Klaus Ergenzinger

EADS Astrium nulling interferometer breadboard for DARWIN and GENIE

Within the context of the ESA TRP programme for DARWIN, a Nulling Interferometer Breadboard for the Near-Infrared was developed and tested. Its basic principle is recombining two light beams relying on a highly symmetric optical design (autobalanced Sagnac Core). Two different star simulators have been implemented, based on a) amplitude division and b) on wavefront division. The required achromatic Pi phase shift was implemented using a) dispersive phase shifter, and b) periscopes (geometrical pupil and field rotation). Due to the extremely symmetric optical design, very good star suppression up to 400 000 has been achieved. OPD control better than 1 nm RMS has been demonstrated over hours.

DARWIN mission and configuration trade-off

The European DARWIN mission aims at detection and characterization of Earth-like exo-planets as well as at aperture synthesis imaging. The method to be applied is nulling interferometry in the mid-infrared wavelength regime. The DARWIN instrument consists of a flotilla of free-flying spacecraft, one spacecraft carrying the optics for beam recombination and three or more spacecraft carrying the large collector telescopes. We provide a trade-off of different configuration, payload, and mission concepts. We discuss various two and three-dimensional aperture configurations with three or four telescopes, beam routing schemes, phase modulation methods, and beam recombination and detection schemes as well as different launch vehicle configurations, launch scenarios, and orbits. We trade the different DARWIN concepts by assessing the performance in terms of science return, development risk, and planning.

Terrestrial exo-planet science by nulling interferometry: instrument design and scientific performance

The detection of terrestrial exo-planets in the habitable zone of Sun-like stars as well as the proof of biomarkers is one of the most exciting goals in Astrophysics today. A nulling interferometer operated in the mid-infrared wavelength regime allows for overcoming the obstacles of huge contrast ratio and small angular separation between star and planet. Dedicated missions, as ESAs DARWIN or NASAs TPF-I, are implemented as a closely controlled formation of free-flying spacecraft which carry the distributed payload. We discuss various implementation alternatives and present an optimized design of the DARWIN instrument including the science payload and the formation-flying subsystem. We analyze the achievable scientific performance of the DARWIN instrument by taking into account the target properties and the instrument performance. We show that the DARWIN mission is feasible and that the mission goals can be fulfilled.

X-Array aperture configuration in planar or non-planar spacecraft formation for DARWIN/TPF-I candidate architectures

The missions DARWIN and TPF-I (Terrestrial Planet Finder-Interferometer) aim at the search and analysis of terrestrial exo-planets orbiting nearby stars. The major technical challenge is the huge contrast ratio and the small angular separation between star and planet. The observational method to be applied is nulling interferometry. It allows for extinguishing the star light by several orders of magnitude and, at the same time, for resolving the faint planet. The fundamental performance of the nulling interferometer is determined by the aperture configuration, the effective performance is driven by the actual instrument implementation. The x-Array, an aperture configuration with 4 telescopes allowing for phase chopping and decoupling of the nulling and imaging properties, provides highest instrument performance. The scientific goals necessitate an instrument setup of high efficiency and utmost symmetry between the beams concerning optical path length, beam profile and state of polarization. Non-planar spacecraft formations allow for a simpler spacecraft design which comes at the cost of inherent constellation and beam asymmetry, of increased complexity of the beam relay optics and of instrumental errors synchronous to the planet signal demodulation frequency. Planar formations allow for perfect efficiency and symmetry but need deployable structures for the secondary mirror and the sunshield due to launcher accommodation constraints. We present a discussion of planar and non-planar implementations of the x-Array aperture configuration and identify for both the critical items and design drivers. We compare the achievable instrument performance and point out the constraints for each spacecraft formation.

