Europe made great advances in planetary exploration with the space probe to Halley's comet. The current and future plans incorporated in the Horizon 2000 core programme are minimal but balanced. They are currently threatened by lack of resources: it would be unforgivable to leave this field to the large space powers no

Balsiger, Hans

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Science and Public Policy,volume 18, number 4, August 1991, pages 214-218, Beech Tree Publishing. 10 Watford Close, Guildford, Surrey GUI 2EP, England.Planetary explorationEurope and the large solar system projectsHans BalsigerEurope made great advances in planetary explor-ation with the space probe to Halley's comet. Thecurrent and future plans incorporated in theHorizon 2000 core programme are minimal butbalanced. They are currently threatened by lackofresources: it wouldbe unforgivable to leave thisfield to the large space powers now.Hans Balsiger is Professor of Physics, Physikalisches Institut,Universitat Bern, Sidlerstrasse 5, CH-3012 Bern, Switzerland.SINCE SOLAR SYSTEM science began inthe early 17th century, when some of themore spectacular discoveries were made bythe telescope and when, for example Descartesproposed a remarkably accurate view on the for-mation of the Sun and the planets; European scien-tists have played an important role in this field. Inthe 50s a strong community developed which ana-lysed with novel instrumentation the only samplesavailable from space, the meteorites. This samecommunity made important contributions to theanalysis of lunar samples provided by the Apolloastronauts and by the unmanned USSR lunar mis-sions. Its expertise will again be called upon whensamples from Mars and from a cometwillhopefullybecome available shortly after the turn of thecentury.The space age ofsolar system exploration beganin 1962with the Venus flyby ofMariner-2, and hereEuropeans had to assume the role of junior part-ners in the programmes of the US and USSR spaceagencies. The lack of its own launcher and therelatively small budget restricted the EuropeanSpace Agency (ESA) to space missionsclose to theEarth with payloads dedicated to astronomy ormagnetosphere/solar wind science.Several attempts were made to get a planetarymission approved within ESA, but it took until1980 for the now well-known Giotto mission toComet Halley to be selected. In the meantime,several national programmes had profited from thegenerous hospitality of the two space powers andthus were able to fly experiments on planetarymissions andto gain experience in this field.In this presentation some highlights of the firstand highly successful European deep spacemission to Comet Halley are discussed, and a pre-214 0302-3427/91/040214-5 US$03.00 © Beech Tree Publishing 1991 Science and Public Policy August 1991view is given of future ESA solar system missionswhich are already scheduled or in the planningphase.For the present purpose solar system explora-tion is divided into three fields:• the study of planetary bodies, including moons,asteroids, comets, meteorites, and dust;• the investigation of the plasmas in the solarsystem, that is the solar wind, the planetary mag-netospheres, including their interaction with thesolar wind;• the study of the Sun itself, including the sourceregion of the solar wind, the corona.In the first field, the main European expertise untilrecently has been in the laboratories where me-teorites and lunar samples have been, and are still,analysed. These laboratories are very competitiveworld-wide, and they would have the expertise tomake important contributions when Mars andcometary material is returned to earth. In addition,of course, Europe has recently gained a head startin cometary chemistry and physics with its Giottomission to Halley's comet.In the second field, European scientists havealso managed to make important contributions.Firstly, based on the facts that such investigationsdo not necessarily need deep space probes (Earth'smagnetosphere) and that they are somewhat lesscomplex than those for planetary explorations, ittook Europe's scientists a relatively short time tocatch up with their colleagues. In some cases theyeven managed to take the lead in developing newtechniques (for instance in the measurements ofelectric fields by tracking electron beams or in theanalysisof plasma composition).Secondly, the Scandinavian countries have along history of research in auroral phenomena andhave, since the beginning of the space age, been inthe forefront of all investigations relating to aur-orae. Hence, research of the terrestrial upper at-mosphere and magnetosphere, both experimentaland theoretical, has been strongly developed.For the third field there has also always been abroad interest among ground based observers inEurope. With its first cornerstone ESA will in thenear future make its space-based contribution inGiotto was able to cross the contactsurface of Halley's comet and itallowed the gas and ion massspectrometers to analyse the innercoma, the atmosphere/ionosphere,which was undisturbed by the solarwindScience and Public Policy August 1991Europeand the large solarsystemprojectsthe form of the Solar and Heliospheric Observa-tory, SOHO. It is especially noteworthy that thisobservatory will include the most complete pay-load for helioseismology to date. This techniqueallows the investigation of the inner structure ofthe Sun and will thus greatly advance our under-standing of the physicsof this our nearest star.I shall concentrate on the planetary exploration.It is the most costly, because of