galileo at jupiter the first ganymede encounter press kit

8/8/2019 Galileo at Jupiter the First Ganymede Encounter Press Kit

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NATIONAL AERONAUTICS AND SPACEADMINISTRATION

GALILEO A TJUPITER:T H E F I R S T GANYMEDEENCOUNTERPRESS K ITJULY 1996

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Douglas IsbellHeadquarters,Washington, DC

Franklin ODonnellJet Propulsion Laboratory,Pasadena, CA

Contacts

Policy/Program Management

Galileo M ission

Ann Hutchison Atmospheric Descent ProbeAmes Research Center,Mountain View, CA

202/358- 1753

818/354-5011

415/604-4968

CONTENTSGENERAL RELEASE ................................................................................................................................................ 1MEDIA SERVICES INFORMATION ...................................................................................................................... 4GALILEO QUICK LOOK ........................._................................................................................................................ORBITER MISSION................................................................................................................................................... 9THE JOVIAN SYSTEM .................................................................................. ........................................................ 11INTERPLANETARY CRUISE SCIENCE ............................................................................................................. 12ATMOSPHERIC PRO BE MISSION ...................................................................................................................... 16TELECOMMU NICATIONS STRATEGY ............................................................................................................. 18THE SPACECRAFT ................................................................................................................................................. 26TECHNOLOGY BENEFITS FROM GALILEO ............................... ......................................................................PROGRAlWPROJECT MANAGEMENT.............................................................................................................. 31

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RELEASE: 96-122GALILEO READIES FOR CLOSE FLYBY OF JUPITERS BIGGEST MOON

Now residing in orbit around Jupiter, NASAs Galileo spacecraft has successfullycompleted its first close flyby of Jupiters largest moo n, Ganym ede, at 6:29 U niversal Timeon June 27 (1 1:29 p.m. Pacific Daylight Time on June 26).Equipped with 10 scientific instruments, Galileo flew just 835 kilometers (5 19 miles)above Ganym edes surface to provide the most detailed images and other information everobtained about the icy satellite. Images and other data gathered by the spacecraft have beenradioed back to E arth in the days follow ing the flyby , and will continue for several weeks thissummer.On June 23 , Galileos particle detectors and magnetic fields instruments beganmaking nearly continuous measurements as the spacecraft approached Ganym ede. Its opticalinstruments then began periodic observations, including the first round of picture-taking(other than engineering images taken for navigation purposes) since months before thespacecraft entered orbit around Jupiter o n D ecember 7, 1995.Selected images of Ganymede taken by Galileo will be released in a televised new sconference at the Jet Propulsion Laboratory on July 10.With a 5,262-kilometer (3,269-mile) diameter, Ganym ede is the largest moon in thesolar system -- bigger than M ercury and abo ut three-quarters the siz e of Mars. It possesses avariety of familiar Earthlike geologic formations including craters and basins, grooves andmountains. The bulk of the satellite is abou t half water ice and half rock.Portions of its surface are relatively brigh t, clean ice wh ile the other regions arecovered with darker dirty ice. The da rker areas appe ar to be ancient and heavily cratered,while the lighter regions display ev idenc e of tectonic activity that may have b roken up the icycrust. A thin layer of ozone has been foun d in Ganymedes surface by astronomers.Galileo will return high-resolution images show ing features o n Ganym ede as small as10 meters (about 33 feet) across. Instruments on board have assessed Ganym edes surfacechemistry and searched for signs of an atmosphere around the big moon . Measurements havebeen m ade to characterize Ganym edes grav ity field and to determine if it possesses amagnetic field.In the days just before and after the Gan ymed e flyby, Galileos other studies included

a search for auroral activity o n Jupiters nightside and observations of other Jovian moons:Io, Europa and Callisto. The Io torus, a hot, dough nut-shaped ring of charged particles

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Jupiter- Ganymede CIAEarth

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Media Services InformationNASA Television Transmission

NASA Television is available through the Spacenet 2 satellite on transpond er 5,channel 9 ,6 9 degrees west longitude, frequency 3880 MH z, audio subcarrier 6.8 MH z,horizontal polarization. The schedule for coverage of television transmissions during theGalileo mission is available from the Jet Propulsion Laboratory, Pasadena, CA ; Am esResearch Center, Mountain View, CA; Kennedy Sp ace Center, FL ; and NASA Headquarters,Washington, DC.Statu s Reports

Status reports on Galileo mission are issued by the Jet Propulsion Laboratorys PublicInformation Office. They may be accessed online as noted below.Briefings

On July 10, 1996 at 10 a.m. PDT (1 p.m. EDT ), preliminary science results from theGany mede encounter will be featured in a NAS A Space Science Update originating at the JetPropulsion Laboratory and televised live on NASA TV (see NA SA TV information above).Internet Information

Extensive inform ation on the Galileo mission, including an electronic copy o f thispress kit, press releases, fact sheets, status reports and im ages, is availab le from the JetPropulsion Laboratorys World W ide Web home page at http://www.jpl.nasa.gov. Inaddition to offering such public affairs materials, the JPL h om e page links to the GalileoProjects W eb home page, http://www.jpl.nasa.gov/galileo, which offers additionalinformation o n the mission.The general JPL site may also be accessed via Internet using anonym ous file transferprotocol (FTP) at the address ftp.jpl.nasa.gov. Users should log o n with the usernameanonymous and enter their E-mail address as the password. For users without Internetaccess, the site may additionally be accessed by modem at 8 18/354- 1333.

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Quick Look Facts: Galileo MissionA note about the times used here: Because of Jupiter's great distance, a speed-of-light radio transmission romGatileo takesfrom 35 minutes to nearly one hour to reach receivers on Earth. The pne-way light time isshortest when the spacecrafi is closer to Earth at it orbits Jupiter, and longest when the spacecrc@ is moredistant. The Galileo spacecraft event times used below are all Earth-received times. On arrival day, Galileo 'sone-way ight time was approximately 52 minutes. During the Ganymedeflyby, the one-way light time will beapproximately 37 minutes.

