Name Date Signature Name Date Signature Name Date Signature hotm ESPRESSO Preliminary Specifications for the Main Collimator VLT-SPE-ESP-13520-0150, Issue 3.0 October 17th, 2013 Prepared Ana B. Fragoso October 17, 2013 Approved Released Centro de Astrofísica da Universidade do Porto Universidade de Lisboa, CAAUL and LOLS INAF, Osservatorio Astronomico di Trieste INAF, Osservatorio Astronomico di Brera Observatory of the University of Geneva Physics Institute, University of Bern Instituto de Astrofísica de Canarias European Southern Observatory
Transcript
Name Date Signature
Name Date Signature
Name Date Signature
hotm
ESPRESSO
Preliminary Specifications for the Main Collimator
VLT-SPE-ESP-13520-0150, Issue 3.0
October 17th, 2013
Prepared Ana B. Fragoso October 17, 2013
Approved
Released
Centro de Astrofísica da Universidade do Porto Universidade de Lisboa, CAAUL and LOLS
INAF, Osservatorio Astronomico di Trieste
INAF, Osservatorio Astronomico di Brera
Observatory of the University of Geneva
Physics Institute, University of Bern
Instituto de Astrofísica de Canarias
European Southern Observatory
VLT-SPE-ESP-13520-0150, Issue 3.0 3/23
Change Record
Issue/Rev. Date Section/Page affected Reason/Remarks
1.0 28/02/2013 All First version
2.0 01/07/2013 All
3.0 17/10/2013 Applicable Documents/7
Reference Documents/7
Table of Contents
Chapter 1. Introduction........................................................................................................................................ 7 1.1 Scope of the Document.......................................................................................................................................................7 1.2 Documents...............................................................................................................................................................................7
4.3.4 Chips on the MC ..........................................................................................................................................................................14 4.3.5 Mass .................................................................................................................................................................................................14 4.3.6 Thickness guideline ..................................................................................................................................................................14 4.3.7 Mechanical references .............................................................................................................................................................15
4.3.8 Optical references ......................................................................................................................................................................15 4.3.8.1 Geometry and position .......................................................................................................... 15 4.3.8.2 Tolerances ............................................................................................................................ 16
4.4 Mechanical Performance Requirements ..................................................................................................................16 4.4.1 Long term stability ....................................................................................................................................................................16 4.4.2 Thermal stability due to uniform temperature ............................................................................................................16
4.7.1 Transport obligations ..............................................................................................................................................................17 4.7.2 Handling and storage requirements..................................................................................................................................17
Chapter 6. Verification at factory ...................................................................................................................18
Appendix A Drawing (TBU) ................................................................................................................................21
Appendix B Opto-mechanical Concept ...........................................................................................................22
VLT-SPE-ESP-13520-0150, Issue 3.0 5/23
List of Figures Figure 1. Spectrograph optical layout (TBU).........................................................................................................................9 Figure 2. Footprint onto MC (collimated beam)...................................................................................................................9 Figure 3. Footprint onto MC after the diffraction grating (dispersed collimated beam). Colour rays by
wavelengths ........................................................................................................................................................................... 10 Figure 4. Tolerances in size for the MC. Units are mm. .................................................................................................. 13 Figure 5. Main parts of the mount........................................................................................................................................... 22 Figure 6. Kinematic concept for mirrors .............................................................................................................................. 22 Figure 7. Fixed DOF (in red) and free DOF (in blue)........................................................................................................ 23
List of Tables
Table 1. Environmental conditions (TBC) ........................................................................................................................... 17 Table 2. Handling and Storage Conditions at IAC facilities........................................................................................... 17 Table 3. Handling and Storage Conditions at Geneve ..................................................................................................... 17 Table 4. Handling and Storage Conditions at Paranal Observatory .......................................................................... 18 Table 5. Verification Matrix ...................................................................................................................................................... 20
VLT-SPE-ESP-13520-0150, Issue 3.0 7/23
Chapter 1. Introduction
1.1 Scope of the Document
Manufacturing specifications for the ESPRESO Main Collimator are established in that document.
