CNES (French Space Agency) is in charge of the development of the X-IFU instrument for Athena. The main sensor array detection chain sub-system of the X-IFU instrument is one of the major sub-subsystem of the instrument, as the main contributor to the performance. This sub-system involves major partners of the X-IFU instrument, e.g GFSC, SRON, VTT, APC, and IRAP. The purpose of this paper is to present the baseline of the definition of the X-IFU detection chain in the frame at end of phase A/beginning of phase B. The readout is based on Time Domain Multiplexing (TDM). There are strong design issues which couple the different sub-components of the detection chain (the main sensor array, the cold electronics stages, and the warm electronics). The detection chain environment (thermal, mechanical and EMI/EMC environment) also requires a transverse analysis. This paper focuses on those aspects while providing design description of the sub-components of the detection chain.
High-resolution spectropolarimetry is a technique used to study many astronomical objects including stellar magnetic fields. It has mainly been used on ground for optical and, more recently, infrared (IR) observations. Space mission projects including ultra-violet (UV) high-resolution spectropolarimetry, such as Pollux onboard LUVOIR proposed to NASA, are being studied in Europe under CNES leadership. Bringing a spectropolarimeter into space means that the instrument should be prepared for space environment including temperatures. The UV polarimeter we are considering is composed by a rotating modulator and an analyzer. Both components are made of magnesium fluoride (MgF2). The modulator is a rotating block of waveplates in molecular adhesion, each plate having its own fast axis. The analyzer is a Wollaston prism, also made with molecular adhesion. MgF2 being birefringent, the plates and prism are anisotropic and will dilate and retract due to thermal changes differently along their fast and slow axes. Each plate having its own fast axis, the thermal changes will create stress at the interfaces, i.e. at the molecular adhesion between the plates. This study focuses on the most critical part: the plates of the modulator. To demonstrate the resistance of the modulator and increase its technological readiness level (TRL), an optical bench including interferometry has been set at the Paris Observatory. It allows us to observe in real time the state of the molecular adhesion between plates as they are submitted to thermal changes in a vacuum chamber. Additional samples have been tested in a thermal vacuum chamber at CNES. This article describes the modulator using molecular adhesion, the test experiments, and the conclusion of this thermal study. Although molecular adhesion broke in 2 samples during thermal cycling, most samples survived which provides encouraging results for this technique.
Global atmospheric chemistry monitoring from space is a key to follow up air quality and provide the repeatable global coverage needed to explain the different mechanisms explaining global warming effects. Space observations with high revisit frequency allow following air mass and pollution clouds movements, both over continents and oceans. Whereas sounders like IASI (Infrared Atmospheric Sounding Interferometer) on board MetOp satellite are mostly designed for meteorological applications, CNES started studying alternative concepts to dedicate new instruments to some selected molecular species. A patent released in 1998 by CNES  is at the basis of a static configuration of Michelson interferometers, sampling each interferogram at once. New perspectives to reduce existing instruments in terms of mass, volume and complexity and to create constellations of small satellites or micro-satellites were opened. CNES either proposed this concept for CO2 concentration monitoring (Carbosat and Minicarb missions) in the near infrared or CO and O3 atmospheric profiles retrieval (SIFTI instrument on TRAQ mission ) in the thermal infrared. Though TRAQ was finally not selected by ESA, a validation of this concept has been undertaken in parallel with SIFTI phase A studies with the development of a breadboard called MOPI (which stands for ‘Maquette Optique de Performances Infrarouges’ in French, approximately translated into ‘Optical Breadboard for Infrared Performances’). In this paper, we will first describe the instrumental concept. The second part will detail the different conception choices made to design MOPI and, finally, the third part will present the next steps awaited for this breadboard.