Laun ch and dep loyment: ST S-34 Atlantis and IUS October 18 , 1989Venus flyby (about 16,000 km/9,500 mi) February 10, 1990Earth 1 flyby (about 1,000 km/620 mi) December 8, 1990Asteroid Gaspra flyby (about 1,600 km /950 mi) October 29, 1991Earth 2 f lyby (about 300 M 1 9 0 mi) December 8, 1992

Asteroid Ida flyby (about 2,400 km/1,400 mi) August 28, 1993Probe release July 12, 199511 :07 p.m. PD T

Jupiter arrival (probe and orbiter) December 7, 1995Io f lyby (about 1,000 M 6 2 0 mi)

Probe atmospheric entry and relay

December 7,199 510:38 a.m. P STDece mber 7, 19952 5 6 p.m. PST

Probe mission duration: 57 minutesJupiter Orbit Insertion (JOI): December 7,19 955: 19 p.m. PSTJupiter moon encounters:opportunity; no im aging or spectral data)Io: Dec. 7, 199 5 (Only magnetic fields and particle data were taken at thisGanymede: June 27. 1996 and Sept. 6, 1996; April 5,1 99 7; May 7 , 1997Callisto: November 4, 1996; June 25, 1997; Sept. 1 7, 1997Europa:Dec.19, 1996; Feb. 20 a ndNov . 6 , 1997Galileo End of Mission: Dece mbe r 7, 1997

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Quick Look Facts (continued)Jupiters Satellites

Name

MetisAdrasteaAmaltheaThebeIoEuropaGanymedeCallistoLedaHimaliaLysitheaElaraAnankeCarmePas iphaeSinope

Discovery

Voyager, 1979Voyager, 1979Barnard, 1892Voyager, 1979Galileo, 1610Galileo, 1610Galileo, 1610Galileo. 16 I OKowal, 1974Perrine, 1904Nicholson, 1938Perrine, 1905Nicholson. 195 1Nicholson, 1938Melotte, 1908Nicholson. 1914

Mean dist . to Period, Radius, NotesJupi te r , km. days krn.127,960 0.3 (20)*128,980 0.3 1 2 x 818 1,300 0.5 135 x 7522 1,900 0.7 ( 5 0 )42 1,660 1.8 1,815 density 3.57**; volcanic670,900 3.5 1,569 density 2.97**; icy crust1,070,000 7.2 2,63 1 density 1.94* *; deep ice crust1,883,000 16.7 2,400 density 1.86**; deep ice crust1 1,094,000 239 (8) long, tilted elliptical orbit1 1,480,000 250 (90) in family with Leda1 1,720,000 259 (20) in Leda family1 1,737,000 260 (40) in Leda family2 1,200,000 63 1 (15) retrograd e in long, highly tilted,22,600,000 692 (22) in family with Ananke23,500,000 735 (35) in An anke family23,700,000 758 (20) in Ananke family

elliptical orbit

* Radius numbers in parentheses are uncertain by more than 10%**Density is in grams per cubic centimeter (waters density is 1)Jupi te r s Rings

Inner Halo ring, about 100,000 to 122,800 kilometers from Jupiters center.Main ring, 122,800- 129,200 kilometers from center.Out er Gossamer ring, 129,200 to about 2 14,200 kilometers.No te that satellites Metis, Adrastea and Am althea orbit in the outer part of he ring region.Th e jovian satellites are named for Greek and Roman gods. Nam es of new moon s are conferred by theInternational Astronomical Union.

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.Galiieo Orbiter and Jupiter Atmospheric Probe

_ _rbiter Probe

Mass, kilograms (pounds) 2,223 (4,890) 339 (746)Usable propellant mass 925 (2,035) --Height 6.15 m (20.5 ft) 86 cm (34 in.)Instrument payload 12 experiments 7 experimentsPayload mass, kg (Ib) 118 (260) 30 (66)Electric power Radioisotope Lithium-sulfiu

thermoe lectric battery, 730 watt-hoursgenerators(570-470 w atts)

Shuttle Atlantis (STS-34) Crew (Johnson Sp ace Center)Donald E. Williams, CommanderMichael J. McCulley, PilotShannon W. Lucid, Mission SpecialistFranklin R. Chang-Dim, Mission SpecialistEllen S. Baker, Mission SpecialistGalileo ManagementGalileo Project (Jet Propulsion Laboratory)W illiam J. ONeil, Project ManagerNeal E. Ausm an, Jr., Mission DirectorMatthew R. Landano, Deputy Mission DirectorDr. Torrence V. Johnson, Project ScientistAtmospheric Probe (A mes Research Center)Marcie Sm ith, Probe ManagerDr. Richard E. Young, Prob e ScientistGalileo Program (N ASA Headquarters)Donald Ketterer, Program ManagerDr. Jay Bergstralh, Program ScientistDr. W esley Huntress Jr., Associate Adm inistrator for Space Science



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Orbiter MissionGalileos two-ye ar orbital tour of the Jovian sy stem is an elaborate square dancerequiring the spacecraft to swing around one moon to reach the next. Th e June 27-encou nterof Gan yme de is the first of these satellite swingbys. It will shorten and change the shape of

Galileos ensuing orbit.Each time the orbiter flies closely pa st one of the major inner moons, G alileos coursewill be changed due to that satellites gravitational effects. Careful targeting allows eachflyby to direct the spacecraft on to its next satellite encounter and the spacec rafts next orbitaround Jup iter.Over the course of its two-year mission, Galileo will fly by Ganymede four times,Callisto three, and Europa three. Becau se of the dangerous, high-radiation environmentwhere Io resides, Galileo could only fly closely past that volcanic moon once, on arrival day.Repeat passes through that neighborhood would likely have damaged the spacecraftselectronics.Galileos satellite encounters will be at altitudes as close as 200 kilometers (125miles) above the surfaces of the moons, and typically 100 to 300 times closer than theVoyager flybys of the same moons.

I = loSUN E=EUROPA4\ G = GANYMEDEC = CALLISTO

1Gal i leos Eleven Or bi t Trek Around Jupi ter 1

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The goals are to to determine the surface chem ical composition, geo logical featuresand g eophysical history o f the four moons. Galileos scanning instrum ents will scrutinize thesurface and features of each. After a week or so of satellite observation, w ith its taperecorder full of data, the spacecraft will spend the next mon ths in orbit playing o ut-theinformation to Earth. Through out the 23-month orbital tour, Galileo will continuously gatherand return data on the dynamic Jovian magnetospheric and dust environm ent.Galileos Orbital Tour, 1995-1997

Th e spacecrafts orbital tour consists of 11 different elliptical orb its arou nd Jupiter.Each orbit (except one) includes a close flyby and gravity assist at Gany med e, Callisto orEuropa, near the inner (Jupiter) end of the orbit. Th e outer end of the orbit will vary from 5to almost 20 million kilometers (3.2 to more than 12 million miles). No close flyby isplanned for Orbit 5 , when Galileo is out of communication due to solar conjunction -- theperiod w hen the Sun will be between Jupiter and Earth. Distant scientific encounters w ithadditional satellites are scheduled for a number of orbits, and the spacecraft will observe Io atmedium range on every orbit.

