AURA New Initiatives Office IAU Joint Discussion 8 July 17, 2003 Larry Stepp Future Giant Telescope (FGT) Projects and Their Technological Challenges.

AURA New Initiatives Office

IAU Joint Discussion 8

July 17, 2003

Larry Stepp

Future Giant Telescope (FGT) Projects and Their Technological Challenges


Outline

• Introduction: how FGTs will advance beyond current-generation telescopes

• A brief history of FGTs

• Current concepts for FGTs

• Technology challenges common to all


Current-Generation Telescopes

• 8- to 10-meter telescopes have achieved better performance at lower relative cost by reducing the size and mass of telescope & enclosure– Improvements in polishing and testing techniques have

enabled faster primary mirrors– Active optics has achieved tighter alignment tolerances and

enabled mirrors to be made lightweight– Faster primaries, lighter mirrors, alt-azimuth mounts & FEA

have resulted in smaller, stiffer telescope structures– Smaller, stiffer structures have allowed enclosures to be

smaller and better ventilated, improving local seeing

• As a result, sub-half-arc-second images are becoming commonplace


Mayall Keck

350 tonnes 270 tonnes

• Cost in 1973: $10.6 M • Adjusted to 1992: $33.7 M • Projected cost of 10m in

1992: $400 M

• Actual cost of Keck 10m telescope in 1992: $110 M


Future Giant Telescopes

• FGTs will continue the trends of the current generation– Faster primary focal ratios– Relatively lighter structures

• And they will advance beyond the Current Generation– Integral adaptive optics systems– Smart structures

• This will enable FGTs to have:– An order of magnitude more light-gathering power– Better image quality and resolution

• Diffraction-limited at > 1 micron

• However, significant technological challenges must be solved to make this possible


A Brief History of Future Giant TelescopesThe Kitt Peak Next Generation Telescope

• 25-m telescope• Segmented f/1 primary• Radio-telescope style mount• Concept from 1977


A Brief History of Future Giant TelescopesThe National New Technology Telescope (NNTT)

• 16-m telescope• MMT-type • Four 8-m f/1.8 primary

mirrors• Concept from 1986


A Brief History of Future Giant TelescopesMore Concepts Were Advanced in the Early 1990s

J. R. P. Angel, Filled Aperture Telescopes in the Next Millennium, SPIE 1236, 1990.

A. Ardeberg, T. Andersen, B. Lindberg, M. Owner-Petersen, T. Korhonen, P. Søndergård, Breaking the 8m Barrier - One Approach for a 25m Class Optical Telescope, ESO Conf. and Workshop Proc. No. 42, 1992.

M. Mountain, What is beyond the current generation of ground-based 8-m to 10-m class telescopes and the VLT-I?, SPIE 2871, 1996.

F. N. Bash, T. A. Sebring, F. B. Ray, L. W. Ramsey, The extremely large telescope: A twenty-five meter aperture for the twenty-first century, SPIE 2871, 1996.

V. V. Sytchev, V. B. Kasperski, S. M. Stroganova, V. I. Travush, On conceptual design options of a large optical telescope of 10...25 metre class, SPIE 2871, 1996.


Current Concepts for FGTsLarge Aperture Telescope (LAT)

• LAT Consortium – Cornell– Chicago– Illinois– Northwestern

• Site: high Atacama desert or Antarctica

Design concept for LAT

From a presentation by Ed Kibblewhite


Large Aperture Telescope (LAT)

Interesting Features of Concept:• Adaptive primary mirror

– Design shown would have 36-m primary with 28-m adaptive central zone

• Science goals emphasize IR and sub-millimeter wavelengths

• Low PWV sites provide logistical challenges



Design Parameters• Optical design: TBD

• Primary mirror diameter 20-m to 36-m

• Primary mirror focal ratio TBD (~ f/1)

• Secondary mirror diameter TBD

• Final focal ratio TBD

• Field of View: 5’ - 10’

• Instrument locations: Cassegrain

• Elevation axis location: Below primary mirror



Key Technical Challenges– Cost-effective fabrication of lightweight, off-axis aspheric

segments– Structure needs high damping– Momentum compensation for adaptive segments– Efficient segment co-phasing systems– Laser guidestar beacons

– Site survey studies of CN2 profile

More information is available at:http://astrosun.tn.cornell.edu/atacama/atacama.html


Magellan 20

• Partner organizations include:– Carnegie– Harvard– Smithsonian– MIT– Arizona– Michigan

• Site: Las Campanas, Chile

Design Concept for Magellan 20

From a presentation by Roger Angel


Magellan 20

Interesting Features of Concept:

• Primary consists of seven 8.4-m mirrors

• Segmented, adaptive secondary

• Ground-conjugate adaptive optics

• Allows later incorporation into a 20-20 interferometer


Magellan 20

Design Parameters• Optical design: Aplanatic Gregorian

• Primary mirror diameter 26-m (22-m equiv.)

