed o f l i g h t w i l l t ake 4S minutes to reach th e spacec ra f tt h e r e , wi th a round t r i p t ime of 90 minutes . This w i l l demandprec i se ly planned command o p e ra t i o n s . Although Pioneer cans to re f ive commands, it w i l l be con t ro l l ed most ly by f r eq u en ti n s t r u c t i o n s from E ar th .

To car ry out th e miss ion , the advanced communicat ionst echnology of NASA's Deep Space Network (DSN) w i l l be s t r a inedto th e l i m i t . The DSN's 64-meter (2 l0 - foo t ) "b ig d ish" an tennas ,one o f which now hears the Mar iner 9 spacec ra f t i n Mars o r b i tw i l l have to hear seven t imes as fa r as Pionee r approaches Ju p i t e r .

Pionee r ' s e igh t -wa t t s ig n a l , t r an s mi t t ed from Ju p i t e r ,w i l l reach DSN antennas wi th a power of 1/100 ,000 ,000 ,000 ,000 ,000w at t s . Col lec ted fo r 19 mil l ion yea rs , t h i s energy would l i g h ta 7 .S -w a t t Chris tmas t ree bulb fo r one- thousandth o f a second.

Pionee r F i s a new des ign fo r the ou te r s o l a r sys tem, b u tit r e t a i n s many t e s ted subsystems o f its predecessors , th ePionee r 6 to 9 spacec ra f t . All four are still opera t ing inin te rp lane ta ry space . P ionee r 6 i s in its seven th y ea r .

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- 4 -The 260-ki logram (570-pound) Pioneer F i s sp in-s tab i l i zed ,

giving i t s ins t ruments a fu l l - c i r c l e scan. It uses nuclearsources fo r e lec t r i c power because so la r rad ia t ion i s too weaka t Ju p i t e r fo r an e f f i c i e n t solar-powered system.

I t s 2.75-meter (n ine-foot) dish antenna w i l l be locked onthe Earth l ike a big eye throughout the miss ion - - changing i t sview d i rec t ion as the horne p lane t moves to and f ro in i t s o r b i taround the Sun. Th e e n t i r e f l i g h t path i s in , o r very c lose to ,th e plane of Ear th ' s o r b i t , the ec l ip t i c .

Ju p i t e r i t s e l f i s little unders tood.

It broadcas ts predic tably modulated radio s igna l s ofenormous power. Though it has only 1/IOOOth the mass of theSun, it may have Sun-l ike i n t e rna l processes , apparent lyrad ia t ing about four t imes as much energy as it rece ives fromso la r rad ia t ion .

In addi t ion to helium, the p l ane t ' s atmosphere containsammonia, methane, hydrogen, and probably water, the sameing red ien t s bel ieved to have produced l i f e on Earth about fourb i l l i on years ago. Because of the p la ne t ' s i n t e rna l hea t source ,many sc i en t i s t s be l ieve t h a t la rge reg ions below th e f r ig idcloud l ayer are around room temperature . These condi t ionscould al low the p lane t to produce l i v ing organisms desp i tethe fac t t h a t it rece ives only 1/27th of the so la r energyrece ived by the Earth .

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J up i t e r i s probably more than 75 pe rcen t hydrogen, the maincons t i tuen t of the universe . Th e p lane t may have no so l idsurface . Due to i t s high grav i ty , it may go from a th ick gaseousatmosphere down to oceans of l i qu id hydrogen, to a s lushy l aye r ,and then to a so l id hydrogen core . Ideas of how deep beneathi t s s t r iped cloud l ayer s any so l id hydrogen " icebergs" o r"cont inents" might l i e vary by thousands of ki lometers .

Astronomers have long seen v io len t c i rcu la t ion of thep l ane t ' s l a rge -sca le cloud f ea tu res . A poin t on J u p i t e r ' sequato r moves a t 35,400 km/hr (22,000 mph), compared with1,600 km/hr (1,000 mph) fo r a s imi la r p o in t on Ear th ' sequato r .

The most b iza r re f ea tu re of th e p lane t i s the Grea t RedSpot , known as the "Eye of J up i t e r . " This huge ova l i s48,000 ki lometers (30,000 miles) long and 13,000 ki lometers(8,000 miles) wide, la rge enough to swallow up seve ra l Earths

with ease . The Red Spot may be an enormous s tanding columnof gas , o r , says one s c i e n t i s t , a " ra f t " of hydrogen ic ef loa t ing on a bubble o f warm hydrogen in the coole r hydrogenatmosphere, and bobbing up and down a t 30-year i n t e rva l s , sot h a t the Spot disappears and reappears . The Spot appears toro ta te a t a d i f f e r e n t speed from the p lane t . I t s red co lo rmay be due to the presence of organic compounds found in ag igan t ic l igh tn inq charge in the Jovian atmosphere, accordingto one theory .

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- 6 -Poten t i a l benef i t s of th e Pioneer J up i t e r mission and

o ther s l ike it inc lude increased knowledge of "col l i s ion lessplasmas" of the so l a r wind. This bears d i r e c t ly on the"ul t imate" clean system fo r e l ~ c t r i c power product ion ,con t ro l l ed hydrogen fus ion. The f indings may also lead to.be t t e r understanding of Ear th ' s weather c y c l e s "a n d to i n s igh t sin to Ea r t h ' s atmosphere c i rcu la t ion through study of Jup i t e r ' sr ap id ly ro ta t ing a tmosphe re . There may aiso be ind ica t ionsof Jovian re sources , such as perhaps a quant i ty of petrochemicalsequ iva len t to Ear th ' s consumption fo r a mil l ion years .

Pioneer F spacecra f t w i l l carry a 30-kilogram (65-pound)experiment payload . I t w i l l make 20 types of measurements ofJ u p i t e r ' s atmosphere, rad ia t ion be l t s , hea t balance, magneticf i e l d , moons, and o ther phenomena. It also w i l l charac te r izethe he l iosphere (sola r atmosphere) : perhaps the i n t e r s t e l l a rgas; cosmic rays ; as te ro ids ; and meteoroids between the Earthand 2.4 b i l l i on ki lometers (1.5 b i l l i on miles) from th e Sun.

A second, almost i de n t i c a l spacecra f t , Pioneer G, w i l lbe launched to J up i t e r in ea r ly Apr i l of 1973.

NASA's Office of Space Science assigned pro jec t managementfo r the tw o Pioneer J up i t e r spacecra f t to NASA's Ames Researchcen te r , Mountain View, C a l i f . , near San Francisco. The space-c r a f t are b u i l t by TRW Systems, Redondo Beach, Cal i f . Thesc i en t i f i c ins t ruments are suppl ied by NASA Centers ,un ive r s i t i e s and pr iva te indus t ry .

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Tracking i s by NASA's Deep Space Network, operated by th eJ e t Propuls ion Laboratory, Pasadena, C al i f . NASA's LewisResearch Center , Cleveland, manages the launch veh ic le , whichi s b u i l t by General Dynamics, San Diego, C al i f .

Cost of tw o Pioneer Ju p i t e r spacecra f t , sc i en t i f i cins t ruments , and da ta process ing and ana lys i s i s about $100mil l ion . This does not include cos ts of l aunch vehic les anddata acqu is i t ion .

The 30-minute evening launch window opens progress ive lye a r l i e r each day - - approximate ly 9:00 pm EST, on Feb.-27,and a t 7:00 pm by March 13, 1972.

Depending on l aunch da te , the t r i p to Jup i t e r wi l l takefrom 630 to 795 days with a r r iva l da tes between Nov. 21, 1973,and July 27, 1974.


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MISSION PROFILE

Pioneer F w i l l be launched toward Jup i t e r and even tua lescape from the s o l a r system on a d i r e c t -a sc e n t t r a j e c t o ryfrom Cape Kennedy in a d i r ec t i o n 4.S to 20 degrees south o fs t r a i g h t e a s t , pass ing over South Afr ica shor t ly a f t e r launchveh ic l e burnout .

The t r i p w i l l fol low a curving path about a b i l l i onki lometers long (620 mil l ion miles) between th e o rb i t s ofEar th and Ju p i t e r . The path w i l l cover about 160 degreesgoing around the Sun between launch p o i n t and Ju p i t e r .Because of th e changing pos i t ions of the Ear th and Ju p i t e r ,th e sh o r t e s t t r i p t imes are fo r launches during th e ear ly daysof the two-week launch per iod . These ear ly d a t e s would putthe Ear th - Jup i te r l i ne fa r from th e Sun during f lyby, r e s u l t i n gin l e ss in te r fe rence by th e Sun with da ta t ransmiss ion fromthe spacec ra f t and with simul taneous t e l escope observa t ions o fJu p i t e r from Earth .

The high-energy launch marks t h e _ f i r s t use of a t h i rds tage , the '1'E-M-364-4, with th e Atlas -Centaur launch veh ic l e .A f t e r l i f t o f f , burnout of the 1,829,000-newton (411,000-pound) - th rus t , s t age -and-a -ha l f Atlas boos te r w i l l occur inabout four minutes . Stage separa t ion and i gn i t ion of the130,000-newton (30 ,000-pound)- th rus t Centaur second s tagew i l l then t ake place and th e hydrogen-fueled Centaur enginew i l l burn fo r about 7.S minutes . The 10 .7-meter - long (3S-foot)aerodynamic shroud covering th e t h i rd s tage and the spacec ra f tw i l l be j e t t i soned a f t e r leaving the atmosphere , about 12

seconds a f t e r Centaur engine i gn i t ion .At about 13 minutes a f t e r l i f t o f f , smal l so l i d - fu e lro ck e t s w i l l spin up th e 6S,860-newton ( lS ,OOO-pound)- thrus tt h i rd s tage and the a t t ached spacec ra f t t o 60 rp m fo r s t ab i l i t y

during s tage f i r i ng . The t h i rd s tage w i l l then i gn i t e and burnfo r about 44 seconds.About two minutes a f t e r th i rd s tage burnout (16 minutesa f t e r l i f t o f f ) , Pioneer F w i l l separa te from th e t h i rd s tageand be on Jup i t e r t r a j e c t o ry .During powered f l i g h t , launch vehic le and spacec ra f t w i l l

be monitored from the Mission Control Center a t Cape Kennedyv ia Estern Tes t Range t racking s t a t ions and by a t racking shipin mid-At lan t i c .Seventeen minutes a f t e r launch, NASA's Ascension I s l andt r a ck ing s t a t i o n w i l l be able to send commands if n ~ c e s s a r yto th e spacec ra f t .

