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OWL TECHNOLOGIES

OWL TECHNOLOGIES. Copenhagen, November 2004. Design overview. Optical design. Adaptive, conjugated to pupil; First generation. Adaptive, conjugated to 8km; Second generation. Why a spherical primary / flat secondary ?. System Performance Risk & cost.

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OWL TECHNOLOGIES

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  1. OWL TECHNOLOGIES Copenhagen, November 2004

  2. Design overview

  3. Optical design Adaptive, conjugated to pupil; First generation Adaptive, conjugated to 8km; Second generation

  4. Why a spherical primary / flat secondary ? System Performance Risk & cost • Larger corrected field of view than equivalent Ritchey-Chretien • Low sensitivity to M2 decenters • Corrector  excellent baffling options • Secondary mirror an issue with aspherical primary • Small M2 (< 3-m)  very high sensitivity to disturbances • Large M2 (> 3-m)  severe fabrication issue if convex added tube length if concave (Gregorian) • All wavefront control functions with 6 surfaces • Multi-conjugate AO (2 mirrors 2- and 4-m, conjugated to 0, 8 km) • Moderately large FOV (0.5 – 2 arc min) an essential mode • Needs re-imaging; OWL provides dual conjugate with 6 surfaces only ! • Maintainability: 3,000 segments, all identical & interchangeable.

  5. Why a spherical primary / flat secondary ? • Use of planetary polishers or large stiff figuring tools • Lower segment edge misfigure • Stable reference, repeatability of radius of curvature • No warping harness • Structured blanks possible (SiC a serious option) • Less stringent requirements on blanks internal stresses • Segment size up to ~2.3-m possible • Limited by cost-effective transport in standard container • No aspherization  weak size-dependence • Performance losses • Lower throughput than a Ritchey-Chretien (option: enhanced coatings ?) • Higher emissivity (option: single surface corrector for very small field of view ?) System PerformanceRisk & cost

  6. Why a spherical primary / flat secondary ? • Spherical polishing • Simple and predictable processes, stable and predictable yield • Stable reference (rigid tools) • Fast process, high efficiency; OWL polishing tool area = 36  largest GTC tool area ! • Simple test set-upUnique matrix no segments matching risk • TBC: No edge cutting, polished hexagonal SystemPerformanceRisk & cost

  7. Segment assembly Total quantity: 3048 + 216 + TBD spares

  8. Actuators - Outline of specifications Load cases (nominal, tension and compression) • Glass segments: 0 to 170 kg / actuator • Lightweight SiC segments: 0 to 40 kg / actuator Accuracy • 2 stages Position Actuator Concept • Coarse stage ± 0.05 mm. • Fine stage ± 5 nm - Goal ± 2 nm • Extractor ± 1 mm Stroke • Coarse stage 20 mm • Fine Stage 0.5 mm - Goal 1mm • Extractor 150 mm TBC ClosedLoop Bandwidth • Fine stage 5Hz - Goal 10 Hz. • Coarse stage 0.1 Hz. Max. cost (unit cost for a production of 10,000 units) • Glass segments: < € 3,500.- Goal < € 2,500.- • SiC segments < € 2,500,- Goal < € 2,000.-

  9. Position sensors • Capacitive, inductive or optical • Mounted at segments edges • Measurement range  0.5 mm (TBC) • Differential accuracy over full range  5 nm Goal  2 nm • Maximum measurement frequency 20 Hz Goal 50 Hz • Re-calibration frequency  once per week • Maximum heat dissipassion TBD (minimize) • Maximum unit cost (20,000 units) € 1,250.- Goal € 750.-

  10. Azimuth tracks Sliding enclosure M2 Handling tool M1 Covers Maintenance facility

  11. 140 -m 310 -m 157 -m

  12. Altitude tracks Altitude bearing Azimuth structure & bogies

  13. Corrector & instrumentation Structure ribs (6-fold symmetry) Altitude cradles & bogies

  14. All dimensions as multiple of segment size • Standardization • Ease of integration • Ease of maintenance • Optimal loads transfers

  15. Eigenfrequency (Hz) Moving mass (t) (rigid body motion) Optomechanics Fractal design - Low-cost, lightweight steel structure • 14,800 tons moving mass (60 times “lighter” than VLT)Mass reduced to ~8,500 tons with SiCAmple safety margins (stresses, buckling) • 2.6 Hz locked rotor eigenfrequency • Low thermal inertia (developed surface, natural internal air circulation inside structural elements) • Differential M1-M2 decenters under gravity Piston 3.4 mmLateral 17.6 mmTilt 3.4 arc secs

  16. 20305 Reducing sensitivity by design • Innocuous lateral M1-M2 decenters • Parallelogram-shapedstructural modules favour lateral over angular decenters • Lose centring tolerances • Corrector favourably located (stiffness) • Ample design space

  17. Instrument racks • 6 focal stations; switch by rotating M6 about telescope axis. • Max. instrument mass 15 tons each. • Local insulation & air conditioning • Issue: needs rigid connection with corrector (TBC).

