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UlyssesUlyssesAchievements: first in situ investigation of the inner heliosphere from the solar

equator to the poles; first exploration of the dusk sector of Jupiter’smagnetosphere; fastest spacecraft at launch (15.4 km/s)

Launch date: 6 October 1990Mission end: planned September 2004Launch vehicle/site: NASA Space Shuttle Discovery from Kennedy Space Center,

USALaunch mass: 370 kg (including 55 kg scientific payload)Orbit: heliocentric, 1.34x5.4 AU, inclined 79.1° to ecliptic, 6.2 year periodPrincipal contractors: Dornier (prime), British Aerospace (AOCS, HGA), Fokker

(thermal, nutation damper), FIAR (power), Officine Galileo (Sun sensors), Laben(data handling), Thomson-CSF (telecommand), MBB (thrusters)]

Ulysses is making the first-everstudy of the particles and fields inthe inner heliosphere at all solarlatitudes, including the polarregions. A Jupiter flyby in February1992 deflected Ulysses out of theecliptic plane into a high-inclinationsolar orbit, bringing it over the Sun’ssouth pole for the first time inSeptember 1994 and its north pole10.5 months later. Ulysses spent atotal of 234 days at latitudes >70°,reaching a maximum 80.2° in bothhemispheres. The mission wasoriginally to end in September 1995,but Ulysses’ excellent health and theprospect of important new sciencehas resulted in operations beingextended for a second solar orbit.After crossing the ecliptic in April1998, Ulysses headed back towardsthe Sun, passing over the south polefor a second time in November 2000,and the north pole in October 2001.In contrast to the polar passes in1994/95, which took place nearsolar activity minimum, the returnto high latitudes is under muchmore active conditions.

The unique data from Ulysses haveadded a new dimension to ourknowledge of the Sun’s environment,the heliosphere. Importantaccomplishments include thecharacterisation of two distinctlydifferent solar-wind states (fast windfrom the poles filling a large fraction

of the heliosphere, and slow windconfined to the equatorial regions),the discovery that high- and low-latitude regions of the heliosphereare connected in a much moresystematic way than previouslythought, the first-ever directmeasurement of interstellar gas(both in neutral and ionised state)and dust particles, and the precisemeasurement of cosmic-ray isotopes.These, together with numerous otherimportant findings, have resulted inmore than 700 publications to datein the scientific literature.

Ulysses in ESTEC’s Test Centre

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ESA and NASA signed the MoU29 March 1978 for the InternationalSolar Polar Mission (ISPM) as a 2-craft mission launched by a singleShuttle and 3-stage Inertial UpperStage (IUS) in February 1983. Jupitergravity assists would have thrownthem into opposing solar orbits.NASA awarded TRW the contract forthe US spacecraft in July 1979;Dornier was selected in September1979 as leader of the STARconsortium for ESA’s spacecraft. USbudget cuts in February 1981 sawNASA unilaterally cancelling itsspacecraft to save $250-300 million.NASA would still provide launch,tracking and the RTG. Shuttle andother problems delayed the launch toMay 1986 – now using a cryogenicCentaur upper stage – but theChallenger accident of January 1986postponed all flights. Safety concernsprompted the final switch to an all-solid 3-tier IUS/Payload AssistModule (PAM) upper stage.

Ulysses’ record 15.4 km/s speed tookit across the Moon’s orbit in only 8 h.The deployment of the 5.55 m radialboom on 7 October 1990 reduced thespin to 4.7 rpm. Beginning withEPAC, the science instruments wereturned on starting 19 October andchecked out over several weeks. The

7.5 m axial boom was deployed on4 November.

After travelling 993 million km andalready collecting importantinformation on the interplanetarymedium, Ulysses began the Jupiterencounter by detecting the bowshockcrossing at 17.33 GMT 2 February1992, some 113 RJ out, more distantthan Pioneer (100 RJ) and Voyager(60 RJ). It approached through thelate morning region of themagnetosphere at about 30ºN, camewithin 378 400 km of the cloudtops(5.3 RJ) at 12.02 GMT 8 February1992, and then exited unscathed onthe previously unexplored evening

Ulysses’ high-gainantenna points

continuously towardsEarth, returning 8 h of

realtime and 16 h ofrecorded data every

day on the Sun’sdomain

Following the successful completion of itsprimary mission, Ulysses is now makingfurther passes over the Sun’s poles.

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dominated by the Sun’s southernpole. This could be seen in theconsistently negative polaritymeasured by the magnetometer fromApril 1993. Increasing latitude alsoreduced the intensity of chargedparticles.

Passage over the Sun’s south poleprovided the first long-term in situobservations of high-speed solarwind flowing from the large coronalhole that covers that polar cap atsolar minimum. Measurements ofionised interstellar neutral gas(‘interstellar pickup ions’) led to amajor advance in understanding theprocesses affecting this componentof the heliospheric particlepopulation.

Unexpectedly, the magnetometersdetected a wide variety offluctuations at many spatial scalesin the Sun’s high-latitude field. Theyare believed to represent relativelyunevolved turbulence originating atthe southern polar coronal hole.Another important finding was thatthe magnetic field radial componentvaries relatively little with latitude.This is contrary to the expectationthat the imprint of the underlyingdipole-like magnetic field at theSun’s surface, showing an increasein the radial field at the poles, wouldbe detected at Ulysses’ position.Simply, there was no south magneticpole at high latitudes. Undoubtedlyrelated to the large-scale fluctuationsin the polar magnetic field was thedetection of an unexpectedly smallincrease in the influx of cosmic raysover the poles. It was hoped that themuch-reduced effects of solarrotation over the pole would result ina smooth near-radial magnetic field,providing easy access to low-energycosmic rays.

side, at high southern latitudes, havingspent more than a week in themagnetosphere. Just before closestapproach, Ulysses entered themagnetosphere’s polar cap. The close13.5 km/s flyby produced the highecliptic inclination – IUS/PAM couldhave reached only 23º without theassist. A major finding was that thesolar wind affects the magnetospheremuch more than expected. Themagnetic field in the dusk sector is notrotating with the planet and is sweptdown into the magnetotail. Also,Jupiter’s intense radiation belts reachonly to 40º latitude, whereas Earth’sextend to 70º. Ulysses passed directlythrough the Io plasma torus (onlyVoyager 1 preceded it), which plays akey role in refuelling themagnetosphere with plasma.

