Encounter With Jupiter

8/7/2019 Encounter With Jupiter

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TABLE 1. DISTANCES DURING ENCOUNTER

DATE TIME DISTANCE FROM JUPITER, MILES STAGE OFENCOUNTER

NO V 8 2.26 A.M 14,680,0001 1 10.26 A.M. 12,821.000 1

22 6.26 A.M. 7_084,00025 5,180,0006.26 P.M.27 6.26 P.M. 4,077,000 2

28 6 26 P.M. 3,508,00029 6.26 P.M. 2,923,00030 6.26 P.M. 2,313,000

DEC. 1 6.26 P.M. 1,666,000 32 6.26 P.M. 943,8003 6.26 P.M. 81,000 4

M,259---5 6.26 P M 1,660,0006 6.26 P.M. 2,313,0007 6.26 P.M. 2,922,000 58 6.26 P.M. 3,508,0009 6 26 P.M. 4,076,000

10 6.26 P.M 4,633,0001 1 6.26 P.M 5,180,000

E N C O U N T E R W I T H J U P I T E R

PIONEER TO JUPITER,ENCOUNTER WITH JUPITER

At orecisely 6.26 p.m. PST on December 3,1973, P ioneer 10 will hurtle past Jupiteronly 81,00 0 miles above the cloud tops(Figure One). During the two weeks aroundthat date a team of spacecraft controllers,analysts, and scientists at NASA's Ames Re-

search Center, end personnel of NASA's DeepSpace Network, will run a three-shift, 24-hours-a-day control operation. Constantlyalert to danger to the spacecraft from poss iblebut unpredictable problems due to unknownsin the environment of Jupiter, these menwill send up to 15 ,000 commands to thedistant spacecraft during this period.

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Figure 1. Pioneer flying over the Great RedSpot.

They have been rehearsing their roles formonths now, getting prepared to tackleevery conceivable problem that might ariseto endanger this first mission to Jupiter,giant of tha Solar System.

Their job is complicated by the 92 minutesneeded for signals to reach Jupiter. To saveweight and keep the cost of the spacecraftlow, the Pioneers are controlled by peoplesending commands from Earth rather thanmaking the spacecraft completely automatic.But controllers have to wait an hour-and ahalf from sending a command to knowingthe spacecraft has done what they want it todo. That's the time that radio waves, travel-ing at 186,000 miles per second, take totravel to the spacecraft and back.

Welt in advance of Jupiter encounter, themen at Pioneer control turn on most of thespacecraft's subsystems and scientific instruments. They leave them operating throughout the encounter. If all goes well only a fewroutine spacecraft operations will then needto be commanded, such as checking that thepointing direction is correct so that signalsare directed accurately toward Earth, orchanging, as needed, the precise order inwhich information is returned to Earth. Only5 of the 11 scientific instruments requirecommands. Most commands are to directthe sequence of pictures of Jupiter and itssatellites.

In the months before encounter controllerstest all the backup systems of the spacecraftso that spares carried aboard can be sw itchedon to take over if some equipment fails as thespacecraft encounters the Jovian environment. For example, the radiation beltsmight seriously damage equipment and scien-tific instruments, and charged par t icles mightstick to the spacecraft, especially when it is

in Jupiter 's shadow, and arcing could pro-duce false commands to it.

Also, the mighty gravity of Jupiter couldpull the spacecraft askew on its spin axis.And the spinning of the spacecraft coulditself produce problems, turning the space-craft into an electrical generator as it spins inJupiter's magnetic field.

Finally, Jupiter could possess dust belts in aring around the equator. While this dustwould be invisible from Earth, impact withit could damage the s p acecraf* as it movesthrough the plane of Jupiter's equator justafter closest approach to the planet.

So the men of Pioneer control have to be ontheir toes every second of the encounterperiod, ready to issue correcting commandsto right any problems that might arise.

News from the spacecraft arrives back atEarth on three large antennas-210 footdishes as large a s football fields. One is in theMojave Desert at Goldstone, California. Another is at Madrid, Spain, while the third isnear Canberra, Australia. As the Earth turnson its axis, and the spacecraft with Jupitersets at one of these Earth stations, the space-craft rises at the next station. So signals canbe received 24 hours each day.

And these giant antennas—the last two werecompleted and put into operation while Pio.neer was on its way to Jupiter—can track the

spacecraft to the enormous distance of morethan 1.5 billion miles. Then the signals willtake 4 hours to reach Earth.

