1. TMT.OPT.PRE.07.045.DRF01 14 September 2007 1 Requirements and Conceptual Design of M2 System Ben Platt Myung Cho Mark Sirota 14 September 2007

2. TMT.OPT.PRE.07.045.DRF01 14 September 2007 2 Outline Ben Platt –Overview and System Requirements Myung Cho –Modeling Conceptual Mirror Support Design Mark Sirota –M2S Control Systems Overview

3. TMT.OPT.PRE.07.045.DRF01 14 September 2007 3 Secondary Mirror System (M2S) Overview and System Requirements Ben Platt 14 September

4. TMT.OPT.PRE.07.045.DRF01 14 September 2007 4 Outline M2 System Decomposition External Interfaces M2 System Description and Overview M2 System Requirements

5. TMT.OPT.PRE.07.045.DRF01 14 September 2007 5 M2S Decomposition M2 System (M2S) M2 Cell Assembly (M2CA) –M2 Mirror (M2M) {blank and polishing} –M2 Support System (M2SS) {actuators, load cells, cabling} –M2 Cell (M2C) {cell structure} –M2 Control System - Cell (M2CSC) {electronics, software, sensors} M2 Positioner Assembly (M2PA) –M2 Hexapod (M2H) {actuators, base, platform} –M2 Control System - Positioner (M2CSP) {electronics, software, sensors} M2 Interface Panel (M2I) {electrical/fluid interface with Telescope Structure}

6. TMT.OPT.PRE.07.045.DRF01 14 September 2007 6 M2 External Interfaces Draft Copies of the ICDs will be made available for this study.

7. TMT.OPT.PRE.07.045.DRF01 14 September 2007 7 M2S Description The two major subsystems of the M2S are: –M2 Positioner Assembly –M2 Cell Assembly A Hexapod was chosen for the M2 Positioner because it seemed to be the simplest configuration to produce the 6 DOF required to control the position of the M2 Mirror. A meniscus mirror with an active support system was chosen because the print-through bumps will be smooth and can be corrected by adaptive Optics. M2 Positioner Assembly M2 Cell Assembly M2 Interface Panel

8. TMT.OPT.PRE.07.045.DRF01 14 September 2007 8 M2S Top Level Requirements Mirror must conform to the optical prescription Mirror must maintain its shape, position in the presence of disturbances, i.e., Changing gravity orientations, (1 to 65 degrees) Temperatures changes, (2 to 15 C) Wind buffeting and transmitted vibrations, (external wind speed = 0 to 15.6 m/s) The M2 active support system shall be able to correct mirror figure errors that develop after leaving the optics shop. 3.6 m 1.5 m

9. TMT.OPT.PRE.07.045.DRF01 14 September 2007 9 M2S Top Level Requirements Mirror must maintain high reflectivity over a broad range of wavelengths (0.34 to 28 microns) System must be designed to be safe for personnel and equipment, (ORD*, Section 3.6) System must be reliable and maintainable, (ORD, Section 3.5) System must conform to interfaces and comply with mass and space envelope limits, (ICDs)** System must be compatible with observing environment *ORD = Observatory Requirements Document **ICD = Interface Control Document

10. TMT.OPT.PRE.07.045.DRF01 14 September 2007 10 M2S Top Level Requirements Cross sectional area ≤ 5 m^2 perpendicular to the optical axis Average Drag coefficient < 1.5 Total mass < 6000 kg. Must incorporate alignment features for the Global Metrology System (GMS). Relatively easy installation and removal of M2CA Designed to allow CO2 cleaning, in situ washing

11. TMT.OPT.PRE.07.045.DRF01 14 September 2007 11 M2 Cell Assembly (M2CA) The M2CA consist of the Cell, Mirror and Support System The M2 System shall maintain a set of Look-Up-Tables (LUT) storing actuator commands to correct for polishing errors as well as different gravitational and thermal deformations of the mirror surface.

12. TMT.OPT.PRE.07.045.DRF01 14 September 2007 12 M2M Prescription and Dimensions Material:Low Expansion Glass or Glass Ceramic Clear Aperture:3.048 m Vertex Radius of Curvature:-6.22788 m Conic Constant:-1.318228 Clear Aperture OD 3.024 m ID 0.22 m

13. TMT.OPT.PRE.07.045.DRF01 14 September 2007 13 M2M Polish Requirements All figure requirements are with the mirror in the M2CA with the passive lateral and active axial supports. The surface figure requirement is completely described with a normalized Structure Function based on a Kolmogorov atmosphere, with tip/tilt removed.