Orbit1

234(5)6789101 1

Satellite EncounterGanymedeGanymedeCallistoEuropa(Solar conjunction)EuropaGanymedeGanymedeCallistoCallistoEuropa

DateJune 27 , 1996September 6November 4December 19

February 20 , 1997April 5May 7June 25September 17November 6

Altitude, km (miles)500 (300)259 (161)1,102 (685)693 (431)(no close flyby)587 (365)3,056 (1,899)1,580 (982)416 (258)524 (326)1,124 (698)



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The Jovian SystemJupiter is the largest planet in the solar system. Its radius is 44.400 miles (71,500kilometers), more than 1 1 times Earths, and its mass is 3 18 times that o f our planet. It ismade m ostly of light elements. principally hyd rogen (8 1 percent) and helium (1 8 percent).

Its atmosphere and clouds are deep and dense. and a significant amount of energy is emittedfrom its interior. It has no solid surface. Its gases become hotter and den ser w ith increasingdepth.Early Earth-based telescopic observations showed bands and spots in Jupitersatmosph ere; on e huge storm system, the Red Spot, has been seen to persist over threecenturies. Th e light and dark bands and some of the spots have disappeared and reappearedover periods of many years, and as the quality of Jupiter observation has improved, so has theamou nt of variability seen in the clouds.Atmospheric features were seen in greatly improved detail with the Pioneer and

Voyager missions of the 1970s. The Voyager encounters in the spring and summ er of 1979allowed the observation of short-term variations in real time as Jupiter turned beneath thespacecrafts cam eras. Astronom ers using Earth-based infrared teles cop es have recentlystudied the natu re and vertical dynam ics of deeper clouds, and the new- Earth - and space-based telescopes observe Jupiters atmospheric developments and clim ate changes, m ostnotably during the C omet Shoem aker-Levy 9 impacts.Sixteen Jov ian satellites are known. The four largest, discovered by Galileo in 1610,are about the size of sm all planets, and were seen by V oyagers experim enters to have thevaried terrain of small worlds. The innermost of these, Io, has active sulfurou s volcanoes,

discovered by Voyager 1 and further observed by Vo yager 2, Earth-based in fix ed astronomyand the H ubble Space Telescope. Io and Europa are about the size and density of Earthsmoon (3-4 times the density of water) and probably mos tly rocky inside. Eur opa may alsoexhibit surface activity. Ganym ede and Callisto, further out from Jupi ter, are the size ofMercu ry but les s than twice as dense as water; their interiors are proba bly abou t half ice andhalf rock, with m ostly ice or frost surfaces which sho w distinct and interesting features.Of the others, eigh t are in inclined, highly eccentric orbits far from the p lanet, andfour (three discovered by the V oyager missions in 1979) are close to the planet. Voyageralso discovered a thin ring system at Jupiter in 1979.Jupiter ha s the strongest planetary magnetic field known; the resu lting region of itsinfluence, called the magnetosph ere, is a huge teardrop-shaped bubble in the solar windpointing away from the Sun. The inner part of the magnetically-constrained charged-particlebelt is doughn ut-shaped, but farther out it flattens into a disk. Th e ma gn etic poles are offsetand tilted relative to Ju piters axis of rotation, so the field appears to wo bble around withJupiters rotation (about every 10 hours), sweeping up and dow n across the nner satellitesand making waves throughout the magnetosphere.


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Interplanetary Cruise ScienceGalileo has already returned a wealth of surprising new inform ation from the "targetsof opportunity" it has observed on the way to Jupiter. Tw o first-ever asteroid encountersyielded close-up imag es of the asteroids Gaspra and Ida, and the extraordinary discovery of a

moon (later named Dactyl) orbiting Ida.Lunar science

In 1992, Galileo revisited the north pole of the M oon explored by early spacecraft,imaging the region for the first time in infrared color and providing n ew inform ation aboutthe distribution o f minerals on the lunar surface. The sp acecraft flew within 68,000 miles(1 10,000 kilometers) of the Moon on Dec. 7, 1992, obtaining multispectral lunar images,calibrating Galileo's instruments by comparing their data to those of previous lunar missions,and getting additional baselines for comparing our Moon with the Jovian satellites Galileowill be exploring.A m ajor result of Galileo's first lunar flyby wa s the confirmation o f the existence of ahuge ancient impact basin in the southern part of the Mo on's far side. Th e presence of thisbasin was inferred from Apollo data in the 1970s but its extent had never been m appedbefore. Galileo imaged the M oon's north pole at several different wavelengths (includinginfrared), a feat never before accom plished. Scien tists found evidence that the Moo n hasbeen mo re volcanically active than researchers previously thought.The near-infrared mapping spectrometer (NIM S) imaged the polar region in 204waveleng ths, another first in lunar mapping. The space craft also collected spectral data fordark mantle deposits, areas of local explosive vo lcanic eruptions. Th ese maria deposits aremo re compositionally diverse toward the near side of the Mo on. Specifically, scientistsdiscovered that titanium is present in low to intermediate am ounts toward th e far side,suggesting that the far side has a thicker crust. Th is type of spectral data also allowsscientists to determine the sequence of meteoric impacts and the thickness of ancient lavaflows.In observing the features of the Imbrium impact basin on the n ear side ofthe Moon, the im aging team found the Moon to have been more volcanicallyactive earlier than previously thought. They found hidden maria, or"cryptom aria," are overlain by other features visible only throug h special

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-_--

COMPLETE PRIMARYMISSION DATA RETURNASPRAOCT 29,1991JUPITER JAN 1,19 94

COMET S-L IMPACT

PROBE RELEASE EXPLORATION

GANYMEDE, CALLISTO,EUROPA, ENCOUNTERSJUPITER ARRIVALAN D lo ENCOUNTERDEC 7,1995

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spectral bands. Nearly 4 billion years ago, the impact in the Imbrium basin threw o ut atremendo us amo unt of rock and debris that blanketed the M oon an d caused erosion of thehigh land terrain. This blanketing and sculpture can be seen in Galileo s images of the northpole. _ _Gaspra

Nin e m onth s into its two-year E arth-to Earth orbit, Galileo entered the a steroid belt,an d on Oct. 29, 1991, it accom plished the first-ever asteroid enco unter. It passed about 1,600kilometers (1,000 m iles) from the stony asteroid Gaspra at a relative speed o f about 8kilom eters per second (1 8,000 miles per hour); scientists collected pictures of Gaspra andother data on its composition and physical properties. These revealed a cratered, complex,and irregular body about 19 by 12 by 11 kilometers (12 by 7.5 by 7 miles), w ith a thincovering of dirt-like regolith and a possible mag netic field.Id a

On Aug . 28, 1993, Galileo had a second asteroid encounter, this time w ith Ida, alarger, mo re distant body than G aspra. There, G alileo made the discov ery of the first moon o fan asteroid. Ida is about 55 kilometers or 34 miles long; like G aspra, it is very irregular inshape; it rotates every 4.6 hours around an offset axis. App arently, like Ga spra, it may have amag netic field.

