Download The Giant Segmented Mirror Telescope - GSMT

The Giant Segmented Mirror Telescope
Euro50 - GSMT - XLT Meeting
LMS, 08/02/02
AURA New Initiatives Office
The USA Decadal Review
•
In May 2000, the US astronomy decadal review committee
recommended, as its highest priority ground-based initiative, the
construction of a 30-meter Giant Segmented Mirror Telescope
(GSMT)
•
In response, AURA formed a New Initiatives Office (NIO) to
support scientific and technical studies leading to the creation of
a GSMT
•
NIO is a joint venture of the National Optical Astronomy
Observatory (NOAO) and the Gemini Observatory
•
Goal is to ensure broad astronomy community access to a 30m
telescope contemporary with NGST.
Euro50 - GSMT - XLT Meeting
LMS, 08/02/02
AURA New Initiatives Office
N IO Organization
NIO Management Board
William Smith -- President of AURA
Jeremy Mould -- Director of NOAO
Matt Mountain -- Director of Gemini Observatory
Project Scientist
Steve Strom
Program Manager
Larry Stepp
System Scientist
Brooke Gregory
Admin. Assistant
Jennifer Purcell
Opto-Mechanical
Myung Cho
Controls
George Angeli
Adaptive Optics
Ellerbroek - Gemini
Instruments
Barden - NOAO
Mechanical Designer
Rick Robles
Structures
Paul Gillett
Optics
Hansen - Gemini
Sites
Walker - NOAO
Euro50 - GSMT - XLT Meeting
LMS, 08/02/02
AURA New Initiatives Office
AURA New Initiatives Office
Approach to GSMT Design
Three Parallel efforts:
• Understand the scientific context for GSMT in NGST / ALMA era
• Develop the key science requirements
• Address challenges common to all ELTs
• Site testing and selection
• Cost-effective segment fabrication
•
•
•
•
Characterization of wind loading
Hierarchical control systems
Adaptive optics
Cost control techniques
• Develop a Point Design
• Based on initial science goals & instrument concepts
Euro50 - GSMT - XLT Meeting
LMS, 08/02/02
AURA New Initiatives Office
Science Programs
Science
Theme
Large Scale
Structure
Planet Formation
Environments
Tomography of
Galaxies and
pre-Galactic
Fragments
Resolved Stellar
Populations
High-dynamic
range science
Field of View
Wide:
>20 arc minute
Narrow:
<5 arc second
2 arc minute
2 arc minunte
Narrow:
<5 arc second
Wavelength
0.4m <  < 1.1 m
3m <  < 25 m
1m <  < 2.5m
1m <  < 2.5 m
1m <  < 2.5m
Image quality
Seeing limited
< 0.5 arc second
Diffraction-limited
low-emissivity
< 0.1 arcsecond
Diffraction limited
Strehl ratio > 0.9
Instrumentation
Multi-Object
Spectrograph
R = 1000 - 5000
High-resolution
spectrograph
R = 100,000
Deployable IFU
spectrograph
R = 5000 – 10,000
Imager
Coronagraph
Euro50 - GSMT - XLT Meeting
LMS, 08/02/02
AURA New Initiatives Office
Site Testing and Selection
 Survey of candidate sites by remote
sensing (satellite data)
• Regions of interest:
• Mauna Kea
• Western United States and Mexico
• Chile
• Parameters determined:
• Cloud cover
• Precipitable water vapor
• Collaborators:
• Cornell
• ESO
• University of Tokyo
• CELT
• UNAM & INAOE (Mexico)
Euro50 - GSMT - XLT Meeting
LMS, 08/02/02
AURA New Initiatives Office
Site Testing and Selection
 Construction of turbulence profilometer (MASS – Multi-Aperture
Scintillation Sensor)
• Uses scintillation measurements of a single star to measure:
• Isoplanatic angle, characteristic strengths and altitudes of the
few dominant turbulence layers
• Integral seeing producing by the whole atmosphere
Euro50 - GSMT - XLT Meeting
LMS, 08/02/02
AURA New Initiatives Office
Site Testing and Selection
 Atmospheric turbulence modeling and measuring
• Direct measurements of seeing and wind speed
• Computational fluid dynamics
• Collaborators
• CELT
• UNAM (Mexico)
• Cornell
Digital elevation model of Chajnantor region
Euro50 - GSMT - XLT Meeting
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AURA New Initiatives Office
Site Testing and Selection

Sodium layer measurements at Cerro Tololo
•
Collaborating on Gemini study to answer
questions about variation of sodium layer