• Primary mirror focal ratio f/0.7

• Secondary mirror diameter 2.5-m

• Final focal ratio f/10

• Field of View: 12’ - 20’

• Instrument locations: Nasmyth

Nasmyth (vertical)

Cassegrain



Magellan 20

Key Technical Challenges– Fabrication & testing of highly-aspheric 8.4-m off-axis segments– Segmented adaptive secondary mirror– Laser guidestar beacons– Multi-conjugate adaptive optics

More information is available at:http://helios.astro.lsa.umich.edu/magellan/intro/science_case_march16.htm


High Dynamic Range Telescope

• Design developed by:– Univ. of Hawai’i

• Site: Mauna Kea, Hawai'i– (replace the CFHT)

Design concept for HDRT

From a paper by Kuhn et al




• Rapidly switchable narrow-field & wide-field modes• Segmented

secondary mirrors

• Concept for bi-parting enclosure

• Adaptive structure



Design Parameters• Optical design: Gregorian (NF)

3-mirror anastigmat (WF)


• Primary mirror focal ratio f/1

• Secondary mirror diameter six @ 0.14-m (NF)

six @ 2.3-m (WF)

• Tertiary mirror diameter 7-m

• Final focal ratio f/15 (NF); f/1.9 (WF)

• Field of View: 3” (NF); 2 degrees (WF)

• Instrument locations: Central

• Elevation axis location: Above primary mirror



• Key Technical Challenges– Fabrication of & testing of 6.5-m off-axis aspheric primary

mirror segments– Fabrication & testing of 2.3-m off-axis secondary mirror

segments– Adaptive telescope structure– Laser guidestar beacons

More information is available at:http://www.ifa.hawaii.edu/users/kuhn/hdrt.html


Large Petal Telescope

• Design developed by:– Obs. Astron. Marseille-

Provence– Obs. Astron. de Paris


Design concept for LPT

From a paper by Burgarella et al




• Primary consists of six or eight 8-m sector-shaped, meniscus segments

• 3-mirror or 4-mirror optical design

• Simultaneous use of 6-8 instruments

• Adaptive telescope structure



Design Parameters• Optical design: 3- or 4-mirror anastigmat

• Primary mirror diameter 20-m +


• Secondary mirror diameter 2.5-m to 5-m

• Final focal ratio f/5 to f/7.5

• Field of View: 1 degree

• Instrument locations: Cassegrain




• Key Technical Challenges– Fabrication & testing of 8-m off-axis aspheric primary mirror

segments– Fabrication & testing of secondary mirror– Adaptive telescope structure– Multi-conjugate adaptive optics– Laser guidestar beacons

More information is available at:http://www.astrsp-mrs.fr/denis/ngcfht/ngcfht.html


Very Large Optical Telescope (VLOT)

• Design developed by:– HIA– AMEC


Design Concept for VLOT

AMEC Dynamic Structures




• Considering concept with 8-m diameter central mirror surrounded by sector-shaped smaller segments

• Calotte dome concept



Design Parameters• Optical design: Ritchey-Chrétien

• Primary mirror diameter 20-m




• Field of View: 20’

• Instrument locations: Nasmyth (vertical)




Key Technical Challenges– Cost-effective fabrication of lightweight, off-axis aspheric

segments– Fabrication & testing of secondary mirror– Laser guidestar beacons– Multi-conjugate adaptive optics– Laser guidestar beacons

More information is available at:http://www.hia-iha.nrc-cnrc.gc.ca/VLOT/index.html.


California Extremely Large Telescope (CELT)

• CELT Partnership– Caltech– Univ. of California

• Site: TBD (Mauna Kea or northern Chile or Mexico)

Design concept for CELT

From the CELT Greenbook



• Scaled up Keck design with 1080 segments arranged in 91 rafts

• Large Nasmyth platforms



Design Parameters• Optical design: Ritchey-Chrétien




• Tertiary mirror major axis 4.38-m


• Field of View: 20”






• Key Technical Challenges– Cost-effective fabrication of 1080 off-axis aspheric primary mirror

segments– Fabrication & testing of secondary mirror– Fast tip-tilt-piston of secondary and tertiary mirrors– Efficient segment co-phasing systems– Laser guidestar beacons– Multi-conjugate adaptive optics

More information is available at:http://celt.ucolick.org/


Giant Segmented Mirror Telescope

• Design by AURA New Initiatives Office– NOAO– Gemini

• Site: TBD (Mauna Kea or northern Chile or Mexico)

Design Concept for GSMT

From animation by Rick Robles




• Prime focus instrument

• Aperture stop at secondary

• Adaptive secondary



Design Parameters• Optical design: Cassegrain (or R-C)



• Secondary mirror diameter 2-m

• Final focal ratio f/18.75

• Field of View: 20”

• Instrument locations: Prime focus

Nasmyth

Cassegrain (moving & fixed)




• Key Technical Challenges– Cost-effective fabrication of 618 off-axis aspheric primary mirror

segments– Efficient segment co-phasing systems– Adaptive secondary mirror– Laser guidestar beacons– Multi-conjugate adaptive optics– Adaptive telescope structure

More information is available at:www.aura-nio.noao.edu/


Euro50

• Euro50 partners– Lund University– Inst. de Astrofisica de

Canarias– Dept. of Physics,

Galway, Ireland– Tuorla Observatory– Optical Science Lab.– National Physical Lab.