Th e closest-approach distance was about 2,400 kilometers (1,500 miles), with arelative speed of nearly 12.6 kilometers per second or 28,000 m iles per hour.Idas satellite, later named Dactyl, was fou nd in a camera fiarne an d an infrared scan.The 1.5-kilometer satellite was estimated to be about 100kilometers (60 m iles) from thecenter of the asteroid.

Com et Shoemaker-LevyTh e discovery of Comet Shoem aker-Levy 9 in May 1993 provided an exciting newopportunity for Galileos science team.Th e Galileo spacecraft, approaching Jupiter, was the only observation platformcapab le of making m easurements in line of sight to the co mets imp act are a on Jupiters far

side. Although there was no additional fimding available for this new target of opportunityan observation program was planned for Galileos remote sensing instruments. All ofGalileos observations had to be programmed in advance into the sp acecraft computer,notwithstanding uncertainties in the predicted impact times. The d ata wer e stored on thespacecraft (on e tape load plus some computer memory sp ace) for playback at the 10 bits-per-sec on d rate. Playback con tinued, with necessary interruptions for other activities, until lateJanuary 1995.

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Galileo 's imaging system used different meth ods to cover the time uncertainties(am oun ting to hours) of the impacts for different events. Repeated im aging, rather like avery s low m otion picture, captured the very last imp act (fragment W) which appeared to last26 minutes. A smeared im age, producing a streak representing the night-side impact fireballam ong sm ears showing Jupiter and some satellites, provided b rightness histories of tw oevents, the impact of fragments K and N. The photopolarimeter-radiometer detected threeevents. Th e infrared spectrometer detected two events, providing critical information on thesize, temperature and altitude of the impact fireball and the heating of the atmospehre by theimpact "fallback." Galileo scientists have combined their data to produc e interpretivehistories of the 90-seco nd impact events.Interplanetary Dust

In the sum me r of 1995, Galileo found itself flying through the m ost intenseinterplanetary dust storm ever measured. It was the largest of several dust stormsencountered by Galileo since December 1994, when the spacecraft was still almost 110million miles (about 175 million kilometers) from Jupiter. Galileo discovered that thevolcanic moon Io is the source of the dust.

Scientists believe the particles em antating from Io are electrically charged and thenaccelerated by Ju piter's powerful m agnetic field. Calculations indicate the d ust is speedingthrou gh interplanetary space at between nearly 90,000 an d 450,000 miles per hour (40 and200 kilometers per seco nd), depending on particle size. Ev en at such high speeds, these tinyparticles pose n o dange r to the Galileo spacecraft because they are so tiny.

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Atmospheric Probe MissionOn July 13, 1995. the G alileo spacecraft spun up to 10 rpm and aim ed its cone-shapedJupiter atmospheric entry probe toward its Jupiter entry point 5 1 million miles (82millionkilometers) away. Guillotine-like cable cutters sliced though umbillicals connecting the two,

and the probe was released from the main s pacecraft for its solo flight to Jupiter.On D ec. 7, 1995, the probes descent into Jupiter provided the first-ever on-the-spotmeasurem ents of Jupiter or any other outer planet. Instruments on board identified thechemical componen ts of Jupiters atmo sphere and their proportions, and searched for clues toJupiters history and the origin of the so lar system.Six hours before entry the com ma nd unit signaled the probe to w ake up, and threehours later instruments began collecting data on lightning, radio em issions and chargedparticles.

The probe struck the atm osphere at an angle of only 8 degrees to the horizon -- steepenough so it wouldnt skip out again into space, yet sh allow enough to survive the heat andjolting deceleration of entry. The probe entered the equatorial zone traveling the samedirection as the planets rotation.During its entry, the incandescen t gas cap ahead of the probe would have appeared asbright as the Sun to an observer and twice as hot (15,555 degrees Celsius or 28,000 degreesFahrenheit) as the solar surface. With the exception of nuclear radiation, the probes entrySUN b EARTH

\

was like flying through a nuclear fireball. Theprobe was subjected to wrenching forces as itdecelerated from 106,000 mph to 100 mph (about170,000 to about 160 km per hour) in just twominutes -- a force estimated at up to 230 timesEarths gravity.The Galileo orbiter, about 214,000kilometers (13 3,000 miles) above, linked up withthe probes radio signal w ithin 50 seconds. Itreceived the prob es precious science-datatransmissions and stored them both in thespacecraft tape recorder and in computer memory.

Successful transmission of all the probe data wascompleted by April 1996.



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(450 km, 5 X 10-8 bar, -8"C , 0 min)

DROGUE PARACHUTE0 km , 0.08 bar, -160"C, 1.88 m in)' AIN PARACHUTE DEPLOYEMENT(d (48 km , 0.09 bar, -161"C, 1.92 min)rrrthTELEMETRY TO ORBITER LV-(42 km, 0.13 bar, -163"C, 2 .25 m i n k T A

EARTH SURFACE PRESSURE -(0 km, 1 O bar, -107"C, 8.33 min)4l-2--7-- HEAT SHIELD DROPS OFF(45 km , 0.10 bar, -162"C, 2.05 m in)

- . -4--- - . .r I--I --\ %6 ( -134 km, 20 bars, 14OoC,60 min TO-163 km , 30 bars, 192 "C, 78 rnin)PRIMARY DATA REQUIREMENT(-92 km, 10 bars, 63"C, 38 m in)17


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Telecomm unicat ions StrategyThis s pring, Galileo received the last of two long-d istance electronic brain transplantsthat have endowed the spacecraft comp uters with ne w capa bilities. The successful operationmeans Galileo can still achieve the majority o f its scientific o bjectives desp ite the-failure of

its main comm unications antenna to open as com manded .The upgrades to Galileo's on-board com puter software and its ground-basedcommunications hardware were developed and tested by JPL in response to what would havebeen a profound loss for the orbiter portion of the missio n. (The s pacecra ft's Jupiteratmospheric probe mission could have been executed without the new techniques, but theupgrades did enhance the orbiter's ability to reliably record an d re-transmit the probe data.)The new telecommunications strategy now in use by the Galileo project hinges onmore effective use o f the spacecraft's low-gain antenna, w hich is limited to a very low datarate compared to the main, high-gain antenna.The sw itch to the low-gain antenna and its lower data rate means that far fewer databits will be returned from Jupiter. However, Galileo's new s oftw are increases its ability toedit and com press the large quantity of data collected and th en trans mit it to Earth in ashorthand form. New technology has also been used to greatly sharpen the hearing of thetelecommunications equipment that receives Galileo's whisper of a signal from Jupiter.Together, these efforts should enable Galileo to fulfill at least 70 percent of its originalscientific objectives.

