Table 1. Number and type of launches during ESRO's first eight years, as proposed by the Interim STWG to the Third Session of COPERS, in Munich on 24/25 October 1961
At a time when all space programmes have to redefine their goals following the end of the Cold War, and when some Member States are questioning whether the (modest) pace that marked the first 35 years of European space science should not be slower and the budget allocated to that activity reduced, it is useful to look back and assess whether ESA, and before it ESRO, have been good for science and have played the roles as outlined in their Conventions. It is also useful and enlightening to assess whether ESA has conducted its programme efficiently.
Looking back, one can broadly identify four phases in the development of space science in Europe, characterised by:
These four phases will be reviewed here, paying more attention to the first two because they contain all the ingredients which, filtered over time and with increasing experience, formed the basis for ESA's success today.
The first phase, which John Krige, one of the ESA historians, has called 'The Auger Years' (ESA publication HSR-8, May 1993) covering the pre-ESRO and ESA era was marked by a strong determination to create a European Space Science Programme and by the simultaneous development of national programmes in the future ESA Member States, the creation of CNES in France as early as 1963 being one such example.
The key element in this phase was the famous Blue Book prepared by the Scientific and Technical Working Group (STWG) of COPERS, under the Chairmanship of L. Hulthen, from the Royal Institute of Technology in Stockholm, with R. Luest as Coordinating Secretary.
The outline of this programme is shown in Table 1, which somewhat reflects the community's lack of realism and maturity at that time. Nevertheless, it was endorsed as such by the Plenipotentiaries who signed the ESRO Convention in June 1962. Already at that time, a dichotomy could be detected between the smaller Member States, which favoured the rocket programme in order to gain experience, and the larger ones which, not having to rest on this element, favoured the inclusion of the bigger elements, i.e. the spacecraft and the space probes. In fact, the Blue Book was more a declaration of intent than a definitive programme.
It would be the task of the new organisation's Launching Programme Advisory Committee (LPAC), the ancestor of ESA's present Space Science Advisory Committee (SSAC) and, as such, a body composed of a small number of scientific experts, and of its Science and Technical Committee (STC), a delegate body and the ancestor of ESA's SPC, to transform the content of the Blue Book by Spring 1965 into a programme which, it was assumed, would be achieved within pre-set financial limits.
Three main areas of controversy confronted the LPAC, chaired at that time by Reimar Luest. The first issue was to maintain a fair distribution between the various fields of science (which did not automatically translate into a balance between the resources allocated to each field, astronomy missions generally being more expensive).
The second issue concerned the concept of a common bus for astronomy satellites of the TD series, with the aim of saving cost. This concept never materialised: only one TD spacecraft was built. Today, ESA is seriously trying to develop one common bus for its astronomy missions XMM, Integral and possibly STARS, a project yet to be approved.
Finally, there was the issue of the large satellites, which were supposed to be the main justification for establishing a European Space Research Organisation to develop missions larger than those that could be carried out by a single nation. Neither of the two large projects, the Large Astronomical Satellite (LAS) and the comet mission, ever materialised. Major descoping and numerous iterations had to be undertaken before they could eventually reach a stage where they could both be built within realistic financial limits and fulfil the interests of the scientific community, through the IUE and Giotto missions.
This first phase ended in 1968 with the successful launches of ESRO-2, ESRO-1A and Heos-1. In the interim, 56 sounding rockets were sent aloft between 1964 and 1967, almost half of them dedicated to ionospheric and auroral studies. The most active countries in this programme were the UK (35% of the proposals received by 1967), Germany (22%), France and Sweden (12%), the latter probably because of the existence of Esrange, in Kiruna.
These numbers, impressive as they are, in fact compare very badly with the original plan established by the STWG. They show how difficult it was to achieve a balanced scientific programme over a short period which would satisfy the diverse interests of the scientific community. It slowly became apparent that the desired balance might be better achieved over a longer term, within the framework of a financially more realistic programme. Nearly 16 years passed before ESA was able to formulate such a plan.
