gregor upgrade of the gct on teneriffe with a 1.5m solar telescope

GREGORUpgrade of the GCT on Teneriffe

with a 1.5m Solar Telescope

O. von der Lühe, W. Schmidt, D. Soltau (KIS, Freiburg)

F. Kneer (USG, Göttingen)

J. Staude (AIP, Potsdam)

April 19, 2023 GREGOR 2

Motivation German ground based solar science

needs access to a new large solar facility of the 3m class to stay competitive (LEST, AST)

A step „in between“ is widely regarded as necessary to validate enabling technology (adaptive optics)

A modern 1.5 m solar telescope opens new scientific opportunities

The 45 cm Gregory Coudé Telescope is 35 years old, has lived its scientific life

Izaña is a developed observatory with established administrative procedures


GREGOR Main Characteristics 1.5 m diameter, direct pointing,

Gregorian Telescope with centered tertiary (LEST inheritance)

Open Telescope tube, fully retractable dome (DOT inheritance)

Alt-Az mount Lightweighted optomechanical structure Integrated adaptive optics system Focus redirectable to two laboratories FOV 300 arcsec, feff 75 m

Low instrumental polarization NIR and TIR* capability Dead-reckoning pointing & tracking


GREGOR Cross SectionNew, fully retractable dome

Telescope tube and

mount

External mirror elevator

Wind shield, retractable

Science foci


Tradeoffs Evacuated / He-filled telescope

+ internal seeing (vacuum, He-filling)-- internal seeing (closed dome)+ contamination protection-- wind protection (closed dome during operation)- weight (must withstand vacuum)- window

Open Telescope- internal seeing (open telescope)

++ internal seeing (retracted dome)- dust protection- wind protection++ weight (can be lightweighted)++ no window


Critical Areas• Internal seeing

• Wind buffeting

• Contamination

• Track ambient temperature!– athermal structure– thermally controlled primary

mirror– thermally controlled heat trap at

primary focus– evacuated coudé path*

• Increase resonance frequency– lightweight optics– lightweight structure

• Use windshields above design windspeed

• Cleaning procedure


Optical Design Triple Gregorian optics f/1.75, 1.5 m primary 300 arcsec field stop at F1 Polarimetric calibration optics at

F2 Field lens near F2 to place 110

mm pupil near M6 and M7* Fast guiding / DM can be placed

at M6 and M7 F/50 tertiary focus can be placed

in two labs Feff = 75 m


Optics Highlights• Use C/SiC technology for first three

mirrors– lightweighted

– primary weight ~150 kg

– high CTC - uniform temperature

– active mirror cooling to dispose of 170 W absorbed sunlight

– air flushing or cold plate for TC

– surface figuring considered most critical item

– six DOF precision control of M1/M2 alignment

– M3 used for focussing


Solar Lite M1 development at DSS

Two halves of Solar Lite 1m main mirror greenfelt bodies during joining and prior to infiltration.

Pictures courtesy Dornier Satteliten Systeme


Adaptive Optics I

Major enabling technology item Critical for combining high spatial

with high spectral resolution at sufficient sensitivity

Integrated into telescope (M6/M7) Serves all foci Major development item Development of AO for VTT

Simultaneous compensated and uncompensated image taken with the NSO / Sac Peak Solar Adaptive Optics System (Rimmele, 1999)


Adaptive Optics II

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.40

0.2

0.4

0.6

0.8

1

150 Hz, strong300 Hz, strong600 Hz, strong150 Hz, weak300 Hz, weak600 Hz, weak

Srehl vs. r0 and f3dB for 64 DOF

r0 [m]

Str

ehl


Adaptive Optics Requirements Analysis

• High Level Goal: Strehl > 0.5 for more than 50% of the time. Feasible only with 256 DOF and fc > 200 Hz.

• Reasonable "first start" system: 64 DOF and fc > 150 Hz achieves Strehl > 0.5 for 20% of the time and Strehl of 0.25 for 50% of the time. Should be doable with today's technology.

• 66 DOF: Zernike polynomials n = 10 ( ~100 actuators)

• 256 DOF means all Zernike polynomials up to n = 22 ( ~400 actuators)


AO Top Level Requirements

No. of degrees of freedom 66

No. of channels for Dm / WFS 100 (TBD)

Closed loop bandwidth 150 Hz

Overall residual WFE due to system at tertiary focus < / 10

Tip-Tilt compensation range:

< 5 Hz

5 Hz ... 100 Hz

5 arcsec

1 arcsec

Deformable mirror deformation range, overall 15 µm ptv

Wavelength range for WF Sensor Visible

Intensity contrast of target structure 0.5 %

Fraction of sunlight used for WFS < 10 % (< 50 %)

Lifetime 5 yrs


GREGOR Instrumentation

• Acommodation at two levels– main observing room

– spectrograph room

– plenty of space

• Redeployment from VTT– Göttingen FPI Filtergraph

– POLIS

• New IR instruments


GREGOR Infrastructure

• Removal of old dome and elevator hut• Erection of new, fully retractable dome• Erection of removable windshield system• Increase of inner tower height• Installation of new external elevator• Installation of new control room in living quarters


Programmatics

• Realisation as a purely German Project– established, lean structure already in place (DFG, KIS & partners)

– easier to sell to funding bodies

– collaboration with German industry

• International participation TBD– moral support and advice welcome

– dissemination of experience gained

• Exploitation through existing procedures – CCI IT

– collaborations


Planning & Schedule I

• Done:– Major concept tradeoffs

– Top level design studies (Telescope, AO)

– M1 design study (Dornier)

• Under way:– Science & Financial Plans, Proposal preparation

– Engineering study of Telescope

– Realization of M3 to study surface technologies

– Subsystem studies


Planning & Schedule II• Preparatory phase to continue until End `99

• Detailed Design Phase (2000 - mid 2001)– detailed designs of Telescope optics, optomechanics, control by Industry– designs of focal instruments by Institutes– civil engineering design– adaptive optics at VTT

• Construction Phase (mid `01 - mid `03)– construction / AIV of telescope– construction of AO system– civil engineering works– erection of dome and telescope

• Verification and Tests (mid `03 - early `04)– Integration of FP instruments– system level tests


Financing

• Total cost estimated to 7.2 MDM (± 20%)

• Thorough industrial cost assessment pending

• About 40% from operational budgets of Partner institutes

• Remaining funds through third party proposals

• Proposal by end of year

gregor upgrade of the gct on teneriffe with a 1.5m solar telescope

Documents

telescope internal

gregorian telescope

telescope m6m7serves

open telescope internal

gregory coud telescope

inheritanceopen telescope

solar telescopeo

wind protection closed