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The Giant Segmented Mirror Telescope. 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) - PowerPoint PPT Presentation
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AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
The Giant Segmented Mirror Telescope
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
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.
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
N IO OrganizationNIO Management Board
William Smith -- President of AURAJeremy Mould -- Director of NOAOMatt Mountain -- Director of Gemini Observatory
Project ScientistSteve Strom
Program ManagerLarry Stepp
System ScientistBrooke Gregory
Opto-MechanicalMyung Cho
Mechanical DesignerRick Robles
StructuresPaul Gillett
ControlsGeorge Angeli
Adaptive OpticsEllerbroek - Gemini
InstrumentsBarden - NOAO
OpticsHansen - Gemini
SitesWalker - NOAO
Admin. AssistantJennifer Purcell
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
AURA New Initiatives OfficeApproach 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
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Science Programs
ScienceTheme
Large Scale Structure
Planet Formation Environments
Tomography of Galaxies and pre-Galactic Fragments
Resolved StellarPopulations
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 0.4m < < 1.1 m 3m < < 25 m 1m < < 2.5m 1m < < 2.5 m 1m < < 2.5m
Image quality Seeing limited< 0.5 arc second
Diffraction-limitedlow-emissivity
< 0.1 arcsecond Diffraction limited Strehl ratio > 0.9
Instrumentation Multi-Object Spectrograph
R = 1000 - 5000
High-resolution spectrographR = 100,000
Deployable IFU spectrograph
R = 5000 – 10,000
Imager Coronagraph
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
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)
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
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
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
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
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
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
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Characterization of Wind LoadingTest 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)
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Gemini 8-meter Telescope
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Sensor locations
3-axis anemometers
Pressure sensors, 32 places
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Sensor Locations
Pressure sensors
Ultrasonic anemometer
Ultrasonic anemometer
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Simultaneous Animations (c00030oo)
Wind Pressure (N/m2) Mirror Deformation (microns)
Wind Speed at 5 Locations (m/sec)
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
0.001 0.01 0.1 1 10100
Zern
ike
mo d
e s
Bandwidth [Hz]
~100
~50
~20
~10
2
Controls Approach:Hierarchical Subsystems
aO (M1)
AO (M2)
Main Axes
LGS MCAO
Secondary rigid body
temporal avg
spatial & temporal avg
spatial & temporal avg
spatial & temporal avg
spatial avg
spatial avg
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Point DesignKey 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
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Optical Design
M1 diameter: 30 metersM1 focal ratio: f/1
M2 diameter: 2 metersM2 focal ratio: f/18.75
Optical design: Classical Cassegrain
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
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
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
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
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Initial Point Design Structure
Typical 'raft', 7 mirrors per raft
Special raft - 6 places, 4 mirrors per raft
1.152 m mirror across flats
Circle, 30m dia.
Plan View of Structure Pattern of segments
Gemini
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Initial Structural Analysis
X Y
Z
Output Set: Mode 1, 2.156537 Hz, Deformed(0.0673): Total Translation
Horizon Pointing - Mode 1 = 2.16 Hz
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
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.
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Current structural concept
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
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
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
One-piece Central Raft
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Stray Light BafflesIf Needed
Primary baffle: 14 m long
Secondary baffle: 3 m diamater
Fully baffled field of view: 5 arc min
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Controllable Elements
Active Systems:
• Active structural elements– Active alignment– Active damping
• M2 rigid body motion– ~ 5-10 Hz– Five axes
• M1 segment figure control– Based on look-up table ~ 0.1 Hz– Astigmatism, focus, trefoil, coma
• M1 segment rigid body position – ~ 1 Hz– Piston, tip & tilt
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Controllable Elements
Adaptive Systems:
• High-order narrow-field conventional AO– ~ 10,000 – 50,000 actuators
• Multi-conjugate wide-field AO– ~ 3 DMs; ~ 8500 actuators– Laser Guide Stars
• Adaptive secondary mirror– ~ 20-50 Hz– ~ 2400 actuators
• Adaptive mirror in prime focus corrector
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Active and Adaptive Optics will be integrated into Telescope and Instrument concepts from the start.
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
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
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Multi-Object Multi-Fiber
Optical Spectrograph(MOMFOS)
Located at prime focus
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Multi-Object Multi-Fiber
Optical Spectrograph(MOMFOS)
Located at prime focus
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Diffraction-limited Coronagraph
Located at co-moving Cassegrain focus
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Instrument LocationsPrime Focus
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Instrument LocationsCo-moving Cassegrain Focus
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Instrument LocationsFixed-gravity Cassegrain Focus
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Instrument LocationsMCAO-fed Nasmyth Focus
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
MCAO System
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Mayall, Gemini and GSMT Enclosuresat same scale
Mayall Gemini GSMT
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
McKale Center – Univ of Arizona
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
GSMT – at same scale
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
Some Possible GSMT Enclosure Designs
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
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
AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02
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
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