height, thickness and column density with:
• Latitude
• Season
• Time of night
300mw laser launched from laser room
on Cerro Tololo
Euro50 - GSMT - XLT Meeting
LMS, 08/02/02
AURA New Initiatives Office
Characterization of Wind Loading
Test at Gemini South
 Opportunity arose during integration of Gemini South to do a
full-scale wind test in realistic conditions
 Gemini enclosure has large vent gates – permits testing a range
of enclosure conditions
 Gemini dummy mirror has equivalent properties as the real
primary mirror, but can be instrumented
 Gemini M1 is above the EL axis - open to the wind flow (similar
to concepts for future larger telescopes)
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Gemini 8-meter Telescope
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Sensor locations
3-axis anemometers
Pressure sensors, 32 places
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Sensor Locations
Ultrasonic anemometer
Ultrasonic anemometer
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Pressure sensors
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AURA New Initiatives Office
Simultaneous Animations
(c00030oo)
Wind Pressure (N/m2)
Mirror Deformation (microns)
Wind Speed at 5
Locations (m/sec)
Euro50 - GSMT - XLT Meeting
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AURA New Initiatives Office
Controls Approach:
Hierarchical Subsystems
LGS MCAO
~100
spatial & temporal avg
~50
AO (M2)
spatial & temporal avg
~20
spatial avg
aO (M1)
temporal avg
~10
spatial avg
Secondary
rigid body
2
spatial & temporal avg
Main Axes
0.001
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0.01
0.1
LMS, 08/02/02
1
10
100
AURA New Initiatives Office
Point Design
Key Features
• Fast aspheric primary
– Stigmatic image after two reflections
• Radio telescope-type design
• Structural advantages
• Accommodates large instruments
• Adaptive secondary
– Wind-buffeting compensation
– Atmospheric correction in IR, with low emissivity
– First stage in higher-order adaptive systems
• Prime focus instrument
– Convenient plate scale for seeing-limited observations
– Enables wide-field science
Euro50 - GSMT - XLT Meeting
LMS, 08/02/02
AURA New Initiatives Office
Optical Design
Optical design:
M1 diameter:
M1 focal ratio:
Classical Cassegrain
30 meters
f/1
M2 diameter: 2 meters
M2 focal ratio: f/18.75
Euro50 - GSMT - XLT Meeting
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Radio Telescope Structural Design





Lightweight steel truss structure
Fast primary focal ratio
Small secondary mirror
M2 supported on tripod structure
Elevation axis behind M1
• Span between elevation bearings is less than M1 diameter
• Allows direct load path
Euro50 - GSMT - XLT Meeting
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AURA New Initiatives Office
Initial Point Design Structure
Concept developed by Joe Antebi
of Simpson Gumpertz & Heger
• Based on radio telescope
• Space frame truss
• Single counterweight
• Cross bracing of M2 support
Euro50 - GSMT - XLT Meeting
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Initial Point Design Structure
Plan View of Structure
Pattern of segments
Typical 'raft', 7 mirrors per raft
1.152 m mirror
across flats
Gemini
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Special raft - 6 places, 4
mirrors per raft
Circle, 30m dia.
AURA New Initiatives Office
Initial Structural Analysis
Z
X
Y
Output Set: Mode 1, 2.156537 Hz, Deformed(0.0673): Total Translation
Horizon Pointing - Mode 1 = 2.16 Hz
Euro50 - GSMT - XLT Meeting
LMS, 08/02/02
AURA New Initiatives Office
A Few Parameters
from the Structural Analysis
• Total weight of elevation structure – 700 tonnes
• Total moving weight – 1400 tonnes
• Gravity deflections ~ 5-25 mm
– Primarily rigid-body tilt of elevation structure
• Lowest resonant frequencies ~ 2 Hz
Large size and low resonant frequency make wind buffeting a key
issue.
