PLATO (PLAnetary Transits and Oscillation of stars) is a candidate for the M3 Medium-size mission of the ESA Cosmic Vision programme (2015-2025 period). It is aimed at Earth-size and Earth-mass planet detection in the habitable zone of bright stars and their characterisation using the transit method and the asterosismology of their host star. That means observing more than 100 000 stars brighter than magnitude 11, and more than 1 000 000 brighter than magnitude 13, with a long continuous observing time for 20 % of them (2 to 3 years). This yields a need for an unusually long term signal stability. For the brighter stars, the noise requirement is less than 34 ppm.hr-1/2, from a frequency of 40 mHz down to 20 μHz, including all sources of noise like for instance the motion of the star images on the detectors and frequency beatings. Those extremely tight requirements result in a payload consisting of 32 synchronised, high aperture, wide field of view cameras thermally regulated down to -80°C, whose data are combined to increase the signal to noise performances. They are split into 4 different subsets pointing at 4 directions to widen the total field of view; stars in the centre of that field of view are observed by all 32 cameras. 2 extra cameras are used with color filters and provide pointing measurement to the spacecraft Attitude and Orbit Control System (AOCS) loop. The satellite is orbiting the Sun at the L2 Lagrange point. This paper presents the optical, electronic and electrical, thermal and mechanical designs devised to achieve those requirements, and the results from breadboards developed for the optics, the focal plane, the power supply and video electronics.
HARMONI is the E-ELT’s first light visible and near-infrared integral field spectrograph. It will provide four different spatial scales, ranging from coarse spaxels of 60 × 30 mas best suited for seeing limited observations, to 4 mas spaxels that Nyquist sample the diffraction limited point spread function of the E-ELT at near-infrared wavelengths. Each spaxel scale may be combined with eleven spectral settings, that provide a range of spectral resolving powers (R ~3500, 7500 and 20000) and instantaneous wavelength coverage spanning the 0.5 – 2.4 μm wavelength range of the instrument. In autumn 2015, the HARMONI project started the Preliminary Design Phase, following signature of the contract to design, build, test and commission the instrument, signed between the European Southern Observatory and the UK Science and Technology Facilities Council. Crucially, the contract also includes the preliminary design of the HARMONI Laser Tomographic Adaptive Optics system. The instrument’s technical specifications were finalized in the period leading up to contract signature. In this paper, we report on the first activity carried out during preliminary design, defining the baseline architecture for the system, and the trade-off studies leading up to the choice of baseline.
Innovative optical designs allow tackling the spot elongation issues in Shack-Hartman based laser guide star wavefront sensors. We propose two solutions using either a combination of two arrays of freeform microlenses, or a combination of freeform optics, to perform a shrinkage of the laser spots as well as a magnification of the SH focal plane. These approaches will drastically reduce the number of needed pixels, thus making possible the use of existing detectors. We present the recent advances on this activity as well as the estimation of performance, linearity and sensitivity of the compressed system in presence of aberrations.
HARMONI is a visible and NIR integral field spectrograph, providing the E-ELT’s core spectroscopic capability at first light. HARMONI will work at the diffraction limit of the E-ELT, thanks to a Classical and a Laser Tomographic AO system. In this paper, we present the system choices that have been made for these SCAO and LTAO modules. In particular, we describe the strategy developed for the different Wave-Front Sensors: pyramid for SCAO, the LGSWFS concept, the NGSWFS path, and the truth sensor capabilities. We present first potential implementations. And we asses the first system performance.
FIREBALL (the Faint Intergalactic Redshifted Emission Balloon, funded by CNES-NASA, PI C.Martin, Caltech) is a balloon-borne 1m telescope coupled to an ultraviolet Multi Object Spectrometer (MOS), designed to study the faint and diffuse emission of the circumgalactic medium. The third flight of the experiment is planned in summer 2017. The goal of this paper is to describe the accurate pointing system of the 5-metres high / 1500kg gondola - that has been designed to fulfill stringent pointing requirements: less than 1 arcsec in elevation and cross elevation, and about 1 arcmin in field rotation (around the line of sight axis), over long integration time (a few hours). The pointing system is based on a multi stage closed loop scheme (4 Degrees Of Freedom), relying on a 1DOF gondola azimuth controller, a 2DOF gimbal frame supporting a 1.2-meter plano siderostat, and a 1DOF field rotation control system. The attitude determination is based on the hybridization of two accurate sensors: a Fiber Optic Gyrometer measurement unit and a star sensor integrated inside the instrument. The manuscript presents the design of the ACS. We also focus on flight train stability issues - due to the pendulum and torsion modes -, on the geometric equations specific to a siderostat pointing system, and on the description of the tests facilities.