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JUPITER ATI.,A.UNCH

PIONEER HBJOCBn'RICTRAJECTORY: ESCAPEfROM SOlAR S"t'STaII

,.."DC)tMl AlIit()NAUfC:S .... spact ~ f l l a ' ' ' ' '..Mn YAK'" a ...... MOHf" ,. 0 ( 6&801 '"

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Miss ion c o n t ro l w i l l s h i f t from th e Miss ion Direc to r a tCape Kennedy to the Fl igh t Direc tor a t th e Pioneer Miss ionSuppor t Area , (PMSA) a t the Space F l ig h t Operat ions Fa c i l i t y(SFOF) a t th e J e t Propuls ion Labora to ry , Pasadena, C al i f .At abou t 25 minutes a f t e r launch, th e DSN's Johannesburg,South Afr i ca , s t a t i on w i l l lock on th e spacec ra f t and can sendcommands. By then , Pioneer F w i l l have emerged from Ear th ' sshadow and begin to g e t t iming data from i t s Sun-sensor .Johannesburg may t u rn on th e Jovian Trapped Radia t ion ins t rumentin o rd e r to c a l i b ra t e it aga ins t measurements of the knownr ad i a t i o n in Ear th ' s Van Allen be l t s .

Ins t rument Xurn-OnAbout 32 minutes a f t e r launch, Pioneer F 's on-boardsequencer w i l l i n i t i a t e despin down to about 21 rpm from th e60-rpm spin impar ted before t h i rd s tage i gn i t ion . The sequencer

then w i l l s t a r t deployment, of the four nuclear power sources ,th e Radioiso tope Thermoelec t r ic Generators (RTGs), us ing spacec r a f t spin to s l i de them o u t on t h e i r t r u s s e s t h ree meters (10fee t ) from the cen te r of the spacec ra f t . Th e sequencer w i l l nex ti n i t i a t e deployment of th e magnetometer to 6.6 meters (21.5 fee t )f rom the spacecra f t cen te r by unfolding i t s l igh tweigh t boom.When boom deployments are comple te , spacec ra f t spin r a t e w i l lbe down to f ive rpm, al lowing th e s c i e n t i f i c ins t ruments toscan a f u l l c i r c l e f ive t imes a minute .

At launch plus 43 minutes , turn-on of the remaining 10s c i e n t i f i c ins t ruments w i l l beg in . Because of the pos s ib i l i t yof high vol tage a rc ing , some ins t ruments w i l l be al lowed tooutgas . Fl igh t d i rec to rs w i l l t u rn them on th e second andt h i rd day of the miss ion .

About t h ree hours a f t e r l i f t o f f , con t ro l l e rs w i l l commandthe spacecra f t to t u rn i t s e l f so t h a t i t s high-gain dish antennapoin t s a t Earth . This w i l l grea t ly i nc rea se s igna l s t reng th .Before t h i s , th e spacecra f t w i l l have been communicating v iai t s r ea r - f ac in g , low-gain antenna. This maneuver w i l l t akeabout, two hours to comple te . It a l so puts th e spacec ra f t inpos i t ion fo r proper hea t balance .At e ig h t hours a f t e r launch, Pioneer F w i l l " r i s e" a t theDSN's Goldstone , Cal i f . , s t a t i on . Golds tone w i l l t r im sp inr a t e to th e normal 4.8 rpm. The automat ic Conscan system(whereby th e spacec ra f t uses the p a t t e r n of th e incoming radios igna l to re f ine i t s Ear th -po in t ing) w i l l be t e s t ed and used.In th e f i r s t few days a f t e r launch, DSN s pe c i a l i s t s a tPasadena w i l l perform in tens ive computer ca lcu la t ions toe s t a b l i sh the prec i se t r a j e c t o ry .

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- 10 -During th e ear ly days of the miss ion, th e imaging photo

pola r imete r exper iment ~ J l l make maps of the br igh tness of the~ k y , as the spacecra f t ro t a t e s , in order to c o r re l a t e Pioneer 'Rzod iaca l l i g h t measurements with ground-based observa t ions .Simultaneous measurements of zod iaca l l i g h t w i l l be made byDudley Observatory , Alban, N.Y., from Mt. Haleakala , Hawaii .

Midcourse Correc t ionsFour days of accura te t racking w i l l have found any e r ro r sin launch ve loc i ty and d i rec t ion . A second Conscan maneuverw i l l e s t a b l i s h prec i se Ear th -po in t fo r re fe rence . The tiSNw i l l then command change of spacecra f t a t t i t u d e , f i r i ng o ft h ru s t e r s fo r th e f i r s t midcourse ve loc i ty change to e l imina tee r ro r s in aiming a t J up i t e r , and r e tu rn to Ear th -po in t .At about a week a f t e r l aunch , th e spacecra f t and i t sopera t ions team w i l l have se t t l ed i n to / t he in te rp lane ta rycru i se phase of the mission. Analysts w i l l r egu la r ly assess

performance o f sys tems and ins t ruments and develop s t r a tegyto g e t around any malfunct ions .The so l a r wind and magnet ic f i e l d ins t ruments w i l l bemapping th e i n t e rp lane ta ry medium. The par t i c l e experimentersw i l l map d i s t r i bu t ion of so l a r and ga lac t i c cosmic ray p a r t i c l e s ,and th e u l t r a v i o l e t photometer w i l l measure n eu t r a l hydrogen.The meteoroid and dus t de tec to r s w i l l ga ther da ta on s izes andd i s t r i bu t ion o f i n t e rp lane ta ry mat te r . Zodiacal l i g h t measurements w i l l be made per iod ica l ly by th e photopolar imeter

ins t rument and th e meteoroid t e lescopes to help determineamounts o f i n t e r p l an e t a r y mate r ia l .Conscan maneuvers to sharpen Ear th -po in t w i l l be commandedrou t ine ly every th ree days, and l a t e r in th e mission every

Week o r two.At th e end o f th e f i r . s t month, a second midcourse ve loc i tychange w i l l be made if needed.Within seve ra l months, i f spacecra f t opera t ion has becomerou t ine , con t ro l personnel w i l l move from th e Pioneer MissionSupport Area a t Pasadena to th e Pioneer Mission Analysis Areaa t the Ames Research Center , Mountain View, Cal i f . Contro l

o f Pioneer i s a t th e J e t propuls ion Laboratory (JPL) in Pasadenadur ing c r i t i c a l phases o f the mission because of the g r ea t e rcomputer and di sp lay capab i l i ty the re and th e SFOF's ab i l i t yto support many systems ana lys t s .

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- 11 -

Asteroid TraverseAt about four months a f t e r launch, Pioneer Jup i t e r w i l len t e r the As te ro id Bel t and begin at tempts to observe l i g h tsca t t e red by as te ro id mate r i a l with th e four on-boardt e l e scopes .The number of smal l pa r t i c l e s in th e b e l t i s uncer ta inby seve ra l orders o f magnitude. Determining t h i s number i s ,in f a c t one of th e key ob jec t ives . Emergency procedures w i l lbe developed and p r ac t i c e s fo r poss ib l e subsystem malfunct ionsdue to impact of a high-ve loc i ty - - around ~ 8 , 3 0 0 km/hr(30,000 mph) - - dus t p a r t i c l e .During ear ly par t s of the miss ion , command, t r ack ing , andda ta r e tu rn w i l l be pr imar i ly by the DSN's 26-meter (8S-foot)antennas loca ted a t 120 degree i n t e rv a l s around the Ear th a tGoldstone, Cal i f . ; Johannesburg, South Africa ; and Canberra ,Aus t ra l i a . At g r ea t e r ranges from Ear th , th e 64-meter (210-foot)

dish anter inaGat Golds tone w i l l t rack th e spacecra f t . In mid-1973,when the tw o l a rqe overseas dishes become opera t iona l , these w i l lalso be used. The highly sens i t ive 64-meter dishes w i l l also beused fo r c r i t i c a l maneuvers, such as midcourse ve loc i ty co r rec t ions

At Jup i t e r d is tance , th e 26-meter dish antennas w i l l beable to rece ive 64 da ta b i t s p e r second (bps) , th e 64-meterdishes 1,024 bps.

At about 300 days from l aunch , th e spacecra f t w i l l passalmost d i r e c t ly behind th e Sun, caus ing communication d i f f i c u l t i e sfo r a few days because of the Sun's rad io no i se .A year of t r a ck ing may show need fo r a fu r the r smal lve loc i ty change to a l t e r f lyby po in t s l i gh t l y , o r change a r r i v a lt ime by a few minutes .

Facto rs in Plane t EncounterHalfway to Jup i t e r (31S to 400 days) , de ta i l ed planningfo r th e week-long f lyby w i l l begin . J u p i t e r ' s r ad i a t i o n b e l t s ,perhaps a mil l ion t imes s t ronge r than Ear th ' s b e l t s , pre sen t ase r ious hazard . Most fu ture oute r p lane t missions w i l l beshaped by t h i s problem of J u p i t e r ' s rad ia t ion be l t s - - missionsto Ju p i t e r and also those us ing J u p i t e r ' s grav i ty and o r b i t a l

speed to inc rease ve loc i ty fo r t r i p s to p lane t s f a r t h e r out .Mission planners must know how c lose they can sa fe ly approachth e g ian t p lane t and what rad ia t ion hazard they w i l l have top ro t e c t aga ins t .- more -


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SOLAR SYSTEMESCAPE

TRAJECTORY

------- - 4 -

PIONEER FIG ENCOUNTER WITH JUPITER

MAGNETIC FIELD LINES

o TO EARTHPIONEER

TRACK

EXPERIMENT MEASUREMENTS(III MAGNETOSPHERE BOUNDARY(III TRAPPED RADIATION(III MAGNETIC FIELD

(III IONOSPHERE(III ATMOSPHERE COMPOSITION

AND MIXING(III CLOUD STRUCTURE

(III THERMAL BALANCE(III HYDROGEN I HELIUM RATiO(III MASS: JUPITER I MOONS

JUPITER ORBIT

ASSUMED U M IT OFJUPITER'S DISTURBANCEIN THEINTERPLANETARY MEDIUM

NATIONAL AfItOtUUTIC$ ANO Y'AQ ~ I " I A ' 1 I O f I IAMI, I,,"UICH CINTIII M() f f f f t 'taD (AU'OIINU\


17/88

- 12 -

It i s planned t h a t Pioneer F wi l l f ly through the be l t sa t one J up i t e r diameter , 140,000 ki lometers (87,000 miles)from the p la ne t ' s v i s ib l e surface . High energy protons(hydrogen nuc le i ) and e lec t rons in the be l t s could pene t ra tethe spacecra f t and 4egrade the funct ioning of v i t a l t r a ns i s to r sor c i rcu i t ry . Mission con t ro l l e rs may have to opera te acr ippled spacecra f t a f t e r f l i g h t through J u p i t e r ' s rad ia t ionbe l t s ; or spacecra f t da ta t ransmiss ion could be cu t o ffe n t i r e ly and the mission t e rmina ted a t J up i t e r , but determin-at ion of the sever i ty of th e hazard i s one of Pioneer ' sob jec t ives .

