European Space Agency, ESA

ESA Preview 2014

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2014 has all the elements to become an interesting year for Europe in space… Exciting launches, new European astronauts on the ISS, new satellites and landers and important decisions that will mark the direction of Europe’s future space programme. But 2014 starts with one name: ROSETTA.


ESA Highlights 2013

Copyright ESA

2013 has been a year of firsts, farewells and astonishing findings. It began with ESA astronaut Luca Parmitano training for the Volare Mission in Russia’s Star City and it ended with Gaia, ESA’s billion-star surveyor, lifting off from Europe’s spaceport in Kourou. But a lot more has happened in between!



13 December 2013

ESA’s billion-star surveyor Gaia, less than a week from launch, is now tucked up inside the fairing that will protect it during the first few minutes of ascent into space.

Last week, Gaia was loaded with the propellants it will need to journey to its ‘L2’ destination, a gravitationally stable location 1.5 million km away from Earth, from where it will survey our Milky Way galaxy.

After fuelling, it was mounted on the Soyuz adapter and added to the Fregat upper stage, which will boost Gaia towards L2.

Meanwhile, the basic assembly of Soyuz – the boosters, core stage and third stage – has been completed in its integration building.

In the coming days, the Soyuz lower stages and the upper assembly containing Gaia will be transported to the launch pad and mated.

Launch is scheduled for 9:12:19 GMT (10:12:19 CET) on 19 December.

Follow the launch campaign on our dedicated blog.



29 November 2013

Multilateral agreements for Euclid and Gaia have been signed at the Science Programme Committee meeting, held on 28 November 2013 at ESA Headquarters in Paris, France.

The Euclid MLA provides the legal framework for the provision of the scientific instruments and their elements for the Euclid payload, and the legal framework for part of the Science Ground Segment for Euclid.

This agreement is between the European Space Agency and the funding agencies of the eleven European countries participating in the Euclid Mission Consortium: the Agenzia Spaziale Italiana (Italy); the Centre National d’Etudes Spatiales (France); the Deutsches Zentrum für Luft- und Raumfahrt e.V. (Germany); the Danish Space Research Institute (Denmark); the Fundação para a Ciência e a Tecnologia (FCT), Space Office (Portugal); the Ministerio de Economía y Competividad (Spain); the Nederlandse Onderzoekschool Voor Astronomie (The Netherlands); the Norwegian Space Centre (Norway); the Romanian Space Agency (Romania); the United Kingdom Space Agency (UK); and the University of Helsinki (Finland). Switzerland participates via PRODEX.

The infrared sensors for the Near-Infrared Spectroscopy and Photometry Instrument (NISP) will be provided by NASA in line with a Memorandum of Understanding signed in January 2013.

To be launched in 2020, Euclid’s 1.2 m-diameter telescope and two scientific instruments will map the shape, brightness and 3D distribution of two billion galaxies covering more than a third of the whole sky and looking back over three-quarters of the history of the Universe.

In addition, a revised MLA for Gaia has been signed. The Gaia MLA defines the terms and conditions governing the commitment of each party to Gaia data processing. The revised agreement adds the Archive Access Coordination Unit (known as CU9) to the Data Processing and Analysis Consortium (DPAC) – the body of scientists who have been entrusted with the data processing and analysis for the Gaia mission. CU9 will be responsible, along with the Gaia Science Operations Centre, for providing a repository for Gaia data products as well as access tools to maximise the scientific exploitation of the Gaia data set.

The data processing ground segment is a fundamental element of the mission, which will conduct an astrometric survey of 1 billion stars – approximately 1 per cent of the stellar populations of our Galaxy, the Milky Way – after launch from Kourou in December.



23 October 2013

Updated 22 November 2013: Arianespace have announced that Gaia is scheduled to launch on 19 December 2013 at 09:12:18 UTC.

Updated 29 October 2013: The upcoming launch manifest of Arianespace has now been established. Gaia is scheduled for launch on 20 December.

On 22 October, the decision was taken to postpone the launch of ESA’s Gaia mission after a technical issue was identified in another satellite already in orbit.

Gaia shares some of the components involved in this technical issue and prompt notification of this problem has allowed engineers working on the final preparations for Gaia’s launch to take additional precautionary measures.

The issue concerns components used in two transponders on Gaia that generate ‘timing signals’ for downlinking the science telemetry. To avoid potential problems, they will be replaced.

The transponders will be removed from Gaia at Kourou and returned to Europe, where the potentially faulty components will be replaced and verified. After the replacements have been made, the transponders will be refitted to Gaia and a final verification test made.

As a consequence of these precautionary measures, it will not be possible to launch Gaia within the window that includes the previously targeted launch date of 20 November.

The next available launch window is 17 December to 5 January 2014.

More details will be given as soon as they are available. The new launch date will be announced when the timeline for completing the additional work has been confirmed and the overall launch manifest of Arianespace has been established.

Gaia is ESA’s billion-star surveyor, designed to provide a precise 3D map of our Milky Way galaxy in order to understand its composition, formation and evolution.



22 October 2013

Due to recently-discovered technical issues, ESA has decided to perform additional verifications on its Gaia satellite, and therefore we have requested that Arianespace postpone the Gaia launch, currently scheduled for November 20, 2013.

A new launch date will be announced as soon as the availability of the satellite is confirmed.



21 October 2013

ESA’s billion-star surveyor Gaia will be launched from Europe’s spaceport in Kourou on 20 November to begin a five-year mission to map the stars with unprecedented precision.


Gaia’s main goal is to create a highly accurate 3D map of our Milky Way Galaxy by repeatedly observing a billion stars to determine their positions in space and their movement through it.

Other measurements will assess the vital physical properties of each star, including temperature, luminosity and composition. The resulting census will allow astronomers to determine the origin and the evolution of our Galaxy.

Gaia will map the stars from an orbit around the Sun, near a location some 1.5 million km beyond Earth’s orbit known as the L2 Lagrangian point.

The spacecraft will spin slowly, sweeping its two telescopes across the entire sky and focusing their light simultaneously onto a single digital camera, the largest ever flown in space – it has nearly a billion pixels.


Date: 27 June 2013
Satellite: Gaia
Copyright: ESA/ATG medialab; background image: ESO/S. Brunier

For the last two months Gaia has been rigorously tested in Kourou as part of the launch campaign.

Getting ready for launch is an extremely busy phase for the mission teams, but it’s also extremely exciting and rewarding to see our mission so close to launch,” says Giuseppe Sarri, ESA’s Gaia project manager.

Earlier this month the spacecraft’s sunshield passed the final deployment test in the cleanroom in Kourou. It has now been stowed in its final configuration ready for the launch.

Shortly after launch, the sunshield will be deployed, forming a 10.5 m-wide ‘skirt’ around Gaia’s base.

The shield has two purposes: to shade Gaia’s sensitive telescopes and cameras from sunlight, allowing them to cool to their operating temperature of -110°C, and to provide power to operate the spacecraft. The Sun-facing side of the shield is partially covered with solar panels to generate electricity.


Date: 10 October 2013
Satellite: Gaia
Copyright: ESA-M. Pedoussaut

“With this important milestone – and others – now completed, we are working through an intensive checklist of final activities that will culminate in the much-awaited launch of our ‘discovery machine’,” adds Giuseppe.

Tomorrow at ESOC, ESA’s European Spacecraft Operations Centre in Darmstadt, Germany, the Gaia Mission Control Team will conduct a full simulation for the critical launch and early orbit phase of the mission.

Meanwhile, back at Kourou, Gaia will be transferred to the fuelling facility to fill the tanks of its propulsion system, used to orient the spacecraft once it reaches space.

In the first week of November, the spacecraft will be mounted on the Soyuz launcher adapter and then integrated with the upper stage, which will eventually help boost Gaia onto its journey to L2.

The Soyuz fairing will then be added, the nose cone that protects the sensitive spacecraft during the first four minutes of launch.

On 15 November, Gaia will be moved to the launch pad for integration with the Soyuz launcher itself. Finally, the rocket will be fuelled.

Gaia’s launch time is set for 20 November at 08:57:30 GMT, and will be streamed live on the ESA Portal.

We are excited to see the launch less than one month away, but there are still a lot of final preparations to complete,” says Timo Prusti, ESA’s Gaia project scientist.

Our quest to create an enormous stellar census to solve questions on the origin, structure and evolutionary history of our home Galaxy, and to discover tens of thousands of supernovas, previously unseen asteroids and even planets around nearby stars, is finally about to begin.

Follow the launch campaign via the Gaia blog.

For further information, please contact:

Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954

Giuseppe Sarri
Gaia Project Manager

Timo Prusti
Gaia Project Scientist

(This article was originally posted on ESA’s Space Science Portal.)



27 June 2013

ESA’s billion-star surveyor, Gaia, has completed final preparations in Europe and is ready to depart for its launch site in French Guiana, set to embark on a five-year mission to map the stars with unprecedented precision.


Gaia’s main goal is to create a highly accurate 3D map of our Milky Way Galaxy by repeatedly observing a billion stars to determine their precise positions in space and their motions through it.

Other measurements will assess the vital physical properties of each star, including its temperature, luminosity and composition.

The resulting census will allow astronomers to determine the origin and the evolution of our Galaxy.

Gaia will also uncover tens of thousands of previously unseen objects, including asteroids in our Solar System, planets around nearby stars, and exploding stars – supernovas – in other galaxies.

Gaia will be ESA’s discovery machine,” says Alvaro Giménez, ESA’s Director of Science and Robotic Exploration.

It will tell us what our home Galaxy is made of and how it was put together in greater detail than ever before, putting Europe at the forefront of precision astronomy.

Gaia builds on the technical and scientific heritage of ESA’s star-mapping Hipparcos mission, reflecting the continued expertise of the space industry and the scientific community across Europe.

It’s extremely rewarding to see the next generation of our high-precision observatories built and ready to answer fundamental questions about the cosmos.

Gaia will be launched later in 2013 on an Arianespace Soyuz rocket from Europe’s Spaceport in Kourou, French Guiana, and will map the stars from an orbit around the Sun, near a location some 1.5 million km beyond Earth’s orbit known as the L2 Lagrangian point.


Date: 27 June 2013
Satellite: Gaia
Copyright: ESA/ATG medialab; background image: ESO/S. Brunier

During its five-year mission, the spacecraft will spin slowly, sweeping its two telescopes equipped with the largest digital camera ever flown in space – with nearly a billion pixels – across the entire sky.

Gaia will measure a billion stars, roughly 1% of all the stars spread across the Milky Way.

As Gaia moves around the Sun, it will repeatedly measure the position of each star, allowing it to determine the distance through a perspective effect known as parallax.

Combined with the other measurements, these data will equip astronomers with the information they need to reconstruct the history of the Milky Way.

The mission will also discover new asteroids in our own Solar System and planets orbiting around other stars.

Gaia should even be able probe the distribution of dark matter, the invisible substance that is detected only through its gravitational influence on celestial objects.

It will test Einstein’s General Theory of Relativity by watching how light is deflected by massive objects like the Sun and its planets, as well as other stars.

Gaia will observe each of its billion stars 70 times on average over five years. That works out as some 40 million observations per day!” says Giuseppe Sarri, ESA’s Gaia Project Manager.

The herculean effort of processing all of the data will be carried out by the European scientific community working with ESA,” adds Timo Prusti, ESA’s Gaia Project Scientist.

The resulting huge stellar census will provide the information needed to tackle an enormous range of important problems related to the origin, structure and evolutionary history of our home Galaxy.

For further information, please contact:

Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954

Giuseppe Sarri
Gaia Project Manager

Timo Prusti
Gaia Project Scientist

(This article was originally posted on ESA’s Space Science Portal.)



20 March 2013

The Director of Science and Robotic Exploration has released an Announcement of Opportunity (AO) for membership in the science team of the Gaia mission. The invitation to respond to this AO is presented here, followed by the AO schedule. The AO document and the Science Management Plan can be accessed from the right-hand menu. The deadline for receipt of proposals is 30 April 2013.

Subject: Release of Announcement of Opportunity for membership in the Gaia Science Team

Dear Colleague,

I am pleased to announce the release, today, of the Announcement of Opportunity for membership in the Gaia Science Team (GST). The Gaia mission, a global astrometric survey mission, is an element of ESA’s Scientific Programme, which is foreseen to be launched in September 2013.

Proposals are solicited for individual membership in the GST, whose mandate is to advise the Agency on all scientific matters regarding the Gaia mission as described in the Science Management Plan. The appointment of one of the photometry scientists in the GST as the Gaia Data Processing and Analysis Consortium (DPAC) chair has led to a vacant position in the team. As a result to the present Announcement of Opportunity one new photometry scientist will be selected, for a renewable period of three years.

The successful applicant is expected to have a keen interest and proven track record in at least one of the scientific fields to which Gaia will make a significant contribution. In order to complement the science coverage of the current GST, expertise in the area of our Solar System is a strong asset. Applicants for the position of the photometry scientist are expected to have a good understanding of the aspects of all Gaia instruments and specifically of the spectrophotometer.

Membership in the GST is on an individual basis; all scientists from institutions located in ESA Member States are eligible to apply. The GST with the new appointment as a result to the present Announcement of Opportunity is anticipated to first meet in July 2013. As described in the Announcement of Opportunity, the Gaia Science Team will be selected ensuring that they are to a reasonable degree independent from the management activities of DPAC.

With the present letter I therefore invite interested members of the scientific community to respond to the Announcement of Opportunity, available on line at Responses to the Announcement of Opportunity are due by 30 April 2013 following the procedure described in detail at

Yours sincerely,

Alvaro Giménez-Cañete
Director of Science and Robotic Exploration



19 November 2012

The European Space Agency (ESA) solicits through the present Announcement of Opportunity (AO) proposals for the provision of the Archive Access Co-Ordination Unit (CU9) in the Gaia Data Processing and Analysis Consortium (DPAC). The deadline for proposal submission is 10 January 2013.

Note: The deadline for submissions has passed

The Gaia mission, a global astrometric survey mission, is an element of ESA’s Scientific Programme, which is approaching the operational phase of the mission with launch scheduled for October 2013. Proposals are solicited from ESA Member States, for the Gaia DPAC Archive Access Co-Ordination Unit, which will provide for scientists access to all data products produced by the Gaia science ground segment.

The data processing ground segment is a fundamental element of the mission with the remaining essential Co-Ordination Unit required to provide access to the DPAC results. The Archive Access Co-Ordination Unit will be, similarly to the rest of DPAC, a collaboration between the ESA Gaia Science Operations Centre and a substantial broad scientific community funded by national funding agencies.


The AO information package is available as a zip file, linked from the right-hand menu, and includes the following 3 documents:

  • Revised Gaia Science Management Plan (ESA_SPC-2006-45.pdf)
  • Gaia Intermediate Data Release Scenario (GAIA-CG-PL-ESA-TJP-011-01.pdf)
  • AO for the Gaia Data Processing Archive Access Co-Ordination Unit (GAIA-CG-PL-ESA-TJP-013-01.pdf)


Proposals should be submitted electronically by email to: and no later than 10 January 2013.

In addition a copy of the complete proposal must be sent to each of the funding agencies which will later be requested to provide financial support to the CU9 activities.

Note: The deadline for submissions has passed


Further questions on the AO itself, or on the associated approval process, should be addressed by e-mail to:

Dr. Timo Prusti
Gaia Project Scientist



15 September 2011

ESA’s Gaia mission has passed another major milestone after the completion of 10 state-of-the-art mirrors that will be used to measure the precise positions of a billion stars. With the delivery of the last of these complex mirrors, Europe has further reinforced its position as the world leader in silicon carbide mirror technology.

Gaia will be the most advanced astrometry mission ever flown. The space observatory is designed to scan the entire sky and to pinpoint the locations of about one thousand million stars in our Galaxy. The position of each of its target stars will be measured about 70 times during the five-year mission.

In order to carry out this unprecedented stellar census, Gaia will carry two telescopes that point in different directions in order to study widely separated areas of the sky. Each telescope comprises four identical sets of mirrors (M1 to M4). Two additional mirrors (M5 and 6) are used by both telescopes to direct the light into the same focal plane.

Although the mirrors are all rectangular, they vary considerably in size and shape. The primary mirrors (M1) are concave and measure 1.46 x 0.51 m, while the convex secondary (M2) mirrors measure 0.35 × 0.16 m.

Light from the latter pair is reflected onto the concave, tertiary (M3) mirrors, whose dimensions are 0.65 × 0.28 m. The optics are completed by the flat M4 combiner mirrors (dimensions 0.19 × 0.07 m), and the M5 and M6 mirrors (dimensions 0.55 × 0.34 m).

All of the mirrors were fabricated from blanks made of sintered silicon carbide (SiC), which were made by Boostec in France. After preliminary grinding and lapping to achieve a flat surface, all of the mirror blanks were sent to Schunk Kohlenstofftechnik in Heuchelheim, Germany, where they were coated with a layer of silicon carbide, using a process known as chemical vapour deposition (CVD).

