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 Whor
2、ton 11:00 am MSFCs 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,B. Gregory, L. Stepp 11 September 2001,GSMT Overview,AURA NIO: Mission,In response to
3、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
4、, by playing a key role in scientific and technical studies leading to the creation of a GSMT.”,AURA New Initiatives Office,Adaptive Optics Ellerbroek/Rigaut (Gemini),Controls George Angeli,Opto-mechanics Myung Cho,Contracted Studies,Objectives: Next 2 years,Develop point design for GSMT & instrumen
5、ts 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,AURA New Initiatives
6、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”?,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 stud
8、y that evaluates all possible options A design that anyone is proposing to build,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 inst
9、ruments Origin of large-scale structure Enable high sensitivity mid-IR spectroscopyDetection of forming planetary systemsTelescope design should be driven by needs of instruments,Point Design: Basic Design Concepts,Explore a radio telescope approach Possible structural advantages Possible advantages
10、 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 de
11、sign,Radio Telescope Structural Design,Fast primary focal ratio Lightweight steel truss structure Small secondary mirror Secondary supported on tripod structure Elevation axis behind primary mirror Span between elevation bearings is less than diameter of primary mirror allows direct load path,Optica
12、l Design,Primary diameter: 30 meters,Primary focal ratio: f/1,Secondary diameter: 2 meters,Secondary focal ratio: f/18.75,Optical design: Classical Cassegrain,Point Design Structure,Concept developed by Joe Antebi of Simpson Gumpertz & Heger Based on radio telescope Space frame truss Single counterw
13、eight Cross bracing of M2 support,Point Design Structure,Plan View of Structure Pattern of segments,Gemini,Lower Elevation Structure,Primary Mirror Segments,Factors favoring large segment size: Reduces number of position sensors & actuators Simplifies alignment procedures Reduces overall complexity
14、Reduces number of unique segment typesFactors 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 se
15、gments Asphericity goes as square of segment diameter Reduces sensitivity to segment position & rotation,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),Segment
16、 Support,Point design axial support is 18-point whiffletree FEA Gravity deflection 15 nm RMS,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 inc
17、lude: Site selection for low wind speed Optimizing enclosure design Dynamic compensation Adaptive Optics Active structural damping,Initital Structural Analysis,Horizon Pointing - Mode 1 = 2.16 Hz,Structural Analysis,Total weight of elevation structure 700 tonnes Total moving weight 1400 tonnes Gravi
18、ty deflections 5-25 mm Wind buffeting response 10-100 microns Deflections are primarily rigid-body motions Lowest resonant frequencies 2 Hz,Instruments,NIO team developing design concepts Multi-Object, Multi-Fiber, Optical Spectrograph MOMFOS Near IR Deployable Integral Field Spectrograph NIRDIF MCA
19、O-fed near-IR imager Mid-IR, High Dispersion, AO Spectrograph MIHDAS Build on extant concepts where possible Define major design challenges Identify needed technologies,Multi-Object Multi-Fiber Optical Spectrograph (MOMFOS),20 arc-minute field60-meter fiber cable700 0.7” fibers3 spectrographs, 230 f
20、ibers eachVPH gratingsArticulated collimator for different resolution regimes Resolution Example ranges with single gratingR= 1,000 350nm 650nmR= 5,000 470nm 530nmR= 20,000 491nm 508nmDetects 13% - 23% of photons hitting the 30m primary,Mid-Infrared High Dispersion AO Spectrograph (MIHDAS),Adaptive
21、Secondary AO feedOn-Axis, Narrow Field/Point SourceR=120,0003 spectrographs2-5 mm (small beamed, x-dispersed), 0.2 arc-second slit length10-14 mm (x-dispersed), 1 arc-second slit16-20 mm (x-dispersed), 1 arc-second slit10-14 mm spectrograph likely to utilize same collimator as 16-20 mm instrument. D
22、ifferent Gratings and Camera.2-5 mm spectrograph may require additional AO mirrors.,Near Infra-Red Deployable Integral Field Spectrograph (NIRDIF),MCAO fed1.5 to 2.0 arc-minute FOV1 2.5 mm wavelength coverageDeployable IFU units1.5 arc-second FOV per IFU probe31 slices per IFU probe (0.048” per slic
23、e)26 deployable units,MCAO Near-IR Imager,f/38 input with 1:1 reimaging optics1.5 to 2 arc-minute field of viewMonolithic 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 arrays0.004 arc-second per pixel samplingAlternative
24、 approach is to have deployable capability for imaging over a subset of the total field.,Instrument Locations on Telescope,Fixed Gravity CassDirect-fed NasmythFiber-fed NasmythPrime FocusCo-moving Cass,View showing Fixed Gravity Cass instrument,MOMFOS with Prime Focus Corrector,Conceptual design fit
25、s in a 3m dia by 5m long cylinder,Instrument Locations on Telescope,View showing Co-moving Cass instrument,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),MCAO Sy
26、stem: Current Layout,Instrument Locations on Telescope,MCAO-fed NIRDIF or MCAO Imager,Cass-fed MIHDAS,Fiber-fed MOMFOS,Mayall, Gemini and GSMT Enclosures at same scale,Mayall,Gemini,GSMT,McKale Center Univ of Arizona,GSMT at same scale,Key Point-Design Features,Radio telescope structure Advantages:
27、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,Key Point-Desi
28、gn 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,Key Point-Design Features,Paraboloidal primary Advantages: Good ima
29、ge 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,Key Point-Design Features,2m diameter adaptive secondary mirror Advantages: Correction
30、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,Key Point-Design Features,Prime focus location for MOMFOS Advantages: Fast focal ratio leads to instrume
31、nt of reasonable size Adaptive prime focus corrector allows enhanced seeing performance Disadvantages: Issues of interchange with M2,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 t
32、able 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,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 actuatorsActive and Adaptive Optics will be integrated into GSMT Telescope and Instrument concepts from the start,