A minor hazard i s Jup i t e r ' s massive radio emiss ionsJwhich may i n t e r f e r e with Pioneer ' s radio s igna l s a t t imesbut do no permanent damage to th e equipment.

Test s of the spacecra f t in magnetic f i e lds higher thanJup i t e r ' s have shown s l i g h t e f f e c t s bu t no se r ious problems.J u p i t e r ' s la rge e lec t r i c f i e lds are no t expected to a f f e c tthe spacecra f t .Because Jup i t e r ' s grav i ty w i l l a l t e r spacecra f t course ,

the ac tu a l f lyby w i l l be a wide loop around the p lan e t . Thespacecra f t w i l l approach from the p la ne t ' s s u n l i t s ide , thenswing almost completely around i t s dark s ide . Plane tro ta t ion as ide , Pioneer F w i l l pass over about two t h i rds ofJ u p i t e r ' s v i s ib l e surface a t var ious a l t i t udes .It w i l l approach J up i t e r in a counterclockwise d i rec t ion(looking down a t the North Pole) . I t s path on the p la ne t ' ssurface w i l l pass over p a r t of Jup i t e r ' s southern hemisphere ,

cross the equa tor a t an angle of 14 degrees , and e x i t overthe nor thern hemisphere.Targe t ing

The t a rge t p o in t a t Ju p i t e r has been se lec ted so t h a t thespacecra f t w i l l achieve: a good survey of J u p i t e r ' s s t rongmagnetic f i e ld and i t s in tense rad ia t ion be l t ; good viewangles for the ins t ruments t ha t look a t the p lane t ; and a shor tpassage behind the p lane t .Other t a rge t ing cons ide ra t ions are to have a pos t -encoun tert r a jec tory resu l t ing in so l a r system escape, to pass c lose toone of Jup i t e r ' s moons, and to avoid b io lo g i ca l contaminat ion.A bas ic f lyby f ac to r i s to have s imultaneous t rackingfrom two Ear th s t a t i ons during the c r i t i c a l f ive hours beforeper i aps i s ( c loses t approach).

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Experimenters would, in add i t ion , l i ke to have one of theJovian moons pass between th e spacecra f t and Earth to use. e f f e c t son th e spacecra f t radio s igna l to look fo r an atmosphere ont h a t moon. They also would l i ke to view the Grea t Red Spotand the shadow o f a moon on J u p i t e r ' s surface to measuret empera tu res .

Not a l l of these secondary opt ions can be taken dur ingone f lyby. Which ones w i l l be se lec ted w i l l be determineda f t e r launch by f lyby t iming , spacecra f t hea l th , and s c i e n t i f i ci n t e r e s t .Flyby Operat ions

At seve ra l weeks before p e r i a p s i s , miss ion con t ro l w i l lmove back to th e Pioneer Mission Supp ort Area, Pasadena.The g r ea t e r DSN c a pa b i l i t i e s w i l l be es p ec i a l l y needed

to handle th e increased volume o f spacecra f t command andana lys i s a c t i v i t y . Because communication t ime to Ju p i t e r w i l lbe around 45 minutes , commands must be prec i se ly t imed inadvance fo r performance a t a pa r t i c u l a r po in t over th e p lane t .Five commands can be s tored in advance on th e spacecra f t .Ten days before p e r i a p s i s , c o n t ro l l e r s w i l l command af i n a l Conscan maneuver to es tab l i sh a prec i se spacecra f ta t t i t ude fo r the f lyby . Biases may be inc luded fo r observede f f e c t s o f Jovian grav i ty and th e p la ne t ' s magnetic f i e l d ,which could cause d r i f t in spacecra f t a t t i t ude . Afte r t h i sthe re w i l l be no fu r the r th rus t ing by th e spacecra f t enginesbecause these might i nva l ida te severa l of the s c i e n t i f i cmeasurements made near Ju p i t e r .As th e spacecra f t i s sucked in by th e g ian t p la ne t ' sgrav i ty , i t s ve loc i ty r e l a t i ve to Ju p i t e r w i l l inc rease in20 days from an approach speed o f 33,000 km/hr (20,000 mph)to 126,000 km/hr (78,000 mph) a t peria .ps is .Tracking s t a t i ons w i l l prepare to handle e f f e c t s o f t h i sfour- fo ld inc rease in speed on th e two-way Doppler measurementsused to t rack th e spacecra f t . Doppler s h i f t w i l l grow veryl a rge , and t h i s w i l l be complicated by loss o f communicationwhen th e spacecra f t passes behind th e p lane t a f t e r p e r i a p s i s .Exper imenters w i l l c a l ib r a t e t he i r ins t ruments beforef lyby, and w i l l change sens i t i v i t y ranges of the high energyp a r t i c l e , so l a r wind and magnetic f i e ld ins t ruments fo r th efa r more i n t ense phenomena a t th e p lane t .

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19/88

- 14 -These experiments w i l l then look fo r th e f i r s t J u p i t e re f f e c t s , the bow shock wave in th e so l a r wind , J u p i t e r ' smagnetic f i e ld , and Jovian e f f e c t s on s t reams o f highenergy so l a r p a r t i c l e s .For the f lyby i t s e l f , Pioneer F w i l l be c lose toJu p i t e r fo r about four days (100 hours) with dis tance

from J u p i t e r ' s cloud tops a t per iaps i s 140,000 ki lometers(87,000 miles ) . At 50 hours before p e r i a p s i s , Pioneerins t ruments w i l l see th e p lane t in a lmost ' fu l l s u n l ig h t .A t 40 minutes before per i aps i s , Jup i t e r w i l l be h a l f dark ,and a t per iaps i s i t s e l f about 60 pe rcen t o f Ju p i t e r w i l l bedark . Afte r p e r i a p s i s , the spacec ra f t w i l l con t inue to seel e s s than a ha l f -phase Ju p i t e r .

The imaging photopolar imeter w i l l have begun makingp o la r i z a t i o n and i n t e ns i t y measurements o f J u p i t e r ' s re f l ec tedl i g h t s e v e ra l weeks ou t from th e p lane t . Sta r t ing a t about20 hours , 1 .3 mil l ion ki lometers (800,000 miles ) , fromp e r i a p s i s , the ins t rument w i l l begin to a l t e rn a t e thesemeasurements ltd th the t ak ing o f images. The p o la r i z a t i o n andi n t e ns i t y measurements w i l l provide c lues on the phys ica lproper t i e s o f J u p i t e r ' s clouds and atmosphere.The u l t r a v i o l e t photometer w i l l examine Jup i t e r ' s upperatmosphere fo r hydrogen/hel ium r a t i o , atmosphere mixing r a t e ,

t empera tu re , and fo r evidence o f an aurora l oval near thepoles on th e p la ne t ' s day s id e . It w i l l have a two-hourviewing period 30 hours b e fo re p e r i ap s i s and a second twohours o f observa t ion between 26 and e ig h t hours from p e r i a p s i s .The in f ra red rad iometer w i l l look fo r Jovian r ad i a t i o n

from an i n t e rn a l hea t source, h o t spo t s in th e oute r atmosphere , and cold spo t s a t the polep ind ica t ing i cecaps o ff rozen methane. It w i l l measure the a tmosphere ' s hydrogen/hel ium r a t i o . I t s observa t ion per iod w i l l be the l a s t 80 to90 minutes leading up to p e r i a p s i s . Throughout i t s observa t ions ,it w i l l have a good view o f the boundary between l i g h t anddark ( the t e rmina to r ) .Beyond Ju p i t e r

As th e spacecra f t passes behind the p lan e t fo r an hourand re -emerges , ground s t a t i o n s w i l l record d i f fus ion e f f e c t son its radio s igna l s to ca l cu l a t e the dens i ty and composi t iono f J u p i t e r ' s atmosphere.

Afte r p e r i a p s i s , so l a r wind , p a r t i c l e , and magnetometerexperiments w i l l look fo r p l ane ta ry e f f e c t s on th e in te rp lane ta rymedium behind th e p lan e t . Going away from the p lan e t , th e p o l a r i meter w i l l con t inue to measure c h a ra c t e r i s t i c s o f sun l igh tsca t t e red by J u p i t e r ' s atmosphere.- more -


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- 15 -

After th e p lane t encounter , Pioneer w i l l r e tu rn to i t sin te rp lane ta ry c ru i se mode o f opera t ion .The bas i c Pioneer F miss ion i s defined to l a s t throughencounter and about three months t he r e a f t e r . (The cos t s ofabout $100 mil l ion cover only t h i s bas i c miss ion . ) Although

th e spacecra f t has been des igned fo r th e bas ic miss ion , it i sn ot poss ib l e to p re d i c t exac t ly how long it w i l l cont inue tofunct ion a f t e r encounter . Besides the unce r t a in ty of thepar t i c l e and r ad i a t i o n damage, th e bas ic l i f e expectancy o fth e p a r t s and the exac t r a t e o f power system degradat ion area lso no t known fo r su re . Another var iab le i s th e amount o freo r i en ta t ion and ve loc i ty adjus tment maneuvers t h a t w i l l beneeded.

