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September 02 2008
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What this talk is?

• It is the idea a part of the Nahual Consortium
  has about the present state and desired future
  development of the mechanical architecture of the
  instrument.
• It is just a proposal for discussion. It is fully
  opened to all the ideas, comments, suggestions,
  Nahual is a very complex instrument and it is not
  an easy task to put it on the best design path.
• It is the input to the mechanical WBS and
  schedule proposals. They will be presented and
  discussed on session 4 this meeting.

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Science RequirementsMain Mode

• Spectral Domain 1 2.4 µm
• Spectral Resolution gt 50.000
• Radial Velocity Accuracy 1 m/s (1 hr to
  days/months/years)?
• Simultaneous Wavelength Calibration
• No moving parts

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Science RequirementsOptional Modes

• Spectral Domain 0.9 2.5 µm
• Spectral Resolution 500 to 61.000
• Long Slit / Image Slicer
• AO needed on some modes
• Wavelength Tuning
• Cold mechanisms needed to change between
  configurations
• To be implemented ONLY if they are compatible
  with the Main Mode architecture/functionality/oper
  ation

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Mechanical Functional BaselineMain Mode

• Working Temperature lt 100 K (cryogenic
  environment)?
• Image Stability 0.1 to 0.01 pixel
• According the Radial Velocity Error Budget
  (TBD)?
• Specified values according similar instruments
• Temperature Stability in the Cold Bench lt 0.01 K
• According the Zemax-Ansys Instrument Model
  (TBD)?
• Specified values according similar instruments
• Time Stability 1 hr to years
• According the Calibration Procedure (TBD)?
• No Cold Mechanisms involved
• Located in the GTC Nasmyth platform

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Similar Instruments

• GIANO _at_ TNG
• Spectral Range 0.9 2.5 µm (cryogenic)?
• Spectral Resolution gt 46.000
• RV accuracy lt 10 m/s (lt 0.1 K)?
• PRVS _at_ GEMINI
• Spectral Range 0.9 1.8 µm (not fully
  cryogenic)?
• Spectral Resolution gt 70.000
• RV accuracy lt 3 m/s long-term (lt 1 m/s goal)?

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Similar Instruments

• SPIROU _at_ CFHT
• Spectral Range 0.9 2.4 µm (cryogenic)?
• Spectral Resolution gt 50.000 (70.000 goal)?
• RV accuracy lt 1 m/s (lt 0.01 K)?
• HARPS _at_ 3.6 m Telescope
• Spectral Range visible (non-cryogenic)?
• Spectral Resolution gt 120.000
• Long-term RV accuracy lt 1 m/s (lt 0.01 K)?

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Optical Layout. Main Mode
Camera
OAP3
Detector
OAP1-OAP2
Cross Disperser
FP2
FP1
Echelle
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Sizes of Optical Components
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Mechanical Layout. Fractal Proposal
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Auxiliary Module. Fractal Proposal
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Calibration Module. Fractal Proposal
Integrating sphere and lamps
Gas cell
Cryostat window
IR camera
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System architecture.Present status

• Mechanical architecture proposed by Fractal is
  partially driven by the cryogenic Auxiliary
  Module (Optional Mode) configuration, as well as
  the configuration/position of the Calibration
  Module
• A new cryogenic layout, only shaped by the Main
  Mode configuration (according the science
  requirements), is under study
• The space around the entrance window is very
  crowded. The configuration and position of the
  Calibration Module will be optimized after the
  Main Mode architecture is established
• The feasibility of the Optional Modes will be
  studied after the Main Mode architecture is
  established

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Mechanical Layout. Main Mode
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Mechanical Layout. Main Mode
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Cryogenics concept. Present status

• The design of Nahual will be based on Gianos
  highly stable cryogenics concept. Recent cold
  tests of Giano show an actively controlled
  temperature stability better than 0.01 K for
  short periods of time (2 hours). Long-term
  stability remains to be tested.
• Results from Giano, as well as the implications
  for Nahual, will be presented within other talk
  this meeting.
• Same idea (to adapt the Gianos cryogenics
  concept) is being considered by the Spirous team
  (at the Observatoire Midi-Pyrénées)?

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Cryogenics concept. Design status (I)?

• LN2 will be an integral part of the optical bench
  to guarantee a close contact between LN2 and the
  bench surface.
• LN2 temperature will be maintained stable by
  controlling the pressure of the N2 boiling gas
  down to 1 mbar (TBC)?
• Detailed concepts of the cold shield (to attain
  an isothermal environment in the optical bench)
  and the intermediate shield (or shields), using
  thick aluminium plates and MLI blankets (10 to 30
  layers), will be presented in this meeting.

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Cryogenics concept. Design status (II)?

• A detailed steady-state thermal model, predicting
  a density of radiation better than 0.8 W/m2 , has
  been developed for this configuration.The model
  will be presented and commented within other talk
  this meeting. Proposals to avoid hot-spots will
  be also presented.
• A vibration-free pulse-tube cooler will be used,
  if needed, to cool the detector and the vacuum
  getter (down to 10 K)?

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Cryogenics concept. Giano design
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Cryogenics development

• A collaborative framework is under discussion
  between the interested groups (presently Arcetri,
  IAC and UL) to share the tasks to design,
  manufacture, integrate and test a cryostat for
  Nahual. This will allow to identify the final
  temperature stability that can be reached with
  the Nahual configuration during long periods of
  time (as requested in the science requirements).
• The private companies involved in the design and
  manufacturing of Giano (Studio Tomerelli and
  Criotec Impianti) would participate in the
  development of Nahual cryogenics as far as it is
  possible.
• The schedule and detailed task sharing will be
  discussed during this meeting.

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Support Trusses concept

• The following alternatives are being studied for
  the trusses supporting the cold bench
• Gianos isostatic hexapod
• Same concept, but using flexures/flexural pivots
  at the interfaces
• G-10 isostatic or hyperstatic supports. Flat
  plates of cylinders
• Use of titanium instead of stainless steel
• A detailed analysis of alternatives will be
  presented within other talk this meeting

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Cryogenic wheel mechanisms

• Wheel design could be based on proven concept
  from existing instruments

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GTC Nasmyth envelope compliance
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