ESA: Dark Universe Mission (Euclid)

[bystander]

Dark Universe Mission Blueprint Complete
ESA Space Science | UK Space Agency | 2012 June 20

Artist’s impression of Euclid. (Credits: ESA/C. Carreau)

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ESA’s Euclid mission to explore the hidden side of the Universe – dark energy and dark matter – reached an important milestone today that will see it head towards full construction.

Selected in October 2011 alongside Solar Orbiter as one of the first two medium-class missions of the Cosmic Vision 2015–25 plan, Euclid received final approval from ESA’s Science Programme Committee to move into the full construction phase, leading to its launch in 2020.

The committee also formalised an agreement between ESA and funding agencies in a number of its Member States to develop Euclid’s two scientific instruments, a visible-wavelength camera and a near-infrared camera/spectrometer, and the large distributed processing system needed to analyse the data they produce.

Finally, the committee agreed on a Memorandum of Understanding between ESA and NASA that will see the US space agency help to provide infrared detectors.

Nearly 1000 scientists from 100 institutes form the Euclid Consortium building the instruments and participating in the scientific harvest of the mission.

“This formal adoption of the mission is a major milestone for a large scientific community, their funding agencies and also for European industry,” said Alvaro Giménez Cañete, ESA’s Director of Science and Robotic Exploration.

“It took a lot of hard work to get this far, but we now have a solid blueprint for a feasible space telescope which enables very accurate measurements that will bring to light the nature of dark energy,” said Yannick Mellier, the Euclid Consortium lead.

In the coming months, industry will be asked to make bids to supply spacecraft hardware, such as the telescope, power systems, attitude and orbit controls, and communications systems.

Euclid will use a 1.2-m diameter telescope and the two instruments to map the 3D distribution of up to two billion galaxies and dark matter associated with them, spread over more than one third of the whole sky.

Stretched across ten billion light-years, the mission will plot the evolution of the Universe’s structure over three-quarters of its history.

Euclid is optimised to answer one of the most important questions in modern cosmology: why is the Universe expanding at an accelerating rate, rather than slowing down due to the gravitational attraction of all the matter in it?

The discovery of this cosmic acceleration in 1998 was rewarded with the Nobel Prize for Physics in 2011 and yet we still do not know what causes it.

The term ‘dark energy’ is often used to signify this mysterious force, but by using Euclid to study its effects on the galaxies and clusters of galaxies across the Universe, astronomers hope to come much closer to understanding its true nature and influence.

“Euclid addresses the cosmology-themed questions of ESA’s Cosmic Vision and it’s fantastic that we are moving forward into the next stage of development – we’re one step closer to learning more about the Universe’s darkest secrets,” said René Laureijs, ESA’s Euclid project scientist.

Looking into the dark: Ahead with the Euclid mission
Max Planck Institute for Extraterrestrial Physics | 2012 June 20

Euclid jumps final hurdle
University College, London | 2012 June 20

Illuminating the dark: Ahead with the Euclid mission
UK Space Agency | 2012 June 21

Looking into the dark
University of Nottingham | 2012 June 21

Euclid and the Geometry of the Dark Universe
Universe Today | Jenny Winder | 2012 June 21

viewtopic.php?t=18412

[Ann]

Personally I'm thoroughly fascinated by dark energy, much more so than I'm intrigued by dark matter. If nothing else, dark energy represents a much larger chunk of the universe than dark matter, so semi-ignoring it is like closing one's eyes to three fourths of everything! Personally I'm somewhat bemused by my impression that astronomical community prefers to discuss dark matter over dark energy.

Well, now ESA and NASA are joining forces to find out more about 3/4 of the cosmos.

NASA signs on to European dark energy mission
Stephen Clark, Spaceflight Now, wrote on 26 January 2013:

NASA has agreed to provide infrared detectors for the European Space Agency's Euclid dark energy mission, a contribution worth approximately $50 million which buys U.S. scientists membership in a consortium of researchers steering the project's scientific objectives.

Artist's concept of the Euclid spacecraft. Credit: ESA

The Euclid mission, due to launch in 2020, is devoted to unraveling the nature of dark matter and dark energy, two constituencies making up more than 95 percent of the universe. Euclid will carry two science instruments and a 3.9-foot telescope to map the shape, distribution and brightness of two billion galaxies up to 10 billion years old.

Euclid will chart the rate of the universe's expansion over the last three-quarters of its history. Scientists attribute the universe's accelerating expansion to dark energy, a mysterious force comprising more than two-thirds of the mass-energy content in the cosmos.

Traditional matter, the stuff we can see and touch, makes up 4 percent of the universe. Dark matter, a more exotic set of poorly understood, invisible particles, fills a quarter of the universe.

Dark energy makes up about 70 percent of the composition of the cosmos. It's enough to counteract the gravitation pull of normal matter and dark matter, forcing the frontiers of the universe outward and accelerating the rate of its expansion.