Due to the swingby e f fec t , Jup i t e r ' s grav i ty and o r b i t a lve loc i ty w i l l have speeded up th e spacec ra f t to s o l a r systemescape speed, and w i l l have ben t th e spacecra f t t r a j e c t o ryinward toward J u p i t e r ' s o r b i t a l pa th . Cruise ve loc i tyr e l a t i ve to th e Sun (not th e plane t ) of 38,500 km/hr (24,000mph) w i l l have increased to 79,200 km/hr (49,320 mph).

Although Pionee f ' s ob jec t ive i s to make measurements ofJ u p i t e r , it i s poss ib l e t h a t sdme "bonus" da ta w i l l be obtaineda f t e r l eaVing th e p lane t .The most i n t e r e s t i ng exper imenta l ques t ions beyond Ju p i t e rw i l l be: What i s th e f lux o f g a l a c t i c cosmic rays and th ed i s t r i bu t ion o f n eu t r a l hydrogen, non-solar -wind plasmas andi n t e r s t e l l a r hydrogen and helium? What do these t e l l aboutth e i n t e r s t e l l a r space beyond tne boundary o f the he l iosphere

(the Sun ' s atmosphere)?Of equal i n t e r e s t w i l l be the search fo r the he l iosphereboundary i t s e l f , "where th e so l a r wind s tops blowing" andi n t e r s t e l l a r space begins . The p l a s m a ~ magnet ic f i e l d , highenergy p a r t i c l e , and u l t r av i o l e t photometer experiments w i l lshare these tw o searches .During t h i s pos t -encoun ter pe r iod , communicat ions dis tancew i l l grow s t ead i ly longer . Incoming s igna l s w i l l become almosti n f i n i t e s i m a l and th e t ime requi red to command th e spacecra f tand g e t a response w i l l lengthen to hours .Only th e most in tens ive and soph is t i ca ted e f fo r t s by theDeep Space Network w i l l al low communication with th e spacec ra f ta t a l l as it pene t ra tes f a r o ut beyond any areas prev ious lyexplored d i r e c t ly by man and h is machines.

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Th e spacec ra f t w i l l cross the o r b i t of Saturn a t about 1 .5b i l l i on ki lometers (950 mil l ion miles ) from the Sun, aboutf ive years a f t e r l aunch , and w i l l cross Uranus' o r b i t a t about2 .9 bil , l ion ki lometers (1.8 b i l l i o n miles ) from th e Sun e i g h tyears a f t e r launch - - bu t c o ~ u n i c a t i o n w i l l no t be possib lea t t h i s gre a t d is tance . .

Pioneer w i l l then cont inue i n to i n t e r s t e l l a r space . Sixyears a f t e r J up i t e r encounte r , a t around 3 .2 b i l l i on ki lomete rs(two b i l l i o n miles ) , th e spacec ra f t f l i gh t pa th w i l l havecurved 87 degrees fu r the r around the $un than th e J up i t e rf lyby po in t . I t s ve loc i ty r e l a t ive to the Sun a t t h i s po in tw i l l be 53,300 km/hr (33,100 mph). From then on, i t s f l i gh tpa th w i l l curve still f a r t he r around the Sun, another 25degrees . At t h i s po in t , fa r out in i n t e r s t e l l a r space it wi l lproceed away from th e Sun in es s en t i a l l y a s t r a igh t l i ne , andi t s veloc i ty w i l l have dropped to a permanent 41,400 km/hr(25,700 mph) away from the S u n ~

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THE ASTEROIDS

The as te ro ids t r a v e l around the Sun in e l l i p t i c a l o rb i t sl ike smal l p lane t s . The Astero id Be l t l i e s between theorb i t s of Mars and Ju p i t e r , between di s t ances from th e Sun of270 mil l ion to 555 mil l ion ki lometers (170 mil l ion to 345mil l ion mi le s ) .

The Bel t i s a region roughly 280 mil l ion ki lometers(175 mil l ion miles) wide c i r c l i ng th e Sun and extending about40 mil l ion ki lometers (25 mil l ion miles) above and below th eplane of the Ear th ' s o r b i t .

S c i e n t i s t s be l ieve th e as t e r o id s condensed ind iv idua l lyfrom the p r imord ia l gas cloud which formed th e Sun and p lan e t s ,o r t h a t they are debr i s from th e break up o f a very smal lp lane t . Clear ly , they con ta in impor tan t in fo rmat ion on th eor ig in of the so la r sys tem.

Passage o f Pioneer Ju p i t e r through the Asteroid Be l t w i l lallow the f i r s t survey o f th e dens i ty o f as te ro ids too smal lto be seen by t e l escope and of fragments and dus t in th e Bel t .This w i l l be o f s c i e n t i f i c i n t e r e s t b u t i s even more impor tan tto exp lo ra t ion miss ions . Since the Bel t i s too t h i ck to f lyover or under , a l l o u t e r p lane t miss ions must f ly through it.And assessment , by an ac tua l f l i g h t , of the Be l t ' s hazard tofu tu re spacec ra f t w i l l be th e i r s t cons ide ra t ion .

There i s es t imated to be enough mate r i a l in the B e l t tomake a p lane t with a volume about 1/1000th t ha t of the Ear th .Astronomers have i de n t i f i e d and ca lcu la ted o rb i t s fo r1,776 a s t e ro i d s , and the re may be 50,000 in th e s ize rangefrom th e l a rge s t 770-ki1ometer . (480-mi1e)-diameter Ceres ,down to bodies one mile in diameter .In addi t ion to a s t e ro i d s , th e Bel t i s presumed to con ta inhundreds of thousands of as te ro id fragments , and uncountableb i l l i o n s of dus t pa r t i c l e s ranging down t o mi l l i on ths andb i l l i o n t h s o f a gram. Two zones o f heav ier concen t ra t ionso f fragments and d u s t a re bel i eved to e x i s t a t di s t ances fromthe Sun of 400 and 480 mil l ion ki lometers (250 and 300 mil l ionmi le s ) .While concen t ra t ions and s i ze s o f these smal ler p a r t i c l e sand dus t a re unknown, one es t imate i s t ha t an area as l a rge as

th e uni ted S ta t e s placed in th e Bel t would rece ive impacts bye i g h t pa r t i c l e s with a mass o f one gram o r g r ea t e r every second;o r one pinhead-s ized pa r t i c l e with a mass o f one mil l ion th ofa gram would pass through one square meter every month.

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- 18 -In th e cen te r of the Bel t , a s te ro ids and pa r t i c l e s o rb i tth e Sun a t about 17 ki lometers (10 miles) p er second. ~ r h e s epar t i c l e s would impact th e spacecra f t (which has i t s ownv e lo c i t y i n somewhat th e same d i rec t ion) a t about 48,000 km/hr(about 30,000 mph). In shor t , a s t e ro ida l mater ia l i s t h in ly

spread , bu t pene t ra t ing .

A few as te ro ids s t ray fa r beyond th e Bel t . Hermes cancome within about 350,000 k i l o m e t ~ r s (220,000 miles) of theEar th , o r c lose r than th e Moon. I ca rus , another as te ro idcomes to within nine mil l ion miles of th e Sun.Many meteor i tes which surv ive atmosphere en t ry and landon Earth are be l i eve to be a s t e ro i d a l mate r i a l . These meteor i tesare most ly s tony , bu t some are i ron and some con ta in l a rgeamounts o f carbon.How severe a hazard to Pioneer F does th e As tero id Bel tpose?One study examined th e orb i t s of 1,735 known as te ro idsr e l a t i ve t o t y p i c a l f l i g h t paths o f Pioneer F through th e Bel t .In genera l , about ten as te ro ids came within about 14,959,900ki lometers (9,275,138 miles) of the spacecra f t .The c l o se s t approach was by an as te ro id seven ki lometers(4.4 miles) in d iameter which came within 4,370,000 ki lometers(2,715,000 miles) of the spacecra f t . The l a rge s t as te ro idencountered 23 ki lometers (14.3 miles) in diameter , came noc l o se r than 40 mil l ion ki lometers (25 mil l ion miles ) . Even

if the es t imated number o f " la rge" as t e r o id s in th e Bel t i sinc reased 50 t imes , from 1,700 to 100,000, l ike l ihood of ac lose approach i s i n s ign i f i c a n t .In sh o r t , th e t h r e a t of baseba l l , green pea, o r evenBB-sized as te ro ids i s probably neg l ig ib le . The most se r ioushazard comes from pa r t i c l e s of 1/10 to l / lOOOth o f a grammass. Smaller par t i c l e s a re too smal l to do damage.Meteoroids with a m a ~ s o f l / lOOth gram, which t r a ve l a tabout 54,000 km/hr (33,600 mph) r e l a t i ve to th e spacecra f t

near Ear th , can pene t ra te a s ing le shee t of aluminum onecent imete r th ick . At J up i t e r , these par t i c l e s t r a ve l onlyabout 25,200 km/hr (15,660 mph).Tota l numbers o f par t i c l e s in th e 1/10 to l / lOOOth grams i ze range a re unknown and can only be es t imated . Sp acec ra f tdes igners be l ieve they have given Pioneer F a good sa fe tymargin .

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- 19 -

COMETS

Throughout th e Pioneer F miss io n , cometary pa r t i c l e sp re s e n t some hazard .At Ear th , about h a l f o f cometary pa r t i c l e s t r a v e l ins t reams which fol low th e o r b i t a l paths o f ex i s t i n g o r d i s s i

pated comets . When these s t reams ( the Leonids , th e Perse ids ,e t c . ) i n t e r s e c t Ear th ' s o r b i t , meteor showers r e s u l t as th ep a r t i c l e s burn up in th e atmosphere . Cometary p a r t i c l e s t reamso r b i t the Sun in long oval s . Usua l ly these o rb i t s aret i l t e d out o f the e c l i p t i c by 30 degrees or more.The o t h e r h a l f of th e cometary pa r t i c l e s near th e Earthappear sporad ica l ly .Cometary pa r t i c l e s have average speeds r e l a t i ve to the

s p a c e c ra f t o f 72,000 km/hr (45,000 mph), and a l / lOOth gramcometary p a r t i c l e can pene t ra t e a one cen t ime te r - th i ckaluminum shee t . Thei r speed a t Ju p i t e r w i l l be down to32,400 km/hr (20,000 mph).


