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SAC Specification

Doc No. SALT-1523AS0001 Issue Draft of 35

APPROVAL SHEET

TITLE : SAC SPECIFICATION

DOCUMENT NUMBER : 1523AS0001 ISSUE : Draft

SYNOPSIS : This document describes the technical requirementsof the SAC subsystem of the Southern AfricanLarge Telescope (SALT).

KEYWORDS : SAC, Corrector, Spherical Aberration, PayloadAlignment, PFIS

PREPARED BY : Leon Nel Manager: Tracker, Payload and TCS

APPROVED : Gerhard Swart SALT System Engineer

: Kobus Meiring SALT Project Manager

DATE : February 2001

This issue is only valid when the above signatures are present.

SAC Specification


ACRONYMS AND ABBREVIATIONS

mm micronarcsec Seconds of arcCCAS Centre-of-Curvature Alignment SensorCCD Charge-coupled Device (Camera)COTS Commercial off the shelfEE(50) Enclosed Energy is 50% of total energyFoV Filed-of-ViewFWHM Full Width Half MaximumHET Hobby-Eberly TelescopeHRS High-resolution SpectrographI/O Input/Output (Device)ICD Interface Control DossierIR InfraredLRS Low-resolution SpectrographMMI Man-Machine InterfaceMTBF Mean Time Between FailuresMTTR Mean Time to Repairnm nano-metreOEM Original Equipment ManufacturerPC Personal ComputerPFIS Prime Focus Imaging SpectrographPFP Prime Focus PlatformPI Principal Investigator (Astronomer)RA, DEC Right Ascension and DeclinationRMS Root Mean SquareSA SALT AstronomerSAC Spherical Aberration CorrectorSALT Southern African Large TelescopeSO SALT OperatorSW SoftwareTAC Time Assignment CommitteeTBC To Be ConfirmedTBD To Be DeterminedTCS Telescope Control SystemUPS Uninterruptible Power SupplyUV Ultraviolet (light)

SAC Specification


DEFINITIONS

Acquisition time This is the length of time required to put the target at adesired position (a bore-sight), within the offsetpointing requirement, from end-of-slew, until start ofthe integration

Offset accuracy This is the ability to place a given point in the sky onthe bore-sight once the telescope has acquired anobject in the FoV.

Target This is a point in the sky. If the target is not visible tothe acquisition imager, then the target is defined asan offset from a visible star that is within the focalplane field of view.

Technical Baseline This is the design baseline that is required to fulfil therequirements of the SALT Observatory ScienceRequirements, Issue 7.1, and is the topic of thisSpecification.

SAC Specification


TABLE OF CONTENTS

1 Scope.................................................................................................... 81.1 Identification..........................................................................................................................81.2 System overview .................................................................................................................8

2 Referenced documents..................................................................... 103 Customer Furnished Equipment and Responsibilities.................. 114 Functional Requirements ................................................................. 124.1 Schematic Description ......................................................................................................124.2 Summary of SAC functions..............................................................................................144.2.1 Operational Functions......................................................................................................144.2.2 Maintenance and Support Functions ...............................................................................154.3 Major Control Functions ...................................................................................................154.3.1 Subsystem modes, States and Events............................................................................154.3.2 Functional Flow Diagram..................................................................................................154.3.3 Function descriptions.......................................................................................................154.3.4 Operational Concept ........................................................................................................15

5 SAC Technical Requirements........................................................... 155.1 Schematic diagram ............................................................................................................165.2 SAC Interfaces....................................................................................................................175.2.1 SAC External Interfaces ..................................................................................................185.2.2 SAC Internal Interfaces....................................................................................................195.3 SALT SAC Characteristics................................................................................................195.3.1 Performance Characteristics...........................................................................................19

5.3.1.1 SAC Error Budget.........................................................................................................195.3.1.2 SAC Optics...................................................................................................................195.3.1.3 SAC Structure..............................................................................................................20

5.3.2 Physical Characteristics ..................................................................................................215.3.2.1 Obscuration..................................................................................................................215.3.2.2 Mass.............................................................................................................................215.3.2.3 Envelope.......................................................................................................................225.3.2.4 Maximum surface temperatures...................................................................................22