The Euclid mission objective is to understand why the expansion of the Universe is accelerating by mapping the geometry of the dark Universe by
investigating the distance-redshift relationship and tracing the evolution of cosmic structures. The Euclid project is part of ESA's Cosmic Vision
program with its launch planned for 2020.
The NISP (Near Infrared Spectro-Photometer) is one of the two Euclid instruments and is operating in the near-IR spectral region (0.9-2μm) as a
photometer and spectrometer. The instrument is composed of:
- a cold (135K) optomechanical subsystem consisting of a SiC structure, an optical assembly (corrector and camera lens), a filter wheel mechanism, a
grism wheel mechanism, a calibration unit and a thermal control system
- a detection subsystem based on a mosaic of 16 Teledyne HAWAII2RG cooled to 95K with their front-end readout electronic cooled to 140K,
integrated on a mechanical focal plane structure made with Molybdenum and Aluminum. The detection subsystem is mounted on the optomechanical
- a warm electronic subsystem (280K) composed of a data processing / detector control unit and of an instrument control unit that interfaces with the
spacecraft via a 1553 bus for command and control and via Spacewire links for science data
This presentation describes the architecture of the instrument at the end of the phase B (Preliminary Design Review), the expected performance, the
technological key challenges and preliminary test results obtained on a detection system demonstration model.
EAGLE is an instrument under consideration for the European Extremely Large Telescope (E-ELT). EAGLE will be
installed at the Gravity Invariant Focal Station of the E-ELT. The baseline design consists of 20 IFUs deployable over a
patrol field of ~40 arcmin2. Each IFU has an individual field of view of ~ 1.65" x 1.65". While EAGLE can operate with
the Adaptive Optics correction delivered by the telescope, its full and unrivaled scientific power will be reached with the
added value of its embedded Multi-Object Adaptive Optics System (MOAO). EAGLE will be a unique and efficient
facility for spatially-resolved, spectroscopic surveys of high-redshift galaxies and resolved stellar populations. We detail
the three main science drivers that have been used to specify the top level science requirements. We then present the
baseline design of the instrument at the end of Phase A, and in particular its Adaptive Optics System. We show that the
instrument has a readiness level that allows us to proceed directly into phase B, and we indicate how the instrument
development is planned.
The ISS (Integral-field Spectrograph System) has been designed as part of the EAGLE Phase A Instrument Study for the
E-ELT. It consists of two input channels of 1.65x1.65 arcsec field-of-view, each reconfigured spatially by an imageslicing
integral-field unit to feed a single near-IR spectrograph using cryogenic volume-phase-holographic gratings to
disperse the image spectrally. A 4k x 4k array detector array records the dispersed images. The optical design employs
anamorphic magnification, image slicing, VPH gratings scanned with a novel cryo-mechanism and a three-lens camera.
The mechanical implementation features IFU optics in Zerodur, a modular bench structure and a number of highprecision
EAGLE is an instrument for the European Extremely Large Telescope (E-ELT). EAGLE will be installed at the Gravity
Invariant Focal Station of the E-ELT, covering a field of view of 50 square arcminutes. Its main scientific drivers are the
physics and evolution of high-redshift galaxies, the detection and characterization of first-light objects and the physics of
galaxy evolution from stellar archaeology. These key science programs, generic to all ELT projects and highly
complementary to JWST, require 3D spectroscopy on a limited (~20) number of targets, full near IR coverage up to 2.4
micron and an image quality significantly sharper than the atmospheric seeing. The EAGLE design achieves these
requirements with innovative, yet simple, solutions and technologies already available or under the final stages of
development. EAGLE relies on Multi-Object Adaptive Optics (MOAO) which is being demonstrated in the laboratory
and on sky. This paper provides a summary of the phase A study instrument design.
The reliability of active optic for telescopes and instrumentation is now good enough to make them available for day to
day use in working observatories. Future telescopes and their associated instruments will benefit from this technology to
offer innovative concepts, optimal performance and improved reliability.
An optical design of the multi-objects spectrograph EAGLE using, active surfaces, is detailed in this article. The first
active component is a steering mirror, included in the target acquisition system, able to compensate for large astigmatism
variations due to the variable off-axis design. This innovative design also includes two variable curvature mirrors
authorising focus compensation and adding a zoom facility. A complete description of these active mirrors mechanical
principle is presented, from elasticity theory to opto-mechanical design. The prototypes of these active mirrors with their
complete test bench are detailed.
