1. Agenda GSMT Controls Workshop, 11 September, 2001 9:00 am GSMT Overview – Brooke Gregory, Larry Stepp 9:30 am Pointing Control for a Giant Segmented Mirror Telescope – Patrick Wallace 10:00 am Implications of Wind Testing Results on the GSMT Control Systems -- David Smith 10:30 am To be defined – Mark Whorton 11:00 am MSFC's Heritage in Segmented Mirror Control Technology – John Rakoczy 11:30 am Current concepts and status of GSMT control system – George Angeli 12:00 pm Lunch 1:00 pm Informal discussions 5:00 pm Adjourn

2. B. Gregory, L. Stepp11 September 2001 GSMT Overview

3. AURA NIO: Mission In response to the AASC call for a Giant Segmented Mirror Telescope (GSMT) AURA formed a New Initiatives Office (NIO) –collaborative effort between NOAO and Gemini to explore design concepts for a GSMT NIO mission “ to ensure broad astronomy community access to a 30m telescope contemporary in time with ALMA and NGST, by playing a key role in scientific and technical studies leading to the creation of a GSMT.”

4. AURA New Initiatives Office Adaptive Optics Ellerbroek/Rigaut (Gemini) Controls George Angeli Opto-mechanics Myung Cho Contracted Studies

5. Objectives: Next 2 years Develop point design for GSMT & instruments Develop key technical solutions –Adaptive optics –Active compensation of wind buffeting –Mirror segment fabrication Investigate design-to-cost considerations Carry out conceptual design activities that support and complement other ELT efforts Develop a partnership to build GSMT

6. AURA New Initiatives Office Approach to GSMT Design Parallel efforts: Understand the scientific context for GSMT Develop the key science requirements Address challenges common to all ELTs Wind-loading Adaptive optics Site Develop a Point Design Based on initial science goals Key part is conceptual design of instruments

7. What is a “Point Design”? l 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 l A point design is not: –A trade study that evaluates all possible options –A design that anyone is proposing to build

8. Point Design: Scientific Motivations Enable high-Strehl performance over several arc-minute fields – Stellar populations; galactic kinematics; chemistry Provide a practical basis for wide-field, native seeing- limited instruments –Origin of large-scale structure Enable high sensitivity mid-IR spectroscopy – Detection of forming planetary systems Telescope design should be driven by needs of instruments

9. Point Design: Basic Design Concepts Explore a radio telescope approach –Possible structural advantages –Possible advantages in accommodating large instruments Use aspheric optics – good image after two reflections Incorporate an adaptive M2 –Compensate for wind-buffeting –Reduce thermal background –Deliver enhanced-seeing images Explore prime focus option –Attractive enabler for wide-field science –Cost-saving in instrument design

10. Radio Telescope Structural Design l Fast primary focal ratio l Lightweight steel truss structure l Small secondary mirror l Secondary supported on tripod structure l Elevation axis behind primary mirror l Span between elevation bearings is less than diameter of primary mirror – allows direct load path

11. Optical Design Primary diameter: 30 meters Primary focal ratio: f/1 Secondary diameter: 2 meters Secondary focal ratio: f/18.75 Optical design: Classical Cassegrain

12. 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

13. Point Design Structure Plan View of StructurePattern of segments Gemini

14. Lower Elevation Structure

15. Primary Mirror Segments Factors favoring large segment size: –Reduces number of position sensors & actuators –Simplifies alignment procedures –Reduces overall complexity Reduces number of unique segment types l Factors favoring a small segment size: –Reduces complexity of segment support (i.e. whiffletree) –Reduces shipping costs (big jump at ~ 2.4 meters) –Reduces size & cost of equipment for: polishing, ion figuring, coating & handling –Reduces asphericity of individual segments Asphericity goes as square of segment diameter Reduces sensitivity to segment position & rotation

16. Primary Mirror Segments Size chosen for point design: 1.15-m across flats -- 1.33-m corner to corner 50 mm thickness Number of segments: 618 Maximum asphericity ~ 110 microns (equal to Keck)

17. Segment Support Point design axial support is 18-point whiffletree FEA Gravity deflection 15 nm RMS

18. Wind Loading Primary challenge may be wind buffeting –More critical than for existing telescopes Structural resonances closer to peak wind power Wind may limit performance more than local seeing Solutions include: –Site selection for low wind speed –Optimizing enclosure design –Dynamic compensation Adaptive Optics Active structural damping

