European Space Agency Science Programme

A selection of missions from the ESA Science Programme, clockwise from top left; the Huygens lander, the Rosetta orbiter, the LISA observatory, and the Herschel telescope

The Science Programme[1][2][a] of the European Space Agency is a long-term programme of space science and space exploration missions. Managed by the agency's Directorate of Science, The programme funds the development, launch, and operation of missions led by European space agencies and institutions through generational campaigns. Horizon 2000, the programme's first campaign, facilitated the development of eight missions between 1985 and 1995 including four "cornerstone missions" – SOHO and Cluster II, XMM-Newton, Rosetta, and Herschel. Horizon 2000 Plus, the programme's second campaign, facilitated the development of Gaia, LISA Pathfinder, and BepiColombo between 1995 and 2005. The programme's current campaign since 2005, Cosmic Vision, has so far funded the development of ten missions including three flagship missions, JUICE, Athena, and LISA. The programme's upcoming fourth campaign, Voyage 2050, is currently being drafted. Collaboration with agencies and institutions outside of Europe occasionally occur in the Science Programme, including a collaboration with NASA on Cassini–Huygens and the CNSA on SMILE.

Governance

ESA Science Programme advisory structure[8][9][10]
Director of
Science		Science Programme
Committee
(SPC)
Space Science
Advisory Committee
(SSAC)		Independent
advisors
Astronomy
Working Group
(AWG)		Solar System and Exploration
Working Group
(SSEWG)		Ad hoc
working groups

The Science Programme is managed by the European Space Agency (ESA)'s Directorate of Science,[11] and its goals include the proliferation of Europe's scientific presence in space, fostering technological innovation, and maintaining European space infrastructure such as launch services and spacecraft operations.[11] It is one of ESA's mandatory programmes in which each member state of ESA must participate.[12][13] Members contribute an amount proportional to their net national product to ensure the long-term financial security of the programme and its missions.[14] The programme's planning structure is a "bottom up" process that allows the European scientific community to control the direction of the programme through advisory bodies.[7][15] These bodies make recommendations on the programme to the Director General and the Director of Science,[16][17] and their recommendations are independently reported to ESA's Science Programme Committee (SPC) – the authority over the programme as a whole.[16][18] The programme's current advisory structure consists the Astronomy Working Group (AWG) and the Solar System and Exploration Working Group (SSEWG),[8][9] who report to the senior Space Science Advisory Committee (SSAC) that reports to the agency's directors.[17] Membership on the advisory bodies last three years,[19] and the chairs of the AWG and SSEWG are also members of the SSAC.[8][9][19] Ad hoc advisory groups may also be created to advise on certain mission proposals or the formulation of planning cycles.[10]

Missions in the programme are selected through competitions in which members of the European scientific community submit proposals to ESA.[20] During each competition, the agency outlines one of four mission categories for which proposals need to meet the criteria of.[21] These are the "L"-class large missions, the "M"-class medium missions, the "S"-class small missions, and the "F"-class fast missions, each with differing budget caps and implementation timelines.[5][21] The proposals are then reviewed by the AWG, SSEWG, engineers at ESA, and any relevant ad hoc working groups, as part of a feasibility study known as "Phase 0".[22][23] Missions which require new technologies to be developed are reviewed during these studies at the Concurrent Design Facility at the European Space Research and Technology Centre.[24] After the study, up to three proposals are selected as finalists in "Phase A", in which a preliminary design for each candidate mission is formulated.[23][25] The SPC then makes a final decision on which proposal proceeds to phases "B" through "F", which include the development, construction, launch, and disposal of the spacecraft used in the mission.[26][27][28] During Phase A, each candidate mission is assigned two competing contractors to build their spacecraft, and the contractor for the winning mission is chosen during Phase B.[25][27]

History

Background

Setbacks on the joint American-European Ulysses mission (left), and the successes of the Ariane 1 (right), were catalysts for an autonomous European scientific programme

The European Space Agency (ESA) was established in May 1975 as the merger of the European Space Research Organisation (ESRO) and the European Launcher Development Organisation.[29][30][31] In 1970, the governing Launch Programme Advisory Committee (LPAC) of ESRO made a decision not to execute astronomy or planetary missions, which were perceived as beyond the budget and capabilities of the organisation at the time.[32][33] This meant that cooperation with other government space agencies and institutions was necessary for large-scale scientific missions.[33] This policy was effectively reversed in 1980, when ESA's then-Director of Science, Ernst Trendelenburg, and the agency's new authoritative Science Programme Committee (SPC) selected the Giotto flyby reconnaissance mission to comet Halley and the Hipparcos astrometry mission for launch.[34][35] In addition to the selection of the International Ultraviolet Explorer observatory in March 1983,[35] the three were the first European science missions launched aboard Arianespace launch vehicles, which gave Europe autonomy over its launch services.[36][37] This, in addition to the lack of a long-term plan for scientific missions, along with budget setbacks from NASA on the collaborative International Solar Polar Mission (later named Ulysses),[38] spurred the development of a long-term scientific programme through which ESA could sustainably plan missions independent of other agencies and institutions over lengthier periods.[38][39] The leadership and advisory structure of ESA's Directorate of Science changed immediately prior to the programme's establishment. In the 1970s, ESA's Science Advisory Committee (SAC), which succeeded the LPAC, advised the Director General on all scientific matters; the Astronomy Working Group (AWG) and the Solar System Working Group (SSWG) also reported directly to the Director General.[40] In the early 1980s, the SAC was replaced with the Space Science Advisory Committee (SSAC), who were tasked to report to the Director of Science on developments in the AWG and SSWG.[41] In addition, former SAC chair Roger-Maurice Bonnet replaced Trendelenburg as Director of Science in May 1983.[42]

Horizon 2000

Formulation

"Over the past 25 years, space science has progressed from the pioneering and exploratory stage to a firmly established mature branch of fundamental science. The time has come to identify what the main thrusts of European space science should be for the coming decades to consolidate Europe's position in the forefront of scientific development."