The High-Gain A ntennaThe 4.8-meter-wide (l6-foot), um brella-like high-gain antenna is m ounted at the topof the spacecraft. When unfurled, the antenna's hosiery -like wire m esh stretche s over 18umbrella ribs to form a large parabolic dish. Galileo w as to have u sed this dish to radio itsscientific data from Jupiter. This high-performance, X-band antenn a wa s designed totransmit data back to Earth at rates of up to 134,400bits of digital information per second(the equivalent o f about on e imaging frame each m inute).Galileo's original mission plan called for the high-gain antenna to o pen shortly afterlaunch. For the Venus-Earth-Earth Gravity-Assist (VEE GA) trajectory mission, however,the heat-sensitive h igh-gain antenna had to be left closed an d stow ed behind a large sun

shad e to protect it during the spacecraft's passage th rough t he inn er solar system. During thisportion of Ga lileo's journey , two small, heat-tolerant low -gain antenn as provided thespacecraft's link to Earth. One of these S-band antennas, m ounted on a boom , w as added tothe spacecraft expressly to bolster Galileo's telecommunications during the flight to Venus.The o ther primary low-gain antenna mounted to th e top of the high-gain was destined tobecome the only m eans through which Galileo will be able to accomplish its mission.

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The Antenna ProblemOn April 11, 1991, after Galileo had traveled far enough f rom the h eat of the Su n, thespacecraft executed stored computer commands designed to unfurl the large high-gainantenna. But telemetry received minutes later showed that something went wr on g. T he

motors had stalled and the antenna had only partially open ed.In a crash effort over the next several weeks, a team of more than 100 technicalexperts from JPL and industry analyzed Galileo's telemetry and cond ucted ground testingwith an identical spare antenna. They deduced that the problem was most likely due to thesticking of a few antenna ribs, caused by friction between their standoff pins and so ckets.The excessive friction between the pins and sockets has been attributed to et clm g ofthe surfaces that occurred after the loss of a dry lubricant that had been bonded to the standoffpins during the antenna's manufacture in Florida. Th e antenna was originally shipped to JPLby truck in its own special shipping container. In December 1985, the antenna, again in its

own shipping container, w as sent by truck to NAS A's Kennedy Space Center (KSC) inSTOWEDRIBS 9, I O , 11

Florida to await launch. After theChallenger ac ciden t, Galileo and itsanten na had to be shippe d back to JPLin late 1986. Finally, they werereshipped to KSC for integration andlaunch in 1989. The loss of lubricant isbelieved to have occurred due tovibration the antenna experiencedduring those cross-country truck trips.Extensive analysis has shownthat, in any case, the prob lem existed atlaunch and w ent undetected; it is notrelated to sending th e spacecraft on theVEEGA trajectory o r the resultingdelay in antenna deployment.

Attempts to Free the A ntennaW hile diagnosis of the problem

continued, the G alileo team sent avariety of com mand s intended to freethe antenna. Mo st involved turning thespace-craft toward and away from theSun, in the hope that warming andcooling the apparatus would free theA FTE R H A M M E R I N G RIB # 2 N O W A T 43 "

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stuck hardware through thermal expansion and contraction. None o f these attemptssucceeded in releasing the ribs.Further engineering analysis and testing suggested that "hamm ering" the antennadeployment motors -- turning them on and off repeatedly -- might d eliver the force needed to

free the stuck pins and open the antenna. After more than 1 3,000 hamm erings betweenDecem ber 1992 and January 1993, engineering telemetry from the spacecraft showed thatadditional deployment force had been generated, but it had not freed the ribs. Otherapproaches w ere tried, such as spinning the spacecraft up to its fastest rotation rate of 10 rpmand ham mering the m otors again, but these efforts also failed to free the antenna.Project engineers believe the state of the antenna has been as w ell-defined as long-distance telemetry and laboratory tests will allow. After the years-long cam paign to try tofree the stuck hardw are, the project determined there was no ionger any significant prospectof the antenna being deployed.Nevertheless, o ne last attempt was m ade in March 1996, after the orbiter's mainengine was fired to raise Galileo's orbit around Jupiter. This "perijove raise maneuver"delivered the largest acceleration the ex perienced since launch, and it followed three othermildly jarring e vents: the release of the atmospheric probe, the orbiter deflection maneu verthat follows probe release, and the Jupiter orbit insertion engine firing. The se shocks, too,failed to jar the stuck ribs enough to free the antenna. This was the last attempt to open theantenn a before radioing the new software to the spacecraft to inaugurate the advan ced datacompression techniques designed specifically for use with the low-gain antenna.

Th e Low-Gain AntennaTh e difference between G alileo sending its data to Earth using the high-gain antennaand the low-gain is like the difference between the concentrated light from a spotlight versusthe light emitted diffusely from a bare bulb. If unfurled, the high-gain would transmit databack to ground-based Deep Space Network (DSN) collecting antennas in a narrowly focusedbeam. The low-gain antenna transmits in a comp aratively unfocused broadcast, and only atiny fraction o f the signal actually reaches DSN receivers. Because the received signal is10,000 times fainter, data must be sent at a lower rate to ensure that the conten ts are clearlyunderstood.Without any new enhancem ents, the low-gain antenna's data transm ission rate at

Jupiter would be limited to only 8-16 bits per second (bps), compared to th e high-gain's134,400 bps. How ever, the innovative software changes, when coupled with hardware andsoftw are adaptations at Earth-based receiving stations, have increased the data rate fromJupiter by as much as 10 times, to 160 bps. The data compression methods allow retention ofthe mo st interesting and scientifically valuable information, while minimizing or eliminatingless valuable data (such as the dark background o f space in an image) before transmission.Tw o different methods of data compression will be used. In both methods, the data arecomp ressed onbo ard the spacecraft before being transmitted to Earth.20

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The first method, called "lossless" comp ression, allows the da ta to be reformattedback to their original state once on the ground. This technique is routinely used in personalcomp uter modem s to increase their effective transmission rates. Th e second compre ssionmethod is called "lossy," a term used to describe the dissipation of electrical energy, butwhich in this case refers to the loss of some original data through mathematicalapproximations used to abbreviate the total amou nt of data to be sent to the ground. Lossycomp ression w ill be used to shrink imaging and plasma wave data down to as little as 1/80thof its original volume.Customizing Receivers on Earth

S-band telecomm unication was once the standard for space missions, and several S-band performance-enhancing capabilities were implemented at DSN tracking stations in the1980s. For G alileo and its S-band low -gain antenna, these capabilities have been restored atthe Canberra, Australia, 70-meter antenna. Because Australia is in the southern hemisphereand Jupiter is in the southern sky during G alileo's tour, the Canberra complex receives m ostof Galileo's data.

