ARENA workshop on Telescope and Instrument robotization at Dome-C Playa la Arena, Tenerife, 2007.03.27 Aligning robotic telescopes within the inversion

ARENA workshop on ARENA workshop on Telescope and Instrument robotization at Telescope and Instrument robotization at Dome-CDome-CPlaya la Arena, Tenerife, 2007.03.27Playa la Arena, Tenerife, 2007.03.27

Aligning robotic telescopes within the inversion layer (the life of the robotic optician)

Michael I. AndersenMichael I. AndersenAstrophysikalisches Institut PotsdamAstrophysikalisches Institut Potsdam

ARENA workshop on ARENA workshop on Telescopes and Instrument Robotization at Dome Telescopes and Instrument Robotization at Dome CCPlaya la Arena, Tenerife, 2007.03.27 Playa la Arena, Tenerife, 2007.03.27

Aligning robotic telescopes in the inversion Aligning robotic telescopes in the inversion layer layer M.I. AndersenM.I. Andersen

The challenge IThe 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)



The Challenge IIThe Challenge II



Challenge IIIChallenge 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.



The challenge IVThe challenge IV

As part of commisioning, to As part of commisioning, to establish the initial alignment during establish the initial alignment during summer, i.e. in daylight!summer, i.e. in daylight!

To maintain and optimize this To maintain and optimize this alignment at temperatures 40 alignment at temperatures 40 degrees below ‘commisioning degrees below ‘commisioning temperature’, without much need temperature’, without much need for human intervention.for human intervention.



Two case studiesTwo case studies

Small telescope, ‘ICE-T’, 60/80cm Small telescope, ‘ICE-T’, 60/80cm Schmidt Schmidt (talk by Strassmeier)(talk by Strassmeier)

Large telescope, ‘PILOT’, 2.4m Large telescope, ‘PILOT’, 2.4m ‘classical’ Alt-Az Richey-Cretien ‘classical’ Alt-Az Richey-Cretien telescope telescope (talk by Storey)(talk by Storey)



ICE-TICE-T

• 2 x F/1.17 60cm Schmidt

• 7.7deg square FOV.

• Fixed passband.

• 10k x 10k monolitic CCD



ICE-T optical layoutICE-T optical layout



The ICE-T challengeThe ICE-T challenge

Keep the PSF stable, with a uniform defocusKeep the PSF stable, with a uniform defocus → → passive design with self compensationpassive design with self compensation

Good optical quality mirror and good passive mirror Good optical quality mirror and good passive mirror

support (corrector less important).support (corrector less important).

Passive focus compensationPassive focus compensation (Aluminum + Aluminum)(Aluminum + Aluminum)

(Carbon fibre + CeSic ((Carbon fibre + CeSic (ΔΔCTE CTE <<2 x 10^-7) )2 x 10^-7) )

(Carbon fibre + Zerodur ((Carbon fibre + Zerodur (ΔΔCTE CTE <<few x 10^-7) )few x 10^-7) )



Alignment of ICE-TAlignment of ICE-T

On-sky daytime alignment very difficultOn-sky daytime alignment very difficult

(defocussed bright star fainter than sky)(defocussed bright star fainter than sky)

Align at home and ship assembled systemAlign at home and ship assembled system

(test on-sky before shipping)(test on-sky before shipping)

Need for autocollimation test on Dome-CNeed for autocollimation test on Dome-C

(large flat mirror or collimator)(large flat mirror or collimator)



The NOT as The NOT as ‘‘a warm PILOT twina warm PILOT twin’’

2.5m active optics F/2 primary



CTE problemsCTE 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)



Low CTE materialsLow CTE materials

Carbon fibre(excellent, alsoat -80C)

Zerodur(thermal inertiais an issue)

CeSic(excellent, butexpensive)



Daytime alignment of the Daytime alignment of the NOTNOT

• “Pupil imaging” of M2 and M1.

• Assumption: M1 and M2 mirror figure ‘concentric’ with clear aperture.

• Rotator axis defines optical axis.



Conclusions IConclusions I

Commisioning and operations of Commisioning and operations of the opto-mechanical system must the opto-mechanical system must be an integral part of the be an integral part of the instrument design.instrument design.

Plan carefully for being able to do Plan carefully for being able to do all steps of commisioning in full day all steps of commisioning in full day light.light.



Conclusions IIConclusions II

Use passive systems where ever Use passive systems where ever possible, e.g. through matching CTEs, possible, e.g. through matching CTEs, when possible.when possible.

Consider carefully which adjustments Consider carefully which adjustments should be under remote control.should be under remote control.



Active opticsActive optics vsvs (GL)AO(GL)AO

You definitely need either AO or Active You definitely need either AO or Active optics to utilize the site to the limit.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 Robotic autonomous AO not yet

demonstrated (it is a killer technology – demonstrated (it is a killer technology – it can kill your project).it can kill your project).



Conclusion IIIConclusion III

Your science goals mustYour science goals must and will drive the choice of and will drive the choice of solutions for your project! solutions for your project!

Documents

ARENA workshop on Telescope and Instrument robotization at Dome-C Playa la Arena, Tenerife, 2007.03.27 Aligning robotic telescopes within the inversion