1 DESIGN REQUIREMENTS DOCUMENT FOR SECONDARY MIRROR SYSTEM (M2S) TMT.OPT.DRD DRF30 October 17, 2012
2 Page 2 of 60 TABLE OF CONTENTS 1. INTRODUCTION Introduction... 6 Purpose Scope... 6 Applicable Documents... 7 Reference Documents... 8 Standards... 8 Change Record... 9 Abbreviations and Acronyms... 9 M2S Interfaces Summit Facilities (SUM)...12 Telescope Structure (STR)...12 Power Lighting and Grounding System (PL&G)...12 Communications and Information System (CIS)...12 Telescope Control System (TCS)...12 Observatory Safety System (OSS)...12 Engineering Sensors (ESEN)...12 Optical Cleaning (CLN)...13 Coating (COAT) Test Instruments (TINS)...13 Optical Handling Systems (HNDL) OVERALL DESCRIPTION Perspective Summary of the Thirty Meter Telescope Optical Design...14 Introduction to the Secondary Mirror System (M2S) System Functions...17 User and Operator Characteristics...17 Constraints Lifetime...18 Observatory Availability...18 Standards...18 Power availability Assumptions and Dependencies...19 Coordinate Reference Systems...19 Telescope Motion during Telescopee Observing Operations and the influencee on M2S Telescope elevation motion influence on M2S during tracking operations Handling the M2 System Preparing the interface hardware before installing the M2POS...21 Installation and removal of the M2 Positioner (M2POS)...21 Installation and removal of the M2 Cell Assembly Maintenance of the M2 System M2 Mirror Cleaning...23 M2 Mirror Stripping and Coating SPECIFIC REQUIREMENTS 25
3 Page 3 of General Requirements Size and Mass...25 Coordinate Systems and Units...26 System Alignment Tolerances Materials...27 Fasteners, Components and Subassemblies s...28 Electronics and Software...28 Electromagnetic Compatibility...28 General Safety Requirements Personnel Safety Requirements Hardware Safety Requirements Reliability...30 Maintenance Cleaning Coating Environmental Requirements Observing Performance Conditions Requirements...33 Facility Performance Conditions Requirements...34 Component Functional Conditions Requirements...34 Survival Conditions Requirements...34 Earthquake Survival Requirements M2S Observing Operations Requirements Stiffness Requirements...35 Calibrations...36 M2S Observing Operations Motion Requirements M2S Pointing Requirements M2S Requirements for Slewing M2S Requirements for Target Acquisition: Offsets, Nods and Dithers Image Jitter Requirements Image Jitter during Guided Tracking Jitter during Adaptive Optics (AO) Guidingg Thermal Requirements M2 Cell Assembly (M2CA) M2 Mirror (M2M) M2 Finished Mirror (M2M) surface figure specifications Zernike definition SlopeRMS Equation Processes for calculating SlopeRMS for M2 Mirror Surface Figure Error Sources...48 M2 Mirror Surface Figure Process for the static error terms: Residual Polishing Errors and Static Thermal Distortion M2 Mirror Surface Figure Process for the dynamic error terms: Dynamic Thermal distortion, Gravity effect nominal and Gravity effect manufacturing M2MM thermal requirements...50 M2MM cleaning and coating requirements...50 M2 Support System (M2SS)...50 M2 Cell M2 Positioner Assembly General M2 Positioner Assembly Requirements...51 M2 Positioner Assembly Reliability and Maintenance...51 General M2POS Requirements...51
4 Page 4 of M2 Control System (M2CS) Command and Control Calibration M2S Safety and Fault Monitoring: M2CS Telemetry Initialization, Power Up, and Power Downn M2CS diagnostics and self-calibration Interfaces between M2CA and M2PA...57 Interfaces between the M2 System and other observatory systems Interface between Telescope Structure (STR) and M2S...57 M2 System (M2S) Interfaces to Summit Facilities SUM...58 Interface between M2S and Power, Lightingg and Grounding System (PL&G)...58 Interface between Communication and Information System (CIS) and M2S...58 Interface between M2S and Telescope Control System (TCS)...58 M2 System (M2S) to Observatory Safety System (OSS)...58 M2 System (M2S) to Engineering Sensors ( ESEN)...58 M2 System (M2S) to Optical Cleaning Systems (CLN)...58 M2 System (M2S) to Optical Coating System (COAT)...58 M2 System (M2S) to Test Instruments (TINS)...59 M2 System (M2S) to Optical Handling System (HNDL) Interface with the M2 Celll Assembly Lifting Fixture (M2CALF) Interface with the M2 Positioner Lifting Fixture (M2PALF) 59
5 Page 5 of 60 TABLE OF FIGURES Figure 1. Scope of this DRD relative to TMT WBS... 7 Figure 2. TMT Telescope Optical Design Figure 3. The M2 Assembly shown in its location in the telescope (excluding M2CS) Figure 4 Concept for the M2S shown on the telescope top end (M2CS not shown) Figure 5. M2 System (not showing the M2CS) Figure 6. M2 Positioner (not showing the M2CS) Figure 7. ACRS, ECRS and M2CRS Coordinate Systems Figure 8. The Aerial Service Platform (ASP) shown in several locations Figure 9. Service Platform for accessing M2S during maintenance, removal, and installation Figure 10. M2CA and M2PA interfaces Figure 11. M2S Volume Allocation Figure 12. Alignment Tolerances for M2S (units are mm) Figure 13. Tracking Drift Allocations Figure 14. NFIRAOS Error Rejection Transfer Functions (Magnitude units are mas/mas) Figure 15. Allowable Tolerance Zone for Radius of Curvature and Conic Constant Figure 16. Mirror surface figure evaluation process Figure 17: A functional block diagram of the M2 Positioner Control System (M2CS) LIST OF TABLES Table 1. List of external Interface Control Documents (ICDs) for the M2S 11 Table 2. Summary Optical Design Parameters 15 Table 3. Power types available on the telescope 18 Table 4. Coordinate System Definitions 19 Table 5. M2S Mass Distribution 25 Table 6. M2S top-end mounted maximum cross-sectional area requirements 26 Table 7. Environmental conditions 33 Table 8. Required range of motion of the M2S using M2CRS origin and axes 33 Table 9. Earthquake Definitions 35 Table 10. Maximum Slew and Settle Time Requirements 38 Table 11. M2 System Maximum Tracking Velocities and Accelerations 38 Table 12. Allowable Stresses in Glass or Glass Ceramic 43 Table 13. M2 Mirror Size Table 44 Table 14. SlopeRMS Allocations 47
6 Page 6 of INTRODUCTION 1.1 INTRODUCTION This design requirements document (DRD) contains the design requirements for the Thirty Meter Telescope (TMT) Secondary Mirror System (M2S). This document is intended to describe the environmental, functional and performance requirements that must be met by the M2S, and to enable design and verification thereof. This document captures requirements specified in the top level requirements documents: Observatory Architecture Document (OAD), Observatory Requirements Document (ORD), Operations Concept Document (OCD), and system engineering error budgets. It provides flow down and interpretation at the level of M2S. Also included are requirements that originate at the level of this document. Section 1 describes this document. Section 2 describes TMT and the overall M2S. Section 3 lists requirements for M2S. Paragraphs in Section 3 marked as Discussion are for information only and are not requirements. 1.2 PURPOSE This DRD provides a comprehensive list of the technical requirements and constraints governing the design of the M2S. It will be used by: - The supplier of the M2S to guide design, engineering and planning of the system - The TMT Systems Engineering Group members to coordinate the design development of the TMT observatory - Review board members who will review the design of the M2S at design reviews and project status reviews 1.3 SCOPE The scope of this document is shown schematically in Figure 1. This document covers requirements for the deliverables of the TMT Work Breakdown Structure (WBS) elements: TMT.TEL.OPT.M2.CA, TMT.TEL.OPT.M2.POS and TMT.TEL.OPT.M2.INFC. WBS element TMT.TEL.OPT.M2.CA is the Secondary Mirror Cell Assembly. It contains the following subassemblies: - Completed M2 mirror (M2M) polished with bonded interface pads - Support system of the M2 Mirror (M2SS) - M2 Cell (M2C) which interfaces with the M2SS and the M2 Positioner - Support hardware consisting of test equipment, mass simulators, handling fixtures, shipping containers and spare parts WBS element TMT.TEL.OPT.M2.POS is the Secondary Mirror Positioner Assembly (M2PA). It contains the following subassemblies: - M2 Positioner (M2POS) the hexapod that provides rigid body motion to adjust the position of the M2 mirror to accommodate gravity sag changes as the telescope rotates, thermal changes, and systematic manufacturing tolerances - M2 Control System (M2CS) the electronics and software that controls the M2POS and cables between the M2CS and the M2POS - Support hardware test equipment, mass simulators, a software simulator, handling fixtures, spare parts, and shipping containers
7 Page 7 of 60 The M2 Interface Hardware, TMT.TEL.OPT.M2.INFC includes: - the mechanical hardware that creates the physical, repeatable, shimmed interface between the telescope structure and the M2POS - Cables, hoses and connectors that will interface from the M2CS to the telescope-supplied interface panel providing power, data, and coolant. The following items have their own requirements or specification: - Optical Coatings: TMT.TEL.OPT.COAT.M2M2, (RD3) - M2 Cleaning Support Hardware: TMT.TEL.OPT.CLN.M2. - Specialized M2 Handling Equipment designed for use at the TMT Observatory: TMT.TEL.OPT.HNDL.M2. - Telescope Structure including the top end where M2S interfaces and the M2 Interface Panel for power, data and coolant: TMT.TEL.STR.STR - The M2 Blank specification (RD2) TMT Telescope TMT.TEL TMT Telescope Optics - TMT.TEL.OPT M2 System - TMT.TEL.OPT.M2.ASSY o M2 Cell Assembly TMT.TEL.OPT.M2.ASSY.CELL M2 Mirror Blank* M2 Mirror Polished with bonded interface pads* M2 Mirror Support System M2 Cell Structure Support Hardware o M2 Positioner Assembly TMT.TEL.OPT.M2.ASSY.POS M2 Positioner M2 Positioner Control System Support Hardware o M2 Interfaces: TMT.TEL.OPT.M2.INFC Electrical Mechanical Included in this document Not included in this document * Documents M2 Mirror Blank Specifications and M2 Mirror Surface Figure Specifications are referenced in this document and apply to requirements in this document o o o o o M2 Coating Equipment TMT.TEL.OPT.COAT.M2M2 M2 Assembly, Integration & Test TMT.TEL.OPT.M2.INT M2 Handling Hardware TMT.TEL.OPT.HNDL.M2 Crane and lift fixtures for installation onto telescope Handling and transportation carts for observatory M2 Cleaning fixtures TMT.TEL.OPT.CLN.M2 Telescope Global Metrology TMT.TEL.OPT.INS Figure 1. Scope of this DRD relative to TMT WBS 1.4 APPLICABLE DOCUMENTS Applicable documents are top level documents that provide requirements that flow down to the current document.
