Transcript The Adaptive Mirror for the E-ELT

The Adaptive Mirror for the E-ELT
E. Vernet, M. Cayrel, N. Hubin (ESO)
R. Biasi, G. Angerer, M. Andrighettoni, D. Pescoller (Microgate)
D. Gallieni, M. Tintori, M. Mantegazza (ADS)
A. Riccardi, M. Riva, G. Pariani, R. Briguglio, M. Xompero (INAF)
Outline
•
•
•
•
•
•
M4 key functional requirements
Positioning system & wavefront correction
AO requirements & additional features
Current design of M4
Demonstration prototype design & objectives
Project timeline
An adaptive mirror in the E-ELT
Main goals:
– Provide adaptive correction
– Cancel part of telescope wind
shaking & static aberrations
10 degree FOV
2 Nasmyth focii
In plane centering &
tip-tilt system
Positioning system
• Decentering capability of +-20 mm (0.5mm accuracy, 0.05
resolution)
• Tip-tilt capability of +-2 arcmin (0.5 arcsec accuracy, 0.27
resolution)
• Cross-coupling with tilt <54
mas/mm PV lateral displacement
• Cross-coupling with lateral
displacement 1.85 micron/arcsec
PV tilt
• 0.5mm position stability in xy & 1
arcsec orientation stability (with
LUT), 0.5mm position stability in z
(without LUT)
Courtesy of Adoptica
Wavefront corrector
Correct for both low and high spatial frequencies wavefront errors
Stroke budget includes:
• Quasi static term(<1Hz) for misalignment errors due to gravity
• Term for wavefront errors due to wind load on the telescope
structure, M1, M2 (tip, tilt, focus, coma, astigmatism)
• Stroke for atmospheric disturbances (15% of total stroke)
• Stroke for manufacturing, gravity and thermal effects (35%)
TOTAL STROKE BUDGET: 140 micron
50%
AO specifications
Best
Median
Bad
Worst
Seeing
0.5arcsec
0.85arcsec
1.1 arcsec
2.5 arcsec
Lo
25 m
50 m
100 m
100 m
Tau o
0.7msec
2.5msec
2.5msec
1.5msec
Fitting nm rms
120
145
180
0.5’’ FWHM
• Temporal WFE <60nm rms
• -3dB Closed loop bandwidth > 400Hz
• Segment cophasing
Additional features
• Thermal control:
– optical surface within [-0.5,+1]ºC
– Any other external surface within [-1.5,1.5]ºC
• Diagnostics
• Maintainability
• Safety functions:
– Earthquake detection
Current design characteristics
• 5190 actuators (4326 in pupil)
• 6 segment shells ~2mm thick
• Light-weighted structural
reference body
• A “mirror cell” with load
spreaders
• Hexapod for tip-tilt and
decentering
• A rotator for Nasmyth selection
Courtesy of Adoptica
Shells
• Each segment has comparable size
as DSM (1 m radial direction, 1.2m
on other direction)
• Av. thickness tolerance incl wedge
:+-15 micron
• Local error:10 micron PtV wedge
removed
• 31.5 mm triangular actuator
pattern
• Residual optical error after fitting
14nm rms WF (goal 8nm rm WF)
• 24 membranes for lateral restraint
Brick concept
• Self standing Line Replaceable Unit
• Modularity: three types of bricks with
respectively 15, 28, 36 actuators
• Voice coil motors
• Mounting structure + cooling plate for
actuators & electronics
• Electronics:
– Capacitive sensor board
– Voice coil driver board
– Power + logic on a fin identical for all brick types
• Tool for alignment and fixation on the
reference body structure
Courtesy of Adoptica
Actuators and local sensors
• Updated voice coil motor more compact: 36mm long and 15
mm diameter screwed on the cold plate
• Same contactless technology but enhanced design for more
reliable actuators
• New capacitive sensor armature design, signal pick-up
strategy and contacting to electronics boards to overcome the
problems seen on current units (major source of non working
actuators)
Reference body
• Triangular structure
• ~2500 m diameter
• Conical central hole for optical beam
clearance
• Structure overall thickness 300mm
with smaller ribs 100mm thick.
• ~ 25mm thick front face
• Two materials currently traded-off:
Zerodur and SiC
• Reference body holds 180 bricks
(about 2 kg each)
Courtesy of Adoptica
Demonstration Prototype
upgrade
•
•
•
•
800 mm long, 454mm large
Using same shell as phase B DP
New reference body following M4 design
10 pre-production bricks 15mm thick with
28 actuators (some partially covered by
shells)
• Liquefied gas used for cooling
• Compliant with real time, control, safety
and timing interface requirements
Courtesy of Adoptica
DP objectives
• System performance:
–
–
–
–
–
–
–
–
Voice coil actuator design,
Capacitive sensor armature,
Capacitive sensor pick-up,
Shell edge controllability,
Cophasing stability,
Cooling plant efficiency,
Power dissipation,
SW ad HW safety features
• Design validation:
•
•
•
•
•
Brick concept,
Brick interfaces,
Reference body material,
Control aspects,
Cooling plant design
Project timeline
•
•
•
•
•
•
DP Reference body material selection: mid September 13
DP Start of procurement: Oct 13
Sub-systems assembly readiness review: Dec 13
DP Electromechanical Testing: late Spring 14
DP Optical Testing: Summer 14
Preliminary design review: September 14