14. TMT.OPT.PRE.07.045.DRF01 14 September 2007 14 M2M Structure Function Parameters Calculated from the Structure Function are: –RMS WFE: 204 nm –Surface RMS Slope Error: 0.403 µrad –Surface P-V Slope Error:1.45 µrad Where: D(x) is the structure in units of (nm) 2 A = Leading coefficient = 314626 B = High frequency errors (surface roughness) = 2 nm x = Separation between point pairs, similar to spatial frequency. d = Diameter of beam footprint = 3.046 m r 0 = Fried’s parameter = 2.88 m Where:

15. TMT.OPT.PRE.07.045.DRF01 14 September 2007 15 M2 Mirror Support System (M2SS) M2 must maintain its optical figure from zenith to 65 degrees zenith angle M2 support system must be able to correct figure errors after mirror acceptance testing: –Optical test errors –Temperature change –Coating thickness & stress Print-through bumps must be smooth (low frequency) so they are correctable by adaptive optics

16. TMT.OPT.PRE.07.045.DRF01 14 September 2007 16 M2C Top Level Requirements Support mass of actuators and mirror Stiffness sufficient to allow M2S to have first resonant frequency > 15 Hz. Provide structural interface for M2 Hexapod Provide safety restraints for seismic and handling loads Present minimum wind resistance Maintenance: –Allow access for maintenance of actuators –Allow for ~ monthly CO2 cleaning and ~ semi-annual washing –Allow for periodic recoating of the mirror surface (Mirror must be easily removed from cell.) Seeing: –Must not deteriorate the telescope internal seeing, (Temperature difference between mirror optical surface and ambient air shall be < 0.65 C (TBC).)

17. TMT.OPT.PRE.07.045.DRF01 14 September 2007 17 M2 Support System (M2SS) Performance of NOAO Conceptual Design Myung Cho

18. TMT.OPT.PRE.07.045.DRF01 14 September 2007 18 Total of 60 axial supports on a four (4) concentric ring arrangement mounted at the mirror back surface Axial supports oriented parallel to the optical axis (vertical, Z-axis) Optimization for axial support forces in two (2) groups and for minimum surface RMS error Mirror substrate chosen to be solid meniscus 100 mm thick, to produce smooth print-through bumps that can be corrected by adaptive optics Conceptual Axial support design 60 supports on 4 rings

19. TMT.OPT.PRE.07.045.DRF01 14 September 2007 19 Axial support print-through: P-V = 49 nm surface; RMS = 10 nm surface Axial support performance (mirror face down; gravity in local -Z) Optimized axial support forces: Ring 1 = 251 N; Ring 2,3,4 = 323 N

20. TMT.OPT.PRE.07.045.DRF01 14 September 2007 20 Conceptual Lateral Support design Lateral support: 24 passive system Edge support concept –Schwesinger-like pattern –Equally spaced Lateral support force constraints in optimization –No lateral force groups –Self equilibrium for lateral gravity –Minimum active force requirement No support mount pads in analyses for lateral optimization –No mount pad weight –No lateral support linkage

21. TMT.OPT.PRE.07.045.DRF01 14 September 2007 21 Lateral support layout: –24 lateral supports around the edge mounted on the mid- plane of M2 –Passive support (push/pull) –Support force resultant in 3 directions (Fx, Fy, Fz) –M2 assembly fits inside D=3.6m (outer diameter of envelope shown) Lateral support system D=3.6m envelope

22. TMT.OPT.PRE.07.045.DRF01 14 September 2007 22 Lateral support optimization (lateral support force alone) Surface RMS = 2nm with F(x,y,z) max = 390N; 1180; 100N Optimized lateral support forces for minimum surface RMS M2 Gravity balanced by Lateral support forces alone –24 lateral support forces are in a self static equilibrium with the lateral gravity No axial force applied

23. TMT.OPT.PRE.07.045.DRF01 14 September 2007 23 Natural frequency modes (first 10 mirror bending modes) *First 10 mirror bending mode shapes are similar to low order Zernike polynomials Mirror mass = 1934 Kg in the model Natural frequencies and mode shapes (free-free)*

