Ludovic Duvet

Euclid: ESA's mission to map the geometry of the dark universe

Euclid is a space-borne survey mission developed and operated by ESA. It is designed to understand the origin of the Universes accelerating expansion. Euclid will use cosmological probes to investigate the nature of dark energy, dark matter and gravity by tracking their observational signatures on the geometry of the Universe and on the history of structure formation. The mission is optimised for the measurement of two independent cosmological probes: weak gravitational lensing and galaxy clustering. The payload consists of a 1.2 m Korsch telescope designed to provide a large field of view. The light is directed to two instruments provided by the Euclid Consortium: a visual imager (VIS) and a near-infrared spectrometer-photometer (NISP). Both instruments cover a large common field of view of 0.54 deg2, to be able to survey at least 15,000 deg2 for a nominal mission of 6 years. An overview of the mission will be presented: the scientific objectives, payload, satellite, and science operations. We report on the status of the Euclid mission with a foreseen launch in 2019.

The Euclid Mission

Euclid is a high precision survey mission under development by the European Space Agency to investigate the properties of Dark Energy and Dark Matter by means of a weak lensing and baryon acoustic oscillations experiments. The technical capabilities of Euclid are such that it also addresses other cosmological and astronomical topics, providing an unprecedented science legacy. The survey mission will carry out an imaging and spectroscopic survey of the entire extragalactic sky (20,000 deg2). Euclid carries a meter class telescope which feeds two instruments: a visible imager (VIS), a near-infrared photometer combined with a medium resolution spectrometer (NISP). The two instruments have identical sized field of views (0.5 deg2) and will operate simultaneously in step-and-stare mode. The nominal mission period is 5 years. We describe the mission, the satellite, and the payload concepts, which we have adopted at the start of the definition phase.

Euclid Mission: building of a reference survey

Euclid is an ESA Cosmic-Vision wide-field-space mission which is designed to explain the origin of the acceleration of Universe expansion. The mission will investigate at the same time two primary cosmological probes: Weak gravitational Lensing (WL) and Galaxy Clustering (in particular Baryon Acoustic Oscillations, BAO). The extreme precision requested on primary science objectives can only be achieved by observing a large number of galaxies distributed over the whole sky in order to probe the distribution of dark matter and galaxies at all scales. The extreme accuracy needed requires observation from space to limit all observational biases in the measurements. The definition of the Euclid survey, aiming at detecting billions of galaxies over 15 000 square degrees of the extragalactic sky, is a key parameter of the mission. It drives its scientific potential, its duration and the mass of the spacecraft. The construction of a Reference Survey derives from the high level science requirements for a Wide and a Deep survey. The definition of a main sequence of observations and the associated calibrations were indeed a major achievement of the Definition Phase. Implementation of this sequence demonstrated the feasibility of covering the requested area in less than 6 years while taking into account the overheads of space segment observing and maneuvering sequence. This reference mission will be used for sizing the spacecraft consumables needed for primary science. It will also set the framework for optimizing the time on the sky to fulfill the primary science and maximize the Euclid legacy.

Charge-coupled devices for the ESA Euclid M-class mission

The European Space Agency has funded e2v’s development of an image sensor for the visible instrument in the Euclid space telescope. Euclid has been selected for a medium class mission launch opportunity in 2020. The project aims to map the dark universe with two complementary methods; a galaxy red-shift survey and weak gravitational lensing using near infrared and visible instruments. The baseline for the visible instrument was to be the CCD203-82, which has been successfully flown on NASA’s Solar Dynamics Observatory. However, to optimise the device for Euclid, e2v have designed and manufactured the CCD273-84. This device has a higher-responsivity lower-noise amplifier, enhanced red response, parallel charge injection structures and narrower registers which improve low signal charge transfer efficiency. Development models for Euclid have been manufactured with a thinner gate dielectric than standard for improved tolerance to ionising radiation. This paper describes the imager sensor in detail and focuses on the novel aspects of the device, package and interface.

Successful evaluation for space applications of the 2048×1080 DMD

Next-generation infrared multi-object spectrographs (MOS) for ground-based and space telescopes could be based on MOEMS programmable slit masks. This astronomical technique is used extensively to investigate the formation and evolution of galaxies. ESA has engaged a study for a technical assessment of using a DMD from Texas Instruments for space applications. The DMD features 2048 × 1080 mirrors on a 13.68μm pitch, where each mirror can be independently switched between an ON (+12°) position and an OFF (-12°) position. For MOS applications in space, the device should work in vacuum, at low temperature, and each MOS exposure would last for typically 1500s with micromirrors held in a static state (either ON or OFF). A specific thermal/vacuum test chamber has been developed for test conditions down to -40°C at 10-5 mbar vacuum. Imaging capability for resolving each micromirror has also been developed for determining degradation in any single mirror. Our first tests reveal that the DMD remains fully operational at -40°C and in vacuum. A 1038 hours life test in space conditions, Total Ionizing Dose radiation, thermal cycling and vibrations/shocks have also been successfully completed. These results do not reveal any concerns regarding the ability of the DMD to meet environmental space requirements. Detailed analysis of micromirror throughputs has also been studied for a whole set of tests, and shows a rather low variation and no impact of the space environment. We have also developed a bench for MOS demonstration using MOEMS devices. DMD chip has been successfully tested revealing good contrast values as well as good functionality for applying any mask pattern, demonstrating its full ability for space instrumentation, especially in multi-object spectroscopy applications.