THE ENCOUNTER SEQUENCE

Because Jupiter' s gravity bends the spacecraft's course, the actual flyby is a wideloop around the planet. Pioneer 10 approaches from Jupiter's .unl. t side, then

swings almost completely around its darkside. Planet rotation aside, Pioneer 10 fliestwo thirds of the way around Jupiter atvarious distances. During the 48 hours ofclosest approach of Pioneer, Jupiter completes five rotations on its axis.

Pioneer 10 approaches in a counterclockwisedirection—the same direction as Jupiter rotates—as seen from above the planet's northpole. Its path on the planet's surface passesover part of Jupiter's southern hemisphere,crosses the equator at an angle of 14 degreeand leaves the planet over the northernhemisphere.

There are five stages in the two-month Proeer encounter p eriod from November 4,

1973 through January 3, 1974. (See TableOne.) Stage One is the three weeks, Novemb4 through 24, during which the spacecraftpasses from interplanetary space into theouter regions of the Jovian system, movingfrom about 15 million to 6 million milesfrom the planet.

Stage T wo covers en try into the inner systeSometime between November 25 and 29,Pioneer is expected to pass through the bowshock wave in the solar wind created byJupiter's magnetic field and thus enter this

magnetic field, the magnetosphere, of Jupit

Stage Three is that period when Pioneer con-tinues flying through the outer magneto



TABLE 2 . TIMES O F CROSS ING SATELLITE ORBITS

SATELLITE DA TE TIM E DISTANCE FRO M JUPITER, MILES

HADES N O V. 8 2.26 A.M . 14,680,000POSEIDON 8 10.26 A.M. 14,420,000PAN 9 1226 A .M. 13,840,000A N D R A S T E A 1 1 10.26 A.M. 12,821,000

DEM ETER 22 2.26 P.M. 7,231,000H E R A 22 2.26 A.M. 7,243,000HESTIA 22 6 .26 A .M . 7,085,000CALLISTO DEC. 2 12.26 P.M. 1,125,000G A N Y M E D E 3 4.26 A.M. 496,400EUROPA 3 10.26 A .M . 372,5001 0 3 2.26 P.M. 221,300A M A LT H E A 3 6.26 P.M."P IONEER DOES NOT GET CLOSE ENOUGH TO JUPITER TO CRO SS THIS ORBIT

TABLE 3 . SOME IMPORTANT EVENTS

DATE TIME EVENT

NOV. 24 6.26 P .M . ENTER THE BOW SHOCK W AVE (EARLIEST)2 8 6.26 P.M. ENTER JUPITER 'S MAG NETIC FIELD (EARLIEST)

DEC. 3 11.26 P.M. E N T E R C R I T IC A L R E G I O N O F I N T E N S E R A D I AT IO N(RADIATION B ELT)

6.36 P.M. C R O S S E Q U AT O R IA L Z O N E W IT H P O S S I B L E D U S TH A Z A R D

6.41 P.M. GO BEHIND 10 (OCCULTATION)7.4 2 P.M . G O B E HIN D JU PIT ER ( OC C ULTATIO N )8.16 P.M. ENTER INTO JUPITER'S SHADOW

4 12.26 A.M. LEAVE HAR D RADIATION BEH IND1 9 - LEAVE THE BOW SHO CK

JAN. 2 - END OF ENCOUNTER SEQUENCE

TABLE 4 . SOME EXPERIMENTS '

DATE TIME EVENT

N O V. 3 0 2.26 P.M. FIRST ULTRAV IOLET LOOK ATJUPITERDEC. 2 7.05 A.M. INFRARE D LOOK AT CA LLISTO

3 3.17 A.M. IN F R A R E D L O O K AT G A N Y M E D E8 .40 A .M . SE C O N D U LTR A VIO LE T LO O K AT JU PITE R

11.08 A.M. INFRARED LOOK AT EUROPA12.38 P.M. IN F R A R E D L O O K AT 1 0

3.45 P .M . LO O K AT TH E G REAT RED SPO T4.18 P .M . IN FR ARED INSPECTIO N O F JUPITER6.14 P.M. IN F R A R E D L O O K A T A M A LT H E A

phere from about 3 to 2 million m iles fromhe planet dur ing Novem ber 30 through

December 2.tage Four is the period of closest approach.t covers the last day and a half (38 hou rs)efore closest approach of 81,00 0 miles on

Decem ber 3. Here is where the spacecraftmakes its most important measurements andlies by the big inner satellites. It takes hun-reds of pictures and flies through the radia-on belts.

tage Five takes place as Pioneer flies awayrom Jupiter and repeats many of theearliere q u e n c e s i n re v e r s e o r d e r.