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- 20 -

JUPITERWhat We Know

Though many myster ies concerning t h i s b i g , b r i l l i a n tp lan e t remain to be so lved , hundreds o f years o f astronomicalobserva t ions and ana lys i s have provided a s tock o f informa-t i o n . Gal i l eo made th e f i r s t t e lescop ic observa t ions anddiscovered J u p i t e r ' s four l a rg e r moons in 1610.

Seen from Earth , Ju p i t e r i s th e second b r i g h t e s t p lan e t ,and four th br igh te s t ob jec t , in th e sky. It i s 773 mil l ionki lometers (480 mil l ion miles) from th e Sun, and c i r c l e sth e Sun once in j u s t under 12 years . The p lane t has 12moons, the four oute r ones in backward o r b i t from th ed i r e c t i o n most moons go. Two o f th e moons, G a ~ y m e d e andC a l l i s t o , are about th e s i ze o f the p lan e t Mercury. Twoo th e r s , 10 and Europa, are s imi l a r in s ize to the Ear th ' smoon.Ju p i t e r completes a ro ta t ion once every 10 hours , thes hor t e s t day o f any of the nine p lan e t s . Because o f J u p i t e r ' ss i z e , t h i s means t h a t a p o in t a t the equator on i t s v i s ib l esur,face (cloud tops) races along a t 35,400 km/hr (22,000 mph),compared to a speed o f 1600 km/hr (1000 mph) fo r a s imi la rp o in t on Ear th .This t remendous ro t a t i o n a l speed (and f lu id charac te rof the plane t ) makes Ju p i t e r bulge a t i t s equato r . J u p i t e r ' s

po la r diameter o f about 124,000 ki lometers (77,000 miles) i s19,000 ki lometers (11,800 miles) smal le r than i t s eq u a to r i a ldiameter o f about 143,000 ki lometers (88,900 mile s ) .J u p i t e r ' s v i s i b l e surface (cloud top area) i s 62b i l l i on square ki lometers (23.9 b i l l i on square miles ) .The p la ne t ' s grav i ty a t cloud top i s 2.36 t imes t h a t o f Ear th .The mass o f th e p lan e t i s 318 t imes the mass of Ear th .I t s volume i s 1,000 t imes Ea r t h ' s . Because o f th e resu l t inglow dens i ty (one-fourth o f the Ear th ' s o r 1 .3 t imes thedens i ty o f water ) , most sc i en t i s t s are su re t h a t the p lan e ti s made up o f a mixture o f elements s imi l a r to t h a t in the

Sun o r th e pr imord ia l gas cloud which formed th e Sun and p lan e t s .This means the re a re very la rge propor t ions (a t l e a s t th reequa r t e r s ) o f th e l i g h t gases hydrogen and hel ium. Scientist","have i de n t i f i e d hydrogen, deuterium ( the heavy i so tope o fhydrogen) , methane (carbon and hydrogen) , and ammonia(n i t rogen and hydrogen) by spec t roscop ic s tud ies o f J u p i t e r ' sc louds .- more -


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JUPITER'S VISIBLE_ SURFACENORTH POLAR REGION

N I NORTH NORTH NORTH TEMPERATE BELT I NORTH NORTH TEMPERATE ZONENORTH NORTH TEMPERATE BELTNORTH TEMPERATE ZONENORTH TEMPERATE BELTNORTH TROPICAL ZONENORTH EQUATORIAL BELTEQUATORIAL ZONE

EQUATORIAL BANDEQUATORIAL ZONENORTH COMPONENT OF SOUTHEQUATORIAL BELT .

' '---- SOUTH EQUATORIAL BELTr- - SOUTH COMPONENT OF SOUTHEQUATORIAL BELTi I i i _ ~ - - - - SOUTH TROPICAL ZONEGREAT RED SPOT

SOUTH TEMPERATE BELTSOUTH TEMPERATE ZONE

SOUTH SOUTH TEMPERATE BELTSOUTH SOUTH TEMPERATE ZONE

SOUTH POLAR REGIONNATIONAl AERONAUTJCS AND Sf.a ADMlNfSntATlONAMES RESEARCH CfNTU. MOffETT flflO, CAUfOIINlA


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- 21 -

Clouds, Curren t s , and Visua l Appearance . Seen through at e lescope , the l igh ted hemisphere (of J up i t e r (the only oneseen from th e Earth) i s almost c e r t a i n l y a view of the topso f g igan t ic regions o f tower ing mult i -colored clouds .Over a l l , due to i t s ro t a t i o n , the p lan e t i s s t r iped

o r b a n d e d , p a r a l l e l with i t s equa tor , with l a rge dusky,gray regions a t both pole s . Usual ly between the two pola rregions are f ive permanent , b r i g h t salmon-colored s t r i p e s ,known as Zones, and four da rke r , s l a t e -g ray s t r i p e s , knownas Bel ts - - th e South Equator ia l Bel t , fo r example.The p lan e t as a whole changes hue per iod ica l ly , poss ib ly asa r e s u l t o f th e Sunls I I -y e a r ac t i v i t y cyc le s .

The Grea t Red Spot in th e southern hemisphere i sf requent ly b r i g h t r ed , and s ince 1 6 ~ 5 has disappeared complete lyseve ra l t imes . It seems to br ighten and darken a t 3D-yeari n t e rva l s .Sc i e n t i s t s agree t h a t th e cold tops in the Zones areprobably l a rge ly ammonia vapor and c rys t a l s , and the graypola r regions may be condensed-methane. Th e b r i g h t cloudZones have a complete range o f colors from yellow and d e l i c a t egold to red and bronze. Clouds in th e Bel ts range fromgray to blue-gray .In add i t ion to th e Bel ts and Zones, many smal le rf ea tu res - - s t r e a k s , wisps , arches , loops , pa tches , lumps,and spo t s - - can be seen . Most are hundreds o f thousandso f ki lometers i n s i ze .Circu la t ion of these cloud fea tu re s has been ident i f i edin a number of obse rva t ions . The Grea t Equa to r i a l Curren t(The Equa to r i a l Zone) , 20 degrees wide , sweeps around th ep l a n e t 410 km/hr (255 mph) f a s t e r than the cloud regionson e i t h e r s ide o f it, and i s l i ke s imi la r atmospheric j e ts t reams on Ear th . The South Trop ica l c i r c u l a t i n g cu r r en t i sa well-known f ea tu re , as i s a cloud cur ren t which sweepscomplete ly around the Great Red Spot .Many o ther fea tu re s o f the c l rcu la t ion o f th e atmospherehave been observed.When Ju p i t e r passed in f r o n t o f s t a r s in 1953 and again

in 1971, ast ronomers were able to ca lcu la te roughly the molecularweigh t o f i t s upper atmosphere by th e way it re f rac ted thes t a r s ' l i gh t . They found a molecular weight o f around 3.3which means a la rge propor t ion o f hydrogen (molecular weight 2)because a l l o ther e.i.,:;ments a re f a r heav ie r . (Helium i s 4,carbon 12, and ni t rogen 14.)- more -


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- 22 -

Under Jovian grav i ty , a tmospher ic pressure a t th e cloudtops i s ca lcu la ted to be up to ten t imes one atmosphere onE ar t h .

The t r anspa ren t atmosphere above the c louds can beobserved spec t roscop ica l ly and i n po la r i zed l i gh t . It i sbel i eved to be a t l e a s t 60 ki lometers (35 miles) th ick .

S c i e n t i s t s have suggested from c loud- top observa t ionsby t e l escope t h a t th e genera l c i rcu la t ion p a t t e r n o f J u p i t e r ' satmosphere i s l i ke t h a t of Ear th , with c i r c u l a t i o n zonescorresponding to Ear th ' s eq u a to r i a l , t r o p i c a l , s u b - t r o p i ca l ,t ,emperate, subpolar 1 and pola r reg ions . However, Ju p i t e r ISp o l a r reg ions (from an a tmospher ic c i rcu la t ion s tandpoint )appear to begin a t about 26 degree l a t i t ude from the equa to r ,i ns t ead o f a t 60 degrees as on Ear th .Magnetic Fie lds and Radia t ion B el t s . Among th e nine plane t sonly Ju p i t e r and Ear th a re known to have magnetic f ie , lds .Evidence fo r J u p i t e r ' s magnetic f i e ld and r ad i a t i o n be l t scomes from i t s rad io emiss ions . The only phenomenon knownt h a t could produce th e p la ne t ' s dec imet r i c (very highf requency) radio waves i s t rapped e lec t rons gyra t ing aroundth e l i nes o f such a magnet ic f i e ld . When such e lec t ronsapproach the speed o f l i g h t , they emi t radio waves.

Radio emiss ions ind ica te t h a t J u p i t e r ' s magneticf i e ld i s t o r o id a l (doughnut-shaped) with nor th and southpoles l ike th e Ea r t h ' s . It appears around 20 t imes ass t rong as Ear th ' s f i e ld and presumably con ta ins high energypro tons (hydrogen nucle i ) and e lec t rons t rapped from th eso l a r wind. The f i e l d ' s cen te r appears to be near thep la ne t ' s ax i s o f ro ta t ion and south of the eq u a to r i a lplane . Jup i t e r s' powerful magnet ic f i e ld can hold more pa r t i c l e st rapped from the so la r wind than can Ea r t h ' s f i e l d , and itcan inc rease pa r t i c l e ene rg ie s . As a r e s u l t , p a r t i c l econcen t ra t ions and energ ies could be up to a mil l ion t imeshigher than fo r Ea r t h ' s r ad i a t i o n b e l t s , a f lux o f a b i l l i o npa r t i c l e s o r more pe r square cen t imeter p e r sedond.

Because Ju p i t e r has such high grav i ty and i s so cold a tth e top o f i t s a tmosphere , the t r a ns i t i on reg ion betweendense atmosphere and vacuum i s very nar row. As a r e s u l t , ther ad i a t i o n be l t s may come much c lose r to th e p lan e t than fo rEar th .

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- 23 -

Jovian Radio Signa ls . Earth rece ives more radio noise fromJ up i t e r than from any source except the Sun. J up i t e rbroadcas t s three kinds o f radio noise : (1 ) the rmal fromthe temperature- induced motions of th e molecules in itsatmosphere ( typ ica l wavelength, 3 cent imeters ) ; (2 ) dec i metr ic (cent imeter range) - - from the grya t ions o f e lec t ronsaround the l i nes o f force of the p la ne t ' s magnetic f i e ld( typ ica l wavelength 3-70 cen t ime te r s ) ; and (3) decametr ic(up to lOs of meters) - - be l ieved from huge discharges ofe l e c t r i c i t y ( l ike l igh tn ing f lashes) in J u p i t e r ' s ionosphere(wavelength 70 cent imete rs to 60 meters ) .