Euclid will address the origin of dark energy, helping scientists determine if the force is a cosmological constant, an exception to Einstein's theory of general relativity, or some other property. During its six-year mission, Euclid will also yield clues about the fate of the universe.

NASA will provide 16 infrared detectors and four spare detectors for one of Euclid's two science instruments, the space agency announced Thursday.

"NASA is very proud to contribute to ESA's mission to understand one of the greatest science mysteries of our time," said John Grunsfeld, associate administrator for the agency's science mission directorate.

Euclid will cost ESA more than 600 million euros, or about $808 million. ESA's member states, funding the mission outside of ESA's collective framework, will fund nearly 25 percent of Euclid's cost.

Europe's financing, coupled with the value of NASA's contributions, will put Euclid's total cost at about $1 billion.

The 4,600-pound spacecraft is scheduled to launch on a Soyuz rocket in 2020. It will be stationed at the L2 Lagrange point one million miles from Earth.

NASA has nominated 40 scientists for the Euclid Consortium, an international group of 1,000 scientists overseeing development of Euclid's instruments and in charge of analyzing data from the mission after its launch.

"ESA's Euclid mission is designed to probe one of the most fundamental questions in modern cosmology, and we welcome NASA's contribution to this important endeavor, the most recent in a long history of cooperation in space science between our two agencies," said Alvaro Gimenez Canete, ESA's director of science and robotic exploration.

NASA is working on a U.S.-led mission to study dark energy. The Wide-Field Infrared Survey Telescope, or WFIRST, could launch by 2025 with adequate funding, according to NASA officials.

Ann

[bystander]

This artist's concept shows the Euclid spacecraft. The telescope will launch to an orbit around the Sun-Earth Lagrange point L2. (Image Credit: ESA/C. Carreau)

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NASA Officially Joins ESA's 'Dark Universe' Mission
NASA | JPL-Caltech | Euclid | 2013 Jan 24

NASA Joins ESA’s ‘Dark Universe’ Mission
ESA Space Science | 2013 Jan 24

Euclid overview
Euclid in depth

viewtopic.php?f=44&t=29232

[Chris Peterson]

Personally I'm thoroughly fascinated by dark energy, much more so than I'm intrigued by dark matter. If nothing else, dark energy represents a much larger chunk of the universe than dark matter, so semi-ignoring it is like closing one's eyes to three fourths of everything! Personally I'm somewhat bemused by my impression that astronomical community prefers to discuss dark matter over dark energy.

I agree, dark energy is much more interesting. After all, dark matter is probably just another kind of particle, not so different from other particles we already know about. Dark energy, on the other hand, is fundamental to cosmology in so many interesting ways.

I don't think your assessment of professional interest is entirely accurate, however. The thing is, dark matter is much more immediate to much observational astronomy, and to fundamental astronomical questions like how stars and galaxies form, and why we see the structures we see. Dark energy is hardly connected with most of this kind of astronomy at all, but is core to issues of cosmology- itself only a subset of the larger astronomical picture. Dark energy is the subject of intense study and discussion, but given the rather arcane theories around it, those discussions generally are pretty far from the sort of material that gets regularly reported on.

[bystander]

JPL to Lead U.S. Science Team for Dark Energy Mission
NASA | JPL-Caltech | Euclid | 2013 Feb 12

NASA Goddard Team to Participate in Dark Energy Mission
NASA | Goddard | LIBRAE | Euclid | 2013 Feb 12

Astrophysicists Join Mission to Solve 'Dark' Mysteries of Universe
John Hopkins University | Euclid | 2013 Feb 12

[bystander]

Euclid Dark Universe Mission Ready to Take Shape
ESA Science & Technology | Euclid | 2015 Dec 17

Artist's impression of Euclid. Credit: ESA/C. Carreau

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Euclid, ESA's dark Universe mission, has passed its preliminary design review, providing confidence that the spacecraft and its payload can be built. It's time to start 'cutting metal'.

"This is really a big step for the mission," says Giuseppe Racca, Euclid's project manager. "All the elements have been put together and evaluated. We now know that the mission is feasible and we can do the science."

First proposed to ESA in 2007, Euclid was selected as the second medium-class mission in the Cosmic Vision programme in October 2011. Italy's Thales Alenia Space was chosen as the prime contractor in 2013.

Since then, the mission's design has been studied and refined. This has involved a wide range of detailed technical designs, in addition to building and testing key components.

The outcome of Euclid's recent review was positive, opening the door to the industrial contractors and external instrument teams building the spacecraft and payload for real. Airbus Defence & Space in France will deliver the complete payload module incorporating a 1.2 m-diameter telescope feeding the two science instruments being developed by the Euclid Consortium. ...