8 Page 8 of 60 AD1 AD2 AD3 - Operations Concept Document (OCD), (TMT.OPS.MGT ) - Observatory Requirements Document (ORD), (TMT.SEN.DRD ) - Observatory Architecture Document (OAD), (TMT.SEN.DRD ) 1.5 REFERENCE DOCUMENTS Reference documents contain information complementing, explaining, detailing, or otherwise supporting the requirements and information included in the current document. RD1 TMT Work Breakdown Structure version (TMT.BUS.SPE RD2 RD3 RD4 RD5 RD6 RD7 RD8 M2 Blank Specification Document (TMT.OPT.SPE ) Design Requirements Document for Telescope Optical Coatings (TMT.OPT. DRD ) TMT Environmental Safety and Health Process Guidelines (TMT.PMO.MGT ) TMT Guidelines for Reliability Analysis (TMT.XXX.XXX.XX.XXX) TMT Guidelines for Software Safety (TMT.SFT.TEC ) TMT Structural Design Safety Guidelines, TMT.XXX.XXX.XX.XXX Site-Specific Seismic Hazard Assessment of Proposed Thirty Meter Telescope Site, Mauna Kea, Hawaii (TMT.STR.TEC REL01) 1.6 STANDARDS Standards documents describe general safety, design and workmanship standards required by the TMT Project for hardware to be delivered to TMT observatory. If comparable alternate standards are proposed by the hardware supplier, the supplier has the responsibility to demonstrate that the proposed standards are equal or better than those listed below. The TMT project office must approve the replacement of the standards listed below with alternate proposed standards. The following list of standards is TBC. SD1 Procedures for Performing a Failure Mode, Effects and Criticality Analysis: MIL-STD- 1629A SD2 Occupational Safety and Health Standards: OSHA 1910 a. Subpart D Walking-Working Surfaces: i Definitions ii General Requirements iii Guarding floor and wall openings and holes iv Fixed ladders b Control of hazardous energy SD3 U.S. Department of Energy Handbook on Electrical Safety, draft for R&D: DOE-HDBK a. Section 3.0 Electrical Hazard Analysis b. Section 11.0 Enclosed Electrical/Electronic Equipment c. Section 12.0 Requirements for Electronics equipment approval d. Section 13.0 Electronic R&D Equipment
9 Page 9 of 60 SD4 SD5 SD6 SD7 Geometric Dimensioning and Tolerancing: uniform practices for stating and interpreting and related requirements on engineering drawings: ASME Y Metallic Materials and Elements for Aerospace Vehicle Structures: metallic material definitions, formulas, principles, failures, properties, metallurgical joints, and analysis procedures: MIL-HDBK-5J Design Criteria for Controlling Stress Corrosion Cracking: MSFC-GuSPEC-522B Handbook for Corrosion Prevention and Deterioration Control in Electronic Components and Assemblies: MIL-STD-1250A SD8 Fasteners General Requirements for bolts, screws, studs, and nuts: ISO 8992:1986 SD9 Standard Specification for Annular Ball Bearings for instruments and Precision Rotation Components: ASTM F SD10 Lift Sling Design: 540-PG A SD11 Standard Practice for Performance Testing of Shipping Containers and Systems: ASTM D 4169 SD12 U. S. Military Surface Quality Specification MIL-PRF-13830B 1.7 CHANGE RECORD Revision Date Section Modifications CCR28 30 Nov, 2007 All Initial release CCR29 03 Oct, 2012 All Update to current requirements and format 1.8 ABBREVIATIONS AND ACRONYMS AO Adaptive Optics APS Alignment and Phasing System ASP Aerial Service Platform CC Conic Constant CLN Optical Cleaning System COAT Optical Coating System CTE Coefficient of Thermal Expansion DRD Design Requirements Document ENC Enclosure FEA Finite Element Analysis GMS Global Metrology System GUI Graphical User Interface HNDL Optical Handling System ID Inner Diameter
10 Page 10 of 60 LUT Look-up Table M1 Primary Mirror M1CS M1 Control System M2C M2 Mirror Cell structure M2CA M2 Cell Assembly M2CALF M2 Cell Assembly Lifting Fixture M2CS M2 Control System M2I M2 Interface Panel M2INF Interface hardware between the M2S and the telescope M2M Polished Secondary Mirror with bonded pads M2PA M2 Positioner Assembly M2PALF M2 Positioner Assembly Lift Fixture M2POS the M2 positioner not including the control system M2S Secondary Mirror System M2SS - M2 Mirror Support System MTBF Mean Time Between Failure MUT Mirror Under Test N/A Not Applicable OAD Observatory Architecture Document OCD Operations Concept Document OD Outer Diameter ORD Observatory Requirements Document OSS Observatory Safety System PSSN Normalized Point Source Sensitivity PL&G Power, lighting and grounding system Removed MUT MUT with some Zernikes removed REQ Requirements RMS Root Mean Square RoC Radius of Curvature SlopeRMS Slope RMS STR Telescope Structure TBC To Be Confirmed - this item still needs to be confirmed TBD To Be Determined - this item still needs to be determined TCS Telescope Control System TINS Test Instruments TMT Thirty Meter Telescope
11 Page 11 of 60 Z 1 Noll Zernike Piston term Z 2 Noll Zernke Tip term Z 3 Noll Zernike Tilt term Z 4 Noll Zernike Focus term Z 7 Noll Zernike Coma term Z 8 Noll Zernike Coma term Units: as arcsecond G acceleration caused by the Earth s gravity at its surface = m/s 2 hpa hectopascal where 1 hpa = 100 Pa Hz Hertz K Kelvin m meter mas milliarcsecond mm millimeter MPa megapascal nm nanometer N Newton N-m Newton-meter Pa Pascal; unit of pressure; 1 Pa = 1 N/m 2 s second VAC volts alternating current W Watt m micrometer µrad microradian 1.9 M2S INTERFACES Interfaces between the M2 System and other TMT Observatory subsystems are defined in the documents listed in Table 1. Table 1. List of external Interface Control Documents (ICDs) for the M2S Summit Facilities (SUM) to M2System (M2S) SUM to M2S ICD Telescope Structure (STR) to M2 System (M2S) STR to M2S ICD M2 System (M2S) to Power Lighting and Grounding System (PL&G) M2S to PL&G ICD Communications and Information System (CIS) to M2 System (M2S) CIS to M2S ICD M2 System (M2S) to Telescope Control System (TCS) M2S to TCS ICD
12 Page 12 of 60 M2 System (M2S) to Observatory Safety System (OSS) M2 System (M2S) to Engineering Sensors (ESEN) M2 System (M2S) to Optical Cleaning Systems (CLN) M2 System (M2S) to Optical Coating System (COAT) M2 System (M2S) to Test Instruments (TINS) M2S to OSS ICD M2S to ESEN ICD M2S to CLN ICD M2S to COAT ICD M2S to TINS ICD (note: these documents are not completed or available. Section 3.7 at the end of this document covers the currently known ICD requirements) Summit Facilities (SUM) The M2CS may have equipment located in the computer room of the summit facilities if desired. If needed, the Summit facilities must provide space, mountingg racks and power for this equipment Telescope Structure (STR) The telescope top end is the part of the Telescope Structuree where the M2 Positioner will be mounted. The mechanical interface between the telescopee top end and the M2POS will include shimss and interfacee hardware so that the interface can be adjusted to accommodate fabrication tolerances of the telescope and to create a repeatable interface. The location and space envelope of the M2CS (likely not at the top end of the telescope) will also be defined in this ICD. This ICD will also include an agreed method for modeling the dynamic interaction between the telescope structure and the M2S and maximum accelerations caused by 200-year and 1000-year earthquakes. Additionally, the Telescope Structure subsystem is responsible for routing electrical power, data cables and coolant to the M2S and will provide an M2 interface panel that the M2CS will mate with for connection to these resources Power Lighting and Grounding System (PL&G) The Power Lightingg and Grounding System will distribute filtered power with groundingg to all telescope-mounted subsystems and will provide lighting for maintenance Communications and Information System (CIS) The Communicatio n and Information System contains hardware, software and cabling to implement a generalized communications network throughout the observatory. It also includes a distributed time clock system with an accurate time reference to all observatory subsystems. The M2S, via the M2CS, will transmitt and receive data through the CIS cabling network forr the purpose of receiving time information and communicating with other telescope systems. The data that is transmitted from the M2S through the CIS will include positions, velocities, currents, temperatures, health status, etc. This interface will include specifying the volume of data thatt will be transferred to and from the M2S Telescope Control System (TCS) The M2 Control System (M2CS) will receive time-tagged position demands from the Telescope Control System to direct M2S motions. The M2CS will use its internal calibration model that is based on measured performance to provide positional error compensation (perhaps in the form of Look-Up Tables (LUTs)). The positioning solutions for TCS position demands may include calibrated error compensation based on data collected during telescope commissioning and operations Observatory Safety System (OSS) The M2S will receive interlock demand signalss from the OSS via the M2CS, and will send state of healthh messages and interlock requests back to the OSS via the M2CS Engineeringg Sensors (ESEN) The observatory engineering telemetry will require sensors to be mounted on the M2S. The sensors will measure structural temperature, air temperature, wind speed, dew point, etc. Data from the engineering sensors will be transmitted through the CIS andd will be available for observatory subsystems. Thesee sensors will not be used for internal M2S calibration or closed-loop control since
13 Page 13 of 60 the sampling rates will be too slow. The M2S will mount thee sensors in prescribed locations and willl route the cables from them to the M2 interfacee panel Optical Cleaning (CLN) The M2M will be cleaned using CO2 snow and fluids. The telescope will be oriented horizonof the M1 pointing during cleaning operations to minimize the risk of debris falling on the surface segments or M3 system. Accesss to the M2S during cleaning will be provided by an aerial service platform (ASP). For fluid cleaning, the M2CA must incorporate features (such as an inflatable seal and an attachable catchment surface) to guide fluid to drainage ports and to prevent fluid from running into areas behind the M2M. CO2, cleaning fluids, compressed air, and vacuum lines will be mounted to the aerial service platform and routed along the platform support structure so that they are accessible from the platform basket Coating (COAT) Periodically, the M2CA will be removed from the telescope for mirror recoating. A crane, an aerial service platform, and the M2CA lift fixture (M2CALF) will safely remove the M2CA from its telescopee mount and lower it to a handling cart on the observatory floor. While the M2CA is mounted on the handling cart, the M2 Mirror (M2M) will be removed from thee M2CA, placed on a rolling transport cart, and taken to the coating chamber area where the old coating will be removed (stripped) from the surface. The mirror will be transferred from the transport cart to a coating fixture which will support it inside the coating chamber while the new coating is deposited. The rolling transport cart, the cleaning and stripping facilities, the coating fixture, the coating chamber and lift fixtures required to move the M2M between them are included in the Coatingg subsystem Test Instruments (TINS) M2S will interface with one test instrument: the Global Metrology System (GMS). The GMS will include three laser trackers that are mounted to the TMT telescope structure and one mobile laser tracker. The laser trackers will be used to measure positions of optical subsystems periodically. Also, during installation, they will be used to enable positionn scanning to determine interface shims for optical subsystems. The M2S will be required to incorporate targets for the GMS so that the M2POS and the M2CA positionss can be measured. Some targets will be permanent so that positions can be measured while the M2S is mounted to thee telescope, and some targets will be removed after installation is complete. Any targets that are mounted around the perimeter of the M2M will be removed before recoating then replaced repeatably after coating Optical Handling Systems (HNDL) The lift fixture to install and remove the M2POS, the lift fixture to install and remove the M2CA, the handling cart for the M2CA, and proof-load weights for testing the fixtures are includedd in the Optical Handling System. The equipment is designedd to move the M2 System components around the TMTT observatory safely. The M2 System components must be designed to interface with the handling equipment so that handling operations are safe both for personnel and for the optical components.
