Technical development status
Authors: J.B. Daban (1), C. Gouvret (1), A. Agabi (1), T. Guillot (2), F.
Fressin (2), L. Abe (1), N. Crouzet (2), Y. Fanteï-Caujolle (1), S. Peron (1), S. Ottogalli (1), J.P. Rivet (2), F.X. Schmider (1), F. Valbousquet (6), P.E. Blanc (3), M. Dugué (1), A. Roussel (1), P. Assus (1), Y. Bresson (1), A. Blazit (1), E. Bondoux (1), Z. Chatilla (1), A. Le Van Suu (3), M. Merzougui (3), E. Fossat (1), H. Rauer (4), A. Erikson (4), F. Pont (5), S. Aigrain (5), N. Tothill (5).
Affiliation: (1) Laboratoire FIZEAU, UNS/OCA, Nice - France
(2) Laboratoire CASSIOPEE, UNS/OCA, Nice - France (3) Observatoire de Haute-Provence, France
(4) Deutsches zentrum für Luft und Raumfahrt, Germany (5) Exeter Observatory, Exeter, United Kingdom
(6) Optique et Vision, Antibes, France
Outline:
¾ Project partners ¾ Tech Specs
¾ Optical design
¾ Mechanical design
¾ Focal Box thermal issues ¾ Mount and Dome
¾ Schedule
Main Tech Specs (1)
FoV: 1° x 1°, and scale: ~ 1 arcsec / pixel Science spectral band: 600-800nm.
PSF size and shape:
9 size: 2 pix < FWHM < 3 pix all over the FoV.
9 aspect: ~ Gaussian, no sharpen edges, no central hole. 9 energy spread:
• 97.7% of the energy inside a 3 on-axis FWHM diameter circle.
• 35 to 90% of the energy inside a 1 on-axis FWHM diameter circle.
• Energy in 1 pixel around the PSF peak must be between 4% and 50% of the total PSF energy.
Main Tech Specs (2)
PSF uniformity over the FoV:
9 Variation of the PSF energy inside a 3 on-axis FWHM diameter circle must be < 1.3%.
9 Variation of the PSF energy inside a 1 on-axis FWHM diameter circle must be < 70%.
Flux stability: Flux variation in a 3 on-axis FWHM diameter circle should be less than 0.1% for one hour.
Image position stability: goal 0.2 pix, maximum 2 pix for 2 hours.
Duty cycle: 90% of clear sky time, minimum 75%. Temperature: operating range: -40°C to -80°C
variation speed: up to 20°C / day
Optical design (1)
Newtonian 40cm, F/D 4.6, 42% central obscuration
Focal Box including: double window, M3 dichroïc plate, corrector, science detector, M4 mirror, guiding detector.
Science CCD: 4Kx4K pixels (36x36mm) at 0.2mm behind focus
Catania, 17/9/08 M1 M2 Double window M3 M4 Corrector Science CCD
Guiding CCD Designed by C. Gouvret
Catania, 17/9/08
Optical design (2)
PSF uniformity over the FOV
Coupes de PSF dans le champ
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1 -40 -20 0 20 40 position X (µm) ir ra d ian ce r e la ti ve 0°x0° 0.125°x0.125° 0.25°x0.25° 0.375°x0.375° 0.5°x0.5° C. Gouvret
Voie science 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 400 500 600 700 800 longueur d'onde (nm) fl ux s o rt a n t / f lux i n c ide nt Aluminium protégé Melles Argent protégé SESO
Argent protégé OCA
Al(180) protégé OCA
Al(210) protégé OCA
Voie guidage 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 400 500 600 700 800 longueur d'onde (nm) fl ux s o rt a n t/ fl ux i n c ide nt Aluminium protégé Melles
Argent protégé SESO
Argent protégé OCA
Al(180) protégé OCA
Al(210) protégé OCA
C. Gouvret Catania, 17/9/08
Optical design (3)
Mirrors coating: Al vs Ag
Science path Guiding path
wavelength wavelength
Ag
Catania, 17/9/08
Optical design (4)
Some positioning specifications
Stability: +/- 0.05mm Accuracy: +/- 0,25mm M2 position (XYZ) Sub-assemblies Stability: +/- 0.01mm Accuracy: +/- 0.25mm
Corrector position (XYZ)
Stability: +/- 0.01mm Accuracy: +/- 0.25mm
M3 position (XYZ)
Stability: +/- 0.01mm Accuracy: +/- 0.1mm
Double window focus (Z)
Stability: +/- 0.01mm Accuracy: +/- 0.1mm
Double window alignment (XY)
Optics in focal box
Stability: +/- 0.1mm Accuracy: +/- 0.1mm
Focal box focus (at the entrance window) (Z)
Stability: +/- 0.05mm Accuracy: +/- 0.5mm
Focal box alignment (at the entrance window) (XY)
Stability: +/- 0.05mm Accuracy: +/- 0.5mm
Mechanical design (1)
Serrurier structure
Catania, 17/9/08
Carbon fiber bars Invar sleeves Aluminium alloys parts Carbon fiber covering Instrument weight: 95Kg
Mechanical design (2)
Structure finite element analysis
Catania, 17/9/08
Bending analysis
Catania, 17/9/08 Thermal expansion analysis with ∆T= 30°C ⇒ ~150µm defocus at Focal Box entrance window ⇒ Need of autofocus device on the science CCD
Mechanical design (3)
Estimated performances compared with the specs: 9 energy spread in the PSF:
• energy inside a 3 x FWHM diameter circle: E > 98.6% spec: E > 97.7%
• energy inside a 1 FWHM diameter circle: 55% < E < 66%, spec: 35% < E < 90%
• energy in 1 pixel around the PSF peak: 6.9% < E < 12%, spec: 4% < E < 50%
9 PSF uniformity over the FOV:
• variation of the PSF energy inside a 3 x FWHM diameter circle: 0.3%, spec: < 1.3%
• variation of the PSF energy inside a 1 x FWHM diameter circle: 17%, spec: < 70%
9 flux variation due to mechanical bending and thermal
expansion of the telescope: variation in a 3 x FWHM diameter circle: < 0.06% for one hour, spec: < 0.1%
Catania, 17/9/08
Mechanical design (4)
Catania, 17/9/08
Aluminium lateral stops
Catania, 17/9/08
Mechanical design (5)
Focal Box thermal solution (1) Catania, 17/9/08
The issue is:
How to keep the sensitive parts (cameras, dichroïc coating) at “comfortable” temperature…
…without making: 9 instrument seeing
9 thermal distortion of lenses ?
M2
Dichroïc coating needs T°>-40°C Cameras shutters needs T°>0°C
Cameras and signal converters electronic needs T°>-10°C
Shutters T° order: +5°C
Focal Box thermal solution (2) Catania, 17/9/08
Cameras’ room T° order: -10°C Dichroïc’s room T° order: -20°C Outer T°: -80°C ↔ -40°C Fused silica (low CTE)
Mount and Dome (2)
Dome Galactica 12ft
Schedule of the next months
Technical studies are done except the mechanical design of the Focal Box (September-October 2008).
Optics manufacturing: 9 Primary mirror: done
9 Secondary mirror and other optics:
delivery in December 2008 / January 2009 Mechanics manufacturing:
9 Telescope mechanical assembly: December 2008 9 Focal box assembly: February 2009
Instrument Software: delivery in February 2009
On sky tests at Nice Observatory: March → July 2009 Shipping to Dome C: August 2009
Catania, 17/9/08