5.3.2.4.1 Objects in the optical path.....................................................................................225.3.2.4.2 Objects outside the optical path............................................................................22

5.3.2.5 Minimum surface temperatures....................................................................................225.3.2.5.1 Objects in the optical path.....................................................................................225.3.2.5.2 Objects outside the optical path............................................................................22

5.3.2.6 Component/module replacement ..................................................................................225.3.3 Environmental Requirements............................................................................................23

5.3.3.1 Normal Operational Environment ..................................................................................235.3.3.2 Marginal Operational Environment................................................................................235.3.3.3 Survival Environment....................................................................................................23

5.4 Operation and Maintenance Requirements..................................................................245.4.1 Packaging, handling, storage...........................................................................................245.4.2 Product Documentation....................................................................................................24

SAC Specification


5.4.3 Personnel and Training ....................................................................................................245.4.3.1 Operation......................................................................................................................245.4.3.2 Maintenance.................................................................................................................24

5.4.4 Availability........................................................................................................................255.4.4.1 Science Efficiency .......................................................................................................25

5.4.4.1.1 Reliability ...............................................................................................................255.4.4.1.2 SAC Maintainability................................................................................................25

5.4.4.2 Measures to achieve efficiency...................................................................................255.5 Design and Construction constraints............................................................................265.5.1 General design guidelines and constraints......................................................................265.5.2 Materials, Processes and Parts.......................................................................................265.5.3 Electromagnetic Radiation................................................................................................265.5.4 Workmanship ...................................................................................................................275.5.5 Interchangeability.............................................................................................................275.5.6 Safety ..............................................................................................................................27

5.5.6.1 Safety-critical failures..................................................................................................275.5.6.2 Software safety...........................................................................................................275.5.6.3 Safe initialisation...........................................................................................................275.5.6.4 Local electric operation................................................................................................27

5.5.7 Ergonomics ......................................................................................................................275.5.8 Special commissioning requirements...............................................................................27

5.5.8.1 SAC optical Axis ..........................................................................................................275.5.8.2 SAC Test System.........................................................................................................27

5.5.9 Software..........................................................................................................................275.5.10 Computer Hardware ........................................................................................................285.5.11 Electrical Design...............................................................................................................285.5.12 Future growth..................................................................................................................28

6 Subsystem technical requirements ................................................. 296.1 Major Component List ......................................................................................................296.2 Major Component Characteristics .................................................................................306.2.1 Integrated SAC.................................................................................................................31

6.2.1.1 Optical Elements...........................................................................................................316.2.1.2 Light Baffles.................................................................................................................316.2.1.3 SAC Structure..............................................................................................................31

6.2.2 SAC Test Bench ..............................................................................................................316.2.3 Handling Equipment..........................................................................................................31

7 Test Requirements ............................................................................ 317.1 Verification cross-reference Matrix...............................................................................317.2 Detailed Test Methods......................................................................................................32

8 Notes................................................................................................... 32 APPENDIX A: LIST OF TBC’S AND TBD’S

SAC Specification


TABLE OF FIGURES

Figure 1. SALT Subsystems......................................................................................................8Figure 2. SALT Pier, structure, primary mirror and tracker ..................................................9Figure 3. Facility and Dome.................................................................................................... 10Figure 4. Payload & Hexapod: SAC Rotating ...................................................................... 12Figure 5. Payload & Hexapod: SAC non-Rotating.............................................................. 13Figure 6. Major Components of the SAC Subsystem........................................................ 16Figure 7. SAC Interfaces ......................................................................................................... 17Figure 8. SAC : Layout & Dimension .................................................................................... 30

SAC Specification


LIST OF TABLES

Table 1 SAC external interfaces (refer Figure 7).................................................................. 18Table 2 SAC Internal Interfaces (see Figure 7 )................................................................... 19Table 3 SAC Mass Budget....................................................................................................... 22Table 4 Normal Operational Environment............................................................................ 23Table 5 Marginal Operational Environment.......................................................................... 23Table 6 SALT Survival Operating Environment .................................................................... 24Table 7 Part identification......................................................................................................... 26Table 8 SAC system.................................................................................................................. 29Table 9 Verification cross-reference Matrix (TBD21) .......................................................... 32

SAC Specification


1 Scope

1.1 Identification

This document specifies the requirements for the Spherical Aberration Corrector (SAC) system ofthe Southern African Large Telescope. Where applicable, the possible growth paths for laterupgrades have been identified. The optical requirements are specified in a separate document,SALT-1523AS0002 “ SAC Optical specification” as referenced in section 2 of this document.