The present paper describes the current baseline optical design of POLLUX, a high-resolution spectropolarimeter for the future LUVOIR mission. The instrument will operate in the ultraviolet (UV) domain from 90 to 390 nm in both spectropolarimetric and pure spectroscopic modes. The working range is split between 3 channels – far (90-124.5 nm), medium (118.5-195 nm) and near (195-390 nm) UV. Each of the channels is composed of a polarimeter followed by an echelle spectrograph consisting of a classical off-axis paraboloid collimator, echelle grating with a high grooves frequency and a cross-disperser grating operating also as a camera. The latter component integrates some advanced technologies: it is a blazed grating with a complex grooves pattern formed by holographic recording, which is manufactured on a freeform surface. One of the key features underlying the current design is the large spectral length of each order ~6 nm, which allows to record wide spectral lines without any discontinuities. The modelling results show that the optical design will provide the required spectral resolving power higher than R ~ 120,000 over the entire working range for a point source object with angular size of 30 mas. It is also shown that with the 15-m primary mirror of the LUVOIR telescope the instrument will provide an effective collecting area up to 38 569 cm2 . Such a performance will allow to perform a number of groundbreaking scientific observations. Finally, the future work and the technological risks of the design are discussed in details.
The Darwin mission is a project of the European Space Agency that should allow around 2015 the search for extrasolar planets and a spectral analysis of their potential atmospheres in order to detect gases and particularly tracers of life. The basic concept of the instrument is a Bracewell nulling interferometer. It allows high angular resolution and high dynamic range. However, this concept, proposed 25 years ago, is very difficult to implement with high rejection factor and has to be demonstrated in laboratory before being applied in space. Theoretical and numerical approaches of the question highlight strong difficulties: - The need for very clean and homogeneous wavefronts, in terms of intensity, phase and polarisation distribution ; - The need for achromatic optical devices working in a wide spectral range (typically 6 to 18 microns for the space mission). A solution to the first point is the optical filtering which has been successfully experimentally demonstrated at 10 microns using a single mode laser. We focus now on the second point and operate a test bench working in the near infrared, where the background constraints are reduced. We present this test bench and the first encouraging results in the 2-4 microns spectral range. We particularly focus on recent optical developments concerning achromatic component, and particularly the beam combiners and the phase shifter, which are key-points of the nulling interferometry principle. Finally, we present the future of this experimental demonstration, in the thermal infrared, covering the real and whole spectral range of Darwin.
PEGASE, a spaceborne mission proposed to the CNES, is a 2-aperture interferometer for nulling and interferometric imaging. PEGASE is composed of 3 free-flying satellites (2 siderostats and 1 beam combiner) with baselines from 50 to 500 m. The goals of PEGASE are the spectroscopy of hot Jupiter (Pegasides) and brown dwarves, the exploration of the inner part of protoplanetary disks and the validation in real space conditions of nulling and visibility interferometry with formation flying.
During a phase-0 study performed in 2005 at CNES, ONERA and in the laboratories, the critical subsystems of the optical payload have been investigated and a preliminary system integration has been performed. These subsystems are mostly the broadband (2.5-5 μm) nuller and the cophasing system (visible) dedicated to the real-time control of the OPD/tip/tilt inside the payload. A laboratory breadboard of the payload is under definition and should be built in 2007.
New types of sounders dedicated to selected species could be used on small satellites to monitor atmospheric chemistry
with simpler instruments. A new kind of Fourier transform spectrometer has been patented by CNES a few years ago.
Based on a static configuration, two projects are being studied at CNES with laboratory breadboards. One is dedicated to
CO2 concentration monitoring in near infrared. The other one works in thermal infrared to study CO and O3 atmospheric
profiles. MoLI breadboard, with a new highly integrated interferometric core, will be used for a long time measurement
of CO2 concentration. MOPI is another breadboard under development to transpose this concept in thermal infrared
during the SIFTI phase A study. These new generation spectrometers consist in a Michelson interferometer with
staircase mirrors assembled by molecular adhesion. They are adapted to narrow spectra sounding from space and could
lead to totally static and highly stabilized instruments.