14 Page 14 of OVERALL DESCRIPTION PERSPECTIVE Summary of the Thirty Meter Telescope Optical Design Per [REQ-1-OAD-1000] of the OAD, the telescope optical design shall be a Ritchey Chrétien configuration as shown in Figure 2. A summary of the optical design parameters extracted from Table 13 of AD3 is shown in Table 2. The aperture stop is located at the Primary Mirror. Proposed dimensions for the Secondary Mirror Blank are shown in RD2. Figure 2. TMT Telescope Optical Design
15 Page 15 of 60 Table 2. Summary Optical Design Parameters Surface Optical Beam Footprint (meters) Radius of Curvature (meters)) Conic Constant Distance to Next Surface (meters) Primary Mirror Secondary Mirror Secondary Mirror Focal Surface 30.0 Ø (to farthest segment corner) 3.0 Ø (unvignetted over 15 arcmin of FOV) Elliptical, long axis 3.50 short axis Ø for 15 arcmin FOV (flat) (medial field curvature) N/A N/A N/A Introductionn to the Secondary Mirrorr System (M2S) Telescopee Optical Axis M2 System Elevation Axis -X Nasmyth Platform +X Nasmyth Platform Figure 3. The M2 Assembly shown in its location in the telescope (excluding M2CS). The Secondary Mirror System (M2S) of the Ritchey-Chrétien optical design reflects the light from the F/1 primary mirror and converts it to an F/15 beam for the science instruments. Figure 3 shows the M2S located in the TMT Telescope but does not show the M2 Control System which can be located off of the telescope structure. One concept for the M2S is shown mounted to the telescope top end in Figure 4. The un-mounted M2S is shown in Figure 5 and the M2 Positioner is shown inn Figure 6 both are shown without the M2 Control System.. As the telescope rotates about the elevation axis, the telescope structure sag will change as the direction of the gravity vector direction changes with respect to the telescope structure beams.
16 Page 16 of 60 Therefore, the M2S must adjust its position based on the stiffness of the structures involved and the elevation angle of the telescope. At the supplier facility, the gravity deflection and thermally induced motion of the M2 System may be calibrated. The motion of the M2 System will be calibrated along with the entire telescope to accommodate gravitational and thermal deformations after installation on the telescope. M2 Positioner (hexapod) Telescope Top End Structure M2 Mirror integrated in the M2CA Figure 4 Concept for the M2S shown on the telescope top end (M2CS not shown) M2PA M2CA Figure 5. M2 System (not showing the M2CS)
17 Page 17 of 60 Stationary Frame Hexapod Arm (6) Figure 6. M2 Positioner (not showing the M2CS) Moving Frame 2.2 The major functions of the M2 System are as follows: 2.3 SYSTEM FUNCTIONS Support the M2 Mirror (M2M) safely under all conditions that it will encounter when on or offf the TMT telescope Support the M2M so that the surface figure meets the surface figure specifications during telescope observing operations Based upon commands received from the Telescope Control System, adjust the rigid body position of the M2 Mirrorr to optimize the optical performance of the telescope during telescope observing operations Isolate the M2M optical surface from vibrations to meet requirements during telescope observing operations Send telemetry through the CIS to other telescope assemblies ncluding engineering data such as encoder readings, voltages, currents, temperatures and other selected indicators of system health as well as results of internal health tests Provide safety alerts and respond to interlock demands from the Observatory Safety System Enable installation on the telescope, removal from the telescope, maintenance, and cleaning. USER AND OPERATOR CHARACTERISTICS During observing operations, the M2S will be operated as an autonomous subsystem of the Telescope Control System (TCS). The M2CS will receive motion demands from the TCS and will direct its own positioning in response. When the telescopee is not observing, the M2S may be operated through either the TCS or a local interface such as a plug-in laptopp to accomplish testing, handling and maintenance. Access to the local interface should be adjacent to the M2S when the telescope in pointed horizontally and dockedd at the telescope top end maintenance platform.
18 Page 18 of Lifetime CONSTRAINTS The observatory has a planned lifetime of 50 years. Components and systems must therefore be specified and/or designed to last a minimum of 50 years, subject to appropriate planned maintenance or replacement. Where equipment cannot reasonably be expected to last 50 years for reasons of obsolescence etc., it should comply with thee appropriate industry standards in order to facilitate future replacement or upgrades Observatory Availability TMT requires 97% availability for science during observing time defined as 10 hours per night. Standards Compliance Standards The observatory must comply with local and national standards relevant to its construction and operation. These will be the standards in force at Mauna Kea in Hawaii, USA. If standards other than those listed are preferred by the supplier, they may be proposed for TMT Project approval. The supplier must demonstrate that proposed alternate standards are equivalent to those listed Power availability The telescope facility will provide electrical power types shown in Table 3. Table 3. Power types available on the telescope ID Voltage Power Conditioning Phase Back Up Type H3D 480Y277V None 3 None H3DG 480Y277V None 3 Generator L3D 208Y120V None 3 None L3DG 208Y120V None 3 Generator L3C 208Y120V Clean 3 None L3CUG 208Y120V Clean 3 UPS L1C* 120V Clean 1 None L1CUG* 120V Clean 1 UPS The power conditioning types are currently identified as either clean or none, depending on the anticipated level of power conditioning that will be applied. These descriptions will be replaced with
19 Page 19 of 60 reference to the appropriate standard. All three phase power will be delivered in four wire Y configuration with at least full size neutral to allow use of single legs to neutral. Voltages listed are the nominal voltages for the power type. Nominal frequency of supplied power is 60Hz. Delivered power quality (voltage and frequency variation) is TBD. *Single phase 120V power (L1C and L1CUG) will be taken off as single legs to neutral from the delivered 4 wire 3 phase power at a local distribution box. 2.5 ASSUMPTIONS AND DEPENDENCIES The requirements for the M2S are influenced by the performance of the M1 Segments, the telescope structure, the Alignment and Phasing System, the On-Instrument Wave Front Sensors, and the Mount Control System, all of which work in concert with the M2S to create the wavefront that reaches the science instruments. If any of these subsystems changes significantly, then the requirements on the M2S may also be required to change. 2.6 COORDINATE REFERENCE SYSTEMS The M2 System shall be described using the following coordinate reference systems that are defined in AD3, Section 6.1, and defined below in Table 4. The following Coordinate Systems are used: ACRS: Azimuth Coordinat Reference System ECRS: Elevation Coordinate Reference System M2CRS: Secondary Mirror Coordinate Reference System Table 4. Coordinate System Definitions Coordinate System Origin X axis Y axis Z axis Azimuth (ACRS) The center of the azimuth journal circle, in the plane of the azimuth journal, 3.5m above the level of the OFCRS Points to the East, in the plane of the azimuth journal Points to the North, in the plane of the azimuth journal Right hand complement to x and y axes. Parallel to local gravity Elevation (ECRS) The intersection of the Z axis of ACRS with the elevation axis of the telescope Parallel to the X axis of the ACRS, collinear with the elevation axis of the telescope Rotated around the X axis according to the RH rule, by the zenith angle Right hand complement to the X and Y axes; points to zenith at zero zenith angle Secondary Mirror (M2CRS) The intersection of the Z axis of the ECRS with the M2 optical surface Parallel to the X axis of the ECRS Right hand complement to the X and Z axes Points to the origin of the ECRS, in the line of the Z axis of the ECRS The ECRS and M2CRS coordinates are shown in Figure 7.
20 Page 20 of 60 Figure 7. ACRS, ECRS and M2CRS Coordinate Systems 2.7 TELESCOPEE MOTION DURING TELESCOPE OBSERVING OPERATIONS AND THE INFLUENCE ON M2S The telescope will rotate about the ECRS X-Axis from zenithh angle 1 to 65 during observing operations. As this occurs, the M2CRS will rotate with respect to the gravity vector about the M2 X- axis so that the angle between the gravity vector and the M22 Z-Axis will equal the zenith angle. The M2 Positioner will accommodate sag of the M2S and the telescope structure as the zenith angle changes. The gravity print-through of the support system acting on thee M2 Mirror will also be influenced by the zenith angle of the telescope. As part of the telescope calibration sequence, the changes in M2 rigid body position and M2M surface figure caused by gravity print-through will be measured and adjustments of the segments of the M1 Mirror will be calibrated to minimize the optical effect. To minimize the amplitude of M1 Mirror accommodation errors, the surface of the M2 Mirror may require figuring to remove the print-through effect at a pre-determined zenith angle. The telescope will perform the following motions during observing operations: - Pointing is the blind operation to align the telescope to the sky and occurs without optical feedback. - Slewing is the motion equired to move from one pointing position to another pointing position. - Tracking is smoothly following the motion of a target across the sky based on the calculated trajectory of the target. - Guiding is closed-loop tracking using optical feedback from instrument wave front sensors or guide cameras. - Offsetting, Nodding and Dithering: o Acquisition offsetting is the process of repointing of the telescope over small angles (less than 1 degree) without any feedback in order to establish alignment of the science target with the active instrument. o Guider offsetting is the process of repointing of the telescope from one guiding location to another with the assistance of guider feedback.
21 Page 21 of 60 o AO Guider offsetting, is the process of repointing of the telescope from one guiding location to another with the assistance of guider r feedback and adaptive optics image correction. o Nodding is the process of repetitively offsetting the telescope between two positions on the sky, with a dwell time at each end point where the system is in guiding mode. o Dithering is the process of repetitively offsetting the telescope between more than two positions on the sky, with a dwell time at each end point where the system is in guiding mode. The M2 System will require rigid body adjustment during these operations whenever the change in telescope zenith angle is large enough to require M2S adjustment in order to meet optical requirements. The need for M2 motion will be calibrated and managed by the TCS Telescope elevation motion influencee on M2S during tracking operations Sidereal tracking velocity of astronomical objects depends on telescope azimuth angle, telescope elevation angle and instrument position on the Nasmyth platforms. The telescope is required to track extra-solar system astronomical objects with a sidereal rate 15 arcsec/sec and solar system objects with a maximum rate arcsec/sec. The angular velocity of the telescope zenith angle depends on the telescope latitude, the sidereal rate of targets, and the azimuth angle. cos sin (1) wheree ω z = s = lat = a = telescope angular velocity sidereal or solar system rate telescope latitude location azimuth angle From equation (1), the maximumm zenith angle velocity occurs when sin(a) = 1 or when a = 90 or 270. Since the telescope latitude at Mauna Kea is 19.8, the maximum value for ω z is:, 15.5 (2) 2.8 HANDLING THE M2 SYSTEM The M2S will be installed on the TMT telescope as two subassemblies: the M2PA and the M2CA. Both subassemblie s will be raised and lowered into positionn with dedicated lift fixtures. During installation, the M2PA and the M2CA will be surveyed so that the assembly is accurately aligned. During operation of the telescopee there will be times when the M2S will be surveyed with the Globall Metrology System (GMS) to check the rough alignment of the M2S Preparing the interface hardware before installingg the M2POS First, the interface hardware will be attached to the M2 mounting features of the Telescope Top End. Nominal shims will be in place. Prior to installing the M2POS, a mass mockup of the M2 System will be installed onto the interface hardware and surveyed to determine the position accuracy of the interface hardware. The shims will be adjusted to position the interface hardware so that M2S will be correctly placed when it is installed. The mass mockup will then be removed Installation and removal of the M2 Positioner (M2POS)
22 Page 22 of 60 Next, the M2POS will be installed with the telescope in the horizon-pointing orientation. The dedicated lifting fixture for the M2POS and a facility crane and cable assembly will be used to lift the M2POS into position. During lifting operations, the M2POS must be locked so that no tip, tilt or translation can occur during installation. Access to mechanically fasten the M2POS to the interfacee hardware on the M2 Support Tower will be provided by the aerial service platform shown in Figure 8 and a service platform that unfolds from the side of the dome shown in Figure 9. Once all facility interfaces have been mated, the M2POS should be fully functional. A mass mock-up of the M2CA will be installed ontoo the M2POS. The telescope will be tilted around the elevation axis and the M2POS will be rotated and tilted while being surveyed to verify that the M2POS is positioned, operating and communicating correctly. The mass simulator for the M2CA will then be removed. During normal operations, the M2POS will not be removed from the telescope once it is finally installed; but the option to remove the M2 Positioner in casee of failure must be retained Installation and removal of the M2 Cell Assemblyy A dedicated lifting fixture and the facility crane and cable assembly will be used to lift the M2CA into position. Access to mechanically fasten the M2CA to the M2POS during the lift will be provided by the Aerial Service Platform (Figure 8) and a service platform that unfolds from the side of the dome (Figure 9). The M2CA will be removed from the telescopee for mirror recoating approximately every two years. The design of the interface between the M2CA and the M2POS should incorporate features to ensure repeatable, accurate installation and removal. Figure 8. The Aerial Service Platform (ASP) shown in several locations
23 Page 23 of 60 Figure 9. Service Platform for accessing M2S during maintenance, removal, and installation 2.9 MAINTENANCE OF THE M2 SYSTEM Access to the M2S when it is mounted on the telescope is required for installation, inspection, cleaning, maintenance, and repair. Maintenance of the M2SS will take place with the telescope pointing toward the horizon. The aerial servicee platform (Figure 8) and the service platform that unfolds from the side of the dome (Figure 9) will provide access to the mirror surface and the back side of the M2S. Periodically, the M2CA will be removed from the telescope for mirror recoating. A crane, the aerial service platform, and the M2CA lift fixture (M2CALF) will safely remove the M2CA from its mount on the telescope and lower it to a handling cart on the Observatory floor. While the M2CA is mounted on the handling cart, the M2 Mirror (M2M) will be removed from the M2CA, placed on a rolling transport cart, and taken to the coating chamber area. The old coating will be removed (stripped) from the surface. The mirror will be transferred from the transport cart to a coating fixture which will support it inside the coating chamber when the new coatingg is deposited.. The coating equipment interfaces are described in the M2S to COAT ICD M2 Mirror Cleaning Frequent cleaning of the M2 Mirror reflective surface will enhance telescope throughput and prolong the life of the reflective coating. Two types of cleaning are planned: CO 2 snow cleaning and fluid cleaning. Both cleaning activities will occur during the day, with the M2 System mounted on the telescope, and the telescope oriented to point horizontally. For CO 2 cleaning, a spray nozzle will be used to spray CO 2 onto the surface to dislodge particles.