24. TMT.OPT.PRE.07.045.DRF01 14 September 2007 24 Active Optics Performance M2 active supports can correct low order Zernike modes First 10 Zernike modes (Z4 – Z10) were modeled with noise-free for a perfect system to determine to determine –Residual RMS surface error from Reference surface RMS of 1000 nm –Maximum actuator force to correct Reference surface –aO error (residual RMS ÷ Reference RMS) or Gain (1/aO error)

25. TMT.OPT.PRE.07.045.DRF01 14 September 2007 25 Typical Zernike Surfaces (FRINGE Zernikes) Z04 Z07 Z08 Z10 Zernike ID. R(r,  ) Aberrations 4 r 2 cos(2  ) astigmatism 5 r 2 sin(2  ) astigmatism 6 (3r 2 -2)r cos(  ) coma 7 (3r 2 -2)r sin(  ) coma 86r 4 - 6r 2 + 1asphere 9 r 3 cos(3  ) trifoil 10 r 3 sin(3  ) trifoil

26. TMT.OPT.PRE.07.045.DRF01 14 September 2007 26 BACKUP Myung Cho

27. TMT.OPT.PRE.07.045.DRF01 14 September 2007 27 Lateral support force distribution (shown in Right-half) Plane X-Y Force components Isometric view Plane Y-Z

28. TMT.OPT.PRE.07.045.DRF01 14 September 2007 28 Lateral support force and direction (listed in Right-half) force component (N) force direction (degree) Angle ( o )

29. TMT.OPT.PRE.07.045.DRF01 14 September 2007 29 Continue with Overview and System Requirements Ben Platt

30. TMT.OPT.PRE.07.045.DRF01 14 September 2007 30 M2 Hexapod Top Level Requirements Quasi-Static Regime: –Provides static support of the M2CA over the elevation range of the telescope (0 to 90 degrees) –Capable of articulating the M2CA over 5 DOFs and maintain rotation about the optical axis, with respect to the telescope structure, with high precision and repeatability. Dynamic Regime: –Capable of moving quickly to a new position (slewing) –Don’t introduce vibrations to the telescope –Capable of moving in a smooth controlled trajectory at a commanded speed and acceleration Seeing: –The hexapod and it’s control electronics shall not degrade the seeing conditions, The heat emitted from the hexapod shall be less than TBD w. (Liquid coolant will be provided.) Maintenance: –Designed for long life and high reliability –Components shall be designed for ease of service and maintenance, (Ability to replace an actuator in the telescope.)

31. TMT.OPT.PRE.07.045.DRF01 14 September 2007 31 M2 Interface Plate TMT Will Provide an Interface Plate on the Telescope Structure for Connecting all Cables, Wires and Hoses.

32. TMT.OPT.PRE.07.045.DRF01 14 September 2007 32 M2 Control System – Cell (M2CSC) Mark Sirota

33. TMT.OPT.PRE.07.045.DRF01 14 September 2007 33 M2 Control System-Cell Summary Description & Requirements –The M2 Control System–Cell (M2CSC) provides local control for the M2 Cell Assembly (M2CA). –The M2CSC is independent and separate from the M2 Control System-Positioner (M2CSP). –The primary external M2CSC control interface is with the Telescope Control System (TCS) via a single Ethernet connection. –The M2CSC will meet all performance requirements over the following conditions. Zenith angles between 0 and 65 degrees Zenith angle rates up to 30 arcseconds/seconds Temperatures between 2 and 15 degrees C –The M2CSC will be capable of maintaining the M2 mirror figure without requiring zenith angle or temperature data from the TCS at rates any faster than once every 100 seconds.

34. TMT.OPT.PRE.07.045.DRF01 14 September 2007 34 M2 Control System-Cell Summary Description & Requirements –The M2 Mirror shape will settle to its final shape within 15 seconds of the completion of any move between zenith angles of 0 and 65 degrees. – “Cell Control” look up table (LUT) Contains the set-points for each force actuator as a function of zenith angle and temperature. The values contained in the Cell Control LUT are provided by the TCS. Initial values for the Cell Control LUT will be developed during testing at the optics shop and supplied by the M2CA vendor. Zenith angle and temperature are provided to the M2CSC by the TCS at a constant rate of ~ 0.1 Hz. The M2CA won’t require complete calibration of the Cell Control LUT more frequently than once per year. Bias only corrections (zero point corrections) to the LUT will be allowed on a monthly time scale.