On Novem ber 8 , dur ing Stage One of thenco unter, Pioneer 10 crosses the o bit of

Ha des, outermost sa tellite of ,Jupiter (TableTw o). In the next few days i t succe ssivelycrosses the orbits of Pan and Andrastea. ByNovem ber 11 Pioneer crosses the orbit ofDem eter a t 7 mi l lion miles f rom Jupi ter,then Hera and Hestia. But the Jovian systemi s so big that despi te the high speed ofPionee r it is not until Dec em ber 3, the dayof closest approach, that Pioneer crosses theorbits of the inner satellites. It com es w ithin865 ,200 miles of Callisto, which is as large as

the planet Mercury. Next is close approachto Ganym ede ( la rger than M ercury) o f2 7 7 , 3 0 0 m ile s , t h e n t o w i th in 1 9 9 , 4 7 0miles of Europa (size of Earth's Mo on), and221 ,840 m i les o f to ( la rge r than M oon) .Pioneer approaches to 11,470 miles of the

orbit of the innerm ost satel l ite Abut does not cross it.

First evidence a t the spacec raft ofpresence may com e on NovembStage Tw o of the encou nter beginthe earliest date for passage throughshockwave created as the solar wind planet's magnetic field (see T able Thearliest date for entering Jupiter's mf ield is Novem ber 29 . Studies of

can tell us about Jupiter's interior about the in tense radio s ignals fplanet.

Th e f irs t u l t raviole t inspe ct ion os tarts on N ovember 30 and cont i38 ho urs, examining Jupiter 's uppsphere to determine proportions of and helium there. Also the instrulook for polar glows o r auroras (SFour).

A second viewing period, beginninbefore closest approac h, lasts for fBut the ear ly v iew m ay be m ost because closeness to Jupiter may binstrument with too much radiatio

Infrared inspec tion begins 18 houclosest approach to measure temperf irst L'al lis to, then G anym ede, Eand Am althea. Star t ing 2 hoursminutes before closest approa ch, tment takes tempera ture m easureJupi ter i t se l f, i ts prom inent feacluding the G reat Re d Spo t, andh e m i s p h e r e .Starting on November S an instrumas IPP (short for imaging photopolinspects light reflected from Jupite

mine the na ture of the a tmospherthe clouds as well as the structure position of the cloud layers. This ialso inspec ts the satellites. An d it television ca m era to provide infthat is used to m ake pictures of thand its satellites.

At around six hours before closest Pioneer 10 enters the zone of ha rdknow n as the radiation belts and staing this region to precise ly define ito spacecraft flying close by the gi

Three hours before c loses t approGreat R ed Spot i s probed by a vscientific instrumen ts to gain a be tstanding of this mysterious region.

Closest approach is called periapsip lace a t 6 .26 p .m. PST , on Decwhen Pioneer literally skims acrosstops at 82,000 m iles an hour; perhfaster. Ten minutes afterward Pionethrough the equa torial plane an dcoun ter any dust belt that ma y bethere. An increase in dust concenup to 10 00 t imes that in the interenvironmen t might occur, but hopenough to damage the spacec raft.



TABLE 5. PHOTOGRAPHS (IMAGES) OF JOVIAN OBJECTS

DATE APPROXIMATE NUMBEROF PICTURES OBJECT

JUPITERNOV. 26 1227 26 JUPITERZ9 25 JUPITER

30 20 JUPITERDEC. 1 26 JUPITER2 10

2 23 JUPITER2 10

2 CALLISTO2 GANYMEDE

3 1 8 JUPITER1 1 0

1 EUROPA

4 23 CRESCENT SHAPED JUPITER5 22 JUPITERE 1 6 JUPITER7 3 1 JUPITER8 25 JUPITER

9 38 JUPI1 ER10 20 JUPITER

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At 15 minutes after closest approach, thespacecraft passes behino lo. As it does sorefraction effects bend and weaken the radiosignals from the spacecraft and enable scien-tists to calculate what sort of an atmosphereto possesses. It could be that an electricallycoarged atmesp )ere links up lines of force inJupiter's magnetic field and causes en ormouselectrical discharges in Jupiter's atmosphere

to generate po werful radio signals receivedon Earth from the planet. Pioneer shouldbe able to check if this is true.