24 Page 24 of 60 For fluid cleaning, the fluid must be prevented from reachingg the back of the M2 Mirrorr and Cell Assembly. One possible method to do this would be to incorporate an inflatable seal designed into the M2 Cell that will be pressurized during fluid cleaning to seal the edge of the M2 mirror against the M2 Cell. Fluid will be gently dispersed onto the M2 Mirror reflective surface to dissolve dirt, with very gentlee local rubbing only where soil will not rinse off. A drainn that is designed into the M2 Cell will connect to a tube that will carry effluent to a storage container. Pressurized clean dry air will be used to dry the mirror after fluid cleaning M2 Mirror Stripping and Coating The M2 Cell Assembly will be removed from the telescope approximately every two years so that the M2 Mirror can be recoated following the steps described in Sections The finished M2 Mirror must be undamaged during the process of stripping off the old coating using chemicals and must be able to withstand the conditions within the coating chamber.
25 Page 25 of SPECIFIC REQUIREMENTS GENERAL REQUIREMENR NTS Size and Mass The M2M shall have a thickness 100mm. [REQ-2-M2-0005for the TMT site (T = 2.3 C). The dimensions describing the M2S apply at the median nighttime temperature [REQ-2-M2-0010] The M2M shall be a hyperboloid mirror with paraxial radius of curvature R = meters and conic constant K = The mirror diameter shall be as given in Table 13. [REQ-2-M2-0020] [REQ-2-M2-0030as shown in Table 5 Discussion: This mass includes the M2CA and the M2PA including all cables and fluid lines The total M2S mass shall be 6.3 metricc tonnes (6,300 kg) and shall be allocated that are required. Discussion: The mass allocation for the M2 Control System applies if it is mounted on the telescope elevation assembly. If the M2CA is mounted off of the elevation assembly, its mass may increasee and the mass assigned in Table 5 mayy be distributedd to the M2CA and M2POS. Table 5. M2S Masss Distribution Total M2 System Mass (kg) M2 Mirror Cell Assembly M2 Positioner M2 Control System Margin (TBC) (TBC) 250 (TBC) 350 (TBC) The M2CA and the M2POS shall have interface dimensions shown in Figure 10. [REQ-2-M2-0035] Figure 10. M2CA and M2PA interfaces [REQ-2-M2-0040structure shall have a cross-sectional area perpendicular to the telescopee optical axis that is less The subassemblies of the M2S that are mounted to the top end of the telescope than the allocations assigned in Table 6.
26 Page 26 of 60 Table 6. M2S top-end mounted maximum cross-sectional area requirements Total cross-sectional area (m 2 ) 4 M2CA M2PA Figure 11. M2S Volume Allocation Coordinate Systems and Units Discussion: Limiting the transverse cross-sectional area allows wind pressure on the telescope to be controlled. [REQ-2-M2-0045] During observing operations, the M2S shall fit within the volume shown in Figure 11 for all M2 System observing tilt and rotation angles. If the M2CS is located at the top end of the telescope, it must also fit within this volume, but if it is placedd remotely, a separate space envelope must be defined for it that will not affect telescope operation. [REQ-2-M2-0050] The M2 Coordinate Reference System (M2CRS) shall be as described in Section 2.6, Table 4 and illustrated in Figure 7. [REQ-2-M2-0060] Metric units shall be used for all M2S interfaces System Alignment Tolerances
27 Page 27 of 60 Figure 12. Alignment Tolerances for M2S (units are mm) Discussion: When the alignment tolerances of this requirement have been achieved, the range of motion given in [REQ-2-M2-0690] provides adequate additional motion to perform the remaining adjustments for M2M alignment during telescope observing. Discussion: The tolerances in REQ-2-M shall be divided between the M2CA hardware and the M2POS hardware so that the equirement can be met. Discussion: [REQ-2-M2-0065when the gravity vector is aligned with the M2CRS Z-Axis, the temperature is 2 C and the M2POS The position of the M2 Mirror in the M2SS shall satisfy the tolerances of Figure 12 position settings place the M2M vertex at the M2CRS origin. Shimming may be used to ensure that the hardware complies with REQ-2-M Materials
28 Page 28 of Fasteners, Components and Subassemblies The M2S shall be designedd with metric components and fasteners. All components and subassemblies shall comply with SD9, SD10, and SD11, as All M2S drawings shall comply with SD Electronics and Software M2S shall be designed to operate using the electrical power as shown in Table 3. All M2S electronics shall comply with SD2b and SD3. All M2S software shall comply with RD6.. [REQ-2-M2-0070conditions described in Section 3.2, materials shall meet design properties, be corrosion resistant The M2S shall be designedd to comply with SD5, SD6,, and SD7 so that, under all and anti-galling; and so that galvanic or other chemical corrosion will not occur. [REQ-2-M2-0072] [REQ-2-M2-0074] All fasteners shall comply with SD8. [REQ-2-M2-0076during maintenancee when the M2S is mounted on the telescope shall be captive or tethered. All fasteners and components on the M2S that may be loosened or unfastened [REQ-2-M2-0078applicable. [REQ-2-M2-0080] [REQ-2-M2-0085] [REQ-2-M2-0090] [REQ-2-M2-0095] [REQ-2-M2-010operational mode with full interfacing with the TMT softwaree The M2S shall be operated in two modes: an independent simulation mode or an system Electromagnetic Compatibility Discussion: The M2 system will be installed and operated in an environment shared with other electronic equipment that will generate electromagne etic interference. Such sources include computer systems, power switching systems, pulse-width-modulated drive systems, portable radios, etc. The M2S should be designed for low electromagnetic emissions and to meet operating requirements when exposed to the expected electromagnetic environment per the guidelines in SD1. Electromagnetic compatibility testing will not be required; but if electromagnetic problems are encountered when thee M2S is installed on telescope, the supplier must fix the problem. [REQ-2-M2-0110that operational performance of all M2 System componentss will not malfunction or be degraded when all components within the M2S are operating together at their designed levels in the presence of The M2S shall be designedd following guidelines in Sections 11 and 13 of SD3 so externally generated electro-magnetic interference and so that the M2S shall not emit excessive electro-magnetic interference. [REQ-2-M2-0120from 310nm to 28,000nm. During observing operations, the M2S shall not emit light in the wavelength range General Safety Requirements
29 Page 29 of 60 [REQ-2-M2-0170] The safety priority of the M2S shall be: (i) protection of persons, (ii) guarding integrity of M2S hardware and other TMT hardware that interfaces with M2S, and (iii) protection of scientific data. [REQ-2-M2-0190] The M2S shall be prevented from uncontrolled movement (tip, tilt and translation) at all stages of assembly, installation and operations, with power on or off Personnel Safety Requirements [REQ-2-M2-0200] The M2S shall comply with the referenced sections of SD2. [REQ-2-M2-0210] All metallic components of the M2S shall have sharp edges de-burred. [REQ-2-M2-0220] Any M2S component that must be manually lifted during assembly, installation, removal, servicing, etc. shall have a mass of 20kg Hardware Safety Requirements [REQ-2-M2-0225] Electrical equipment (M2POS and the M2CS) shall have emergency stop switches located conveniently for maintenance access to terminate power to the M2S in the case of an emergency. The emergency stop switch shall be connected to the nearest interface to the OSS. [REQ-2-M2-0230] M2S shall not cause damage (i.e. over-heating or collision) to itself or adjacent hardware either through commanded or un-commanded motions. [REQ-2-M2-0240] M2S hardware shall not sustain any damage or cause any damage to or harm to personnel or other telescope subsystems if power is lost to any or all M2S components at any time. [REQ-2-M2-0250] Any M2 component whose failure would compromise the structural integrity of the M2 Mirror must be either fail-safe (ie. a redundant load path must be provided) or demonstrated to have a fatigue life at least 10X higher than the expected number of cycles. Discussion: In Requirements REQ-2-M to Req-2-M below, the term limit load refers to the calculated maximum load condition of the hardware in all conditions. A torque factor is calculated as follows:. Discussion: TMT will provide the expected number of cycles per year (TBD). [REQ-2-M2-0260] Ductile metallic components (i.e. those with elongation-at-break >10%) shall be designed to have a factor of safety at limit load 1.5 relative to the 0.2% offset yield stress. [REQ-2-M2-0270] Brittle metallic components (i.e. those with elongation-at-break <10%) shall not be used. [REQ-2-M2-0280] M2S structural components shall be designed to have a factor of safety at limit load 3.0 times the yield strength of the material de-rated with fatigue factors that represent the 50 year life of the M2S. The M2 Mirror glass or glass-ceramic and bonded joints are excluded from this requirement. [REQ-2-M2-0290] The stress in all components that participate in precision location of the M2 Mirror (i.e. metering rods and positioning pins do participate, but screw threads do not participate), at limit
30 Page 30 of 60 load shall be maintained below the elastic limit of the component s material with a factor of safety of 1.2. Discussion: Any components that perform structural and positioning functions shall meet the more stringent requirements. [REQ-2-M2-0300limit load 3.0 times the bolt yield strength, 2.0 times the stress that would create bolt slippage for critical alignments, and 1.5 times the stress that would create bolt slippage for non-detrimental alignments. [REQ-2-M2-0310] For any bonded joint, the joint shall be designed to have a factor of safety at limit load 3.0 relative to the allowable shear stress for the particular combination of adhesive, adherand, primer, and surface preparation. For any bolted friction joint, the joint shall be designedd to have factors of safety at [REQ-2-M2-0320ceramic shall not exceed the values given in Table 12, under the conditions described in the table. The maximumm principal stress at any point in the M2 Mirror glass or glass- No factors of safety need be applied, and residual stresses in the glass may be neglected. Discussion: These values correspond to a probabilityy of failure of 1/10,000 for the M2 Mirror during the 50-year lifetimee of the observatory. This probability is based on an assumed glass- ceramic mirror with any stressed surfaces polished too remove sub-surface or torque capability factor of 1.5, flaws. [REQ-2-M2-0330relative to the maximum expected load. Any motors or actuators shall have a force [REQ-2-M2-0340fasteners, covers, tools, etc. from falling under all conditionss including alll handling, maintenance, operating and all earthquake conditions at all possible orientations Reliability The M2S shall be designedd to prevent itss oils, coolant, cleaning fluids, particles, [REQ-2-M2-0380following the guidelines therein to identify, evaluate, eliminate, and quantize possible failures. [REQ-2-M2-0390] The M2S shall be designedd to operate for 10 hours continuously each night, in The M2S shall comply with RD5. FMECA analyses of M2S shall be performed Observing Operating Conditions, with a total expected operating lifetime of 50 years. [REQ-2-M2-0400are lost due to failures. Discussion: The specification for reliability is an average over the lifetime of the system. The M2S shall be designedd so that less than 1.8 hours of observing time per year Discussion: Observing time is defined as 10 hours per night (REQ-1-OCD-3055will not accrue time against this of AD3). Maintenancee will be scheduled during the day and requirement. Discussion: A failure that occurs during observing and cannot be repaired until the next day should be considered as losing half a night s observing (5 hours), i.e. the failure should be assumed to occur halfway through that night. Discussion: This is flowed down from [REQ-1-OAD-0322] and may require highh Mean Time Between Failure (MTBF) on the components, redundant systems, the ability to rapidly repair failures in situ, performance monitoring for replacing components before they fail, diagnosticss and trouble-shooting features and a maintenance plan for performing periodic maintenance and calibration during daytime.