At the end of February 1992, the Sun,Earth and Ulysses were in directopposition, the best time to detectgravitational waves by observing anarcmin shift in the craft’s position.Although they were not positivelyidentified by this radio scienceexperiment, new upper limits were setwith a factor of 20 improvement insensitivity. Important observationsinclude the first direct detection ofionised O, N and He (and neutral He)atoms arriving from interstellar space,and the measurement of micron-sizeddust grains from interstellar space.This first-ever measurement of theinterstellar 3He/4He ratio sugests thatthe amount of dark matter created inthe Big Bang was greater thanpreviously believed.

By mid-1993, Ulysses was permanentlyimmersed in the region of space

Ulysses was launched on an IUS topped by aPAM final kick stage. (Boeing)

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Ulysses is sampling the Sun’s sphere ofinfluence in 3-D for the first time.

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Measurements made by Ulysses during one complete orbit of the Sun, in theform of a polar diagram. The traces show (from the inside moving out) thesolar wind speed increasing from 400 km/s near the equator to 750 km/s atlatitudes >20-30°, the magnetic field polarity, the intensity of acceleratedinterplanetary particles, and the intensity of incoming cosmic rays.

Further information on the Ulysses mission can be found at http://sci.esa.int/ulysses/The Ulysses Qualification Model is displayed at the Noordwijk Space Expo at ESTEC

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Installed on its kick stages at Cape Canaveral,Ulysses is ready for installation aboard the

Space Shuttle. (NASA)

After crossing the ecliptic at adistance of 5.4 AU in April 1998 (thuscompleting the first out-of-the-eclipticorbit), Ulysses headed back towardsthe increasingly active Sun, passingover the south pole for a second timein November 2000, and the northpole in October 2001. The solar windstructure is fundamentally different;the speed measured during 1998-2000 is persistently variable. Thereare no signs of the stable streamstructure seen earlier, and the windspeed rarely exceeds 600 km/s.Although magnetic field compressionsrelated to stream interactions areseen, these show no persistentrecurrence and extend to the highestlatitudes covered to date.

Moving back towards the equator,Ulysses left the fast solar wind(750 km/s) in which it had beenimmersed for more than 18 months,crossed briefly into the equatorialregion dominated by slow wind(400 km/s) and once again becameimmersed in the fast wind, this timefrom the north pole. The boundarieswere strikingly symmetric:22ºS/21ºN. The magnetic fieldchanged from negative (directedinwards) to positive (outwards),reflecting the configuration of theSun’s dipole-like surface field. Theradial component’s strengthcontinued to show no change withlatitude. With the exception of the N-Ssolar wind asymmetry and cosmic-rayintensity, the north pass wasgenerally similar to the south pass.

An unexpected result was the findingthat Ulysses crossed the distant tailof Comet Hyakutake in 1996. Not wellunderstood at the time, the signaturein the magnetic field, solar wind andlow-energy ion data was recognised in1999 to be cometary in origin. Withthis result. Ulysses set a record forthe observation of the longest (3.8 AU)comet tail.

In June 2000, ESA’s ScienceProgramme Committee approvedadditional funding to continueoperations until September 2004. Akey argument for the extension was toobserve the effects of the Sun’smagnetic polarity reversal on theheliosphere’s structure. From 2002,however, the RTG will not be able topower the full payload. The power-sharing strategy guarantees a set ofcore measurements coveringfundamental solar wind and magneticfield parameters, as well as a numberof energetic particle and cosmic raychannels.

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Ulysses principalfeatures.

Locations of Ulysses’scientific instruments.

See the table forexplanation of the

acronyms.

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Ulysses Scientific Instruments

Instrument Measurements Instrumentation Mass Power Data(kg) (W) (bit/s)

SWOOPS Solar Wind Plasma ions 0.257-35 keV/Q; 2 electrostatic analysers 6.7 5.5 160electrons 1-903 eV + channel electron multipliers

SWICS Solar Wind elemental & ion charge electrostatic analyser 5.6 4.0 88Ion Composition composition, T & speed of time-of-flight/

145 km/s (H+)-1352 km/s (Fe+8) energy measurementsolar wind ions

DUST Cosmic Dust 2x10-9-2x10-15g multi-coincidence impact 3.8 2.2 8detector with channeltron

MAG Magnetic Field ±0.01-44 000 nT triaxial vector helium and 4.8 5.1 80fluxgate magnetometers

GRB Solar X-rays/ 5-150 keV 2 Si solid-state 2.0 2.6 40Cosmic Gamma Bursts + 2 CsI scintillation detectors

EPAC/ Energetic Particle 0.080-15 MeV/nucleon composition 4 solid-state detectors 4.3 4.0 160GAS Composition Interstellar Neutral Helium LiF-coated conversion plates

with channel electron multipliers

HISCALE Low-Energy Ions 0.050-5 MeV ions; 2 sensor heads with 5.8 4.0 160& Electrons 30-300 keV electrons 5 solid-state detectors

COSPIN Cosmic Rays/ 0.3-600 MeV/nucleon; 5 solid-state detectors 14.8 14.8 160Solar Particles 4-2000 MeV electrons + double Cerenkov and

semiconductor telescopefor electrons

URAP Radio & Plasma Waves 0-60 kHz plasma waves 72.5 m radial dipole antenna 7.4 10.0 2321-940 kHz 7.5 m axial monopole antenna10-500 Hz magnetic fields 2-axis search coil

Radio Science investigations (Coronal Sounding and Gravitational Wave Experiments) were conducted during the primary missionphase.

