Roberto Ragazzoni INAF – Astronomical Observatory of Padova Feasibility of the aspheric lens Catania, June On behalf and with extensive inputs from the Telescope Group (D. Magrin, D. Piazza, W. Benz, J. Farinato, S. Basso, M. Ghigo, M. Munari, P. Spano’, G. Piotto, M. Barbieri, E. Pace, S. Scuderi, I. Pagano, L. Gambicorti, C. Arcidiacono, R.U. Claudi, V. Viotto, M. Dima, G. Gentile, R. Canestrari, S. Desidera, S. Benatti)

Roberto Ragazzoni INAF – Astronomical Observatory of Padova Feasibility of the aspheric lens Catania, June On behalf and with extensive inputs from the Telescope Group (D. Magrin, D. Piazza, W. Benz, J. Farinato, S. Basso, M. Ghigo, M. Munari, P. Spano’, G. Piotto, M. Barbieri, E. Pace, S. Scuderi, I. Pagano, L. Gambicorti, C. Arcidiacono, R.U. Claudi, V. Viotto, M. Dima, G. Gentile, R. Canestrari, S. Desidera, S. Benatti) This is still the “old” PLATO 1.0 group

The aspheric issue…  We have been asphericized by an hard life (thank you Silvio…)  We had two offers from manufacturer for actually making one (in S-FPL51) for test (SESO & Silo)  We have a detailed plan and feasibility by Sagem-Reosc that already manufactured two similar sets for a different space project (and they made similar comments as Zeiss quotation in RUAG report!)  ESA challenged themselves to improve Thales design to achieve performances and found they need two aspherics  Asphere is on a lens with one flat surface  MediaLario is testing their manufacturing abilities on glass S-FPL51 From a summarizing slide of June 15, 2011 (3 yers ago…)

The aspheric issue…  We have been asphericized by an hard life (thank you Silvio…)  We had two offers from manufacturer for actually making one (in S-FPL51) for test (SESO & Silo)  We have a detailed plan and feasibility by Sagem-Reosc that already manufactured two similar sets for a different space project (and they made similar comments as Zeiss quotation in RUAG report!)  ESA challenged themselves to improve Thales design to achieve performances and found they need two aspherics  Asphere is on a lens with one flat surface  MediaLario is testing their manufacturing abilities on glass S-FPL51 From a summarizing slide of June 15, 2011 (3 yers ago…)

The team background  Rosetta Wide Angle Camera design  An off-axis tilted FoV design with aspheric mirrors  Emphasys was on detection of faint gasesous features from comet nuclei  Clean PSF: unobstructed pupil, monochromatic and low scatter design  None of the above does apply to PLATO!  Several ground based 4m and 8m class instruments (all with aspheric surfaces)

Postcards sent around…

Two of the lens has an aspheric surface surprisingly similar in size and deviation!

January 2010 Isabel Escudero

Purpose of study.  Modify Thales design as follows:  Entrance aperture diameter: 15% bigger.  FOV: from a circle of 28º diameter to a square of 28º side length.  Image: quality equivalent to that of Thales design for the whole new FOV (criterion is 90% EEC diameter)  Focal length: same as original  Add Fused Silica plate in front  Aspherics necessary?

Comparing sizes. ThalesScience Plato_v10Plato_v20

Comparing performance

Conclusions: Thales_v10/_v20.  Two aspheric surfaces are required for larger EP & FOV.  If FOV = 28º diameter circle, one aspheric surface is enough.  Fused silica plate becomes a lens: curvatures and aspheric are needed.  Note values of distortion (=> calibration and post- processing for field superposition).  Note large angles of edge field object at image plane: relevant for radiometry.

Conclusion by ESA…

Do we need aspheres…?  Yes…  Accordingly to ESA (upgrading of THALES design) at least two;  With our own design (actually all the “last” versions) just one.