Driven by mission deadlines which require the entire optical assembly to be combined and tested well in advance of Gaia’s launch, ESA managers decided to use different contractors in France, Belgium and Germany for completion of the mirrors.

The final lapping and polishing was a slow, meticulous process which required each mirror to be shaped to a precision of about 10 nanometres (10 millionths of a millimetre) RMS. The remarkable smoothness of the resulting surfaces means that, for example, if the Gaia M1 mirror was scaled to the size of the Atlantic Ocean, any bumps on the surface would be only a few centimetres high.

Each of the 38 kg primary mirrors was shaped by the French company Sagem, located close to Paris. The M2, M4, M5 and M6 mirrors were milled and polished by AMOS of Liege, Belgium; and the M3 pair was produced by Carl Zeiss Optronics GmbH in Oberkochen, Germany. In addition, two flat mirrors required for testing of the telescopes were made by Sagem.

The final phase in their manufacture involved the addition of layers of reflective coating, using a process known as physical vapour deposition (PVD). During this process, which was carried out in high vacuum at temperatures between 150 and 500°C, an enhanced silver coating was deposited on each mirror, forming a very thin, homogeneous layer. Most of the mirrors were coated by Sagem, with Zeiss completing the work on the M3 mirrors.


The result has been a set of 10 mirrors with outstanding physical and optical characteristics, and an industrial team with unrivalled expertise in SiC mirror manufacture.

Since the design process began in 2006, the Gaia team has learned how to produce a set of sintered silicon carbide mirrors which is not only extremely strong and ultra-stable – with about twice the rigidity of steel – but also lightweight and with a high thermal conductivity,” said Matthias Erdmann, ESA’s Gaia Payload Systems Engineer responsible for optics and ceramics.

Although these are not the first silicon carbide mirrors that have been made for a space mission, no mirrors as large as the Gaia primary mirror have previously been coated using the CVD process,” he added.

The degree of similarity of the mirror pairs is also quite unique. This is particularly important for Gaia, since each telescope must have similar optical capabilities, with diffraction limited viewing and minimal wavefront errors. Their outstanding optical characteristics achieve new standards that will be of great value to the development of future space observatories.

As a result of this programme, the European industrial team has been able to master all of the processes required for making state-of-the-art space mirrors, and become the world leader in silicon carbide mirror technology.

In July this year, one complete set of telescope mirrors integrated on the Payload Structural Model was subjected to vibration tests at the Intespace test and integration centre in Toulouse, France. The tests confirmed the stability of the assembly and demonstrated that the optical path will not change when the spacecraft will experience the loads generated during the launch.

The integration of the last two mirrors of the second telescope is now ongoing, so that the entire optical system can be aligned. This will clear the way for the flight Payload Model to be completed and give the green light to a series of functional and performance tests in the thermal vacuum chamber.


Matthias Erdmann
Gaia Payload Systems Engineer
Phone: +31 71 56 58885

Giuseppe Sarri
Gaia Project Manager
Phone: +31 71 56 54966



06 July 2011

Another milestone in the development of Gaia, ESA’s ultra-sensitive space astrometry mission, was passed on 1 June when the 106 electronic detectors of its billion pixel camera were assembled like a large mosaic for the first time.


Date: 22 April 2011
Satellite: Gaia
Depicts: Gaia CCDs integration onto the CCD support structure
Location: Astrium, Toulouse, France
Copyright: Astrium

During its ambitious mission to map one thousand million stars, the spinning Gaia spacecraft will monitor each of these pinpoints of light up to 70 times over a five year period. In order to detect distant stars about one million times fainter than the eye can see, Gaia will carry 106 charge coupled devices (CCDs), each of which is, effectively, a miniature camera.

These rectangular detectors, each measuring 6 × 4.7 cm, with a thickness of only a few tens of microns, are precisely fitted together on the CCD support structure (CSS). The gap between each CCD package is about 1 millimetre.

Made of silicon carbide, a material that provides remarkable thermal and mechanical stability, the CSS weighs about 20 kg. The overall CCD mosaic, a key part of the complete focal plane assembly, measures 1 × 0.5 metres.


Date: 06 June 2011
Satellite: Gaia
Depicts: All Gaia CCDs integrated onto the CCD support structure
Location: Astrium, Toulouse, France
Copyright: Astrium

The contract to provide the Gaia CCDs was awarded to e2v Technologies of Chelmsford, UK, in summer 2005, and their production kept the company busy for more than 5 years. Each CCD converts incoming light into electrical charge and stores it as a tiny data package, or pixel, until it can be read by the onboard computer. The Gaia CCDs feature 4500 pixels in the along scan direction and 1966 pixels for across scan. With an overall total of about a thousand million pixels, Gaia’s focal plane is the largest digital camera ever built for a space mission.

Over the past few weeks, technicians from the mission’s prime contractor, Astrium France, have been carefully bolting and aligning each of the CCDs onto the support structure at the company’s facility in Toulouse. Working in double shifts inside a Class 100 clean room, the rectangular focal plane mosaic has grown at a rate of about four CCDs per day.


The completed focal plane is arranged in seven rows of CCDs. The main array, which comprises 102 detectors grouped into four fields, is dedicated to star detection. A further four CCDs are used for monitoring the stability of the ‘basic angle’ of 106.5 degrees between the two telescopes and the quality of the optical performances.

The mounting and precise alignment of the 106 CCDs is a key step in the assembly of the flight model focal plane assembly,” said Philippe Garé, ESA’s Gaia Payload Manager.

As the two telescopes of the spinning Gaia spacecraft sweep across the sky, the images of stars in each field of view will move across the focal plane array. They will be detected first by the star mapper CCDs. Each of the two strips of seven CCDs detects star images only from its assigned telescope.

The confirmed star images will then move across a block of 62 astrometric field CCDs, where they are assigned tracking ‘windows’ and given a precise time stamp by a rubidium atomic clock.


Date: 06 July 2011
Satellite: Gaia
Depicts: Schematic of the Gaia focal plane
Copyright: ESA – Alexander Short

Next, the star images enter the photometric field where two rows of CCDs produce low-resolution spectra in different wavelength bands. The blue CCDs spread the light at wavelengths between 330 and 680 nm, while the spectrum created by the red CCDs goes from 640 to 1000 nm. These spectra are used for gathering colour information on the stars and for correction of the optical aberrations in the astrometric part of the instrument.

Finally, the star images enter the spectroscopic field where a spectrograph only allows light in the narrow band of 847 to 874 nm. The filtered light is then dispersed over 1100 pixels to detect characteristic spectral lines in this band. Subsequent analysis on the ground enables stellar velocities in the radial (line-of-sight) direction to be calculated, based on the red or blue shifts of the spectral lines.

Located 1.5 million km from Earth, Gaia will operate at a temperature of minus 110°C (163.15 K). This low temperature will be maintained by passive thermal control, including the cold radiator on the focal plane assembly and a giant sunshade attached to the top of the spacecraft.

In parallel to the assembly of the CSS, Astrium is working on the cold radiator and the proximity electronics module. We are aiming to bring together all three parts of the focal plane assembly by October of this year,” noted Garé.


Philippe Garé
Gaia Payload Manager
Phone: 31 (0)71 565 5671

Giuseppe Sarri
Gaia Project Manager
Phone: +31 (0)71 565 4966

Timo Prusti
Gaia Project Scientist
Phone: +31 (0)71 565 4794



06 June 2011

Professor Michael Perryman, the scientific leader of ESA’s Hipparcos mission, and a founding father of its successor mission, Gaia, has been awarded the 2011 Tycho Brahe Prize from the European Astronomical Society. The prize recognises the extraordinary work accomplished by Perryman in shepherding the field of astrometry to its successful leap into space-based observations and demonstrating the importance of measuring stellar positions for a plethora of astronomical applications.


Image via

British astrophysicist Michael Perryman has been inextricably linked to the field of space-based astrometry since the 1980’s when, shortly after receiving his PhD from Cambridge University, UK, he joined ESA and quickly became acquainted with one of the scientific projects being studied by the Agency at the time: the Hipparcos mission, the first space-based telescope dedicated to measuring the positions, motions and distances of stars. With a background in theoretical physics and extragalactic astronomy, it was not immediately obvious that astrometry was a discipline that could capture his interest, but Perryman was soon captivated by the ingenious and elegant technique of the new satellite concept and by its immense scientific potential.

Astrometry, the branch of astronomy dealing with the precise measurement of stellar positions, has a long history that dates back to ancient Greece and even earlier civilisations. The invention of the telescope in the seventeenth century represented a fundamental turning point in the field, allowing the compilation of larger and much more precise catalogues of stars than the famous ones created by Hipparchus (in the second century BC) and Tycho Brahe (in the sixteenth century AD), who had charted the sky with the naked eye.

The accuracy in astrometric measurements increased almost continuously throughout modern history, along with technological improvements to astronomical instrumentation, until it reached a point in the second half of the twentieth century when further significant improvements seemed beyond immediate reach. Observational barriers imposed by the Earth’s atmosphere limited the accuracy that could be achieved with ground-based measurements of stellar positions: the next leap for astrometry would require a dedicated space telescope.

The Hipparcos mission was conceived in the late 1960s by French astronomer Pierre Lacroute and, when accepted into the ESA science programme in 1980, Perryman was appointed project scientist. In this role, he ensured that the scientific goals of the mission remained the key drivers throughout the development of the satellite. Hipparcos was launched in 1989 and, with Perryman assuming the role of operations manager in addition, observed for 3.5 years before operations ceased in March 1993.

The scientific reach of the Hipparcos mission has gone well beyond astrometry and has had profound implications for the fields of stellar and galactic astronomy, as well as cosmology and fundamental physics.

This prestigious award recognises Perryman’s “crucial role in the fostering of high precision, global stellar astrometry from space, in particular the development of the Hipparcos mission,” and acknowledges his pivotal work leading this fully European enterprise “through many difficulties to its ultimate success.”

The exciting progress of the Hipparcos mission, from concept to launch and beyond, including an account of its many astronomical applications, is reported in Perryman’s book “The Making of History’s Greatest Star Map”, published in 2010. The mission is also presented, in the broader framework of astrometry, in a comprehensive textbook also written by him, “Astronomical Applications of Astrometry: Ten Years of Exploitation of the Hipparcos Satellite Data”, published in 2009.

Notes to Editors

The Tycho Brahe Prize of the European Astronomical Society is awarded annually in recognition of the development or exploitation of European instruments, or major discoveries based largely on such instruments.

ESA’s Hipparcos space astrometry mission was a pioneering European project which pinpointed the three-dimensional positions of more than one hundred thousand stars with high precision, and more than one million stars with lesser precision.

Launched in August 1989 Hipparcos successfully observed the celestial sphere for 3.5 years before operations ceased in March 1993. Calculations from observations by the main instrument generated the Hipparcos Catalogue of 118 218 stars charted with the highest precision. An auxiliary star mapper pinpointed many more stars with lesser but still unprecedented accuracy, in the Tycho Catalogue of 1 058 332 stars. The Tycho 2 Catalogue, completed in 2000, brings the total to 2 539 913 stars, and includes 99 per cent of all stars down to magnitude 11, almost 100 000 times fainter than the brightest star, Sirius. Central to the mission’s success were four major pan-European scientific teams: the Input Catalogue Consortium led by Dr Catherine Turon (Paris), the NDAC and FAST Data Analysis Consortia led by Prof. L. Lindegren (Lund) and Prof. J. Kovalevsky (Grasse) respectively, and the Tycho Data Analysis Consortium led by Prof. E. Hoeg (Copenhagen).

Related publications

M. Perryman et al., “The Hipparcos Catalogue“, A&A, 323, L49-52, 1997

M. Perryman, “The Making of History’s Greatest Star Map“, 2010 (book)

M. Perryman, “Astronomical Applications of Astrometry: Ten Years of Exploitation of the Hipparcos Satellite Data“, 2009 (book)


Michael Perryman



01 March 2011

NOTE – The deadline for submissions has passed

Dear Colleagues,

ESA hereby invites groups in Member States, wishing to participate in the preparatory activities for the Gaia archive access working group, to submit a Letter of Interest to ESA outlining their area of expertise and potential contribution.

The deadline for submitting ‘Letters of Interest to participate in the preparatory activities for the Gaia archive access’ is 15 April 2011.

Gaia is an ESA science mission aiming to determine accurate positions, distances, proper motions, and photometry for some one billion stars in our Galaxy and beyond, with radial velocities for a significant fraction. Comprehensive details are given at the ESA site The launch of Gaia is scheduled for early 2013, with an operational period of 5 years. The final data products can appear only 2-3 years after the end of the operations, but early intermediate releases will be made available to the community as soon as possible.

While ESA funds for the satellite in its entirety, including payload, the data reduction is a task that will be carried out by nationally funded Gaia Data Processing and Analysis Consortium (DPAC) which was selected for the task in 2007. The Announcement of Opportunity (AO) leading to the selection of DPAC had archive access activities excluded explicitly from the call with a statement that the archive access unit will be added later to the selected consortium in full agreement with the consortium (i.e. DPAC).

Preparations toward the archive access unit have been recently started by establishing the Gaia Archive Preparation (GAP) group. The approach to prepare for the DPAC archive access unit is to utilize GAP to bring together scientists and engineers responding to this call for Letters of Interest and already existing relevant DPAC participants to ensure links to the overall data processing efforts currently underway.

The purpose of the present call for Letters of Interest is to select additional members to GAP. While no financial commitment is requested, the respective funding authorities should be informed of the participation and plans. The responses to the present call for Letters of Interest will be evaluated and selected by ESA. Preference is given to responses from groups rather than individuals. Participation to the GAP activities must be funded by the selected groups themselves. The work of GAP will continue for about a year, until a formal AO for DPAC CU9 (Coordination Unit for Archive Access) is issued. After that the GAP activities will be terminated.

The Letter of Interest should be submitted using the form available through the right-hand menu of this web-page. Please provide sufficient details of your interests and planned commitments (possible funding, area of work, existing links to Gaia or major archive initiatives etc.). In order to take these plans into consideration, a response by 15 April 2011 is requested.

Yours sincerely,

Ana Heras
Coordinator for Astronomy and Fundamental Physics Missions

Further information may be requested from the Gaia Project Scientist
Timo Prusti



23 November 2010

Another milestone in the development of ESA’s Gaia spacecraft has been passed with the successful conclusion of two parallel test programmes during October. These tests demonstrated that Gaia’s focal plane assembly (FPA) – the ‘eyes’ of the spacecraft – is structurally and functionally fit for flight.

Gaia has been designed to map the entire sky with unprecedented accuracy. Over its 5-year mission, it will repeatedly observe 1 thousand million stars in order to pinpoint their positions and brightness. This will be made possible by using two medium-sized telescopes to direct starlight through a focal plane assembly fitted with large CCD detectors.

In order to ensure that this key part of the spacecraft’s optical system is capable of functioning properly, an engineering model of the FPA underwent a series of electrical and functional tests in a vacuum chamber at the premises of Astrium in Toulouse. These involved passing an optical image of a star pattern across one row of the focal plane. As each stellar image passed across each of the 16 CCDs, it was detected, confirmed and tracked as a star by the video processing unit (VPU) – the ‘brain’ of Gaia. The VPU created small ‘windows’ around each star which ‘remembered’ its location in the sky image.

The windowing of the confirmed stars is a key aspect of Gaia’s operations since it enables the data to be automatically discarded from any parts of the sky image that are lacking recognised stars. Without this intelligent software processing, Gaia would be swamped by the vast amount of data it records and sends back to Earth.

We need to use windowing because of the telemetry limit on the spacecraft,” explained Timo Prusti, the Gaia Project Scientist. “Only so much data can be stored on board and sent back to Earth, even at a rate of 4-8 Megabits per second. During most of the mission, there will only be 8 hours of contact time with the ground stations in which to download 24 hours of data, although this contact time will be doubled when Gaia is observing the mass of stars across the galactic plane.”

The windowing approach allows Gaia to observe a thousand million stars and to transmit the recorded information without swamping the telemetry download capability. The successful tests of the FPA and the video processing system, which selects and tracks the stars across the focal plane, were a major step in the development of the Gaia flight model,” he added.

A structural model (SM) of the FPA, which comprised all of the flight model structural parts, also completed a separate series of mechanical tests at the Toulouse premises of INTESPACE. By placing the SM on a shaker, engineers confirmed the ability of the FPA to survive the stresses of launch.

“Having tested and validated both the electronic and the mechanical sides of the FPA, we are now ready to start assembly of the flight model,” said Philippe Gare, the Gaia Payload Module Manager.