Satellite configuration: box-shapedaluminium bus supports body-mounted aluminium/CFRP HGA,RTG boom and several sciencebooms: 5.55 m radial boom carriesfour sensors for HED, STO and HUSexperiments (see table), 7.5 m axialboom acts as monopole for STO andtwo wire booms 72.5 m tip-to-tip asdipole for STO.

Attitude/orbit control: spin-stabilisedat 5 rpm, with fixed HGA pointingcontinuously at Earth. Two sets of4x2 N hydrazine thrusters (33 kgsupply stored at 22 bar) provide spincontrol and trajectory corrections.Attitude determined by Sun sensorsand HGA X-band signal angle.

Power system: RTG provided 284 Winitially, decreasing to 221 W by2001.

Communications/data: Ulysses istracked 8 h/day by the 34 mantennas of NASA’s Deep SpaceNetwork. Operations are controlled bya joint ESA/NASA team at NASA’s JetPropulsion Lab in California. 1.65 m-diameter HGA downlinks realtimedata at 1024 kbit/s interleaved withplayback of stored data at 20 W8.4 GHz X-band. 5 W S-band2112/2293 MHz up/down is used fordual-frequency radio scienceinvestigations. Two redundant taperecorders each store 45.8 Mbit at128/256/512 bit/s.

ESA named the project after Homer’s mythological hero and in reference to Dante’sdescription in the Inferno of Ulysses’ urge to explore ‘an uninhabited world behind the Sun’.

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ERSERSAchievements: first European radar satellites, first long-duration civil radar satellitesLaunch dates: ERS-1 17 July1991; ERS-2 21 April 1995Mission end: ERS-1 10 March 2000; ERS-2 continues full operations. 3-year

projected livesLaunch vehicle/site: Ariane-4 from Kourou, French GuianaLaunch mass: ERS-1 2384 kg on-station BOL (888 kg payload, 318 kg hydrazine);

ERS-2 2516 kg on-station BOL Orbit: ERS-1 782x785 km, 98.5° Sun-synchronous with 35-day repeat cycle during

most of operational phase; ERS-2 784x785 km, 98.6° Sun-synchronous, phasedwith ERS-1 for 1-day revisits

Principal contractors: Dornier (prime), Matra (bus), Marconi Space Systems (AMI),Alenia Spazio (RA), British Aerospace (ATSR); ERS-2 added Officine Galileo(GOME)

ESA launched ERS-2 to ensurecontinuity of service until Envisat’sappearance in 2001, and the pairingwith ERS-1 made newdemonstrations possible. The twosatellites operated simultaneouslyfrom August 1995 to May 1996 – thefirst time that two identical civilSynthetic Aperture Radars (SARs)had worked in tandem. The orbitswere carefully phased for 1-dayrevisits, allowing the collection of

The European Remote Sensing (ERS)satellite is the forerunner of a newgeneration of environmentalmonitoring satellites, employingadvanced microwave techniques toacquire measurements and imagesregardless of cloud and lightingconditions. Such techniques had beenused previously only by NASA’s short-lived Seasat mission in 1978, andduring brief Space Shuttleexperiments.

ERS is unique in its systematic andrepetitive global coverage of theEarth’s oceans, coastal zones andpolar ice caps, monitoring waveheights and wavelengths, wind speedsand directions, precise altitude, iceparameters, sea-surface temperatures,cloud-top temperatures, cloud coverand atmospheric water vapourcontent. Until ERS appeared, suchinformation was sparse over the polarregions and the southern oceans, forexample.

ERS is both an experimental and apre-operational system, since it hashad to demonstrate that the conceptand the technology have maturedsufficiently for successors such asESA’s Envisat, and that the systemcould routinely deliver to end userssome data products such as sea-icedistribution charts within a few hoursof the satellite observations.

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TheGlobal Ozone

Monitoring Experiment(GOME) aboard ERS-2 clearly

showed a deep ozone hole over theSouth Pole in October 1996. (ESA/DLR)

ERS view of flooding in Northern Europe in January1995. This image was created by superimposingtwo Synthetic Aperture Radar images and assigningdifferent colours to each. The first image wasacquired on 21 September 1994 and the second on30 January 1995. Flooded areas appear in blue.

ERS in orbitalconfiguration. During itsremarkable career,ERS-1 generated about1.5 million SAR scenes.More than 3500scientists havepublished more than30 000 scientific papersbased on ERS data.(Dornier)

‘interferometric’ image pairsrevealing minute changes.

ERS-1 was held in hibernation asa backup from June 1996, whileERS-2 continued full operations. ItsSAR Image mode was activated dailyfor battery conditioning. On 8 March2000 a computer failure was followedthe next day by an unrelated gryo

control failure, leading to batterydepletion on 10 March. During itsremarkable career, major progresswas made in environmental andgeophysical applications such asdisaster monitoring and riskmanagement. It is hoped that ERS-2will continue operations until at leastMetop-1 is commissioned in 2006.