19. Initital Structural Analysis Horizon Pointing - Mode 1 = 2.16 Hz

20. Structural Analysis Total weight of elevation structure – 700 tonnes Total moving weight – 1400 tonnes Gravity deflections ~ 5-25 mm Wind buffeting response ~ 10-100 microns Deflections are primarily rigid-body motions Lowest resonant frequencies ~ 2 Hz

21. Instruments NIO team developing design concepts – 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 Build on extant concepts where possible Define major design challenges Identify needed technologies

22. Multi-Object Multi-Fiber Optical Spectrograph (MOMFOS) 20 arc-minute field 60-meter fiber cable 700 0.7” fibers 3 spectrographs, ~230 fibers each VPH gratings Articulated collimator for different resolution regimes Resolution Example ranges with single grating R= 1,000 350nm – 650nm R= 5,000 470nm – 530nm R= 20,000 491nm – 508nm Detects 13% - 23% of photons hitting the 30m primary

23. Mid-Infrared High Dispersion AO Spectrograph (MIHDAS) Adaptive Secondary AO feed On-Axis, Narrow Field/Point Source R=120,000 3 spectrographs 2-5  m (small beamed, x-dispersed), 0.2 arc-second slit length 10-14  m (x-dispersed), 1 arc-second slit 16-20  m (x-dispersed), 1 arc-second slit 10-14  m spectrograph likely to utilize same collimator as 16-20  m instrument. Different Gratings and Camera. 2-5  m spectrograph may require additional AO mirrors.

24. Near Infra-Red Deployable Integral Field Spectrograph (NIRDIF) MCAO fed 1.5 to 2.0 arc-minute FOV 1 – 2.5  m wavelength coverage Deployable IFU units 1.5 arc-second FOV per IFU probe 31 slices per IFU probe (0.048” per slice) ~26 deployable units

25. MCAO Near-IR Imager f/38 input with 1:1 reimaging optics 1.5 to 2 arc-minute field of view Monolithic imager -  5.5 mm/arc-second plate scale!  685 mm sized detector array for 2 arc-min field!  28K by 28K detector!  7 by 7 mosaic of 4K arrays  0.004 arc-second per pixel sampling Alternative approach is to have deployable capability for imaging over a subset of the total field.

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

27. MOMFOS with Prime Focus Corrector Conceptual design fits in a 3m dia by 5m long cylinder

28. Instrument Locations on Telescope View showing Co-moving Cass instrument

29. MCAO/AO foci and instruments MCAO optics moves with telescope Narrow field AO or narrow field seeing limited port MCAO Imager at vertical Nasmyth elevation axis 4m Oschmann et al (2001)

30. MCAO System: Current Layout

31. Instrument Locations on Telescope MCAO-fed NIRDIF or MCAO Imager Cass-fed MIHDAS Fiber-fed MOMFOS

32. Mayall, Gemini and GSMT Enclosures at same scale Mayall Gemini GSMT

33. McKale Center – Univ of Arizona

34. GSMT – at same scale

35. Key Point-Design Features Radio telescope structure –Advantages: Direct load path to elevation bearings Cass focus can be just behind M1 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

36. 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

37. 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

38. 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) Goal: 8000 actuators 30cm spacing on M1

39. Key Point-Design Features Prime focus location for MOMFOS –Advantages: Fast focal ratio leads to instrument of reasonable size Adaptive prime focus corrector allows enhanced seeing performance –Disadvantages: Issues of interchange with M2

40. Key Enabling Techniques: Active and Adaptive Optics Active Systems: M1 segment rigid body position – ~ 1 Hz – Piston, tip & tilt M1 segment figure control – – Based on look-up table ~ 0.1 Hz – Low order -- Astigmatism, focus, trefoil, coma M2 rigid body motion – ~ 5-10 Hz – Five axes – active focus & alignment, image stabilization Active structural elements (?) – Active alignment – Active damping

41. Key Enabling Techniques: Active and Adaptive Optics Adaptive Systems: Adaptive secondary mirror ~ 20-50 Hz ~ 1000-10,000 actuators Adaptive mirror in prime focus corrector Multi-conjugate wide-field AO ~ 3 DMs Laser Guide Stars High-order narrow-field conventional AO ~ 10,000 – 50,000 actuators Active and Adaptive Optics will be integrated into GSMT Telescope and Instrument concepts from the start