Table 1. Number and type of launches during ESRO's first eight years, as proposed by the Interim STWG to the Third Session of COPERS, in Munich on 24/25 October 1961
*This article is based in large part on a paper presented at a Colloquium organised in Kiruna on 7-8 September 1994, on the occasion of the retirement of Prof. Bengt Hultqvist as Director of the Swedish Institute of Space Physics.
This second phase saw the transition from ESRO to ESA, and the disappearance of ELDO, the European Launcher Development Organisation. By the end of 1968 only one new project, TD-1, had been approved and the time was ripe for taking new decisions in order to avoid a severe lack of continuity in the scientific institutes as well as in industry. In the first half of 1969, three small satellites were approved: ESRO-1B (Boreas), a follow-up to ESRO-1, launched in October 1969, Heos-A2, launched at the beginning of 1972, and ESRO-IV launched in November 1972. In early July 1969, Cos-B and Geos were approved to be part of the second phase of the ESRO programme. These were in fact the last projects to be approved within the ESRO framework.
Hermann Bondi, who took up his duties as ESRO's Director General in November 1967, requested that the LPAC define the Organisation's long-term scientific policy through a careful selection of new feasibility studies. To fulfil this mandate, the LPAC set up a Geophysics and an Astrophysics Panel, the reports of which were presented to the LPAC in January 1970. They contained decisive and surprising - as well as courageous - recommendations.
It took two days of lively discussions in the LPAC, chaired by Reimar Luest, to establish ESRO's future scientific policy based on these recommendations. Four research fields were given priority:
Planetary exploration, ultraviolet astronomy and solar physics were excluded from these recommendations. Nevertheless, still envisaged, optimistically, was the launch between 1975 and 1980 of three medium-sized and three to five small satellites (compared with the three actually launched, namely Geos, ISEE-2 and IUE).
Following this exercise, between June 1970 and April 1971, the LPAC started to discuss which satellites would follow Cos-B and Geos.
They gave first priority to Helos, an X-ray positioning mission, later to be renamed Exosat. They also tried to safeguard and rescue the interests of the ultra-violet-astronomy community by recommending that ESRO should participate in NASA's SAS-D project, a recommendation that was taken up and approved by the ESRO Council in July 1971. Hence IUE - still with us today - was born, ironically an ultraviolet mission corresponding to one of the fields excluded from the LPAC's list of priorities.
In the meantime, ESRO was entering the crisis that was to give birth to ESA. The science budget was kept to a minimum annual level of 27 MAU, in practice a ceiling that could only be raised in 1985 with the approval of Horizon 2000*. Under the chairmanship of G. Puppi, the ESRO Council accepted the famous 'first package deal', which opened the door to applications missions. The sounding-rocket programme was eliminated and Esrange was given back to Sweden under an appropriate protocol.
Also of fundamental importance was the decision to give Europe independent access to space through the development of the Ariane launcher.
In 1973, the Council had to decide which projects should be undertaken between 1975 and 1980 in the framework of the new organisation, ESA. After a two-day symposium at ESRIN (I) on 26-27 February 1973, attended by some 100 European scientists, the LPAC reconfirmed its earlier choice of Helos. Other potential candidates for selection were participation in the IMP Mother/Daughter mission, or in a Venus orbiter, both NASA missions. The LPAC chose the 'Daughter' rather than the 'Mother' spacecraft, and thus ISEE-2 was born.
With ISEE-2, IUE and Spacelab (ESA's participation in the NASA Space Transportation System), ESA was tying its own programmes more and more to those of NASA. This cooperation was to be further extended with the participation in the Large Space Telescope (Hubble) and the Out-of-Ecliptic mission, later renamed the International Solar Probe Mission (ISPM), and known finally as Ulysses.
At the end of these first two phases, ESRO was forced to be more realistic in its objectives. It was recognised that, instead of launching a large scientific satellite each year plus several small ones, only one medium-size satellite could be launched every two or three years. At the same time, however, the scientists had learnt to establish priorities. They had admitted that only those ideas for which they could achieve a consensus among themselves were destined to succeed. This situation opened the way to the more mature phases in which, in addition, the scientists suddenly realised not only the possibilities offered on the worldwide scene by international cooperation, but also what the limits were.
* In fact, the LPAC considered the correct level to be somewhere between 43 and 47 MAU.
