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

14 September 2007 1TMT.OPT.PRE.07.045.DRF01

Requirements and Conceptual Design of M2 System

Ben PlattMyung ChoMark Sirota

14 September 2007


Outline

Ben Platt – Overview and System Requirements

Myung Cho – Modeling Conceptual Mirror Support Design

Mark Sirota – M2S Control Systems Overview


Secondary Mirror System (M2S) Overview and System Requirements

Ben Platt

14 September


Outline

M2 System Decomposition

External Interfaces

M2 System Description and Overview

M2 System Requirements


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}


M2 External Interfaces

Draft Copies of the ICDs will be made available for this study.


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


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



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



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


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.


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


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.


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 = 314626B = High frequency errors (surface roughness) = 2 nmx = Separation between point pairs, similar to spatial frequency.d = Diameter of beam footprint = 3.046 mr0 = Fried’s parameter = 2.88 m

2323

5

42.375.136.10 Bd

x

d

x

d

xAxD

35

0

230

2

500

r

mnmA

Where:

M2 SQRT(D(x))

0

50

100

150

200

250

300

350

400

0.000 0.200 0.400 0.600 0.800 1.000

x/d

Sq

ua

re r

oo

t o

f D

(x),

(n

m)


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


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).)


M2 Support System (M2SS)Performance of NOAO Conceptual Design

Myung Cho


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 errorMirror 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


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


Conceptual Lateral Support design

Lateral support: 24 passive systemEdge 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


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


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


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)*

mode frequency mode shapeID (hz)

1 63.8 0 astigmatism 2 63.8 45 astigmatism 3 145.7 0 trefoil4 145.7 30 trefoil5 177.7 focus6 251.9 0 quadfoil7 251.9 45 quadfoil8 271.0 0 coma9 271.0 90 coma

10 381.0 pentafoil


Active Optics Performance

Raw data Active Optics Correction aOZernike P-V rms P-V rms Fmax error

ID (nm) (nm) (nm) (nm) (N) (%)4 4715 1000 46.2 6.4 34.8 0.65 4825 1000 51.1 6.4 33.0 0.66 5506 1000 737.0 87.9 483.3 8.87 5506 1000 736.9 87.9 467.1 8.88 3337 1000 660.8 171.6 595.9 17.29 5535 1000 192.8 22.6 124.8 2.3

10 5535 1000 194.7 22.9 106.4 2.3

M2 active supports can correct low order Zernike modesFirst 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)


Typical Zernike Surfaces (FRINGE Zernikes)

Z04 Z07

Z08 Z10

Zernike ID. R(r,) Aberrations

4 r2 cos(2) astigmatism

5 r2 sin(2) astigmatism

6 (3r2 -2)r cos() coma

7 (3r2 -2)r sin() coma

8 6r4 - 6r2 + 1 asphere

9 r3 cos(3) trifoil

10 r3 sin(3) trifoil


BACKUP

Myung Cho


Lateral support force distribution(shown in Right-half)

Plane X-Y

Force componentsIsometric view

Plane Y-Z


Lateral support force and direction (listed in Right-half)

force component (N) force direction (degree)Angle (o)

ID ANGLE Fx Fy Fz (X-Y)x (X-Y)y (Y-Z)y (Y-Z)z1 -82.5 97.88 400.76 97.15 76.28 13.72 13.63 76.372 -67.5 284.93 510.10 91.49 60.81 29.19 10.17 79.833 -52.5 388.60 682.25 77.03 60.33 29.67 6.44 83.564 -37.5 382.62 890.74 60.34 66.75 23.25 3.88 86.125 -22.5 280.62 1077.71 38.66 75.41 14.59 2.05 87.956 -7.5 108.32 1176.08 11.76 84.74 5.26 0.57 89.437 7.5 -108.32 1176.08 -11.76 95.26 5.26 0.57 90.578 22.5 -280.62 1077.71 -38.66 104.59 14.59 2.05 92.059 37.5 -382.62 890.74 -60.34 113.25 23.25 3.88 93.88

10 52.5 -388.60 682.25 -77.03 119.67 29.67 6.44 96.4411 67.5 -284.93 510.10 -91.49 119.19 29.19 10.17 100.1712 82.5 -97.88 400.76 -97.15 103.72 13.72 13.63 103.63


Continue with Overview and System Requirements

Ben Platt


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

accelerationSeeing:

– 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.)