Ano ther critical, ongoing.DSN upgrade has been the addition of so-called Block Vreceivers at the tracking stations. These receivers, which are being installed for mu lti-mission use, allow all of Galileo's signal power to be dedicated to the data stream bysuppressing the traditional carrier signal, thus allowing use o f higher da ta rates.Finally, the 70-meter and two 34-m eter DSN antennas at Canberra have been arrayedto receive Galileo 's signal concurrently, with the received signals electronically com bined .The arraying technique allows more of the spacecraft's weak signal to be captured, therebyenabling a higher data rate, which translates into the receipt of more data. In addition, otherarraying is used for Galileo: the 64-meter Parkes Radio Telescope in Australia is arrayedwith the Canberra antennas, as is the 70-meter DSN antenna in Goldstone, CA, w hen its viewof Galileo overlaps with Canb erra's.

The Tape R ecorder ProblemGalileo's tape recorder is a key link in techniques developed to com pensa te for theloss of use of Galileo's high-gain antenna. The tape recorder is to be used to stor einformation, particularly im aging data, until it can be compressed and edited by spacec raft

com puters and radioed via Galileo's low-gain antenna back to Earth.On Oct. 11, 1995, with just w eeks to go before Jupiter arrival, the tape record ermalfunctioned. Data from the spacecraft showed the recorder failed to cease rewinding afterrecording an image of Jupiter.A week later, following extensive analysis, the spacecraft tape recorder was testedand pr'oved still operational, but detailed study o f engineering data indicates that th e tape



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recorder can be unreliable under some operating conditions. Th e problem appears to bemanageable, how ever, and should not jeopardize return of th e full com plement of im ages ofJup iter and its mo ons that are to be stored on the recorder for playback o ver the course of themission. ,_ -

On Oct. 24, the spacecraft executed comman ds for the tape recorder to wind an extra25 times around the section of tape involved in this anom aly. This section had been possiblyweakened w hen the recorder was stuck in rewind mode for abou t 15 hours. Indications werethat the tape had not m oved during this entire time. The drive mechanisms had been slippingand possibly rubbing against the tape. Spacecraft engineers are uncertain about the conditionof this area of tape so it is now off-limits for future recording. Th e extra tape wound overit secures that area of tape, eliminating any stresses that could tear the tape a t this potentialweak sp ot. Unfortunately, the approach image of Jupiter that Galileo took October 11 1995wa s stored on the off-limits portion of tape and will not be played back. M ore significantly,Galileo pro ject officials also decided not to take pictures of Io and Europa on Dec. 7, 1995 inwhat w ould have been the closest encounter of Io (from a distance of 600 miles or 1,000kilometers). Instead, the tape recorder was completely devoted that day to gathering datafrom Galileos Jupiter atmospheric probe.

Engineers have continued to analyze the tape recorders condition to fully understandits capabilities and potential weaknesses. Their goal has been to ensu re safe operation of thetape recorder while minimizing loss of any of the objectives of the orb iter portion of themission.Very few o f Galileos original measurement objectives have had to be completelyabandoned as a result of the high-gain antenna problem. For the most part, scienceinvestigations o n the spacecraft have adapted to the lower data rates using a variety oftechniques, depending on the nature of the experiment. The new software and DSN receiverhardware has increased the information content of the data Galileo returns by at least 100times m ore than what would have been otherwise possible.The onboard data processing made possible by the P hase 2 software now permits thespacecraft to store and transmit nearly continuous observations of the jovian magnetosphereand ex tensive spectral me asurements of the planet and its satellites in the infrared, visible,and ultraviolet, including more than 1,500 high-resolution images.W hile tens o f thousands of images would be required for large-scale movies of

Jupiters atmo spheric dynam ics, the hundreds of images allocated to atmosp heric imagingwill allow in-depth study of several individual features in the cloud s of Jupiter. Coop erativeobservations with Hubble Space Telescope investigators and ground-based observers haslong been planned as part of the Galileo mission to provide information o n the global state ofJupiters atmosp here.Like a tourist allotted one roll of film per city, the Galileo team has selected itsobservations carefully for each encounter to ensu re that the maxim um am oun t of new and



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interesting scientific information is returned. The imaging cam paign will focus on the planetand the four large Galilean moons, but it will also cover the four inner minor satellites andJupiter's rings.For the orbiter portion of the mission, it is useful to realize that Galileo, wcth its

sophisticated instrume nts, closer satellite flybys, and long du ration in Jo vian orbit, wasspecifically designed to answer many of the questions that the Pioneer and Voyagerspacecraft were unable to answer. Non e of those characteristics have been affected by theloss of the high-gain antenna: only the total volume of data has been reduced.As a result, when Galileo examines a class of phenomena, fewer samples of that classcan be studied, and o ften, the spectral or temporal resolution w ill be reduced to lessen thetotal volume of data. Nevertheless, the resulting informa tion will provide unique insight intothe jovian system.Som e specific impacts from the loss of the high-gain antenn a include: elimination of

color global imaging of Jupiter once per orbit; elimination of glob al studies o f Jupiter'satmospheric dynamics such as storms, clouds, and latitudinal bands (efforts to imageatmosp heric features, including the G reat Red Spot, are still planned, how ever); a reductionin the spectral and spatial coverage of the moons, which provided context for study of high-resolution observ ations of their key features; and reduction of much of the so-called fieldsand particles microphysics (requiring high tempo ral- and spectral-frequency sampling of theenvironment by all instruments) during the cruise portion o f each orbit. M ost of the fieldsand particles microphysics, however, w ill be retained during the satellite encounters.

