1. A Tour of the Largest Ground-Based Telescopes Being Developed
Big Glass
A Tour of the Largest Ground-Based Telescopes Being Developed

2. Giant Magellan Telescope (GMT) Las Campanas, Chile First Light 2024

3. Large Binocular Telescope (LBTO) Mt Graham, AZ, 2007

4. Large Synoptic Survey Telescope (LSST), Cerro Pachon Ridge, Chile First Light 2022

5. What do All These New Observatories have in Common?
They’re built with
BIG GLASS:
8.4 meter primary mirrors

6. Caris Mirror Lab at U of Arizona Steward Observatory

7. Building the Giant Mirrors Used in these Telescopes

8. The Honeycomb structure controls weight and adaptation to temperatures
Small-scale casting showing honeycomb structure in relation to thickness of mirrored surface
One of 1750 alumina-silica cores used in casting an 8.4 meter mirror
The Honeycomb structure controls weight and adaptation to temperatures

9. Special borosilicate glass is melted in the spin-casting operation

10. Spin-casting the fourth of seven 8
Spin-casting the fourth of seven 8.4-meter mirrors destined for the Giant Magellan Telescope (GMT).
The mold cools slowly for three months after casting to prevent introduction of impurities and imperfections
Casting the Mirror

11. Moving the cast blank in preparation for grinding & polishing

12. Grinding and Polishing
Grinding pedestal is visible in the background; back of mirror is ground flat at this station; front is ground to prepare for polishing.
Long bar hanging across the left-center is a laser-measuring device to ensure mirror surface is ground to exacting specifications
Grinding and Polishing

13. Polishing the Aspherical (parabolic) surface
The final polishing stage deploys a “stressed-lap” polishing tool that consists of a polishing disk which bends actively to match the varying curvature of the surface
The entire mirror surface is polished in stages; here a cleaning assembly is lowered onto the surface
Polishing the Aspherical (parabolic) surface

14. When Complete the Seven Segments will comprise the primary mirror for the GMT, totaling 84.5 ft across

15. GMT’s Mission and Stats
Location: Las Campanas Peak, Chile
Elevation 8,500 ft
300 nights / year viewing (minimal rainfall)
Purposes: search for exoplanets; study dark matter & dark energy; study formation and fate of galaxies
Scheduled first light: 2024

16. LSST Goals
will image the entire visible sky every few nights (thus capturing changes and opening up the time-domain window to the observable universe)
Map the interior of the Milky Way—our galactic home
in 10 years of observing, the goal is to record the greatest movie ever made
billions of objects will be imaged in six colors in an unprecedentedly large volume of our universe

17. LSST Technical Innovations
camera (3200 megapixels, the world’s largest digital camera) each image the equivalent of 40 full moons
telescope (simultaneous casting of the primary and tertiary mirrors; two aspherical optical surfaces on one substrate)
data management (20-30 terabytes of data nightly, nearly instant alerts issued for objects that change in position or brightness)
Public facility—access to images and database for amateur astronomers

18. What other ELTs are in the works (Extremely Large Telescopes) and how do they differ from these?
Thirty Meter Telescope (TMT), Mauna Kea, Hawaii
European Extremely Large Telescope (E-ELT), Cerro Amazones, Chile
Hint: Like the James Webb Space Telescope, these two telescopes will use large numbers of 1.44 meter hexagonal mirrors in coordinated arrays

19. Thirty Meter Telescope (TMT) Mauna Kea, HI 2022 (date delayed)

20. TMT Stats 30-meter diameter 492 optical segments (individual mirrors)
Mauna Kea Observatory, Hawaii, 13,290 ft
Scheduled First Light 2022
Status: delayed by court order driven by Hawaiian protests

21. European Extremely Large Telescope (E-ELT) Cerro Amazones, Chile, 2024

22. E-ELT Stats Overall diameter of primary = 39.3 meters
798 individual hexagonal mirror segments
Each segment 1.45 meters across, 50 mm thick
Located on Cerro Amazones, Chile, at 10,040 ft.
Status: budget approved by European
First light scheduled for 2024

24. Relevant Websites Large Synoptic Survey Telescope
Giant Magellan Telescope Observatory (this site has many good links, including more detail about Univ. of Az’s manufacture of 8.4 meter mirrors)
Thirty Meter Telescope (site may be down)
Large Binocular Telescope Observatory
Caris Mirror Lab