project galileo a return to jupiter

8/8/2019 Project Galileo a Return to Jupiter

1/12


2/12


3/12

The Discoverer

he great Italian astronomer Galileo Galileishocked the world in January 1610 when heannounced his discovery of four satellitesorbiting Jupiter. His discovery provided

proof to Nicolaus (_opcrnicus'theory that Earth and the otherplancts orbit the Sun, and Earthis not the center of the universe.Oalilco told the story of hisdiscovery:"On the seventh day of

January in the present year 1610,at the first hour of the night,when [ was viewing the hcavcnlybodies with a telescope, Jupiterpresented itself to me; andbecause I had prepared a veryexcellent instrument for myself, Iperceived (as 1 had not before,on account of the wcakncss ofmy previous instrtm_cnt) thatbeside the planet there wcrethree starlets, small indeed, butvery bright."(ialilco thought those

"starlets" wcrc just more of thefixed stars that his telescopewas allowing him to discoverwith astounding regularity. Butthe next night hc saw theyhad changed position. Thenight after that was cloudy.

Then, on January 10, hc saw onlytwo "starlets," the third havingdisappeared behind Jupiter.On the llth:+'1 had now decided beyond all

qt,cstion that there existed in theheavens three stars wanderingabout Jupiter :is do Mercury and'bnus about the Sun, and thisbecame plainer than daylightfrom observations on similaroccasions that followed."On January 13, 1610, Galileo

spotted the fourth satellite.Although hc nearly paid fi)rhis observations and later

writings with his lift', Galileoremained the most rcspcctcdscientist of his time. _day, thosefour satcllitcs-Io, Europa,Ganymede, and Callisto- arccalled the Galilcan satellite> inhis honor.

1


4/12

The Mission

NASA project to orbit Jupiter and send aninstrumented Probe into the giant planet'satmosphere is under way at the JetPropulsion Laboratory. The mission, called

Project Galileo aftcr the Italianastronomer, will begin an in-depth cxploration of thc Joviansystem: Jupiter, the Galileansatellites, and thc giant, invisiblemagnetosphere surroundingJupiter. Scientists believe thatJupiter is made of the originalmaterial from which starsform, largely unmoditied bynuclear processes. ('.lose- rangestudies of Jupiter should provideimportant information aboutthe beginning and developmentof our solar system and providenew insights into phenomenathat directly relate to ourunderstanding of all the planets.Project Galileo was originally

scheduled for launch in early1982 as the scientific successor tothe Voyager mission to Jupiter.The Galileo Probe was designedto be attached to the Orbiter,and the combination spacecraftwas scheduled to be launched

from an Earth-orbiting SpaceShuttle. The relative positions ofEarth, Mar_, and Jt,pitcr at thattime make it possible to _end aheavy spacecraft to Jupiter viaMars in a relatively short time.Problems in the Space Shuttlcdevelopment, however, havedelayed the Galileo latmch until]984, when Mars will again bc ma useful position, although notas favorable as in 1982.While the 1982 mission

represented a more unifiedtechnical approach, the 1984mission will still permit theoriginal scientific objectives. Butnow two spacecraft will makethe trip: an Orbiter spacecraftand an instrumented Probeflying aboard a Probc-(_arricrspacecraft.


5/12

ThecurrentOrbiter>_imilartothespacecraftesignedorthe 198,2 latmch, but willaccommodate a largcr rocketpropulsitm system for amaneuver at Mars.The Orbiter is scheduled to

bc launched in February 1084 ona trajectory that will send ittoward the planet Mars. Onehundred days after launch, theOrbiter will fly within a fewhundred kilometers of thesurface of Mars. The Orbiterwill use Mars' gravity and a longburn of its own rocket motor toboost it the rest of the way toJupiter.The Orbiter will arrive at