The powerful decametr ic radio waves or ig ina te a tknown longi tudes and have been shown to be r e l a t e d topassages of Jup i t e r ' s c lose moon, Io , whose o r b i t i s2.5 p lan e t diameters , 350,000 ki lometers (about 218,000miles ) , above the tops of J u p i t e r ' s cloud l aye r . Somesc i en t i s t s bel ieve t ha t conduc t iv i ty of Io i s s u f f i c i e n tt o l ink up magnetic l i nes o f force to the p la ne t ' s ionosphere , al lowing huge e l e c t r i c a l discharges o f b u i l t upe l e c t r i c a l po te n t i a l .

The power of these r egu la r decametr ic radio burs t si s equa l to the power o f severa l hydrogen bombs. Thei raverage peak value i s 10,000 t imes grea te r than the powero f Jup i t e r ' s dec imet r ic s igna l s .Temperature. The average temperature a t the tops of Jup i t e r ' sclouds appears to be about -145 degrees C. (-229 degrees F . ) ,based on many observa t ions of J u p i t e r ' s i n f ra red rad ia t ion .But r ecen t s t e l l a r occu l ta t ion s tud ies i nd ica te t ha t mucho f the d i f fuse ou te r atmosphere i s c lose to room t empera ture ,and t h a t the top l ay e r i s a t about 20 degrees C. (68 degrees F.) .Only about 1/27th as much hea t from the Sun a r r ives a t Jupi te r .as a r r ives a t Earth . Recent i n f ra red measurements madefrom high a l t i t ude a i r c r a f t sugges t t h a t the g ian t p lane trad ia t es about 2.5 to three t imes more energy than itabsorbs from th e sun. The quest ion i s , what i s th e sourceof t h i s energy? The shadows o f Jup i t e r ' s moons on th ep l an e t appear to measure ho t t e r than surrounding s u n l i tregions .

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- 24 -

Ju p i t e r UnknownsSc ie n t i s t s are reasonably su re o f most o f th e precedingphenomena and observa t ions , though it w i l l be impor tant tocheck them a t c lose range with Pioneer F. They have few

explana t ions o f these observed phenomena, and they knowvery little about other aspec ts of the p lan e t . What i shidden under th e heavy Jovian clouds? How i n t ense are th erad ia t ion be l t s? Most o f the s ta tements which follow ares c i e n t i f i c guesses o r very genera l approximat ions .Life . Perhaps th e most i n t r igu ing unknown i s th e poss ib l epresence o f l i f e in J u p i t e r ' s atmosphere .

Est imates o f the depth o f th e Jovian atmosphere beneathth e cloud l ayer vary from 100 to 6,000 ki lometers (60 to3,600 miles ) . The composi t ions and i n t e rac t ions of the gasesmaking up the atmosphere are unknown. I f th e atmosphere i sdeep, it must a lso be dense . By one es t imate , with anatmospheric depth o f 4,200 ki lometers (2,600 miles ) , p res -sure a t the Jovian "sur face" would be 200,000 t imes Ear th ' satmospher ic pressure due to the t o t a l weight o f gas in thehigh Jovian grav i ty . One source c i t e s e ig h t d i f f e r e n tproposed models o f J u p i t e r ' s atmosphere.However, s c i e n t i s t s do appear to agree on the presenceo f l i qu id water drople ts in the atmosphere. Since the p lane ti s be l ieved to have a mixture o f elements s imi la r to t h a tfound in the Sun, it i s a lmos t sure to have abundant oxygen,And most o f t h i s oxygen has probably combined with th e .

abundant Jovian hydrogen as water .I f l a rge reg ions of J u p i t e r ' s atmosphere come c loseto room temperature , both l i qu id water and water ic e shouldbe presen t .J u p i t e r ' s atmosphere con ta ins ammonia, methane, andhydrogen. These cons t i tuen t s , along with water , a re thechemical i ng red ien t s o f the pr imord ia l "soup" be l ieved tohave produced th e f i r s t l i f e on Earth by chemical evo lu t ion .

On t h i s evidence, Ju p i t e r could contain the bui ld ing blockso f l i f e .- more -


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- 25 -

Some sc i en t i s t s sugges t t ha t the p lane t may be l i ke ahuge fac tory turning out vas t amounts o f l i f e - suppor t ingchemica ls (complex carbon-based compounds) from these rawmater ia l s , using i t s own i n t e rn a l energy. I f so , l i f e coulde x i s t withou t pho tosyn thes i s . Any so l a r photosynthes iswould have to be a t a very low l ev e l s ince Ju p i t e r rece ivesonly 1/27 th of Ear th ' s so l a r energy. It would probably below energy l i f e forms a t most (p lants and microorganisms) becausethe re i s be l ieved to be no f ree oxygen. Life forms would f l o a to r swim because a so l id su r face , if any, would be deep withinJu p i t e r a t very high pre ssure s .

P lane t St ruc tu re . While the re are wide di f fe rences amongs c i e n t i s t s on p lan e t s t ru c t u re , most proposed models containelements l i ke the fo l lowing:Going down, it i s bel i eved t h a t temperature r i s e ss t e a d i l y . The cloud tops may c o n s i s t of super -co ld ammonia

c r y s t a l s , under la id by a l ayer of ammonia drop le t s , underwhich may be a region o f anunonia vapor . Below t h i s may bel ayer s of ic e c r y s t a l s , water d r o p l e t s , and water vapor .Below t h i s i s e i t h e r th e plarie:tis s o l id su r face , o r l i qu idhydrogen oceans . S t i l l lower i s a region o f meta l l i chydrogen c rea t ed by high Jovian grav i ty with perhaps acore o f rocky s i l i c a t e s and meta l l i c elements . The coremight be ten t imes th e mass o f the Ear th by one es t ima te .Some t he o r i s t s doubt t h a t the p lane t has any so l idmater ia l a t a l l , b ut i s e n t i r e l l i q u i d . Others proposea gradual th ickening from s lush to more r i g i d mater ia l .Most p lane to log i s t s th ink th e Grea t Red spo t may bea column of gas , the cen te r o f an enormous vor t ex , r i s ingfrom J u p i t e r ' s su r face to the top of the atmosphere. Knownin physics as a Taylor column, such a vor tex would have tobe anchored by a prominent surface f ea tu re , e i the r a highspo t o r huge depress ion . The Red spo t has c i rc l ed thep lane t more than once r e l a t i ve to v i s ib l e cloud fea tu re sin the p as t hundred years .Some sc i en t i s t s suggest t ha t J u p i t e r ' s surface i t s e l fmay be ro ta t ing a t varying r a t e s of speed r e l a t i ve to th ea tmosphere , thus moving th e spo t . The ro ta t ion of the

p la ne t ' s magnetic f i e l d , t racked by th e t iming o f i t s radioemiss ions , i s be l ieved th e b e s t measure o f ro ta t ion r a t eo f th e p lane t .- more -


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UPPERATMOSPHERE

CLOUD TOPS - - - - - - - - - -______AMMONIA CRYSTAlS .z1AMMONIA DROPlETS =- .------=7::fiGAMMONIA VAPOR ------ . ~

ICE CRYSTALSWATER DROPlETSWATER VAPOR

UQUID AND/OR SCUD HYDROGENMETAlUC HYDROGEN

INTERNAL ENERGYSOURCE GRAVITATIONALOR RADIOACTIVEROCKY SIUCATES

METAlliC ELEMENTSMODEL OF JUPITER INTERIOR ",..

tvU1PJ


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A Hot Plane t . Theor i s t s sugges t t h a t J up i t e r i s amost la rgeenough to be a smal l s t a r . Because of measurements of excesshe a t r ad ia ted by the plane t , cur ren t J up i t e r theo r ie sc a l l fo r a r e l a t ive ly hot core , compared with e a r l i e r ideasof a supercold i n t e r i o r .

One hypothes is holds t h a t despi te the f ive b i l l i on yearss ince format ion of the p.lanets, J up i t e r has no t completedi t s gr av i t a t i ona l condensat ion. This continued se t t l i ngtoward the cen ter (as little as one mil l imeter per year)could produce the requi red hea t energy. ' I f the p lane t hasa rocky core , some of the heat ing could ~ e from decay ofr ad ioac t ive ma te r i a l in the core .Magnetic Fie ld . In t e rna l heat a lso could expla in themagnetic f i e ld . A hot core might be a f lu id core . Con-vect ive and r o t a t i ona l motion of e l ec t r i c a l l y conductingf lu ids a t temperatures of 10,000 degrees C (18,000 degrees F)may genera te the f i e l d . Or it could be genera ted by conduct iveatmosphere l aye r s below the clouds which would s tore andl a t e r re l ease energy.

With knowledge of Jup i t e r ' s magnetic f i e ld , s c i en t i s t sshould be able to make in ferences about the p lane t ' sin t e rna l s t r uc tu r e , pa r t i cu l a r l y i t s f lu id component .Moons. Jup i t e r ' s 12 na t u ra l s a t e l l i t e s have some oddcha rac te r i s t i c s . The second moon, 10, appears to be br igh te rfo r 10 minutes a f t e r emerging from Jup i t e r ' s shadow. I fso , the s imples t explanat ion , suppor ted by r ecen t s t e l l a roccul ta t ion observa t ions , i s t h a t 10 has an atmosphere(probably ni t rogen or methane) which "snows out" on thesur face when 10 i s on the co ld , dark s ide and revapor izeswhen back in sunl igh t . 10 also i s d i s t i n c t l y orange inco lo r and has odd r e f l ec t i ng prope r t i e s . Most of the sun-l i g h t reaching the moon ', s sur face i s s t rongly sca t t e redback , making 10 extremely br i gh t . This r e f l e c ~ i o n propertyi s bel ieved to be more pronounced fo r 10 than fo r any o the rknown ob jec t in the s o l a r system.

