optics overview d - welcome to the dkist | dkist · 2020. 1. 22. · optics •design overview...
TRANSCRIPT
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Optics•Design Overview
–Overview–Performance
•Coude Feed•Gregorian
•Prime Focus
•Primary Mirror Overview•Secondary Mirror Overview
Jim OschmannRon Price
Optical Design Overview
• Primary Mirror– 4 meter clear aperture, off axis (12 meter parent)– F/2
• Heat stop at prime focus– Allows 3-5 arc minutes through system– Potential occulting disk area
• Secondary Mirror– 600 mm off axis gregorian– Gregorian focus at f/13
• Feed Optics– Relay image to Coude area– F/69 (over elevation & azimuth axis)– Contains Deformable and tip/tilt mirrors for AO– Further interface optics for specific instruments needed
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M2
M4
DM
M3
M3
M4
M2
M1
Coude Focus
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Coude Focus
0.1”
Gregorian Focus
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Gregorian Focus
0.2”
Prime Focus
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Prime Focus
13 arc sec
Primary Mirror Overview
• Blank Configuration• Blank Material• Polishing• Support System• Procurement Schedule
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Preliminary Mirror Blank Configuration
Ø12100 PARENT PARABOLOID
4000
(4100)
100
ALL DIMENSIONS IN MM.
Ø4237
SURFACE A
SURFACE B
ATST PRIMARY MIRROR
PARENT PARABOLOID
GEOMETRICAL AXIS OF ATST PRIMARY MIRROR BLANK
AXIS A,GEOMETRICAL AXIS OF
PARENT PARABOLOID
A
SECTION A-A
Mirror Blank Material
• Selection of mirror blank material is driven by large temperature gradients from front to back
• Ultra-low-expansion material is needed to maintain optical figure under these conditions
• Preferred materials:– Schott Zerodur® low expansion glass ceramic– Corning ULE® titanium doped fused silica
• Alternate materials– Silicon Carbide example being worked for Gregor– LZOS AstroSitall
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Mirror Blank Thickness
• Mirror blank thickness is a trade-off based on several competing factors
Thinner:
More support print-thru
Decreased weight
Decreased thermal inertia
Decreased resistance to wind buffeting
Higher handling stress
Higher resonant frequency
Thicker:
Less support print-thru
Increased weight
Increased thermal inertia
Increased resistance to wind buffeting
Lower handling stress
Lower resonant frequency
Blank
Thickness
100 mm
Mirror Blank Status
• On-going discussions being held with Schott and Corning
• ROMs for cost and schedule provided• No significant difference between off-axis and
on-axis blanks• Blank will be generated to a best-fit spherical
contour (~10mm deviation from final shape)
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Primary Mirror Polishing
• Preliminary Specifications have been developed:– F/number: f/2 (parent mirror Ø12m f/0.7)– Surface figure: off-axis paraboloid– Conic Constant: K= -1.00– Paraxial ROC: 16 meters– Surface Roughness: 20 A rms or better– Figure Accuracy: 85% encircled energy within
0.13 arc second at 550 nm– Testing Support: supported on actual system
hardware or equivalent– Optical Testing: Full and sub-aperture
interferometry
Primary Mirror Polishing Feasibility Study
• Due to unique off-axis configuration, ATST issued an RFP in July, 2002 for a Primary Mirror Polishing Feasibility Study
• RFP was sent to:
U of A/SOML Brashear LP (Contraves ) Kodak Goodrich (Hughes Danbury) Rayleigh Optical SAGEM (REOSC)
• Contracts to produce Polishing Feasibility Studies awarded to:
U of A Brashear LP Rayleigh Optical SAGEM
• Each contractor’s study will propose and evaluate grinding & polishing processes, testing methods, specifications achievable, timescale, costs
• Concentration on f/2 configuration• Compare with on-axis case• Studies to be completed in 6 months / available for ATST CoDR
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Primary Mirror Support System
• Actively controlled mirror supports– 80 – 120 axial supports in
concentric rings– 48 – 72 lateral supports
around periphery of mirror
• Two general approaches:– Passive hydraulic 3-zone
system with superimposed active forces
– Electro-mechanical actuators
PRELIMINARY SUPPORT PATTERNFOR 120 AXIAL SUPPORTS
Primary Mirror Procurement Schedule
• General Discussions / Visits to Blank Fabricators 2 months• Prepare / Issue RFP for Primary Mirror Blank 1 month• Contractor Response Time 2 months• Source Selection Process 1 month• Contract Negotiations / Approval / Award 2 months• Blank Fabrication 20 months• Blank Generation 6 months• Acid Etching of rear and sides of blank 1 month• Transporation of blank to Polisher 1 month• Grinding / Polishing / Testing 30 months• Transportation of finished mirror to site 1 month• Integration of mirror into primary mirror cell 2 months• Coating of primary mirror 1 month
Total Time Required 70 months(~6 years)
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Basis for Procurement Schedule Estimates
• ROM cost and schedule inputs provided by blank fabricators
• Discussions / Feasibility Studies by mirror polishing contractors
• Direct and indirect experience from WIYN, SOAR, Gemini and VISTA telescope projects
Secondary Mirror Overview
• Blank Properties• Polishing• Support / Positioning System
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Secondary Mirror Blank
• 60 cm diameter• Lightweight, structured design• Materials under evaluation:
– Silicon Carbide– ULE– Zerodur– Beryllium
• Silicon Carbide has the best resistance to bending due to thermal gradients (solar heat load)
Secondary Mirror Polishing
• Secondary Mirror will be a concave ellipsoid• Preliminary specifications will be developed over
the next 2-3 months• Discussions with polishers will be conducted to
identify any risk or cost issues
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Secondary Mirror Support/Positioning System
• Support – Secondary mirror will attach to positioning system kinematically via three points
• Positioning – Five (possibly six) degrees of freedom required
• Hexapod or conventional five-axis system are being considered