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ERS-2 undergoing finallaunch preparations atKourou, French Guiana.(ESA/CSG/Arianespace)

El Niño is a disruption of theocean-atmosphere in the tropicalPacific that affects weatheraround the globe. The 1997-98El Niño is one of the strongest thiscentury, with increased rainfallcausing destructive flooding in theUS and Peru, and drought in thewestern Pacific, also associatedwith devastating fires. Thephenomenon is characterised by arise of up to 40 cm in sea level andup to 8°C in sea-surfacetemperature in the easternequatorial Pacific and falls of up to40 cm/6°C in the western equatorialPacific. They are closely monitored bythe ERS Radar Altimeter and Along-Track Scanning Radiometer. Theimage above shows the state of thePacific Ocean in November 1997. Theheight of this 3D image representssea-level anomalies, ranging from-40 cm to +40 cm; the colours indicatesea-surface temperature anomaliesranging from -6°C (blue) to 8°C (red).

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ERS-2 in the LargeEuropean AcousticFacility at ESTEC.

The 'normal' state of the ocean issuch that the sea level on the

western side is higher than on theeastern side. This difference is due

to the Trade Winds blowingconstantly from east to west,

causing the waters to pile up at thewestern side. Also due to the Trade

Winds, the surface water on theeastern side is constantly trans-

ported westward, and replaced bycold, nutritious water rising from

deeper layers. So generally along theSouth American coast, cold and

nutritious waters prevail, while onthe western side there is warm

surface water. During an El Niñoevent the Trade Winds relax, andbecome very weak (and may even

reverse). This causes the warmsurface waters to flow back eastward, and stops the up-

welling on the eastern side. No moreupwelling means that the sea-surface

temperatures rise, implying a sea levelrise.

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ERS Earth Observation Payload

Active Microwave Instrument (AMI)

Incorporates two separate 5.3 GHz C-band 4.8 kW-peak power radars:a Synthetic Aperture Radar using a 1x10 m antenna for the image andwave modes; a 3-beam scatterometer for the wind mode. SAR imaging:30 m resolution, linear-vertical polarisation, 37.1 µs transmit pulsewidth, 105 Mbit/s data rate, 100 km swath width, with 23° incidentangle at mid-swath (up to 35° using experimental roll-tilt attitudecontrol system mode). SAR wave mode: operates at 200 km intervalsalong-track for 5x5 km images to provide ocean wave speed anddirections. AMI Wind Scatterometer: three antennas (fore/aft360x25 cm, mid 230x35 cm) providing fore/mid/aft beams sweep500 km swath in 50 km cells for surface wind vectors: 4-24 m/s,0-360±20°.

Radar Altimeter (RA)

The 120 cm-diameter nadir-viewing, 13.8 GHz, 1.3°-beamwidthaltimeter measures, in Ocean Mode, wind speed (2 m/s accuracy),1-20 m wave heights (50 cm accuracy, 2 km footprint), and altitude to5 cm. Ice Mode operates with a coarser resolution to determine icesheet topography, ice type and sea/ice boundaries.

Along-Track Scanning Radiometer and Microwave Sounder (ATSR-M)

An experimental 4-channel IR radiometer for temperaturemeasurements and a 2-channel nadir-viewing microwave sounder forwater vapour measurements. IR Radiometer: scanning at1.6/3.7/10.8/12 µm, 0.5 K resolution over 50x50 km, 1 km spatialresolution; 500 km swath. ERS-2 added 0.55/0.67/0.78 µm visiblechannels to improve monitoring of land applications, such asvegetation moisture. Microwave Sounder: 23.8/36.5 GHz channelsmeasuring the vertical column water vapour content within a 20 kmfootprint, providing corrective data for ATSR sea-surface temperatureand RA measurements.

Global Ozone Monitoring Experiment (GOME, ERS-2 only)

Near-UV/visible scanning spectrometer measuring backscatteredEarth radiance in 3584 pixels over four channels, 240-316/311-405/405-611/595-793 nm, to determine ozone and trace gases introposphere and stratosphere.

Precise Range/Range Rate Experiment (PRARE)

For precise orbit determination with ranging accuracy of 3-7 cm using8.5 GHz signals transmitted to a network of mobile groundtransponders. ERS-1 PRARE failed within 3 weeks because ofradiation damage, but ERS-2’s improved design remains operational.

Laser Retroreflector

Also permits precise range/orbit determination, but less frequentlythan PRARE, and RA calibration.

Further information on ERS and other ESA

Earth observation projects can be found at

http://earth.esa.int

Satellite configuration: payload supportmodule, 2x2 m, 3 m high, above aplatform derived from Matra’s 3-axisSpot platform providing power, AOCSand overall operational management.Total 11.8 m high, 11.7 m deployedspan.

Attitude/orbit control: primary attitudecontrol by reaction wheels, unloadedby magnetorquers. Hydrazine thrustersprovide orbit adjust and furtherattitude control. Pitch/roll informationfrom Digital Earth Sensor, yawreference from Sun sensor; supportedby 6 gyros. ERS-2 began 1-gyro controlin Feb 2000, and switched to gyrolesscontrol (using DES and X-axis RW) inFeb 2001 to preserve remaining goodgyro for critical operations.

Power system: twin 2.4x5.8 m Si-cellsolar wings sized for 2.2 kW after2 years, supported by four 24 Ahnickel cadmium batteries.

Communications: controlled from ESOCat Darmstadt, Germany with ESAground receiving stations at Salmijärvi,near Kiruna (Sweden, primary station,also for TT&C), Fucino (I), Gatineau(CDN), Maspalomas (E), Prince Albert(CDN), plus national & foreign stationse.g. at Fairbanks (Alaska, US),Neustrelitz (D), West Freugh (UK), AliceSprings (Australia). SAR’s 105 Mbit/simage data returned in realtime only,available only when the wave/windmodes are inactive (other datarecorded onboard, thus providingglobal coverage). ESA’s ESRIN ERSCentral Facility (EECF) facility atFrascati (I) is the user service and datamanagement centre and prepares themission operation plan for ESOC, withprocessing/archiving facilities at Brest(F), Farnborough (UK), DLROberpfaffenhofen (D) and Matera (I).Some products, such as from the windscatterometer, are available within 3 hof observation.