Horizon 2000 survey committee, 1984[43]

In November and December 1983, ESA made the first open call for mission proposals to the European scientific community, based on an idea for a community-driven programme presented by Bonnet to the SPC in late 1983.[44][45][46] The call yielded 68 proposals – 30 in the field of astronomy and 34 in the field of solar physics, with 4 miscellaneous concepts also submitted.[46][47][48] An ad hoc "survey committee" led by then-SRON Director Johan Bleeker was convened,[49][50] consisting members of the SSAC, CERN, the European Science Foundation, the European Southern Observatory, and the International Astronomical Union,[51] to examine the proposals submitted.[10][52] Throughout early 1984, the survey committee formulated plans for a series of missions divided into three categories – "cornerstones" which would cost two annual budgets over a long implementation timeline, medium-size missions which would cost one annual budget, and small-size missions that would cost half an annual budget.[53][54] The budget for the Science Programme was 130 million accounting units (MAU) annually in 1984, and a 7% annual increase until 1991, when the budget would be fixed at 200 MAU per year onwards, was proposed.[55] Medium-size and small-size categories would later be merged into a single medium-size category that would represent missions costing half a budget.[56] This category was internally referred to as the "blue missions", named after their representation as blue boxes in a publicised diagram of the plan.[56] Each of the original three cornerstones of the plan were assigned a specific field of science that competing proposals would aim to fill,[54] while the objectives of medium-sized missions were left open to be competitively selected alongside mission proposals.[56][57][58] The cornerstones selected were a comet sample-return mission, an X-ray spectroscopy mission, and a submillimetre astronomy mission.[59][60][61] Cornerstone objectives that were not selected due to financial and technical shortcomings, but mentioned by the survey committee as possibilities beyond Horizon 2000, included a solar probe, a Mars rover, and a two-dimensional interferometry mission.[62]

The survey committee's final meeting was held on San Giorgio Maggiore, Venice in June 1984, where the "Horizon 2000" plan was presented to ESA's then-Director General Erik Quistgaard, and leading members of the European scientific community.[54][63][64] The broad objectives of Horizon 2000 were to expand scientific knowledge, establish Europe as a developmental centre of space science, provide opportunities to the European scientific community, and spur innovation in the space technology industry.[65] At the meeting, an additional fourth cornerstone presented by the SSWG was adopted – the Solar-Terrestrial Science Programme (STSP) consisting the Solar and Heliospheric Observatory and Cluster proposals, which became the first missions to be selected for launch under Horizon 2000.[66][67] Quistgaard presented the Horizon 2000 plan at the 1985 Ministerial Council in Rome, where it was approved with only a 5% annual increase of the budget through to 1989, instead of the requested 7% through to 1991.[64][68][69] This was only enough to fund around half of Horizon 2000's objectives.[69] However, an extension of the 5% annual increase through to 1994 was approved at the 1990 Ministerial Council in The Hague, which allowed all Horizon 2000 missions to be fully funded.[70][71][72]

Implementation

The selection of SOHO (pictured) and Cluster was challenged early in development due to financial concerns

The X-ray Multi-Mirror Mission (XMM) was conceived as the X-ray spectroscopy cornerstone mission at an ESA workshop in Lyngby in June 1985, consisting a space observatory with twelve low-energy and seven high-energy telescopes.[73] Due to practical constraints, the mission's payload was reduced to seven telescopes overall by 1987,[74] though the success of EXOSAT inspired mission planners to improve the efficiency of the mission's observations by placing the spacecraft in a highly eccentric orbit,[75][76] allowing the payload of the spacecraft to be reduced to its final design of three large telescopes – each with a reflecting area of 1,500 cm2.[75][77] By 1986, the cost of the STSP cornerstone was forecast to exceed its allocated 400 MAU budget,[78][79] and in a February 1986 meeting, the SPC was presented with the possibility of cancelling the cornerstone in favour of a medium-size mission selection between SOHO, Cluster, and the Kepler Mars orbiter proposal,[78][80] which had gained popularity among members of the SSAC.[81] The Space Shuttle Challenger disaster, which occurred the month before, had an effect on proceedings, as SOHO was intended to be launched via the Shuttle.[82] Despite this, the SSWG, SSAC, and SPC reaffirmed a commitment to the STSP cornerstone by descoping SOHO and limiting Cluster to three spacecraft,[83][84] and reaching a collaboration agreement with NASA in October 1986 that would reduce the mission's cost – they would provide testing, launch services, and operations of SOHO and contribute various scientific instruments,[85][86] while cancelling their Equator mission in favour of a fourth Cluster spacecraft on which American scientific instruments would be flown.[87][b]

The first medium-class mission was selected from proposals formulated by ESA in 1982, prior to Horizon 2000.[89] A Titan Probe that would piggyback on the American Cassini spacecraft was proposed by a group of American and European scientists,[89] and was selected alongside the American-European LYMAN ultraviolet and QUASAT very-long-baseline interferometry observatories as finalists.[90][91][92] The European-Soviet Vesta multiple-flyby minor planet mission and GRASP gamma-ray observatory competed,[93][94] but were rejected by the AWG and SSWG.[92][95] After budget cuts resulting from the Challenger disaster forced NASA to retract its support for LYMAN and QUASAT,[96] the Titan Probe was selected by the SPC in November 1988,[92] and renamed Huygens in honor of Christiaan Huygens, who discovered Titan in 1655, per the suggestion of Swiss astronomers at the meeting.[97] In the competition for the second medium-class mission in June 1989, a consortium of American and European institutions proposed INTEGRAL, a gamma-ray observatory that combined GRASP with the American Nuclear Astrophysics Explorer (NAE),[98] which had lost selection for NASA's Explorers Programme that year.[99] NASA supported the proposal, and the Russian Academy of Sciences later offered launch aboard a Proton launch vehicle in exchange for observation time on the mission.[100][101] Despite concerns about NASA's commitment to the mission and their funding sources,[102] INTEGRAL was selected by the SPC in June 1993, with NASA contributing Deep Space Network services and a spectrometer.[103][104] In response, INTEGRAL was selected by NASA as an Explorers mission without competition.[105] This, along with concerns about the sensitivity of the spectrometer designed for the mission, proved controversial among NASA's advisory bodies.[105][106] In September 1994, ESA and NASA resolved to end NASA's involvement with the spectrometer, citing a lack of financial support.[107] CNES promptly assumed the financial burden, and led the design and manufacturing of a new spectrometer.[108]

Rosetta and FIRST were selected in November 1993 as the third and fourth cornerstone missions,[109] with the latter mission eventually being rechristened the Herschel Space Observatory. COBRAS/SAMBA, later rechristened Planck, was selected as the third medium-sized mission in July 1996.[110][111] As of December 2016, four Horizon 2000 missions, including three cornerstone and one medium-sized mission, remain operational.