IMAGING PLAYBACK100-200 IMAGESlORBlTI APE RECORDER]

HIGH-SPEEDCOMPRESSOR

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Highlights of Jupiter Science Returned Via Galileo's Low -Gain Antenna:- 100 percent of probe data (mission accomplished).- Nearly con tinuous, real-time survey of jovian magn etosphere for two y ears- Approximately 1,500 images of the four G alilean satellites, four inner mino rsatellites, Jupiter and its rings- Ten very close encounters: Europa (3), Callisto (3) and Ganymede (4)- Five V oyager-class (less than 80,000 km) encounters with Galilean satellites

Ground Systems and Spacecraft OperationsGalileo communicates with Earth via NASA's Deep Space Network (DSN), whichhas a complex of large antennas w ith receivers and transmitters located in the California

desert, in Australia and in Spain, linked to a network co ntrol center at JPL in Pasadena, CA.Th e spacecraft receives comman ds, sends science and engineering data, and is tracked bydoppler and ranging measurements through this network. Mission control responsibilitiesinclude comm anding the sp acecraft, interpreting the engineering and scientific data it sendsin order to understand how it is performing and responding, and analyzing navigation dataobtained by the Deep Space Netw ork. The controllers use a set of complex computerprograms to help them control the spacecraft and interpret the data.The G alileo spacecraft carries out its complex operations, including maneuvers,scientific observations and com mun ications, in response to stored sequences which are sentup to the orbiter periodically through the Deep S pace Netwo rk in the form of comm and

loads.The sp acecraft status and health are mo nitored through data from 1,418 onboardmeasu rements. T he Galileo flight team interprets these data into trends to ave rt or workaround equipmen t failure. Their conclusions become an important input, along withscientific plans, to the sequence design process. The telemetry monitoring is supported bycomputer programs written and used in the mission support area.Navigation is the process of estimating, from radio range and doppler measurements,the position and velocity o f the spacecraft to predict its flight path and to desig n course-correcting mane uvers. These calculations must be done with computer support. Th e Galileomission, w ith its complex g ravity-assist flight to Jupiter and 10 gravity-assist satelliteencounters in the Jovian system, is extremely depen dent on consistently accurate navigation.In addition to the p rograms which d irectly operate the spacecraft and are periodicallytransmitted to it, the mission op erations team uses softw are amounting to 650,000 lines ofprogramming code in the sequence design process; 1,6 15,000 lines in the telemetryinterpretation; an d 550,000 lines of code in navigation. These all had to be written, checked,



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tested, used in mission simulations and, in many instrument cases, revised before the m issioncould begin.Science investigators are located variously at JPL or at their home laboratories, linkedby com puter comm unications. From either location, they are involved in developing the

sequences affecting their experiments an d, in some cases, helping to chang e preplannedsequences to follow up on unexpected discoveries with second looks.

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The SpacecraftThe G alileo mission and systems were designed to investigate three broad aspects ofthe Jovian system : the planet's atmosph ere, the satellites and the magnetosphere. Thespacecraft was constructed in three segments, which help focu s on these areas: 1 )'the

atmospheric probe; 2) a non-spinning section of the orbiter carrying cameras and otherremote sensors; 3) the spinning main section of the orbiter spacecraft w hich includes thefields and particles instruments, designed to sense and m easure the environme nt directly asthe spacec raft flies through it. The spinning section also carries the commun icationsantennas, the propulsion module, flight computers and most support system s.Th is innovative "dual spin" design allows part of the orb iter to rotate co nstantly atthree rpm, and part of the spacecraft to remain fixed. This m eans that the orbiter can easilyaccommodate magnetospheric experiments (which need to take measurements while rapidlyswe eping about) wh ile also providing stability and a fixed orientation for cam eras and othersensors. The spin rate can be increased to 10 revolutions per m inute for additional stabilityduring m ajor propulsive m aneuvers.Galileo's atmospheric probe weighed 339 kilograms (746 pounds), and included adeceleration mod ule to slow and protect the descent module, wh ich carried ou t the scientificmission.The d eceleration m odule consisted of an aeroshell and an aft cove r, designed to blockthe heat generated by friction during the sharp deceleration of atmos pheric entry. Inside theshells were the descent module and its 2.5-meter (8-foot) parachute. T he descent modulecarried a radio-relay transmitter and six scientific instruments. O perating at 128 bits per

second, each o f the dual L-band transmitters sent nearly identical stream s of scientific data tothe orbiter. Probe electronics were powered by batteries with an estimated capacity of about18 amp-ho urs o n arrival at Jupiter.Probe instruments included an atmospheric structure group o f sensors m easuringtemperature, pressure and deceleration; a neutral mass spectrometer and a helium-abundancedetector supporting atmospheric composition studies; a nephelometer for cloud location andcloud-particle observations; a net-flux radiometer measuring the difference, upw ard versusdown ward, in radiant energy flux at each altitude; and a lightninghadio-emission instrumentwith a n energetic-particle detector, measu ring light and radio em issions a ssociated withlightning and energ etic particles in Jupiter's radiation belts.



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PLASMA-WAVELOW-GAINANTENNA \

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PLASMA SCIENCEy HEAVY ION COUNTER (BACK)DUST DETECTOR

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At launch, the o rbiter weighed about 2,223 kilograms (4,900 pounds), not countingthe upper-stage-rocket adapter but including about 925 kilograms of usable rocket propellant.This propellant was used in almost 30 relatively small maneuvers during the long gravity-assisted flight to Jup iter, t h e e large thrust maneuv ers including the one that put the craft intoits Jupiter orbit, and w ill be used for the 30 -some trim m aneuvers planned for the rest of themission. It is also consum ed in the small pulses that turn and orient the spacecraft.The propulsion module consists of twelve 10-newton thrusters, a sing le 400-newtonengine, the m onomethyl-hydrazine fuel, nitrogen-tetroxide oxidizer, and pressurizing-gastanks, tubing, valves and control equipment. (A thrust of 10 newtons would suppo rt a weightof about one kilogram or 2.2 pounds at Earths surface.) The propulsion system wasdeveloped and built by Messerschmitt-Bolkow-Blohm MBB ) and provided by Germany as apartner in Project G alileo.In addition to the scientific data acqu ired by its 10 instruments, the Galileo orbiteracquires and can transmit a total of 1,418 engineering measuremen ts of internal operating