In January 1974, the AWG and SSWG identified eleven missions from which the Agency's next scientific project(s) should be selected in 1976. Continuing with the practice started by the choice of Cos-B and Geos, and then of Helos and ISEE-2, in an attempt to maintain a balance (or due perhaps to an impossibility to choose between astronomy and magnetospheric missions), they decided to participate with NASA in the Large Space Telescope and the Out-of-Ecliptic mission.
This, in a sense, was the natural consequence of the earlier ESRO LPAC recommendations which constrained European missions to small or medium-sized projects, while the USA and the Soviet Union were already planning very ambitious and challenging missions. If it did not want to stagnate, Europe had no choice other than to cooperate. Furthermore, cooperation with NASA was developing at a high rate, with Spacelab representing an important part of the US Space Transportation System. A strong wind of optimism was blowing as a result of the possibilities offered by international cooperation.
However, clouds started to form. The Europeans learnt that doing business with NASA was just that, something brought home on a daily basis to the engineers involved in the development of Spacelab and the scientists involved in the selection of instruments for the Large Space Telescope. The ISPM crisis then opened their eyes as they realised for the first time the fragility of agreements signed by their trans- Atlantic counterparts. The Memorandum of Understanding, the official document establishing the basis for the cooperation, which had a binding significance on the European side, had a different interpretation for the Americans, with NASA's budget submitted to yearly discussion at the White House and in Congress. The crisis came in the same period as the arrival of Ariane, which was successfully launched for the first time on Christmas Eve 1979, giving Europe full autonomy in accessing space. These two events together explain the series of decisions taken between 1980 and 1983. Giotto and Hipparcos were selected by the SPC in 1980 (again with great difficulties in deciding between astronomy and solar- system missions) and ISO in March 1983. All three missions were to use the Ariane launcher and were originally European-only missions.
This marked a turning point in ESA's science policy. First a planetary mission, namely Giotto, was selected. It was the first science mission to be launched by ESRO/ESA with its own means, and the first scientific spacecraft carried by Ariane. Hipparcos, an optical astrometry mission, had no equivalent in any other programme. With these two highly-original medium-size missions launched by Ariane, Europe finally achieved space maturity and independence, even taking over the world lead in the areas of comet science and space astrometry. This trend was confirmed by the selection of ISO, which opened the door for European astronomers (already involved in IRAS) to the highly competitive field of infrared astronomy, entering into direct competition with NASA's SIRTF*.
The positive effects of the ISPM crisis for Europe should not be overlooked. Firstly, Europe realised that it could master its own destiny and assume a position of leadership in several areas. Secondly, Ulysses was ultimately launched successfully by NASA in October 1990, and on 13 September accomplished its first high-latitude pass over the Sun's south pole. Thirdly, with Giotto and the series of comet missions launched by the Soviets and the Japanese, international cooperation took on a new dimension, with the world's main space agencies/institutes involved in the InterAgency Consultative Group (IACG), in which for everyone involved cooperation was the only 'leader'!
It is against this background that ESA could enter the fourth phase of its space-science policy with the advent of Horizon 2000 and Horizon 2000 Plus.
* More than eleven years l later, NASA's SIRTF mission is still not decided upon, and ISO remains the only infrared telescope to be launched before the end of the millenium.
In 1983, it became clear that ESA could no longer continue with its existing method of selecting project after project, without a long-term perspective and some kind of commitment that would allow the scientific community to prepare itself better for the future. ESA too needed a long-term programme in space science. On the other hand, there was some opposition to such an approach on the basis that it would discourage too early those scientists whose area of science would not be covered, leading to a possible loss of support for the ESA Science Programme. The way out was to draw up a programme whose perspectives were sufficiently balanced, following in a sense the first ideas set out by the LPAC in 1970, without ruling out the possibility of introducing new ideas at regular intervals. In addition, the level of the Agency's science budget, unchanged since 1971, confronted the scientific community with the risk of asphyxiation. The only possibility for Council changing that level rested on the assessment of a substantive plan and a reference framework for future space-science activities. It was this set of circumstances that made it possible to initiate the 'Horizon 2000 exercise'.
