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Osservatoriodi Arcetri
Potsdam 16-17 May 2002 - 1st light LBT AO: PDR
Optical Test Tower for the LBT Adaptive Optics
System
A. Riccardi1, P. Salinari1, S. Esposito1, D. Gallieni2
1Osservatorio Astrofisico di Arcetri, Italy2ADS International, Italy
Potsdam 16-17 May 2002 - 1st light LBT AO: PDR
Osservatoriodi Arcetri
A. Riccardi
Purpose of the test tower
Main target:Test and characterization of the
Optical Closed Loop for the Complete and Final AO System
before 1st light
Adaptive Secondary Tests:•Optical Flattening and calibration•Optical behavior at “mountain” ambient temperature•Dynamical Behavior at “mountain” atmospheric pressureWFS Optical Test:•Optical interaction with LBT672•Optical Closed loop operation
Potsdam 16-17 May 2002 - 1st light LBT AO: PDR
Osservatoriodi Arcetri
A. Riccardi
Optical Layout Concept
Elliptical secondary
F2
F1
F/15.0
F/1.22
137
13
mm
106
4.7
mm911mm
Potsdam 16-17 May 2002 - 1st light LBT AO: PDR
Osservatoriodi Arcetri
A. RiccardiInterferometer light injection
Fisba interferomet
er
Movable beam-splitter
Beam to/from AdSec
Beam to WFS
110mm 45mm
190
mm
Potsdam 16-17 May 2002 - 1st light LBT AO: PDR
Osservatoriodi Arcetri
A. Riccardi
Reference OpticsWFS needs exit pupil on the AdSec mirror!No simple reference sphere:Collimating optics+flat on the pupil image
Parabola+flat Single Aspheric lens+flat
Spheric obj+flat
Potsdam 16-17 May 2002 - 1st light LBT AO: PDR
Osservatoriodi Arcetri
A. Riccardi
Reference Optics
Reference optics
Commercial Thorlab C240-TMBF/0.8 diam:8mmbetter then /20 PtV on-axisMolded – highly aspherical
Design: 3 lenses, 4sph surf, 2flat surfF/1.1, /20 PtV on-axis(microscope obj:Trapped back-focus)
Parabola F/1.1 Diam:10-20mmBetter then /20 PtV on-axisBetter behavior off-axis>0.06 to allow +/-200vw of tilt
Potsdam 16-17 May 2002 - 1st light LBT AO: PDR
Osservatoriodi Arcetri
A. RiccardiOptical Test Tower in Arcetri
15m optical bench to simulate the telescope
Arcetri Solar Tower
Reference optics
Tube supported byIsolators (pendolum) Optical Bench (WFS unit)
Potsdam 16-17 May 2002 - 1st light LBT AO: PDR
Osservatoriodi Arcetri
A. Riccardi
Optical Test Tower
Lab
WinchMass:5200kg (tube+Adsec+OptBench+Complete WFS unit)
Tube height: 13.5mIn/Out diameter: 1.1/1.2m
Assembly:6 sections with flanges
Potsdam 16-17 May 2002 - 1st light LBT AO: PDR
Osservatoriodi Arcetri
A. RiccardiVibration isolators and supports
3 Newport I-4000 Pneumatic Isolators (max load: 6300kg)resonance frequency: 1.0Hz (vert) 1.3Hz (hor.)Damping: 15% of the critical dampingDiam: 355mm H: 317mm
Potsdam 16-17 May 2002 - 1st light LBT AO: PDR
Osservatoriodi Arcetri
A. Riccardi
Top isolators
Heavy-load isolators (horizontal and vertical springs and vertical leveling system)
Isolators (horizontal springs and leveling system)
5m
14m
CM
6mIron/steel Ring rigidly connected to the structure (section)
Isolators between the tube top and the ring
Iron/steel ring rigidly connected to the top tower structure
Enidine or Fabreeka Air SpringPreload 1000kg/actFreq 2.5-3.5Hz
Potsdam 16-17 May 2002 - 1st light LBT AO: PDR
Osservatoriodi Arcetri
A. Riccardi
Dynamics (FEA)
18Hz(Hexapod
mode)
27Hz(Bending)
Tip-Tilt and Piston(Rigid modes):1.4Hz, 1.9Hz, 0.98Hz(isolators)
Potsdam 16-17 May 2002 - 1st light LBT AO: PDR
Osservatoriodi Arcetri
A. Riccardi
Thermal stabilization
Thermal control:
Goal: 0.2K stability, max.
DT=30K wrt ambient
Double cylinder structure
20mbar pressure in the gap (Acetone: liquid-vapour eq.)
3cm hd polyurethane outer skin (3kW@T=30K)
Potsdam 16-17 May 2002 - 1st light LBT AO: PDR
Osservatoriodi Arcetri
A. Riccardi
Alignment procedure
Interferom.: F/10Mirror: F/15
1. Hex to move the spot on F12. Hex to move the spot on F2 keeping the spot on F13. Interf. Stage to set the focus4. Hex+Interf. Stage to compensate spherical ab.
Reference Optics mechanical pre-alignment:+/-3mm x-y (WFS +/-0.1 pix)+/-5mm z (WFS z+ stage clearance)+/-2deg (F/1.1 instead of F/1.2)
WFS
BS
Potsdam 16-17 May 2002 - 1st light LBT AO: PDR
Osservatoriodi Arcetri
A. RiccardiOptomechanical tolerances
Source of error Defocus PtV
Tilt PtV
Shell-RefOpt distance 0.28 wv/m
Interfer.-Shell distance 1.1wv/mm
Shell+RefOpt decentering
0.21wv/m
Shell+RefOpt tilt 14wv/arcsec
Shell or RefOpt decentering
2.9wv/m
Shell tilt 20wv/arcsec
Target: /10 focus stability in 7.5sec (differential meas. time)
0.8 K/min (invar) 1.5 K/min (steel)
Target: /10 in 1.5sec (single meas. Time) 23nm/s
Active control of the Tip-Tilt (AdSec?)
Potsdam 16-17 May 2002 - 1st light LBT AO: PDR
Osservatoriodi Arcetri
A. RiccardiTower tilt and Hexapod disp/tt
G
Wind
RefOpt
Hexapod flexion:3.3 nm/arcsec5.1 arcsec/arcsec
Potsdam 16-17 May 2002 - 1st light LBT AO: PDR
Osservatoriodi Arcetri
A. Riccardi
Wind and test towerf*
PSD
[ra
d2]
Vwind=10m/sTop 8m subject to wind
Wind Static Force: 120NGust Wind Force: 86N rmsTower tilt: 7.5 arcsec rms
0.15 vw PtV of tilt (rms)(resonance at 1Hz)
Critical measurements withV<3m/s or active tiltcompensation with AdSec
It is not a problem at the telescope (the dome is closed)
Potsdam 16-17 May 2002 - 1st light LBT AO: PDR
Osservatoriodi Arcetri
A. Riccardi
Conclusions
Test tower facility not charged to the project
Optical test tower design is on progress Civil works (started) Mechanical design (ready for manufact. design) Opical design Thermal control Tilt stabilization
Must be operative for the end of electronic tests of LBT672 (2nd-half 2003)