Horizon 2000 Plus

The Gaia astrometry mission was launched as one of three missions in the Horizon 2000 Plus campaign.

Horizon 2000 Plus was an extension of Horizon 2000 programme prepared in the mid-1990s, planning missions in the 1995–2015 timeframe.[112] This included two further cornerstone missions, the star-mapping GAIA launched in 2013, and the BepiColombo mission to Mercury launched in 2018; and also a technology demonstrator LISA Pathfinder launched in 2015, to test technologies for the future LISA.

All of the Horizon 2000 and Plus missions were successful, except for the first Cluster which was destroyed in 1996 when its launch rocket exploded. A replacement, Cluster 2, was built and launched successfully in 2000.

Cosmic Vision

Main article: Cosmic Vision

Cosmic Vision 2015–2025 is the current programme of ESA's long-term planning for space science missions. The initial call of ideas and concepts was launched in 2004 with a subsequent workshop held in Paris to define more fully the themes of the Cosmic Vision under the broader subjects of astronomy and astrophysics, Solar System exploration and fundamental physics. By early 2006 the formulation for a 10-year plan based around 4 key questions emerged:

In March 2007 a call for mission ideas was formally released, which yielded 19 astrophysics, 12 fundamental physics and 19 Solar System mission proposals.

Large class

Large class (L-class) missions were originally intended to be carried out in collaboration with other partners with an ESA-specific cost not exceeding 900 million euros. However, in April 2011 it became clear that budget pressures in the US meant that an expected collaboration with NASA on the L1 mission would not be practical. The down-selection was therefore delayed and the missions re-scoped on the assumption of ESA leadership with some limited international participation.[113] Three L-class missions have been selected under Cosmic Vision: JUICE, a Jupiter and Ganymede orbiter launched in April 2023; Athena, an X-ray observatory planned for launch in 2035;[114] and LISA, a space-based gravitational-wave observatory planned for launch in 2035.[115] In April 2024, ESA identified a mission to the Saturn system, including a tour of several Saturn moons, as the science case for the next large scale mission (L4) and the first from ESA's "Voyage 2050" vision.[116]

Medium class

The Euclid near-infrared observatory, launched as the second Cosmic Vision M-class mission.

Medium class (M-class) projects are relatively stand-alone projects and have a price cap of approximately 500 million euros. The first two M-class missions, the Solar Orbiter heliophysics mission to make close-up observations of the Sun,[117] and the Euclid visible to near-infrared space telescope, aimed at studying dark energy and dark matter,[118] were selected in October 2011.[119] PLATO, a mission to search for exoplanets and measure stellar oscillations, was selected on 19 February 2014,[120] against EChO, LOFT, MarcoPolo-R and STE-QUEST[121] After a preliminary culling of proposals for the fourth M-class mission in March 2015, a short list of three mission proposals selected for further study was announced on 4 June 2015.[122][123][124] The shortlist included the THOR plasma observatory and the XIPE X-ray observatory.[124] ARIEL, a space observatory which will observe transits of nearby exoplanets to determine their chemical composition and physical conditions,[124] was ultimately selected on 20 March 2018.[125][126] The competition for the fifth M-class mission concluded in June 2021, with the EnVision Venus orbiter ultimately being selected for launch in 2031.[127] The SPICA far-infrared observatory and THESEUS gamma-ray observatory were the other two proposals.[128]

Small class

Small class missions (S-class) are intended to have a cost to ESA not exceeding 50 million euros. A first call for mission proposals was issued in March 2012; the winning proposal would need to be ready for launch by 2017.[129] Approximately 70 letters of Intent were received.[130] CHEOPS, a mission to search for exoplanets by photometry, was selected as the first S-class mission in October 2012 and will launch in Fall 2019.[131][132] SMILE, a joint mission between ESA and the Chinese Academy of Sciences to study the interaction between Earth's magnetosphere and the solar wind, was selected as the second S-class mission from thirteen competing proposals in June 2015.[133] As of June 2023, SMILE is scheduled for launch in May 2025.[134]

Fast class

At the ESA Science Programme Committee (SPC) Workshop on 16 May 2018, the creation of a series of special opportunity Fast class (F-class) missions was proposed. These F-class missions will be jointly launched alongside each M-class mission starting from M4, and would focus on "innovative implementation" in order to broaden the range of scientific topics covered by the mission. The inclusion of F-class missions into the Cosmic Vision program will require an increase of the science budget.[135] F-class missions must take under a decade from selection to launch and weigh less than 1,000 kg.[136] The first F-class mission, Comet Interceptor, was selected in June 2019.[137][138] On 2 November 2022, ESA announced the F-class mission ARRAKIHS, to be launched in the early 2030s.[139]

Missions of Opportunity

Occasionally ESA makes contributions to space missions led by another space agency. Missions of opportunity allow the ESA science community to participate in partner-led missions at relatively low cost. The cost of a mission of opportunity is capped at €50 million.[140] ESA missions of opportunity include contributions to Hinode, IRIS, MICROSCOPE, PROBA-3, XRISM, ExoMars, Einstein Probe, and MMX.[140] A contribution to SPICA (Space Infrared Telescope for Cosmology and Astrophysics), a Japanese JAXA mission, was evaluated as a mission of opportunity within Cosmic Vision. It is no longer considered within that framework,[141] though SPICA was one of the mission proposals being considered for M5.

Voyage 2050

The next campaign of the ESA science programme is Voyage 2050, which will cover space science missions operating from 2035 to 2050. Planning began with the appointment of a Senior Committee in December 2018 and a call for white papers in March 2019.[142]

Three Large class and six to seven Medium class missions are currently anticipated in this plan, as well as smaller missions and missions of opportunity.[143] On 11 June 2021, the Senior Committee published the Voyage 2050 plan, and recommended the following science themes for the next three Large class missions:[144]

  • Moons of the giant planets – a mission to an ocean-bearing gas giant moon.
  • From temperate exoplanets to the Milky Way – a mission to either characterize exoplanets or investigate the Milky Way's formation history.
  • New physical probes of the early Universe – a mission to investigate the early universe through the cosmic microwave background, gravitational waves, or other fundamental astrophysical phenomena.