Following a Call for Mission Concepts issued in Autumn 1983, to which the European scientific community responded with some 68 proposals (Table 2), a Survey Committee and several Topical Teams were formed to set priorities, assess technical maturity in the various fields, and formulate recommendations to ESA's then Director General Erik Quistgaard, for him to present to the Council of Ministers in January 1985 in Rome. The whole exercise was conducted by the scientific community for the scientific community.
In June 1984 in Venice, when the Survey Committee held its last meeting, priorities had been courageously established (though not an easy task) - so-called 'Cornerstones' were approved in four domains: solar-terrestrial physics (STSP), comet science (CNSR, now called Rosetta), X-ray (XMM) and submillimetre astronomy (FIRST). In addition, the plan also included both small and medium-size projects, as in previous ESRO/ESA recommendations, but with no a priori exclusion of disciplines, so that a community not 'served' directly by the Cornerstones could still find its place in responding to the regularly released Calls for Ideas'. In this way, the programme had an element of flexibility, and its content could be adapted to the evolution of science (STEP), as well as to the opportunities offered by international cooperation (Cassini/Huygens).
Furthermore, the philosophy underlying Horizon 2000 was to contain the costs of missions within a fixed envelope, forcing the scientific community to limit its ultimate ambitions and ESA's management to adopt an even more efficient approach.
The existence of Horizon 2000 had an immediate and very important effect the ESA science budget was granted an annual increase of 5% above inflation (not an easy decision to take!), an increment that was to be implemented over ten years. For the first time also, closer coordination with national programmes could be established, thereby avoiding inefficient competition between national and ESA's resources. Coordination with other international programmes also became easier.
Interestingly, the concept of international cooperation also evolved. In order for ESA to be master of its own future and not be dependent upon decisions taken outside its own control, it became clear with time that the Cornerstones ought to be placed under ESA leadership and be consistent with ESA's own technical and financial means, with cooperation bringing new, added capabilities to these purely European missions. On the other hand, greater risks could be taken at the level of small- or medium-sized projects which, as in the case of Huygens, could represent a small or even medium share of bigger missions being undertaken by other agencies.
With the Cornerstones forming fixed, pre-identified elements in the programme, the scientists but also industry knew ahead of time (20 years for the last Cornerstone) in which direction they ought to invest their efforts and pursue the long-lead-time technological developments necessary to bring projects into existence. The Cornerstones also achieved the long-sought-after balance between the community's main scientific fields of interest.
A similar approach is now being followed in the preparation of 'Horizon 2000 Plus' which covers the period 2005 2016 and contains three Cornerstones:
and four medium-size missions, several of which can be missions on the Space Station or small satellites. This programme is described in detail in ESA Special Publication SP-1180:
'Horizon 2000 Plus - European Space Science in the 21st Century'.
Table 2. Comparison of responses to 'Calls for Mission Concepts'
Figure 1-3 show the evolution in the capabilities of the ESRO and ESA science missions since 1968 in terms of weight in orbit, power, and bit rate. There has clearly been a steady increase in mission capabilities since early ESRO times, which is reflected most dramatically in with satellite weights closely mirroring both the evolution in launcher capabilities and the growth in scientific ambitions. Since it is unlikely that launchers more powerful than Ariane-5 (or the Ariane-5 class) will be available in the near or even more distant future, scientists must face a situation in which the weight of their spacecraft will probably be capped at no more than 3 to 4 tons, with no room for expansion.
Table 3 shows the payload weights on ESRO and ESA scientific satellites; although there are substantial fluctuations, the tendency has clearly been towards flying bigger payloads. The number of scientists involved per mission also varies greatly, from just a few to more than one hundred for ISO and Ulysses, to a maximum of 195 on Soho and 180 on Cluster.
ISO
Soho
Cluster
Table 4 lists the groups with major experiment hardware involvement. Given that there are approximately 60 hardware groups in Europe, this shows that 20 to 40% of them can be involved at some stage in any of the ESA missions, a proportion that tends to increase with time.