35. TMT.OPT.PRE.07.045.DRF01 14 September 2007 35 M2 Control System - Cell Summary Description & Requirements –Calibration and Diagnostics The M2CSC will provide a telemetry stream that consists of parameters such as currents, sensor values, etc. The M2CSC will include a diagnostic and calibration mode which supports –control of individual actuators and the reading of individual sensors. –support on-sky measurement of individual actuator influence functions The M2CSC will have the capability of receiving and executing M2 Support command offsets from the TCS at rates up to once per second. (This will be used to gather data required to build a new Cell Control LUT) –Interfaces Control and data transmission between the TCS and M2CSC will be via a single Ethernet connection. All control, power, utility, utility interlocks, engineering sensor, and local control interfaces are via the M2 Interface Panel. –E-Stop, Safety, Fault Handling, Alarms

36. TMT.OPT.PRE.07.045.DRF01 14 September 2007 36 M2 Control System - Cell

37. TMT.OPT.PRE.07.045.DRF01 14 September 2007 37 M2 Control System – Positioner (M2CSP) Mark Sirota

38. TMT.OPT.PRE.07.045.DRF01 14 September 2007 38 M3 Control System-Positioner Summary Description & Requirements –The M3 Control System–Positioner (M3CSP) provides local control for the M3 Positioner (M3P). –The M3CSP is independent and separate from the M3 Control System-Cell (M3CSC). –The primary external M3CSP control interface is with the Telescope Control System (TCS) via a single Ethernet connection. –The M3CSC will meet all performance requirements over the following conditions. Zenith angles between 0 and 65 degrees Zenith angle rates up to 30 arcseconds/seconds Temperatures between 2 and 15 degrees C –The M3CSP will receive and execute rotation and tilt position commands from the TCS.

39. TMT.OPT.PRE.07.045.DRF01 14 September 2007 39 M3 Control System - Positioner Summary Description & Requirements –Calibration and Diagnostics The M3CSP will provide a telemetry stream that consists of parameters such as currents, sensor values, etc. The M3CSP will include a diagnostic and calibration mode which supports control of individual actuators and the reading of individual sensors. –Interfaces Control and data transmission between the TCS and M3CSP will be via a single Ethernet connection. All control, power, utility, utility interlocks, engineering sensor, and local control interfaces are via the M3 Interface Panel. –E-Stop, Safety, Fault Handling, Alarms

40. TMT.OPT.PRE.07.045.DRF01 14 September 2007 40 M3 Control System - Positioner Core performance characteristics –These numbers are representative and will be updated over the next several weeks.

41. TMT.OPT.PRE.07.045.DRF01 14 September 2007 41 M3 Control System - Positioner

42. TMT.OPT.PRE.07.045.DRF01 14 September 2007 42 Backup Slides

43. TMT.OPT.PRE.07.045.DRF01 14 September 2007 43 M2M Polish WFE Average WFE is determined from Nolls’ model of a Kolmogorov atmosphere Equivalent Ro from: D = 30 m aperture –Convert to RMS wavefront error: –WFE is independent of wavelength because Ro ~ λ 6/5 WFE budget is matched to an atmospheric wavefront To be further corrected by AO

44. TMT.OPT.PRE.07.045.DRF01 14 September 2007 44 The equation below is a normalized structure function for a Kolmogorov atmosphere with tip tilt removed. Over a beam of diameter d the mean square phase variance at two points separated by a distance x is given by: Structure Function Equation 3

45. TMT.OPT.PRE.07.045.DRF01 14 September 2007 45 M2 Structure Function Terms The scaling factor A is a function of wavelength λ and the ratio of the telescope beam to Fried’s parameter r o : Where: D(x) is the structure and it is in units of nm 2 A = Leading coefficient B = Uncorrected wavefront error x = Separation between point pairs, similar to spatial frequency d = Beam footprint r 0 = Fried's Parameter

46. TMT.OPT.PRE.07.045.DRF01 14 September 2007 46 M2M Polish Structure Function Curve

47. TMT.OPT.PRE.07.045.DRF01 14 September 2007 47 Optical Coating Requirements

48. TMT.OPT.PRE.07.045.DRF01 14 September 2007 48 Observing Operating Conditions