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