The completion of the functional and qualification tests on the focal plane assembly engineering and structural models was a fundamental step in the development of the Gaia detection system,” said Giuseppe Sarri, the Gaia Project Manager. “The tests on the engineering model demonstrated that the detection chain works in the environmental conditions expected in space and that the performances are compliant with the requirements, therefore giving confidence that the Gaia scientific objectives will be met. The mechanical tests confirmed the robustness of the overall focal plane to sustain the launch loads. Last but not least, the assembly of both models validated the very complex and delicate integration procedures required to build the flight model.”


Philippe Gare
Gaia Payload Module Manager
Directorate of Science and Robotic Exploration
ESA, The Netherlands
Phone: +31 71 5655671

Giuseppe Sarri
Gaia Project Manager
Directorate of Science and Robotic Exploration
ESA, The Netherlands
Phone: +31 71 5654966

Timo Prusti
Gaia Project Scientist
Directorate of Science and Robotic Exploration
ESA, The Netherlands
Phone: +31 71 5654794



13 September 2010

ESA’s mission to measure the precise positions of a billion stars reached an important milestone on 3 September with the delivery of its first primary mirror. The second primary mirror is near completion and scheduled to arrive at the Toulouse test and integration centre of prime contractor EADS Astrium during October.

Gaia will carry two identical telescopes, each fitted with four mirrors (M1 to 4). A further two mirrors (M5 and 6) will send the light from these dual instruments into the same focal plane. To date, six of the 10 rectangular mirrors have been delivered. They are: the M3A tertiary mirror, whose dimensions are 0.65 x 0.275 m; both of the M4 combiner mirrors (dimensions 0.19 x 0.07 m), and the M5 and M6 mirrors (dimensions 0.54 x 0.36 m), in addition to the M1A primary mirror (dimensions 1.49 x 0.54 m).


Date: 13 September 2010
Satellite: Gaia
Copyright: Image courtesy of Sagem, France

All of the mirrors have been fabricated from blanks made of sintered silicon carbide (SiC), a relatively new material in mirror fabrication for space missions. The blanks were made by Boostec in France. Silicon carbide was selected because it allows each mirror to be extremely strong and rigid, but lightweight and with a high thermal conductivity – important not only for its on-orbit performance, but also for minimizing deformations caused by Earth’s gravity during ground testing.

Each primary mirror is shaped by the French company Sagem (located close to Paris), using computer-guided milling and polishing machines, and weighs about 40 kg. To achieve sufficient smoothness, all of the mirror blanks were coated with a thin layer of silicon carbide by chemical vapour deposition before polishing started. This process was carried out by Schunk Kohlenstofftechnik in Heuchelheim, Germany. The polishing is a slow, painstaking process which requires each mirror to be polished to a precision of about 10 nanometres RMS. To appreciate this technical achievement one can consider that if the Gaia M1 mirror was scaled to the size of the Atlantic ocean, any bumps on the surface would be of the order of a few centimetres.

The mirrors also have an unusual curved shape, which is calculated using a very precise mathematical formula so that there will be no distortion of the incoming light across the telescopes’ field of view and at all wavelengths from blue to red.

After polishing, the surface is coated with enhanced silver reflective coating. This coating involves the addition of a dielectric amplification layer, which protects the silver from tarnishing and enhances its reflectivity across the entire spectral range (320 – 1000 nanometres) to be studied by Gaia.

“The mirrors are being integrated on the structural payload module in order to complete the optical train and enable testing to begin,” said Matthias Erdmann, ESA’s Gaia payload system engineer. “Their shape and size were determined by the room available within the payload fairing of the Soyuz-Fregat launcher.”

“The M1 mirrors have a collecting area about 11 times bigger than the primary mirror of its predecessor, ESA’s Hipparcos astrometry spacecraft, enabling them to collect many more photons,”said Jos de Bruijne, Deputy Project Scientist for Gaia.

“The combination of size, smoothness and special shape is required to provide a wide angle of view – about 0.7 degrees – and a small wave front error that will give extremely sharp images of a billion stars in our Galaxy.”


Gaia will view two widely separated areas of the sky, using two identical telescopes. Over its five-year mission, it will scan the entire sky, observing each of its target stars about 70 times. By accurately monitoring the two-dimensional star positions on the sky, it will be possible to infer their lateral motions across the sky and to calculate their precise three-dimensional locations, even for objects as far away as the galactic centre. Gaia will also measure the spectra of the brightest 15% of those stars, mainly in order to determine their radial velocities. Launch of Gaia on a Soyuz-Fregat is currently scheduled for November 2012.


Matthias Erdmann
Gaia Payload System Engineer
Science Projects Department
Directorate of Science & Robotic Exploration, ESA, The Netherlands
Phone: +31 71 56 58885

Giuseppe Sarri
Gaia Project Manager
Science Projects Department
Directorate of Science & Robotic Exploration, ESA, The Netherlands
Phone: +31 71 565 4966

Jos de Bruijne
Deputy Gaia Project Scientist
Research & Scientific Support Department
Directorate of Science & Robotic Exploration, ESA, The Netherlands
Phone: +31 71 565 5989

Timo Prusti
Gaia Project Scientist
Research & Scientific Support Department
Directorate of Science & Robotic Exploration, ESA, The Netherlands
Phone: +31 71 565 4794



29 June 2010

With the launch of Gaia only two years away, the European science community is actively engaged in training the next generation of young astronomers who will exploit the flood of data from this ‘Cornerstone’ science mission.

In many ways, Gaia is a follow-on to ESA’s groundbreaking Hipparcos satellite, which mapped the sky between 1989 and 1993. Hipparcos was the first space mission designed for astrometry – the precise measurement of the positions, distances and proper motions of stars.


Date: 24 April 2007
Satellite: Gaia
Depicts: Artist’s impression of Gaia
Copyright: ESA

Although Gaia builds on the European expertise established through Hipparcos, the new mission will take astrometry to a new level of complexity and precision. Over its five-year lifetime, Gaia’s three instruments will gather huge amounts of astrometric, photometric and spectroscopic data on stars in the Milky Way, as well as more distant galaxies, quasars and Solar System objects.

Hipparcos could detect stars to the 12th magnitude, whereas Gaia will go down to 20th magnitude,” explained Timo Prusti, ESA Project Scientist for Gaia. “Hipparcos measured the positions of almost 120 000 stars, but Gaia will map over one billion stars. As for the error in parallax determination, Hipparcos was accurate to within one milliarcsecond, but Gaia’s positional data will be about 100 times more precise.”

Various initiatives are already under way to ensure that the European scientific community is ready to handle and analyse this deluge of data. More than 400 scientists from many different countries have been selected by ESA for the Gaia Data Processing and Analysis Consortium (DPAC) in order to prepare for the extremely challenging task of processing all of the data, with the eventual creation of an all-sky catalogue.


Date: 30 June 2010
Satellite: Gaia
Depicts: ELSA Fellows
Copyright: Image courtesy of Stefan Jordan

Meanwhile, 15 PhD and post-doctorate students have been funded for the past four years under the European Leadership in Space Astrometry (ELSA) programme, working in collaboration with DPAC. Supported by the European Community’s Sixth Framework Programme (FP6), the students have been collaborating on specific problems related to the astrophysical, instrument modelling, algorithmic, numerical and software engineering aspects of the mission. Their activities complement, and are partly integrated into, the joint European effort to develop a complete scientific data analysis system for Gaia.

Projects undertaken by the ELSA fellows have included development of improved models of stars, their spectra and spatial distributions, and methods to solve the complex mathematical equations required to determine their positions.

Another important contribution has involved modelling the effects of long-term exposure to particle radiation on Gaia’s detectors.

This was not originally seen as part of the preparations for Gaia, but it has been very valuable,” said Lennart Lindegren of Lund Observatory, Sweden, the scientific coordinator for ELSA. “Gaia will be placed in an orbit at the L2 Lagrange Point, 1.5 million kilometres from Earth, where it will be fully exposed to charged particles from the Sun. This will cause a gradual deterioration of the CCDs over the 5-year mission, but the work done under ELSA will hopefully make it possible to eliminate most of the effects.

As ELSA draws to a close, another community-based initiative, known as the Gaia Research for European Astronomy Training (GREAT) project, is getting under way. Although everyone in ELSA is also involved in GREAT, the two projects are very different.

ELSA has helped to prepare for the creation of the Gaia catalogue,” said Lennart Lindegren, “while GREAT will prepare the community to use the data once it has been produced.”

Over 550 researchers from 17 European countries and ESA will be participating in the network, which is organised by the Gaia Science Team and the Data Processing and Analysis Consortium Executive (DPACE).

GREAT will cover all of the areas of scientific study covered by Gaia,” said Nicholas Walton, chairman of the GREAT network and a researcher at the Institute of Astronomy, University of Cambridge, UK. “Its overall objective is to support a science-oriented network which will address the scientific issues in which Gaia will have a major impact.”

Initial funding for five years to cover attendance at conferences and workshops, and visits to other institutions, has been provided by the European Science Foundation. These will help to bring the Gaia community together and enable scientists to share their expertise and ideas,” he added.

Since Gaia will detect large numbers of supernovas, microlensing events, novas, gamma ray burst afterglows, and other interesting transient or anomalous phenomena, the most recent workshop involved discussions about the impact that Gaia will have on studies of these objects and the importance of follow-up observations by ground-based instruments. A previous meeting looked at the ways in which Gaia will revolutionise studies of star formation and the evolution of open star clusters. Five more GREAT workshops and conferences are being organised for the coming year.

Discussions with the European Union concerning funding under the Seventh Framework Programme (FP7) for 17 Early Stage Researchers are currently in progress, and it is hoped that this Initial Training Network will be able to start in early 2011.



28 July 2009

At the end of June the Gaia mission passed a significant milestone when the 17 individual segments of the torus, a key structural element of the spacecraft, were brazed into one coherent structure at the BOOSTEC premises at Bazet near Tarbes, France. The successful results of this process were concluded after a Mandatory Inspection Point of the torus on Monday 20 July 2009.

The 3-metre diameter, quasi-octagonal torus, which will support the two Gaia telescopes and the focal plane assembly, is composed of 17 individual custom-built Silicon Carbide segments.

Construction of the individual segments began 15 months ago at BOOSTEC. In the intervening period the individual segments have been milled, sintered and lapped. Each element has been subject to stringent quality checks and has undergone static-proof tests to confirm the mechanical integrity of the pieces. (See “Constructing the Gaia torus” for further details.)

Silicon carbide for light-weight, robust structures

The scientific requirements of the mission (for example, astrometric measurements accurate to 24 microarcsec (at V= 15 magnitude)) translate to a requirement for a payload platform that is mechanically and thermally ultra stable. For these reasons all elements of the torus are constructed from Silicon Carbide (SiC), a ceramic material whose physical characteristics make it the material of choice for structures which must be both light-weight and robust. The low thermal expansion coefficient and high thermal conductivity of SiC mean that it is a very stable material which can quickly dissipate thermal gradients, and with a Young’s Modulus of about 420 GPa it is twice as stiff as steel.

Final steps: assembly, alignment & brazing

Starting on 28 April the torus began to take shape as the individual elements were assembled together and precision aligned using laser trackers and reference points on the torus segments. A special braze paste was applied to the interface points between each of the segments (Figure 3). When heated above 1000 °C this paste melts and seals the joints by capillary action – the torus then becomes one complete unit.

The completed torus was placed in the brazing furnace at BOOSTEC on Wednesday 24 June and remained there until the morning of Monday 29 June. After a cooling-down period the torus was removed from the furnace and moved to the laboratories for post-brazing quality control. This included a thorough visual inspection of external and internal surfaces – the latter by means of borescopes – and ultrasonic inspection to confirm the integrity of the structure.

(The furnace at BOOSTEC was built for brazing the Herschel 3.5-metre diameter primary mirror, and has also been used for the optical bench for the JWST NIRSPEC instrument.)

Torus complete – payload module assembly to follow

Once the torus will be delivered to EADS Astrium, the Gaia prime contractor, at Toulouse, the assembly of the Payload Module, including the torus and mirrors, will next begin.



22 July 2009

On 11 July the qualification model of the Gaia Deployable Sunshield Assembly (DSA) was installed inside the Large Space Simulator (LSS) at the ESTEC test facilities in Noordwijk, the Netherlands. Over the coming days the DSA will undergo a thermal vacuum and thermal balance test in simulated space conditions. The LSS is the only facility in Europe large enough to perform this test.



Date: 03 July 2009
Satellite: Gaia
Depicts: Deployable sunshield QM, during deployment test
Location: Cleanroom at ESTEC, Noordwijk, The Netherlands
Copyright: ESA

Gaia will perform micro-arcsecond astrometry of 1 billion objects in our Galaxy and beyond. In order to achieve the required measurement precision the spacecraft and payload must be shielded from direct sunlight and maintained at a stable, low temperature since any thermal instability can affect the final accuracy of the measurements that will be made.

The thermal stability of the Gaia spacecraft will be largely determined by a large sunshield with a diameter of 10.2 metres when fully deployed, which Sun-facing area must remain flat within 10mm deviation over the entire spacecraft lifetime. The sunshield assembly is composed of 12 rigid rectangular panels and 12 foldable triangular sections. In order to fit inside the launcher fairing the assembly must be folded against the sides of the Gaia spacecraft. After launch the sunshield will deploy to form a large flat structure at the base of the spacecraft, supporting two parallel blankets of multi-layer insulation (MLI) which will act as thermal shields so that the solar flux is damped by a factor of 280. The large size and foldable MLI sections make this a unique sunshield design. (See also: ‘Deployable sunshield’ in the right-hand menu for more details on the DSA.)


The qualification model (QM) of Gaia’s deployable sunshield assembly is functionally representative of the flight model and comprises 3 rigid panels (plus the 2 sections of foldable MLI between them).

The forthcoming thermal vacuum and thermal balance (TV/TB) test is part of a comprehensive qualification test campaign designed to verify the compliance of the DSA with design and operational specifications. The QM test campaign includes functional testing (deployment), vibrational testing (launch conditions), environmental testing (including the TV/TB test), and life-cycle testing (ensuring its endurance with multiple deployment tests).


On 29 June the QM DSA arrived at ESTEC after transport from the SENER premises in Spain. (SENER is developing the Gaia sunshield. The company is subcontractor to EADS Astrium, responsible for the overall design and development of the complete spacecraft. The frames and the blankets of the sunshield are supplied to SENER by RUAG, Switzerland.) Over the next few days the DSA was unpacked and prepared for a deployment test at ambient conditions inside the ESTEC cleanroom. The MLI blankets were attached to the DSA, and a zero-g kit – three masts with pulleys and counterweights used to simulate weightlessness – was installed. The deployment test involved the sunshield opening from its stowed configuration to its fully deployed configuration and was successfully completed on 3 July, see Figure 1.

On 11 July the QM DSA was transferred to the Large Space Simulator (LSS) for the TV/TB test. The LSS with its 9.5-metre diameter main chamber is the only facility in Europe where tests of the QM DSA can be performed in deployed configuration under simulated space conditions. The rectangular panels of the sunshield each measure about 0.8m × 3.2m and once deployed the QM DSA measures roughly 6.0m × 4.0m.


The main objective of the thermal vacuum and thermal balance (TV/TB) test is to verify:

  • The deployment performance in simulated orbit conditions
  • The alignment and planarity (flatness) of the DSA once it is deployed and exposed to the Sun
  • The thermal performance of the sunshield

To this end several tests will be performed inside the LSS:

  1. Deployment test under ambient conditions, at room temperature and ambient pressure (for reference measurements)
  2. Deployment tests in cold vacuum
    Inside the LSS chamber the environmental conditions will be regulated to simulate conditions encountered during operations in space. Shrouds with liquid nitrogen flowing through them will cool the chamber to below 100K (-173 °C). The chamber will be vacuum pumped to a pressure of less than 10-8 bar (or a hundred millionth of the normal pressure at sea level).
  3. Verification of the planarity in cold vacuum, with and without Sun simulation
    The planarity of the deployed sunshield will be tested with videogrammetry measurements. This technique uses video observations of reflectors placed at specific points on the DSA to accurately determine the relative positions of these points during the test. Deviations from the desired flat shape of the DSA in its deployed configuration can be identified this way.
  4. Test thermal performance with Sun simulation
    The thermal performance will be monitored by temperature sensors attached at a number of positions on the DSA and by temperature map measurements of the Sun-exposed surface of the deployed sunshield using an infrared camera.

During the TB/TV test the solar illumination will be simulated at different intensity levels with special lamps generating up to 1400 Wm-2 (just over 1 solar constant).  The collimated light beam from these lamps is horizontal so the sunshield will be deployed from horizontal to vertical position while inside the LSS. A mask in the form of a large foil shield, with a window exactly matching the shape of the deployed DSA, stands in front of the opening where the collimated beam enters the main chamber. This mask allows light to impinge directly only onto the Sun side of the DSA and blocks light that would otherwise pass the DSA and reflect inside the vacuum chamber back onto the shadow side of the DSA. Weightlessness conditions will be simulated using the zero-g kit.