31 Page 31 of 60 The reliability of the M2S design shall bee compatible with a 50-year lifetime. [REQ-2-M2-0410] Discussion: During the 50 year lifetime of the telescope, the following statistics are expected: - Expected number of Tracking scenarios between TBD and TBD zenith angles is TBD per night. - Expected number of elevation slews to new science objects is 20 per night with average slew angle of 15 degrees. [REQ-2-M2-0420establishing controll system zero position updates shall be permissible once per month. Discussion: Zero position updates reset the control system indicators that establish absolute The M2S shall not require re-calibration more frequently than once per year. Re- position. Discussion: This requirement limits the temporal and d spatial level of drift permitted in the performancee of all M2S components comprising the entire M2S both mechanically and electrically Maintenance [REQ-2-M2-0500preventive maintenance. Preventive maintenance means servicing, repairing, and replacing components and subsystems based on their expected lifetime, rather than waiting for their failure. The M2S shall be able to operate and meet all the requirements for 50 years with [REQ-2-M2-0510mounted to the telescope with access providedd by the aerial service platform or the dome-mounted top end service platform with the telescope pointing toward horizon. The M2S shall be designedd so that all maintenance can be performed with M2S [REQ-2-M2-0520for the foreseeable future. For instance, standard components and standard metric fasteners shall As a goal, components shall be chosen such that replacements will be available be used where possible. [REQ-2-M2-0530components will be required, operational spares shall be produced when the original components In cases where M2S components are custom fabricated, if replacement of the are fabricated in a quantity to meet the lifetimee requirement for M2S. [REQ-2-M2-0540that planned maintenance can be accomplished in less thann 2 hours while the M2S is mounted to the telescope Cleaning [REQ-2-M2-0580] The M2S shall be compatible with CO2 Cleaning that will be performed with the All components of the M2S shall be designed to be serviceable or replaceable so Telescope pointed toward the horizon with access to the M2S provided by the aerial service platform. CO2 Cleaning interfaces are described in the M2S to CLN ICD, Section TBD. [REQ-2-M2-0570toward the horizon, with access to the M2S provided by the aerial servicee platform. Fluid Cleaning of the M2 Mirror shall be performed with the Telescope pointed [REQ-2-M2-0575] Fluid Cleaning interfaces ncluding methods for draining fluids from the surface of M2M and for sealing to prevent fluid access to the back of the M2 Cell shall be incorporated. Discussion: The sealing method can be integrated into the M2Cell and are further described in the M2S to CLN ICD, Section TBD.
32 Page 32 of Coating [REQ-2-M2-0580] The M2CA and the M2 Mirror will interface with lifting and handling fixtures during recoating. All interfaces shall comply with the M2S to COAT ICD, Section TBD. [REQ-2-M2-0600] Any material that goes into the coating chamber with the mirror shall be cleanable, vacuum compatible, and shall not outgas to interfere with application of a durable coating. [REQ-2-M2-0610] For any components attached or bonded to the M2 Mirror, the bonded assembly shall not develop stresses during the coating process that could create cracks, fatigue or damage in the M2 Mirror. Discussion: During the coating process, thermal constraints described in RD3, Section 2.4 are: - the surfaces of the M2 Mirror where attachment features are bonded must stay less than 80 C during mirror coating. - The M2 Substrate temperature must stay less than 100 C during mirror coating. [REQ-2-M2-0620] Any components attached or bonded to the M2M shall have venting paths for any captured air volumes. Discussion: This prevents slow air leakage from interfering with the coating chamber ability to reach deep vacuum. 3.2 ENVIRONMENTAL REQUIREMENTS Discussion: Environmental conditions shown in Table 7 are derived from AD2, the Observatory Requirements Document, Section Observing Performance Conditions refer to the range of conditions for full performance level operations when science observing will be performed. - Facility Performance Conditions refer to the range of conditions present within the enclosure during maintenance operations. Performance of the M2 System may be reduced within these conditions. It is under these conditions that servicing and maintenance operations will typically be performed. - Component Functional Conditions refer to the range of conditions present in laboratories or repair stations where mechanical and electrical components of the M2 System may be repaired or maintained when removed from the M2 System located on the telescope. Components within the M2S must function within the Component Functional Conditions, but are not required to meet requirements. - Survival Conditions refer to conditions that the M2 System must survive repeatedly, but not operate during them.
33 Page 33 of 60 Table 7. Environmental conditions Condition Property Altitude of operating site Observing Performance Conditions Facility Performance Conditions Component Functional Conditions Survival Conditions Ambient air temperature Ambient air relative humidity (non-condensing) Ambient air pressure range ,000 (TBC) ,800 (TBC) Temporal air temperaturee gradient Spatial air temperature gradient any direction Telescope zenith angle range Ambient temperature Ambient air relative humidity, (non-condensing) Ambient air pressure range Telescope zenith angle range Ambient air temperature range Ambient air pressure range Ambient air relative humidity, (non-condensing) Ambient temperature Ambient air relative humidity, (non-condensing) Ambient air pressure range Temporal temperature gradient , , , (TBC) 0.05 (TBC) , , ,500 TBD Wind speed during 3 second gust Telescope zenith angle range Value Minimum Maximum Units m Celsius % Pascals Celsius per hour Celsius per meter degrees Celsius % Pascals degrees Celsius Pascals % Celsius % Pascals Celsius per minute meter per second degrees Observing Performance Conditions Requirement ts [REQ-2-M2-0690gravity Under Observing Performance Conditions summarized in Table 7, with the vector aligned with the +Z-axis of the M2CRS, the M2S shall have the full range of motion shown in Table 8 from a starting position with the axes and vertex of the M2 Mirror located at the M2CRS origin and aligned with the M2CRS axes describedd in Table 4. Table 8. Required range of motion of the M2S using M2CRSS origin and axes X Y Z Rxx Ry positive direction negative direction 15 mm -15 mm 9 mm -21 mm 7 mmm -16 mmm 242 arcsec arcsec 249 arcsec -249 arcsec Discussion: Due to gravity deflection, thermal rangess and gradients, and manufacturing errorsrs of the telescope and optics, the M2S requires the ability to adjust and align for observing using the limits of the range of motion provided.
34 Page 34 of Facility Performance Conditions Requirements Component Functional Conditions Requirements s Survival Conditions Requirements [REQ-2-M2-0700] Under Observing Performance Conditions summarized in Table 7, the M2 System shall meet all the requirements stated in Section 3.3 Discussion: The TMT telescope will be observing andd collecting data in Observing Performancee Conditions. The M2 System must meet all performance requirements necessary for required telescope image quality when within this range of conditions. Discussion: TMT telescope will rotate about the elevation axis through the zenith angle range described in Table 5. This will result in a varying gravity vector affecting the M2S. [REQ-2-M2-0720] All M2 maintenance and calibration operations shall be achievable over the Facility Performance Conditions defined in Table 7. [REQ-2-M2-0730requirements in Section 3.3 shalll degrade smoothly and repeatably to predictable performance levels as conditions drift outside of Observing Performance Conditions. Discussion: When testing the performance of the M2S in Facility Performance Conditions, Under Facility Performancee Conditions summarized in Table 7, M2S performance measured performance values must meet or predict that performance requirements described in Section 3. 3 will be met when the M2S environment is in Observing Performance Conditions. Discussion: Testing, servicing, maintenance and repair of the M2s when mounted on the telescope as described in Section 2.8 and Section 2.99 will be performed in Facility Performancee Conditions. [REQ-2-M2-0740translate from the nominal location over a range of motion greater than equired for observing performance conditions. Discussion: M2 motion limits must be increased from the required observing range to account for travel limits and hard stops, Within Facility Performancee Conditions, the M2S shall be able to tip, tilt and etc. [REQ-2-M2-0770] All subassemblies and components of the M2S shall function over the range of Component Function Conditions found in Table 7; but performance may be degraded. Discussion: The M2S will not be expected to meet Observing Performance Requirements unless the conditions meet Observing Performance Conditions. [REQ-2-M2-0790] The M2S shall be designedd to survive without damage repeated exposure to the Survival Conditions listed in Table 7. Discussion: Survival conditions can occur without warning and therefore equipment must be able to withstand these conditions in any operating or non-operating state. [REQ-2-M2-0800mounted on the telescope in lesss than 2 hours to determinee if there has been any damage and to After exposure to Survival Conditions, it shall be possible to inspect the M2S ensure that the M2S can safely return to normal operations..
35 Page 35 of Earthquake Survival Requirements Discussion: TMT Earthquake level definitions are from AD2, Sections through and are summarized in Table 9. Table 9. Earthquake Definitions TMT Earthquake Definitions Frequent Earthquakes: 10- The levels of a 10-year period earthquake year return period have a 10% probability of being exceeded earthquakes. in a one year period. Infrequent Earthquakes: The levels of a 200-year period earthquakee 200-year return period have a 22% probability of being exceeded earthquakes. in a 50 year period. Very Infrequent The levels of a 1000-year period Earthquakes: 1000-year earthquake have a 5% probability of being return period earthquakes. exceededd in a 50 year period. M2S equivalent static acceleration TBD (TBC) ACRS-X axis: 2.1 G ACRS-Y axis: 2.1 G ACRS-Z axis: 1.8 G (TBC) ACRS-X axis: 3.5 G ACRS-Y axis: 3.6 G ACRS-Z axis: 3.1 G 3.3 M2S OBSERVING OPERATIONS REQUIREMENTSS Discussion: All requirements in this section shall be met when the TMT Observatory is performing observing operations. The applicable environmental conditions will be Observing Performancee Conditions as described in Table 7. Discussion: All requirements in this section shall be met by the combined performance of the M2CA and the M2PA Stiffness Requirements [REQ-2-M2-0810] The M2S shall survive Frequent and Infrequent Earthquakes as defined in Table 9 without any damage. [REQ-2-M2-0820damage to the M2 Mirror and only damage to the mechanical and electrical components that is The M2S shall survive Very Infrequent Earthquakes as defined in Table 9 with no limited to what can be repaired within one week. [REQ-2-M2-0825observatory as a result of a very infrequent earthquake. [REQ-2-M2-0830] The M2M shall be protected during any earthquake, even if there is a loss of It shall not be possible for the M2S to cause damage to other sub-systems of the electrical power caused by the earthquake. [REQ-2-M2-0835telescope in less than 2 hours to determine if there has been any damage and to ensure that the After an earthquake, it shall be possible to inspect the M2S mounted on the M2S can safely return to normal operations. [REQ-2-M2-0850structure, shall be higher than 15 The lowest resonant frequency of the M2S, if it were attached to an infinitely stiff Hz.