Euro50 - GSMT - XLT Meeting
LMS, 08/02/02
AURA New Initiatives Office
Current structural concept
Euro50 - GSMT - XLT Meeting
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AURA New Initiatives Office
Primary Mirror Segments
•
Segment dimensions
– 1.15-m across flats -- 1.33-m corner to
corner
– 50 mm thickness
•
•
•
Number of segments: 618
Maximum departure from sphere 110
microns
– Comparable to Keck
Axial support is 18-point whiffletree
– FEA Gravity deflection 15 nm RMS
Euro50 - GSMT - XLT Meeting
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AURA New Initiatives Office
One-piece Central Raft
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Stray Light Baffles
If Needed
Primary baffle: 14 m long
Secondary baffle: 3 m diamater
Fully baffled field of view: 5 arc min
Euro50 - GSMT - XLT Meeting
LMS, 08/02/02
AURA New Initiatives Office
Controllable Elements
Active Systems:
•
•
•
•
M2 rigid body motion
– ~ 5-10 Hz
– Five axes
M1 segment rigid body position
– ~ 1 Hz
– Piston, tip & tilt
M1 segment figure control
– Based on look-up table ~ 0.1 Hz
– Astigmatism, focus, trefoil, coma
Active structural elements
– Active alignment
– Active damping
Euro50 - GSMT - XLT Meeting
LMS, 08/02/02
AURA New Initiatives Office
Controllable Elements
Adaptive Systems:
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•
•
•
Adaptive mirror in prime focus corrector
Adaptive secondary mirror
– ~ 20-50 Hz
– ~ 2400 actuators
Multi-conjugate wide-field AO
–
–
~ 3 DMs; ~ 8500 actuators
Laser Guide Stars
High-order narrow-field conventional AO
– ~ 10,000 – 50,000 actuators
Euro50 - GSMT - XLT Meeting
LMS, 08/02/02
AURA New Initiatives Office
Active and Adaptive Optics will be integrated into
Telescope and Instrument concepts from the start.
Euro50 - GSMT - XLT Meeting
LMS, 08/02/02
AURA New Initiatives Office
Instruments
• NIO currently developing design concepts for 5
instruments:
–
–
–
–
–
Multi-Object, Multi-Fiber, Optical Spectrograph – MOMFOS
Near IR Deployable Integral Field Spectrograph – NIRDIF
MCAO-fed near-IR imager
Mid-IR, High Dispersion, AO Spectrograph – MIHDAS
Diffraction-Limited Near IR Coronagraph
Euro50 - GSMT - XLT Meeting
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Multi-Object
Multi-Fiber
Optical
Spectrograph
(MOMFOS)
Located at prime focus
Euro50 - GSMT - XLT Meeting
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AURA New Initiatives Office
Multi-Object
Multi-Fiber
Optical
Spectrograph
(MOMFOS)
Located at prime focus
Euro50 - GSMT - XLT Meeting
LMS, 08/02/02
AURA New Initiatives Office
Diffraction-limited Coronagraph
Located at co-moving Cassegrain focus
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Instrument Locations
Prime Focus
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Instrument Locations
Co-moving Cassegrain Focus
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Instrument Locations
Fixed-gravity Cassegrain Focus
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Instrument Locations
MCAO-fed Nasmyth Focus
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MCAO System
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Mayall, Gemini and GSMT Enclosures
at same scale
Mayall
GSMT
Gemini
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McKale Center – Univ of Arizona
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GSMT – at same scale
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Some Possible GSMT Enclosure Designs
Euro50 - GSMT - XLT Meeting
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AURA New Initiatives Office
Plans for the Next 10 Months
 Complete “GSMT Book” in electronic form – will be
available next month at:
www.aura-nio.noao.edu
 Involve community in understanding GSMT scientific
context
 Continue work on point design
 Develop integrated modeling of telescope response to
disturbances (mainly wind)
 Continue site testing efforts
 Develop cost estimates & cost-reduction strategies
Euro50 - GSMT - XLT Meeting
LMS, 08/02/02
AURA New Initiatives Office
Plans for the Next 10 Months
 Develop collaborations to work on:
•
•
•
•
•
Site testing
Segment fabrication methods
Characterization of wind loading
Adaptive optics
Development of cost estimates and estimating methods
 Build partnership to proceed with GSMT design
Euro50 - GSMT - XLT Meeting
LMS, 08/02/02
AURA New Initiatives Office