The inner moons in order of dis tance from the plane tare : t iny Amalthea, diameter 160 ki lometers (100 miles) ,which orb i t s J up i t e r twice a day a t only 1 .5 plane t diameters ,106,000 ki lometers (66,000 miles ) , above the cloud tops ;the four la rge moons 10, Europa, Ganymede, and C al l i s t o ,whose or b i t s l i e between 422,000 ki lometers (262,000 miles tand 1,882,000 ki lometers (1,117,000 miles) from J up i t e r .

Beyond those are the seven t iny ou te r moons. The i nnert h ree of these , Hes t i a , Hera, and Demeter , have orb i t s whichl i e between 11.5 and 11.7 mil l ion ki lometers (7.2 and 7.3mil l ion miles) from Jup i te r .- more -


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Orbi t s o f the four outermost , Andras tea , Pan, Poseidon,and Hades, l i e between 20.7 mil l ion and 23.7 mil l ion k i l o mete+s (12.9 and 14.7 mil l ion miles) o f Ju p i t e r . All a rein re t rograde o r b i t s , moving counter to the usua l d i r ec t i o no f p l a n e t r o t a t i o n . This suggests t h a t they may be as t e ro idscap tured by J u p i t e r ' s powerful g ra v i t y . Diameters o f s ix o fthe o u t e r moons range from 15 to 40 ki lometers (9 to 24m i l e s ) , with Hes t i a , the seven th , having a diameter o faround 130 ki lometers (80 miles) .

O r b i t a l per iods o f the four l a rge i n n e r moons rangefrom 1 .7 days ( fo r 10) to 16.7 days. O r b i t a l per iods o fth e i n n e r t h ree o f the o u t e r seven moons a re around 250 days.While th e four f a r t h e s t -o u t , backward-orb i t ing moonscomplete t h e i r c i r c u i t s o f Ju p i t e r in around 700 days .

The backward o r b i t o f th e f a r o u t e r moon, Poseidon,i s high ly i nc l ined to the equato r , and wanders so much dueto var ious g r av i t a t i o n a l p u l l s t h a t ast ronomers have ad i f f i c u l t t ime f ind ing it.

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THE HELIOSPHERE

Pioneer F may explore much o f the he l iosphe re , th eatmosphere o f the Sun crea ted by the gases f lowing outwardfrom th e so l a r sur face . Th e spacecra f t may survey a regiono f space 2.4 b i l l i on ki lometers (1.5 b i l l i on miles) widebetween the orb i t s o f Earth and Uranus. It has a goadchance o f l ea rn ing something about the i n t e r s t e l l a r spaceou ts ide the he l iosphere .The t h in ly dif fused s o l a r atmosphere i s hundreds oft imes l e s s dense than the b e s t vacuums on Ear th . Yet iti s impor tant . The ion ized gas known as th e so l a r wind,a 50-50 mixture of protons (hydrogen nuc le i ) and e l ec t r o n s ,f lows o u t from the 3,600,000 degree F (2,000,000 degree C)corona o f the Sun in a l l d i r ec t i o n s a t average speeds of

1 .6 I? i l l ion km/hr (one mil l ion JP,ph). Sola r cosmic rayswhich a re high energy pa r t i c l e s thrown o ut by th e hugeexplos ions on the Sun ' s ro t a t i o n . It conta ins complex e l e c t r i cf i e lds .The s o l a r wind i n ~ e r a c t s with i t s e l f through c o l l i s i o n so f i nd iv idua l s o l a r wind s t reams. It i n t e r a c t s with so l a rand g a l a c t i c cosmic ray p a r t i c l e s , and with the p lane t s ,t h e i r atmospheres , magnetic f i e l d s , and s a t e l l i t e s .

Where does th e so l a r wind s top blowing? Where i s theboundary between th e s o l a r atmosphere and th e i n t e r s t e l l a rgas? Est imates from 300 mil l ion to 16 b i l l i onki lometers (200 mil l ion to 10 b i l l i on miles) from the Sun.In addi t ion to the p lane t s , moons, a s t e ro i d s , comets

and d u s t , the he l iosphere i s t raversed by e lec t romagnet icrad ia t ion from the Sun, , radio waves, i n f ra red andu l t r a v i o l e t waves, and v i s ib l e l i gh t . Ear th ge ts most o fits energy from t h i s rad ia t ion .

In te rp lane ta ry space a l so conta ins cosmic ray pa r t i c l e scoming from elsewhere in the galaxy a t nea r l i g 2 ~ speeds.This means enormous par t i c l e energ ies , up to 10 (1 fol lowedby 20 zeros) e lec t ron vo l t s . There are a l so neu t ra l hydrogenatoms, bel ieved pa r t o f the i n t e r s t e l l a r gas from which theSun and p lane t s formed.The study o f these i n t e r p l an e t a r y phenomena has avar i e ty o f pra c t i c a l e f f e c t s and research app l ica t ions .For example, storms o f so l a r pa r t i c l e s s t r i k ing Earthi n t e r r u p t rad io communications and sometimes e l e c t r i c powert ransmiss ion .

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The he l iosphere can be thought o f as a huge par t i c l ephysics l abora to ry where many phenomena occur t ha t areimpossible to produce and s tudy on Ear th . For example,man i s unable to acce le ra te nuc lear p a r t i c l e s in Earth l abora t o r i e s to the near l i g h t speeds reached by g a l a c t i c cosmicray p a r t i c l e s . These pa r t i c l e s w i l l be s tudied by Pioneerins t ruments .So l a r wind pa r t i c l e s are so t h in ly spread t h a t theyr a r e l y c o l l i d e and only th e magnetic f i e ld and e l e c t r o s t a t i cf i e l d s l ink them t oge the r as a c o l l i s i on l e s s ion ized gas( c o l l i s i o n l e s s plasma). Even though c o l l i s i o n l e s s , theseplasmas t r ansmi t waves o f many kinds because o f t h i s magneticf i e l d l inkage .Knowledge o f these plasmas sheds l i g h t on an a rea o fcu r r en t high i n t e r e s t - - how to contain plasmas in magneticf i e lds . Doing t h i s would allow con t ro l of the hydrogen

thermonuclear r eac t ion cont inuously on a smal l sca le togenera te v i r t ua l l y unl imi ted e l e c t r i c power by a cleanprocess .A ll t h i s involves spec i f i c re l a t ionsh ips such as thef a c t t h a t temperatures o f so l a r wind ions and e lec t ronsnear Ear th a re a lmost the same, while theory pred ic t s t h a tthe e lec t rons should be severa l hundred t imes ho t t e r .How i s energy t rans fe r red between them to equa l ize th et empera tu res? How fa r o u t from th e Sun do these temperaturesremain equal? Why?Knowledge o f plasmas a lso he lps us unders tand suchcosmic phenomena as s t a r format ion .

Sola r Wind, Magnetic F ie ld , and Sola r Cosmic Rays. Nearthe Ear th , the speed o f the so l a r wind var ies from one tothree mil l ion km/hr (600,000 to 2,000,000 mph), depending onac t i v i t y o f the Sun. I t s temperature var ies from 10,000degrees to 1,000,000 degrees C (18,000 to 1,800,000 degrees F ) .Near the Earth , c o l l i s i o n s between s t reams o f th e s o l a rwind use up about 25 pe rcen t o f i t s energy. The wind alsof luc tua tes due to fea tu re s o f the ro t a t i n g so l a r corona,where it o r i g i n a t e s , and because o f various wave phenomena.

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Th e f a s t e s t so l a r cosmic ray pa r t i c l e s j e t o u t fromth e Sun in s t reams which t rave l in near ly s t r a i g h t l i n e s ,cover ing the 150 mil l ion ki lometers (93 mil l ion miles) toth e Earth in as little as 20 minu tes . Slower par t i c l es t reams take one o r more hours to reach Earth and tend tofollow th e curving i n t e r p l an e t a r y magnetic f i e ld .The p o s i t i v e ions are 90 percent pro tons and tenpe rcen t helium nuc le i , with occas iona l mucle i of heav ie relements .There are from none to 20 f l a re events on th e Suneach year which produce high energy s o l a r p a r t i c l e s , with

th e l a rg e s t number of f l a r e s a t the peak o f the I I -y e a rcyc le .Depending on th e e f f e c t of the he l iosphe re , Pioneer Fmay f ind whether the boundary of the so l a r atmosphere( the end o f th e wind) i s a shock wave o r a tu rbu len tregion. It w i l l seek to lea rn if th e s t r u c t u ~ e o f thes o l a r magnetic f i e ld break.s d o w ~ beyond Mars ' orb i t .

Plane ta ry In te rac t ions and Neut ra l Hydrogen. Since Ju p i t e ri s expected to have a magnetic f i e ld l i ke t h a t of Ear th ,a bow shock wave should form in th e so l a r wind i n f r o n t o fth e p lane t . There should be a magnetic envelope around thep lane t , shu t t ing ou t t he . s o l a r wind, and a t r a i l i ng magnetict a i l .Pioneer F ins t ruments should eas i ly charac te r ize

ionized pa r t i c l e s swept from th e atmospheres o f J up i t e r ,i t s Moons, o r th e as te ro ids because t h e i r proper t i e sw i l l grea t ly d i f f e r from those o f pa r t i c l e s o f so l a r o r ig in .

Pioneer w i l l look fo r hel ium, as wel l as neu t ra l hydro-gen. Helium would be p a r t o f th e i n t e r s t e l l a r gas whichhas forced i t s way in to the he l iosphere as th e so l a r systemmoves through it a t 72,000 km/hr (45,000 mph). Hydrogeni s bel i eved to be an i nd i r e c t r e s u l t o f th e c o l l i s i on o fin te rp lane ta ry hydrogen with th e he l iosphe re . Pioneer Fa l so w i l l measure the u l t r a v i o l e t glow o f the i n t e r s t e l l a rgas beyond th e he l iosphere boundary which pene t ra tes thei nne r so l a r system.

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Galac t ic Cosmic Rays. Galac t ic cosmic ray pa r t i c l e s usua l lyhave fa r higher energies (ve loc i t i e s ) than s o l a r cosmicr ays . These pa r t i c l e s may g e t t he i r t remendous energiesfrom the explos ion o f s t a r s (supernovas) , the col lapse ofs t a r s (pu l sa r s ) , o r acce le ra t ion in the co l l id ing magneticf i e lds of tw o s t a r s . Pioneer s tud ies o f these pa r t i c l e smay s e t t l e ques t ions o f t h e i r or ig in in our galaxy andimpor tan t fea tu re s o f the ' o r ig in and evolut ion of the galaxyi t s e l f . These s tud ies should answer such ques t ions as thechemical composi t ion o f s t e l l a r sources o f cosmic raypar t i c l e s in the galaxy.