36 Page 36 of 60 Discussion: A lower resonant frequency would increase susceptibility to amplification of the ground acceleration in an earthquake. Discussion: This requirement will dominate the stiffness requirements below. [REQ-2-M2-0855] The torsional stiffness of the M2S structure about the M2CRS rotation axes Rx, Ry, and Rz shall be greater than 65 x 10 6 N-m/radian RMS.. Discussion: This stiffnesss is calculated using the allocation for motion caused by dynamic wind force on the M2S. [REQ-2-M2-0860shall be greater than 9 x 10 6 N/m RMS. The linear stiffness of the M2S structure in the M2CRS x and y axes directions Discussion: This stiffnesss is calculated using the allocation for motion caused by dynamic wind force on the M2S. [REQ-2-M2-0870greater than 5 x 10 6 N/m RMS. The linear stiffness of the M2S structure in the M2 CRS z axis direction shall be Discussion: This stiffnesss is calculated using the allocation for motion caused by dynamic wind force and the effect on M2S focus and spherical aberrations Calibrations Discussion: In order for the M2 system to meet the requirements specified in this document, calibration of the system is allowed. This calibration will enable some errors affecting the performancee of the M2 system to be routinely and reliably removed under operational conditions. It is expected that the M2 system will incorporate parameterized models of the significant error sources affecting it, whichh will be used to modify thee commands applied to the servo system. The modifiedd commands will compensate for the errors and enable the M2 system to meet or exceed the performance requirements. The parameterized models shall be no more complexx than is necessary to enable the calibrated system to meet or exceed the performancee requirements. For the sake of this document, the parameterized models will be called Look-Up Tables (LUTs). Discussion: There are two levels of calibration for thee M2S: the supplier calibration and the telescope calibration. Supplier calibration will occur at the supplier facility y with the goal l of developing a model for calibration corrections thatt will enable the M2S to perform to the equirements in this document when the M2S is mounted to the telescope. The model used for supplier calibration must be approved by the TMT Project. Telescope calibration will be accomplished by adjusting positionss of the M1 segments, the M2 Mirror, the tilt of the telescope using the mount control system, and the tilt and rotation of the M2 System. Telescope calibration will correct thee repeatable M2S rigid body positioning errors that can be described by parametric equationss of order 1 or r2, and may be linear or sinusoidal functions. It will l use variables: ambient temperature and telescope zenith angle.
37 Page 37 of 60 The M2S supplier is not responsible for performing telescope calibration, but must supply a system capable of being calibrated in this manner. After the application of the calibration compensations, the residual l errors must meet the requirements listed below in Section 3.3 Examples of repeatable errors are those caused by gravity vector changes, misaligned hexapod arms, encoder errors, temperature conditions, control system bias, etc. The supplier calibration process may be as follows: 1. At the supplier facility, measure the difference between the M2S actual position and commanded position at two or three gravity orientations through the full range of motion of the M2S system (see Section 2.7.1). The selectionn of gravity orientations should enable accurate calculation of expected actual performance errors throughout the gravity vector range of M2S during observation. 2. At the supplier facility, measure the difference between the M2S actual position and commanded position at two or three temperatures through the full observing range of motion. The thermal environment should have timee to equilibratee at each selected temperature. The temperatures should be selectedd to enable accurate calculation of expected actual performance errors throughout thee temperature range of the observational performance conditions. 3. Create a simple model of the telescope calibration assuming that the compensators of the telescope can remove all M2S errors that can be described by parametric equations of order 1 or 2. The model will use the variables of ambientt temperature and telescopee zenith angle. Have the TMT project office approve the model. 4. Using the model from step 3, subtractt the M2S errors that it can describe from the calculated expected thermal and gravitational performance errors, leaving residual errors that are order 3 or higher. 5. Create parametric models that describe the residual M2S errors based on gravity vector and ambient temperature. 6. Develop two Look-up Tables based on the models in step 5 - one for gravity-caused errors and one for temperature-caused errors. The Look-up Tables will provide modifications to the M2S servo-systems so that the M2S will adjust to eliminate the residual errors remaining after step 4 to within the requirement accuracies described in Section 3.3. Discussion: All requirements in Section 3.3 apply after supplierr and telescope calibrations have been performed M2S Observing Operations Motion Requirements s M2S Pointing Requirements Discussion: The pointing repeatability errors in this section are allocated to the M2S. Errors caused by other elements of the telescope system are not includedd and have their own allocations described elsewhere. Discussion: The pointing repeatability error allocations below cover the more stringent of the M2S allocated errors for image pointing, pupil shift, and wavefrontt aberration.
38 Page 38 of 60 [REQ-2-M2-0920] At any telescope zenith angle within the observing range, the M2S shall be able to rotate the M2 Mirror about the M2CRS X and Y axes to any angle within the range of motion defined in REQ-2-M with a repeatable M2 rotation error that is less than 0.5 arcseconds RMS (TBC). [REQ-2-M2-0930] At any telescope zenith angle within the observing range, the M2S shall be able to translate the M2 Mirror along the M2CRS X and Y axes to any position within the range defined in REQ-2-M with a repeatable M2 translation error that is less than 7 µm RMS (TBC). Discussion: The allocations for motion error for the rotations about the X and y axes and the translations along the X and Y axes were derived from the M2S allocation of the telescope wavefront budget for the M2S contribution to wavefront error. [REQ-2-M2-0940] At any telescope zenith angle within the observing range, the M2S shall be able to translate the M2 Mirror along the M2CRS Z-axis to any location within the range defined in REQ-2- M with a repeatable M2 translation error that is less than 2 µm RMS (TBC). Discussion: The allocation for z-axis position was derived from the M2S allocation of the telescope wavefront error M2S Requirements for Slewing Discussion: Slewing is defined in Section The time to slew and settle is the sum of the time required to reach and stop at the new position and the time required for vibrations and oscillations to settle to the commanded position within the error allocation described in the pointing requirements section, Section Discussion: M2S shall slew over the motion range given and settle within the time allotted as shown in Table 10. Maximum Slew and Settle Time Requirements Table 10. Maximum Slew and Settle Time Requirements M2CRS Motions slew and Requirement Slew Condition x y z Rx Ry settle time (mm) (mm) (mm) (arcsec) (arcsec) (seconds) REQ-2-M Small motions REQ-2-M Large motions M2S Tracking Requirements [REQ-2-M2-0950] During tracking, the M2S shall smoothly follow the commanded path within the range of motions provided in Table 8. [REQ-2-M2-0960] During tracking, the M2S shall have velocities and accelerations ranging from zero to ± the maximum velocity and acceleration values shown in Table 11. Table 11. M2 System Maximum Tracking Velocities and Accelerations M2 System Tracking Motion Maximum Velocity Maximum Acceleration x y z Rx Ry mm/sec mm/sec mm/sec arcsec/sec arcsec/sec mm/sec^2 mm/sec^2 mm/sec^2 mas/sec^2 mas/sec^2
39 Page 39 of 60 Discussion: During tracking, the M2 System may slow to instantaneously stop then turn around. [REQ-2-M2-0970that may drift to be no worse than the values given in Figuree 13 over times less than the given During tracking, the M2S shall travel withh no position feedback with accuracies durations. durations dx and dy (µ µm) Rx and Ry (arcsec) 10 sec sec sec sec dx and dy drift (µm) dx and dy Rx and Ry Rx and Ry drift (arcsec) 0 0 sec 1000 sec 2000 sec Time Elapsed 3000 sec sec Figure 13. Tracking Drift Allocations M2S Requirements for Target Acquisition: Offsets, Nods and Dithers Discussion: All offsets, nods and dithers take place while the telescope is tracking a position on the sky. All distances moved are therefore in addition to the motion necessary to maintain tracking. Discussion: For offsets, nods, and dithers, the M2S will move small angles with no optical guider position feedback. The error allocations for these small motions are relative to the starting position and are not based on absolute position accuracy. [REQ-2-M2-1000commanded translations of < 20 µm along the Y and Z axes, and rotations about the X-axis of <1.5 When pointing anywhere within the ranges described in REQ-2-M2-0690, for arcsec, the M2S shall be able to position with relative errorss less than 15 µm RMS in translation and 0.5 arcsec in rotation. These values are TBC. [REQ-2-M2-1500] The M2S shall be able to reach and settle at commanded positionss of up to 20 µm in translation and up to 1.5 arcsec in rotation within less s than 3.5 seconds. Discussion: These small motions may be exercised consecutively and repeatedly throughout the entire 10 hour observing scenario of one night Image Jitter Requirements Discussion: Image Jitter is the non-repeatablee difference between the commanded position and the actual position during observation. Examples of image jitter sources
40 Page 40 of 60 are: bearing run-out; friction; stiction; control system errors; internal and external vibration; etc. Discussion: The image jitter requirements apply to the position of the surface of the M2 Mirror and include all non-repeatable motions of the M2S. The image jitter contributions from telescope structure and other telescope motions are allocated elsewhere. Discussion: Response to vibration from external sources and caused internally to the M2 System are included in this requirement Image Jitter during Guided Tracking Discussion: During guided tracking, jitter errors with frequencies up to 0.1Hz will be corrected by other control systems of the telescope. [REQ-2-M2-1700] During guided tracking, the M2S residual jitter (after correction) shall be less than: 1.4 µm RMS in x and y translation 46 mas RMS in Rx and Ry rotation Jitter during Adaptive Optics (AO) Guiding Discussion: During AO Guiding, the AO system is able to compensate for jitter error based on the rejection transfer function curve shown in Figure 14. The ability to sense jitter is influenced by the brightness of the reference star close to the observation target. The update frequency of the AO jitter compensation is dependent on the integration time required to detect the reference star position. The curve represents the AO system error rejection performance for the expected minimum-brightness reference star. The curve shows that the error rejection capability has the characteristic of a second-order high-pass filter with a break frequency of 15 Hz. Above the break frequency, the errors are unattenuated; below the break frequency they are attenuated at a rate of 40dB/decade. For errors with frequencies less than 15 Hz, the following equation applies: 10 where: error residual = the RMS residual error at frequency F after AO compensation error = the original RMS error magnitude at frequency F before AO compensation magnitude = the magnitude value from the curve in Figure 14 at frequency F
41 Page 41 of 60 Figure 14. NFIRAOS Error Rejection Transferr Functions (Magnitude units are mas/mas) [REQ-2-M2-1720] The residual jitter error after AO correction shall be less than the following values: 8 nm RMS in x and y translation 0.3 mas RMS in Rx and Ry rotation) Thermal Requirements Discussion: The goal of the M2S design should be too minimize thermal gradients by facilitating good air flow around the components of the M2CA and M2POS. The design goal should also minimize self-induced thermal gradients that would cause motion of the M2CA perpendicular r to its axes of rotation. Discussion: It is desired that the temperature difference from the M2 Mirror optical surface to the ambient air shall be less than 0.65 Celsius sincee this will promote the best seeing conditions. The design of the M2 Cell should permit air circulation to enable this goal to be obtained. [REQ-2-M2-1850] The total heat transmitted (through convection, conduction and radiation) to the telescope environment by the M2S components shall be less than 600 Watts. Discussion: through the The M2POS and the M2CS shall meet this requirement either by design or use of facility-provided coolant.