M2 Interface Plate

TMT Will Provide an Interface Plate on the Telescope Structure for Connecting all Cables, Wires and Hoses.


M2 Control System – Cell (M2CSC)

Mark Sirota


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.


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.


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)

– InterfacesControl 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


M2 Control System - Cell

M2

SUPPORTS

M2Cell

ControlProcessor

&Amplifiers

Cell Control Delta Forces

Zenith AngleTemperature

MIRROR

M2 CELL

Actuator Commands

Sensor MeasurementsTelemetry

Alarms and Faults

Control Commands

M2 Control System_Cell

M2 Interface Panel

E-Stop

Power

Coolant

PositionerService Loop

Power(if required)

Coolant(if required)

Local ControlEthernet Port

M2 Control System - Cell Functional Block Diagram

Σ

M2

MIRROR

CellControl

LUT(Forces)

(non volatile)

Engineering Sensors

Da

ta

Data

Cell Control LUTBuild and

Management

Cell Contol LUT Data

TelescopeControlSystem

TCS M2CS_Cell Adaptor

DataManagement

System

UtilityInterlocks

M2 Cell Assembly

ShapeMeasurements

Alignment &PhasingSystem

Shape to ForceTransformation

stars

Data

.


M2 Control System – Positioner (M2CSP)

Mark Sirota


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.


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.

– InterfacesControl 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



Core performance characteristics– These numbers are representative and will be updated over the next several weeks.

Requirement Value Comment

Travel Range

Tilt +/- 8 degrees

Rotation +/- 180 degreesRepeatability

Tilt 1500 m-arcseconds

Rotation 3000 m-arcseconds

Piston 175 µ-meters RMSDifferential Accuracy

Tilt 200 m-arcseconds RMS

Rotation 200 m-arcseconds RMS

Piston 30 µ-meters peak

Max change in piston with simultaneos tilt and rotation

moves (< 15 arcseonds).Jitter

Tilt 100 m-arcseconds RMS

Rotation 100 m-arcseconds RMS

Piston 5 µ-meters RMS With trend removedTracking Speeds Tilt +/- 5 arcseconds/second Rotation +/-10 arcseconds/secondSlew Time < 2 minutesSettling Time < 10 seconds

Turnarounds can occur(tracking trough zero speed)

over 15 arcseconds

over the full travel range

Command minus M3 actual with trend removed



.

M3Rotator/Tilt

ControlProcessor

&AmplifiersM3 Rotator Positions

Rotation & Tilt

Zenith angleTemperature

Telemetry

Alarms and Faults

Control Commands

M3 Control System-Positioner

M3 Interface Panel

E-Stop

PowerCoolant

M3 Cable Wrap

Power(if required)

Coolant(if required)

Local ControlEthernet Port

M3 Control System – Positioner Functional Block DiagramD

ata

AlignmentMeasurements

Data

M3 Positioner Control

stars TCS

TCS M3CS_P Adaptor

APS

DMS

UtilityInterlocks

M3 Positioner Assembly9/5/2007

.

.

M3

TILT

MECHANISM

Limit and Home Switches

Rotator Commands

M3

ROTATOR

Rotator & Tilt Commands

Rotator and Tilt Encoders

Engineering Sensors

Pointing Kernel

Positiondata

Transformation to delta

mechanical angle

Dat

a

Limit Switches


Backup Slides


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 ~ λ6/5

WFE budget is matched to an atmospheric wavefront

To be further corrected by AO


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

22235

42.375.136.10 Bdx

dx

dx

AxD

•3


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 ro:

Where: D(x) is the structure and it is in units of nm2

A = Leading coefficientB = Uncorrected wavefront errorx = Separation between point pairs,

similar to spatial frequencyd = Beam footprintr0 = Fried's Parameter

35

2 302

500

ormnmA


M2M Polish Structure Function Curve

M2 SQRT(D(x))

0

50

100

150

200

250

300

350

400

0.000 0.200 0.400 0.600 0.800 1.000

x/d

Sq

ua

re r

oo

t o

f D

(x)


Optical Coating Requirements


Observing Operating Conditions

Documents

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