On 11 July the sunshield was lowered, in stowed configuration, into the LSS chamber using an overhead crane. In the remaining days leading up to TV/TB test the set-up and the sunshield were prepared inside the LSS chamber.

A dry run of the deployment inside the LSS was performed on 17 July under normal cleanroom conditions with the chamber still open. After bringing the sunshield back to its stowed configuration the chamber door was closed on 20 July, signalling the start of the TV/TB test in simulated space conditions. The test is scheduled to last until 27 July.

When the TV/TB test has been completed, the QM DSA will be removed from the LSS and moved back to the clean room where the life cycle deployment testing in ambient conditions will be completed before delivering the qualification model of the DSA to the Gaia prime contractor. Upon successful completion of this test campaign the manufacture of Gaia’s flight model sunshield will commence, incorporating all results from the QM test campaign in the definitive design and assembly of the flight model DSA.



02 March 2009

The latest issue of the ESA Bulletin carries an article about ESA’s ‘billion-pixel camera’ for Gaia.

Gaia, ESA’s global space astrometry mission, is designed to measure the positions, distances, space motions, and many physical characteristics of some one billion stars in our Galaxy and beyond. The primary mission product, the Gaia catalogue, constructed from five years of continuous scanning of the celestial sphere, will provide scientists with the measurements needed to significantly improve our understanding of the composition, formation, and evolution of our Galaxy.


Date: 06 March 2009
Satellite: Gaia
Depicts: Four astrometric field (AF) CCDs
Copyright: e2v technologies

One of the keys to achieving this scientific goal is a large focal plane carrying 106 state-of-the-art CCDs. In fact, when Gaia is launched from ESA’s spaceport in Kourou, French Guiana, by the end of 2011 it will carry the largest digital camera in the Solar System. In ESA Bulletin 137, Philippe Garé, Giuseppe Sarri and Rudolf Schmidt describe the progress that has been made in developing and procuring the sophisticated CCDs that make up this unique space camera.



13 February 2009

The Gaia video processing unit (VPU) development activity has recently been finalized with the delivery of the engineering model (EM) from Astrium UK to Astrium France. The unit is responsible for the real-time processing and commanding of star data transmitted by the focal plane assembly.

The VPU incorporates a dedicated Astrium-developed pre-processing board, and for the bulk of the processing, a SCS750 PowerPC board from Maxwell Technologies, Inc., of San Diego, USA.

Each of these units (seven in parallel will be operating on Gaia) exhibits a processing power of more than 1000 MIPS. With such a vast processing power, Gaia will contain more number-crunching capability and flexibility than any other ESA-built satellite.

The Maxwell SCS750 board has recently successfully passed the Equipment Suitability Review where all aspects of its qualification programme and its suitability for use on Gaia were assessed.

Both the algorithm development teams in Astrium France (Toulouse) and the VPU development teams in Astrium UK (Stevenage and Portsmouth) have through these milestones proven their competance and dedication to the success of Gaia.



30 January 2009

An important milestone has been reached for the Gaia Radial Velocity Spectrometer (RVS): the full-size demonstrator model of the RVS grating – a key component responsible for the dispersion of the light into constituent wavelengths – has been built by industry and was delivered to ESA last month.


Date: 10 December 2009
Satellite: Gaia
Depicts: Demonstrator model of the RVS grating
Copyright: ESA

The Fraunhofer Institut für Optik und Feinmechanik (IOF) in Jena (D) has designed, built and tested the demonstrator model of the grating, within the frame of a feasibility study issued by ESA. The successful manufacture of the grating is a key milestone, as it proves that the large transmission grating, with dimensions of 20.5 cm × 15.5 cm, can be built to meet the demanding requirements for the RVS.

The RVS is one of the three integrated instrument functions of the Gaia payload. Part of the light collected by the large telescopes on the Gaia spacecraft will pass though the RVS to perform high-resolution spectroscopic observations of stars that pass through the field-of-view. The stellar velocities derived from these data, in combination with the accurate position measurements that will also be acquired by the Gaia payload, will create a detailed three-dimensional spatial map – 6-dimensional phase-space map – of our Galaxy.


To perform the spectroscopic observations the RVS will have a blazed transmission grating in the optical path for dispersion of the light. In general, transmission gratings have numerous parallel grooves on their surface which cause light passing through the grating to emerge in an interference pattern. At specific angles the light interferes constructively and these peaks are referred to as orders. Within each order light is also dispersed by wavelength.

Blazed transmission gratings have specifically designed groove cross-sections that cause most of the incident light to be transmitted into a selected order of the interference pattern. This is expressed in the efficiency, which is the ratio of the amount of light dispersed into the desired order (m=+1 for RVS) to the amount of incident light.

The common groove cross-section for blazed gratings is a saw-tooth pattern in the surface layer of the grating. But the RVS grating is made with a challenging technique to realise a unique groove cross-section. This was needed to be able to meet all requirements for the RVS: the resolution for separating the constituent wavelengths must be λ/Δλ=11 500; the grating needs to have a very small wavefront error (a measure for the deviation from a perfect surface); and the efficiency needs to be >70%.



Date: 30 January 2009
Satellite: Gaia
Depicts: Electron microscope image of RVS grating grooves
Copyright: Fraunhofer Institut für Optik und Feinmechanik

The blazed transmission grating developed by IOF for the RVS is a 9 mm thick fused silica plate, of which the top surface layer has been carefully etched with an accuracy of about 20 nm in depth to form the grating grooves (Figure 2).

Rather than the regular saw-tooth pattern for the grating cross-section, the RVS grating has a unique sequence of discrete patches with a block shape. The pattern is a repeated set of five blocks of increasingly smaller widths. The spacing between the patches as well as the width of each individual patch is smaller than the wavelengths that the RVS will study (which lie in the narrow near-infrared band between 847-874 nm).

This means that at these wavelengths the light does not “see” the individual patches, but rather the integrated profile of the patches. The net effect is the same as for a regular saw-tooth pattern, but the discrete patches allow for all the optical requirements to be met, including the very high efficiency.

The development of the RVS grating by IOF was tackled in two steps. In June 2008 a small-scale version was made to prove that the required pattern of sub-wavelength scale patches (called the binary index modulation structure) could be made using a challenging technique. The full-size demonstrator model was successfully created a few months later and delivered to ESA on 10 December 2008. This success now clears the way for developing the actual flight model of the blazed transmission grating that will fly onboard Gaia early in the next decade.



02 September 2008

The ESA Gaia Science Team and the Gaia Data Processing and Analysis Consortium are working with others in the community to build the European science capacity to successfully exploit the Gaia cornerstone mission. One aspect of this work will be carried out via the GREAT (Gaia Research for European Astronomy Training) programme. A Call for Expression of Interest in Participating in the GREAT programme has been issued with a deadline for receipt of proposals of 17:00 GMT (19:00 CEST) on 26 September 2008.

The purpose of this call is to gauge community interest in participating in a GREAT proposal to the European Science Foundation for a Research Network Programme to fund a range of networking and training opportunities to fortify the Gaia community and to address key Gaia science topics.

GREAT will bring together relevant scientific expertise by promoting topical workshops, training events, exchange visits, conferences and so forth with the aim of addressing the major scientific issues that the Gaia satellite will impact upon.

The GREAT steering committee are aiming at a Research Network Programme structured around building science capacity around the key Gaia science areas:

  • Galactic Dynamics
  • Galactic Archeology
  • Stellar Physics
  • Star Formation and evolution
  • Fundamental physics and the Reference Frame
  • Extrasolar planets and Non Single Stars
  • Solar System
  • The IT challenge from Gaia

The call is open to the entire astronomical community (Europe and world-wide), in particular, those who will benefit from the use of the astrometric, photometric and spectroscopic data obtained with the Gaia satellite.

The deadline for receipt of expressions of interest is: 26 September 2008, 17:00 GMT (19:00 CEST) 

Full details are available from the GREAT web site (see link in right-hand menu)



08 May 2008

Sebastien Bouquillon (SYRTE/Obs. de Paris), Ricky Smart (INAF/OATo, Torino) and Alexandre Andrei (Observatorio Nacional, Rio de Janeiro) have used the 2.2m telescope of the European Southern Observatory at La Silla, Chile, to take several photographs of NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) satellite in its orbit, which is about 1.5 million kilometres from Earth. Perhaps surprisingly, they did so as part of the preparations for ESA’s Gaia mission, which scientifically is totally unrelated to WMAP.


Date: 05 April 2008
Depicts: Composite view of WMAP satellite sky positions
Copyright: Sebastien Bouquillon (SYRTE/Obs. de Paris), Ricky Smart (INAF/OATo, Torino) and Alexandre Andrei (Observatorio Nacional, Rio de Janeiro)

The main goal of the Gaia mission is to make the largest, most precise three-dimensional map of our Galaxy. To this end Gaia will survey the entire sky to detect and very accurately measure the position and motion of each star down to mV~20 that passes its field of view.

The correct scientific evaluation of Gaia’s position measurements makes it necessary that the absolute velocity of the spacecraft with respect to the Solar-System barycentre must be known to 2.5 mms-1, or to one part in 10 million, and the absolute position to 150 metres, or to one part in a thousand million.

This tremendous requirement cannot be satisfied by the usual satellite tracking techniques using their own radio signals, at least not for all times in Gaia’s five-year science mission. It can be done, however, if sunlight reflected from the spacecraft is used for direct position measurements of the spacecraft on the sky. In orbit, Gaia will appear as a very faint speck of light, moving slowly among the distant background stars. This ground-based optical tracking of Gaia was proposed by Ulrich Bastian (ARI, Heidelberg) a few years ago. Martin Altmann (also at ARI, Heidelberg) will be in charge of organizing and coordinating the ground-based optical tracking of Gaia in the years 2012 to 2017. He will need the support of quite a number of observers and observatories for this purpose.


What has all this to do with NASA’s WMAP? Well, the ground-based optical tracking concept must of course be tested. Like WMAP, Gaia will be located at the second Earth-Sun Lagrange point L2, about 1.5 million kilometres from Earth. Like Gaia, WMAP has a deployable sunshield, partly covered with insulation material and partly with solar panels. The Gaia shield is about 11 metres in diameter and inclined by 45° to the Sun direction, that of WMAP is about 4.5 metres and inclined by 22.5°. With all these parameters, WMAP is a reasonable (photo-)model for the brightness and observability of Gaia. If the sunshield materials were strictly the same, and the proportion of insulation and solar panel areas similar, WMAP could be expected to be roughly 1.5-2 magnitudes fainter than Gaia. The actual brightness difference is still uncertain to some degree, however.

The above picture shows WMAP flying past the stellar background. Three images taken on 5 April 2008 at time intervals of a few minutes were added up to create this composite frame. Before superposition, the three images (actually black-and-white images) were artificially coloured red, green and blue. For the stars, these three colours added up to neutral white. In contrast, the WMAP satellite shows up as the string of coloured points – since it is the only object having moved between the times the three images were taken. In addition to WMAP and a number of stars, a faint galaxy is visible as a slightly fuzzy blob at top centre of the picture.

The team acknowledges Dale Fink, Navigator of WMAP Spacecraft Control Team, for his specially supplied orbital ephemeris of WMAP.

Technical info
The exposures were 60 seconds each in the V band. Alexandre Andrei got a preliminary brightness of V=19.4 for WMAP, using the IRAF software, calibrating with 5 UCAC-2 stars, and applying a R-to-V magnitude correction. The WMAP ephemeris predicted an apparent magnitude for La Silla, at the time of observation, of V=18.7.

Web story author
Carmen Blasco, Science Directorate, ESA, The Netherlands
Phone: +31-71-565-4690



30 November 2007

A dedicated workshop designed to introduce the next generation of astrometry specialists to the science of Gaia successfully concluded this week in Leiden.


Date: 30 November 2007
Depicts: Group photo of ELSA School participants
Location: Lorentz Centre, Leiden University, the Netherlands
Copyright: Courtesy of Berry Holl

The ELSA School on the Science of Gaia ran from 19 to 28 November and was jointly organized by the ELSA network and the Lorentz Centre at Leiden University. Although especially designed for the newly appointed ELSA Fellows (9 PhD students and 5 post-docs) the workshop was also open to participants from outside the network. The programme was arranged with morning lectures covering the key scientific goals of Gaia, technical aspects such as satellite development, and a special workshop on Grid applications relevant to Gaia. Afternoons were assigned to student exercises which covered topics as diverse as: calculating the gravitational light deflection due to the Sun and Jupiter; deriving orbital parameters for binary systems from astrometric observations; determining the zero point of the Cepheid period-luminosity relation from Hipparcos parallaxes, and extracting stellar streams associated with the Sagittarius dwarf galaxy from the Sloan Digital Sky Survey data. Students also prepared poster papers describing their research and presented these to the school participants.

ELSA is a Marie-Curie research training network which brings together world-leading expertise in space astrometry with specialists on numerical algorithms and software engineering for the purposes of preparing for the scientific exploitation of data from ESA’s Gaia mission and training the next generation of researchers in this uniquely European speciality to maintain and extend European leadership in space astrometry.

The ELSA network is funded by the European Community’s Sixth Framework Programme from 2006 to 2010. During this period a number of dedicated workshops will be organised for ELSA Fellows with the aim of consolidating the acquired expertise. The workshop series will conclude with a dedicated conference on the simulation and analysis of space astrometry planned for 2010.



07 June 2007

At its most recent meeting in Paris, ESA’s Science Programme Committee (SPC) has approved the proposal by the Gaia Data Processing and Analysis Consortium (DPAC) submitted in response to the AO for Gaia data processing, issued last November.

The approval of the SPC marks an important milestone for the Gaia mission, scheduled for launch in December 2011. DPAC now formally is responsible for the building and operation of the mission’s data processing ground segment.

Gaia will produce ~100 TB of raw data during its nominal five years of operation at L2. It will be a major challenge, even by the standards of computational power in the next decade, to process, manage and extract the scientific results necessary to build a self-consistent solution of the relative position of all the objects in the sky detected by Gaia. The resulting phase space map of our Galaxy, the Milky Way, will contain kinematic, spectroscopic and photometric information of an unprecedented nature and completeness.

The demanding requirements to fulfil this task led to the decision by the scientific community to pool all their efforts into one consortium (DPAC) which would be responsible for the entire pipeline processing – from ingestion of the raw data to the catalogue output.


DPAC is a collaboration between the ESA Gaia Science Operations Centre (SOC) – located in Villafranca del Castillo near Madrid, Spain – and a substantial and broad scientific community. It comprises more than 300 individuals (scientists and software engineers) from 15 countries and 6 Data Processing Centres. The pan-European consortium is organized into eight Coordination Units (CU) each of which is dedicated to a particular aspect of the full data processing task:

      CU1: System Architecture
      CU2: Data Simulations
      CU3: Core Processing
      CU4: Object Processing
      CU5: Photometric Processing
      CU6: Spectroscopic Processing
      CU7: Variability Processing
      CU8: Astrophysical Parameters

A ninth unit (CU9: Catalogue Access) will be added through selection in a separate future AO when a more detailed view of the actual Gaia data products and required access methods is available.

The DPAC was formed in 2005 from the existing Gaia working groups. These groups had already done substantial work for example with early software development and running of feasibility studies. With the approval by the SPC, DPAC may now continue the work up to completion of the final Gaia catalogue in ~2020.



01 March 2007

The Science Directorate of the European Space Agency has released an Announcement of Opportunity (AO) for membership in the science team of the Gaia mission. The invitation from the Director of Science to respond to this AO is presented here. The AO document and the Science Management Plan can be accessed from the right-hand menu.
The deadline for receipt of proposals has now passed.

Date: March 1, 2007

Subject: Release of Announcement of Opportunity for membership in the Gaia Science Team

Dear Colleague,

The Science Directorate of ESA is releasing today the Announcement of Opportunity for membership in the Science Team of the Gaia mission. The Gaia mission, a global astrometric survey mission, is an element of ESA’s Scientific Programme, which is foreseen to be launched in December 2011.

Proposals are solicited for individual membership in the Gaia Science Team, whose mandate is to advise ESA on all scientific matters regarding the Gaia mission. As described in the Science Management Plan, the Gaia Science Team is due to be renewed at the time when the mission moves from design to development phase, with the Preliminary Design Review marking this transition foreseen for June 2007. A total of seven scientists will be selected, for a renewable period of three years, as members in the Gaia Science Team: two astrometry scientists, two photometry scientists, two radial velocity spectrometer scientists and one data analysis scientist.