Jupiter in mid-198,6, about oneyear beR)rc the Probe. It willphotograph the region where the[>robe will enter to enst,reachievement of the originalmission's goals. As the Orbiternears its closest approach toJupiter, it will tire its rctrorockctengine for about 50 minutes toslow thc spacecraft and permitcapture by the planet, xX:ithin afew hours of closest approachto Jupiter, the Orbiter will flypast the volcanic satellite, [o,for close scientif ic observation.lo's gravity will further slowthe spacecraft.At that point the spacecraft

will bc orbiting Jupiter in anelliptical path, ranging frommore than 15 million kilometers(9.3 million miles) to 285,000kilometers (178,000 miles) aboveJupiter's cloud tops. Thereafter,the orbit will change through aseries of elliptical paths to take

the spacecraft to all regions ofJupiter's environment. That willbc accomplished by usinta thegravity of thc satellites to bendthc orbit each time the spacecraftcomes close to one of them.Eventually the orbit will be soaltered that the spacecraft'scloscst approach to Jupiter willbe 900,000 kilometers (560,000mile>) above Jupiter's cloud tops.During at least one orbit, the

spacecraft will fly through andstudy Jupiter's magnetotail theportion of thc magnetic regiondirectly opposite thc Sun to adistance of 150 times the radiusof Jupiter, more than 10 millionkilometers (6.2 million miles)from the planet. Observations ofthe magnetotail arc not pos>iblcfrom Earth or with flyby space-craft because the spacecraft passclose to Jupiter, and thcirtrajectories arc too stronglydeflected to reach that region.The Orbiter will complete 11

orbits of Jupiter while makinga close flyby of one (]alilcansatellite-[o, Europa, Ganymede,or Callisto-on each orbit. TheOrbiter, carrying 1 l scicntiticinstruments and weighing about2,660 kilograms (5,864 pounds)at launch, will transmit scicntiticand engineering data at rates upto 115,000 bits per second,kicanwhilc, the Probe will bc

launched one month after theOrbiter, in March 198,4, and willbc transported to Jupiter on aspecial Probe-Carrier spacecraft.Traveling on a longer trajectorythat does not pass Mars, the

3


6/12

GanymedeProbe and its (_arrier will reachJupiter one year later thanthe Orbiter, in the summer of1987. After being released fromthe l'robe-(_arrier spacecraft,the Probe will descend towardJupiter's thick atmosphere.

Scientists want the instrument-laden Probe to enter Jupiter'slight-colored Equatorial Zone,between 1 and 5.5 degrees northor south latitude. They bclicvcthe topmost clouds of thatportion of Jupiter's atmosphereconsist primarily of ammonia.By entering at that location, theProbe should be able to measureJupiter's important cloud laycrs.

As the Probe strikes the upperlayers of Jupiter's atmosphere,it will slow so rapidly that itwill feel the effects of 400 timesEarth's gravity. Once thestrongest deceleration forces havepassed, the Probe will deploy aparachute. The descent modulewill begin to take atmosphcricmeasurements and transmit itsfindings to the Probe-(;arrierspacecraft for relay back toEarth. Forty minutes aftcr entry,scientists expect the Probe toreach an atmospheric density of

about 10 bars (10 times theatmospheric pressure at Earth'ssurfilce), below what are believedto be Jupiter's lowest waterclouds.At the end of 60 minutes, thc

Probe will have penetrated 15 to20 Earth atmospheres. Belowthat, increasing temperature andpressure- and weakening radiosignals-will evt:nt ually bring theProbe mission to an end.Meanwhi le, the Probe-( :arrier

spacecraft will monitor radiosignals from the Probe, pickingup its scientific reformation andrelaying it to Earth. The dataalso will be recorded on theProbe Carrier fi_r later playbackif needed.Once the Probe's work is

done, the mission operationsemphasis will revert to theOrbiter. The primary mission isscheduled to end about 20months after Probe arrival atJupiter.

I0

The Galileo Orbiter willincorporate a new dual-spindesign. Part of the spacecraft willbe three-axis stabilized so thecamera and some other instru-ments can be accurately andsteadily pointed. The otherportion will spin so itsinstruments can sweep Otlt spaceto make thcir measurements.Since Jupiter is too fitr from theSun for solar cells to provideelectric power, the Orbiter willuse radioisotope thermoelectricgenerators similar to those flownon the two Voyager spacecraft.