In general, the word “shall” is used to indicate mandatory requirements while descriptive statementsare used to provide non-mandatory information

1.2 System overview

The purpose of SALT is to collect light from astronomical objects, accurately focus it onto thetelescope focal plane from where it will proceed into an optical instrument while tracking the relativemovement of the target across the sky to maximise exposure time. The SALT system comprises thesubsystems depicted in Figure 1 below:

Figure 1. SALT Subsystems

This specification will focus on the SAC(1523) which is a subsystem of the Payload (1520) in thebreakdown of Figure 1. Figure 2 and Figure 3 below are schematic representations of the internal

1000TelescopeSystem

1100Facility

1200TelescopeStructure

1300Dome

1400Primary Mirror

1500Tracker &Payload

1600Commissioning Instrument

1700TCS

1510Tracker

1520Payload

_21 PayloadComputer

_23 SAC

_22PayloadStructure

_24 Guidance System

_26Moving BaffleFold MirrorsFixed Baffle

_27ThermalControl

l Control_28CalibrationSource

_29 Cable & Tube Handlers

_25 ADC

SAC Specification


layout of the telescope , the facility and dome

Figure 2. SALT Pier, structure, primary mirror and tracker

Tracker & Payload

Structure

Primary Mirror & Truss

Air bearingsAzimuth Pier

Main Instrument room

SAC Specification


Figure 3. Facility and Dome

Since the Primary mirror is spherical the reflected rays will be highly aberrated thus the need for theSpherical Aberration Corrector (SAC). The SAC receives light from the Primary Mirror and its opticalelements correct the spherical aberrations and bring the light to a focus at the focal plane, fromwhere it will enter into the various instruments. The SAC is a subsystem of the payload. Therelationship physically and functionally between the SAC and payload as well as the SAC functionsare described in the rest of this document.

2 Referenced documents

SALT DB000531 SALT Observatory Science Requirements, Issue 7.1, D.A.H. Buckley,dd. 31 May 2000

LWR95055 Hobby-Eberly Telescope Operations Requirements Document, L.W.Ramsey, dd. 27/11/95, edited by D Buckley

HET Tech Report #67 Statement of Work – HET Tracker, October 1994HET Tech Report #44 HET Error Budget, April 94

Keck Visit ReportScience with SALT, DAH Buckley, March 1998SPIE proceedings (various)

SALT-1000AS0027 SALT External Interface Control Dossier SALT-1000AS0013 SALT Electrical Interface Control DossierSALT-1000AS0014 SALT Physical Interface Control DossierSALT-1000AA0030 SALT Safety AnalysisSALT-1000AS0031 SALT Axes and Calibration definitionSALT-1000AA0017 SALT Error BudgetSALT-1000BS0021 SALT Requirements for Built-in TestingSALT-1000BS0010 SALT Software StandardSALT-1000BS0011 SALT Computer StandardSALT-1000AS0032 SALT Electrical Requirements

SALT Report of Interim Project Team, April 1999SALT-1000AS0033 SALT Support RequirementsSALT-1000AS0040 SALT Operational Requirements

Applicable South African Building and Construction StandardsApplicable South African Legal RequirementsSafety, Health and Environment Act

SALT-1520AS0001 Payload SpecificationSALT-1523AS0002 SAC Optical Specification

SAC Specification


3 Customer Furnished Equipment and Responsibilities

None

SAC Specification


4 Functional Requirements

4.1 Schematic DescriptionThe Payload will be supported and positioned by the Tracker near the paraxial focus of the PrimaryMirror.

Figure 4 and Figure 5 illustrates the components of the Payload and their relationship to the Hexapodsystem of the Tracker for the rotating and non-rotating options respectively.

