Industrial Activities


 

Astrium GmbH

Friedrichshafen

 

 

 

DARWIN:

 

The DARWIN mission aims at the search and the analysis of terrestrial exo-planets which orbit nearby stars at distances up to 25 parsecs. 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.

 

Artistic view of the DARWIN mission.

 

Within a DARWIN System Assessment Study the overall architecture has been defined and a preliminary design has been elaborated.

 

After a thorough trade-off of all different mission options, the optimum DARWIN mission includes a planar x-Array spacecraft formation employing pupil-plane beam recombination, directly injected by an Ariane 5 ECA into a transfer to a Halo orbit at L2. The launch composite stack is separated early in LEOP and dispersion and range keeping manoeuvres are applied by using chemical propulsion.

 

The proposed instrument concept allows by far for the best scientific performance at lowest risk concerning development and operation.

 

The instrument implementation is perfectly symmetric w.r.t. optical path length, transmission and state of polarization, most efficient due to the recombination scheme implementation and the larger collecting area, and least sensitive to perturbations.

The proposed DARWIN instrument allows for screening of 446 targets of the catalogue and for analyzing of 51 targets by spectroscopy during the nominal mission time of 5 years and of 81 targets within the extended mission time of 10 years.

The beam combiner spacecraft (left) and the collector spacecraft (right) in stowed configuration.

 

 



                                  
planar formation                         planet signal                  non-planar formation

x-Array aperture configuration in planar and non-planar spacecraft formation.
By array rotation the planet signal is modulated.

 

GENIE:

 

GENIE is intended to be installed at the VLTI to make a pre-selection of potential DARWIN targets as particularly poor know-ledge is available on the zodiacal dust clouds surrounding the star/planet systems of interest. To allow for optimum performance, GENIE shall operate in the L' band.

 

Block diagram of the GENIE instrument as designed by Astrium showing the proposed Bracewell baseline and the optional split-pupil module optimised for the detection of zodiacal light. Numerous chalcogenide single-mode fibres are mandatory for interfacing the liquid nitrogen cooled detectors.

The GENIE instrument is seen as  technical and scientific precursor for DARWIN.

 

Astrium GmbH proposed an elegant and modular instrument concept. A Bracewell interferometer as baseline, operating with any two telescopes from VLTI can be installed first. Later a split pupil nuller can be added dedicated to the detection of zodiacal-clouds as the thermal background can be almost perfectly eliminated.

 

Astrium GmbH proposed to use a static in-band fringe tracker using one polarisation of the scientific band for OPD control and performing the scientific measurements with the orthogonal polarisation. This principle is also employed for the MIDI instrument. Doing it this way, no internal laser metrology is required as fringe tracker and nulling beam combiner use the same beam combiner.

 

Exo-zodiacal dust cloud observation performance of the proposed GENIE instrument.

 

 

 

Breadboard and Hardware Activities:

 

Optical/infrared space interferometry breadboard (OISI):

 

The Optical/Infrared Space-borne Interfero-metry project OISI has been initiated 1994 with support from the German space agency DLR as preparatory work towards future space-born actively controlled optical instru-ments and in particular for DARWIN.

 

OISI is a dual-beam Michelson interferometer with active optics and sensors, mounted onto an active structural element of 3 m baseline length. It depicts attitude dead band compen-sation, internal angular alignment, and internal and external optical path length control are accomplished by a layered control approach with active optics including laser sensors, white light fringe sensors, angular and linear mirror actuators.

 

The optical path difference is sensed by a fringe sensor unit.

Fringe sensor unit.

 

As star simulator a table-mounted mech-anically rigid Michelson interferometer was used. The short-stroke delay line is realized by a cat’s eye delay line, featuring a voice coil and the piezo system.

OISI breadboard simulating two collector spacecraft and one combiner spacecraft.

 

The optical instrument architecture is similar to the DARWIN instrument approach in terms of OPD metrology and control.

