The Thirty Meter Telescope

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The Thirty Meter Telescope

• Jerry Nelson, UCSC
• 2005 December 8

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Contents

• Lessons of History and Predicting the Future
• Scientific Potential of TMT
• TMT Organization
• TMT conceptual design
• Overall structure
• Optical design
• Primary mirror
• Segment geometry
• Segment fabrication
• Active control
• Enclosure
• Adaptive Optics
• Status

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Predicting the future

• Proposed Future Ground Based Telescopes
• California Extremely Large Telescope (CELT) 30 m
• 20/20 (University of Arizona study) 30 m
  equivalent
• Giant Magellan Telescope 20m
• Euro 50 (Lund University study) 50m
• OWL (ESO study) 100m (lt60m)
• TMT (merger of CELT, GSMT, VLOT) 30m
• Major Issues (mainly cost)
• mass production of optics
• active control
• adaptive optics
• structural issues
• enclosure/ weather protection

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Science Potential for TMT

• Increased angular resolution
• With AO can reach 0.007 arc second resolution
  (100x improvement)
• Study morphological details of most distant
  galaxies (cosmology)
• Study details for star and planet formation
• Study stellar evolution in globular clusters
• Quasars and Active Galactic Nuclei (black holes)
• Solar system objects
• Increased light gathering power
• With TMT can collect 9x the energy from an object
  (over Keck)
• Spectroscopy of most distant objects known
• Planet searches and their study

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Scientific Potential

• Seeing limited observations
• 0.3-1.0 µm
• Scale 2.18 mm/arc second (f/15)
• Wide field of view available 20 arcminutes
• Diffraction limited observations
• 1-25µm, mainly 1-2.5µm
• Thermal IR possible, but not most important
• At 1 µm angular resolution of 7 mas
• Resolution element size 15µm (at f/15, 1 µm
  wavelength)
• Large field of view 1 arc minute at 1 µm with
  multi conjugate AO

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Thirty Meter Telescope

• TMT is a project to build a 30-m telescope
• UC and Caltech are partners (CELT) Canada
  AURA
• Design and prototyping money is here
• 70M total needed
• 35 UCCaltech (CELT) from Moore Foundation
• Canada contributes 17.5M
• AURA should contribute 17.5M (highly uncertain)
• Site is unknown (several candidates being
  studied)
• Project manager (Gary Sanders from LIGO)
• Project scientist (J. Nelson)
• Project office in Pasadena

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TMT Project Organization
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Original Point Designs
GSMT
CELT
VLOT
http//www.hia-iha.nrc-cnrc.gc.ca/VLOT/index.html
http//celt.ucolick.org/
www.aura-nio.noao.edu/
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Site Selection

• We have a team of research scientists studying
  potential sites for TMT
• Sites are being studied in Chile, San Pedro
  Martir (Baja) and Mauna Kea, HI
• Measurements include
• Weather (cloudiness, wind, temperature, humidity,
  dust)
• Atmospheric seeing (total seeing with DIMMs,
  profile with MASS and with SODARs)
• Expect to select qualified sites in 2007
• Hope for competition between qualified sites to
  host TMT

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TMT Optical Design

• Primary is 30m in diameter
• 738 segments, 1.2 m dia each
• Shape actively controlled (segment piston, tip,
  tilt)
• f/1.0 ellipsoid
• Final f/15 Aplantic Gregorian
• Secondary 3.5m in diameter (concave)
• 20 arc minute field of view with 0.5 arc second
  images
• 1 arc minute FOV with 0.001 arc second images
  (design)
• Science from 1 to 65 zenith angle
• Instruments at Nasmyth platforms
• Articulated tertiary allows direct feed to
  multiple instruments with no additional optics (3
  mirrors total)
• 2 platforms 15x30 m
• Possible lower or upper platforms

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TMT Optics
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30m Primary Mirror Concept
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TMT
Keck
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TMT Reference Design
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32m
2m
40m
34m
60m
20m
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Segment Fabrication

• Segments are off axis sections of ellipse
• Requirements 20 nm rms surface (better than
  Keck)
• 90 µm deviation from sphere (Keck was 100µm)
• Fabrication study contracts (3) in place Sagem,
  Zygo, ITT-Tinsley
• Stressed mirror polishing (oap to sphere) favored
  by all
• Planetary polishing to increase efficiency
  (simultaneous polishing of multiple mirrors)
• Low expansion material will be used
• Final figure corrections with ion figuring likely
• Segment warping harnesses (WH)
• Will remove low spatial frequency segment errors
  caused by testing errors, polishing errors,
  support errors, thermal errors, alignment errors
• Will ease tolerances (and costs) of fabrication,
  etc

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Planetary polishing to produce 800 segments
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Full stressing fixture
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Planetary Stressed Mirror Polishing
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Passive segment support

• Design work contracted to Hytec (Los Alamos)
• Basic requirements
• Support segments against gravity and thermal
  disturbances
• Maintain desired surface figure to 5 nm rms
• Accurately maintain segment in desired location
• Provide interface between actuators and mirror
• Provide stiff (50Hz natural frequency) support
• Allow for handling of segments for coating and
  recoating
• Allow for warping harnesses to adjust low order
  shape of segment
• Inexpensive to design, build, install, adjust
• Zero maintenance for life of telescope