They are mainly following the ISO Standards. If some other Standard is used, it is explicitly
mentioned.
Comments from possible suppliers and expert people have been taken into account in the
specification of the element.
1.2 Documents
1.2.1 Applicable Documents
AD-1 ESPRESSO MC Drawing VLT-DWG-ESP-13520-SP-
020100-00-B
1 10.05.2013
1.2.2 Reference Documents
RD-1
1.3 Acronyms and Abbreviations
1.3.1 Acronyms
AD Applicable Document
ADC Atmospheric Dispersion Corrector
APSU Anamorphic Pupil Slicer Unit
AR Anti-Reflective
BC Blue Camera
BDS Blue Detector System
BTM Blue Transfer Mirror
BXD Blue Cross Disperser
CA Clear Aperture
CCD Charge Coupled Device
CCL Combined Coudé Laboratory
CIU Calibration Injection Unit
CR Coudé Room
CT Coudé Train
CU Calibration Unit
DC Dichroic
EE Exit End
EG Echelle Grating
EPT ESPRESSO Project Team at the IAC
ESO European Southern Observatory
8/23 ESPRESSO Project
ESPRESSO Echelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations
ExpM Exposure Meter
FEU Front End Unit
FL Fiber Link, Field Lens
FPCS Fabry-Perot Calibration Source
FSU Field Stabilization Unit
FT Feed Through
GP Gerardo Periscope
IAC Instituto de Astrofísica de Canarias
IE Input End
LDLS Laser Driven Light Source
LFC Laser Frequency Comb
MC Main Collimator
MCLCS Main Collimator Local Coordinate System
OB Optical Bench
PSU Pupil Stabilization Unit
RC Red Camera
RD Reference Document
RDS Red Detector System
RFM Red Folding Mirror
RFU Refocusing Unit
RTM Red Transfer Mirror
RXD Red Cross Disperser
SP Spectrograph
SU Calibration Selector Unit
TBC To Be Confirmed
TBD To Be Defined/To Be Developed
TBU To Be Updated
ThAr Thorium Argon
TS Toggling System, Thermal System
UT Unit Telescope
VLT Very Large Telescope
VV Vacuum Vessel
XD Cross Disperser
VLT-SPE-ESP-13520-0150, Issue 3.0 9/23
Chapter 2. Functional description
ESPRESSO spectrograph optical design is based onto a white-pupil asymmetric
configuration.
A large off-axis parabolic mirror acts as main collimator and is used in double-pass: to
illuminate a large mosaic echelle grating (ESPRESSO main disperser) and to collect
dispersed light towards transfer optics. Once the light is dispersed by the echelle, a dichroic
beam-splitter mirror, located near an intermediate focal plane, splits light into two
optimized arms: Blue and Red. Each arm consists of re-imaging optics, specific cross-
disperser VPH grism and a refractive lens camera.
The spectrograph optical layout is shown in figure below just as to give an idea of the
orientation and position of the elements. The sketch is not representative of final
dimensions or sizes.
Figure 1. Spectrograph optical layout (TBU)
The OAP mirror acting as MC is used in double-pass. First it is used to collimate light
coming from the slit and illuminate the EG. Second, it collects dispersed light and sends it
towards transfer optics. Corresponding footprints are shown in figures below.
Figure 2. Footprint onto MC (collimated beam)
MC
g
Aperture Full X Width : 700.0000Aperture Full Y Height: 380.0000
Scale: 400.0000 Millimeters
10/23 ESPRESSO Project
Figure 3. Footprint onto MC after the diffraction grating (dispersed collimated beam). Colour rays by wavelengths
Chapter 3. Local Coordinate System
The collimator local coordinate system (MCLCS) is named (X, Y, Z).
The origin is in the mirror apex.
Y is perpendicular to Z. Positive sense is from the mirror centre to the apex.
Z is aligned with the mirror axis of revolution. Positive direction defined towards the
parabola focus.
See drawing in Appendix A or AD-1.