 

OISI focussed at system engineering, the key technology aspects and at the development of a dynamic end-to-end simulation tool (BeamWarrior). The main technical goals of the test-bed are:

·      Interferometer control architecture

·      Internal nm-laser metrology

·      External metrology (guide-star fringe tracking)

 

With delay line driven OPD control, statistical errors as low as 2.5 nm rms have been achieved, which is in the range of the DARWIN requirements.

 

OISI optical delay line (piezo and voice coil driven).



Multi-aperture imaging interferometer nulling breadboard (MAII):

The main challenge of the DARWIN mission is deep and stable star light nulling. With the multi-aperture imaging interferometer bread-board, funded by ESA and by Astrium GmbH, deep and stable nulling has been demonstrated with a DARWIN representative operational instrument.

 

Optical architecture of the nulling breadboard.

 

The breadboard has been realized as a Bracewell nuller operating in the near infrared. The developed nulling device is fully representative for the DARWIN mission requiring a star light suppression by a factor of 105 over a wide wavelength range in the mid-infrared wavelength regime.

 

The nuller is based on an auto-balancing Sagnac interferometer. Two different phase shifters are implemented, a perfectly achro-matic phase shifter realized by periscopes and a dielectric phase shifter. The target simulator features two point sources of adjustable radiometry and angular separation, repre-senting star and planet. The sources also allow for demonstrating the basic DARWIN imaging mode. The source simulator can be operated in two ways, either as a wave front dividing source or as an amplitude dividing source

 

Measured nulling performance of the breadboard.

 

The optical path difference between the tow arms was very stable over many hours in closed loop operation. A star light suppression of 4×105 has been demonstrated with a polarised 1306 nm laser diode.

Nulling Breadboard:View on realised hardware.

 



Single-Mode Fibers for DARWIN:

Astrium GmbH has developed and tested mid-infrared single-mode waveguides under ESA contract, together with ART Photonics. By different manufacturing processes and with different materials, fibres with various refractive index profiles have been developed

 

silver-halide
step-index

silver-halide
photonic-crystal

chalcogenide glass
step-index

Examples of fibre samples manufactured.

 

The lower wavelength range from about 6.5 to 10 microns can be covered by chalcogenide glass fibres which are produced by conventional drawing techniques. The entire wavelength range and in particular the upper wavelength range from about 10 to 20 m can be covered by fibres made of poly-crystalline silver-halide. Three different manufacturing techniques for the fibre preforms have been realised:

·        Conventional mechanical combining of core and cladding performs,

·        Casting methods of inserting the melted core material into the cladding

·        Tube-in-tube method of producing the core and cladding preform in one step from the melt.

 

The fibres are fabricated from the preform by a one-step or multi-step mechanical extrusion procedure.

 

The fibres have been characterized in an interferometric test setup for their modal wavefront filtering capability. We have set up a Mach-Zehnder interferometer with a CO2 laser operating at a wavelength of 10.6 micron.

 

Photograph of the test setup.

 

The improvement in rejection ratio when applying the single-mode fibre compared to the case without single-mode fibre is designated as the fibre's filter action. The rejection ratio of the interferometer itself was in the order of about 100, with the modal filter at the output, rejection ratios of some ten thousands have been obtained thus yielding filter actions in the order of some hundreds.

 

Typical output beam profiles of fibre samples made of chalcogenide glass or silver-halide, respectively.

 

 

 

 

BeamWarrior / FINCH:

 

Astrium GmbH has successfully realised the FINCH opto-dynamic system simulator for DARWIN within a four years contract with ESA. FINCH allows for establishing and simulating fully nonlinear opto-dynamical models with the aid of the included optical simulation program BeamWarrior and with SimuLink as part of Matlab, taking into account all important non-linear effects of modal wavefront filtering.

 

Astrium GmbH developed DARWIN optical models for instrument concepts with different aperture configurations (TTN, Bow-Tie, Z-array, x-Array), planar and non-planar spacecraft formations (e.g. EMMA) and pupil-plane and image-plane beam recombination schemes.