Figure 4. Payload & Hexapod: Layout

SAC Specification


Figure 5. Payload & Hexapod: Dimensions

The SAC shall be non-rotating (TBC1), in other words the SAC will be fixed to the Hexapod of theTracker and not rotating with respect to the Primary Mirror. All the other instruments on the Payloadwill rotate relative to the SAC. This decision shall be confirmed during the design phase of the SACand Tracker.

The Payload will be supported and positioned by the Tracker near the paraxial focus of the primaryMirror.

SAC Specification


The coordinate system, in which the location of the Payload subsystems is described, is called thePayload Mechanical Frame (PMF) and is defined in Figure 4 above. A detailed description of allcoordinate systems is given in SALT-1000AS0031: SALT Axes and Calibration definition, listed inSection 2.

4.2 Summary of SAC functions

4.2.1 Operational Functions

The operational functions of the SAC System in SALT are to:

a) Receive light from Primary Mirror and correct its optical aberrations (SAC)The SAC will be positioned angularly at angles between 28.5 and 45.5 degrees relative to verticaland +- 8.5 degrees to horizontal. The requirements for this function are fully specified in “ SACOptical Specification”, as referenced in section 2. b) Prevent scattered light from degrading the imageThe requirements for this function are fully specified in “ SAC Optical Specification”, as referencedin section 2.c) Provide structural support for:

1) SAC Optical ElementsThe SAC optical elements and internal baffles shall be supported by the SAC structure underthe specified operational environment such that the performance requirements are met. Thesupports of these elements shall make provision for alignment adjustment in case of recoatingof optical elements.

2) Payload Alignment System of TrackerThe tracker will use the measurements from the payload alignment system to position the SACperpendicular to and on the paraxial focus of the primary mirror. The sensors envisaged forthese measurements are at least two autocollimators mounted at the paraxial focus of theprimary mirror at an angle that intersects with the primary mirror centre of curvature. It istherefore of utmost importance that these sensors be mounted with great accuracy relativeto the SAC optical axis.

3) Moving BaffleThe function of the moving baffle is to prevent any light not emanating from the primary mirrorsurface to enter the instruments. Since the pupil of SALT will be sweeping across the primarymirror during a track, the moving baffle will have to sweep in the opposite direction to ensurethe requirement above. If the SAC is non rotating it reduces the degrees of freedom requiredby the moving baffle and therefore simplifies its motion. The moving baffle shall be located atthe exit pupil.

4) ADCThe function of the ADC is to compensate for the atmospheric dispersion. The reason forsupporting it on the SAC structure if the SAC is non rotating is the same as for the movingbaffle. The ADC will be positioned between the last optic of the SAC and the moving baffle.

d) Interface to the hexapod system (if non rotating) or rotation stage (if rotating) of the

SAC Specification


Tracker.This issue shall be finalised during the design phase of the Tracker and SAC.

e) Provide an airtight cover around the SAC to allow for slight positive pressurizationto keep dust and humid air out.

In order to extend the lifetime of the coatings on optical surfaces and instruments a slightpositive pressure is required on the payload to keep dust and humid air out.

4.2.2 Maintenance and Support Functions

a) Provide SALT with a test for the assembled SAC.Part of the SAC system will be the test optic assembly and associated accessories, for testing theassembled SAC, to enable realignment of the optical elements and alignment of the payloadsubsystems. The requirements for this function are fully specified in “ SAC Optical Specification”,as referenced in section 2.

b) Provide adjustment capability to position focal plane and optimise image qualityWhen the SAC is integrated with the payload, adjustments are necessary to position the focalplane with respect to the other instruments and with respect to the rotation axis of the payload andto optimise image quality over the full field of view. The SAC system shall provide this adjustmentcapability.

c) Provide handling points – for installation/removal to/from payloadThe integration or removal of the SAC from the payload, require convenient attachment locationson the SAC structure. The dome crane will be used for this purpose.

4.3 Major Control Functions

4.3.1 Subsystem modes, States and Events

NA4.3.2 Functional Flow Diagram

NA

4.3.3 Function descriptions

NA

4.3.4 Operational Concept

The telescope operation is detailed in ‘SALT 1000AS0040’, see section 2. The Tracker shall positionthe SAC according to the position of the target. The maximum angular deviations from the lineperpendicular to the primary mirror vertex (defined as the optical axis) are +- 8.5 degrees in bothaxes. The optical axis is however tilted 37 degrees relative to the local vertical. Once installed andaligned on the Tracker the SAC shall only be removed for recoating of its mirrors. This must bepossible without removing any other part of the payload except for subsystems attached to theSAC.