The achromatic phase shifter (APS) is a component of the Bracewell nulling interferometer studied in preparation
for future space missions (viz. Darwin/TPF-I) focusing on spectroscopic study of Earth-like exo-planets. Several
possible designs of such an optical subsystem exist. Four approaches were selected for further study. Thales
Alenia Space developed a dielectric prism APS. A focus crossing APS prototype was developed by the OCA,
Nice, France. A field reversal APS prototype was prepared by the MPIA in Heidelberg, Germany. Centre Spatial
de Liege develops a concept based on Fresnel's rhombs. This paper presents a progress report on the current
work aiming at evaluating these prototypes on the Synapse test bench at the Institut d'Astrophysique Spatiale
in Orsay, France.
Nulling interferometry has been suggested as the underlying principle for an instrument which could provide direct detection
and spectroscopy of Earth-like exo-planets, including searches for potential bio-signatures. This paper documents
the potential of optical path difference (OPD) stabilisation with dithering methods for improving the mean nulling ratio
and its stability. The basic dithering algorithm, its refined versions and parameter tuning, are reviewed. This paper takes
up the recently presented results1 and provides an update on OPD-stabilisation at significantly higher levels of nulling
The Darwin/TPF mission aims at detecting directly extra solar
planets. It is based on the nulling interferometry, concept proposed
by Bracewell in 1978, and developed since 1995 in several European and
American laboratories. One of the key optical devices for this
technique is the achromatic phase shifter (APS). This optical
component is designed to produce a π phase shift over the whole
Darwin spectral range (i.e. 6-18 μm), and will be experimentally
tested on the NULLTIMATE consortium nulling test bench (Labèque et
al). Three different concepts of APS are being simulated: dispersive plates focus crossing and field reversal. In this paper, we show how thermal, mechanical and optical models are merged into a single robust model, allowing a global numerical simulation of the optical component performances. We show how these simulations help us to optimizing the design and present results of the numerical model.
In the context of the Darwin mission, aiming to detect terrestrial extrasolar planets, European Space Administration (ESA) has an R&D program trying to solve the crucial problems, like flotilla spacecraft control, optical spatial filtering, etc... One of the key optical devices of this mission will be Achromatic Phase Shifter (APS) able to accurately provide a 180° phase shift in the IR 6 - 18 microns range. The Institut d'Astrophysique Spatiale (IAS) is leading, in the frame of an ESA granted contract, an European consortium of 9 universities and companies, named Nulltimate, aiming to develop and test three different APS. IAS itself is in charge of the cryogenic test bench facility which is presented here.
The Darwin mission is a project of the European Space Agency that should allow around 2015 the search for extrasolar planets and a spectral analysis of their potential atmospheres in order to detect gases and particularly tracers of life. The basic concept of the instrument is a Bracewell nulling interferometer. It allows high angular resolution and high dynamic range. However, this concept, proposed 25 years ago, is very difficult to implement with high rejection factor and has to be demonstrated in laboratory before being applied in space. Theoretical and numerical approaches of the question highlight strong difficulties :
- The need for very clean and homogeneous wavefronts, in terms of intensity, phase and polarisation distribution ;
- The need for achromatic optical devices working in a wide spectral range (typically 6 to 18 microns for the space mission).
A solution to the first point is the optical filtering which has been successfully experimentally demonstrated at 10 microns using a single mode laser. We focus now on the second point and operate a test bench working in the near infrared, where the background constraints are reduced. We present this test bench and the first encouraging results in the 2-4 microns spectral range. We particularly focus on recent optical developments concerning achromatic component, and particularly the beam combiners and the phase shifter, which are keypoints of the nulling interferometry principle. Finally, we present the future of this experimental demonstration, in the thermal infrared, covering the real and whole spectral range of Darwin.
Several concept of space missions dedicated to the direct detection and analysis of extrasolar planets are based on nulling interferometry principle. This principle, which is theoretically very promising requires the capability of propagating and combining beams with very high accuracy in term of amplitude phase and polarization. In order to validate the principle of nulling interferometry, it is necessary to develop laboratory techniques of recombination. In this paper, we present a new test bench that should allow measuring rejection rate up to 105 in a large spectral band between 2 and 4 microns.