  18. Controlled optical system Kinematics pointing, compensation for sky rotationMetrology: encoders, on-sky guide probe Pre-setting bring optical system into linear regimeMetrology: internal, tolerances ~ 1-2 mm, ~5 arc secsCorrection: re-position Corrector, M3 / M4 / M5 Phasing keep M1 and M2 phased within tolerancesMetrology: Edge sensors, Phasing WFSCorrection: Segments actuators Field Stabilization cancel “fast” image motionMetrology: Guide probe Correction: M6 tip-tilt (flat, exit pupil, 2.35-m) Active optics finish off alignment / collimation relax tolerances, control performance & prescriptionMetrology: Wavefront sensor(s)Correction: Rotation & piston M5; M3 & M4 active deformations Adaptive optics atmospheric turbulence, residualsMetrology: Wavefront sensor(s)Correction: M5, M6, …

  19. Controlled opto-mechanical system I – Pre-setting Corrector re-centering + 2 (TBC) surfaces within the corrector Internal metrology (e.g. fiber extensometer) Typical accuracy: 10 ppm goal 1 ppm Bandwidth << 1 Hz High operational reliability

  20. Fast steering mirror M6, dia. 2.35m Friction drives Azimuth: 246 units Elevation: 154 units Bandwidth ~0.5 Hz Guide probes at technical focusaccessible FOV 10’ Controlled opto-mechanical system II – Kinematics

  21. M6 adaptive & tip-tilt unit

  22. 5 Wavefront Sensorsat each technical focus (FOV 10’) + feedback AO Refocus & fine centering Controlled opto-mechanical system III – Active optics Dual conjugate active optics Deformable M3 & M4 VLT-type mirrors

  23. Two segmented mirrors Bandwidth ~5 Hz TBC Edge sensors (capacitive, Inductive or optical) Mach-Zehnder phasing sensor On-sky calibration off-axis Controlled opto-mechanical system IV – Phasing

  24. Mach-Zehnder calibration sensor Interferogram (ideal conditions) Complex geometry, But fully predictable Localized signal 2k x 2k camera sufficient for adequate sampling

  25. X – tilts same signs Y – tilts opposite signs X – tilts opposite signs Piston only Phase Signal Features Antisymmetry axis Y Antisymmetry axis X Antisymmetry axis Y Symmetry axis Y Piston, Tip, and Tilt: Examples

  26. Illumination on the pyramid WFS AO Simulations on OWL. 125 sub-apertures across pupil, 11198 actuators on M6 Bright NGS on-axis, 1 kHz frame-rate, ~1 sec of real-life PSF 4 ms coherence time, 0.5’’ seeing (at 0.5 mm) OWL pupil + cophasing M1 & M2: 35 nm WFE RMS each K band, Strehl ~70% Atmosheric Wavefront

  27. MCAO simulation

  28. 2 arc minutes field, l=2.5 mm 2 adaptive mirrors, 8000 actuators each 3 guide stars Sqrt stretch

  29. Adaptive mirrors LBT – 911 mm diameter, 672 actuators MMT – 642 mm diameter, 336 actuators

  30. Adaptive mirrors Capacitive sensors (ref.plate) (MMT336) aspherical shell 642mm dia. 2mm thick Magnets (12mm diam.)

  31. Extreme AO • High performance adaptive optics at visible wavelength • Need for 105-106 actuators  MOEMs • Time scale : beyond 2015 • Some effort going on but need to ramp up • Positive factor: limited stroke necessary, large deformable mirrors act as first stage • Technology review, design, production & testing of demonstrators foreseen in OWL Phase B

  32. Adaptive Optics Today 2008 2015 2019 IR Deformable Mirrors LBT (JWST) Prototype OWL 1st Gen. 2nd Gen. Diameter 1-m (2-m) 0.3-m 2-m 3.2-m Actuator spacing 30 mm 15 mm 15-25 mm 20-25 mm XAO correctorMoems/Pzt Detector 256x256 ? 512x512 1kx1k AO real time controlAlmost OK Reference stars NGS (LGS) NGS NGS / LGS • High sky coverage in the near-IR (better filling of metapupil) • LGS needed ~2018; lower number of LGS, • Cone effect requires novel approaches e.g. PIGS (Ragazzoni et al)