Successful applicants are expected to have a keen interest and proven track record in at least one of the scientific fields to which Gaia will make a significant contribution. The key science goal of Gaia is the understanding of the structure and history of the Milky Way, with extra-solar planets, minor solar system bodies, stellar astrophysics, general relativity (and more) also figuring prominently in Gaia’s science case, as described extensively in the Information Sheets on science topics. Applicants for the positions of astrometry, photometry and radial velocity scientists are expected to have a good understanding of the aspects of the Gaia instruments relevant to the position they are applying for and to their stated scientific interests, as well as of the impact of instrumental issues on the science return from the mission. Details of the current instrumental design of Gaia are available in the Information Sheets on Payload and Spacecraft. Applicants for the position of data analysis scientist are expected to have a good understanding of the data analysis approach being implemented for Gaia (see Information Sheets on accuracy) and of the impact of data analysis issues on the mission’s science return.

Membership of the Gaia Science Team is on an individual basis and is open to all scientists from institutions located in ESA Member States. The Gaia Science Team appointed as a result to the present Announcement of Opportunity is anticipated to first meet in September 2007.

As described in the Announcement of Opportunity, the Gaia Science Team will be selected ensuring that they are to a reasonable degree independent from the management activities of the Gaia Data Analysis and Processing Consortium (DPAC). The Announcement of Opportunity for the DPAC closed on December 11, 2006, and a single proposal has been received. Selection of the proposing consortium by the Science Program Committee is currently planned to take place in May 2007. The selection of the Gaia Science Team members in response to the present Announcement of Opportunity is currently planned to take place at the same time. Should the selection of the DPAC consortium for whatever reason be delayed, the Science Directorate reserves the right to delay the selection of the Gaia Science Team, to ensure consistency between the two processes.

With the present letter I therefore invite interested members of the scientific community to respond to the Announcement of Opportunity, available on line at Responses to the Announcement of Opportunity are due by  April 4, 2007 following the procedure described in detail at:

Yours sincerely,

David Southwood

Director of Science



09 November 2006

The AO Deadline for Submission has Passed

Dear Sir, dear Madam,

The Science Directorate of ESA is releasing today the Announcement of Opportunity for the constitution of the Gaia Data Processing and Analysis Consortium (DPAC). The Gaia mission, a global astrometric survey mission, is an element of ESA’s Scientific Programme, which has recently entered the implementation phase and which is foreseen to be launched in December 2011.

Proposals are solicited for the Gaia DPAC, which will build and operate the Gaia data processing ground segment, a single processing pipeline leasing directly to the intermediate and final mission products. The data processing ground segment is an essential element of the mission, and is expected to be developed as a collaboration between the ESA Gaia Science Operations Centre (SOC) and a substantial and broad scientific community funded by national funding agencies. An overarching proposal from a consortium covering all aspects of the Gaia DPAC is expected in response to the AO. The Agency may however also consider individual proposals of a specialised nature.

With the present letter I invite proposers from ESA Member States to respond to the AO which is available on line (see links in right-hand menu).

Responses to the AO are due by 11 December 2006 following the procedure described in detail here (see links in right-hand menu).

A copy of the response must also be sent to all national funding agencies who will later be asked to support the DPAC activities.

Yours sincerely,

David Southwood

Director of Science



16 October 2006

The processing of Gaia’s extensive data harvest will be a formidable and complex task, for which ESA must rely on the scientific community.

To this end ESA will shortly be issuing an Announcement of Opportunity (AO) for the data processing and analysis, with proposals due a month later. More information and the Science Management Plan timetable are available through the link on the right-hand side.



05 September 2006

A number of software and research positions to work on Gaia-related tasks are offered at European research institutes.

Details of vacancies for Gaia-related research or software positions are available online at the Gaia Science website.



11 May 2006

During a ceremony held in Toulouse on 11 May 2006, ESA officially awarded EADS Astrium the contract to develop and build the Gaia satellite. The goal of this space mission, currently planned for launch in 2011, is to make the largest, most precise map of our own Galaxy to date


Date: 11 May 2006
Satellite: Gaia
Depicts: Spacecraft with fully deployed sunshield
Copyright: ESA

The contract, worth 317 million Euros, has been jointly signed by ESA’s Director of Science, Professor David Southwood, and Antoine Bouvier, Chief Executive Officer for EADS Astrium. The Toulouse branch will lead the Gaia development.

“GAIA is our next grand challenge – to understand our galactic home, the Milky Way,” says David Southwood. “It is a great privilege to meet the team in EADS Astrium and to wish them well in working with us in this great project.”

Gaia will be the most accurate optical astronomy satellite ever built so far. It will continuously scan the sky for at least five years from the second Lagrange point (L2). This position in space offers a very stable thermal environment, very high observing efficiency (since the Sun, Earth and Moon are behind the instrument field of view) and a low radiation environment.



26 January 2006

The Institute of Astronomy and Astrophysics at the Université Libre de Bruxelles is offering a postdoctoral position to participate in the development of algorithms and software – related to eclipsing binaries (and potentially transiting planets) – for the Gaia data processing. The position is funded for two years with the possibility of extensions until the end of the Gaia data processing phase (around 2019). A starting date of 1 May 2006 is envisaged, but is flexible. Evaluation of candidates will begin 1 March 2006; later applications will be considered until a suitable candidate is identified. Further details are available online.



23 December 2005

The Lohrmann Observatory at the  Dresden University of Technology is offering two postdoc positions to participate in the development of algorithms and software for relativistic modelling of microarcsecond astrometric observations and tests of fundamental physics with Gaia data. One position is for development of algorithms and software for Gaia data processing dedicated to finding an optimal scheme for testing relativity with Gaia. The second position is for theoretical and practical refinements of relativistic modelling for Gaia. Both positions are funded until the end of 2009 with the possibility for extensions. A starting date, for both positions, of 1 April 2006 is envisaged, but is flexible. Applications should be submitted by 15 February 2006.



13 December 2005

“The design and performance of the Gaia photometric system” by Jordi et al, has been accepted for publication by the MNRAS. The paper presents the design and performance of the broad- and medium-band set of photometric filters adopted as the baseline for Gaia. The nineteen selected passbands (extending from the ultraviolet to the far-red), the criteria, and the methodology on which this choice has been based are discussed in detail. Photometric capabilities for characterizing the luminosity, temperature, gravity and chemical composition of stars are analysed. The automatic determination of these physical parameters for the large number of observations involved, for objects located throughout the entire Hertzsprung-Russell diagram, are discussed. Finally, the capability of the photometric system to deal with the main Gaia science case is outlined. The paper has been included in astro-ph as astro-ph/0512038.



08 December 2005

Two postdoc positions are available at the Max Planck Institute for Astronomy, Heidelberg, to work on preparations for the Gaia data processing.

The positions involve the development of algorithms for
astrophysical classification and parameter estimation using Gaia
photometric, spectroscopic and astrometric data.  Both positions are
funded for four years, with possible extensions up to the completion
of post-mission processing. A start date of 1 April 2006 is envisaged
but is flexible. Applications received before 15 February 2006 will
receive full consideration. For more information see
the complete advertisement.



26 October 2005

This position is specifically to work on GIBIS (the simulator of the Gaia payload) and the update of GIBIS algorithms following the acceptance of the final mission design, and on the implementation of data analysis algorithms for the determination of stellar radial velocities. The position is initially for one year with a possibility of renewal for a further one or two years.

Further information and contact details are available online (in French).

The deadline for applications is 2 December 2005.



17 October 2005

The second meeting of the Data Analysis Coordination Committee was held at MPI, Heidelberg, 6-7 October.

Under the chairmanship of Francois Mignard, with co-chair Coryn Bailer-Jones, the structure of the Gaia DPAC (Data Processing and Analysis Consortium) was revised slightly, with the resulting coordination units (CUs) with provisional leaders as follows: CU1: System Architecture (William O’Mullane); CU2: Data Simulations (Xavier Luri); CU3: Core Processing (Uli Bastian); CU4: Object Processing (Dimitri Pourbaix); CU5: Photometric Processing (Floor van Leeuwen); CU6: Spectroscopic Processing (David Katz); CU7: Variability Processing (Laurent Eyer); CU8: Astrophysical Parameters (Coryn Bailer-Jones); CU9: Catalogue Access (to be activated nearer to launch). Provisional work breakdown structures are being advanced for all units, representing all steps foreseen for the data analysis.



05 September 2005

One of the technical development activities initiated by ESA after the concept and technology study in 2000 was the development of a fully representative deployable Sunshield for Gaia. The study was carried out by Sener (Spain), and directed by Gerard Migliorero (ESTEC). The specifications called for a ‘bread board’ model of two of the 12 folding panels of an 11-m diameter Sunshield, partly carrying solar panels, and weighing less than 100kg. After deployment, the Sunshield must provide a highly stable mechanical and thermal environment during operation. The study demonstrated that the temperature of the shielded spacecraft can be kept at about 150K, with a stability of a few parts in a thousand over the spin period of 6 hours. The attached movie shows laboratory deployment of the resulting breadboard model.



01 July 2005

The Gaia Project Team in ESA-ESTEC, supported by the ESA Contracts Department, has released the complete package of documentation representing the industrial ‘Invitation to Tender’ for Phases B2/C/D (detailed design, development, launch and commissioning of the Gaia satellite), including the detailed ‘Statement of Work’ and the ‘Mission Requirements Document’. This represents the formal start of the final steps of the Gaia satellite development. The selected industrial prime contractor will be announced in February 2006, and the target launch date is late 2011.



27 June 2005

The first meeting of the Data Analysis Coordination Committee (DACC) was held at ESTEC on 15 and 16 June. The DACC was formally set up by the GST at its 15th meeting in April 2005 and is charged with defining and putting into place the Gaia Data Analysis Consortium (GDAC). The GDAC is expected to start operating in mid-2006 and will conceive, implement and operate the Gaia data processing system. The main tasks of the DACC are to design a workable structure for the data processing and to match the community interests (as expressed by the Letters of Intent) to the required tasks.



13 June 2005

Last Friday, 9 June, David Southwood, ESA director of Science, signed a contract with UK based firm e2v Technologies for the development of CCD camera sensors for Gaia. The firm will be responsible for the production of a 1.5 giga-pixel camera capable of deriving high precision astrometric information for a billion stars.

A report in the New Scientist outlined the reasons for selecting e2v over other chip manufacturers. The company has successfully developed a detector capable of working from 300 to 900 nm with very low noise.

Traditionally CCD detectors have struggled to retain low noise levels at the short wavelength (UV) end of the spectrum. e2v, however, have overcome this problem by literally shaving away over 95% of the silicon substrate, which is responsible for absorbing radiation at key UV wavelengths.



21 April 2005

As part of a new research group at the Max-Planck-Institute for Astronomy (MPIA) in Heidelberg, a postdoc position is available to work with Coryn Bailer-Jones on Gaia and SDSS/SEGUE. SEGUE is the recently approved extension of the SDSS project to the Galactic plane. The position is concerned with the development and application of astrophysical parameter estimation methods for both Gaia and SEGUE.

The project could include:

  • investigation of multidimensional statistical methods for estimating stellar parameters from photometric and spectroscopic data;
  • development of these methods specifically for Gaia using simulated data, investigating such issues as: optimal combination of photometric, spectroscopic and astrometric data; classification of binaries; efficient detection of outliers (e.g. new types of objects);
  • application of these methods to SDSS/SEGUE spectra (and photometry) to determine stellar parameters (in particular Teff, logg, [Fe/H], [alpha/Fe], line-of-sight extinction);
  • identification of stellar populations within SEGUE to address various issues in Galactic structure, e.g. identification of disk or halo overdensities, tracing chemical evolution/distribution in the Galaxy;
  • study of unsupervised (clustering) methods for uncovering new structure in large data sets.

Together with the Centre for Astronomy (ZAH, formerly ARI) at Heidelberg University, the MPIA has put together a significant group to participate both in the Gaia data processing and to exploit the SEGUE data. Coryn Bailer-Jones is a member of the Gaia Science Team and leads the Gaia Classification Working Group. The work on Gaia and SEGUE naturally complement each other, with SEGUE both serving as a test and development ground for Gaia as well as providing scientific returns far in advance of Gaia. Initial data for SEGUE have already been obtained and the collaboration officially starts on 1 June 2005. An approximate 50/50 split is foreseen between Gaia and SEGUE, although the successful candidate will have some freedom to determine this and to define projects.

The position is initially available for one year with an extension of two years beyond this possible. Applications should include a CV and list of publications and should be sent by mail or email to

Coryn Bailer-Jones
Max-Planck-Institut fuer Astronomie
Koenigstuhl 17
D-69117 Heidelberg
email: calj AT
phone: +49 6221 528224

Informal enquiries are also welcome. The position is available immediately (with a start date up to September 2005 possible) and applications will be considered until the position is filled.

For more information see:

Gaia Classification Working Group homepage
Gaia homepage
SDSS homepage
MPIA homepage

The Max Planck Society is an equal opportunity employer. Applications from women, disabled people and minority groups are particularly welcome.



31 March 2005

Gaia in 2004, a status report prepared by the Gaia Project Scientist, summarises the status of the Gaia project at the end of 2004, describes the progress achieved in 2004 with emphasis on the scientific activities, and summarises the major ongoing and planned activities.

The status report can be downloaded as a pdf file (see Related Links).



17 January 2005

Dear Colleagues,

ESA hereby invites individuals or institutes in Member States, wishing to play a role in the Gaia data processing in the years 2006 onwards, to submit a ‘Letter of Intent’ to ESA outlining their possible future involvement.

The deadline for submitting “Letters of Intent to Participate in the Gaia Data Processing” has passed
Enquiries may be directed to

Gaia is an approved ESA science mission aiming to determine accurate positions, distances, proper motions, and photometry for some one billion stars in our Galaxy and beyond, with radial velocities for a significant fraction. Comprehensive details are given at the ESA site (including Information Sheets on the data analysis principles foreseen). The target satellite launch date is currently mid-2011 (to be confirmed by the ESA Science Programme Committee), with an operational period of 5 years. The final data products can appear only 2-3 years after the end of operations (i.e. around 2018), although early-release catalogues of astrometry and photometry are being considered. Data rights on specific objects in the traditional sense are not foreseen. Nevertheless, groups involved in the preparations for the data analysis will have deep and early insight into the results, facilitating early interpretation of the data and the early publications of results.

While ESA pays for the satellite in its entirety, including payload and operations, the data reduction is a task that will be carried out with major contributions from national funding. This request for Letters of Intent is therefore a step in developing the data reduction plans for Gaia, and will be followed by a more detailed Announcement of Opportunity some 5 years before launch.

Over the past four years, ESA and the Gaia scientific working groups have been developing a prototype data analysis system for Gaia. This prototype aims to provide a proof-of-principle of the approach now under study for the mission data analysis. In this model, satellite data will be ingested into a central data base, detected sources will be cross-matched to celestial objects, and the core processing (a global iterative adjustment of the astrometric data) will be carried out within a centralised processing environment. Shell tasks (for example, analysis of the photometric or radial velocity data, analysis of double stars and Solar System objects) will access the centralised data base for further processing. All of these processes will depend on algorithms and a processing infrastructure (both hardware and software) provided to a greater or lesser degree by the Gaia scientific community.

The development of more concrete plans for the next phase of the development of the data analysis, from early 2006 onwards, is now under consideration. To understand better the resources which may be available for the Gaia data processing, and to coordinate the procurement and integration of algorithms, indications of potential interest are now invited.

Foreseen contributions by individuals or multi-national groups may be in any area of the data analysis: for example, studies of specific algorithms, development of code, involvement in the core or shell tasks, plans for involvement in the development or execution of the operational system, provision of computational hardware at the contributing institute or at a central processing facility, or any other sort of associated expertise. The Gaia www site includes, under ‘Opportunities for Research’, some of the specific areas currently open for additional contributions. In addition, further details of open areas and opportunities for research can be found on the web sites of the individual working groups.

Foreseen contributions may be over any relevant time interval, for example, related to activities which are already under way, planned for 2006-08 or beyond, or relevant only for the operational system post-launch (from 2012 onwards).

Two kinds of responses can be foreseen: those from institutes that are already familiar with Gaia due to their current involvement, and those from institutes attracted by the challenge represented by the data reductions but not yet involved in the Gaia effort. Subject to feasibility, this may include participation in the validation of the current prototype, or the proposal of different concepts for the data reduction.

It is not so relevant at this stage whether or not the foreseen contribution may overlap with existing activities, or how it might interface with other activities. On the other hand, potential participants may wish to discuss ideas first with members of the Gaia scientific working groups or Gaia Science Team.

The purpose of the present call for ‘Letters of Intent’ is to conduct a survey of the interest, and scale of effort that might be provided to the Gaia data processing task. Responses will not be considered as commitments. This call also aims to serve as an initiating step in the route to national funding approval. Within ESA, these letters will be used to consider and plan the next steps of the overall coordination.