Near Ear th , numbers of these Galac t ic cosmic raypa r t i c l e s can vary up to 50 percent as so l a r ac t i v i t ypushes them ou t o f th e i nne r s o l a r system a t the peak of theI I -y e a r so l a r cyc le . Par t ic le i n t e n s i t y var ies up to 30pe rcen t due to i nd iv idua l s o l a r f l a r e s . with inc reases ins o l a r a c t i v i t y , th e so l a r wind and magnetic f i e l d push thesepar t i c l e s ou t o f the inner so la r-sys tem.

Galac t ic cosmic rays consis t . o f: protons (hydrogenn u c l e i ) , 85 percent ; helium nuc le i , 13 percent ; nuc le i o fo ther elements , two percent ; and high energy e lec t rons ,one pe rcen t .Pa r t i c l e s raie in energy from 100 mil l ion e lec t ronvo l t s ,(MEV) to 10 MEV.Near Earth ' the average f lux o f these pa r t i c l e s i sfour pe r square cen t imeter p er second, with most pa r t i c l e sin th e 1,000 MEV range. Presumably as th e spacecra f t movestoward th e edge of the blocking so l a r atmosphere, more o fthese medium-energy pa r t i c l e s w i l l be observed.

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- 32 -THE SPACECRAFT

Pioneer Ju p i t e r i s th e f i r s t spacec ra f t designed tot r a v e l in to th e oute r s o l a r system and opera te t h e r e , poss ib lyfo r as long as seven years and as fa r from the Sun as 2 .4b i l l i on ki lometers (1.5 b i l l i on mile s ) .For t h i s miss ion , th e spacec ra f t must have extremer e l i a b i l i t y , be of very l i g h t weigh t , have a communicationssystem fo r extreme d is tances , and employ a non-so la r power

source .The spacec ra f t i s s t a b i l i z e d in space l i ke a gyroscopeby i t s f ive-rpm ro t a t i o n , so t h a t i t s sc i en t i f i c ins t rumentsscan a f u l l c i r c l e f ive t imes a minute . Designers chose spins t a b i l i z a t i on fo r i t s s impl ic i ty and ef fec t iveness .Since the o r b i t planes o f Ear th and Ju p i t e r co inc ide toabout one degree , the spacec ra f t w i l l be in or near Ear th ' s

o r b i t plane ( the e c l ip t i c ) throughout its f l i gh t . To main ta ina known o r i en t a t i o n in t h i s plane , the spacec ra f t sp in axispo in t s cons t an t ly a t Earth . The sp in axis always coincideswith th e cen te r l i ne of the rad io beam, which i s lockedcons tan t ly on Ear th .Spacecraf t nav iga t ion i s handled on Earth by two-wayDoppler t racking and by ang le - t rack ing .For mid-course cor rec t ions , th e Pioneer propuls ion systemcan make changes in ve loc i ty t o t a l i n g 720 km/hr (420 mph).

The spacec ra f t can r e tu rn a maximum o f 2,048 da ta b i t s p e rsecond (bps) to the Ear th , 1,024 bps from Ju p i t e r di s t ance tothe 64-meter (210-foot ) antennas o f the Deep Space Network. Itcan s t o re up to 49,152 da ta b i t s while o t h e r da ta i s beingt r ansmi t t ed .

Pioneer F i s con t ro l l ed l a rge ly from the Ear th r a t h e r thanby sequences of commands s tored in on-board computers.Launch energy requirements to reach Ju p i t e r are fa r higherthan fo r a Mars miss ion , so th e spacec ra f t had to be very l i g h t .Pioneer F weighs only 270 ki lograms (570 pounds). This inc ludes

30 ki lograms (65 pounds) of sc i en t i f i c ins t ruments , and 27ki lograms (60 pounds) o f prope l lan t fo r a t t i t ude changes andmid-course cor rec t ions .Because so l a r energy a t Ju p i t e r i s only four p e rcen t o fenergy received a t the Ear th and grows s t ead i ly weaker beyond

th e p lan e t , des igners se l ec t ed a nuclear power source overso l a r ce l l s .- more -


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RADIOISOTOPE THERMOELECTRICGENERATOR (RTG)RTG DEPLOYME NTDAMPING CABLELOW GAIN ANTENNASEPARATION RING

ASTEROID- METEOROIDDETECTOR SENSOR

THERMAL CONTROLLOUVERSSTELLAR REFERENCEASSEMBLYLIGHT SHIELD

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IMAGING PHOTOPOLARIMETER MAGNETOMETERATTITUDE THRUSTERGEIGER TUBE TELESCOPE

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PLASMA ANALYZERMETEOROID DETECTQ.R SENSOR PANELTRAPPED RADIATION DETECTORHIGH GAIN ANTENNA REFLECTORHIGH GAIN ANTENNA FEED ASSEMBLYMEDIUM GAIN ANTENNA

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- 33 -Th e miss ion ' s 13 experiments a re ca r r i ed ou t by l I on -boa rds c i e n t i f i c ins t ruments . Two exper iments use th e spacecra f t andi t s radio s igna l as ins t ruments .Pioneer Ju p i t e r employs th e r e l i a b l e i n t e rna l systemsproved ou t in th e Pioneer 6 to 9 spacecra f t . A ll four are still

opera t ing i n i n t e r p l an e t a r y space. Pioneer 6 i s in i t s seventhyear . Pioneers 6 to 9 were b u i l t and are operated by th e sameteam which i s carry ing out th e Ju p i t e r miss ions .

For r e l i a b i l i t y , spacecra f t bu i lde r s have employed anin tens ive screen ing and t e s t i ng program fo r par t s and mater ia l s .They have se lec ted components designed to withs tand r ad ia t ionfrom th e sp a c e c ra f t ' s nuclear power source , and from J u p i t e r ' sr ad i a t i o n be l t s . In add i t ion , key systems a re redundant .(That i s , two of th e same component o r subsystem a re providedin case one f a i l s . ) Communications, command and da ta r e tu rnsys tems, propuls ion e l e c t ro n i c s , t h rus t e r s , and a t t i t ude sensorsare redundant .

Vir tua l ly a l l spacecra f t systems r e f l e c t th e need to surviveand r e tu rn da ta for many years a long way from th e Sun and th eEar th .Pioneer F D e s c r i p t ~ o n

The spacecra f t f i t s within th e 3-meter (IO-foot) d iametershroud of the At las-Centaur launch vehic le with booms r e t r a c t e d ,and with i t s dish antenna fac ing forward (upward). Th e Ear th facing di sh antenna i s d e ~ i g n a t e d th e forward end of the spacec r a f t . Pioneer F i s 2.9 meters (9.5 fee t ) long , measuringfrom its f a r the s t forward component, th e medium-gain antennahorn , to i t s f a r the s t rearward po in t , th e t ip of the a f t - f a c i n gornn i -d i rec t iona l antenna. Exclus ive of booms, i t s widestcrosswise dimension i s th e 2.7-meter (9-foot) diameter o f th edish antenna.

Th e ax i s o f spacecra f t ro ta t ion and th e c e n t e r - l i n e o fth e dish antenna a re p a r a l l e l , and Pioneer sp ins cons tan t lyfo r s t a b i l i t y .Th e spacecra f t equipment compartment cons i s t s o f a f l a tbox, top and bottom o f which a re r egu la r hexagons. Thishexagonal box i s roughly 35.5 cm (14 inches) deep and eacho f its s ix s ide s i s 71 cm (28 inches) long. One s ide jo ins

to a smal le r box also 35.5 cm (14 inches) deep, whose top andbottom a re i r r e g u l a r hexagons.

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MAJOR SUBSYSTEMSCD RADIOISOTOPETHERMOELECTRIC MEDIUM-GAINANTENNA

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G) MAGNETOMETER

~ COSMIC RAY TELESCOPE3 INFRARED RADIOMETER4 CHARGED PARTICLE INSTRUMENT TRAPPED RADIATION DETECTOR ULTRAVIOLET PHOTOMETER(j) GEIGER TUBE TELESCOPE IMAGING PHOTOPOLARIMETER PLASMA ANALYZER@ METEOROID DETECTOR SENSOR PANELS ASTEROID-METEOROID DETECTOR SENSOR

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This smal le r compartment conta ins most of th e l I o n - b o a r dsc i en t i f i c exper iments . However, 12.7 kilograms (28 pounds) ofthe 30 ki lograms (65 pounds) of sc i en t i f i c ins t ruments (theplasma ana lyzer , cosmic ray t e lescope , as te ro id-meteoroidt e lescopes , meteoroid sensors , and the magnetometer sensor) aremounted out s ide the ins t rument compartment. The othe r experimentshave openings cu t fo r t h e i r sensors to look out . Together bothcompartments provide 1 .4 square meters (16 square fee t ) o fplat form a rea .

Attached to the hexagonal f r o n t face of the equipmentcompartment i s the 2.7 meter (9-foot) diameter 46-cent imeter(18-inch) deep dish antenna.The high-gain antenna feed and th e medium-gain antennahorn are mounted a t the foca l po in t of the antenna dish onth ree s t ru t s pro jec t ing about 1 .2 meters (4 f ee t ) forward of

the rim of the di sh . The low-gain, omni-di rec t iona l sp i ra lantenna extends about .76 meters (2.5 fee t ) behind the equipment compartment.

Two three- rod t russes , 1200 apar t , p ro j e c t from tw o s idesof the equipment compartment, deploying the spacec ra f t ' snuc lear e lec t r i c power genera tor about 3 meters (10 f e e t fromthe cen te r of the spacecra f t . A t h i rd boom, 120 0 from each ofthe o ther two, pro jec t s from the experiment compartment andpos i t ions th e magnetometer sensor 6.6 meters (21.5 fee t ) fromthe spacecra f t cen te r . The booms are extended a f t e r launch.

At the r im of the antenna d ish , a Sun sensor i s mounted.A s t a r sensor looks through an opening in the equipmentcompartment and i s pro tec t ed from sun l igh t by a hood.Both compartments have aluminum f rames with bottoms ands ide wal l s of aluminum honeycomb. The dish

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