Área de Instrumentación NAHUAL Mechanical Concept Current Status F. Javier Fuentes Instituto de...

Área de Instrumentación

NAHUAL Mechanical ConceptCurrent Status

F. Javier FuentesInstituto de Astrofísica de Canarias

September 02 2008

Área de InstrumentaciónF. Javier FuentesInstituto de Astrofísica de Canarias 2

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.

What this talk is?


Spectral Domain: 1 – 2.4 µm

Spectral Resolution > 50.000

Radial Velocity Accuracy: 1 m/s (1 hr to days/months/years)

Simultaneous Wavelength Calibration

No moving parts

Science RequirementsMain Mode


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/operation

Science RequirementsOptional Modes


Working Temperature < 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 < 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

Mechanical Functional BaselineMain Mode


GIANO @ TNG

Spectral Range: 0.9 – 2.5 µm (cryogenic)


RV accuracy < 10 m/s (< 0.1 K)

PRVS @ GEMINI

Spectral Range: 0.9 – 1.8 µm (not fully cryogenic)


RV accuracy < 3 m/s long-term (< 1 m/s goal)

Similar Instruments


SPIROU @ CFHT

Spectral Range: 0.9 – 2.4 µm (cryogenic)

Spectral Resolution > 50.000 (70.000 goal)

RV accuracy < 1 m/s (< 0.01 K)

HARPS @ 3.6 m Telescope

Spectral Range: visible (non-cryogenic)


Long-term RV accuracy < 1 m/s (< 0.01 K)

Similar Instruments


Optical Layout. Main Mode

Echelle

Cross Disperser

FP1

FP2

OAP1-OAP2

OAP3

Camera

Detector


Sizes of Optical Components

Element Clear aperture (mm)

FP1 ~ 2 x 2

OAP1 , OAP2 109

ECHELLE 109 x 220

FLD1 ~ 10 x 10

FP2 ~ 2 x 2

OAP3 109

CROSS DISP 109

DETECTOR (HAWAII-2) 36.8


Mechanical Layout. Fractal Proposal


Auxiliary Module. Fractal Proposal


Calibration Module. Fractal Proposal

Integrating sphere and lamps

Gas cell

Cryostat window

IR camera


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


Mechanical Layout. Main Mode


Cryogenics concept. Present status

The design of Nahual will be based on Giano’s 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 Giano’s cryogenics concept) is being considered by the Spirou’s team (at the Observatoire Midi-Pyrénées)


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.


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)


Cryogenics concept. Giano design


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.


Support Trusses concept

The following alternatives are being studied for the trusses supporting the cold bench:

Giano’s 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


Cryogenic wheel mechanisms

Wheel design could be based on proven concept from existing instruments


GTC Nasmyth envelope compliance

Área de Instrumentación NAHUAL Mechanical Concept Current Status F. Javier Fuentes Instituto de...

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