Chapter 4. Preliminary Specifications
4.1 Functional Requirements
Source: EPT
ESPRESSO MC will be provided without any kind of cell or mounting.
The corresponding Positioning Mechanism will be designed and provided by IAC (see the
concept in Appendix B).
NOTE: Surface roughness of the non-optical surfaces shall be considered and agreed so as
to assure the suitability for the Positioning Mechanism.
Aperture Full X Width : 700.0000Aperture Full Y Height: 380.0000
Scale: 400.0000 Millimeters
VLT-SPE-ESP-13520-0150, Issue 3.0 11/23
4.2 Optical Requirements
Source: ESPRESSO Optical Group
4.2.1 Optical figure
The optical figure of the MC in local coordinates (MCLCS) shall be an off-axis parabola
following the conic surface equation:
( )
+−+
=2
2
111R
rKR
rz
where:
z: sagitta of the optical surface
R: radius of curvature at vertex
R: distance to the revolution axis
K: conic constant
4.2.2 Radius of curvature at vertex
Paraxial radius of curvature at vertex shall be 6000.0 mm ± 10 mm. (TBC). The surface is
concave.
NOTE: Variations of several millimetres have not effect on image quality. The
manufactured radius of curvature shall be measured and the actual value will be
compensated modifying the distance from the collimator to the pupil.
4.2.3 Off-axis distance
Off-axis distance (parabola vertex to centre of the CA) shall be -420 mm ± 1 mm in Y axis
direction.
4.2.4 Conic constant
The conic constant of the figure of the MC shall be -1.
4.2.5 Surface form tolerance of the optical surfaces
4.2.5.1 Sources of irregularity
The irregularities of the optical surface to which the requirements shall apply includes
irregularities due to the following sources:
• Residuals of the polishing process.
• Gravitational deformation (see orientation in Figure 1. and Appendix B).
• Thermal deformation within nominal environment conditions (Table 1) and for
testing temperature to operation temperature.
12/23 ESPRESSO Project
• Temporal drift (see note in 4.3.3 and requirement related to Long Term Stability,
section 4.4.1).
4.2.5.2 Surface shape accuracy
• < 150 nm P-V, over sub-apertures of 370 x 220 mm.
• < 40 nm rms, over sub-apertures of 370 x 220 mm.
4.2.5.3 Surface slope error2
It is specified for both optical surfaces.
Maximum slope shall be:
• < 0.75 arcsec P-V, up to a spatial frequency of 2 mm.
• < 0.125 arcsec rms, up to a spatial frequency of 2 mm.
NOTE: This requirement means that considering an integration lenght of 2 mm, the
maximum P-V value of the slope error shall be <0.75 arcsec (angle) and the rms value of
the slope error shall be <0.125 arcsec (angle). It complements the surface form tolerance
requirement (shape accuracy), being the first one for midspatial frequency errors.
4.2.6 Surface micro-roughness
The reflecting surface shall be polished to a residual surface roughness of 2nm (rms) or
better over the whole CA.
The way in which the Micro-roughness is measured, shall be proposed by Contractor and
approved by EPT.
4.2.7 Surface Imperfections
According to MIL-C-48497, the surface imperfections of the optical surfaces shall be 40/20.
4.2.8 Coating
Reflecting surface shall be coated ensuring a reflectivity:
• > 97.0 % in average from 400 nm to 750 nm
• > 94.0 % absolute from 375 nm to 800 nm
Maximum angle of incidence: 15 degrees (TBC)
Coating imperfections shall be included in the allowable general surface imperfections and
roughness indication.
NOTE: Interface area with the mechanical parts (see drawing in Appendix A) shall be
completely free of coating or any other material.
2 Surface slope error is specified to control the non-uniform deviations in midspatial frequencies
VLT-SPE-ESP-13520-0150, Issue 3.0 13/23
4.2.9 Resistance to cleaning
The MC coating shall not be adversely affected by materials and procedures used when
cleaning the mirror surface with: CO2 snow, peel off methods and wet cleaning methods. If
some special procedure is required it shall be indicated by the supplier.
