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 Admin. Assistant Jennifer Purcell Program Manager Larry Stepp System Scientist Brooke Gregory Opto-Mechanical Myung Cho Controls George Angeli Adaptive Optics Ellerbroek - Gemini Instruments Barden - NOAO Mechanical Designer Rick Robles Structures Paul Gillett Euro50 - GSMT - XLT Meeting Optics Hansen - Gemini LMS, 08/02/02 Sites Walker - NOAO 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 Field of View Wavelength Image quality Instrumentation

Large Scale Structure Planet Formation Environments Tomography of Galaxies and pre-Galactic Fragments

2 arc minute

Resolved Stellar Populations

Wide: >20 arc minute 0.4

 m <  < 1.1  m Narrow: <5 arc second 3  m <  < 25  m 1  m <  < 2.5

 m

High-dynamic range science

2 arc minunte 1  m <  < 2.5  m Narrow: <5 arc second 1  m <  < 2.5

 m Seeing limited < 0.5 arc second Diffraction-limited low-emissivity < 0.1 arcsecond Diffraction limited Strehl ratio > 0.9

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 Euro50 - GSMT - XLT Meeting Digital elevation model of Chajnantor region LMS, 08/02/02 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) Euro50 - GSMT - XLT Meeting LMS, 08/02/02 AURA New Initiatives Office

Gemini 8-meter Telescope Euro50 - GSMT - XLT Meeting LMS, 08/02/02 AURA New Initiatives Office

3-axis anemometers

Sensor locations

Pressure sensors, 32 places Euro50 - GSMT - XLT Meeting LMS, 08/02/02 AURA New Initiatives Office

Ultrasonic anemometer

Sensor Locations

Ultrasonic anemometer Euro50 - GSMT - XLT Meeting LMS, 08/02/02 Pressure sensors AURA New Initiatives Office

Simultaneous Animations

(c00030oo) Wind Pressure (N/m 2 ) Euro50 - GSMT - XLT Meeting LMS, 08/02/02 Mirror Deformation (microns) Wind Speed at 5 Locations (m/sec) AURA New Initiatives Office

~100 ~50 ~20 ~10 2

Controls Approach:

Hierarchical Subsystems

LGS MCAO

spatial & temporal avg

AO (M2)

spatial & temporal avg

aO (M1)

temporal avg spatial avg spatial avg

Secondary rigid body

spatial & temporal avg

0.001

Main Axes

0.01

0.1

1 10 100 Euro50 - GSMT - XLT Meeting LMS, 08/02/02 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: Classical Cassegrain M1 diameter: 30 meters M1 focal ratio: f/1 M2 diameter: 2 meters M2 focal ratio: f/18.75

Euro50 - GSMT - XLT Meeting LMS, 08/02/02 AURA New Initiatives Office

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 LMS, 08/02/02 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 LMS, 08/02/02 AURA New Initiatives Office

Initial Point Design Structure

Plan View of Structure Pattern of segments Typical 'raft', 7 mirrors per raft Euro50 - GSMT - XLT Meeting Gemini LMS, 08/02/02 1.152 m mirror across flats Special raft - 6 places, 4 mirrors per raft Circle, 30m dia.

AURA New Initiatives Office

Initial Structural Analysis

Euro50 - GSMT - XLT Meeting Z X LMS, 08/02/02 Y Output Set: Mode 1, 2.156537 Hz, Deformed(0.0673): Total Translation Horizon Pointing - Mode 1 = 2.16 Hz 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 LMS, 08/02/02 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 LMS, 08/02/02 AURA New Initiatives Office

One-piece Central Raft

Euro50 - GSMT - XLT Meeting LMS, 08/02/02 AURA New Initiatives Office

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: 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 LMS, 08/02/02 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

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 Euro50 - GSMT - XLT Meeting LMS, 08/02/02 AURA New Initiatives Office

Instrument Locations Prime Focus

Euro50 - GSMT - XLT Meeting LMS, 08/02/02 AURA New Initiatives Office

Instrument Locations Co-moving Cassegrain Focus

Euro50 - GSMT - XLT Meeting LMS, 08/02/02 AURA New Initiatives Office

Instrument Locations Fixed-gravity Cassegrain Focus

Euro50 - GSMT - XLT Meeting LMS, 08/02/02 AURA New Initiatives Office

Instrument Locations MCAO-fed Nasmyth Focus

Euro50 - GSMT - XLT Meeting LMS, 08/02/02 AURA New Initiatives Office

MCAO System

Euro50 - GSMT - XLT Meeting LMS, 08/02/02 AURA New Initiatives Office

Mayall, Gemini and GSMT Enclosures

at same scale Mayall Gemini Euro50 - GSMT - XLT Meeting LMS, 08/02/02 GSMT AURA New Initiatives Office

McKale Center – Univ of Arizona

Euro50 - GSMT - XLT Meeting LMS, 08/02/02 AURA New Initiatives Office

GSMT – at same scale

Euro50 - GSMT - XLT Meeting LMS, 08/02/02 AURA New Initiatives Office

Some Possible GSMT Enclosure Designs

Euro50 - GSMT - XLT Meeting LMS, 08/02/02 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