aura new initiatives office euro50 - gsmt - xlt meetinglms, 08/02/02 the giant segmented mirror...

AURA New Initiatives OfficeEuro50 - GSMT - XLT Meeting LMS, 08/02/02

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)

• 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.


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 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


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


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)


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


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


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


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)


Gemini 8-meter Telescope


Sensor locations

3-axis anemometers

Pressure sensors, 32 places


Sensor Locations

Pressure sensors

Ultrasonic anemometer

Ultrasonic anemometer


Simultaneous Animations (c00030oo)

Wind Pressure (N/m2) Mirror Deformation (microns)

Wind Speed at 5 Locations (m/sec)


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 avg

spatial avg


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


Optical Design

M1 diameter: 30 metersM1 focal ratio: f/1

M2 diameter: 2 metersM2 focal ratio: f/18.75

Optical design: Classical Cassegrain


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


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


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


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


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.


Current structural concept


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


One-piece Central Raft


Stray Light BafflesIf Needed

Primary baffle: 14 m long

Secondary baffle: 3 m diamater

Fully baffled field of view: 5 arc min


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


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


Active and Adaptive Optics will be integrated into Telescope and Instrument concepts from the start.


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


Multi-Object Multi-Fiber

Optical Spectrograph(MOMFOS)

Located at prime focus


Diffraction-limited Coronagraph

Located at co-moving Cassegrain focus


Instrument LocationsPrime Focus


Instrument LocationsCo-moving Cassegrain Focus


Instrument LocationsFixed-gravity Cassegrain Focus


Instrument LocationsMCAO-fed Nasmyth Focus


MCAO System


Mayall, Gemini and GSMT Enclosuresat same scale

Mayall Gemini GSMT


McKale Center – Univ of Arizona


GSMT – at same scale


Some Possible GSMT Enclosure Designs


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


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

aura new initiatives office euro50 - gsmt - xlt meetinglms, 08/02/02 the giant segmented mirror...

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