Figure 1. Weight of ESA science spacecraft as a function of their launch date. The rectangles indicate roughly the weight capabilities of the various launchers. Ulysses was launched by the US Space Shuttle and the weight shown corresponds to the dry mass of the satellite. Huygens is also a special case, being carried aboard the US Cassini satellite to Saturn and Titan. The Hubble Space Telescope would be off-scale in this illustration
Figure 2. Average power consumptions (in Watts) of ESA science spacecraft as a function of launch date
Figure 3. Maximum bit rates (in kbits) of ESA science spacecraft expressed as a function of launch date
Table 3. Evolution in payload weights of ESRO and ESA scientific satellites
Table 4. Number of groups with major experiment hardware involvement
In addition, the observatory-type missions involve a large number of astronomers in the community:
Figure 4 shows the evolution in mission costs. It indicates that, despite the rapid increase in the technical capabilities of the missions, ESA has been able to keep relatively tight control over its costs and has managed to offer regular, and a reasonably constant number of flight opportunities per decade, as shown also in Table 5. According to Figure 4, the missions can be grouped into two families:
Amazingly, the evolution in the cost-to-completion tends to follow the overall trend in the yearly budget for both families of missions.
Figure 4. Evolution in the cost-to-completion (in MAU, 1993 economic conditions) of ESA science satellites launched after 1983 as a function of launch date. The solid curve shows the variation in the science programme's annual budget (also expressed in 1993 economic conditions). The numbers indicate the ratio between the cost-to-completion and the level of the science budget in the year of the launch. For missions to be launched beyond 1995, the cost-to-completion figures are today's estimates
Table 5. Number of ESRO/ESA projects launched/to be launched per decade
These curves prompt the following remarks. The two medium-size missions, M1 (Huygens) and M2 (Integral), are presently maintained at the level of one year of the science budget, even though Integral is a Cornerstone-class mission, and as such might be expected to be found on the upper curve of Figure 4. This is the result of international cooperation and the reuse - for the first time in the history of the ESRO/ESA science programme - of an existing spacecraft bus design, namely that from XMM. On the other hand, missions like Exosat, Hipparcos (a 'small' survey satellite at the outset and a 'blue mission' in Horizon 2000) and ISO (also a blue mission), are of the Cornerstone class.
Table 6 shows the costs (1994 economic conditions) for missions launched after Geos and shows that the cost to launch 1 kg of mission or 1 kg of payload (excluding the payload cost itself) tends to decrease with time. Hence, Cluster is probably the most efficient satellite ever developed by ESA, an effect of the recurrent approach made possible by a mission based on four identical satellites.
These data permit one to derive a typical cost distribution for a given spacecraft and to assess how these costs are shared between ESA (12.5%) and external contracts (87.5%). This data is displayed in Figure 5.
Figure 6 clearly shows that for the missions after Geos, the duration of Phases B and C/D is nearly constant, independent of the size of the mission (virtually identical for Cluster and Exosat), being of the order of 6 years, with two notable exceptions, Ulysses and ISO. The Ulysses case illustrates the effect of the 'redefinition' of the mission by NASA in 1981 and the later effect of the Space Shuttle 'Challenger' accident. In ISO's case, the cryogenic-valve problem has been the main reason for the abnormally long industrial phase.
Not shown in Figure 6 is the time spent prior to the start of Phase A. This varies from mission to mission and is in fact difficult to define properly. It is usually very long, however, sometimes reaching more than ten years. This was the case for IUE and Giotto derived, respectively, from the concept for the LAS and from the second Large Project of the Blue Book. This was also the case for Ulysses, a mission whose concept was first proposed in the late fifties, and for the Hubble Space Telescope. Both were under discussion by ESRO/ESA and NASA back in the early seventies, but were only launched in 1990.
The Horizon 2000 and 2000 Plus Cornerstones have been or are being decided some 20 years before the missions actually fly. This is the time needed to properly define and prepare these missions technologically, before they can be fitted into a realistic budget, which should in principle not exceed two years of the scientific budget. This is characteristic of the way in which Europe (i.e. ESA) operates and is probably the inevitable consequence of the inescapable necessity of tailoring the scope of missions to a realistic budget. It is also a consequence of the relatively slow progress in technological preparation, itself an effect of the rather low financial effort by ESA in the area of technological research compared to the American approach.