conditions including temperatures, voltages, compu ter states and counts. Th e spacecrafttransmitters operate at S-band frequency (2,295 megahertz).Two low-gain antennas (one pointed upward or toward the S un, and on e on adeployable arm to point down, both mounted on the spinning section) supportedcommunications during the Earth-Venus-Earth leg of the flight. The top-mounted antenna iscurrently carrying the comm unications load, including science data and playbacks, in place ofthe high-gain antenna, and is the basis of the redesigned Jupiter sequences. Th e other low-gain antenna has been re-stowed after supporting operations during the early VEEGA phase,and is not expected to be used again.Because radio signals take more than one hour to travel from Earth to Jupiter andback, the G alileo spacecraft was designed to operate using p rograms sent to it in advance andstored in S pacecraft mem ory. A single master sequence program can cover from weeks tomonths o f quiet operations between planetary and satellite encounters. Du ring busyencounter operations, one program covers only about a week.These sequences operate through flight software installed in the principal spacecraftcomp uters. In the comm and and data subsystem software, there are about 35,000 lines ofcode, including 7,000 lines of automatic fault protection software, which operates to pu t thespacecraft in a safe state if an untoward even t such as an onboard computer g litch were tooccur. The articulation and attitude control software has about 37,000 lines of code,including 5,500 lines devoted to fault protection.Electrical power is provided to Galileos equipment by two radioisotopethermoelectric generators. Heat produced by natural radioactive decay of plutonium 238dioxide is co nverted to electricity (570 watts at launch, 485 at the end of the mission) tooperate the orbiter equipmen t for its eight-year baseline mission. This is the same type ofpower source used by the Ulysses mission to study the Sun s polar regions, the two Voyager



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spacecraft missions to the outer planets, the Pioneer Jupiter spacecraft, and the twin V ikingMars landers.Scientific instruments to measure fields and particles, together with the main antenna,the power supply, the propulsion module, most of the comp uters and control electronics, are

mounted o n the spinning section. The instruments include m agnetometer sensors, mountedon an 1 1-meter (36-foot) boom to m inimize interference from the spacecraft; a plasmainstrument detecting low-energy charged particles and a plasma-wave detector to studywav es generated by the particles; a high-energy particle detector; and a detector of cosmicand Jovian dust. It also carries the heavy ion co unter, an engineering experiment added toassess the potentially hazardous charged-particle environments the spacecraft flies through,and a n added ex treme ultraviolet detector associated with theW spectrometer on the scanplatform.The despun section carries instruments and other equipment whose operation dependson a steady pointing capability. The instruments include the camera system;.the near-infrared

mapping spectrometer to make m ultispectral images for atmospheric and mo on surfacechemical analysis; the ultraviolet spectrometer to study gases; and the photopolarimeter-radiometer to measure radiant and reflected energy. The camera system will obtain images ofJupiters satellites at resolutions from 20 to 1,000 times better than Voyag ers best, largelybecause it will be closer. The charge-coupled device (CCD) sensor in Galileos camera ismo re sensitive and has a broader color detection band than the vidicons of Voyag er. Thissection also carries an articulated dish antenna to track the atmospheric probe and pick up itssignals for recording and relay to Earth.

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Technology Benefits Derived from GalileoThe research and developm ent necessary to build and fly Ga lileo has producedseveral technological innovations. _- +Charge-cou pled devices like those in Galileo's television s ystem s are now used insome hom e video cameras, yielding sharper images than ever conceived of in the days beforethe project began . In addition, radiation-resistant compon ents develop ed for G alileo are nowused in research, businesses, and military applications where radiation environm ent is aconce rn. Another ad vance, integrated circuits resistant to cosm ic rays, has helped to handledisturbances to computer memo ry that are caused by high-energy particles; thesedisturbances plague extremely high-speed computers on Earth and all spacecraft.



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Program/Project ManagementGalileos scientific experiments are carried out by m ore than 100 scientists fiom sixnations. In addition, NA SA has appointed 17 interdisciplinary scien tists whose studies reach

across more than o ne Galileo instrument data set. .- -The Galileo Project is managed for NA SAs O ffice of Sp ace Science by the JetPropulsion Laboratory, a division of the California Institute of Technolog y. Thisresponsibility includes designing, building, testing, operating and tracking Galileo. Germanyfurnished the orbiters retro-propulsion module and some of the instrum ents and isparticipating in the scientific investigations. The radioisotope thermoelectric generators weredesigned and built by the General Electric Company for the U.S. Department of Energy.NA SAs A mes Research Center, Mountain V iew, CA , was responsible for theatmosphere probe, which was built by Hughes Aircraft Company , El Segun do, CA. AtAm es, the probe manager is Marcie Smith and the probe scientist is Dr. Richard E. Young.

At JPL, W illiam J. ONeil is project manager, Dr. Torrenc e V. John son is projectscientist, Neal E. Ausman Jr. is mission director, and Matthew R. Landa no i s deputy m issiondirector.At NASA Headquarters, the program manager is Don ald Ketterer. Th e programscientist is Dr. Jay Bergstralh. Dr. Wesley T. Huntress Jr. is associate administrator for theOffice of Space Science.

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ATMOSPHERIC PROBEAtmospheric Structure

Neutral Mass Spectrometer

Helium Abundance

NephelometerNet Flux Radiometer

Lightning/Energetic Particles

Alvin Seiff, NASA Am esResearch CenterHasso Niemann, NASA G oddardSFCUlf von Zahn, Bonn University,FRGBoris Ragent, NASA A mesLarry Sromo vsky, Univ. ofWisconsinLouis Lanzerotti, BellLaboratories

In te rd isc ip l in a ry Inves t iga tor sFrances Bagenal, University of ColoradoAndrew F. Cheng , The John s Hopkins UniversityFraser P. Fanale, University of HawaiiPeter Gierasch, Cornell UniversityDonald M . Hunten, University of ArizonaAndrew P. Ingersoll, California Institute of Techn ologyWing-Huen Ip, NSPO /RDD, TaipeiMichael McElroy, Harvard UniversityDavid Morrison, NASA A mes Research CenterGlenn S. Orton, Jet Propulsion LaboratoryTobias Owen , State University of New YorkAlain Rou x, Centre de Recherches en Physique de IEnvironmentChristopher T. Russell, University of California at Lo s AngelesCarl Sagan, Cornell UniversityGerald Schu bert, University of California at Los AngelesWilliam H. Smyth, Atmospher ic & Environmental Research, Inc.James Van Allen, University of Iowa

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July 9, 1996

Temperature, pressure, density,molecular weight profilesChemical composition

Helium hydrogen rat io

Clouds, so lidliq uid particlesThermal/solar energy profiles

Detect lightning, measureenergetic particles

galileo at jupiter the first ganymede encounter press kit

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