[neufer]

[b][color=#0000FF][size=150]1) spherical aberration[/size][/color][/b]

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[b][color=#0000FF][size=150]3) astigmatism[/size][/color][/b]

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[b][color=#FF0000][size=100] Three-mirror anastigmat of Paul or Paul-Baker form. A Paul design has a parabolic primary with spherical secondary and tertiary mirrors; A Paul-Baker design (i.e., LSST) modifies the secondary slightly to achieve a flat focal plane.[/size][/color][/b]

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<<A three-mirror anastigmat is a telescope built with three curved mirrors, enabling it to minimize all three main optical aberrations - 1) spherical aberration, 2) coma, and 3) astigmatism. This is primarily used to enable wide fields of view, much larger than possible with telescopes with just one or two curved surfaces.

A telescope with only one curved mirror, such as a Newtonian telescope, will always have aberrations. If the mirror is spherical, it will suffer from spherical aberration. If the mirror is made parabolic, to correct the spherical aberration, then it must necessarily suffer from coma and astigmatism. With two curved mirrors, such as the Ritchey–Chrétien telescope, coma can be eliminated as well. This allows a larger useful field of view. However, such designs still suffer from astigmatism. This too can be cancelled by including a third curved optical element. When this element is a mirror, the result is a three-mirror anastigmat. In practice, the design may also include any number of flat fold mirrors, used to bend the optical path into more convenient configurations.

The first were proposed in 1935 by Maurice Paul. The basic idea behind Paul's solution is that spherical mirrors, with an aperture stop at the centre of curvature, have only spherical aberration - no coma or astigmatism (but they do produce an image on a curved surface of half the radius of the spherical mirror, for a mirror in air). So if the spherical aberration can be corrected, a very wide field of view can be obtained. This is similar to the conventional Schmidt design, but the Schmidt does this with a refractive corrector plate instead of a third mirror.

Paul's idea was to start with a Mersenne beam compressor, which looks like a Cassegrain made from two (confocal) paraboloids, with both the input and output beams collimated. The compressed input beam is then directed to a spherical tertiary mirror, which results in traditional spherical aberration. Paul's key insight is that the secondary can then be converted back to a spherical mirror. One way to look at this is to imagine the tertiary mirror, which suffers from spherical aberration, is replaced by a Schmidt telescope, with a correcting plate at its centre of curvature. If the radii of the secondary and tertiary are of the same magnitude, but opposite sign, and if the centre of curvature of the tertiary is placed directly at the vertex of the secondary mirror, then the Schmidt plate would lie on top of the paraboloid secondary mirror. Therefore the Schmidt plate required to make the tertiary mirror a Schmidt telescope is eliminated by the paraboloid figuring on the convex secondary of the Mersenne system, as each corrects the same magnitude of spherical aberration, but the opposite sign. Also, as the system of Mersenne + Schmidt is the sum of two anastigmats: the Mersenne system is an anastigmat, and so is the Schmidt system, the resultant system is also an anastigmat, as third-order aberrations are purely additive. In addition the secondary is now easier to fabricate. This design is also called a Mersenne-Schmidt, since it uses a Mersenne configuration as the corrector for a Schmidt telescope.

Paul-Baker: Large Synoptic Survey Telescope (LSST)

Paul's solution had a curved focal plane, but this was corrected in the Paul-Baker design, introduced in 1969 by James Gilbert Baker. The Paul-Baker design adds extra spacing and reshapes the secondary to elliptical, which corrects field curvature to obtain a flat focal plane.

Korsch: Euclid, James Webb Space Telescope (JWST)

A more general set of solutions was developed by Dietrich Korsch in 1972. A Korsch telescope is corrected for spherical aberration, coma, astigmatism, and field curvature, meaning that images on a flat detector will be the same size at the center as at the edges, and can have a wide field of view while ensuring that there is little stray light in the focal plane.>>

[bystander]

Key Milestone for Euclid Mission, Now Ready for Final Assembly
ESA | Science & Technology | Euclid

ESA's Euclid mission has passed its critical design review, marking the successful completion of a major phase in the progress of the project. The review verified that the overall mission architecture and detailed design of all its elements is complete, ensuring that it will be able to perform the unprecedented galaxy survey needed to tackle the mysteries of the dark Universe, and clearing the way to start assembling the whole spacecraft.

The critical design review (CDR) board meeting took place on 21 November in Noordwijk, the Netherlands. While the individual elements of Euclid – the spacecraft, scientific instruments, launcher, and the operational and science ground segments – had already passed their independent CDRs, the mission-level review focussed on the ensemble of all these elements and ascertained their capability to function together to accomplish the mission's goals. The review verified that the most realistic predictions of the combined performances are compliant with the mission requirements.

The review also assessed the feasibility of Euclid's survey with the designed flight hardware, which will image billions of galaxies across the cosmos at unprecedented sharpness and sensitivity during a nominal mission period of six years.

With the completion of this milestone that validated the whole project – from the spacecraft development to launch and operations, including also the observational methods and data analysis strategy – the assembly, integration and testing of the spacecraft flight model can begin. Immediately after launch, scheduled for June 2022, the ground segment will be ready to take over and start the operations to perform the groundbreaking sky survey.