The performance requirements for the next generation of ground-based instruments for optical and infrared astronomy
on current telescopes and future ELTs are generating extreme requirements for stability, for instance to carry out precise
radial velocity measurements, imaging and spectroscopy with high contrast, and diffraction-limited performance at a
level of tens of milliarcsecond. As it is not always possible to make use of a gravity-invariant focal station, flexure must
be accommodated while still minimising thermal loads for cryogenic instruments. Variable thermal loads are another
source of dimensional changes. High stability will require the minimising of the effects of vibration sources, either from
the telescope systems or mechanical coolers. All this must be done while maintaining mass budgets, an especial
challenge for large, wide-field, multi-object spectrographs.
The very challenging goal of the Vlt-Sphere instrument, Exoplanet direct detection and characterisation, requires
high contrast imaging and extreme adaptive optics.1 In order not to limit the overall imaging performances
of the instrument, all the optics in the common path optical train need to be of the better quality over each
range of spatial frequencies. Three Toric mirrors are placed in the common path to relay the beam to the
deformable mirror and to the instruments. This paper details the Stress polishing principle developed at Laboratoire
d'Astrophysique de Marseille (Lam) to get the better optical quality on the toric surfaces, using a spherical
polishing with full size tools. The elasticity theory giving the optimisation of the blank geometry to be warped
during the stress polishing process is detailed from analytical calculation to finite element analysis. The use of
an angular thickness distribution allows us to reach the better optical quality of the deformation by canceling
higher order terms. We also present the polishing results for the 366mm diameter Toric Mirror manufacturing.
EAGLE is an instrument under conceptual study for the European Extremely Large Telescope (E-ELT). EAGLE will be
installed at the Gravity Invariant Focal Station of the E-ELT, covering a field of view between 5 and 10 arcminutes. Its
main scientific drivers are the physics and evolution of high-redshift galaxies, the detection and characterization of first-light
objects and the physics of galaxy evolution from stellar archaeology. The top level requirements of the instrument
call for 20 spectroscopic channels in the near infrared, assisted by Adaptive Optics. Several concepts of the Target
Acquisition sub-system have been studied and are briefly presented. Multi-Conjugate Adaptive Optics (MCAO) over a
segmented 5' field has been evaluated and compared to Multi-Object Adaptive Optics (MOAO). The latter has higher
performance and is easier to implement, and is therefore chosen as the baseline for EAGLE. The paper provides a status
report of the conceptual study, and indicates how the future steps will address the instrument development plan due to be
completed within a year.
E-ELT will provide a unique opportunity to observe the early universe since its large collecting area will allow detecting
faint objects at high redshifts. Primordial galaxies are a key topic for cosmology and for understanding the behaviour of
the galaxies in the universe. To achieve these observations, future instruments for the E-ELT will have to provide high
sensitivity over a wide range of wavelengths from 1 μm up to 2.5 μm - the upper limit being imposed by the redshift
which shifts the OII and Hα lines.
For the EAGLE instrument mainly devoted to such observations, we have studied the opto-thermal behaviour of the
complete system (TAS - Target Acquisition System - and the spectrograph) to estimate the thermal emission of the
optical and the mechanical parts which become a major contributor to the background above 2.2 μm. The nominal
operating temperature is a key parameter we must define precisely to both reduce the thermal background and optimise
the cooling system in terms of cost and complexity. The results of the simulations show that the TAS and the
spectrograph contribute to the thermal background at a similar level and what the optimal temperature should be. We
then discuss how such an 'optimal design' might be implemented in practice.
X-shooter is a single target spectrograph for the Cassegrain focus of one of the VLT UTs. It covers in a single exposure the spectral range from the UV to the H band with a possible extension into part of the K band. It is designed to maximize the sensitivity in this spectral range through the splitting in three arms with optimized optics, coatings, dispersive elements and detectors. It operates at intermediate resolutions (R=4000-14000, depending on wavelength and slit width) sufficient to address quantitatively a vast number of astrophysical applications while working in a background-limited S/N regime in the regions of the spectrum free from strong atmospheric emission and absorption lines. The small number of moving functions (and therefore instrument modes) and fixed spectral format make it easy to operate and permit a fast response. A mini-IFU unit (1.8" x 4") can be inserted in the telescope focal plane and is reformatted in a slit of 0.6"x 12" .The instrument includes atmospheric dispersion correctors in the UV and visual arms. The project foresees the development of a fully automatic data reduction package. The name of the instrument has been inspired by its capability to observe in a single shot a source of unknown flux distribution and redshift. The instrument is being built by a Consortium of Institutes from Denmark, France, Italy and the Netherlands in collaboration with ESO. When it operation, its observing capability will be unique at very large telescopes.