In November 2018, the Euclid mission passed its critical design review, marking the successful completion of a major phase in the progress of the project and clearing the way to start assembling the whole spacecraft.
Euclid, a mission devised to provide insight into the nature of dark energy and dark matter by accurate measurement of the accelerated expansion of the Universe, emerged from two mission concepts that were proposed in response to the ESA Cosmic Vision 2015-2025 Call for Proposals, issued in March 2007: the DUNE - Dark Universe Explorer - mission proposed to measure the effects of weak gravitational lensing; the SPACE - Spectroscopic All Sky Cosmic Explorer - mission, aimed at measuring the baryonic acoustic oscillations and redshift-space distortion patterns in the Universe.
In October 2007 the ESA advisory structure selected both proposals to enter the assessment study phase, considering them as equally relevant to the investigation of dark energy. ESA then appointed a Concept Advisory Team with the task of identifying the best possible concept for the dark energy mission to be studied during this phase. This team recommended a combined mission which could simultaneously measure weak lensing and baryonic acoustic oscillations (BAOs). The new mission concept was called Euclid, honouring the Greek mathematician Euclid of Alexandria (~300 BC) who is considered as the father of geometry.
The ESA internal pre-assessment phase for Euclid ran from November 2007 until May 2008. The outcome of this study was a preliminary design for the Euclid mission and its payload which formed the basis for the Invitation to Tender that was issued to Industry in May 2008. A parallel competitive contract was awarded to EADS Astrium Friedrichshafen (Germany) and Thales Alenia Space (Italy); these industrial activities were concluded in September 2009.
Two instrument consortia responded to ESA's call for Declaration of Interest for payload studies issued in May 2008. These studies ran from October 2008 until August 2009.
The report of the assessment study, which includes the Euclid science case together with a synthesis of the industrial and instrument consortium studies, was presented to the scientific community in December 2009. In addition, an independent technical review of the assessment study was conducted by ESA. The recommendations of the review board were presented to the scientific community also in December 2009.
In early 2010 ESA's Science Programme Committee recommended that Euclid, along with two other M-class candidate missions (PLATO and Solar Orbiter) proceed to the next phase: a more detailed definition phase during which period the cost and implementation schedule for the mission must be established. This detailed definition phase was completed in mid 2011.
In October 2011, Euclid was selected by the SPC as one of the first two medium-class missions of the Cosmic Vision 2015-2025 plan; Solar Orbiter was the other mission selected at the time.
Euclid received final approval to move into the full construction phase at the SPC meeting in June 2012. At this meeting, the SPC 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. Nearly 1000 scientists from more than 100 institutes form the Euclid Consortium building the instruments and participating in the scientific harvest of the mission. The consortium comprises scientists from 13 European countries: Austria, Denmark, France, Finland, Germany, Italy, the Netherlands, Norway, Portugal, Romania, Spain, Switzerland and the UK. It also includes a number of US scientists, including 40 nominated by NASA. The Consortium is led by Yannick Mellier, Institut d'Astrophysique de Paris, France.
In December 2012, Astrium SAS (Toulouse) has been contracted to design and build the payload module, which includes the telescope and the accommodation for the instruments, which are to be delivered by the Euclid Consortium.
Thales Alenia Space, was selected as the Prime Contractor, with the overall responsible for the building of Euclid satellite, in June 2013.
Euclid passed its preliminary design review in 2015. The successful outcome of this major milestone provided confidence that the spacecraft and its payload can be built, and that the science can be done.
In November 2018, the Euclid mission 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 structural and thermal model of the Euclid spacecraft completed its thermal qualification tests in September 2019 at the Thales Alenia Space premises in Cannes, France.