Missions

Horizon 2000

Horizon 2000 Plus

Cosmic Vision

Timeline

Laser Interferometer Space AntennaEnVision (spacecraft)Advanced Telescope for High Energy AstrophysicsComet InterceptorARIELPLATO (spacecraft)SMILE (spacecraft)Euclid (spacecraft)Jupiter Icy Moons ExplorerSolar OrbiterCHEOPSBepiColomboLISA PathfinderGaia (spacecraft)Planck (spacecraft)Herschel Space ObservatoryRosetta (spacecraft)INTEGRALCluster II (spacecraft)XMM-NewtonHuygens (spacecraft)Cluster (spacecraft)Solar and Heliospheric Observatory

See also

References

Notes

  1. ^ Also known as the ESA Science Programme,[3] ESA's Science Programme,[4][5] or the ESA scientific programme.[6][7]
  2. ^ Equator was a planned mission by NASA to explore Earth's magnetosphere from an equatorial orbit. It was NASA's contribution to a joint mission with the STSP known as the International Solar-Terrestrial Physics (ISTP) programme.[87][88]

Sources

  1. Bonnet, Roger-Maurice [in French]; Bleeker, Johan; Olthof, Henk (1984). Longdon, Norman (ed.). "Space Science – Horizon 2000". ESA's Report to the ... COSPAR Meeting. Noordwijk, Netherlands: ESA Scientific & Technical Publications Branch. ISSN 0379-6566. Archived from the original on 9 July 2019. Retrieved 9 July 2019.
  2. Bonnet, Roger-Maurice [in French] (April 1988). Rolfe, Erica (ed.). Fundamental science and space science within the Horizon 2000 programme. A Decade of UV astronomy with the IUE satellite: a celebratory symposium held at Goddard Space Flight Center. Vol. 2. Greenbelt, Maryland, USA: ESA Publications Division. pp. 85–94. Bibcode:1988ESASP.281b..85B. ISSN 0379-6566. Archived from the original on 15 July 2019. Retrieved 15 July 2019.
  3. Bonnet, Roger-Maurice [in French] (February 1995). Battrick, Bruce; Guyenne, Duc; Mattok, Clare (eds.). "European Space Science - In Retrospect and in Prospect". ESA Bulletin (81). Noordwijk, Netherlands: ESA Publications Division: 6–17. ISSN 0376-4265. Retrieved 7 July 2019.
  4. Bonnet, Roger-Maurice [in French] (2004). "Cassini–Huygens in the European Context". In Fletcher, Karen (ed.). Titan: From Discovery to Encounter: Proceedings of the International Conference, 13-17 April 2004, ESTEC, Noordwijk, the Netherlands. Vol. 1278. Noordwijk, Netherlands: ESA Publications Division. pp. 201–209. Bibcode:2004ESASP1278..201B. ISBN 9789290929970. SP-1278. Archived from the original on 7 July 2019. Retrieved 7 July 2019.
  5. Cogen, Marc (2016). An Introduction to European Intergovernmental Organizations (2nd ed.). Abingdon, England: Routledge. ISBN 9781317181811. Retrieved 8 July 2019.
  6. European Science Foundation; National Research Council (1998). U.S.-European Collaboration in Space Science. Washington, D.C., United States: National Academies Press. ISBN 9780309059848. Retrieved 6 July 2019.
  7. European Space Agency (1995). "The Science Programme". The ESA Programmes (BR-114). Archived from the original on 6 July 2019. Retrieved 6 July 2019.
  8. European Space Agency (2013). "How a Mission is Chosen". ESA Science. Archived from the original on 7 July 2019. Retrieved 7 July 2019.
  9. European Space Agency (2015). "Science Programme". ESA Industry Portal. Archived from the original on 6 July 2019. Retrieved 6 July 2019.
  10. Harvey, Brian (2003). Europe's Space Programme: To Ariane and Beyond. Dublin, Ireland: Springer Science+Business Media. ISBN 9781852337223. Retrieved 9 July 2019.
  11. Jansen, Fred; Lumb, David; Schartel, Norbert (3 February 2012). "X-ray Multi-mirror Mission (XMM-Newton) observatory". Optical Engineering. 51 (1): 011009–011009–11. arXiv:1202.1651. Bibcode:2012OptEn..51a1009L. doi:10.1117/1.OE.51.1.011009. S2CID 119237088.
  12. Krige, John; Russo, Arturo; Sebesta, Laurenza (2000). Harris, R. A. (ed.). A History of the European Space Agency, 1958 – 1987 (Vol. II - The Story of ESA, 1973 to 1987) (PDF). Noordwijk, Netherlands: ESA Publications Division. ISBN 9789290925361. Archived (PDF) from the original on 8 July 2019. Retrieved 8 July 2019.
  13. Wilson, Andrew (2005). ESA Achievements (PDF) (3rd ed.). Noordwijk, Netherlands: ESA Publications Division. ISBN 9290924934. Archived (PDF) from the original on 10 July 2019. Retrieved 10 July 2019.