ERS principal features (ESA). Inset left: ERS-1 imagedfrom 41 km above by France’s Spot-4 Earth observationsatellite on 6 May 1998 over the Tenere Desert of Niger,Africa (CNES). Inset right: the first recorded SAR image(at Kiruna) from ERS-1, taken at 11:50:32 UT 27 July1991 and centred on 79.99°N/15.01°E (ESA).

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EurecaEurecaAchievements: world’s first dedicated microgravity free-flyer; Europe’s first

reusable satelliteLaunch date: 31 July 1992Mission end: 24 June 1993Launch vehicle/site: NASA Space Shuttle from Kennedy Space Center, FloridaLaunch mass: 4490 kg (payload capacity up to 1000 kg)Orbit: released from Shuttle into 425 km, 28.5°, raised to 508 km for experiment

operations, lowered to 476 km for retrieval by ShuttlePrincipal contractors: MBB-ERNO (prime)

ESA began studying the EuropeanRetreivable Carrier (Eureca) in 1978as a follow-on to the mannedSpacelab programme; the ESACouncil approved it in December1981. Eureca was designed to carry amix of experiments totalling up to 1 tfor 6-9 months in orbit, released andretrieved by NASA’s Space Shuttle. Itwas the world’s first free-flyerdesigned specifically to satisfymicrogravity experiments, providing10-5 g conditions for long periods.Although Eureca was controlled fromESOC in Germany, it could operateautonomously for up to 48 h. Animportant feature was reusability:Eureca was capable of making fiveflights over a 10-year period.

Eureca-1 and its 15 experiments (seeseparate box) were launched aboardShuttle mission STS-46 in July 1992and released from the Shuttle’s robotarm by ESA Mission SpecialistClaude Nicollier on 2 August.Eureca’s thrusters raised its orbit by83 km within a week and the6 months of operations began on 18August. Most of the microgravityexperiments were completed byJanuary 1993, but others continuedeven as it Eureca waited for recoveryduring Shuttle mission STS-57 inJune 1993. By that time, its orbithad decayed through atmosphericdrag to 490 km and its thrusterslowered it further to 476 km for NASAastronaut George Low to capture itduring 24 June.

The Eureca-1 mission was rated ashighly successful, and a 1995Eureca-2 mission was planned butESA Ministerial meetings rejectedfurther funding. The carrier wasstored at DASA (ex-MBB/ERNO) inBremen, where it was hoped that aDASA-led consortium could providecommercial flights.

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Eureca’s solar wingswere safely deployedbefore the free-flyer wasreleased. (NASA)

Integration of Eureca atDASA in Bremen.(DASA)

Eureca-1 Payload

ESA’s five microgravity core multi-userfacilities:

– Automatic Mono-ellipsoid Mirror Furnace(AMF)

– Solution Growth Facility (SGF)– Protein Crystallisation Facility (PCF)– Multi Furnace Assembly (MFA)– Exobiological Radiation Assembly (ERA).

Two further microgravity elements were:

– High Precision Thermostat (HPT, Germany)– Surface Forces Adhesion Experiment (SFA,

Italy).

The five space science experiments were:

– Solar Spectrum Experiment (SOSP)– Solar Variation Experiment (SOVA)– Occultation Radiometer (ORA)– Wide Angle Telescope for Cosmic and

X-ray Transients (WATCH)– Timeband Capture Cell Experiment (TICC).

The three technology demonstrations were:

– Radio Frequency Ionization ThrusterAssembly (RITA)

– Advanced Solar Gallium Arsenide Array(ASGA)

– Inter Orbit Communication Experiment(IOC, working with Olympus).

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Eureca – with its solarwings already folded

against its sides – wasrecaptured in June 1993

after almost a year inorbit. (NASA)

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Satellite configuration: total width4.6 m, total height about 2.6 m. Busstructure consisted of carbon fibrestruts connected by titanium nodaljoints. The nodes carried largerhardware loads, while smallerassemblies were fastened to standardEquipment Support Panels.Supported in Shuttle cargo bay bytwo longeron and one keel fitting.Grapple fixture alloweddeployment/retrieval by ShuttleRemote Manipulator System.

Attitude/orbit control: 3-axis control(normally Sun-pointing) bymagnetorquers, supported byReaction Control Assembly of6x21 mN nitrogen thrusters. Orbittransfers between about 400-500 kmby Orbit Transfer Assembly ofredundant 4x21 N hydrazinethrusters (supply sized for twotransfers plus 9-month on-orbit stay).Attitude/rate determination byaccelerometer package, gyros and IREarth and Sun sensors.

Power system: twin deployable/retractable 5-panel Si-cell wings

Processing Eureca atthe Kennedy SpaceCenter for insertion intothe Space Shuttle cargobay. (NASA)

Eureca has been displayed since November 2000 at the Swiss Museum of Transport and Communication in Lucerne. (Courtesy of the Museum)

generated 5 kW at 28 Vdc, providing1 kW average for payload operations(1.5 kW peak). Supported by 4x40 Ahnickel cadmium batteries.

Communications: controlled fromESOC in Darmstadt, Germany.S-band link provided up to256 kbit/s downlink for payloads,with 128 Mbit onboard memory.