The Euclid VIS CCD detector design, development, and programme status

The focal plane array of the Euclid VIS instrument comprises 36 large area, back-illuminated, red-enhanced CCD detectors (designated CCD 273). These CCDs were specified by the Euclid VIS instrument team in close collaboration with ESA and e2v technologies. Prototypes were fabricated and tested through an ESA pre-development activity and the contract to qualify and manufacture flight CCDs is now underway. This paper describes the CCD requirements, the design (and design drivers) for the CCD and package, the current status of the CCD production programme and a summary of key performance measurements.

ESA's CCD test bench for the Euclid visible channel

The visual imaging instrument VIS on board Euclid baselines 36 newly designed CCD273-84 devices from e2v. While these new devices have a 4kx4k format with four readout nodes, the Euclid Imaging Consortium (EIC) has performed extensive test campaigns on both irradiated and un-irradiated devices of the 4kx1k Euclid precursor variant CCD204-22. In support of the CCD development and characterization, and to enable an independent assessment of the Euclid CCDs (the procurement of which is ESA’s responsibility), ESA/ESTEC has built a test bench. This test bench allows for a flexible operation and readout of the CCDs, originally for CCD204 and shortly also for CCD273-84. It provides the basic tools for noise and gain calibration, and CTI, QE, MTF and PRNU measurements. In addition, the bench provides scanning spot illumination with a spot size well below the pixel size, for measurement of the intra-pixel response of the CCDs before and after radiation damage. Such measurements are of great importance for the characterization and modeling of the VIS instrument’s PSF, in particular to enable the prediction of the evolution of the PSF shape under the influence of the L2 radiation environment during the mission. This set-up will also allow for simulation of typical Euclid sky images in the lab. The capabilities and validation of this bench at ESA are described in this paper.

Euclid near-infrared spectrophotometer instrument concept at the end of the phase A study

The Euclid mission objective is to map the geometry of the dark Universe by investigating the distance-redshift relationship and the evolution of cosmic structures. The NISP (Near Infrared Spectro-Photometer) is one of the two Euclid instruments operating in the near-IR spectral region (0.9-2μm). The instrument is composed of: - a cold (140K) optomechanical subsystem constituted by a SiC structure, an optical assembly, a filter wheel mechanism, a grism wheel mechanism, a calibration unit and a thermal control - a detection subsystem based on a mosaic of 16 Teledyne HAWAII2RG 2.4μm. The detection subsystem is mounted on the optomechanical subsystem structure - a warm electronic subsystem (280K) composed of a data processing / detector control unit and of an instrument control unit. This presentation will describe the architecture of the instrument, the expected performance and the technological key challenges. This paper is presented on behalf of the Euclid Consortium.

Space evaluation of 2048×1080 mirrors DMD chip for ESA's EUCLID Mission

Next-generation infrared astronomical instrumentation for ground-based and space telescopes could be based on MOEMS programmable slit masks for multi-object spectroscopy (MOS). This astronomical technique is used extensively to investigate the formation and evolution of galaxies. We are engaged in an ESA study for a technical assessment of using a DMD from Texas Instruments for space applications (for example in ESA EUCLID mission). The DMD features 2048×1080 mirrors on a 13.68μm pitch, where each mirror can be independently switched between an ON (+12°) position and an OFF (-12°) position. For MOS applications in space, the device should work in vacuum, at low temperature, and each MOS exposure would last for typically 1500s with micromirrors held in a static state (either ON or OFF). A specific thermal/vacuum test chamber has been developed for test conditions down to -40°C at 10-5 mbar vacuum. Imaging capability for resolving each micromirror has also been developed for determining degradation in any single mirror. Our first tests reveal that the DMD remains fully operational at -40°C and in vacuum. A 1038 hours life test in space conditions, Total Ionizing Dose radiation, thermal cycling and vibrations/shocks have also been successfully completed. These results do not reveal any concerns regarding the ability of the DMD to meet environmental space requirements. We have also developed a bench for MOS demonstration using MOEMS devices. DMD chip has been successfully tested revealing good contrast values as well as good functionality for applying any mask pattern, demonstrating its full ability for space instrumentation, especially in multi-object spectroscopy applications.

Quantum efficiency performances of the NIR European Large Format Array detectors tested at ESTEC

Publishers Note: This paper, originally published on 10/12/2015, was replaced with a corrected/revised version on 10/23/2015. If you downloaded the original PDF but are unable to access the revision, please contact SPIE Digital Library Customer Service for assistance. The Payload Technology Validation Section (SRE-FV) at ESTEC has the goal to validate new technology for future or on-going mission. In this framework, a test set up to characterize the quantum efficiency of near-infrared (NIR) detectors has been created. In the context of the NIR European Large Format Array (“LFA”), 3 deliverables detectors coming from SELEX-UK/ATC (UK) on one side, and CEA/LETI- CEA/IRFU-SOFRADIR (FR) on the other side were characterized. The quantum efficiency of an HAWAII-2RG detector from Teledyne was as well measured. The capability to compare on the same setup detectors from different manufacturers is a unique asset for the future mission preparation office. This publication will present the quantum efficiency results of a HAWAII-2RG detector from Teledyne with a 2.5um cut off compared to the LFA European detectors prototypes developed independently by SELEX-UK/ATC (UK) on one side, and CEA/LETI- CEA/IRFU-SOFRADIR (FR) on the other side.