Citations

  1. ^ "ESA science programme planning cycles". ESA Science. 4 March 2019. Archived from the original on 7 July 2019. Retrieved 7 July 2019. The Science Programme of the European Space Agency (ESA) relies on long-term planning of its scientific priorities.
  2. ^ ESA 2015, "The Science Programme within the Directorate of Science has two main objectives [...] The Science Programme has a long and successful history..."
  3. ^ ESA Media Relations Office (12 October 2012). "ESA Science Programme's new small satellite will study super-Earths". European Space Agency. Archived from the original on 6 July 2019. Retrieved 6 July 2019. Studying planets around other stars will be the focus of the new small Science Programme mission, Cheops, ESA announced today. [...] The mission was selected from 26 proposals submitted in response to the Call for Small Missions in March [...] Possible future small missions in the Science Programme should be low cost and rapidly developed, in order to offer greater flexibility in response to new ideas from the scientific community.
  4. ^ ESA 1995, "ESA's Science Programme has three primary features that single it out among the Agency's activities [...] ESA's Science Programme has consistently focussed on missions with a strong innovative content."
  5. ^ a b "Call for a Fast (F) mission opportunity in ESA's Science Programme". ESA Science. 16 July 2018. Archived from the original on 7 July 2019. Retrieved 7 July 2019. This Call for a Fast mission aims at defining a mission of modest size (wet mass less than 1000 kg) to be launched towards the Earth-Sun L2 Lagrange point as a co-passenger to the ARIEL M mission, or possibly the PLATO M mission.
  6. ^ ESA 2013, "The ESA scientific programme is based on a continuous flow of projects that fulfil its scientific goals."
  7. ^ a b ESF and NRC 1998, page 36, "The fundamental rule of ESRO, and subsequently ESA, has been that ESA exists to serve scientists and that its science policy must be driven by the scientific community, not vice versa [...] [This] explains the determining influence that ESA's advisory structure has on the definition and evolution of the scientific program."
  8. ^ a b c European Space Agency (2011). "Astronomy Working Group". ESA Cosmos Portal. Archived from the original on 6 July 2019. Retrieved 6 July 2019. The Astronomy Working Group (AWG) provides scientific advice mainly to the Space Science Advisory Committee (SSAC). [...] The chair of the working group is also a member of the SSAC.
  9. ^ a b c European Space Agency (2011). "Solar System and Exploration Working Group (SSEWG)". ESA Cosmos Portal. Archived from the original on 6 July 2019. Retrieved 6 July 2019. The Solar System and Exploration Working Group (SSEWG) provide scientific advice mainly to the Space Science Advisory Committee (SSAC). [...] The chair of the working group is also a member of the SSAC.
  10. ^ a b c ESF and NRC 1998, page 36, "Ad hoc working groups may also by appointed to advise on particular subjects. [...] Another was the so-called survey committee, which formulated the long-term plan for space science (i.e., the Horizon 2000 program) on the basis of input contributed by the European scientific community."
  11. ^ a b ESA 2015, "The Science Programme within the Directorate of Science has two main objectives; To provide the scientific community with the best tools possible to maintain Europe's competence in space; To contribute to the sustainability of European space capabilities and associated infrastructures by fostering technological innovation in industry and science communities, and maintaining launch services and spacecraft operations."
  12. ^ Cogen 2016, page 221, "All member states must participate in the mandatory programmes [...] Today, ESA's mandatory programmes are carried out under the General Budget, the Technology Research Programme, the Science Programme and ESA's technical and operational infrastructure."
  13. ^ ESA 1995, "...it is the only mandatory programme [...] In 1975, when ESRO and ELDO were merged to form ESA, it was immediately decided that the Agency's Science Programme should be mandatory."
  14. ^ ESA 2015, "All Member States contribute pro-rata to their Net National Product (NNP) providing budget stability and allowing long-term planning of its scientific goals. For this reason, the Science Programme is called 'mandatory'.
  15. ^ ESA 2015, "Long-term science planning and mission calls are established through bottom-up processes. This relies on broad participation, with input and peer reviews of the space science community. The ESA Science Programme is foremost science-driven."
  16. ^ a b ESF and NRC 1998, page 36, "They advise the director general and the director of the scientific program on all scientific matters, and their recommendations are independently reported to the SPC."
  17. ^ a b European Space Agency (2011). "Space Science Advisory Committee (SSAC)". ESA Cosmos Portal. Archived from the original on 6 July 2019. Retrieved 6 July 2019. The Space Science Advisory Committee (SSAC) is the senior advisory body to the Director of Science (D/SCI) on all matters concerning space science included in the mandatory science programme of ESA.
  18. ^ Cogen 2016, page 219, "The Council is responsible for the establishment of a Science Programme Committee which deals with any matter relating to the mandatory scientific programme."
  19. ^ a b ESF and NRC 1998, page 36, "Membership on the advisory bodies is for 3 years, and the chairs of the AWG and SSWG are de jure members of the SSAC."
  20. ^ ESA 2013, "These projects are identified and selected using the mechanism of the open call. Whenever appropriate, and compatible with the programme goals and constraints, ESA issues a call for proposals for new science missions."
  21. ^ a b ESA 2013, "The call includes descriptions of the scientific goals, size, cost of the mission, together with programmatic and implementation details. [...] Missions fall into three categories: small (S-class), medium (M-class) and large (L-class), their size reflecting the scientific goals addressed and eventually the cost and development time required."
  22. ^ ESA 2013, "ESA's various scientific advisory committees of experts assess the submissions. [...] ESA’s engineers also make an initial assessment of the feasibility of the missions. [...] Phase 0; Mission analysis and identification..."
  23. ^ a b Bonnet 2004, page 203, "Following a normal cycle of selection, through the Working Group, ESA undertook a feasibility study in 1984-1985, followed by the selection for Phase A in 1986."
  24. ^ ESA 2013, "This identifies any new technology that will need to be developed to make the mission possible. The majority of these studies are conducted internally at ESA's Concurrent Design Facility (CDF)."
  25. ^ a b ESA 2013, "The committees then make recommendations about which missions should proceed to 'Phase A'. [...] Usually two or three missions are downselected for the phase A study, for which two competitive industrial contracts are placed for each mission. Phase A results in a preliminary design for the mission."