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ISOISOAchievements: world’s first space infrared observatory; fundamental discoveries on

the nature of the Universe; far-exceeded design lifeLaunch date: 19 November 1995 (routine science operations began 4 February

1996)Mission end: deactivated 12:00 UT 16 May 1998; last science observation 10 May

1998; cryogen exhausted 8 April 1998Launch vehicle/site: Ariane-4 from Kourou, French GuianaLaunch mass: 2498 kg (2418 kg BOL)Orbit: initially 500x71 850 km, 5.25°; raised to operational 1038x70 578 km, 5.2°,

24 hPrincipal contractors: Aerospatiale (prime), DASA (cryostat payload module)

The spectacular success of theInfrared Space Observatory (ISO) asthe world’s first spaceborneobservatory working in the cool lightof the infrared has provided anentirely fresh perspective on theUniverse. It has proved a major boostto most areas of astrophysics,reaching from the nearby planets tothe most distant quasars, taking instar formation, dark matter andsuperluminous galaxies.

The cryogenically-cooled ISO studiedthe Universe’s 2.5-240 µm IRradiation as a follow-up to the all-skysurvey undertaken by IRAS(8-120 µm) in 1983. However, ISO’ssensitivity at 12 µm was about 1000times greater and spatial resolution100 times higher, and it was operatedfrom ESA’s station in Villafranca,Spain as an observatory, studyingspecific targets for up to 10 h at atime, with more than half of itsobserving time available to thegeneral astronomical community.

Very deep camera and photometerimages were recorded to study theearly evolution of galaxies and to helpdetermine the history of starformation. All the instrumentsobserved many star-forming regionsto study how clouds of dust and gascollapse to form young stars. Manyobservations looked at stars withdiscs of matter to unravel the

mysteries of planet formation. Thespectrometers found abundant waterin many different places: Comet Hale-Bopp, Mars, Titan and the giantplanets in our own solar system,around young and old stars and evenin external galaxies. ISO looked hardat the mysterious ‘ULIRGs’ (ultra-luminous IR galaxies) and shed newlight on whether their prodigiouspower comes mainly from bursts ofstar formation (the ‘baby’ theory) or

http://www.iso.vilspa.esa.es

New-born stars inthe Rho Ophiuchicloud. The brightfuzzy object at topis a new massivestar – muchheavier than theSun – still wrappedin the placentalcloud from whichit formed.(ESA/ISO, CEASaclay, ISOCAMConsortium)

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from stars beingswallowed by blackholes (the ‘monster’theory). ISO foundthe characteristicchemicalsignatures ofstarbursts.

ISO found clear links between stars,comets and Earth’s origin. It foundthe spectral signature of the mineralolivine – a major constituent ofEarth’s interior – in Comet Hale-Boppand in dusty discs encircling youngstars where planetary systems areforming. Many molecular specieswere detected in interstellar space forthe first time, including carbon-bearing molecules such asthe methyl radical andbenzene, providing insightinto the complex organicchemistry necessary toproduce the molecules oflife.

ISO made more than26 000 separateobservations and, by thetime orbital operationsended, the work of detailedanalysis was only juststarting. The flood of resultsshows no sign of abating: almost 700refereed papers were publishedbetween late 1996 and May 2001,and about 100 astronomers everymonth retrieve data from the ISOarchive in Villafranca (E).

Working at these thermalwavelengths meant that ISO’stelescope and detectors had to beencased in a cryostat filled with>2100 litres of superfluid heliumchilled to only 1.8 K above absolutezero. A pre-mission life of about 18months was required before thehelium completely boiled away,

leaving the instrumentsto warm up, but thesupply lasted for10 months longer, until8 April 1998. Thisallowed, for example, twoseries of observations ofthe Taurus-Orion region,an important cradle of

star birth. Even after the cryogen wasexhausted, a few of the short-wavelength detectors in aspectrometer could be used for aspecial scientific programmeinterleaved with final calibrations andtechnology tests. Some extra 150 hwere used to measure almost 300stars at 2.4-4 µm. ISO’s ‘last light’observation, late on 10 May 1998,was of the Canis Majoris hotsupergiant star. The remainingpropellant was then used to lower theperigee in order to speed up theorbit’s decay: ISO is expected toreenter within 20-30 years.

http://sci.esa.int/iso

The Antennae: thecollision of twogalaxies hastriggered starformation withindense IR-bright dustclouds.

Seen in the far-IR, the Andromeda Galaxy (M31) sports multiple rings

rather than the classical spiralform seen in visible light.

ES

A/IS

OP

HO

T

ES

A/IS

OC

AM

ISO’s payload modulewas supported by the

service module below.(Aerospatiale)

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ISO’s telescope anddetectors wereencased in a cryostatfilled with superfluidhelium at 1.8 K.Incoming infraredradiation was fed tothe four scienceinstruments below themain mirror. (DASA)

ISO’s orbit tookit above theworst of Earth’sradiation beltsfor almost 17 hper day.

ISO saw water throughout theUniverse, increasing expectationsof life beyond Earth. Particularlyexciting was finding water onTitan – Saturn’s largest moonand the target of ESA’s Huygensprobe. Titan will help us tounderstand the organic chemistryof the young Earth, with its mixof elaborate organic moleculesresembling the chemical soup outof which life emerged. Thanks toISO, the cosmic history of waterwas traced for the first time.During the violent early stages ofstarbirth, a young star spews outhigh-speed gas, generating ashock wave that heats andcompresses the surroundinghydrogen and oxygen, creatingthe right conditions for water toform. ISO saw the process atwork in the Orion and Sagittariusnebulae. ISO also unexpectedlyfound large amounts of water inthe higher atmospheres of theSolar System’s giant planets. Thewater must be coming fromcometary grains. (ESA/ISO SWS)

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Satellite configuration: cylindrical payload module with conical sunshade and twostar trackers, supported by servicemodule providing basic spacecraftfunctions. Overall size: 5.3 m high, 2.3 mwide. The payload module was a cryostatenveloping the telescope and detectors,cooled by a toroidal tank holding 2250litres of 1.8 K superfluid helium for atleast 18 months’ observations. Somedetectors were cooled to 2 K by copperlinks to the tank; other elements werecooled to 3-4 K by the boiloff gas. Atoroidal tank with 60 litres of normalliquid helium provided cooling on the padfor the last 100 h before launch.