5 SAC Technical Requirements

SAC Specification


5.1 Schematic diagram

The figure below shows the major components of the SAC subsystem. All the underlined items arenot part of the SAC, but are the subsystems that the SAC will interface to. The SAC structure mustalso support the Moving Baffle and ADC.

Figure 6. Major Components of the SAC Subsystem

All the internal interfaces between the SAC subsystem components and external interfaces betweenSAC subsystem and other subsystems of SALT are shown and numbered in the figure below.

SAC Specification


5.2 SAC Interfaces

All the SAC components and potential interfaces are illustrated below.

Figure 7. SAC Interfaces

SA

C S

tru

ctu

re

Not Part of SAC

Optical Elements

T

rack

er H

exap

od

E1

INTERFACES E ** : external 1,2 : internal

Baffles

Tra

cker

Ro

tati

on

Sta

ge

1

2

E2

Pay

load

Alig

nm

ent

Sys

tem

E3

Mo

vin

g B

affl

eA

DC

E4

E5

SAC Specification


5.2.1 SAC External Interfaces

The system interfaces shall comply with the Physical, Electrical and External Interface ControlDossiers referred to in Section 2. The SAC external interfaces are described in the table below.These interfaces will depend on the final decision as to whether the SAC is rotating or not.

Table 1 SAC external interfaces (refer Figure 7)No. Subsystem

1Subsystem 2 Type Direction Interface Description

E1 TrackerHexapodSystem

SAC Structure Physical Both Mountings – bolted, adjustable foralignment, volume & mass limitation

E2 TrackerRotationStage

SAC Structure Physical Both Mountings – bolted, adjustable foralignment, volume & mass limitation

E3 PayloadAlignmentSystem

SAC Structure Physical Both Mountings – bolted, adjustable foralignment, volume limitation

E4 MovingBaffle

SAC Structure Physical Both Mountings – Bolted, adjustable foralignment, volume limitation

E5 ADC SAC Structure Physical Both Mountings – Bolted, adjustable foralignment, volume limitation

SAC Specification


5.2.2 SAC Internal Interfaces

For a complete description of all the interfaces, refer to the interface control dossier, listedin section 2

Table 2 SAC Internal Interfaces (see Figure 7 )No. Subsystem

1Subsystem 2 Type Direction Interface Description

1 SACStructure

SAC OpticalElements

P Mountings, adjustable foralignment

2 SACStructure

Baffles P Mounting

5.3 SALT SAC Characteristics

5.3.1 Performance Characteristics

The SAC subsystem performance characteristics that are required to perform the functions aboveare described below:

5.3.1.1 SAC ERROR BUDGET

The contribution of the SAC to the error budget shall be limited to the values in table 3 below. Theintegrated SAC shall be tested in its operational environment and attitudes and the image quality shallbe better than the value “Total(tested)” in table 3 below. The subsystem interfaces (alignmentsensors and ADC) shall be designed to degrade image quality by less than specified below. The“TOTAL(tested)” specified in table 3 is the value as integrated over attitude and temperaturechanges during operation.

Table 3 SAC Error BudgetContributor Image Quality (arc seconds)

EE(50) EE(80)SAC design Residual 0.062 0.09Manufacturing & Alignment 0.190 0.34Gravity & Temperature effectson SAC Structure

0.106 0.167

TOTAL(tested) 0.226 0.389Subsystem Interface stability(Alignment sensors, ADC,mounting)

0.05 0.05

5.3.1.2 SAC OPTICSThe optical performance requirements for the SAC are described in “ SALT OpticalSpecification”, doc no SALT-1523AS0002, refer to Section 2. The following parameters/itemsare specified:

]

SAC Specification


• Image Quality (paragraph 1.2.4)• Field of View (FOV) (paragraph 1.2.2 and 1.2.12)• Entrance Pupil (paragraph 1.2.1)• Delivered F-ratio (paragraph 1.2.3)• Stray Light (paragraph 1.2.13)• Surface Coating (paragraph 1.2.6)• Test Optics (paragraph 1.2.8)• Optical Surfaces: dimensions, surface description & finish, manufacturing procedure etc are

specified as information only, the specifications above supersede.

