1

ASTRI SST-2MThe Prototype

Telescope

dual-mirror Schwarzschild-Couder

FoV = 9.6° EFL = 2150 mm

Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd

Secondary mirror

monolithic 1.8 m

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.

2

Active Optics systemPrimary Mirror active supports

Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd

M1 segment support

One fixed point Two axial actuators Total stroke > 10 mm Positioning accuracy < 3µm Prototype for lab test

3

Active Optics systemSecondary Mirror active support

Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd

M2 active support

Three axial actuators Tilt + Focus Whiffletrees to share load Total stroke ~ 15 mm

4

Active Optics systemAlignment tracking system

Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd

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

5

Active Optics systemActive Mirror Control Unit

Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd

Telescope Control System

OPC-UA Client Telescope Control Unit

Active Mirror Control Unit (dedicated PC)

Twincat 3 (Beckhoff)

ATSKM M1 M2

Main OPC-UA ServerDB

Engineering interface

ADS

6

Kinematic modelPerformance prediction

Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd

Geometricalmodel

Opticalmodel

Segmentmodel

Behaviourprediction

5

0n

nknk pct

),(2/)(

),(2/)(

2121

2121

ttottv

ttottu

p1 p2

7

Kinematic modelSystem calibration

Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd 7

Example:

Seventh order polynomial Image shifts up to

mm residuals for whole M1 (18 segments) > 99% of residuals are below the

hardware positioning accuracy of actuators

Residuals

8

Conclusions

Daniele Gardiol – SPIE Advanced Telescopes and Instrumentation 2014, Montréal, Quebéc, Canada, June 23rd

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