The Letter of Intent should be submitted using the form found following the ‘Letter of Intent’ links on  the main page of the Gaia www site (  [This form can be found on the list of related links on the right menu of this web page.] Please aim to provide sufficient details of your interests and commitments that further planning and coordination will be possible. In order to take these plans into consideration, a response by 20 March 2005 is requested.

Yours sincerely,

Sergio Volonte
Directorate of Science

Michael Perryman
Gaia Project Scientist



13 December 2004

Two engineering positions have been created at GEPI/Observatoire de Paris for one year with a possibility of renewal for one or two years.

The first position deals with the simulation of the spectrograph of the Gaia satellite and the implementation of data analysis algorithms. The second position concerns the data handling on-board the satellite.

Further details (in French) are available on the Gepi/Observatoire de Paris Gaia web pages.

Closing date for applications is 14 January 2005.



17 November 2004

Leiden Observatory invites applications for a postdoctoral research position to work on the preparation of the photometric data analysis for ESA’s Gaia mission. The study of the photometric data analysis will lead to the design and development of algorithms that will be used during the operational phase of the Gaia mission. The successful applicant will work with Dr. Anthony Brown and is expected to continue to collaborate in original research in related areas part-time. Further details are available on the Leiden Observatory web pages.



17 November 2004

A GASS simulation of Gaia telemetry, corresponding to five years of observations of 1000 astrometric binary stars, has been successfully completed using the GaiaGrid environment.

The Astrometric Binary Star Analysis is one of the shell algorithms selected to be run in the GaiaGrid environment.  In order to test this algorithm realistic simulations of telemetry, covering five years of Gaia observations, for about 1000 astrometric binary stars needed to be generated and then ingested into the GDAAS system.

The generation of simulated data in the context of the Gaia mission is under the responsibility of the Gaia Simulation Working Group. The GASS simulator generates realistic telemetry which can be ingested into GDAAS and used to populate the test databases.

In spite of the relatively small number of objects in the astrometric binary star simulation, the generation of  the telemetry requires a non-negligible computational effort because several aspects of the simulation are not related to the number of objects but rather to the simulated time span. GASS was deployed in the GaiaGrid environment in order to exploit the computational power it provides. In the case of GASS this deployment is particularly effective because the design of the simulation allows it to be completely split into several smaller pieces that can be simultaneously sent to different nodes of GaiaGrid, taking full advantage of the distributed computing environment provided.

The simulations were run in GaiaGrid using the Gridassist workflow tool during a week in October 2004. After some initial testing and fine-tuning, 183 independent jobs were launched to the GaiaGrid environment, covering the full period of five years of simulation. These jobs were automatically distributed to the GaiaGrid nodes by Gridassist and the results were collected in a central repository located at CESCA (Centre de Supercomputació de Catalunya), accessible through the Grid. In summary:

  • The simulation was run in 23 nodes distributed in 8 institutes of 5 countries (see figure of GaiaGrid sites)
  • A total of 3.8 million CPU seconds were used for the tasks
  • A total of 16.5 GB of data were produced and automatically transferred to the central repository at CESCA

The simulation was completed in about 4 days (including some stop times devoted to checking of the partial results). Although the simulation could have been performed without GaiaGrid, the use of this tool made the effort much simpler and shorter.



21 October 2004

A Greek program, ATHINOGAIA, which will support the participation of a Greek team in various Gaia working groups has been awarded a grant of 250,000 Euro from the Greek General Secretariat of Research and Technology.

This followed an open call for proposals aimed at encouraging Greek participation in European and International Programmes. The members of the team are D. Sinachopoulos (Double & Multiple Star Working Group), R. Korakitis (Photometry Working Group), M. Kontizas and E. Kontizas (Classification Working Group). The program will be hosted by the National & Kapodistrian University of Athens.



18 October 2004

In the United Kingdom two posts have been created, for a period of three years, to start developing the data processing pipeline software for the photometric and radial velocity data from Gaia.

The posts are financed through an eScience grant from PPARC, and are distributed over Cambridge (1.5) and Leicester (0.5). One post, at the Institute of Astronomy in Cambridge, is currently advertised. This small group, including Floor van Leeuwen as coordinator and manager, is intended to become the core of a much larger UK effort to provide actual data processing software for some of the core tasks of the Gaia satellite.

The deadline for applications for the Cambrdige position has passed.



13 October 2004

Between 4-7 October, a major symposium dedicated to the scientific aspects of the Gaia mission was held at the Observatoire de Paris, Meudon, France, as ‘Les Rencontres de l’Observatoire 2004’. Attended by 240 delegates, the four-day meeting was an opportunity to present the current status of the Gaia mission to the interested scientific community, and to hear about the results of investigations carried out in the various areas of the mission over the last four years.

The Gaia mission was proposed to ESA in 1994 as part of the Horizon 2000 long-term plan, supported by the Survey Committee if the achievement of 10-microarcsec level accuracies (at 15 mag) could be demonstrated, and approved by ESA’s advisory committees in 2000 after a two-year concept and technology study. During 2002, as a cost reduction exercise, the satellite constraints were modified for accommodation in the smaller Soyuz-Fregat launch vehicle, with only a modest loss in astrometric accuracy. Thus the scientific goals established in 2000 – 1 billion stars to 20 mag, with accuracies of 10 microarcsec at 15 mag, multi-epoch, multi-colour (4 broad and 11 medium band) photometry for all objects; and radial velocities to 1-10 km/s down to 16-17 mag – remain applicable. A selection of some of the papers presented is given here to provide a flavour of the meeting.

The Symposium was opened by the Director of the Paris Observatory, Daniel Egret, and Jean Kovalevsky, who stressed the great challenges and scientific rewards of Gaia. ESA’s Director of Science, David Southwood, presented Gaia in the context of the current ESA science programme. These were followed by presentations of the satellite status by study manager Oscar Pace, the overall Gaia scientific case (Mignard), an overview of the mission (Perryman), the operational principles (Lindegren), accuracy assessment (de Bruijne), and the radial velocity instrument (Katz, Cropper). Presentations were made on the science impacts expected from the mission, including distance scale (Bono), Galaxy dynamics (Binney), Galaxy structure and evolution (Vallenari, Nissen, Haywood, Spite), stellar physics (Lebreton), dark matter (Wilkinson), atmospheric parameters (Recio-Blanco), exoplanets (Queloz).

Activities and overall progress of the 14 scientific working groups formed a major part of the symposium. Presentations covered the relativistic aspects of the data analysis (Klioner), simulations on planet detections (Lattanzi), duplicity and masses (Pourbaix, Soderhjelm), near-Earth asteroids (Hoeg), variability analysis (Eyer), scientific alerts (Wyn Evans), solar system studies (Muinonen, Cellino, Tanga), on-board detection (Arenou), the photometric systems (Jordi), classification (Bailer-Jones), and the quasar reference frame (Claeskens).

Various reports on the massive data analysis preparations gave a detailed perspective on the complexities and challenges facing the on-ground data treatment: the overall simulation chain (Luri, Babusiaux), the current prototype data analysis system (Torra), Grid-related studies (Ansari), and the photometric data analysis (Brown).

Five participants accepted the delicate challenge of summarising the poster presentations in the various categories: Katz, Bastian, Mignard, Breger, and Luri. This effort contributed significantly to the coverage of a large variety of topics in a limited period of time, and was greatly appreciated by the participants.

Several institute directors, including the ESO Director General, participated in the meeting, underlining the long-term strategic importance of Gaia in astronomy. Tim de Zeeuw (Leiden) treated the participants to 30-minutes of inspiring “Concluding Remarks”, underlining the strength of the Gaia scientific case, setting Gaia science in the context of astrophysics in the years 2015-20, and acknowledging the huge progress made in the mission definition over the last four years (see

A highlight of the Symposium was the award by the Paris Observatory of the degree of Doctor Honoris Causa to the Honorary Chair of the Scientific Organising Committee, Adriaan Blaauw, who celebrated his 90th birthday earlier in the year. The Symposium dinner was held on a Seine river boat navigating Paris by night, and taking time out from the magnificent symposium setting of the Observatoire de Meudon.

The chairs of the SOC, Catherine Turon (Paris-Meudon) and Michael Perryman (ESA) were supported in the organisation of the meeting by the Gaia Science Team, an International Advisory Committee including at least one representative from each ESA member state, and an efficient Local Organising Committee, led by Yves Viala (Meudon) and supported by Karen O’Flaherty (ESA). Generous financial support by various organisations (Paris Observatory, CNES, CNRS, ESA and the Gaia industrial leading groups – EADS-Astrium and Alcatel/Alenia), permitted attendance at the symposium by an unusually large representation of younger scientists (PhDs and post-docs) many of whom are already playing a key role in the preparation of the ambitious Gaia mission. Attendees also included collaborators in Greece (recently members of ESA), and some non-member countries (Slovenia, Lithuania, Estonia, Australia). The proceedings of the symposium will be published by ESA in early 2005.

Catherine Turon and Michael Perryman



04 October 2004

More than 200 scientists from around the world gather today at the Observatoire de Paris for the opening of “The Three Dimensional Universe with Gaia”  – a Symposium dedicated to ESA’s Gaia mission.

The purpose of the Symposium are:

  • to present to the scientific community the design chosen for the mission, the final characteristics and performances, and to update the resulting scientific case
  • to bring to the attention of the scientific community the extraordinary potential of Gaia and to share with the younger generation of scientists the expertise acquired during the preparation phases of the Gaia mission, and during all phases of the Hipparcos mission. Students and young researchers have been especially encouraged to participate
  • to organise the next phase of scientific preparation of the mission, in particular the data reduction which constitutes a major challenge with a petabyte of interconnected data which has to be treated in a global and iterative manner, and to prepare for the scientific exploitation of the data.

The Symposium is attended by scientists working on the preparation of Gaia and by members of the large scientific community interested in using the data from the mission.



19 August 2004

Recognising the challenge posed by the Gaia data analysis, the Netherlands organisation for scientific research (NWO) has awarded a grant of 364,000 Euro in support of preparations for Gaia photometric data analysis.

The award will fund a study, led by Anthony Brown (Leiden University), to advance the plans for the analysis of the photometric data from the Gaia satellite. In addition, and in collaboration with DutchSpace (a company with experience in the application of grid technology to large-scale problems), the study will explore how grid technology can be applied to a realistic, large and complex astronomical investigation, such as that posed by the photometric analysis.



31 March 2004

The first phase of the RVS instrument design has come to an end with the final presentation of the work performed to date by the RVS Consortium.

This scientific consortium comprising Mullard Space Science Laboratory, Observatoire de Paris-Meudon, Brunel University, University of Leicester, Osservatorio di Asiago, and University of Ljubljana, and led by Professor Mark Cropper (MSSL), worked with ESA and the industrial System Level Technical Assistance contractors under the direction of ESA Study Manager Oscar Pace. The consortium has refined all aspects of the instrument design (optics, detector, mechanical, thermal, and on-board processing) providing a baseline design for Gaia’s radial velocity spectrograph. This will be refined further during the Definition Study phase, extending to mid-2005.



05 March 2004

On 2-3 March, separate presentations were made by Alcatel/Alenia and EADS-Astrium to ESA representatives (from the Gaia project and outside) and the Gaia Science Team. Extensive presentations summarised the activities which have been carried out under the parallel System Level Technical Assistance Contracts which have been running with these industrial teams for the past two years. As a result, authorisation has been given for Gaia to enter Phase B1, the detailed definition phase, which is expected to start in April 2004, and which will extend for 1 year. Gaia therefore continues to remain on schedule for a launch in 2010.



24 February 2004

Gaia in 2003, a status report prepared by the Gaia Project Scientist, summarises the status of the Gaia project at the end of 2003, describes the progress achieved in 2003, and summarises the major ongoing and planned activities.

The status report is available in pdf format here.



17 November 2003

Testing the high stability optics bench

A prototype ‘basic angle monitoring system’ designed and constructed in a collaboration between EADS Astrium (Toulouse) and TNO TPD (Delft) will be subjected to a series of tests over the coming weeks. The tests are designed to verify that the system can be aligned with the required accuracy, that it can withstand the launch loads without damage or misalignment, and that it provides the thermal stability required for the in-orbit monitoring. For more on the tests see Picture of the week featuring the high stability optics prototype.



12 November 2003

*** IMPORTANT: deadline for applications 24th Nov 2003 ***

*** Contact details below ***

The group of Galactic Astrophysics of the University of Barcelona (UB) has been assigned a doctoral grant in the context of the Spanish “Plan Nacional del spacio”.

This position is open for applications by students having completed a degree in astronomy (or related subjects) or software engineering and willing to complete a Gaia-related PhD in the Astronomy Department of the UB.

Description: the grant is included in the Spanish “Formacion del Personal Investigador” programme. Check the following URL (in Spanish) for details:

Duration: four years (starting in January 2004)

Areas of work:
1- Development of the Gaia simulator
2- Design of the Gaia photometric system
3- Design and implementation of the Gaia database and the data reduction system (GDAAS)

Jordi Torra
Tel: 934021128

Deadline for application submission: 24th November 2003



29 September 2003

The first batch of CCD wafers for Gaia’s Astro (AF) instrument has recently been completed at the UK headquarters of e2v technologies in Chelmsford.

The CCD91-72s represent one of the largest area CCDs produced by e2v. They are nearly 50% bigger than e2v’s successful astronomy products used worldwide in ground-based telescopes. The Gaia device is designed to work in TDI (Time Delay and Integrate) mode. This allows an integrated image to be built up by the continuously scanning satellite, an essential concept at the heart of Gaia’s mission to map with unprecedented accuracy the space position and motions of over a billion stars.

Under contract to EADS-Astrium (Toulouse) to design and manufacture custom designed chips for both the Astro and Spectro instruments on Gaia, e2v is also working with EADS-Astrium to develop advanced packaging techniques using the unique Silicon Carbide capability of EADS-Astrium. These techniques are necessary to achieve the alignment accuracy required across the huge focal plane in order to allow the TDI concept to work. At approximately 0.5 metre square the Astro focal plane of CCDs will be the biggest ever flown in space.

The 32 high performance, large format imaging devices that will be delivered to EADS-Astrium over the next 10 months will be used to verify the operational concepts in the design of the device. They will also be used in the assembly of a test section of the focal plane to be used in alignment tests.

[Pictured above: part of the team from the e2v wafer fabrication area that has produced the initial batch of CCDs. Back row, left to right: Roy Steward, Gaia CCD Project Manager; Pat Mandell, Wafer Fabrication Operative; Sheila Clift, Photolith Inspector; Alan Bidewell, Wafer Fabrication Operative; Glenn Wood, Wafer Fabrication Manager.
Front Row, left to right: Derek Nunn, Team Leader; Phil Etheridge, Line Engineer; Andy Raine, Inplant Operator

Inset: Two CCD91-72 CCDs on a silicon wafer. Each CCD comprises 4500×1966 pixels each 10×30µm in size. (Small test structures are visible on either side of the CCDs.)]



15 September 2003

Members of the Planetary Systems Working Group have reported the first results of their tests of Gaia’s exoplanet detection capabilities, using simulated data matching the results expected from the real mission.

In a detailed `double blind test’, data simulated by Torino Observatory astronomers Mario Lattanzi and colleagues was processed independently by Alessandro Sozzetti (Pittsburgh/CfA), and Dimitri Pourbaix and Sylvie Jancart (Bruxelles). The detection and orbit fitting solutions are in line with the formal predictions, and underline Gaia’s capability of detecting many thousands of exoplanets from their astrometric wobble.  For further details see report PSWG-OAT-002  (see related links).



08 April 2003

Custom-built CCDs, designed and manufactured by Essex-based e2v technologies, have recently captured their first images through Megacam, the wide field camera mounted on the Canada-France-Hawaii Telescope (CFHT).

The forty (40) e2v CCD42-90s represent the largest set of CCDs ever provided for any telescope in the world. e2v is working with the European Space Agency to develop and supply several hundreds of large format CCDs for Gaia.



23 February 2003

It must be one of the oldest questions. When you gaze at the sky, you marvel at its immensity. Have you ever, at some stage of your life, looked up into the night sky and wondered just how many stars there are in space? The question has fascinated scientists as well as philosophers, musicians, and dreamers through the ages.

Look into the sky on a clear night, out of the glare of streetlights, and you will see a few thousand individual stars with your naked eyes. With even a modest amateur telescope, millions more will come into view. So how many stars are there in the Universe? How easy it is to ask this and how difficult it is for scientists to give a fair answer!

ESA’s Hipparcos mission and its successor, Gaia, are star mappers and therefore obvious starting points to derive information. Between 1989 and 1993, Hipparcos mapped over two and a half million stars within our galaxy. Due for launch around 2012, Gaia will extend this work to about a thousand million stars. However, stars are not scattered randomly through space, they are gathered together into vast groups known as galaxies. The Sun belongs to a galaxy called the Milky Way. Astronomers estimate there are about 100 thousand million stars in the Milky Way alone. Outside that, there are thousands of millions upon millions of other galaxies also! The mathematics begins to get vaguer and larger.