• Site: La PalmaDesign Concept for Euro50

From Euro50 web site


Euro50


• Adaptive secondary with composite face sheet

• F/5 focal reducer for seeing-limited observing


Euro50

Design Parameters• Optical design: Gregorian



• Secondary mirror diameter 4-m

• Final focal ratio f/13; also: f/5; f/16; f/20



Folded Cassegrain



Euro50

• Key Technical Challenges– Cost-effective fabrication of 618 off-axis aspheric primary

mirror segments– Efficient segment co-phasing systems– Adaptive secondary mirror– Laser guidestar beacons– Multi-conjugate adaptive optics

More information is available at:http://www.astro.lu.se/~torben/euro50/


Overwhelming Large Telescope (OWL)

• Design by European Southern Observatory

• Site: TBD

Design Concept for OWL

From OWL web site




• Spherical primary mirror

• Flat segmented secondary mirror

• Three aspheric mirrors• Elevation assembly

recessed into ground

• Mount tied to ground by multiple drive bogies



Design Parameters• Optical design: Six-mirror design

• Primary mirror (M1) diameter 100-m


• Secondary mirror (M2) diameter 26-m

• M3 diameter 8.1-m



• Final focal ratio f/7.5


• Instrument locations: Central




• Key Technical Challenges– Fabrication of large numbers of lightweight segments

– Active structure to move corrector

– Efficient segment co-phasing systems

– Multi-conjugate adaptive optics

– 2.4-m adaptive flat mirror

– 3.5-m adaptive curved mirror

More information is available at:http://www.eso.org/projects/owl/


Required Technology Developments:Telescope & Optics

LAT

M20

HDRT

LPT

VLOT

CELT

GSMT

E50

OWL

Lightweight 1-m to 2-m segments

Large numbers of aspheric segments

Fab & test of large aspheric segments

Active/adaptive structure

Fab & testing of large, convex M2s

High-reflectivity durable coatings

Efficient segment co-phasing systems

Large, fast tip-tilt-piston mirrors

75-cm lightweight segment

Required Development

Possibly Required


Required Technology Developments:Telescope & Optics

LAT

M20

HDRT

LPT

VLOT

CELT

GSMT

E50

OWL

Lightweight 1-m to 2-m segments

Large numbers of aspheric segments

Fab & test of large aspheric segments

Active/adaptive structure

Fab & testing of large, convex M2s

High-reflectivity durable coatings

Efficient segment co-phasing systems

Large, fast tip-tilt-piston mirrors


Possibly Required


Required Technology Developments:Adaptive Optics

LAT

M20

HDRT

LPT

VLOT

CELT

GSMT

E50

OWL

Improved analysis & simulation

Large adaptive mirrors

MOEMS deformable mirrors for EXAO

MCAO system designs

Laser guidestar beacons

Large-format, fast, low noise detectors

Wavefront rec. & fast signal processors

Site testing of CN2 distribution


Possibly Required



LAT

M20

HDRT

LPT

VLOT

CELT

GSMT

E50

OWL




MCAO system designs






Possibly Required



LAT

M20

HDRT

LPT

VLOT

CELT

GSMT

E50

OWL




MCAO system designs




Site testing of CN2 distribution LLNL – ESO – CfAO

sum-frequency fiber laser


Possibly Required



LAT

M20

HDRT

LPT

VLOT

CELT

GSMT

E50

OWL




MCAO system designs






Possibly Required


Required Technology Developments:Instruments

• Affordable large near-IR detectors

• Affordable large mid-IR detectors

• Advanced image slicers for IFUs

• Fiber positioners

• MOEMS slit masks for multi-object spectroscopy

• Large-format volume-phase holographic gratings

• Large-format immersed silicon gratings

• Large lenses & filters


Call For International Cooperation

Our needs are so similar and our resources are limited, close cooperation is essential:

• Joint ventures where sensible

• Coordination to ensure studies are complementary

• Open sharing of information as much as possible

AURA New Initiatives Office IAU Joint Discussion 8 July 17, 2003 Larry Stepp Future Giant Telescope (FGT) Projects and Their Technological Challenges.

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