The Extremely Large Telescope (ELT)
Building the biggest optical telescope on earth
37C3, 2023-12-27
Credit: E. Garcés/ESO. Ack.: N. Dubost
About us
We work as software engineers at European Southern Observatory (ESO)
Nicolas works on observatory control software
Linus works on adaptive optics control software
European Southern Observatory (ESO)
European Organization for Astronomical Research in the Southern Hemisphere
Formation: 1962
Intergovernmental Organization, 16 Member States
Chile: Host State
Australia: Strategic Partner
ESO’s Mission is to design, build and operate advanced ground-based observatories, and to foster international collaboration for astronomy
European Southern Observatory (ESO)
ESO HQ,
Credit: E. Graf (graf-flugplatz.de)/ESO
Headquarters: Garching bei München, Germany
(since 1981)
Telescope sites: Atacama Desert, Chile
Staff: ≈750 (HQ: 500, Chile: 250)
Contributions in 2021: 192 M€
Credit: ESO
Credit: Modified from original by Claude Nicollier
La Silla, 2400 m: ESO 3.6m-Telescope, New Technology Telescope, ...
Credit: Zdeněk Bardon/ESO
Paranal, 2600 m: VLT, VLTI, VISTA, ...
Credit: ESO/G. Hüdepohl (atacamaphoto.com)
Chajnantor, 5000 m: ALMA (ESO with partners)
Credit: ESO/Angelos Tsaousis
Reasons for a new telescope
Scientists want to study:
Earth-like exoplanets
Biomarkers on exoplanets
Dark matter
Faint objects in our solar system
Therefore
increase angular resolution ⇒ larger primary mirror diameter
increase light collecting surface ⇒ increase mirror size
more light ⇒ fainter objects observable, shorter exposure times
The Extremely Large Telescope (under construction)
Rendering,
Credit: ESO
The Extremely Large Telescope
Rendering,
Credit: ESO
39.3 m primary mirror diameter
Site: Cerro Armazones, 3045 m
≈23 km east of the Cerro Paranal (VLT)
Cost: ≈1300 M€ (2014 - 2028)
First Light planned for end of 2028
Similar projects: GMT (25 m), TMT (30 m)
Dome (Enclosure)
Protection from the environment (sun, wind, temperature, dust, rain)
Ventilation and air-conditioning to prevent "dome seeing"
Wind screen to deflect wind away from the mirrors
Seismic isolators, separate foundations for Dome and Main Structure
Credit: ESO
Main Structure
Credit: ESO
Credit: ESO
Credit: ESO/L. Calçada/ACe Consortium
M1
Credit: ESO/L. Calçada/ACe Consortium
Monolithic mirror:
Feasible up to ≈10 m diameter
Heavy, e.g. VLT M1 (8.2 m) ≈23 t
Expensive
Logistics/transportation by truck and ship
⇒ Segmented mirror design
M1
Tamai, R. (2022). "ELT Telescope Progress", ELT Instruments Day 2022
6 * 133 = 798 hexagonal segments (+ 133 spares)
Silver coating to be renewed every 2 years
2 segment exchanges per day
6-fold symmetry, 1 spare sector
Position and shape must be maintained to an accuracy of tens of nm
M1 Segment Unit
Tamai, R. (2022). "ELT Telescope Progress", ELT Instruments Day 2022
50 mm thick Zerodur glass-ceramic, 1.4 m diameter
≈250 kg including segment support
3 Position Actuators (PACT) to change piston, tip, tilt
(2394 PACTs)
6 Edge Sensor pairs (ES) to measure piston,
gap and shear to the adjacent segment (≈4500 ES pairs)
9 shape actuators (warping harness, WH) to change
optical characteristics (≈7182)
500 Hz rate for ES read-out and PACT command
Credit: Safran
M2 and M3
M2: 4.25 m, convex, highly aspheric
M3: 4.00 m, concave, mild aspheric
Sub-micron precision hexapod positioning system
≈3 t per mirror, ≈12 t per assembly
M2 unit,
Credit: SENER
M3 unit,
Credit: ESO (L. Calçada)/SENER
Atmospheric Distortion
Credit: Fabian Horst
Turbulence in the atmosphere distorts the path of light
Objects appear blurry, seem to twinkle
⇒ Adaptive Optics
Credit: ESO
Natural and Laser Guide Stars
Use a bright star as reference
Sufficiently bright natural star is not always available, create an artificial star with lasers
(≈20 W optical power)
Excite sodium atoms in the upper atmosphere (80-105 km)
Automatic shut-off when an airplane approaches
Credit: ESO/G. Hüdepohl
Neptune with and without AO,
Credit: ESO/P. Weilbacher (AIP)
M4
Credit: Adoptica/ESO
Main adaptive (deformable) mirror
Flat, 2.4 m diameter, 1.95 mm thin
SiC reference body for stiffness and low weight
5352 voice-coil actuators
+/- 50 µm (max) displacement
1 kHz (max) update rate
Credit: ESO
M5
Flat, 2.7 m * 2.2 m elliptical
Tip-tilt corrections to stabilize the image
Must be very lightweight and very rigid
Switching mechanism selects between instrument platforms (Nasmyth foci)
Credit: ESO
Credit: ESO/ACe Consortium/L. Calçada/M. Kornmesser
Credit: ESO/G. Vecchia
Credit: G. Hüdepohl (atacamaphoto.com)/ESO
Thank You
https://elt.eso.org
Nicolas Beneš
nicolas.benes@eso.org
Linus Karl
linus.karl@eso.org
You can find us at the SFT assembly
Credit: J. Beltrán/ESO
Webcams
Bonus Slides
Atmospheric electromagnetic Opacity
Credit: NASA
Resolution Comparison
Credit: ESO/MICADO consortium
Seismic Isolators
Credit: ESO/S. Egner
Shack Hartmann Wavefront Sensor
Credit: 2pem