1. ASTRI SST-2M The Prototype monolithic 1.8 m
Secondary mirror
monolithic 1.8 m
Telescope
dual-mirror Schwarzschild- Couder
FoV = 9.6°
EFL = 2150 mm
Primary mirror
segmented 4.3 m
18 hex elements
850 mm side-to-side
Focal plane camera
compact (50x50x50 cm3)
based on Si-PMs sensors.
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd

2. Primary Mirror active supports
Active Optics system
Primary Mirror active supports
M1 segment support
One fixed point
Two axial actuators
Total stroke > 10 mm
Positioning accuracy < 3µm
Prototype for lab test
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 2 2

3. Secondary Mirror active support
Active Optics system
Secondary Mirror active support
M2 active support
Three axial actuators
Tilt + Focus
Whiffletrees to share load
Total stroke ~ 15 mm
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 3 3

4. Alignment tracking system
Active Optics system
Alignment tracking system
Each M1 segment is equipped with a laser which beam follows the optical path of the telescope
Spot position is tracked via two CCDs located at the camera edges and provides feedback on mirror tilt
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 4 4

5. Active Mirror Control Unit
Active Optics system
Active Mirror Control Unit
Active Mirror Control Unit (dedicated PC)
Telescope Control System
OPC-UA Client
Telescope Control Unit
Twincat 3 (Beckhoff)
Main
OPC-UA Server DB KM
ATS M1 M2
ADS
Engineering interface
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 5 5

6. Performance prediction
Kinematic model
Performance prediction
Segment
model
Geometrical
model
Optical
model
Behaviour
prediction
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 6 6

7. Kinematic model System calibration p1 p2 Seventh order polynomial
Residuals
Example:
Seventh order polynomial
Image shifts up to
d= ∆𝑥 + ∆𝑦 <80 mm
residuals for whole M1 (18 segments)
> 99% of residuals are below the hardware positioning accuracy of actuators
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 7 7 7

8. Conclusions
active positioning is performed by means of axial actuators driven by stepper motors
an alignment tracking system provides feedback on the mirrors alignment. It will be used also during calibrations
can operate in stand alone mode or within the Telescope Control System
A complete kinematic model predicts system performance, quantifying non- linearities (dominated by the M1 axial actuator behaviour)
A simulation of the calibration procedure shows that it is possible to describe and correct the image shift induced by mirrors tilt over the whole range allowed by the hardware with a seventh order polynomial, being the residuals well below the mechanical accuracy positioning of the actuators
Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 8 8