  26. ^ ESA 2013, "Phase B; Preliminary Definition; Phase C; Detailed Definition; Phase D; Qualification and Production; Phase E; Utilisation; Phase F; Disposal..."
  27. ^ a b ESA 2013, "Results are presented, again in Paris to the various committees, and a final decision on which proposal will be selected for each mission is made. [...] They will eventually lead to the 'adoption' of the mission and to the selection of one of the two industrial contractors to become the responsible for the whole implementation phase..."
  28. ^ Bonnet 2004, page 203–204, "The Titan Probe was eventually selected by ESA's SCP in Nov. 1988 as the first 'blue' mission of Horizon 2000, against four other missions: VESTA, LYMAN, QUASAT, and GRASP."
  29. ^ Krige et al. 2000, page 34, "The Convention establishing the European Space Agency was signed by ten European states on 30 May 1975 [...] At the same time the Conference of Plenipotentiaries adopted a Final Act including ten resolutions. These made allowance for the transition from ESRO and ELDO to ESA..."
  30. ^ Cogen 2016, page 217, "ESA is created in its current form in 1975, merging ELDO with ESRO, by the Convention for the Establishment of a European Space Agency of 30 May 1975."
  31. ^ Parks, Clinton (27 May 2008). "May 31, 1975: European Space Unites Under the ESA Banner". SpaceNews. Retrieved 8 July 2019. Established May 31, 1975, ESA formed from the merger of the European Space Research Organisation (ESRO) and the European Launcher Development Organisation (ELDO).
  32. ^ Krige et al. 2000, page 40, "Astronomy had suffered heavily in ESRO and had been explicitly demoted in priority by the LPAC in 1970."
  33. ^ a b Bonnet 2004, page 201, "At their long term planning meeting in 1970, the LPAC decided not to plan any planetary missions because they were considered at the time too expensive and beyond the financial capabilities of ESRO. Cooperation with NASA or the USSR was the only option for Europe to participate in the exploration of the Solar System."
  34. ^ Bonnet 2004, page 201–202, "The first change from that policy was the proposal of the ESA Science Director, Ernst Trendelenburg, followed by the positive decision of ESA's SPC in 1980, to launch a fast fly-by mission to Halley's comet on the occasion of its return to the vicinity of the Sun in March 1986."
  35. ^ a b Bonnet 1995, page 9, "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."
  36. ^ Bonnet 1995, page 9, "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. [...] All three missions were to use the Ariane launcher and were originally European-only missions."
  37. ^ Bonnet 2004, page 202, "Giotto (the name given to that mission) was the first purely European mission to explore the Solar System with its own launcher: Ariane 1, launched on July 2 1985."
  38. ^ a b Bonnet 1995, page 9, "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."
  39. ^ Bonnet 1995, page 10, "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."
  40. ^ Krige et al. 2000, page 39, "The DG replaced the LPAC with the SAC (Science Advisory Committee) reporting directly to him on all scientific matters [...] A Life Sciences Working Group (LSWG) and Materials Sciences Working Group (MSWG) were also added to the AWG and SSWG, with all working groups reporting to the DG."
  41. ^ Krige et al. 2000, page 43, "The SAC, which had previously advised the Director General on all scientific matters, was now transformed into the SSAC (Space Science Advisory Committee). Its role became to advise the Director of Scientific Programmes on activities covered by the AWG and the SSWG."
  42. ^ Krige et al. 2000, page 43, "The spirited and controversial figure of Ernst Trendelenburg, who had spent almost twenty years in ESRO and then ESA, was replaced as Director of Scientific Programmes on 1 May 1983 by the French space scientist Roger Bonnet, former chairman of the SAC from 1978 to 1980."
  43. ^ Bleeker et al. 1984, page 3, "Over the past 25 years, space science has progressed from the pioneering and exploratory stage to a firmly established mature branch of fundamental science. The time has come to identify what the main thrusts of European space science should be for the coming decades to consolidate Europe's position in the forefront of scientific development"
  44. ^ Bleeker et al. 1984, page V, "The study, which led to the long term plan proposed in this document, was initiated by the Director of the Scientific Programme in September 1983 and was coordinated by a Survey Committee composed of scientists from different areas of fundamental science."
  45. ^ Krige et al. 2000, page 43, "Bonnet presented his idea to a meeting of the SPC in October 1983. The scientific community would be asked to suggest mission concepts which would be assessed by expert teams covering various disciplines in astronomy and the solar system sciences."
  46. ^ a b Bonnet 1995, page 10, "Following a Call for Mission Concepts issued in Autumn 1983, to which the European scientific community responded with some 68 proposals (Table 2)..."
  47. ^ Krige et al. 2000, page 44, "The exercise produced 68 mission concepts, 33 in astronomy and 35 in solar system sciences."
  48. ^ Bonnet 1995, page 10, "Horizon 2000; 2/11 – 31/12/1983; Astronomy 30; Solar Physics 34; Miscellaneous proposals 4; Total no. proposals 68"
  49. ^ Harvey 2003, page 210, "The Agency adopted a team of scientists under Johan Bleeker and made a call for mission concepts: one that was widely supported (70 were received)..."
  50. ^ Bleeker et al. 1984, page V, "Johan Bleeker; Chairman of the Survey Committee"
  51. ^ ESF and NRC 1998, page 36, "The SSAC formed the core of the survey committee. The membership of the survey committee, in addition to the SSAC [...] the European Science Foundation, Centre d'Études et de Recherches Nucléaires (CERN), the European Southern Observatory (ESO), and the International Astronomical Union (IAU)."
  52. ^ Krige et al. 2000, page 43, "Their proposals would be evaluated by a Survey Committee which would draw up a global model programme for the years 1985 - 2004."
  53. ^ Krige et al. 2000, page 44, "The philosophy of Horizon 2000 was to divide projects into three classes: cornerstones, costing two annual budgets, and having long lead times; medium size projects, costing one annual budget, and of the class of then current missions like Giotto, Hipparcos and Ulysses; and low-cost projects, costing 0.5 annual budgets, typically participation in international programmes."
  54. ^ a b c Harvey 2003, page 210, "In the end, the committee produced a report called Space Science Horizon 2000, often referred to as Horizon 2000. This adopted the principle of 'cornerstone' missions, projects that will advance space science substantially in distinct areas over a period of many years."
  55. ^ Krige et al. 2000, page 44, "The overall budget for the programme was set at 200 MAU annually (1983 prices) as from 1991, this level to be achieved by an annual 7% increase over the 1984 budget (about 130 MAU)."
