Adaptive telescope mirror developments in Arcetri

1
Adaptive telescope mirror developments in Arcetri

• A. Riccardi

2
Adaptive secondary concept

• Concept Substitution of conventional M2
  telescope mirror with a thin (1.5-2.0mm)
  deformable shells controlled in position with
  large-stroke (0.1mm) electromagnetic (voice-coil
  like) force actuators and using internal
  capacitive sensors as position feedback

3
Control electronics
Total computational power 78 Gmac/s (32bit
fp) Real-time reconstructor on-boardWFS 30x30
34-47ms (z-m) Slope comm time 20ms
Communication Board
Communication Board



Communication Board

Communication Board

Communication Board

Communication Board
(1x backplane)
(1x backplane)
(1x backplane)
(1x backplane)
(1x backplane)
(1x backplane)
Reference Signal
Reference Signal
Reference Signal
Reference Signal
Reference Signal
Reference Signal
Generator Board (1x backplane)
Generator Board (1x backplane)
Generator Board (1x backplane)
Generator Board (1x backplane)
Generator Board (1x backplane)
Generator Board (1x backplane)
DSP control Board (14x backplane)
48V, 35 A
Power
DSP control Board (14x backplane)
DSP control Board (14x backplane)
DSP control Board (14x backplane)
DSP control Board (14x backplane)
DSP control Board (14x backplane)
DSP control Board (14x backplane)
DSP control Board (14x backplane)
Liquid cooled crates,
each comprehending 2 backplanes (3x)
3 cooled electronics boxes2 crates/box 84 custom
DSP boards 2 DSP/board - 8 acts/board 32-bit
floating-point 470Mmac/s (MMT 16-bit integer
40Mmac/s)
Distribution boards
Actuators
Coil
Gap
Thin mirror
Reference signal
4
Why and adaptive telescope mirror?
Less warm surfaces
WFS
BS
K band 2-2.6 shorter exp. time (MLH, PASP)
TTM
DM
Coll.
Sci. Camera
5
Advantages

• Un solo correttore per tutti i fuochi (es. LBT 4
  fuochi/pup)
• Maggiore riflettività (5 riflessioni eliminate
  0.9850.90)
• Minore emissività IR (1/3-1/4 exp.time K-N
  bg-limited)
• Compattezza della parte di sensing (maggiore
  stabilità)
• Attuatori elettromagnetici con feedback
  capacitivo
• Grande stroke TTMDMchopperFS in ununica
  unità
• Unità robusta rispetto malfunzionamento di
  attuatori
• Tecnologia estendibile a specchi adattivi per
  ELTs
• Grande stroke (wind bufferting)
• 104att., grande numero attuatori ? grandi
  specchi adatt.

6
Overview of developments
MMT Adaptive Secondary (on sky 2000) Joint
venture OAA-Steward MG-ADS contract CAAO
TEC0-TEC1 EU funded underthe ELT-DS
project MG-ADS subcontract INAF
LBT Adaptive Secondary (integration phase, on-sky
2008)
M4-ARU EELT ESO funded developmentMG-ADS
proposal for contract INAF subcontract of MG-ADS
Magellan Adaptive Secondary (copy of LBT, on-sky
???)
VLT Adaptive Secondary (design phase, on-sky
2015) INAF under OPTICON-JRA1 MG-ADS subcontract
with ESO
7
MMT on sky
mV 8.0 (B0V)
Credits http//athene.as.arizona.edu/lclose/AOPR
ESS/
8
Existing adaptive mirror in hardware
INAF, Steward Obs, Microgate Srl, ADS Int. Srl
9
LBT integration progress
10
Next ASM generation VLT-DSM

• VLT-DSM
• 1.1m
• 1170 act.
• 29 mm pitch
• 1 ms response

VLT-DSM


ESO, Microgate Srl, ADS Int. Srl, INAF
11
Current technology a comparison
12
Current technology a comparison
13
Current limitation in BW (or stroke)
Capsens-coil crosstalk Currently it limits
derivative gainSome level of natural damping is
still req. 70um gap 0.7-0.9ms settling
time 100um gap 1.2-1.7ms settling time
Item to solve in the commissioned
studies especially for TEC0 (larger mass, larger
gap, larger derivative
gain required) In case of glass, keeping
constant g-quilting Mass per actuator 6.5g
(LBT,TEC1-30mm)
350g (TEC0-100mm)
30g (TEC0-50mm)
CL Actuator transferfunction (with deriv gain0)
7kHz
14
Noise vs gap (i.e. stroke)
40um gap
70um gap
130um gap
15
TEC0 and TEC1 target

• Feasibility study of 2.5m DM with actuator
  spacing of
• DM-TEC 0 woofer corrector, medium stroke field
  stabilizer
• 50-100mm actuator pitch (2000-500 acts)
• 200mm PtV stroke (2as on-sky for 42m telesc.)
  (300mm goal)
• with high efficiency actuator prototype
• DM-TEC 1 tweeter corrector, low stroke field
  stabilizer
• corrector25-30mm actuator pitch (7800-5400 acts)
• 100mm PtV stroke (1as on-sky for 42m telesc.)
  (200mm goal)
• with scale down prototype (100act)

16
Towards an Adaptive ELT

• Part of the technological solutions currently
  used cannot directly transferred to Adaptive ELT,
  in particular
• Production of optical flat/concave/convex thin
  (2mm) glass shell with diam1m is not proven.
  See FP6 studies by SESO and INAF-Brera.See
  studies with other material like CFRP
• Lateral support from central membrain could
  induce too large stresses (?diam) on glass and
  for membrane buckling. Alternative lateral
  support shall be studied also to avoid holes in
  case of segments
• Current referencecold plate scheme is not
  applicable for large mirrors More favorable
  stiffness-to-mass ratio backplate will be
  studied.
• Larger stroke required (70um - 100-300um)
  larger dynamical range capacitive sensor shall be
  studied with reduced noise at large gap.
  Crosstalk has to be reduced to increase
  electronic damping (large gap with large BW).

17
Comparison among alternative materials
18
CFPR by Composite Mirror applications
Tucson, AZ