4.3 Physical Requirements
4.3.1 Optical Surface clear aperture
Source: ESPRESSO Optical Group
MC Clear Aperture dimensions shall be: 670 x 350 mm^2. (centred)
(See AD-1 or drawing in Appendix A).
NOTE: In case it were convenient, a reduced area on the upper corners of CA will be likely
used to place a reference (see sections 4.3.7 and 4.3.8). Size and shape of the reference
shall be agreed between EPT and the Contractor and shall never invade the footprint area
(Figure 2).
4.3.2 Optical Surface shape and size
Source: ESPRESSO Optical Group
4.3.2.1 Dimensions
Dimensions of the MC shall be: 700 x 380 mm^2.
Tolerance in X axis: ±0.100 mm. (tolerances wrt to the MC central point ; Figure 4).
Tolerance in Y axis: ±0.050 mm. (tolerances wrt to the MC central point ; Figure 4).
NOTE: Tolerances in size are referred to the mechanical centre of the mirror since that is
the point that will define the required area of the parabola.
Figure 4. Tolerances in size for the MC. Units are mm.
350±0.05 350±0.05
190±0.05
2
190±0.05
MC
Centre
14/23 ESPRESSO Project
4.3.2.2 Shape
Shape of the optical surface shall be rectangular.
Sagittal and tangential plane of the parabolic mirror will be parallel to the mirror borders
within a certain tolerances that will define the error in shape (seeAD-1).
Parallelism requirement: TBD
NOTE: Final shape can be adapted to minimized weight or due to mechanical purposes.
That point will be discussed so as to agree.
4.3.3 Material
Source: ESPRESSO Optical Group
Mirror substrate material shall be Zerodur® glass ceramic (or equivalent).
NOTE: Other materials with the same properties could be accepted. It is important to
assure the long term stability of the material selected and low coefficient of expansion in
the range between 17 and 21ºC.
Final material substrate shall be proposed by the manufacturer and approved by EPT.
4.3.4 Chips on the MC
Source: EPT
It shall be accepted that the mirror blank has chips, but they shall meet the following
conditions:
It shall be proved that the chips do not affect the safety life or performances of the mirror.
The chips shall not affect the interface with the mount (interfaces are defined in AD-1).
The chips shall not affect the optical surface.
4.3.5 Mass
Source: EPT
It is expected the MC mass not being higher than 50 Kg. If this value were exceeded, it shall
be lightened.
EPT shall be informed about the final mass so as to approve the supply.
4.3.6 Thickness guideline
Source: EPT
MC thickness shall assure the optical and mechanical requirements.
A minimum thickness of 67 mm is suggested (see AD-1 or Appendix A).
Final thickness shall be proposed by the manufacturer and approved by EPT.
VLT-SPE-ESP-13520-0150, Issue 3.0 15/23
4.3.7 Mechanical references
Source: EPT
Some mechanical references shall be defined to identify the local coordinate system and,
thereby, the parabola axis and the apex.
4.3.7.1 Geometry
The mechanical reference shall be compatible with the opto-mechanical concept (Appendix
B) and will set the orientation of the parabola axis and the position of its vertex.
It will be used to achieve the mechanical integration of the MC on the bench using 3D
measurement machine or a Laser Tracker.
Mechanical reference geometry shall be proposed by the manufacturer and approved by
EPT.
4.3.7.2 Position guideline
The mechanical reference will be in one of the upper corners of the MC, on the optical
surface. Even if it is inside the CA, the reference shall never invade the footprint area
(Figure 2). (See note in section 4.3.1).
Final position will be proposed by the manufacturer and approved by EPT.
