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

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

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

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

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

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

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

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