Telescopes cannot yet see individual stars in distant galaxies. Astronomers are therefore a long way from counting each star. Even the James Webb Space Telescope, the NASA/ESA successor to the Hubble Space Telescope, due for launch around 2010, will be unable to do that. Even if it could, counting the stars in the Universe would be like trying to count the number of sand grains on all the beaches that are on Earth. However, astronomers want surer and smarter ways to arrive at reliable numbers.

Knowing how fast stars form can bring more certainty to calculations. Among other things, ESA’s infrared space observatory, Herschel, launching around 2007, will chart the formation rate of stars throughout cosmic history. If you can estimate the rate at which stars have formed, you will be able to estimate how many stars there are in the Universe today.

In 1995, an image from the Hubble Space Telescope suggested that star formation had reached a crescendo at roughly seven thousand million years ago. Recently, however, astronomers have thought again. Goran Pilbratt, project scientist for Herschel, explains, “The Hubble Deep Field image was taken at optical wavelengths and there is now some evidence that a lot of early star formation was hidden by thick dust clouds.” Dust clouds block the stars from view and convert their light into infrared radiation, rendering them invisible to the HST. “Herschel is designed to view exactly the time in the evolution of the Universe, at the right wavelengths where we think the majority of the obscured star formation can be seen,” says Pilbratt.

So with Herschel, astronomers will see many more stars than previously. We will be one step closer to provide a more reliable estimate to that question asked so often in the past – “how many stars are there in the Universe?”.



03 December 2002

Tomorrow’s spacecraft will be capable of generating more data than they can transmit to Earth. In some cases, this could be more data than can even be comfortably handled by today’s computational methods. What benefits are there for us in this flood of data?

If you know how to transfer huge quantities of data, you could revolutionise some Earthly applications. In the entertainment industry, you could transmit films via satellite to waiting cinemas. Since the information is digital, audiences would see a perfect picture every time. Film distributors would no longer need endless rolls of celluloid film. The menu at cinemas would not be limited to feature films either. You could beam sporting events, musical concerts, and even news reports into cinemas, showing them live.

ESA scientists may have less fun with the challenges of transferring bulk data from space. In 2008, for example, ESA’s Eddington will study ‘starquakes’ and search for planets, generating a 70-megabyte image every few seconds. However, the data link to Earth runs several hundred times slower, at just 130 kilobytes per second. Fabio Favata, project scientist for Eddington, has an ace up his sleeve. “We know which stars we want to observe,” he says. On-board computers can send back only the information relating to the stars, not the black sky in between. This avoids unnecessary transfer.

Sometimes astronomers need information about the whole sky, not just about the pinpointed stars. This is the problem facing ESA’s scientists in the Planck mission. Planck will survey the whole sky, mapping the leftover radiation from the Big Bang. Jan Tauber, Planck’s project scientist says,“We have to retrieve our information in a smart way.” Planck will compare the data with a computer prediction and send back only the differences between the two, thereby transmitting smaller numbers, which you can send faster. On Earth, the same computer prediction reconstructs the full data record.

Around 2010, another ESA mission, Gaia, will have to work out how to manage very large amounts of data. Engineers designed Gaia to discover new objects as well as collect data about known ones. To cut down its data stream, its on-board software will detect every object that enters the spacecraft’s field of view. After that, it defines a small area around the object, and transmits data from that area only. Data compression software reduces the size by a factor of five also.

Gaia will generate a staggering amount of usable data, that is, 1 petabyte (one thousand million million bytes) that scientists need to search and process. Even if you could search an individual data record each second, searching all the records could easily take 30 years. Michael Perryman, Gaia’s project scientist admits, “Clearly we have to set up a system that will handle this amount of data in sensible times.” The Gaia team are working with commercial software producers to construct one of the most sophisticated, indexed databases in history.

Once such a database is developed, we could have huge benefits in Earthly applications. Why? Since the Internet itself is one huge database, Gaia’s advanced techniques could translate into better, faster Internet search engines.


At the turn of the third millennium, the Human Genome Project, to map the genetic code of a human being, had generated 25 gigabytes (a thousand million bytes) of information. At one petabyte, Gaia’s database will be 40 000 times as large.



11 September 2002

Although you can never be certain of predicting future developments in science, there is a good chance of a fundamental breakthrough in physics soon. With a series of unique experiments and missions designed to test our understanding of gravity, the European Space Agency (ESA) hopes to get to the very bottom of it.

Scientists will study space phenomena that do not seem to conform to our perceived understanding of gravity. In this way, they hope to develop a greater comprehension of the Universe.

Gravity is one of the four fundamental forces of nature. It shapes the Universe around us, allowing planets, stars and galaxies to form. However, the more scientists study gravity and its effects on celestial objects, the more mysteries they seem to uncover. One example is the so-called ‘Pioneer anomaly’, named after the NASA space probes Pioneer 10 and 11, on which the effect was first noticed. The anomaly was revealed when a number of spacecraft were seen to be affected by an unknown force that slowed them down. The same behaviour has now been detected on NASA’s Galileo and the joint ESA-NASA Ulysses spacecraft.

Scientists have known for a long time that there appears to be ‘too much’ gravity in the Universe. They can observe the effects of gravitational forces at work, but the origin of these forces cannot be identified. This ‘excess’ of gravity is usually referred to as ‘the missing mass problem’, since scientists assume that only matter can create gravity. It is therefore supposed that the Universe is filled with large quantities of ‘dark matter’ that has yet to be detected. What if that assumption is wrong?

Some theories suggest that gravity might pull a little harder at extreme distances than had previously been considered, so the concept of dark matter may not even be necessary. Alternatively, the anomalies may be the result of a fifth force of nature: one that is very weak and only shows up in the remotest regions of space. Space is an ideal testing ground to examine the existing theories. In the apparent weightlessness of space, scientists can detect the most delicate of forces and can measure them with extreme accuracy.

Developing an ambitious series of space experiments and missions, ESA is focusing its efforts on testing Albert Einstein’s Theory of General Relativity, the most advanced description of gravity ever formulated. One of the first objectives is the detection of gravitational waves. General Relativity has predicted their existence but, so far, they remain undetected. These waves should travel through space like ripples on a pond. LISA, a joint ESA-NASA mission, will be the first space mission to attempt to detect such gravitational waves. Finding them would be the ultimate test of General Relativity. A second objective, to be tested by the ESA Gaia and BepiColombo missions, will be to measure precisely how matter distorts space, searching for any deviation in the amount predicted by General Relativity. Microscope, a mission carried out in coordination with the French National Space Agency (CNES), is designed to test a concept from General Relativity called The Principle of Equivalence. According to this, objects are accelerated by gravity in the same way, independent of their mass and chemical composition. If Microscope detects a violation of this principle, it could be the clearest sign yet of a new dimension to gravity, known as quantum gravity.

Quantum gravity is a much-sought-after theory. Its purpose is to reconcile Einstein’s General Relativity with quantum physics, the most advanced theory describing the fundamental forces in Nature, with the exception of gravity. Quantum gravity supposes that space is granular on the smallest of scales. In a similar way, for example, a beach appears smooth from a distance but is actually composed of individual pieces of sand. Hyper, a mission currently under study at ESA would attempt to detect the quantum granularity of space, as one of its investigations into gravity. Looking further into the future, ESA has taken the first steps in defining a mission which would examine directly the Pioneer anomaly.

With this series of missions, ESA will carry out a unique investigation into the very nature of gravity. This may well provide the next fundamental breakthrough in our understanding of the Universe.

Note to editors


The Laser Interferometer Space Antenna (LISA) is a joint mission with NASA. It is a three-spacecraft mission, designed to detect the ‘ripples’ in space given out by massive black holes. Such ripples are called ‘gravitational waves’ and are a prediction of Einstein’s General Relativity. As yet, they have never been observed and LISA will be the first mission to attempt detection from space. It is scheduled for launch in 2011.


Gaia is a mission that will conduct a census of one thousand million stars in our galaxy. It will monitor each of its target stars about 100 times over a five-year period, precisely charting their movements and changes in brightness. Gaia will be launched on a Russian Soyuz-Fregat rocket sometime in the period 2010-2012. It is expected to discover hundreds of thousands of new celestial objects, such as extrasolar planets and failed stars called brown dwarfs. Within our own Solar System, Gaia should identify tens of thousands of asteroids. During its investigations, Gaia will also be able to measure precisely how matter distorts space, so bending starlight, and will search for any deviation in the amount predicted by General Relativity.


Microscope (MICROsatellite ` trannie Compensie pour l’Observation du Principe d’Equivalence) will test the Equivalence Principle of the general theory of relativity. According to this principle, all objects, independently of their mass and composition, acquire the same acceleration when subject to a gravitational field. Microscope will find out if this principle is correct and universal. If the principle is violated, it may reveal a new, as yet undiscovered, natural force or phenomena at work. It may give us a more complete understanding of the true nature of gravity and of the laws of nature. Scheduled for launch in 2005, Microscope is a joint mission with the French National Space Agency (CNES).


BepiColombo will be a collection of three spacecraft that will provide the most complete exploration yet of Mercury, the innermost planet. The technology required for BepiColombo is being developed at present and the mission is scheduled for launch in 2011. One component of BepiColombo will map the planet, another will investigate its magnetic field and a third will land on Mercury, to study the surface. Among other investigations, BepiColombo will be able to measure precisely how matter distorts space, searching for any deviation in the amount predicted by General Relativity. With BepiColombo, Mars Express, and Venus Express, ESA is the only space agency in the world with current plans to visit each planet in the inner Solar System.

Contact details

Dr Michael Perryman
senior astrophysicist
The Netherlands
Tel.: +31 71 565 3615

Science Programme Communication Service
The Netherlands
Tel.: +31 71 565 3223



18 June 2002

An interview with Didier Queloz, one of the world’s most successful planet hunters.

The last five days have witnessed the unprecedented announcement of 25 new planet discoveries. These discoveries are split almost evenly between European and American astronomers. Didier Queloz and his colleagues at the Observatoire de Genève, Switzerland, have found a dozen of the new planets. Their discoveries include the most tantalising one yet: a planet that closely resembles Jupiter in our own Solar System. The find brings astronomers another step closer to detecting an Earth-like world.

Queloz is a member of ESA’s Scientific Advisory Group for its Darwin planet-search mission. On Friday 14 June 2002, Queloz previewed his latest work at ESA’s European Space Research and Technology Centre (ESTEC) in the Netherlands.

Q: Which new discoveries have you made?

A: We have found 12 new planets. Among them, a new multiple system and most excitingly, a planet very similar to Jupiter (the biggest planet in our Solar System) in the sense that it is about the mass of Jupiter and has a similar orbit. Such planets are called Jupiter analogues by planet hunters and have long been a goal of such searches. It takes 7 years to orbit its star whereas Jupiter takes 12 years (known as the orbital period). The radius of its orbit is about 3.7 AU and Jupiter’s is 5.2 AU. (1 AU is the distance between the Earth and the Sun.and is about 150 million kilometres.) The key element, however, is that it has a circular orbit, not an elliptical one. This reminds us strongly of our own Solar System.

Q: The American-led team announced a much larger planet in an elliptical orbit at about the same distance from another star as Jupiter is from our own Sun. Together with your own Jupiter analogue, do these discoveries mean that planet hunting has entered a new phase?

A: Yes, we are getting much closer to seeing solar systems like our own. The first planets we detected were the ones with short periods, completing an orbit in just a few days. They were the easiest to detect because they give the largest signals. Long-period planets take many years to complete a single orbit and you have to track them for a whole orbit. We have been following this one from the beginning (nearly a decade). They also require better sensitivity. This new planet makes its star move by just 17 metres every second compared to 59 metres per second for the first planet we detected in 1995. Now that we can see long-period planets, we can check for multiple planets in systems already known to contain a single planet and also look for Jupiter analogues that may indicate solar systems like our own. In this way, we can build up a more complete picture of the variety of planetary systems.

Q: What does the future hold for European planet searches from the ground?

A: The future is great. We are building a new instrument for European astronomers with the European Southern Observatory (ESO). This instrument is called HARPS and will be installed on the 3.6 metre telescope in La Silla in Chile. Compared to what we are doing today, HARPS will be about 100 times more efficient, allowing us to reach sensitivities of about 20-30 centimetres per second. We are planning to test it in the laboratory in one month’s time and we have commissioning time scheduled on the telescope in February next year.

Q: How important are ESA’s space-based planet search missions?

A: They are essential. To me, the Eddington mission is really the next step because it is the only way to reach Earth-like systems. Eddington will use the transit method and detect the drop in a star’s light, caused by a planet orbiting in front of it and if you want to get enough accuracy to detect the transit of an Earth- sized world you need to go into space. Eddington will detect ten or a hundred times more planets than we can from the ground. Then Gaia will open another window because it should detect something like ten thousand planets. This is a crucial next step after Eddington because if you look at the past history of stellar astrophysics, people start to understand what is going on only when they can study a few thousand examples of celestial objects.

Q: Finally, the Darwin mission will detect light from Earth-like worlds and analyse their atmospheres for signs of life. What do you consider are its chances of success?

A: ESA’s Darwin is a fantastic project for me because, behind all of this planet quest, is this question of life on other worlds. I am optimistic. Why should Earth be a kind of strange system with life? If we try to look for other intelligence, however, then I think they might be rare; perhaps there is only one civilisation per galaxy. But for basic life, I’m sure it has to be there. So, Darwin is very likely to be successful.

About ESA’s planet-search missions

ESA’s planet-search missions, Eddington, Gaia and Darwin are part of the Cosmic Vision 2020 science programme.

Eddington is scheduled to launch in 2008 and, as well as planet searches, will be capable of detecting the equivalent of earthquakes on nearby stars, giving astronomers key data about their interiors.

Gaia will be launched no later than 2012 and will survey the nearest one billion stars to provide the most precise positional and brightness data ever. This will be invaluable to every aspect of astronomy, from nearby asteroid searches in our Solar System to cosmology and the fate of the Universe. Gaia will detect planets by the transit method and by the way stars wobble in response to their planets’ gravitational pulls.

Finally, Darwin is in the planning phase, with new technology being vigorously developed. It will launch around the middle of the next decade and consist of a flotilla of eight spacecraft that will fly in formation and combine their observations to detect the light from Earth-like planets around other stars. By analysing that light, astronomers will be able to deduce the chemical compositions of distant planets’ atmospheres and search for the telltale chemicals related to life.



12 April 2002

In the past five weeks two asteroids have passed close by Earth, at distances of 1.2 and 3 times the distance to the Moon. Another asteroid has recently been shown to have a 1 in 300 chance of colliding with Earth in 2880. Monitoring known asteroids allows astronomers to predict which may collide with Earth. But that is only true for the asteroids we know of. What about those that lie in the asteroid blind spot between the Sun and Earth? The European Space Agency is studying ways in which its missions can assist in monitoring these unseen but potentially hazardous asteroids.

It is difficult to estimate the danger posed by asteroids. This is, in part, because astronomers do not yet know how many asteroids there are. A recent discovery, made using data from ESA’s Infrared Space Observatory (ISO), showed that there could be nearly two million asteroids larger than one kilometre in the main asteroid belt, between Mars and Jupiter. That is more than twice as many as previously thought.

In addition, even when an asteroid is identified many observations must be made before it is known whether or not it will come close to, or even collide with, Earth.

If the asteroids remained in the main-belt, they would pose no danger to Earth. However, they can be thrown into different orbits by collisions with other asteroids or by the influence of Jupiter’s gravitational field. If their new orbits cross the Earth’s orbit, they could one day collide with our planet, inflicting unprecedented devastation.

A number of ground-based searches are already underway to find as many potentially hazardous asteroids (PHAs) as possible but there is a notorious ‘blind spot’ that telescopes on Earth can never peer into. It is the region of space inside Earth’s orbit, towards the Sun. From Earth, astronomical observations close to the Sun are almost impossible because it means observing during the daytime when only the brightest celestial objects stand out from the blue sky. That means asteroids lurking in this region of space can ‘sneak up’ on the Earth undetected. Asteroid 2002 EM7, which passed close by the Earth on 8 March this year, was one such object and was only detected after it crossed Earth’s orbit to appear briefly in the night sky, before it crossed back into the glare of the Sun.

About 550 similar asteroids are known. They are called the Atens and spend most of their time inside Earth’s orbit, close to the Sun. Traditional estimates suggest there may be several thousand in total and tracking them from Earth is next to impossible. However, a study performed for ESA has shown that the Gaia spacecraft will be able to see clearly into this ‘blind spot’ and keep precise track of the Aten population.