Attitude/orbit control: 3-axis arcsec-control for stable observations of up to10 h incorporated Earth/Sun sensors,star trackers, four rate integrating gyros,four skewed reaction wheels andredundant sets of 8x2 N hydrazinethrusters.

Power system: 600 W provided from twofixed Si-cell body panels (which also actedas thermal shields).

Communications: realtime downlink (noonboard recorders) at 33 kbit/s (24 kbit/sfor science data) to ISO Control Centre atVillafranca, Spain, allowing about 13 h ofcontact daily. NASA’s Goldstone station inCalifornia extended coverage to almost24 h daily. ISO was used scientificallywhile outside the radiation belts, i.e.about 16.75 h per day.

ISO Scientific Instruments

The 60 cm-diameter Ritchey-Chrétien tele-scope fed four focal-plane instrumentsbehind the main mirror for photometry andimaging at 2.5-240 µm and medium/high-resolution spectroscopy at 2.5-196 µm.

ISOCAM

2.5-17 µm camera/polarimeter,1.5/3/6/12 arcsec resolutions, two channelseach with 32x32-element arrays. PI: Catherine Cesarsky, CEN-Saclay, France.

ISOPHOT

2.5-240 µm imaging photopolarimeter,operating in three separate modes as30-240 µm far-IR camera, 2.5-12 µm spectro-photometer, and 3-110 µm multi-band multi-aperture photopolarimeter. PI: Dietrich Lemke, MPI für Astronomie,Germany.

SWS

2.5-45 µm Short Wavelength Spectrometer(two gratings and two Fabry-Perot inter-ferometers), 7.5x20 and 12x30 arcsecresolutions, 1000 and 20 000 spectralresolution. PI: Thijs de Graauw, SRON, Netherlands.

LWS

45-196 µm Long Wavelength Spectrometer(grating and two Fabry-Perot interferometers),1.65 arcmin resolution, 200 & 10 000spectral resolution. PI: Peter Clegg, Queen Mary & WestfieldCollege, UK.

TheWhirlpool Galaxy

was ISO’s ‘first light’ targeton 28 November 1995, when the

telescope was opened to the sky. TheISOCAM image shows regions of star formations

along the spiral arms and on either side of the nucleus.

ISOCAM image of Comet Hale-Bopp inOctober 1996, revealing the comet’s dustcoma 100 000 km across. Inset: ISOCAM.

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SohoSohoAchievements: unique studies of helioseismology, the heating and dynamics of the

corona and transition region, the acceleration and composition of the solar windand coronal mass ejections, comets, the heliosphere and the interstellar wind

Launch date: 2 December 1995Mission end: operations approved to 2003 (2-year design life); further extensions

possibleLaunch vehicle/site: Atlas 2AS from Complex 36, Cape Canaveral Air StationLaunch mass: 1864 kg (655 kg payload, 240 kg hydrazine)Orbit: halo orbit around Sun-Earth L1 libration point (1.5 million km from Earth);

arrived 14 February 1996Principal contractors: Matra Marconi Space (prime, payload module, propulsion

subsystem), British Aerospace (AOCS), Alenia (structure, harness), CASA(thermal control), Saab Ericsson (communications, data handling)

The Solar and HeliosphericObservatory (Soho) is a cooperativeproject between ESA and NASAstudying the Sun, from its deep core,through its outer atmosphere and thesolar wind, into the heliosphere.

Three helioseismology instrumentsare providing unique data – cleanerby at least an order of magnitudecompared to ground observations –on the structure and dynamics of theSun’s interior, from the very deepcore to the outermost layers of theconvection zone. Five complementaryimagers, spectrographs andcoronagraphs observing in EUV, UVand visible-light are providing ourfirst comprehensive view of the outersolar atmosphere and corona, helpingto solve some of the Sun’s mostperplexing riddles, including theheating of the corona and theacceleration of the solar wind.

Three particle instruments explorethe detailed composition, state andvariability of the Earth’s spaceenvironment in space, as influencedby the solar wind, coronal massejections and extragalactic sources.The outward-looking SWAN scans thesky for clues to the changing large-scale structure of the solar wind andits interaction with the intergalacticmedium, as well as giving uniquemeasurements of comet properties.

Soho is providing solar physicistswith their first long-term,uninterrupted view of the Sun,helping us to understand theinteractions between the Sun and theEarth’s environment withunprecedented clarity.

Soho recorded its first solar image on19 December 1995, en route to itsorbit around the L1 Lagrangian point.Halo-orbit insertion occurred on14 February 1996, 6 weeks ahead ofschedule following a launch so

Soho’s Payload Module atMatra Marconi Space

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Left: Soho’s LASCO coronagraph masks the Sun’s brightdisc or order to reveal the much fainter corona. LASCO’sunprecedented sensitivity enables it to see the thin ionisedgas of the solar wind out to the edges of the picture, 22million km from the Sun’s surface. A doomed cometevaporates in the Sun’s atmosphere. The disc image is EIT284 Å, surrounded by UVCS O VI.(LASCO/UVCS/EIT/ESA/NASA)

Right: EIT image in resonance lines of 8- and 9-timesionised iron (Fe IX/X) at 171 Å in the extreme ultraviolet

showing the solar corona at a temperature of about1 million K. This image was recorded on 11 September

1997. It is dominated by two large active region systems,composed of numerous magnetic loops.

(EIT/ESA/NASA)

precise it retained enough hydrazinefor 50 years of operations. Routinescience operations began aftercommissioning was formally completedon 16 April 1996. Since then, Soho hasgenerated a torrent of data that place itcentre stage in solar physics. Scientifichighlights include:

– unprecedented accuracy in modellingthe solar interior, and in measuringsolar irradiance variations;

– detecting plasma rivers beneath thesurface;

– discovering a quasi-periodicoscillation in the rotational shearnear the base of the solar convectionzone;

– discovering a magnetic surface‘carpet’, subducted and replacedevery 1.5-3 days, that may be theenergy source for coronal heating;

– the first detection of a flare-induced‘sun-quake’;

– holographic imaging of the Sun’s farside – the Sun made transparent;

– identifying the source regions of thefast solar wind;

– revealing the highly dynamicnature of the transition region evenin ‘quiet Sun’ areas;

– detecting polar plume oscillationsof 11-25 min indicative ofcompressive waves;

– discovering ‘EIT waves’ and theirrelation to CMEs, dramaticallyimproving space weatherforecasting reliability;

– possibly the first directobservations of a post-CME currentsheet;

– providing invaluable statistics on,and spectacular images and moviesof coronal mass ejections;

– measuring ion temperatures incoronal holes up to 200 million K;

– significantly contributing tounderstanding the acceleration ofthe solar wind;

– discovering large differencesbetween the heating andacceleration mechanisms at play inpolar versus equatorial coronalholes;

– discovering falling coronalstructures;

http://sci.esa.int/soho/

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Soho's Payload Module atMatra Marconi Space.

– initial acceleration of >10 MeVparticles seem to occur when an‘EIT wave’ propagates to the Earth-connected field lines;

– measuring ion freeze-intemperatures and their variationswith element and time;

– discovering >300 Sun-grazingcomets (more than a quarter of allcomet discoveries since 1761!);

– uniquely measuring cometaryoutgassing rates and nucleus sizes;

– detecting active regions on theSun’s far side through their‘lighthouse’ effect.

Soho had returned about 2 millionimages when, on 25 June 1998,control was lost during routinemaintenance operations. Contact wasre-established on 3 August, allowingthe batteries to be charged, and thepropulsion system and its hydrazineto be thawed. Sun-pointing wasrestored on 16 September and Sohowas finally returned to normal modeon 25 September. The firstinstrument (SUMER) was switched on

5 October and all 12 scienceinstruments were back to normal on4 November. Soho’s missioncontinued.

Although the freezing had notseriously affected the instruments,two of Soho’s three gyros weredamaged by the cold. Then, on 21December 1998, the surviving gyrofailed and Soho began firing itsthrusters to maintain Sun-pointing.To halt the rapid depletion ofhydrazine, engineers devisedsoftware to ignore faulty gyro data,making Soho the first 3-axisstabilised spacecraft to operatewithout gyros. Science operationsresumed 2 February 1999.

In order to fulfil its high promise,Soho observations were planned tocontinue at least through the periodof maximum sunspot activity in2000. The two agencies then agreedto extend the mission to 2003,operating Soho as the flagship of amulti-national fleet of solarspacecraft that includes Ulysses andCluster. Further extension is likely.

Satellite configuration: 2.5x2.9 m,total height 3.9 m, 9.5 m spanacross solar array. Instrumentsaccommodated in Payload Module,highly decoupled from ServiceModule, which forms the lowerportion of the spacecraft andprovides power, thermal control,AOCS, pointing andtelecommunications for the wholespacecraft and support for the solarpanels.

Attitude/orbit control: 3-axisstabilisation, Sun-pointing with10 arcsec accuracy, pointing stability1 arcsec per 15 min (10 arcsec per6 months), using 4 reaction wheels

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and two sets (redundant) of eightthrusters. Attitude data from twofine-pointing Sun sensors, two startrackers and three gyros (no-gyrooperations since February 1999).

Power system: 1400 W from twin2.3x3.66 m Si-cell solar wings(payload requires 440 W), supportedby two 20 Ah nickel cadmiumbatteries.

Soho Scientific Instruments

Instrument Principal Investigator

GOLF Global Oscillations at Low Frequencies A. Gabriel, IAS, F

VIRGO Variability of Solar Irradiance and Gravity Oscillations C. Fröhlich, PMOD Davos, CH

MDI Michelson Doppler Imager P. Scherrer, Stanford Univ, US

SUMER Solar Ultraviolet Measurements of Emitted Radiation K. Wilhelm, MPAe Lindau, D

CDS Coronal Diagnostic Spectrometer R. Harrison, RAL, UK

EIT Extreme UV Imaging Telescope J.-P. Delaboudinière, IAS, F

UVCS UV Coronagraph Spectrometer J. Kohl, SAO, US

LASCO Large Angle Spectroscopic Coronagraph R. Howard, NRL, US

SWAN Solar Wind Anisotropies J.-L. Bertaux, SA, F

CELIAS Charge, Element and Isotope Analysis System P. Boschler, Univ Bern, CH

COSTEP Comprehensive Supra Thermal and Energetic H. Kunow, Univ Kiel, GParticle Analyser

ERNE Energetic and Relativistic Nuclei and Electron Expt J. Torsti, Univ Turku, SF

IAS: Institut d’Astrophysique. PMOD: Physikalisch-Meteorologisches Observatorium Davos. MPAe: Max-Planck-Institut für Aeronomie. RAL: Rutherford Appleton Laboratory. SAO: Smithsonian Astrophysical Observatory. NRL:Naval Research Laboratory. SA: Service d’Aeronomie

Communications: science instrumentsnormally return 40 kbit/s(+160 kbit/s when MDI in high-ratemode) at 2.245 GHz S-band toNASA’s Deep Space Network for 12 hdaily; supported by 1 Gbit taperecorder and 2 Gbit solid-staterecorder. Instrument operations arecontrolled from the ExperimentOperations Facility at NASA’sGoddard Space Flight Center.

Soho is providing anunprecedented view of the

Sun and its interior