5.3.1.3 SAC STRUCTURE

a) Image Quality

The temperature and attitude sensitivities shall not degrade the EE(50) and EE(80) imagequalities by more than 0.106 and 0.167 arc seconds respectively. The operationalenvironment is described in section 5.3.3. The attitude can vary between +-8.5 degreesabout both rotation axes, with 37 degrees offset about the x-axis.

b) Mounting of SAC to the Hexapod System (0)

The mountings shall be adjustable to position the focal plane as required and to optimise theimage quality. The ranges and accuracies of adjustment shall be determined in the designphase. Sufficient allowance shall be made to accommodate variances that might occurafter a recoating and assembly operation. The resolutions of adjustment required at thefocal plane are as follow:

• tip and tilt: < 15 arc seconds• Decentre: < 10 mm• Focus: < 100 mm

The final alignment of the SAC optical axis shall be within the above values from therotation axis of the payload.

Once adjusted, it must be locked to prevent it from going out of alignment during operation.

c) Mounting of the Payload alignment system to the SAC Structure

The mounting points shall be provided anywhere along the SAC Structure, as far up aspractically possible. The angle that the collimator beam will make with the SAC optimal axiswill be 3.5 degrees. Two (TBC2) collimator systems will be employed as alignmentsensors. A physical reference of the SAC optical axis shall be provided to enable alignmentof the payload alignment system with the SAC optical axis as well as alignment of the SACoptical axis with the rotation axis of the payload. The accuracy of these mounting pointsshall be such that the adjustment ranges required will not exceed the following:


SAC Specification


The stability of these mounting points, under all operating conditions, shall be betterthan(TBC3):


The payload alignment system shall provide the adjustments to align itself with the SACoptical axis.

d) Mounting of the Moving Baffle to the SAC Structure

The mounting points shall be provided at the exit pupil. The details shall be finalised in thedesign phase. The accuracy of the mounting points shall be such that the adjustmentranges required will not exceed the following:


The moving baffle shall provide the adjustments.

e) Mounting of the ADC to the SAC Structure

The mounting points shall be provided at TBD1 location. The details shall be finalised in thedesign phase. The accuracy of the mounting points shall be such that the adjustmentranges required will not exceed the following:


The stability of these mounting points, under all operating conditions, shall be betterthan(TBC4):


The ADC shall provide the adjustments.

5.3.2 Physical Characteristics

5.3.2.1 OBSCURATION

The optical performance requirements for the SAC are described in “ SALT OpticalSpecification”, doc no SALT-1523AS0002, refer to Section 2.

5.3.2.2 MASS

SAC Specification


The SAC mass, inclusive of all subsystems, shall be less than 150kg (TBC5)

An estimated mass budget for the SAC is as follows (to be finalised in design phase):

Table 4 SAC Mass BudgetSubsystem Mass[kg] % of

TotalSAC Structure 90 60.00SAC Optics 50 33.33Miscellaneous 10 6.67Total 150 100

5.3.2.3 ENVELOPE

The integrated SAC shall not exceed the envelope as indicated in the figure below:

5.3.2.4 MAXIMUM SURFACE TEMPERATURES

5.3.2.4.1 Objects in the optical pathNo surface temperature shall exceed 2 degrees above or below ambient.

5.3.2.4.2 Objects outside the optical pathNa

5.3.2.5 MINIMUM SURFACE TEMPERATURES

NA

5.3.2.5.1 Objects in the optical pathNo surface temperature shall exceed 2 degrees above or below ambient.

5.3.2.5.2 Objects outside the optical path

Na

5.3.2.6 COMPONENT/MODULE REPLACEMENT

All major components that might need removal, must provide for interfaces suitable forusing the dome crane as lifting device (capacity 1ton).Any special lifting or handling fixtures for modules by their nature or orientation requiresuch fixtures for safe lifting and positioning. The SAC shall be fitted on telescope byusing the dome crane - from above and below the Tracker beam.

