1. Pre-focal wave front correction and field stabilization for the E-ELT
L. Jochum, N. Hubin, E. Vernet, P.-Y. Madec, M. Dimmler, M. Mueller, B.Sedghi

2. Outline E-ELT optics layout E-ELT AO components Main axes control
Field Stabilization Unit
Adaptive Unit
Conclusions

3. 5 mirror adaptive telescope
E-ELT Optics Layout
Surface shape
Diameter (mm)
Distance (mm) M1
Concave ellipse
42000
36500 M2
Convex hyperbola
5691 M3
Concave sphere
4032
13645 M4
flat
2636 x 2587
10000 M5
2978 x 2388
5 mirror adaptive telescope

4. E-ELT AO components Disturbers Task for E-ELT pre-focal AO
Atmospheric turbulence
Windload
Gravity and thermal effects
Task for E-ELT pre-focal AO
real time wave front correction for the E-ELT focal plane, reaching diffraction limit of the telescope in the NIR
Correction devices
Telescope main axes control
Field stabilization mirror
Adaptive mirror
Wave front sensing systems
NGS, LGS, laser sources, beam transport and launch, WFS, RTC

5. Main axes control
Residual of main axes control  input disturbance for image stabilization

6. M5 – Field Stabilization Unit
Task: Tip tilt correction for image stabilization
Components:
Mirror
Field stabilization system
Mounting structure
Control system
Auxiliary Equipment
Incoming disturbance:
1” rms residual tip tilt
Dominated by wind shaking
Conservative assumptions:
10m/s wind 10 m
No dome
30% safety margin

7. M5 correction Required output Residual on sky tip-tilt:
< 0.07” rms (goal 0.06”) over the entire frequency range
< 0.004” rms for [9Hz to ] all peaks < 2σ
Conditions:
WFS sampling: 100Hz
RON no noise
WFS delay 10 ms
RTC delay 1 ms
Phase margin >45 deg
Modulus margin >0.6
Communication with RTC [ ]Hz
E-ELT control simulation: main axes + M5
Remaining wave front correction  adaptive mirror with positioning system

8. M4 – Adaptive Unit Components: Tasks: correction of…
Adaptive mirror, Positioning system, Mounting structure, Control system, Auxiliary Equipment
Tasks: correction of…
…small amplitude residual tip-tilt
…high order wavefront (real-time)
Atmosphere
wind shake
low spatial frequency telescope errors
…large amplitude low frequency tip-tilt
…lateral pupil position
Telescope gravity
Thermal load
adapter tracking wobble & run-out errors
Nasmyth foci selection
Adaptive mirror
Positioning system (4 DoF)

9. M4 positioning system requirements
Pupil Lateral correction
Range (mm)
± 20 mm
Min Continuous speed (mm/s)
speed ≥ 1 mm/s
Absolute accuracy (µm)
≤ 100 µm
Resolution (µm)
≤ 50 µm
Bandwidth (Hz)
> 1 Hz
Mechanical tilt correction
Range (")
± 120 (±14" on sky)
Speed ("/s)
10 (1.2"/s on sky)
Absolute accuracy (")
0.5 (0.06" on-sky)
Resolution (")
0.25 (0.03" on-sky)
Cross coupling
Between Tip & tilt (mech ")
0.25
Between lateral & tilt (mech ") over full range
Between lateral & tilt (mech ") during any time period of 0.2 s
0.025
Between tilt & lateral (µm)
< 50
Between two lateral (µm)

10. Adaptive mirror main requirements
Fitting error: 145 nm rms (goal 110)
Temporal error: 60 nm rms (goal 43)
Tip-tilt after M4: kHz WFS sampling
Total stroke defined for worst seeing conditions (2.5arcsec seeing, 100 m outer scale)
Optical quality, mass, power consumption, dynamic behavior, passive stability (lookup tables), environment, ….
High reliability (key element for E ELT)
under median seeing conditions

11. Required tip-tilt correction after M4
Incomming disturbance: 0.119” residual on sky rms after telescope & M5 correction
Wavefront sensor sampling frequency (Hz)
Loop delay ms
Res. on-sky tip-tilt errors (mas rms)
100 11 9
290
4.5
3.5
700
2.4
1.6
1000 2
1.3
1200
1.8
E-ELT control simulation: main axes + M5 + M4
Conservative assumptions:
10m/s wind 10 m
Exponential wind profile
No dome
30% safety margin in original data

12. 3 step disturbance correction
Telescope main axes control
Remaining tip tilt < 1” rms M5
Low frequency, high stroke M4
High frequency, low stroke
1.3 mas residual rms error compatible with diffraction limit in NIR

13. Conclusions
E-ELT will be an adaptive telescope, NIR diffraction limited
In-built Field stabilization mirror
In-built adaptive mirror
Demanding requirements pushing state of the art technology
Feasibility studies, conceptual and preliminary design, breadboarding and prototyping of critical components carried out by industry under ESO contracts
16h00 Armando Riccardi, 16h40 : Daniele Gallieni E-ELT M4AU development at Microgate
16h20 Bruno Crépy, 17h20 Jean-Christophe Sinquin E-ELT M4AU development at CILAS
17h40 Javier Barriga E-ELT M5FU development at NTE

14. c'est tout