4.3.7.3 Tolerances
The mechanical reference shall be positioned with respect to the apex and the axis of the
parabola within the following tolerances (TBC):
• The alignment accuracy along the Xcol axis shall be better than 30 µm
• The alignment accuracy along the Ycol axis shall be better than 30 µm
• The alignment accuracy along the Zcol axis shall be better than 30 µm
• The alignment accuracy about the Xcol axis shall be better than ±10 arcsec
• The alignment accuracy about the Ycol axis shall be better than ±10 arcsec
4.3.8 Optical references
Source: EPT
Optical references shall be used to identify the collimator optical surface during the global
alignment and verification procedure. One example of such kind of reference would be a
flat mirror (centre marked) located at the mirror apex to define the collimator optical axis.
4.3.8.1 Geometry and position
The optical reference shall be compatible with the opto-mechanical concept (Appendix B)
and will set the orientation of the parabola axis.
As a guideline, the optical reference could be placed in one of the upper corners of the MC,
on the optical surface. Even if it is inside the CA, the reference will never invade the
footprint area (Figure 2). (See note in section 4.3.1).
16/23 ESPRESSO Project
Final geometry, characteristics and position of the optical reference will be proposed by
the manufacturer and approved by EPT.
4.3.8.2 Tolerances
The optical references shall be positioned with respect to the mirror apex and the mirror
optical axis within the following tolerances (TBC):
• The alignment accuracy along the Xcol axis shall be better than 30 µm
• The alignment accuracy along the Ycol axis shall be better than 30 µm
• The alignment accuracy along the Zcol axis shall be better than 30 µm
• The alignment accuracy about the Xcol axis shall be better than ±10 arcsec
• The alignment accuracy about the Ycol axis shall be better than ±10 arcsec
4.4 Mechanical Performance Requirements
Source: EPT
4.4.1 Long term stability
The optical surface shall be stable during lifetime (4.5.1). If temporal drift is produced due
to the mirror material, the effect shall be considered as an additional source of irregularity
of the optical surface, which shall be limited (see requirement 4.2.5).
4.4.2 Thermal stability due to uniform temperature
The optical surface shall be stable when the temperature of the system changes uniformly
within 17 and 20ºC. If thermal deformation is produced due to the mirror material, the
effect shall be considered as an additional source of irregularity of the optical surface,
which shall be limited (see requirement 4.2.5).
4.5 Reliability Requirements
4.5.1 Lifetime guideline
Source: EPT
MC should be designed for a minimum lifetime of 15 years (TBC) under the environment
conditions specified in Table 1. This lifetime start at first complete integration on
ESPRESSO spectrograph at Geneva.
4.6 Environmental Requirements
Source: ESPRESSO Team
The Main Collimator will operate inside a vacuum chamber. It shall survive under the
environmental conditions stated in Table 1. (TBC)
The MC requirements shall be fulfilled under the operation conditions.
VLT-SPE-ESP-13520-0150, Issue 3.0 17/23
Lab conditions
(alignment)
Vacuum conditions
(operation) Survival limit
Temperature +20°C +17°C +35°C
Thermal variation 2°C 1 mK 1°C/h
Relative humidity ~40% (controlled) N/A 0% to 100% with
condensation
Atmospheric
pressure ~1 atm ~10-3 mbar (TBC) N/A
Table 1. Environmental conditions (TBC)
4.7 Packaging, Handling, Storage and Transportation
Requirements
Source: EPT
4.7.1 Transport obligations
The Contractor shall be responsible, in cost and risk, to transport the equipment
manufactured from its facilities to the IAC facilities. The package shall be designed to
support normal air and sea transport condition.
The package shall be also designed to be used for preventive maintenance tasks and in case
of reparation. So, the package shall be designed to support at least 10 packing and 10
unpacking operation keeping all its performances.
4.7.2 Handling and storage requirements
The design of the items and packages shall prevent them from being damaged under the
conditions shown in tables below.