An hour after passage behind lo, the space-craft goes behind Jupiter itself for 65minutes. Similar bending and weakening offree electrons in Jupiter's ionosphe re (elec-trified upper atmosphere) and something ofthe density and composition of Jupiter'satmosphere in general. These measurementsare made as the spacecraft both goes behindand em erges from the bulk of Jupiter.

At 2 hours and 51 minutes after closest ap-

proach, Pioneer enters the awesome shadowof the huge planet and remains in darknessfor 51 minutes. On returning intc sunlightPioneer starts to leave the environment ofJupiter and as it heads for the stars of theGalaxy it makes as many similar measure-ments of the Jovian system as when it camein. In the weeks following encounter thespacecraft continues to make m easurementsof the solar wind and of particles and magnetic fields in space. It will try to find outwhat effects Jupiter has on the interplane taryenvironment outside the big planet's orbit.There are several unanswered questions aboutspace beyond Jupiter's orbit that Pioneer

may throw light on. How many and whattypes of cosmic rays come into the SolarSystem from the Galaxy? Wha t is the distri-bution of hydrogen and helium in spac e be-yond Jupiter and where does it originate?Where is the boundary at which the solarwind stops blowing an d interstellar space—the space between the stars—really begins?

Communications may be maintained withPioneer for five years, :hough the missionwas designed for only several months en-counter. As the communications distancebecomes steadily longer, th3 incoming signalswill become incredibly faint. But the link

with Pioneer m ay last until it crosses the orbitof Uranus in 19 79 , then to be lost as the tinyemissary of mankind carries its message ofan intelligent race on Earth into the cosmos.

THE PICTURES OF JUPITER AND ITSSATELLITES

Pictures of Jupiter could be disappointing.Scientists do not know how the equipmentwill stand up to the hostile environment ofthe mighty planet. But if all goes well thepictures .nay provide inspiring views of thebig planet and its planet-sized moons.

Building up pictures of Jupiter and the satel-lites begins on November 5. Early images are

used to test the equipment—then, on Novem -ber 26, the image-making sequence goes to a23 hours-a-day basis. Forty-eight hours be-fore closest approach, the pictures from

Pioneer are expected to oe be tter than anyobtained from Earth with the largest tele-scopes. And by eight hours before encounter,the image of Jupiter fills the field of view ofthe picture m aking system.

There are p lans for more than 300 views ofJupiter and ten of its satellites in the twoweeks period, including some close-ups ofsatellites (s?e Table Five). As Pioneer fliesaround the night side of Jupiter, view anglesimposs ible from Earth are obtained. If the im-aging system withstands the passage throughthe radiation belts spectacular pictures of theclose opproach may reveal features 100 milesacross, of cloud currents and eddies, andprovide new information on features such asthe Great Red Spot. These pictures will bemade available to na tional television as soonas they have been processed by the com-

puters at NASA's Ames Research Center.WHAT TO LOOK OUT FOR

Tele-:ision, radio and newspapers will startcarrying reports on Pioneer's progress abouta month before closest approach. As picturesand results flood back from the Jovian sys-tem, television will give the new s quickly. Aday later newspapers w ill carry more d etailedreports. But for the comp lete story we hsveto wait for weeks or months until sci,;ntistscan analyze the wealth of new informationand w rite interpretive articles for m agazinessuch as Scientific American and ScienceN e v ; A few new spapers will also carry these

detailed science stories, too.

PIONEER 11

From the results of Pioneer 10's flight pastJupiter, project enqineers an d scientists will

decide how Pioneer 11 should be directeits encounter in December, 1974. If Pio1 0isdarr,aged by the environment of Juppart.cularly the radiation and possible dustbelts, Pioneer 11 may be directed to fly byfurther out from the planet. But if Pioneer10 emerge; unscathed, Pioneer 11 migmsent even c loser to further test the radiabelts.

STUDY PRO.ECTS

ONE

Take the various events listed in Tables 1through 5 and make a combined listing ofthe sequential happenings when Pioneerflies through the Jovian system. List the time, what happens, Ind leave a columnremarks about each event.

TWO

Use the list you have made during the encounter. Watch TV, 1^sten to radio, and rthe newspapers to check each event as i

reported. Fill in remarks as to what is dis-

covered. Use this information to check yourstudy projects mad e in connection with ker leaflets of this series. Check your drawor painting of Jupiter !leaflet "?) to see ifyou guessed right what the planet looks Also check and correct your 'unknowns'list of leaflet ==3 .

READING LIST

Watch TV newscasts and special programs

Listen to radio newscasts.Read your local newspaper o r national nmagazines.

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Encounter With Jupiter