Despite this, ESA is currently playing a pioneering and leading role in the field of solar physics with Ulysses and Soho, is leading - and will continue to do so in the next century - in cometary science with Rosetta, and with Huygens will accomplish the first landing ever at a distance beyond the orbit of Mars. ESA is also the world leader in space astrometry with Hipparcos, and it will be ahead in infrared, submillimetre and gamma-ray astronomy with ISO, FIRST and Integral, respectively, while XMM is the most sensitive X-ray satellite planned at this moment in the world. Moreover, Horizon 2000 Plus offers potential new leadership positions in plasma, planetary and solar science, as well as in interferometry and the newly emerging field of gravitational physics.
Figure 5. Typical spacecraft costs (excluding the payload) and the distribution between external (87.5%) and internal expenditures (12.5%)
Figure 6. The durations of the various phases of ESA science projects, indicated by the horizontal bars. The A's and white bars indicate the Phase-A starts and durations, respectively. The B's represent the start of Phase B in industry and the grey bars represent the duration of Phase B and C/D. The launches are represented by white triangles, while the black bars indicate the durations (actual or foreseen) of in-orbit operations. Note the difference in the durations of Phases B/C/D for the Delta and Ariane families (see also Fig. 1), and the near constancy of these Phases for each individual family
Table 6. Scientific spacecraft mass and costs to ESA (excluding cost of payloads, except for Exosat and Hipparcos) updated to 1994 economic conditions
Despite the rapid increase of more than one order of magnitude in the technical capabilities of its missions, ESA has managed to maintain relatively tight control over its costs, enabling it to provide a regular and nearly constant number of flight opportunities per decade. The small (100 kg) satellites launched in ESRO times have been succeeded by missions such as ISO, Soho and Cluster, each weighing several tons.
This dramatic evolution in technical capabilities has not been mirrored in the evolution of the annual science budget. Today's budget, after the annual 5% increase since 1985, is still no higher, in terms of purchasing power, than the ESRO budget of 1964. It takes the same time today for the industrial development of missions weighing several tons, such as Cluster, as it did 15 years ago to develop missions 10 times smaller, such as Exosat. The ESA team managing Cluster is composed of 20 engineers, compared to the 35 who worked on Exosat. It is this strict design-to-cost approach that is allowing spacecraft like Integral, which because of their size and scope would normally qualify as Cornerstone missions, to be envisaged as medium-class missions.
In addition, more scientific opportunities are being offered to the science community: today's missions involve more and more Principal Investigators and an increasing number of Co-Investigators. Moreover, many of ESA's scientific missions are systematically extended beyond their nominal lifetimes and the vastly greater volumes of data being acquired are being systematically archived and made widely available to much larger numbers of users.
These and many similar examples prove that ESA is becoming more efficient with time, for which there are several reasons. Firstly, the evolution in technology is allowing us to design larger missions with a lower price per kilogramme. Secondly, both ESA and industry have acquired substantial experience and have thereby improved in efficiency with the passage of time. Thirdly, the existence of a long-term programme for science first Horizon 2000 and now Horizon 2000 Plus is allowing the necessary technology development to be pursued sufficiently early and the use of common subsystems on a variety of missions.
After some 35 years of endeavour, European space science has finally reached maturity as a result of ESRO's and ESA's efforts. Order has been brought into the management area and a large amount of technical expertise has been acquired. International cooperation can now be seen in a more rational context, based on a more equal partnership, and with new partners involved. In addition, coordination with national programmes is constantly being improved.
Through its mandatory character and the fixing of its budget for five-year periods (so-called 'level of resources'), ESA's Science Programme offers space scientists, primarily in Europe but also around the world, one of the most stable programming elements with missions second to none in their fields, missions that are powerful drivers of technological innovation.
When discussing the future of space science in Europe, one should constantly bear in mind the reasons why the ESA Science Programme has been a success: namely by its
Several of these ingredients were discussed by the early ESRO and later ESA Committees and have been successfully carried through into the ESA science programme. They should by all means be preserved in the future.
ESA Bulletin Nr. 81.