42 Page 42 of 60 [REQ-2-M2-1855] The total heat transmitted from the M2S to the facility coolant shall be less than 1.2kW. Discussion: Coolant will be provided by the observatory facility if required to meet REQ-2- M Discussion: The liquid coolant supplied to the M2S by the facility will be a chilled glycol/water mixture consisting of 35% glycol by volume (TBC). Discussion: Facility-supplied coolant will be supplied at a temperature that is 1 Celsius less than the ambient temperature. Discussion: If coolant is used, after use, it will be returned to the M2S liquid coolant system with a pressure of 5 bars. Discussion: If coolant is used, the integrity of the M2S liquid coolant system will be verified with a pressure test to 10 bars to detect potential problems before installation and operation. [REQ-2-M2-1860] The maximum pressure drop through the M2S liquid coolant system shall be 1 bar. [REQ-2-M2-1880] The coefficient of thermal expansion of the assembled M2S from the structure attachment interface to the M2CRS origin on the optical surface shall match 11.7 x 10-6 m/m/ C ± 10% (TBC). Discussion: The intention is to match the expansion of the steel in the telescope structure so that under ideal uniform thermal conditions, the instruments on the Nasmyth platforms would maintain their alignment relationships to the M2S origin. 3.4 M2 CELL ASSEMBLY (M2CA) [REQ-2-M2-1900] The M2CA shall be implemented so that its share of tolerance errors is 50% of the budget, enabling the M2S to meet positional tolerances described in REQ-2-M [REQ-2-M2-1905] The M2CA shall be implemented so that its share of performance allocations enables the M2S to meet all requirements described in Section 3.3. [REQ-2-M2-1910] The M2CA shall safely support the M2 Mirror at all expected gravity angles and environmental conditions with stresses imposed on the M2 Mirror substrate that are no larger than those shown in Table 12.
43 Page 43 of 60 Table 12. Allowable Stresses in Glass or Glass Ceramic Component supporting Applied Environmental Conditionss M2 Mirror (defined in Table 5) Performance, Observing Operating, or M2 Cell Assembly on Facility Operating Conditions Telescope Operational Basis Survival Conditions (including earthquake) Performance, Observing Operating, or M2 Cell Assembly Facility Operating Conditions interfacing with Handling Operational Basis Survival Conditions Equipment (including earthquake) Performance, Observing Operating, or Handling Equipment (M2 Facility Operating Conditions Mirror lift talons, M2 Mirror Operational Basis Survival Conditions coating fixture) (including earthquake) Maximum Principal Stress in Mirror (MPa) 4.0 (TBC) 7.0 (TBC) 6.0 (TBC) 7.0 (TBC) 6.0 (TBC) 7.0 (TBC) [REQ-2-M3-1920optical surface shall be coated with a durable flat black coating to reduce stray light reflections. Discussion: One design approach would be to include an aperturee ring around outer edge of the M2M as shown in Figure 5. If such a ring is used, it must provide line-of-sight clearance All surfaces of the M2CA visible from thee tertiary mirror other than the M2M for GMS measurements as specified in Section [REQ-2-M2-1925the clear aperture of the M2 mirror No component of the M2S shall obscuree the light path from the primary mirror to surface M2 Mirror (M2M) Discussion: The finished M2M will be polished and will have bonded interface pads. Coating will be performed at the TMT Observatory at the summit of Maunaa Kea. Discussion: The M2 Mirror Coating will l meet the specification RD4, Design Requirements Document for Telescope Optical Coatings, TMT.OPT.DRD [REQ-2-M2-1930] The M2 Mirror Blank shall meet all the specifications in RD2, SECONDARY MIRROR BLANK SPECIFICATI IONS, TMT.OPT.SPE [REQ-2-M2-1935optical and size requirements shown as ideal dimensions inn Table 13. Tolerances on the clear The finished TMT M2 Mirror (M2M) will be a convex hyperboloid and shall meet aperture diameter, the mechanical diameter, and the thickness are TBD. Tolerances on the Radius of Curvature (RoC) and the Conic Constant (CC) are controlled by the M2 Finished Mirror (M2M) surface figure specifications in Section
44 Page 44 of 60 Table 13. M2 Mirror Size Table Mirror Element Finished M2 Mirror Optical Beam Diameter (m) OD: ID: Clear Aperture Diameter (m) OD: >3.060 ID: <0.200 Mechanical Diameter (m) OD: ID: Thickness (mm) Optical Surface Spherical Radius of Curvature (m) Conic Constant [REQ-2-M2-1940] The back surface, edge and chamfers of the M2M shall have a smooth ground finish with a surface roughness that shall be 0.4 µm max. [REQ-2-M2-1945] In order to minimize subsurface damage, grinding shall be done in steps using progressively smaller abrasive grains. Each grinding step shall remove material to a depth of at least 3 times the maximum grain size of the previous grinding step. The final grinding step shall use an abrasive grain size of 15 µm. [REQ-2-M2-1950] The back surface of the mirror shall be polished until all subsurface damage is removed. [REQ-2-M2-1955] Local acid etching of the surface areas where interface pads will be located is required prior to bonding interface pads onto the surface. The acid etching shall remove 50 µm and shall be applied to the area beneath the surface of the interface pads and an area that is beyond the surface of the interface pads by 1 cm. [REQ-2-M2-1960] The entire clear aperture of the optical surface shall be fully polished out, meaning that all subsurface damage from grinding shall be removed. The final polished surface shall be fully transparent. [REQ-2-M2-1965) For all interface pads that are bonded to the surface of the mirror, the excess adhesive shall be removed (wiped away with a dry cotton swab) leaving a smooth fillet. No excess adhesive shall bulge out from the edge of the pad. [REQ-2-M2-1970] The scratch-dig specification for the M2M Optical Surface within the Clear Aperture shall be limited to per SD12 where 60 is the maximum width of a scratch in microns and 40 is the maximum diameter of a dig in units of.01 mm. [REQ-2-M2-1975] Around the outside of the clear aperture of the optical surface, no scratch or dig with surface area larger than 10 mm 2 shall be allowed to penetrate partially within the clear aperture. [REQ-2-M2-1980] The sum of the areas of all surface imperfections within or partially within the Clear Aperture shall be less than 20 mm 2. [REQ-2-M2-1985] No surface imperfection of surface area larger than 100 mm 2 shall be allowed on any surface of the M2M that is outside of the clear aperture including the front surface, the back surfaces and the edges. [REQ-2-M2-1990] The sum of the areas of all surface imperfections on all surfaces of the M2M outside of the clear aperture including the front surface, the back surface and the edges shall be less than 500 mm 2.
45 Page 45 of M2 Finished Mirror (M2M) surface figure specifications [REQ-2-M2-1995] All chips and visible cracks shall be removed by a combination of grinding and etching. Resulting surfaces shall be smooth with radius of curvature no less than 1mm. The resulting features are considered surface imperfections with size restrictions per [REQ-2-M2-1980] to [REQ-2-M2-1990]. No visible cracks shall be allowed to remain on any surface of the M2M. Discussion: A chip is defined as a hollow depression in a surface usually formed where a flake has broken out of the substrate. Discussion: The M2M surface error consists of deviations from the ideal mirror surface caused by the following sources of error. MAIN ERROR SOURCES: M2 Residual Figure Error, including 1. Residual Polishing Errors: surface figure errors polished into the surface of the mirror including radius of curvature and decenter errors, Very high frequency surface error (surface roughness) that results from polishing is constrained in [REQ-2-M2-2030]. 2. Static Thermal Distortion (TBC): effects of f temperature change between optics shop testing and mean observatory temperature at 2 C. Both the mirror substrate and M2 Support Structure (M2SS) contributee to this surface error. The surface errors caused by this error source willl be calculatedd using FEA to predict the resulting MUT with optical surface measurement to confirm the models. M2 DynamicThermal Distortion including 3. DynamicThermal Distortion: changing mirror shape errors due to temperature and temperature distribution differences betweenn the time of on-telescope calibration and the time of actual observation, expected to be 4 weeks at maximum. It includes the combined effect of glass and support system deformations, including glass CTE variations. The range of observing temperatures for the TMT telescopee is 2ºC ±7 ºC. M2 Support Print-Through including 4. Gravity Effect Nominal: surface errors caused by gravity sag of the mirror on the optimized support points as designed (variess with change in gravity vector). The surface errors caused by this error source arise from the gravity load on the mirror resting on the support system as predicted using FEA and reflect the modeled design of the support system. For low order Zernike terms, it is expected that the design will be optimized to have very small influence. Inn these cases, the value that is allocated reflects an allocation for the confidence of thee model and its ability to be optimized. 5. Gravity Effect Manufacturin ng: surface errors caused by support structure manufacturing and assembly errors (varies with change in gravity vector). This errorr will be measured after the mirror is installed in the supportt structure, includes as-built and as-assembled errors and will be difficult to predict. Note: The applicable zenith angle observing range of the telescope is from 1 to 65. The angle between the gravity vector and the M22 Z-axis is equal to the telescope zenith angle and lies in the Y-Z plane of the M2 coordinate system.
46 Page 46 of 60 OTHER ERROR SOURCES: The following error contributions are expected to be small and are accounted for elsewhere: coating stress, substrate and structure creep or slippage, wind pressure, and vibrations. Discussion: Requirements [REQ-2-M2-2000] and [REQ-2-M2-2050] apply to the condition of the M2M when installed in the telescope, at a temperature of 2 C and a telescope zenith angle of 30 degrees. These requirements include the effects of polishing errors, the mirror support, and the change in mirror figure that occurs when changing from optics shop temperature to the average observing temperature. [REQ-2-M2-2000] The paraxial radius of curvature (RoC) and conic constant (CC) of the M2M optical surface shall be as defined in Table 13, within the tolerance zone defined in Figure 15. The equations of the upper and lower bounds of the tolerance zone are: Upper bound: Lower bound: where: dcc = the error in conic constant droc= the error in radius of curvature in meters Discussion: The Ritchey-Chrétien design can be preserved if the radius of curvature and conic constant change in a coordinated manner. This allows a larger tolerance zone than if the requirements are considered individually. Conic Constant vs Radius of Curvature Error in Conic Constant Error in Radius of Curvature (meters) Allowable Tolerance Zone Ideal CC (dcc = 0) Upper Bound dcc Lower Bound dcc Ideal RoC (droc = 0) Upper Bound droc Lower Bound droc Figure 15. Allowable Tolerance Zone for Radius of Curvature and Conic Constant [REQ-2-M2-2010] The aspheric shape of the M2M optical surface shall be centered on the mechanical diameter of the finished M2 Mirror within +/- 3 mm in X and Y directions in the M2CRS coordinate system. [REQ-2-M2-2020] For each source of error, the surface figure error of the M2M relative to the theoretical optical prescription defined in Table 13 shall have a SlopeRMS error of less than the allocations shown in Table 14.
47 Page 47 of 60 Table 14. SlopeRMS Allocations Surface Error Source SlopeRMS Allocation (µrad) Residual Polishing Errors 1.30 Static Thermal Distortion 0.27 Dynamic Thermal distortion 0.42 Gravity effect nominal 0.38 Gravity effect manufacturing 0.13 Discussion: The process for calculating the SlopeRMS for Residual Polishing Errors and Static Thermal Distortion shall be as defined in Section Discussion: The process for calculating the SlopeRMS for Dynamic Thermal distortion, Gravity effect nominal and Gravity effect manufacturing shall be as defined in Section Discussion: The equation for SlopeRMS shall be as defined in Section Zernike definition The Zernike terms used in this requirement are described by the following mathematical forms: 1 Piston Focus 2 cos Tip r sin Coma 2 sin Tilt cos Coma Spherical aberration (3) Where r is the normalized radius, i.e.: r, θ is the angle measured from the x-axis, and the coordinate system is as the M2 Local coordinate as shown in Figure SlopeRMS Equation The SlopeRMS is defined as the Root Mean Square (RMS) of the surface gradient magnitude and is mathematically represented in equation (4):,,,, (4) Where: the sampling grid is N X M points grid spacing is [dx,dy] and S i,j is the surface figure error of grid location i,j The typical unit of SlopeRMS is in μrad. Note that Eq. (4) assumes that the surface Si;j is defined on all N X M rectangular grids, i.e., all N X M grid points represent valid surfaces. When grid points are not valid (i.e., do not lie inside the M2M coated clear aperture) those grid points must be excluded in Eq. (4).