  56. ^ a b c Bonnet 2004, page 203, "In addition, Horizon 2000 offered the possibility of introducing at any stage in the selection process, medium-size or 'blue' missions, so-called because they were represented as blue boxes in the original diagram of the plan, whose cost would not be larger than half the value of the yearly budget."
  57. ^ Bleeker et al. 1984, page 6, "Having established the major missions as the 'cornerstones' of the programme, provisions are to be made within the overall long term programme for a number of typical but as yet unidentified medium and small size missions [...] Detailed identification and selection of these smaller missions will be made at the appropriate time and follow the established competitive procedure."
  58. ^ Bonnet 1995, page 10, "In addition, the plan also included both small and medium size projects [...] but with no i priori [sic] exclusion of disciplines, so that a community not 'served' directly by the Cornerstones could still find a place in responding to the regularly released 'Calls for Ideas'."
  59. ^ Krige et al. 2000, page 44, "The astronomers selected an X-ray spectroscopy mission intended to build a third generation of observatory-class satellites for high-energy astrophysics. Their second cornerstone was in the field of submillimetre heterodyne spectroscopy [...] As for the solar system scientists, one of their cornerstones built on the achievements of Giotto, involving a mission to primordial bodies (comets and asteroids) with a return of pristine materials."
  60. ^ Bleeker et al. 1984, page 10–11, "The four cornerstones are: The Solar Terrestrial Programme (STP) [...] A Mission to Primordial Bodies including Return of Pristine Materials [...] A High Throughput X-Ray Mission for Spectroscopic Studies between 0.1- 20 keY [...] A High Throughput Heterodyne Spectroscopy Mission..."
  61. ^ Bonnet 1995, page 10, "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)."
  62. ^ Bleeker et al. 1984, page 11, "As a follow-up to these four elements it is already possible to identify beyond the horizon 2004 other major thrusts: these are the Solar Probe and the Heliosynchronous Out of Ecliptic Mission in solar terrestrial physics, the Mars Rover in the planetary area, and, in astronomy, two-dimensional interferometry for high spatial resolution in the visible, infrared (IR) and millimetre (mm) wavelength region. These thrusts are beyond the present programme, for technological and financial reasons..."
  63. ^ Krige et al. 2000, page 44, "After the expert teams had prepared their reports an historic meeting of leading members of the European space science community on the San Giorgio Island in Venice from 30 May to 1 June 1984 consolidated the choices between them and produced a long-term plan which received the name Horizon 2000."
  64. ^ a b Bonnet 1995, page 10, "...a survey committee and several Topical Teams were formed to [...] formulate recommendations to ESA's then Director General Erik Quistgaard, for him to present to the Council of Ministers in January 1985 in Rome."
  65. ^ ESA 1995, "The programme objectives are to: contribute to the advancement of fundamental scientific knowledge; establish Europe as a major participant in the worldwide development of space science; offer a balanced distribution of opportunities for frontline research to the European scientific community; provide major technological challenges for innovative industrial developments."
  66. ^ ESF and NRC 1998, page 52, "At the final meeting of the survey committee in May 1984 in Venice, Italy, only three cornerstones were originally foreseen. It was therefore a surprise when a fourth, consisting of the SOHO and Cluster missions, was introduced by the chairman of the Solar System Working Group. [...] This cornerstone was called the Solar-Terrestrial Science Program (STSP)..."
  67. ^ Krige et al. 2000, page 44, "The second, not foreseen in the original outline, sneaked in at the Venice meeting and covered the fields of solar and plasma physics. It involved combining two existing proposals, SOHO and Cluster."
  68. ^ Krige et al. 2000, page 44, "..as a result of which those present agreed to increase the level of the mandatory programme by 5% annually in real terms over the period 1985 - 1989."
  69. ^ a b ESA 1995, "Carrying out Horizon 2000 required a special financial effort from the Member States, amounting to a progressive budgetary increase of 7% per year from 1985 to a steady state in 1992. The Council meeting at Ministerial Level in Rome authorised a slower progression of 5% a year until 1989, thus affording about 50% of the requested increase."
  70. ^ ESA 1995, "The realisation of the entire Horizon 2000 plan became dependent on such a progression of 5% a year being maintained until 1994. This progression was granted by the ESA Council in December 1990, thereby opening the way to full implementation of Horizon 2000."
  71. ^ Bonnet 1995, page 10, "...the ESA science budget was granted an annual increase of 5% above inflation [...] an increment that was to be implemented over ten years."
  72. ^ Krige et al. 2000, page 44, "This was subsequently extended at the Ministerial Meeting in The Hague to enable the programme to reach a level of almost 217 MAU in 1992 (in 1985 prices)."
  73. ^ Lumb et al. 2012, page 1, "...culminating in a mission presentation at an ESA workshop held in Lyngby, Denmark in June 1985. In the papers presented at this conference the mission design contained 12 low-energy and 7 high-energy telescopes..."
  74. ^ Lumb et al. 2012, page 1, "When the report of the telescope working group was delivered in 1987, the consideration of practical constraints had reduced the number of telescopes to a more modest total of 7."
  75. ^ a b Lumb et al. 2012, pages 1, 4, "The mission was approved into implementation phase in 1994, and an improved observing efficiency achieved with a highly eccentric orbit allowed the number of telescopes to be reduced. [...] Effective area (1keV); 1500 cm2"
  76. ^ European Space Agency (4 June 2013). "XMM-Newton Overview". ESA Science. Archived from the original on 9 July 2019. Retrieved 9 July 2019. Following the experience with Exosat, which demonstrated the value of a highly eccentric orbit for long uninterrupted observations of X-ray sources, XMM was to be placed in a 48-hour period orbit using the Ariane 4 launcher.
  77. ^ Wilson 2005, page 206, "The heart of the mission is the X-ray telescope. It consists of three large mirror modules and associated focalplane instruments held together by the telescope's central tube"
  78. ^ a b Krige et al. 2000, page 217, "To this, Bonnet replied that the Executive would offer the SPC the choice between implementing the STSP as a wholeor selecting one of the three projects in competition (SOHO, Cluster and Kepler), but stressed that "if the Executive could implement the STSP Cornerstone within 400 MAU, it would do so unless the SSAC expressed a strong negative opinion on this approach"."
  79. ^ Krige et al. 2000, page 217, "The supporters of Kepler had a good card in their hands, however, i.e. the high cost of the twin SOHO/Cluster mission, well above the 400 MAU ceiling."