Exo-zodi detection capability of the Ground-Based European Nulling Interferometry Experiment (GENIE) Instrument

The Ground-Based European Nulling Interferometry Experiment (GENIE) is intended as an Earth-based precursor for the European Darwin mission that will prepare the Darwin science program and demonstrate the required technology at system level. We propose a compact nulling interferometer design consisting of a two-telescope aperture configuration, an optional split-pupil add-on, and only four active control loops for counteracting environmentally induced disturbances. We show by simulation that the proposed instrument is able to detect, within a few minutes of observation time, exo-zodiacal dust clouds around Sunlike stars at 20 parsecs that are 20 times stronger than the local zodiacal dust cloud density.

EUCLID mission baseline design

EUCLID is a mission to accurately measure the accelerated expansion of the universe. It has been selected for implementation with a launch planned for 2020. EUCLID will map the large-scale structure of the Universe over 15.000 deg2 of the extragalactic sky and it will measure galaxies out to redshifts of z=2 EUCLID consists of a 1.2 m telescope and two scientific instruments for ellipticity and redshift measurements in the visible and near infrared wavelength regime. We present a design for the EUCLID space segment, targeting optimum performance in terms of image quality and stability and maximum robustness with respect to performance, resources and instrument interfaces.

EUCLID mission design

EUCLID, a medium-class mission candidate of ESAs Cosmic Vision 2015–2025 Program, currently in Definition Phase (Phase A/B1), shall map the geometry of the Dark Universe by investigating dark matter distributions, the distance-redshift relationship, and the evolution of cosmic structures. EUCLID consists of a 1.2 m telescope and two scientific instruments for ellipticity and redshift measurements in the visible and nearinfrared wavelength regime. We present a design concept of the EUCLID mission which is fully compliant with the mission requirements. Preliminary concepts of the spacecraft and of the payload including the scientific instruments are discussed.

DARWIN system concepts

The European DARWIN mission aims at the detection of Earth-like exo-planets and at the spectroscopic characterization of their atmospheres. By nulling interferometry in the mid-infrared wavelength regime the stellar flux may be rejected. By spatial and temporal modulation of the interferometer’s receive characteristic the planet signal may be extracted from the background signals. The DARWIN instrument consists of a flotilla of free-flying spacecraft, three to four spacecraft carrying the collector telescopes and one spacecraft carrying the control units and the beam recombination and detection unit. We present different system design concepts for the DARWIN instrument which have been elaborated within the DARWIN System Assessment Study. We discuss various aperture configurations and beam routing schemes as well as modulation methods and and beam recombination schemes.

GENIE: a Ground-Based European Nulling Instrument at ESO Very Large Telescope Interferometer

Darwin is one of the most challenging space projects ever considered by the European Space Agency (ESA). Its principal objectives are to detect Earth-like planets around nearby stars, to analyze the composition of their atmospheres and to assess their ability to sustain life as we know it. Darwin is conceived as a space “nulling interferometer” which makes use of on-axis destructive interferences to extinguish the stellar light while keeping the off-axis signal of the orbiting planet. Within the frame of the Darwin program, definition studies of a Ground based European Nulling Interferometry Experiment, called GENIE, were completed in 2005. This instrument built around the Very Large Telescope Interferometer (VLTI) in Paranal will test some of the key technologies required for the Darwin Infrared Space Interferometer. GENIE will operate in the L’ band around 3.8 microns as a single Bracewell nulling interferometer using either two Auxiliary Telescopes (ATs) or two 8m Unit Telescopes (UTs). Its science objectives include the detection and characterization of dust disks and low-mass companions around nearby stars.

Nonlinear sensitivity analysis for free-flying nulling interferometers

Spectroscopy of exoplanets around near-by stars is one of the most fascinating but also most challenging science goals of our days. The ESA DARWIN mission as well as NASA TPF-I rely on nulling interferometry. The measurement principle underlying their nulling science mode is essentially nonlinear. On the one hand in terms of null depth as a function of amplitude and phase noise, and on the other hand in terms of fiber coupling as function of science beam pointing and lateral offset. We present a performance breakdown and an end-to-end performance simulation for DARWIN with focus on principal limitations, and with a clear distinction between static null depth contributors, dynamic error contributors, and so-called instability noise within the overall system. We additionally discuss the derived next-step development efforts for critical subsystems.