48 Page 48 of Processes for calculating SlopeRMS for M2 Mirror Surface Figure Error Sources Definitions: MUT: Mirror-Under-Test (MUT) is a data set of surface figure errors registered to a grid of locations on the Secondary Mirror (M2M) surface that describes the deviations from a perfect surface. The deviations are given as linear height difference from the perfect surface at each grid location. The MUT epresents surface error of the M2M caused by the error sources under consideration. The MUT is defined within the coated clear aperture of M2M. Removed MUT is the dataa set of surface figure errors that remains after the Noll Zernike terms are calculated then removed from MUT. Sampling grid is the set of locations on the surface of M2M wheree surface deviations are calculated or measured to create the MUT. For the M2M measurements, the sampling grid must be sized so that the spacing between any two measurementss is <1.5 mm. Any points on the sampling grid that do not fall within the boundaries of the M2M coated clear aperture are excluded. SlopeRMS is the root mean square of the calculated slopes of the MUT. For this specification, the equation defining SlopeRMS is given in Section Surface Figure Error is the difference between the height of the ideal surface figure of the mirror at each sampling grid location and the measured or calculated height of the mirror surface at that location. The data set of surface figure errors at each point of a sampling grid is the MUT M2 Mirror Surface Figure Process for the staticc error terms: Residual Polishing Errors and Static Thermal Distortion The following procedure shall be used to evaluate the surface of the finished M2 mirror for the static error terms: Step Process Description Output For each listed error source, determinee the M2M Radius of Curvature (RoC) and Conic Constant (CC), including measurement uncertainty. To meet the requirement, RoC and CCC must fit within the allowable tolerance zone in Figure 15. For each listed error source, measure the surface off M2M, using a sampling grid spacing < 1.5 mm to create the MUT data set. From the MUT, calculate and subtract the piston (Z 1 1), tip (Z 2 ), tilt (Z 3 ), focus (Z 4 ), two comas (Z 7 and Z 8 ), and spherical aberration (Z 11 ) Noll Zernike terms as defined in Section This creates the Removed MUT data set RoC and CC MUT Removed MUT 4 Using the Removed MUT data set, compute SlopeRMS as defined in Section To meet the requirement, SlopeRMS must meet thee allocation for that error term in Table 14. SlopeRMS Allocations. This process is displayed graphically in Figure 16. SlopeRMS
49 Page 49 of 60 Figure 16. Mirror surface figure evaluation process M2 Mirror Surface Figure Process for the dynamic error terms: Dynamic Thermal distortion, Gravity effect nominal and Gravity effect manufacturing The following procedure shall be used to evaluate the surface of the finished polished M2 mirror for the dynamic error terms. Step 1 Process Description For each listed error source, measuree the MUT data set, using a sampling Output MUT grid spacing < 1.5 mm. 2 3 From the MUT, calculate and subtract the piston ( Z 1 ), tip (Z 2 ), tilt (Z 3 ), focus (Z 4 ), and two comas (Z 7 and Z 8 ) Noll Zernike terms as defined in Section This creates the Removed MUT data set. Using the Removed MUT data set, compute SlopeRMS as defined in Section To meet the requirement, SlopeRMS for each error source must be less than the allocation given in Table 14. Removed MUT SlopeRMS [REQ-2-M2-2030including all spatial periods less than 1.5 High frequency surface error or surfacee roughness shall be less than 2 nm RMS mm. Discussion: High Frequency Surface Error may be measured using sub-apertures small enough to obtain the required resolution. The quantity, location and size of the sub-apertures that will be used shall be negotiated and agreed on between the mirror supplier and TMT.
50 Page 50 of M2M cleaning and coating requirements M2M thermal requirements [REQ-2-M2-2060survive temperatures during mirror coating of up to 80ºC with no pad position change or adhesive The adhesivee material selected for the bonded pads of the finished M2M shall degradation. [REQ-2-M2-2065differences in thermal coefficients of expansionn of the materials of the mirror substrate, the pads, and the adhesive shall be calculated based on the lowest survival condition temperature of -16ºC and the coating temperaturee limit of 80ºC. Stresses in the mirror, the bonded pads,, and the adhesive caused by the [REQ-2-M2-2070degrade due to exposure to CO2 snow, alcohol, acetone, detergents and water used for regular The adhesivee material selected for the bonded pads of the finished M2M shall not cleaning of the mirror. Discussion: During cleaning on the telescope, the bonded pads will be protected from cleaning agents; but the listed cleaning agents will bee used to clean the M2M, ncluding its edges and bonded pad areas, after removal from thee telescope and prior to coating. [REQ-2-M2-2075to protect the pads and adhesivee from the caustic chemicalss used to strip old coatings from the M2MM reflective surface. The design of the bonded lateral pads onn the M2M shall enable sealed masking Discussion: It is assumed that the bonded pads of the M2M will be masked during stripping with the work area vented adequately to protect the adhesive from stripping chemicals. It is common that masking is accomplished by taping a plastic sheet around the edge of the mirror. Possible chemicals that will be used for stripping the coating are listed in Section of RD2. [REQ-2-M2-2080degrade due to repeated exposure to a vacuum base pressure of 1 x torr during the mirror The adhesivee material selected for the bonded pads of the finished M2M shall not coating process M2 Support System (M2SS) [REQ-2-M2-2090] The M2SS shall support the M2 Mirrorr so that the mirror surface figure will meet the requirements of Section including support print-through when under Observing Performance Conditions described in Section Discussion: The M2SS should be designed to provide stable support of the M2 Mirror that t does not cause M2 surface figure variation with time. Some possible sourcess of M2 surface figure variation are changes in spring rate of flexures, friction stiction at bearings and joints, and dimensional changes caused by materials creep or outgassingg of bond materials. [REQ-2-M2-2100] The M2SS shall be designed so that the M2M will meet the requirements of Section with a spatially varying wind pressure that iss an average of 2.7 Pascals (TBC) applied across the surface of the M2 Mirror with the pressure varying at a slope of 0.27 Pascals per meter. [REQ-2-M2-2110] The M2SS shall be designed such thatt the M2M will meet the requirements of Section in the presence of a uniform wind pressure of 5 Pascals on the optical surface.
51 Page 51 of 60 [REQ-2-M2-2120] With the M2CA removed from the telescope, the repeatability of installing the M2 Mirror into the M2 Support System in the M2 Cell, shall be millimeters in the M2CRS Z-axis direction and 0.20 millimeter in the M2CRS X-axis and Y-axis directions M2 Cell [REQ-2-M2-2150] The M2C shall be designed to allow for the inspection of all mirror supports while mounted to the telescope, without removing structural portions off the M2CA. [REQ-2-M2-2160] With the M2CA removed from the telescope, the M2C shall be designed so that the repeatability of installing the M2CA onto the M2POS shall be millimeters in the M2CRS Z-axis direction and 0.20 millimeter in the M2CRS X-axis and Y-axis directions. [REQ-2-M2-2170] When the M2CA is removed from the telescope and mounted to the handling cart, the M2 Cell design shall allow for the installation or removal of the M2M within 2 hours using 3 personnel, plus crane operators and safety personnel. Discussion: The M2M lifting fixture used by the supplier during handling at the supplier facility will be used for the M2M removal from the M2 Cell at the TMT Observatory. [REQ-2-M2-2180] The M2 Cell design shall incorporate a method to prevent fluid from getting into the back of the M2 Cell or dropping ontoo the M1 Mirror segments or other parts of the telescope during fluid cleaning. Discussion: This could include an inflatable seal and detachablee catchment surface M2 POSITIONER ASSEMBLY General M2 Positioner Assembly Requirements [REQ-2-M2-2200] The M2PA shall be implemented so that its share of performance allocations enables the M2S to meet all requirements described in Section 3.3. Discussion: An error budget that splitss the error allocations between the M2PA and the M2CA will demonstrate meeting this equirement. [REQ-2-M2-2210] The M2PA shall be designed for full range of motion and safe operation with the M2CA either installed on the M2POS or removed. [REQ-2-M2-2220] The M2PA shall control motions with bandwidths 0.1 Hz M2 Positioner Assembly Reliability and Maintenance [REQ-2-M2-2230] The M2POS design shall support maintenance either via the dome-mounted service platform or the aerial service platform General M2POS Requirements [REQ-2-M2-2240] The M2POS shall be implemented so that its share of tolerance errors is 50% of the budget, enabling the M2S to meet positional tolerances described in REQ-2-M Discussion: the M2POS An error budget that splitss the tolerance allocations between the M2CA and will aid in meeting this requirement.
52 Page 52 of 60 [REQ-2-M2-2250] During installation/removal of the M2CA onto the telescope, the M2PA shall follow a predetermined series of motions to enable accesss which incorporates a fail-safe system to position the M2POS such that it cannot damage the M2CA during installation or removal. Discussion: The M2CS will control the fail-safe mechanical system per REQ-2-M M2 Control System (M2CS) [REQ-2-M2-2300reach up to 80 meters (TBC) in length. If portions of the M2CS are required to be located in close The M2CS shall be located remotely from the M2POS with cabling that may proximity to the M2POS, they shall be identified with location details determined via ICDs. [REQ-2-M2-2390] The M2CS shall utilize a standard industrial controllerr that will be selected by TMT (selection TBD). Discussion: The M2 Control System (M2CS) provides local servoo control of the M2POS. The primary external M2CS control interface is with the Telescopee Control System (TCS). TMT is planning to require a standard industrial controller for the M2CS which is not yet chosen. The standardd is likely to be similar to Allen Bradley, National Instruments, Siemens, Bechtel, or equivalent. Figure 17 is for illustrative purposes and assumes that the requirements on M2POS motions will require a closed loop position control system provided by the M2 Control Processor. Alternative schemes that meet the requirements stated within this document are acceptable. The observatory interface (command and control, faults, telemetry, data) with the M2CS is via the Telescope Control System (TCS). The M2CS will receive a stream of time-stamped command sets containing rotator positions, tilt positions and velocities from the TCS at a 40 Hertz rate. The M2CS will deliver smooth M2S motion that minimizes the difference between the commanded and actual positions (i.e. the instantaneous position error) per the requirements stated in this document. A source of precise time signals will be provided to the M2CS so that it can perform synchronized trajectory and motion calculations. Telescope zenith angle and temperature are available to the M2CS via the TCS at a constant update rate of 0.1 Hertz. The M2CS may include one or more LUTs (M2 Calibration LUTs) that will store the calibration terms required to transform measured positions into corrected positions. The corrections that t might be necessary include position adjustments to eliminate repeatable cross coupling, zenith angle dependence, deterministic encoder errors, etc. The M2 Calibration LUTs will be readable and writable by the TCS enabling additional l in situ calibration as required. Figure 17 also shows that the M2CS receives high level commands from the TCS and provides fault and status information to the TCS. In addition the M2CS provides the TCS with a telemetry stream that consists of various M2CS parameters such as drive motor currents, currents, sensor values, etc. All control, power, utilities, interlocks, engineering sensors, and local control interfaces are via the M2 Interface Panel.
53 Page 53 of 60 Figure 17: A functional block diagram of the M2 Positioner Control System (M2CS) Command and Control [REQ-2-M2-2400] The M2CS shall have the capability of receiving and executing M2 position commands from the TCS at rates up to and including 40 Hz. [REQ-2-M2-2410] The M2CS shall have the capability of receiving and utilizing zenith angle updates from the TCS at rates up to and including 1 Hertz. [REQ-2-M2-2420] The M2CS shall have the capability of receiving and utilizing the observatorywide distributed time signal. Discussion: Universal time (UT) will be required to synchronize the position and time command sets to the actual positions at each commanded instant in time. UT will be distributed via IRIG B, a standard GPS-based Network Time Protocol (NTP) service or IEEE
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