its need of deepspace probes, and it calls for large missions.Past planetary explorationFor a long time it looked as if an independentplanetary exploration would be out of reach forEuropean laboratories and scientists. They learnedtheir trade as guest investigators on spacecraft ofthe big space powers, USA and USSR. Scientistscould contribute experiments or were co-investiga-tors on several planetary missions including thevery spectacular Voyager missions. Only in 1980did ESA select its first, and up to now only, inde-pendent planetary mission, the one to comet Hal-ley. This fortunate event came about becauseNASA cancelled the originally planned jointNASNESA mission to comets Halley andTemple-2.Between 1982 and 1984 a Joint Working Group(JWG) of the Space Science Committee of theEuropean Science Foundation and the SpaceScience Board of the US National Academy ofSciences studied a joint programme of planetaryexplorations based on equal partnership. Many ofthe recommendations of the JWG have been takenup by the agencies, in particular the TitanProbe/Saturn Orbiter mission (now called Cassini/Huygens). But for Europe and ESA the most im-portant development in the field occurred whenthe plan for a long-term strategy was born.The so-called Horizon 2000 was built aroundfour cornerstones, two for astronomy and two forsolar systems science, with smaller missions in be-tween as the flexible element. While one of thesolar system cornerstones was dedicated to solarterrestrial physicsand thus includes the previouslymentioned fields two and three, the other wouldbe a true planetology mission aiming at the returnof cometary material to earth.Horizon 2000 was acknowledged by the minis-terial conference in Rome 1985 as the minimumscience programme ofESA Whereas the financialframework for the core programme was basicallyestablished, it was also recognised that some of themore elaborate missions of the future, such as theEuropean contribution to a Mars mission, wouldnot fit into this framework and would have to findsupplementary financial support.Let me now come to a short presentation ofESA's programme in planetary science. As men-tioned before, the only European planetary215Europeand the large solarsystemprojectsFigure 1. Views of Comet Halley taken during the fly-by ofthe European Glotto probeNota: The source regions of the dust and gas jets on thesunlit side of the comet cover only about 10% of thecomet surfaceThus Giotto was able to cross the so-called con-tact surface or ionopause of the comet and it al-lowed the gas and ion massspectometers to analysethe inner coma, the comet's atmosphere/ionos-phere, which is undisturbed by the solar wind.These analyses demonstrated that comets are in-deed the most primitive bodies in the solar systemanalysed so far, which have retained a lot of thevolatile material (80% water, surprisingly lowamounts of ammonia, methane, and cyanide).Most of these volatiles have been lost in the innerplanets, the moon, and in the meteorites.Halley's chemical and isotopic composition wasfound to be very similar to solar material withpossibly some resemblance to the solar system'sancestor, an unnamed dark interstellar cloud. Thespectacular pictures taken by the camera (Figure1) also revealed the darkest object known so far inthe solar system, a potato shaped nucleus with gasand dust jets coming out of only about 10% of itssurface.missionin the past was Giotto, the fly-by at Halley'scomet on 13/14 March 1986. Of all the inter-national fleet of spacecraft, Giotto was the onlyprobe equipped with a dust shield and it couldtherefore dare to approach the comet much closerthan the others (600 km, compared to 8,000 km ofthe second closest, the Russian VEGA-2 mission).Present and futureGiotto also brings us to the present and near fu-ture. Thespacecraft with about 50% ofthe payloadfunctioning well was tested. at the beginning of1990, and has subsequently beenejected towardscomet Grigg-Skjellerup by means of a close EarthALTITUDE,_."~ ENTRY SPEED - 5.75 - 6.51<m/s1000 km ENTRY ANGLE __60' TO _90'TITAN HUYOENS PROBEENTRY AND DESCENT SCENARIO~< .•,)f#" BEGINNING OF ATMOSPHERIC FRICTION·61. PEAK HEAT FLUX - 20 - S3 W/CM2170 km IMPACT ON SURFACEDESCENTMAINCHUTEDEPLOYED•DESCENT PHASEDURATION: 2 - 3 HRSPROTECTIVE COVERS JETTISONEDINLET PORTS OPENEDDECELERATOR JETTISON~PEAK DECELERATION 10 - 25 gv%~'IiVELOCITYMACH 1.51400m/slo- ENTRY PHASEDURATION'\,3 MIN-300 km-500 km192 kmFigure 2. SCenario for the European Huygens probe descending to the surface of Saturn's moon Titan216 Science and Public Policy August 1991Europeand the large solarsystemprojectsfly-by. This feat by the European OperationsCentre in Darmstadt was the first such gravity-assisted manoeuvre ever performed with a deep-space-probe at the Earth. The new GiottoExtended Mission thus is on its way to investigatethe solar wind interaction of an older, much lessactive comet than Halley.The next planetary mission will be Cassini/Huy-gens, a collaborative mission with NASA whichincludes a Saturn orbiter and a Titan probe. TheEuropean part, selected as a medium sized missionfrom the flexible part of Horizon 2000, will be thesmall but very interesting Huygens probe whichwilldescend through Titan's atmosphere to its sur-face. The launch is scheduled for 1996 but thespacecraft will arrive at Saturn only 6.5 years later,in 2002.The probe with its combined aerobrake andparachute system (see Figure 2) should be a greatchallenge for the European industry. The ex-perimental package which has to survive and toperform analyses in the quite hostile