1 / 43

The GSMT Point Design

Explore the evolution of advanced telescope designs, focusing on the Giant Segmented Mirror Telescope (GSMT) initiative, its groundbreaking features, and scientific motivations. Learn about key point design attributes, optical and structural specifications, and control systems for enhanced observations. Delve into the future prospects of optical and infrared telescopes in astronomy.

wgeorge
Download Presentation

The GSMT Point Design

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The GSMT Point Design Larry Stepp and Brooke Gregory

  2. Advances of the Past Decade

  3. What Lies Ahead? • Astronomers already see the need for more powerful O/IR telescopes, to: • Extend the reach of current ground-based O/IR facilities • Complement space-based telescopes (e.g. NGST) • Complement next generation radio facilities (ALMA; SKA) • What type of facility will provide the needed capabilities a decade hence?

  4. Decadal Review • In May 2000, the 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 • Goal of ensuring broad astronomy community access to a 30m telescope contemporary with NGST.

  5. AURA New Initiatives OfficeApproach to GSMT Design Parallel efforts: • Understand the scientific context for GSMT in NGST era • Develop the key science requirements • Address challenges common to all ELTs • Site testing and selection • Cost-effective mirror fabrication • Characterization of wind loading • Hierarchical control systems • Adaptive optics • Develop a Point Design • Approach integrates initial science goals & instrument concepts

  6. What is a “Point Design”? • A point design is a learning exercise that: • Explores a single, plausible design • Helps identify key technical issues • Helps define factors important to the science requirements • Provides an opportunity to develop necessary analytical methods • A point design is not: • A trade study that evaluates all possible options • A design that anyone is proposing to build

  7. GSMT Point Design: Scientific Motivations • Provide a practical basis for wide-field, native seeing-limited instruments • Origin of large-scale structure in the universe • Enable high-Strehl performance over ~ arc-minute fields • Stellar populations; galactic kinematics; chemical abundances • Enable high sensitivity mid-IR spectroscopy • Detection of stars & planetary systems in formation

  8. Key Point Design 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

  9. 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

  10. 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

  11. 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

  12. Initial Point Design Structure Plan View of StructurePattern of segments Gemini

  13. 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

  14. Initial Structural Analysis Horizon Pointing - Mode 1 = 2.16 Hz

  15. 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.

  16. Gemini 8-meter Telescope

  17. Ultrasonic anemometer Ultrasonic anemometer Pressure sensors Sensor Locations

  18. Simultaneous Animations(c00030oo) Wind Pressure (N/m2) Mirror Deformation (microns) Wind Speed at 5 Locations (m/sec)

  19. Response of structure to wind

  20. 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

  21. Controllable Elements Adaptive Systems: • Adaptive mirror in prime focus corrector • Adaptive secondary mirror • ~ 20-50 Hz • ~ 1000-10,000 actuators • Multi-conjugate wide-field AO • ~ 3 DMs • Laser Guide Stars • High-order narrow-field conventional AO • ~ 10,000 – 50,000 actuators

  22. Controls Approach: Hierarchical Subsystems ~100 ~50 ~20 ~10 2 LGS MCAO spatial & temporal avg Zernike modes AO (M2) spatial & temporal avg aO (M1) spatial avg temporal avg spatial avg Secondary rigid body spatial & temporal avg Main Axes 0.001 0.01 0.1 1 10 100 Bandwidth [Hz]

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

  24. Instruments • NIO team currently developing design concepts for 4 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 Paper by Sam Barden et al immediately after this one.

  25. Instrument Locations on Telescope Prime Focus Fiber-fed Nasmyth Co-moving Cass Direct-fed Nasmyth

  26. Instrument Locations on Telescope Prime Focus Fiber-fed Nasmyth Co-moving Cass Direct-fed Nasmyth Fixed Gravity Cass

  27. MCAO System

  28. MCAO System

  29. MCAO System

  30. Paper on: Adaptive optics requirements, concepts and performance estimates for Extremely Large telescopes by Brent Ellerbroek and Francois Rigaut at 1:10.

  31. Mayall, Gemini and GSMT Enclosuresat same scale Mayall GSMT Gemini

  32. McKale Center – Univ of Arizona

  33. GSMT – at same scale

  34. Some Possible GSMT Enclosure Designs

  35. Summary: Key Point-Design Features • F/1 primary mirror • Advantages: • Reduces size of enclosure • Reduces flexure of optical support structure • Reduces counterweights required • Disadvantages: • Increased sensitivity to misalignment • Increased asphericity of segments

  36. Summary: Key Point-Design Features • Paraboloidal primary • Advantages: • Good image quality over 10-15 arcmin field with only two reflections • Lower emissivity for mid-IR • Compatible with laser guide stars • Disadvantages: • Higher segment fabrication cost • Increased sensitivity to segment alignment

  37. Summary: Key Point-Design Features • Radio telescope structure • Advantages: • Direct load path to elevation bearings • Can have short back focal distance • Allows small secondary mirror – can be adaptive • Allows MCAO system ahead of Nasmyth focus • Allows many gravity-invariant instrument locations • Disadvantage: • Requires counterweight • Sweeps out larger volume in enclosure

  38. Summary: Key Point-Design Features • 2m diameter adaptive secondary mirror • Advantages: • Correction of low-order M1 modes • Enhanced native seeing • Good performance in mid-IR • First stage in high-order AO system • Disadvantages: • Increased difficulty (i.e., cost)

  39. Summary: Key Point-Design Features • Prime focus location for MOMFOS • Advantages: • Fast focal ratio leads to reasonably-sized instrument • Adaptive prime focus corrector allows enhanced seeing performance • Disadvantages: • Issues of interchange with M2 • Requires fibers instead of slits

  40. Plans for Next 15 Months • Involve community in defining GSMT scientific context • Continue structural analysis • Construct hierarchical system control model • Simulate system performance in presence of disturbances • Extend AO development efforts • Continue site testing • Develop cost-reduction strategies • Segment fabrication • Telescope structure • Adaptive optics • Instrument technologies • Enclosures

  41. Acknowledgements Many people have contributed to this work, including: • George Angeli • Joe Antebi and Frank Kan of SG&H • Sam Barden • Dick Buchroeder • Myung Cho • Brent Ellerbroek • Paul Gillett • Brooke Gregory • Charles Harmer • Ming Liang • Matt Mountain • Joan Najita • Jim Oschmann • Jennifer Purcell • Francois Rigaut • Rick Robles • Mike Sheehan • David Smith of MERLAB • Steve Strom Plus many NOAO & Gemini scientists working on the GSMT science case

  42. Information on AURA NIO activities is available at: www.aura-nio.noao.edu

More Related