Callist_4


7/12

w . ... ... .. ... .. ... .. ._'_i_=r'_m_--_''_'_'_--_J_--z_ _ _ '_ -- _--i_

/


8/12

The Planet

ur scientists often refer to Jupiter and its 15satellites as a "mini-solar system:' Theysee a set of similarities between the solarsystem and the Jovian system within it.

Jupiter is drastically differentfrom Earth and the otherterre._trial planets Mercury,Venus, and M_,rs. While theterrestrial planets are mostlyrock, Jupiter's major constituentsare hydrogen and helium, inabout the same ratio as the SunitselfJupiter is the noisiest source

of radio signals, except the Sun,in our sky. Its magnetic field-the largest object in our solar

system-is large enough to reachfrom Earth to Vem,s. Jupitermay not have a _olid surface,but may change gradually froma g,aseous, hydrogen-heliumatmosphere to an interior ofliquid metallic hydrogen. Thetops of the clouds-all that canbe seen of the planet-- arewracked by huge ,torms thatappear to well up from deepwithin Jupiter's interior.The R)ur Gatilean satdlites

differ from each other in muchthe same way as thc planetsdiffer with distance from theSun. 1o has been subjected to agravitational tug-of-war that hasresulted in at least eight large,active volcanoes; Europa appearsto be rocky with an ice crust.Ganymede and Callisto, whiledifferent from each other insignificant ways, both consistmostly of water.

6


9/12

The Expcrimcnt,_

he Galileo 1984 Orbiter will carryinstruments for all 11 scientific experimentsoriginally selected, even though the changein launch date requires changes in the

Orbiter design. The design of theProbc and its seven instrumentsremains csscntially unchanged.The C)rbiter is designed to.:: Inspect the surfaces of the

satellites (the camcras may sccdetails as small as 30 meters,or 100 feet, across) to gaininfi_rmation about their compo-sition, present state, andgeological history.

-;': Make comprehensiveobservations of Jupiter's weather.

.": Study the magnetosphere-its size and shapc and how itchanges, how particles enter andleave it, and how Jupiter'ssatellites aflect it.The Probe is designed to-:: Determine the temperature,

pressure, density, and composi -tion of the various levels ofJupiter's atmosphere down to alevel at which pressure is about10 times that at sea level onEarth, perhaps 129 kilometers(80 milcs) below the cloud tops.

.,!: Measure and comparc theflows of energy through theatmosphere, inward from theSun and outward from Jupiter'sinterior.

Europa ._ .IK

,Ig


10/12

A Return to Jupiter

ven before the time of Galileo, people havebeen interested in Jupiter, our largestplanet. More than 475 scientists--including90 from 10 foreign countries-submitted

proposals to participate inProject Galileo; I 1 5 scientistswcrc selected to fi,rm the (Salilcoscience team.Project (3alilco will be the

[!nitcd States' fifth mission toJupiter; predecessors includePioneer 10 and 11, and \'i_yager 1and 2. Pioneer 10 flew pastJupiter in December 1973, andPioneer 11 arrived one yearlater. Voyager 1 passed Jupiterm March and Voyager 2 inJuly 1070, as the t_o spacecraftcontinue on to .Saturn andbeyond.The Jet l}r{_pulsion Laboratory

is the overall InanaRelnent centerR_r Project ( ;atileo and will buildthe Orbiter spacecraft. The

(.3rbi ter' s rocket propulsion_ystcm will bc provided by theFederal Republic of (k'rmany.NASA's Ames Rewarch (_cnterwill develop the Probe andProbe-(;arrier spacccra(t. Radiosignals From the two spacecraftwill bc received on Earth byJPL's Deep Space Network.

8

"_ GOVERNMENT PRINTING OFFICE : 19,80--784-064


11/12


12/12

National Aeronautics andSpace AdministrationJet Propulsion LaboratoryCalifornia Institute of TechnologyPasadena, California

f_ .R..EOEIVED __,t_ .,-..8TIAt,,. _I"_ ,,_'t,y

C.r\

t,.- C=C

i--"C.,c _,iff

C _C., W,c./ :>-_,..;1 I

t,; IC

4p.*-c, c

G

t-,.C

U.r+ c;,

C,

('. i,C,=,

'4L p:_

c_i

....jC _t"

c

project galileo a return to jupiter

Documents