environmentof Titan's primitive and cold atmosphere (90-170K) should be a similar challenge to the scientists.The descent phase will last 2-3 hours, and it ishoped that the package willstay alive on Titan's icyor liquid ethane surface (90 K) for more than twominutes.For the beginningof the next century ESA plansto launch its planetary cornerstone mission Roset-ta. It is presently being studied as a joint missionwith NASA, and it aims at the return of cometarysamples to Earth and subsequent analysis in labor-atories. As for the Moon, it is recognised that athorough structural, chemical, and isotopic-ana-lysis ofcometary material can only be performed inthe laboratory and not remotely. Of course, themission includes supporting measurements duringthe approach phase and at the landing site; how-ever, its main goal is the return to Earth of a threemeter drill core of cometary material in as undis-turbed a condition as possible. The scenario toachieve that is, of course, quite complex and chal-lenging. Its main phases are described in Figure 3.Even further in the future are unmanned andmanned missions to Mars and/or the establishmentof a lunar base. ESA is not able by itself to competeindependently for these endeavours; however, it~.7, CRUISER - AEROCAPSULESEPARATION5, COMET TO EARTH CRUISE~r~<:»6, RTG SEPARATION3, ON COMET OPERATION6, ENTRY, DESCENT AND RECOVERYTHE ROSETTA MISSION SCENARIO~Y2, EARTH TO COMET CRUISEFigure 3. Main phases of the ESA cornerstone mission RosettaScience and Public PolicyAugust 1991 217Europe and the large solarsystemprojectsplans to make contributions to them. In order tobe ready when the large agencies might extend aninvitation to participate, studies have been, and arebeing, performed.A Mars Exploration Study Team has worked outseveral scenarios for European participation inMars explorations. One of them, a global networkof remote stations for combined seismic, meteoro-logical,geochemical and geophysical observations,which would be deployed either by semi-hard lan-der or penetrators, is presently in an assessmentstudy phase. Another study team has started itswork to assess possible European contributions toscience on and from the moon in the context of amanned lunar base.In discussingEuropean planetology the nationalprogrammes must not be forgotten. They aremainly of the larger countries, can be substantialand are performed on a bilateral basis with thelarge agencies. Examples are the collaboration ofFrance with the USSR in the Venus and Marsprogrammes and the GermanlUSA collaborationsin the Galileo (Jupiter) and CRAF (CometRendez-vous/Asteroid Fly-by) missions.ConclusionI have attempted to demonstrate that the Euro-pean space science community is capable of mak-ing important contributions to solar systemscience. Although ESA's planetary science pro-gramme has just started, what has been achievedand what is under development is quite significant,and the bilateral programmes ofseveral nations arefurther augmenting Europe's role in this field.ESA, ofcourse, cannot compete in sizewith NASAand Intercosmos, but its science programme (Hori-zon 2(00) is nevertheless highly interesting, bal-anced, and competitive, and it can contributeimportant shares to the large planetary missions.There is no doubt in my mind that Horizon 2000has given European space scientists a new self-confidence. For the first time they are acting,rather than reacting to the programmes of the big218agencies.However, this programme could still be jeopar-dised by financial difficulties, not only within ESAbut also in the member countries where the experi-ments for these missions have to be financed.There is hope that the financial difficulties withinthe agency will soon be resolved in such a way thatthe continued implementation of a somewhatstretched Horizon 2000 core programme issecured.It remains a problem that most ESA memberstates have not been able to augment their spacescience budgets in pace with the increase of theESA science programme. This would be requiredin order to equip the spacecraft with the necessaryadvanced instrumentation. There is the additionalproblem that the Horizon 2000 core programmedoes not include the more advanced missionsto themoon and to Mars.If, for some reason, ESA and its member stateswere not able to implement the Horizon 2000 coreprogramme, which is minimal and yet balanced, itwould be a disaster. However, I go one step furtherand claim that Europe could and should also beable to afford an augmented space science pro-gramme, including the more advanced missionsmentioned above. Not only would its GNP allowit,but it is also well known that the science pro-grammes of the agencies are in the forefront inadvancing new technologies, It is in the interests ofESA's other programmes (transportation, tele-communication, and so on) and, more generally, ofEurope's economy, for the science programme tobe increased relative to these programmes ratherthan decreased, as it has been in the past.Considering Europe's cultural heritage in solarsystemscience and after its demonstration with thehighly successful Giotto mission, that it has boththe technologies and the brains to compete suc-cessfully with the large space powers, it would beunforgivable to leave this field to them (and poss-ibly to Japan). I appeal to the members of theAcademia Europaea to support within their coun-tries the European Science Programme, which ismoderate and yet competitive.Science and Public PolicyAugtlSt1991

Europe and the large solar system projects

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