 

Principal optical design of the beam combiner spacecraft payload for a triangular TTN.

The optical models of FINCH serve for validation of optical designs with respect to nulling performance, analysis of deteriorating effects (e.g. polarization), calculation of linear and nonlinear sensitivities and generation of native sensor signals (e.g. the fringe pattern on the FSU detector).

 

Polychromatic transmission map for the triangular TTN+.

 

Utmost symmetry (same history in terms of reflections and transmissions and in particular in hit angles on reflecting mirrors), as it is mandatory for the DARWIN instrument to achieve optimum science performance, is verified with FINCH and BeamWarrior simulations.

 

 

Interferometry related projects:

 

  • Optical/infrared space interferometry breadboard (DLR)
  • Hochpräzise Regelung für Satelliten-Formationen (DLR)

 

  • DARWIN-GENIE instrument definition study (ESA)
  • DARWIN system assessment study (ESA)
  • Definition study of formation flying ground testbed (ESA)
  • Fiber-optic wavefront filtering (ESA)
  • FINCH (ESA)
  • High-precision optical metrology (ESA)
  • Multi-aperture imaging interferometer nulling breadboard (ESA)
  • Optical delay line for DARWIN (ESA)
  • Proba-3 – formation flying demonstration mission (ESA)
  • Single-mode fibres for DARWIN (ESA)
  • Single-mode waveguide for DARWIN (ESA)

 

Publications:

 

