ARENA workshop on Telescope and Instrument robotization at Dome-C Playa la Arena, Tenerife, Aligning robotic telescopes within the inversion layer (the life of the robotic optician) Michael I. Andersen Astrophysikalisches Institut Potsdam

ARENA workshop on Telescopes and Instrument Robotization at Dome C Playa la Arena, Tenerife, Aligning robotic telescopes in the inversion layer M.I. Andersen The challenge I The seeing is fantastic! 0.27” median above the inversion layer (Lawrence et al. 2004) Is the telescope fantastic? (to utilize the best seeing, the telescope essentially must be diffraction limited)

ARENA workshop on Telescopes and Instrument Robotization at Dome C Playa la Arena, Tenerife, Aligning robotic telescopes in the inversion layer M.I. Andersen The Challenge II

ARENA workshop on Telescopes and Instrument Robotization at Dome C Playa la Arena, Tenerife, Aligning robotic telescopes in the inversion layer M.I. Andersen Challenge III The optician goes home with the last flight. The optician goes home with the last flight. There is no dark time to test and align. There is no dark time to test and align. The temperature is completely wrong. The temperature is completely wrong. There are 50 working days per season. There are 50 working days per season.

ARENA workshop on Telescopes and Instrument Robotization at Dome C Playa la Arena, Tenerife, Aligning robotic telescopes in the inversion layer M.I. Andersen The challenge IV As part of commisioning, to establish the initial alignment during summer, i.e. in daylight! As part of commisioning, to establish the initial alignment during summer, i.e. in daylight! To maintain and optimize this alignment at temperatures 40 degrees below ‘commisioning temperature’, without much need for human intervention. To maintain and optimize this alignment at temperatures 40 degrees below ‘commisioning temperature’, without much need for human intervention.

ARENA workshop on Telescopes and Instrument Robotization at Dome C Playa la Arena, Tenerife, Aligning robotic telescopes in the inversion layer M.I. Andersen Two case studies Small telescope, ‘ICE-T’, 60/80cm Schmidt (talk by Strassmeier) Small telescope, ‘ICE-T’, 60/80cm Schmidt (talk by Strassmeier) Large telescope, ‘PILOT’, 2.4m ‘classical’ Alt-Az Richey-Cretien telescope (talk by Storey) Large telescope, ‘PILOT’, 2.4m ‘classical’ Alt-Az Richey-Cretien telescope (talk by Storey)

ARENA workshop on Telescopes and Instrument Robotization at Dome C Playa la Arena, Tenerife, Aligning robotic telescopes in the inversion layer M.I. Andersen ICE-T 2 x F/ cm Schmidt 7.7deg square FOV. Fixed passband. 10k x 10k monolitic CCD

ARENA workshop on Telescopes and Instrument Robotization at Dome C Playa la Arena, Tenerife, Aligning robotic telescopes in the inversion layer M.I. Andersen ICE-T optical layout

ARENA workshop on Telescopes and Instrument Robotization at Dome C Playa la Arena, Tenerife, Aligning robotic telescopes in the inversion layer M.I. Andersen The ICE-T challenge Keep the PSF stable, with a uniform defocus Keep the PSF stable, with a uniform defocus → passive design with self compensation → passive design with self compensation Good optical quality mirror and good passive mirror support (corrector less important). Good optical quality mirror and good passive mirror support (corrector less important). Passive focus compensation Passive focus compensation (Aluminum + Aluminum) (Aluminum + Aluminum) (Carbon fibre + CeSic ( Δ CTE <2 x 10^-7) ) (Carbon fibre + CeSic ( Δ CTE <2 x 10^-7) ) (Carbon fibre + Zerodur ( Δ CTE <few x 10^-7) ) (Carbon fibre + Zerodur ( Δ CTE <few x 10^-7) )

ARENA workshop on Telescopes and Instrument Robotization at Dome C Playa la Arena, Tenerife, Aligning robotic telescopes in the inversion layer M.I. Andersen Alignment of ICE-T On-sky daytime alignment very difficult On-sky daytime alignment very difficult (defocussed bright star fainter than sky) (defocussed bright star fainter than sky) Align at home and ship assembled system Align at home and ship assembled system (test on-sky before shipping) (test on-sky before shipping) Need for autocollimation test on Dome-C Need for autocollimation test on Dome-C (large flat mirror or collimator) (large flat mirror or collimator)

ARENA workshop on Telescopes and Instrument Robotization at Dome C Playa la Arena, Tenerife, Aligning robotic telescopes in the inversion layer M.I. Andersen The NOT as ‘a warm PILOT twin’ 2.5m active optics F/2 primary

ARENA workshop on Telescopes and Instrument Robotization at Dome C Playa la Arena, Tenerife, Aligning robotic telescopes in the inversion layer M.I. Andersen CTE problems Using steel, a temperature change of 0.1 deg reduces Strehl ratio to 80%. Radiative heat loss can intro- duce temperature differences of several degrees! The inversion layer problem (chaotic change of temperature)

ARENA workshop on Telescopes and Instrument Robotization at Dome C Playa la Arena, Tenerife, Aligning robotic telescopes in the inversion layer M.I. Andersen Low CTE materials Carbon fibre (excellent, also at -80C) Zerodur (thermal inertia is an issue) CeSic (excellent, but expensive)

ARENA workshop on Telescopes and Instrument Robotization at Dome C Playa la Arena, Tenerife, Aligning robotic telescopes in the inversion layer M.I. Andersen Daytime alignment of the NOT “Pupil imaging” of M2 and M1. Assumption: M1 and M2 mirror figure ‘concentric’ with clear aperture. Rotator axis defines optical axis.

ARENA workshop on Telescopes and Instrument Robotization at Dome C Playa la Arena, Tenerife, Aligning robotic telescopes in the inversion layer M.I. Andersen Conclusions I Commisioning and operations of the opto-mechanical system must be an integral part of the instrument design. Commisioning and operations of the opto-mechanical system must be an integral part of the instrument design. Plan carefully for being able to do all steps of commisioning in full day light. Plan carefully for being able to do all steps of commisioning in full day light.

ARENA workshop on Telescopes and Instrument Robotization at Dome C Playa la Arena, Tenerife, Aligning robotic telescopes in the inversion layer M.I. Andersen Conclusions II Use passive systems where ever possible, e.g. through matching CTEs, when possible. Use passive systems where ever possible, e.g. through matching CTEs, when possible. Consider carefully which adjustments should be under remote control. Consider carefully which adjustments should be under remote control.

ARENA workshop on Telescopes and Instrument Robotization at Dome C Playa la Arena, Tenerife, Aligning robotic telescopes in the inversion layer M.I. Andersen Active optics vs (GL)AO You definitely need either AO or Active optics to utilize the site to the limit. You definitely need either AO or Active optics to utilize the site to the limit. (GL)AO will limit your Field of View. (GL)AO will limit your Field of View. With active optics you need a tower. With active optics you need a tower. Robotic autonomous AO not yet demonstrated (it is a killer technology – it can kill your project). Robotic autonomous AO not yet demonstrated (it is a killer technology – it can kill your project).

ARENA workshop on Telescopes and Instrument Robotization at Dome C Playa la Arena, Tenerife, Aligning robotic telescopes in the inversion layer M.I. Andersen Conclusion III Your science goals must Your science goals must and will drive the choice of and will drive the choice of solutions for your project! solutions for your project!