Feasibility strategy  ESA never questioned feasibility of one TOU  ESA often being concern about “mass” (well, sort of…) production  Construction is one of the issues..  We focus on demonstrating a fast procedure (less than one week) in the warm…  Aggressive plan to demonstrate we can handle CaF optical elements

Frame connected to the bench, allowing the rotation for lenses insertion from the top and their alignment similarly to what would happen with the final structure, with the possibility to be rotated of 180º to insert the lenses from both sides (L3 will be the first one) TOU BreadBoard Rotating points TOU Dummy Structure Laser Beam Expander Iris1 B/S Back Reflected Light Transmitted Light CCD Iris2

Alternative designs  A design with an aspheric CaF (because SESO claimed that with some manufacturing process that would be easier/cheaper/faster)  A design CaF-free (in case we fail space qualification of CaF lens)  A design taking into account the common directives of manufacturer

Design 4 BK7 G18 CaF2 N-KZFS11 S-FPL53 KZFSN5 BK7

Design 4 - EE 90%EE<30×30 arcsec 2 ~ 2×2 pixels 2 90%EE<37.5×37.5 arcsec 2 ~ 2.5×2.5 pixels 2 90%EE<45×45 arcsec 2 ~ 3×3 pixels 2 2×2 pixels 2

Design 5 BK7 G18 S-FPL51 N-KZFS11 S-FPL53KZFSN5 BK7 S-FPL51

Design 5 - EE 2×2 pixels 2 90%EE<30×30 arcsec 2 ~ 2×2 pixels 2 90%EE<37.5×37.5 arcsec 2 ~ 2.5×2.5 pixels 2 90%EE<45×45 arcsec 2 ~ 3×3 pixels 2

Baseline - EE 90%EE<30×30 arcsec 2 ~ 2×2 pixels 2 90%EE<37.5×37.5 arcsec 2 ~ 2.5×2.5 pixels 2 90%EE<45×45 arcsec 2 ~ 3×3 pixels 2

The CaF issue…  Already flown…  One company (SESO) would prefer as asphere  Baseline design has CaF in the spherical, smallest and more protected position (L3)  We have in our hand a produced L3 identical to the flight one (assuming baseline)  We have two blanks similar in size, glued to the same holder and cured in two different ways now in CNES and UniBern for thermal and vibration tests…  We have an acceptable, although not brilliant, B plan CaF-less

Foreseen Activities (CaF2):  Shipped blank to PD  Shipped to SG  Gluing blank  Curing (th.cycle)  Shipped to PD  Shipped to UniBE  Vibrating  Shipped to CNES  Thermal cycling  Shipped blank to PD  Shipped to SG  Gluing blank  Shipped to PD  Shipped to CNES  Thermal cycling Survived! Remember that L3 in the BB is made in CaF2 as well!

Foreseen Activities (BB):  Mounting lenses on mounts (gluing)  Aligning within tolerances  Testing the “warm” optical quality interferometrically  Measuring the “warm” PSF directly  Measuring the “warm” PSF via Hartmann  Measuring the “cold” PSF directly  Measuring the “cold” PSF via Hartmann  Validation or lessons learned of the alignment process

One aspheric done on purpose…

Various studies issued…

Production plans…

Summary…  Selex: Ok with industrial plan  Sagem/Reosc: Ok with industrial plan  MediaLario: Interested, feasibility Ok, now joining Selex?  Seso: Ok but would prefer CaF2 (technology driven)  RUAG: Market analysis…  Zeiss: doable, delivery time non critical  Asphericon: doable at the limit (delivery time) of their abilitie s  Steinbeis TransferZentrum: identified several technologie s  Leica: doable, but reccomending harder materi al  Fisba: they do not have capabilities (in spite of…)  PrazisionOptik: they do not make aspheres  SwissOptics: they think are doable but exceed the size they handle

What is next…?  Regain informal contact with all industries (some already made on their own… Sagem & MediaLario)  Select one or two for an updated formal adjourned contact  Place the accent on the serial and industrial production  Take –very fastly- a final choice as the overall baseline based on existing informations