Condition Requirement
Altitude 500 m
Temperature +15°C to +30°C
Relative humidity 0% to 100% with condensation
Atmospheric pressure ~ 1atm
Gravity orientation All orientations
Shock Peak acceleration 10g all axes Table 2. Handling and Storage Conditions at IAC facilities
Condition Requirement
Altitude 400 m
Temperature +20°C ± 3°C
Relative humidity 20% to 100%
Atmospheric pressure ~720 mbar
Gravity orientation All orientations
Shock Peak acceleration 10g all axes Table 3. Handling and Storage Conditions at Geneve
18/23 ESPRESSO Project
Condition Requirement
Altitude 2600 m
Temperature -8° to 25°C
Temperature gradient during night -0.4°C/h
Relative humidity 5-20%
Atmospheric pressure 750 mbar
Gravity orientation All orientations
Moderate earthquakes (some times
per year) Mg < 7.75
Shock Peak acceleration 10g all axes Table 4. Handling and Storage Conditions at Paranal Observatory
Chapter 5. Cleanliness Requirements
5.1 Cleanliness
Source: EPT
MC shall be delivered clean: 200-300 surface cleanliness (according to MIL-STD-1246). The
optical surface shall be able to be cleaned at the surface cleanliness level cited above,
without damaging the coating applied. The Contractor shall provide a procedure for
cleaning the mirror.
Chapter 6. Verification at factory
Source: EPT
Verification shall be accomplished by one or more of the following verification methods:
Test (T): When requirements have to be verified by measuring product performance and
functionality. The analysis of data derived from test shall be considered an integral part of
the test.
Demonstration (D): Can be considered as test where qualitative operational performance
and requirements are demonstrated.
Analysis (A): When verification is achieved by performing theoretical o empirical
evaluation by accepted techniques, the method shall be referred to as “Analysis”. An
example is the modelling and computational simulation.
Inspection (I): When verification is achieved by visual determination of physical
characteristics (such as construction features, hardware conformance to document
drawings, etc) the method shall be referred to as “Inspection”.
The Verification Matrix (VM) shows the methods that shall be used to accept each one of
the critical requirements.
NV means No Verification is needed.
VLT-SPE-ESP-13520-0150, Issue 3.0 19/23
Code Header Ver. Method Remarks
Chapter 4. Preliminary Specifications
4.1 Functional Requirements I
4.2 Optical Requirements
4.2.1 Optical figure T
4.2.2 Radius of curvature at vertex T
4.2.3 Off-axis distance T
4.2.4 Conic constant T
4.2.5 Surface form tolerance of the
optical surfaces T
4.2.5.1 Sources of irregularity -
4.2.5.2 Surface shape accuracy T
4.2.5.3 Surface slope error T
4.2.6 Surface micro-roughness T
4.2.7 Surface Imperfections T
4.2.8 Coating T
4.2.9 Resistance to cleaning T
4.3 Physical Requirements
4.3.1 Optical Surface clear aperture T
4.3.2 Optical Surface shape and size T
4.3.2.1 Dimensions T
4.3.2.2 Shape T
4.3.3 Material D
Information on
material shall
be provided
4.3.4 Chips on the MC I
4.3.5 Mass T
4.3.6 Thickness guideline T
4.3.7 Mechanical references T
4.3.8 Optical references T
4.4 Mechanical Performance
Requirements
4.4.1 Long term stability A
4.4.2 Thermal stability due to uniform
temperature A
20/23 ESPRESSO Project
4.5 Reliability Requirements
4.5.1 Lifetime guideline NV
4.6 Environmental Requirements T
4.7 Packaging, Handling, Storage and
Transportation Requirements
4.7.1 Transport obligations I
4.7.2 Handling and storage
requirements I
Chapter 5. Cleanliness Requirements
5.1 Cleanliness D
Table 5. Verification Matrix
VLT-SPE-ESP-13520-0150, Issue 2.0 21/23
Appendix A Drawing (TBU)
22/23 ESPRESSO Project
Appendix B Opto-mechanical Concept
Mount
The optics is hold onto a structural steel frame by 3 points in a kinematic and athermal
way. At the same time each frame is fixed by 3 points to the OB in a quasi-kinematic way.
z
Figure 5. Main parts of the mount
Kinematic mount principle for mirrors
Figure 6. Kinematic concept for mirrors
VLT-SPE-ESP-13520-0150, Issue 2.0 23/23
Figure 7. Fixed DOF (in red) and free DOF (in blue)