  80. ^ Harvey 2003, page 211, "Several other mission possibilities were also discussed; for example, a Mars probe (Kepler)..."
  81. ^ Krige et al. 2000, page 217, "The decision was not however taken without some conflict. One of the new SSAC members, M. Ackerman, did not like the "inferiority situation" in which Kepler had found itself as aconsequence of the introduction of the STSP Cornerstone and insisted that the Mars mission should be maintained in the selection cycle."
  82. ^ Krige et al. 2000, page 219, "The SPC met on 6 February 1986, in the aftermath of the dramatic accident which had destroyed the Challenger Shuttle, killing its crew (28 January). This event threw a new shadow on the STSP programme: firstly, because SOHO was assumed to be eventually launched on the Space Shuttle..."
  83. ^ Krige et al. 2000, page 217, "After a dramatic discussion on the various options, the SSAC agreed that an STSP mission consisting of a descoped SOHO and a three-spacecraft Cluster should eventually be pursued..."
  84. ^ Krige et al. 2000, page 218–219, "The SSWG unanimously agreed to recommend the STSP programme [...] The SSAC, for their part, fully endorsed the SSWG recommendation [...] all SPC delegations finally approved the adoption of the STSP double mission into ESA's Scientific Programme..."
  85. ^ Krige et al. 2000, page 219, "ESA would also develop the SOHO spacecraft (including payload integration) for which NASA would provide testing, launch services and operations. European and US experiments would be included in SOHO and the first Cluster spacecraft."
  86. ^ Wilson 2005, page 160, "The Solar and Heliospheric Observatory (SOHO) is a cooperative project between ESA and NASA..."
  87. ^ a b Krige et al. 2000, page 219, "In the event, a tentative agreement was reached with NASA in October that year, by which ESA would develop four identical Cluster spacecraft, one of which would be launched by NASA in 1993 into an equatorial orbit, thereby replacing NASA's "Equator" ISTP satellite now cancelled, and the three others would be launched in 1994 (free of charge) on an Ariane-5 demonstration flight."
  88. ^ Goddard Space Flight Center. "Equator-S". Space Science Data Coordinated Archive. Archived from the original on 15 July 2019. Retrieved 15 July 2019. Equator-S is different from NASA's ISTP/EQUATOR spacecraft, which was dropped when the ISTP mission was re-scoped in late 1989.
  89. ^ a b Bonnet 2004, page 203, "In response to a call for ideas for new missions released by ESA in 1982, a group of European and US scientists proposed adding a Titan Probe as an element of the US Cassini mission."
  90. ^ Harvey 2003, page 211, "Also in the melting pot for consideration were an ultraviolet observatory (Lyman), a very long baseline interferometry mission (Quasat)..."
  91. ^ Krige et al. 2000, page 220, "All three missions under consideration were recommended by the Working Groups for Phase-A study, the Titan probe for the Cassini mission by the SSWG and Lyman and Quasat by the AWG."
  92. ^ a b c Bonnet 2004, page 203–204, "The Titan Probe was eventually selected by ESA's SPC in Nov. 1998 [sic] as the first 'blue' mission of Horizon 2000, against four other missions: VESTA, LYMAN, QUASAT, and GRASP."
  93. ^ Bonnet 1988, page 87, "Vesta is a trilateral (USSR, CNES, and ESA) mission to the small bodies of the Solar System [...] Each spacecraft will fly-by a minimum of three asteroids [...] A cometary fly-by will also be included."
  94. ^ Bonnet 1988, page 93, "GRASP (Gamma-Ray Astronomy with Spectrometry and Positioning) is a fully European project."
  95. ^ Harvey 2003, page 211, "...a gamma ray observatory (GRASP) and a number of candidates for an asteroid mission (Agora, Vesta)."
  96. ^ Krige et al. 2000, page 220, "Later on, however, NASA informed ESA that because of budgets cuts, in the wake of the Challenger accident, they could no longer consider the Lyman and Quasat projects for the present."
  97. ^ Bonnet 2004, page 204, "At the end of the SPC meeting the Director of the Science Programme reminded delegations that the Saturn moon Titan had been discovered in 1655 by the Dutch astronomer Huygens. In response to the Swiss request, he therefore proposed that the European contribution to the American Cassini project henceforth by known as 'Huygens'."
  98. ^ ESF and NRC 1998, page 54, "The early definition of INTEGRAL attempted to combine the best features of the two earlier gamma-ray missions studied on both sides of the Atlantic [...] In June 1989, in response to the ESA call for new mission proposals, INTEGRAL was proposed jointly [...] on behalf of a consortium of institutes and laboratories in Europe and the United States."
  99. ^ ESF and NRC 1998, page 54, "The renewed discussions of INTEGRAL in Europe following the rejection of GRASP stemmed in part from the NASA Explorer competition of 1989 in which a U.S. gamma-ray spectroscopy mission, the Nuclear Astrophysics Explorer (NAE), had been selected for a Phase A study but then was not selected for flight."
  100. ^ ESF and NRC 1998, page 54, "It was envisioned as a fully-shared ESA-NASA partnership, a view supported by NASA Headquarters."
  101. ^ ESF and NRC 1998, page 54, "In December 1991, the Russian Academy of Sciences offered to provide a Proton launcher, free of charge, as a contribution in exchange for a share of the observing time."
  102. ^ ESF and NRC 1998, page 55, "Moreover, NASA had no previously identified INTEGRAL in its overall mission planning. Given this uncertainty, NASA was unable to make a firm commitment. [...] A suspicion arose within the U.S. space science community that funding the spectrometer would require funds be derived from the Explorer line."
  103. ^ ESF and NRC 1998, page 55, "At ESA's June 1993 meeting, the SPC approved INTEGRAL as ESA's M2 mission, based on an international cooperation in which Russia would provide the Proton launcher and NASA the spectrometer instrument, as well as a contribution to the ground segment."
  104. ^ Wilson 2005, page 236, "Integral was selected by the Agency's Science Programme Committee in 1993 as the M2 medium-size scientific mission. It was conceived as an observatory, with contributions from Russia (launch) and NASA (Deep Space Network ground stations)."
  105. ^ a b ESF and NRC 1998, page 55, "The INTEGRAL mission had still not garnered broad U.S. support or a vocal constituency in the NASA space science advisory process for several reasons [...] the perception that INTEGRAL had never passed the required peer review in the Explorer competition..."
  106. ^ ESF and NRC 1998, page 55, "...early concerns of some astrophysists that the lack of detection of bright descrete sources of line emission [...] implied that the spectrometer planned for INTEGRAL might not be sensitive enough."
  107. ^ ESF and NRC 1998, page 55, "...it became increasingly clear that NASA could not support INTEGRAL at the $70 million level expected by U.S. PIs. [...] Finally in September 1994, a meeting between ESA and NASA led to the conclusion that NASA could not support the U.S. spectrometer PI."
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