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SSA Concept
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Active Control

• Active control algorithm (details by G. Chanan)
• Same idea as Keck edge sensors, actuators,
  least squares fitting
• Error propagation calculated to be acceptable
  10x sensor noise
• Edge sensors
• Relative to Keck, want lower cost, avoid
  mechanical interlace
• New sensor design is still capacitive, but on
  edges of segment
• Design by Mast and LBL engineering
• Actuators
• Relative to Keck, want lower cost, higher stroke
• Keck actuators used roller screw/hydro reducer
  (position actuator)
• TMT contract with Marjan to design and build a
  voice coil based force actuator. This should
  have 4x stroke and be 1/4 Keck cost

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Active Control Summary

• Selected a 0.6 m for segment size
• Item Keck TMT
• segment size 0.9m 0.6m
• segments 36 738
• edge sensors 168 4212
• actuators 108 2214

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Principle of active control with edge sensors
s
P1
Actuator (piston)
P2
Sensor (measures height difference)
P4
P3
Sensor signal depends only on motion of two
neighbor segments
P5
P7
P6
P8
P9
a are constant coefficients that depend only on
geometry
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Keck Sensor Geometry
R 35 m
Mirror Segment
7.5 cm
Sensor Mount
Sensor Body
Conducting Surfaces
Sensor Paddle
2 mm
L
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title
Proposed TMT Sensor Geometry
Non-Interlocking Sensors
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Concept of segment support
Segment
Whiffle Tree
Reference Frame
Moving Frame
Mirror Cell Truss
Actuator
Actuator
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Enclosures
Design options under study (from NIO)
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Adaptive Optics for TMT

• First generation
• NFIRAOS
• Near IR AO system with rms wavefront error 190
  nm. Generates Strehl ratio 0.7 at 2µm
• Hoping to upgrade to rms wavefront 130 nm
  sometime after first light
• Large sky coverage (gt50)
• Na laser guide stars do atmospheric tomography
• Small field of view 10-1
• Remember diffraction limit at 1µm is 0.007 arcsec
• MIRAO
• 5-25µm diffraction limited system

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Science Instruments

• Seeing limited instruments (studies underway)
• HROS high resolution optical spectrometer-
  HIRES
• WFOS wide field optical spectrograph LRIS,
  DEIMOS multi object spectrometer, Fov 20 arc
  min
• Diffraction limited instruments (studies
  underway)
• IRIS
• MIRES
• NIRES
• WIRC
• MOAO

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Construction Phase

• Approval to start ( available) Jan 2008
• Primary mirror detail design review Apr 2008
• Site Development FDR Apr 2008
• Complete enclosure Feb 2012
• Complete telescope installation Oct 2012
• Begin segment installation Aug 2012
• First light with 1/4 segments Jul 2013
• All segments installed, phased Apr 2014
• Begin TMT science Jan 2015

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Development phase

• Conceptual design review May 2006
• Cost review Sept 2006

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TMT AO Development Program

• DDP program addresses TMT AO architecture, design
  and technology development
• Key technologies and demonstrations
• MEMS
• Lasers
• Infrared tip-tilt wavefront sensing
• Open loop control
• Tomography
• Wavefront sensor
• Adaptive secondary technology
• AO development addressed by an 11.7M DDP plan

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• end

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TMT Experience with Adaptive Optics
UC Lick
Palomar
CFHT
Gemini
Keck
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Adaptive Optics has come of age!
Ghez (UCLA) collaborators
Gemini Hokupaa/QUIRC image of Galactic Center.
Expanded view shows IRS 13E W in Kp
40 x 40 arcsecond mosaic, color-composite NIRC2
image (at 2.2 um) of the Galactic Center using
Keck Laser
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NGS / LGS Comparison
NGS-AO best June 2004 (4 nights) 46 best x
(0.50x120) SR0.34, FWHM92 mas
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Keck AO Imaging of Uranus
Courtesy L. Sromovsky
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Representative Construction Budget

• Construction Phase (800M) Possible NSF
  contribution
• 2008 50M 12-25M
• 2009 100M 25-50M
• 2010 160M 40-80M
• 2011 180M 45-90M
• 2012 140M 35-70M
• 2013 100M 25-50M
• 2014 70M 18-35M
• Current range of estimates 600M-800M

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CELT AO Approach

• We are exploring a staged AO implementation, to
  match the evolving technology
• Each level change has a smaller wavefront error
• Each level change requires more and better
  deformable mirrors
• Each level change requires more laser beacons
• Each level change delivers better image quality

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MCAO technology needs
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TMT Reference Design

• Following a detailed engineering study, the
  partnership has agreed on a single basic
  reference design
• 30m filled aperture, highly segmented
• aplanatic Gregorian (AG) two mirror telescope
• f/1 primary
• f/15 final focus
• Field of view 20 arcmin
• Elevation axis in front of the primary
• Wavelength coverage 0.31 28 µm
• Operational zenith angle range 1 thru 65
• Both seeing-limited and adaptive optics observing
  modes
• First generation instrument requirements defined
• AO system requirements defined