  • Oswald Wallner, Klaus Kudielka, Walter R. Leeb, „Nulling Interferometry for Spectroscopic Investigation of Exoplanets – A Statistical Analysis of Imperfections“, The Search for Extraterrestrial Intelligence in the Optical Spectrum III (San Jose), Proc. SPIE 4273, 47–55 (2001)
  • Oswald Wallner, Walter R. Leeb, Peter J. Winzer, „Minimum Length of a Single-Mode Fiber Spatial Filter“, JOSA-A 19,2445–2448 (2002)
  • Reinhhold Flatscher, Ulrich Johann, Zoran Sodnik, "Nulling Breadboard for DARWIN", Proc.  SPIE 4838, 712-720 (2003)
  • Oswald Wallner, Walter R. Leeb, Reinhold Flatscher „Design of spatial and modal filters for nulling interferometers“, Interferometry for Optical Astronomy II (Hawaii), Proc. SPIE 4838, 668–679 (2003)
  • Reinhold Flatscher, Klaus Ergenzinger, Ulrich Johann, "DARWIN Nulling Interferometer Breadboard I: System Engineering and Measurements", Towards Others Earths: DARWIN/TPF and the Search for Extrasolar Terrestrial Planets (Heidelberg), ESA-SP 539, (2003)
  • Rob Vink, N.J. Doelman, Reinhold Flatscher, Zoran Sodnik, “DARWIN nulling interferometer breadboard II: Design and Manufacturing”, Towards Others Earths: DARWIN/TPF and the Search for Extrasolar Terrestrial Planets (Heidelberg), ESA-SP 539, (2003)
  • Oswald Wallner, Walter R. Leeb, Reinhold Flatscher, „Darwin Nulling Interferometer Breadboard III Symmetry Requirements and Modal Filtering“, Towards Others Earths: DARWIN/TPF and the Search for Extrasolar Terrestrial Planets (Heidelberg), ESA-SP 539, (2003)
  • Klaus Ergenzinger, Reinhold Flatscher, Ulrich Johann, Rob Vink, Zoran Sodnik, "EADS Astrium Nulling Interferometer Breadboard for DARWIN and GENIE", 5th International Conference on Space Optics (Toulouse), SP-554 (2004)
  • Oswald Wallner, Viatcheslav Artjuschenko, Reinhold Flatscher, „Development of Silver-Halide Single-Mode Fibers for Modal Filtering in the Mid-Infrared“, New Frontiers in Stellar Interferometry (Glasgow), Proc. SPIE 5491, 636–645 (2004)
  • Oswald Wallner, Josep Maria Perdigues Armengol, Anders Karlsson, „Multi-Axial Single-Mode Beam Combiner“, New Frontiers in Stellar Interferometry (Glasgow), Proc. SPIE 5491, 798–805 (2004)
  • Anders Karlsson, Oswald Wallner, Josep Perdigues Armengol, Olivier Absil, „Three Telescope Nuller based on multi beam injection into single mode waveguide“, New Frontiers in Stellar Interferometry (Glasgow), Proc. SPIE 5491, 831–841 (2004)
  • Klaus Ergenzinger, Michael Kersten, Rainer Sesselmann, Raphael Schwarz, Ulrich Johann,  Rainer Wilhelm, Kevin Scales, Christian Erd, „FINCH: time-dependent simulation of nulling interferometry for the DARWIN mission“, Modeling and Systems Engineering for Astronomy (Glasgow), Proc. SPIE 5497, 226–236 (2004)
  • Oswald Wallner, Reinhold Flatscher, Klaus Ergenzinger, „Exo-zodi detection capability of the Ground-Based European Nulling Interferometry Experiment (GENIE) Instrument“, Appl. Opt. 45, 4404–4410 (2006)
  • Oswald Wallner, Klaus Ergenzinger, Reinhold Flatscher, Ulrich Johann, „DARWIN System Concepts“, 6th International Conference on Space Optics (Noordwijk), ESA-SP 621 (2006)
  • Reinhold Flatscher, Oswald Wallner, Viatcheslav Artjuschenko, Joao Pereira do Carmo, „Manufacturing of Chalcogenide and Silver-Halide Single-Mode Fibres for Modal Wavefront Filtering for Darwin“, 6th International Conference on Space Optics (Noordwijk), ESA-SP 621 (2006)
  • Christoph Voland, Thomas Weigel, Thomas Dreischer, Oswald Wallner, Klaus Ergenzinger, Harald Ries, Rainer Jetter, Amir Vosteen, „Improving the Fiber Coupling Efficiency for Darwin by Loss-Less Shaping of the Receive Beams“, 6th International Conference on Space Optics (Noordwijk), ESA-SP 621 (2006)
  • Oswald Wallner, Klaus Ergenzinger, Reinhold Flatscher, Ulrich Johann, „DARWIN Mission and Configuration Trade-Off“, Advances in Stellar Interferometry (Orlando), Proc. SPIE 6268 (2006)
  • Klaus Ergenzinger, Jean-Francois Pittet, A. Maerki, “System driven design and validation of a cryogenic optical delay line for DARWIN”,Advances in Stellar Interferometry (Orlando), Proc. SPIE 6268 (2006)
  • P. Gondoin, R. den Hartog, M. Fridlung, P. Fabry, A. Stankov, A. Peacock, S. Volonte, F. Puech, F. Delplancke, P. Gitton, A. Glindemann, F. Paresce, A. Richichi, M. Barillot, O. Absil, F. Cassaing, V. Coudé du Foresto, P. Kervilla, G. Perrint, C. Ruilier, R. Flatscher, H. Bokhove, K. Ergenzinger, A. Quirrenbach, O. Wallner, J. Alves, T. Herbst, D. Mourard, R. Neuhäuser, D. Ségransan, R. Waters, G.J. White, „GENIE: a Ground-Based European Nulling Instrument at ESO Very Large Telescope Interferometer“, The power of optical/IR interferometry: recent scientific results and 2nd generation instrumentation (Garching, April 2005), A. Richichi, F. Delplancke and F. Paresce (Eds.), Springer Verlag (2007)
  • Oswald Wallner, Klaus Ergenzinger, Reinhold Flatscher, Ulrich Johann, „X-Array aperture configuration in planar or non-planar spacecraft formation for DARWIN/TPF-I candidate architectures“, Techniques and Instrumentation for Detection of Exoplanets III (San Diego), Proc. SPIE 6693 (2007)

 

 

last update: 08.01.2008