  33. (Pupil shape outdated) Telescope performance (wind) Tracking : low concern • M2 flat ! Design insensitive to M2 lateral decenters • Structural design privileges M2 lateral decenter over M2 tilt • Corrector at very stiff location DYNAMIC ANALYSIS Worst caseS combined (orientation), 10 m/s, conservative drag coefficients Maximum mean displacements out of worst load cases

  34. Wind MODELLING & TESTING • Limited confidence in CFD (Results suspiciously good !) • Wind measurements at Jodrell Bank (2004) • Wind tunnel testing (2004) • Analysis & modelling Courtesy PSP

  35. Wind (pressure distributions) ACCELERATED - ACTUAL ELAPSED TIME 150 SECONDS M1 Corrector M2

  36. Higher local stiffness (substructure supporting segments) increases resistance to high spatial frequencies Use of SiC segments  higher M1 & M2 bandwidth Embedded variable wind screens (up to z~30o) Increase M4 (active mirror) bandwidth ~2-5 Hz(VLT M1 support dimensioned for 1 Hz) Increase range of M6 adaptive correction Operational constraints Site selection … required for AO anyway Variable wind screen embedded in theazimuth structure (notional design); M2 wind screen not shown Wind – design options

  37. Cost estimate (capital investment, 2002 M€) PROVISIONAL • Diffraction-limited instrumentation • (acceptable étendue !) • Assumes “friendly site” • Average seismicity (0.2g) • Moderate altitude • Average wind speed • Moderate investment in infrastructures

  38. Cost estimates (industrial studies) Primary & secondary mirror segments; 1.8-m; polished, prices ex works. Blanks: SiC (2 suppliers A and B) with overocatings (3 suppliers 1, 2, 3) Glass-Ceramics (2 suppliers C and D) Polishing: 2 suppliers, only one shown (both agree within 10%)

  39. Optimized geometry (interface optics-mechanics) All parts fitting in 40-ft containers 1.6-m all-identical segments (~3000 units),single optical reference for polishing 12.8-m standard structural modules (integer multiple of segment size) Friction drive (bogies), hydraulic connection

  40. Cost vs quantity Industrial data Applies to conceptually simple items (e.g. segments, structural nodes) VLT M1 polishing (4 units) OWL segments (industrial studies)

  41. Polishing: factory implementation Size (area) comparable to VLT 8-m production facility

  42. BOOSTEC ECM Meanwhile …

  43. Phase C/D approval 2010 • 8-m mirrors need 6 years • First light early 2016 • Start of science 2017, 60m BUT: long lead items highly standardized  multiple supply lines possible  faster integration possible  ALTERNATIVE ALLOWING FIRST LIGHT IN 2014 (TBC) IS UNDER EVALUATION

  44. 2000 2005 2010 2015 2020 Phase A Phase A review ELT Design Study APE on sky Phase B Site selection First light (50-m) Completion Phase C/D Start of science (60-m) Groundbreaking Timeframe Driven by funding, not by technology

  45. Planned studies 2005 - OWL phase A • Conceptual design of M6 adaptive subunit • Storage and postprocessing of the Jodrell Bank data • Feasibility study for wind tunnel measurements • Wind tunnel measurements (Jodrell Bank model) • Feasibility study for CFD simulations • CFD simulations • Dynamic Analysis of M1 / Corrector M3-M6 Control • OWL Instruments Conceptual Design Studies • Vibration dampers (local modes) • Optimization runs of the mechanical structure • I/F with concrete • Feasibility study M4 figuring / CGH Conceptual Design

  46. ELT Design Study • The R&D part of a phase B • Objectives • Technology development towards a European ELT • Preparatory work for observatory design • Top level requirements • Academic & industrial synergy • Design-independent • Proposal to EC within FP6 - Approved • 39 partners, 47 WPs / Tasks • 42 M€ total, 22 M€ requested • Timescale 2005-2008

  47. ELT Design Study Proposal • The R&D part of a phase B • Objectives • Technology development towards a European ELT • Preparatory work for observatory design • Top level requirements • Academic & industrial synergy • Design-independent • Proposal to EC within FP6 - Approved • 39 partners, 47 WPs / Tasks • 42 M€ total, 22 M€ requested – 8 M€ granted • Timescale 2005-2008 • ESO as coordinator • Contract currently under negotiation with EC IAU Symposium 225 - Lausanne, July 2004 - Slide 50

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