Frangois Mignard of Observatoire de la Cttes d’Azur, France, conducted the study. He found that Gaia would be ideal because it is designed to measure the position of celestial objects with unprecedented accuracy. In addition, since there is no atmosphere in space to scatter the Sun’s rays and create a blinding blue sky, Gaia can see close to the Sun without disturbance.

Gaia is expected to be launched around 2010. Even if ground-based searches have spotted more Atens by that time, the mission still has an essential role to play because it will reveal their orbits to a precision 30 times better than any observation from the ground, thus identifying whether any pose a danger to Earth.

“To know how close these objects will come to Earth is very dependent on how accurately one can measure their orbits. That’s the main contribution that Gaia can be expected to make,” says Michael Perryman, project scientist for Gaia, at ESA’s European Space Research and Technology Centre in the Netherlands.

Gaia’s data will also provide astronomers with a first estimate of these objects’ composition. This knowledge could help to determine methods to divert or destroy asteroids that are set on a collision course with Earth.

Several ESA missions are contributing, or will contribute, to our understanding of minor bodies of the Solar System: these include ISO, Gaia and Rosetta, which will study asteroids Siwa and Otawara. ESA is also considering the addition of an asteroid spotting telescope to its BepiColombo mission.



27 June 2001

About 100 European scientists are gathering in ESTEC over the next two days to consider plans for the scientific organisation of Gaia – ESA’s ambitious mission to help unravel the origin and evolution of our Galaxy. Experts in general relativity, extra-solar planets, and a whole host of other relevant disciplines are coming together to pool their knowledge about how Gaia can best be organised.

Gaia was accepted as one of the next cornerstones missions of the ESA science programme in October 2000. It is an ambitious experiment to map the positions of about one billion stars in our Galaxy, providing an enormous advance in the knowledge of our Galaxy’s structure and composition, and its origin and evolution.

ESA established its world leadership in this field of space science through the Hipparcos star mapping satellite, operated between 1989-1993; Gaia will improve on the Hipparcos results by a colossal three orders of magnitude (factor of 1000) improvement in accuracy, and four orders of magnitude (factor of 10000) in the total number of stars observed.

Through its five-year sky scanning, Gaia will compile an unprecedented census of our Solar System, our Galaxy, and beyond: it will detect new Solar System objects including near-Earth asteroids, tens of thousands of extra-solar planets, hundreds of millions of variable and binary stars, and hundreds of thousands of supernovae. The ESTEC meeting is the first step towards finalising the satellite design, designing the complex data analysis system, and preparing the diverse package of computer programmes necessary to analyse the mass of data that the Gaia satellite will send to Earth after its launch about a decade from now. Experts from a diverse range of disciplines are contributing to these preparations for Gaia.

Gaia project scientist Michael Perryman has no doubt that ESA and the European scientific community can deliver what the recently completed Concept and Technology Study has claimed, and sees a sound organisation of the scientific effort as an essential element of the mission’s success. “There is a lot of excitement about Gaia’s expected scientific impact, our scientific collaborators are pushing hard for ESA to get moving with this programme, and everyone is just hoping that the Science Programme Committee’s directive of a launch not later than 2012 will mean exactly that.”

The impressive line-up of European astronomers participating in this week’s ESTEC meeting certainly provides confirmation of the interest and excitement that the Gaia mission is generating within the European scientific community.



18 June 2001

The 36th annual “John C. Lindsay Memorial Lecture” was delivered by ESA scientist Michael Perryman at NASA’s Goddard Space Flight Center in Maryland, USA. The lecture, on the “Three Dimensional Structure of our Galaxy”, was based on the results from ESA’s Hipparcos mission.

In his lecture, on 8 June, Dr Perryman described how measuring distances to the stars is one of the great challenges which continues to face experimental astronomy and discussed ESA’s past and future contributions to this field.

ESA’s Hipparcos mission (1981-97) determined accurate distances and space motions for 120 000 stars. These measurements have contributed to furthering our understanding of the formation and evolution of our Galaxy, and the stars within it.

Building on the success of Hipparcos and Europe’s expertise in astrometry ESA’s Gaia mission will map the three-dimensional structure of more than one billion stars extending throughout our Galaxy. The scientific return from such a mission is immense and touches on areas as diverse as extra-solar planetary systems and near-Earth objects; the age of individual stars and the age of our Universe; it will probe how stars evolve and will even impact on fundamental physics.

An annual event since 1966, the Lindsay Memorial Lecture is named for the Associate Chief of the Goddard Space Sciences Division and head of the Goddard solar physics program, John C. Lindsay (1916-1965), who pioneered the exploration of the Sun by both satellite and rocket-borne experiments.

The annual lecture coincides with the John C. Lindsay Memorial Award, which is given annually to an employee of the Goddard Space Flight Centre for an outstanding contribution to space science – the 2001 award was presented to Dr Donald Reames for his discovery of trans-iron elements in solar energetic particle events.

Dr Perryman’s lecture was introduced by the Director of Space Sciences at Goddard, Dr Jonathon F. Ormes, and the lecture was attended by the Goddard Space Flight Center Director, Alphonso V. Diaz, by Mrs Lindsay, and by more than 400 Goddard employees and other guests.



14 May 2001

Dozens of young scientists from all over Europe have gathered this week at Les Houches in Savoie, France, for intensive briefings on ESA’s next star-mapping satellite, Gaia. As the successor to the very successful Hipparcos space astrometry project, Gaia was approved last year as an ESA Cornerstone mission to be launched around 2012. Engaging the interest and participation of the next generation of astronomers will be vital for the project’s success.

The Hipparcos satellite (1989-93) revolutionized astrometry, the science of star measurement, by fixing the positions, brightnesses, colours and variations of millions of stars in our vicinity far more accurately than ever before. Astrometry was previously a difficult, backwater subject of interest to only a few specialists. Hipparcos changed all that, with results that are still impacting on every branch of astronomy, from comets to cosmology.

Gaia will be 100 times better than Hipparcos. By charting a billion stars, to much greater distances than Hipparcos, it will give an unprecedented picture of the positions and motions of stars across most of the Milky Way Galaxy. Besides transforming the science of stars and galaxies, Gaia will be a top discoverer of asteroids and alien planets.

“Gaia will deliver its first results more than ten years from now,” notes Michael Perryman, Gaia’s project scientist. “Key individuals have already devoted half their working lives to conceiving and accomplishing Hipparcos, and to inventing Gaia. Who’ll pick up the baton when they retire? That’s the question.”



23 March 2001

A 100 metre-wide space rock known as 2001 EC16 paid a passing visit to Earth’s vicinity earlier today. As it swept by at a little over 1.7 million km from Earth – approximately four and a half lunar distances – the only people to pay it much attention were a dedicated band of astronomers.

However, this will not always be the case. Although there was no danger of a collision between the Earth and 2001 EC16, the day will surely come when luck runs out for our world (and humanity). Our only chance of survival is to detect the space invader long before a head-on collision occurs. This is where two of ESA’s future missions – Gaia and BepiColombo – may be able to play a vital role in forewarning us of impending impacts.

Gaia will be ESA’s successor to the extremely successful Hipparcos astrometry mission. As well as measuring the positions and brightness of stars and galaxies with unprecedented precision, Gaia will be able to detect all kinds of transient objects in its field of view – supernovae, flaring stars and … asteroids.

“Gaia will detect objects brighter than magnitude 20, so we should observe about one billion objects over the whole sky,” said project scientist Michael Perryman. “This means that if there is something there, we will see it. In the case of near-Earth asteroids (NEOs), we should find objects as small as 500 metres in diameter.”

“The precision optics on Gaia will also give a colossal improvement in orbital measurements, allowing astronomers to make very precise, long-term orbit determinations,” he added. “This will allow them to work out whether asteroids measured by Gaia will eventually collide with Earth.”

“Although most of the large near-Earth objects will probably have been found by the time of Gaia’s launch around 2010,” he explained, “the NEO catalogue, compiled from ground observations, will not contain all of the class of NEOs called Atens – asteroids that spend much of their time inside Earth’s orbit. Gaia will be able to observe fairly close to the Sun, so it will carry out a reasonably comprehensive survey of these objects.”

Even Gaia will not be able to detect the entire population of asteroids that cross Earth’s orbit and disappear in the glare of the Sun. However, another ESA mission should make a significant contribution to the ongoing census of potentially hazardous asteroids.

Although BepiColombo’s prime objective is to explore Mercury, it will also be able to search for unknown asteroids in the uncharted region of space between the planet nearest to the Sun and our Earth. These NEOs are particularly dangerous, since they can approach the Earth unseen against the brilliance of the Sun.

“The BepiColombo mission will involve two orbiters and a lander,” explained project scientist Rejean Grard. “One of the orbiters will be used for planet-wide remote sensing and radio science on a polar orbit with periapsis and apoapsis altitudes of 400 and 1500 km. However we are also planning to have a telescope on this orbiter.”

“This telescope would be able to monitor a strip of sky of 6 degrees by 360 degrees as it looks along the orbiter’s direction of motion,” he added. “By detecting asteroids that cross this field of view and comparing measurements made at different times, we could determine their orbits. Preliminary evaluations indicate that there could be up to 100 objects in the selected strip of sky at any one time.”

The Cosmic Shooting Gallery.

2001 EC16 belongs to a growing family of space rocks larger than 100 meters across that can come closer to Earth than 0.05 AU (7.5 million km). Fortunately, none of the known NEOs are presently on a collision course with our planet, although astronomers are finding new ones all the time. At the present time, 291 known potentially hazardous asteroids have been detected.

How many NEOs are out there? No-one knows. Astronomers estimate that there are between 750 and 1100 near-Earth asteroids bigger than 1 kilometre in diameter. There are probably millions of smaller objects in orbits that carry them close to Earth.

Why does it matter? The amount of damage caused by an asteroid impact depends on its size. Asteroids bigger than 1 kilometre would release energy equivalent to 100 000 megatonnes of TNT – equivalent to 10 million times the power of the atomic bomb that flattened Hiroshima. The result would be devastation on a global scale.

The good news is that such events happen on average only once every 300 000 years. The bad news is that collisions with medium-sized objects are much more frequent – once in a few thousand years on average.

Even objects the size of 2001 EC16 pack a significant punch. In 1908, an asteroid or comet just 50 metres across blew up in the atmosphere above Siberia. If this explosion had occurred over central London, the entire city would have been flattened.



13 October 2000

At its 92nd meeting, on 11-12 October 2000, ESA’s Science Programme Committee took the final step to consolidate the future of the science programme by unanimously endorsing the recommendations of the Space Science Advisory Committee of 15 September, which proposed a package to be implemented in the years 2008-2013.

The package consists of five missions and one reserve, namely:

  • The Cornerstone BepiColombo to explore the planet Mercury, which will be the fifth Cornerstone of Horizons 2000, to be launched in 2009 in collaboration with Japan;
  • The Cornerstone Gaia, which will analyse the composition, formation and evolution of our Galaxy by mapping with unprecedented precision one billion stars, to be launched no later than 2012;
  • The Cornerstone LISA, the first gravitational waves space observatory, in collaboration with NASA, at the cost of one Flexi-mission
  • The Flexi-mission NGST, the Next Generation Space Telescope, again in collaboration with NASA;
  • The Flexi-mission Solar Orbiter, the successor of the SOHO and Ulysses missions
  • The “reserve” Flexi-mission Eddington, a mission to map stellar evolution and find habitable planets, which could be implemented depending on the NGST and LISA schedules or provision of further resources.

The SSAC recommended a package instead of a limited number of missions, because the schedule of both NGST and LISA is outside of the control of ESA. These are all exciting missions, which could be implemented between 2008 and 2013 if the yearly budget were to remain at the present level, albeit with a yearly compensation for inflation.

The SPC , while endorsing the SSAC recommendations, added the following resolution:

The SPC supports the recommendation of the SSAC regarding the decision on future Cornerstones and the selection of F2/F3 missions (SSAC(2000)4).
The SPC reiterates the need to revisit the implementation of the selected missions at each decision on the Level of Resources.
The SPC emphasises the need to maintain flexibility for new ideas and the earliest appropriate implementation of Gaia.

With the choices made, by around 2013, ESA will also substantially contribute to creating a catalogue of dangerous NEO’s.

The SPC also approved the other recommendations of the SSAC: – a support costing up to 2 MEuro to the mission COROT (COnvection, ROtation and planetary Transits ) of CNES; – a support costing up to 5 Meuro to the mission MICROSCOPE: MICROSatellite “` trannie COmpensie” pour l’Observation du Principe d’Equivalence.

In return for the support, both missions will be “europeanised”, the details are yet to be worked out.

These missions will also fill the foreseen “gap” in launches of ESA scientific missions, which will extend from 2003 to 2007.

In 2004 the IR mission ASTRO-F, of the Institute of Space and Astronautical Sciences (ISAS) of Japan will also be launched. The SPC recommended the collaboration between ESA and ISAS on this mission, for a total cost to ESA of approximately 3.8 Meuro.

Finally, the SPC will decide the implementation of SMART-2, a technological mission supporting future cornerstones, at an extraordinary meeting to be held on 8 November 2000.

For further information, please contact:

Mr. Hugo Marie
ESA Science Programme Communication Service
Tel: +33 (0)1 5369 7106
Fax: +31 (0)1 5369 7236

Mr. Franco Bonacina
Media Relations Office
Tel: +33 (0) 1 53 69 7155
Fax: +33 (0) 1 53 69 7690



02 December 1998

The Gaia workshop, held at the Lorentz Centre in Leiden (23-27 November), provided many European scientists with an opportunity to consider the scientific potential of the Gaia astrometric mission in the light of the technical study of the instrument just completed by Matra Marconi Space.

The Gaia mission aims to observe more than one thousand million (1 billion) stars and for each of these stars to provide accurate three-dimensional positions, space velocities, and related information (for example, broad-band photometric measurements).

From the workshop discussions and presentations it is clear that only a large scale galactic survey reaching microarcsecond accuracy for the astrometric parameters can rigorously address the fundamental questions of the formation and evolution of our Galaxy. As a by-product of the mission, many important astrophysical issues will also be addressed. These include distance scale and luminosity calibrations, and the search for dark matter in the Galaxy. In addition Gaia will detect large numbers of extrasolar planets and brown dwarfs, hundreds of thousands of new asteroids and millions of multiple star systems. By the end of the five-year mission Gaia observations will result in an unprecedented stereoscopic census of the Galaxy.

In addition to lively discussions on the scientific potential of Gaia, the workshop also considered the potential difficulties associated with the large data volume which will be created by Gaia. A five-year mission which will generate astrometric and photometric measurements for one billion stars presents a challange in terms of data storage and data analysis. Fortunately many large-scale projects are already considering solutions to these problems – solutions from which Gaia can benefit.



23 November 1998

This week plans for the Gaia space astrometry mission will be presented to more than 70 scientists from all over Europe when they gather in Leiden (Netherlands) for the Gaia workshop.

Hosted by The Lorentz Center and Leiden Observatory (University of Leiden), the workshop will provide scientists with the opportunity to learn about the current status and scientific prospects of Gaia. They will also have the opportunity to participate in discussions aimed at consolidating the scientific and technical report to be prepared for the ESA advisory groups.

Gaia (Global Astrometric Interferometer for Astrophysics) is an advanced astrometric mission proposed, in 1995, as a Cornerstone Mission within the ESA Horizon 2000+ science plan, which aims:

  • to measure distances and velocities of more than a billion stars in our Galaxy
  • to provide:
    • highly accurate astrometric data: positions, distances and proper motions (10 microarcsecond at 15 mag);
    • multiplicity and orbital motions;
    • multi-colour photometry at hundreds of separate epochs;
    • radial velocities (a few km/sec at 17 mag).

Gaia’s unique observational strengths are:

  • its unprecedented accuracy (2-3 orders of magnitudes more accurate than Hipparcos, and five orders of magnitude more accurate than ground observations);
  • its extremely large sample observational capabilities (with one billion stars, the catalogue will be 10,000 times larger than Hipparcos; and it will observe 1 per cent of the total number of stars in our Galaxy);
  • its very faint limiting magnitude (at 20 mag, more than 5 orders of magnitude fainter than the completeness limit of Hipparcos);
  • its on-board source detection and measurement capabilities complete to the detection limit of about 20 mag. This will ensure complete and unbiased samples at the faintest magnitudes, and will mean that variables, burst sources, lensing events, etc will be measured as they occur.

As a result Gaia will uniquely address astrophysical issues such as:

  • the formation and evolution of our Galaxy;
  • dynamics of the Local Group Galaxies;
  • the occurrence and statistics of planetary systems (some 200,000 stars within 200 parsec will be rigorously scrutinised for the presence of Jupiter mass planetary companions);
  • wide angle space metric analyses;
  • the luminosity and dynamics of rare astrophysical objects.

3 thoughts on “European Space Agency, ESA

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