SAC Specification


5.3.3 Environmental Requirements

5.3.3.1 NORMAL OPERATIONAL ENVIRONMENT

SALT shall meet all the requirements specified in this document when operated in the night-time outside ambient condition defined in Table 5 below. The SAC structure however willnot be exposed to the maximum wind velocity, since it will be enveloped by the fixed bafflestructure. The SAC structure shall be designed to satisfy the image quality requirementsfor a lateral and axial wind velocity of 1.5m/s.

Table 5 Normal Operational EnvironmentParameter Value NotesMinimum Temperature 0ºCMaximum Temperature 20ºCMaximum nightly temperature range 8ºCMaximum rate environment cooling -1.5ºC/hMaximum rate of environment warming +0.5ºC/h Estimated valueMinimum Humidity 5%Maximum Humidity 97% Non-condensingMaximum wind velocity (outside) 16.8 m/s Gusts up to 22 m/sMaximum wind velocity (inside) 4m/sSite altitude 1798mSolar radiation 0 W/m2 Twilight to dawn

5.3.3.2 MARGINAL OPERATIONAL ENVIRONMENT

The degradation of system performance as a result of the ambient environment specified inTable 6 below, shall not exceed 10% (Error! Reference source not found.6) of thenominal values in paragraph 5.3.1. The SAC structure however will not be exposed to themaximum wind velocity, since it will be enveloped by the fixed baffle structure. The SACstructure shall be designed to satisfy the marginal image quality requirements for a lateraland axial wind velocity of 2.5m/s.

Table 6 Marginal Operational EnvironmentParameter Value NotesMinimum Temperature -10ºCMaximum Temperature 25ºCMaximum rate environment cooling -2.0ºC/hMaximum rate of environment warming +1ºC/h Estimated valueMinimum Humidity 5%Maximum Humidity 97% Non-condensingMaximum wind velocity (outside) 21 m/s Gusts up to 25 m/sMaximum wind velocity (inside) 5.5m/sSolar radiation 0 W/m2 Twilight to dawn

5.3.3.3 SURVIVAL ENVIRONMENT

SALT shall survive when exposed to the day or night ambient environment specified inTable 7 below. Note that the dome and louvers will be closed under these conditions and

SAC Specification


therefore the SAC does not have to be designed for this wind loading, but all SACsubsystems must be able to survive the temperature profile.

Table 7 SALT Survival Operating EnvironmentParameter Value NotesMinimum Temperature -20ºC**Maximum Temperature 45ºC**Maximum Humidity 100% Occasional exposure to condensing

conditions

5.4 Operation and Maintenance Requirements

5.4.1 Packaging, handling, storage

Packaging, handling and storage requirements will be determined for each individual type ofcomponent, taking into account the specific requirements of the component, the method ofshipping and interim storage locations. Storage at SALT will be in the SALT Store Room, indry dust free, air-conditioned conditions. Containers shall be airtight and sufficient for onereturn shipping only, unless otherwise specified.

5.4.2 Product Documentation

a) The SALT SAC shall include operating manuals (details on optical alignment), trainingmanuals, maintenance manuals and calibration procedures.

b) Full size copies of as built component specifications, drawings and CAD files.

All documentation shall be in English.

5.4.3 Personnel and Training

5.4.3.1 OPERATION

SALT will be operated from the control room at the telescope. A SALT operator (SO) and aSALT Astronomer (SA) will be on duty during the whole night, for every operational night. Any ad hoc repair work will be performed by the SAAO standby maintenance staff, to becalled by the SO when required. The SO will have a National Diploma (N6/S3) or equivalentqualification in electronic or mechanical engineering or have adequate experience. The SAwill be a PhD astronomer.

5.4.3.2 MAINTENANCE

SALT will be maintained by the SAAO staff at Sutherland and Cape Town. Personnel willbe trained in the maintenance of SALT, and be granted a “SALT – license” upon completionof training. All maintenance work carried out on SALT will be supervised/signed off by aSALT licensed person. It is anticipated that the following people will be required to maintainSALT:

At Sutherland:Mechanical Technician: 2Electronic Technician: 1

SAC Specification


Electrical Technician: 1In Cape Town:Mechanical Engineer: 1Electronic Engineer: 1Software Engineer: 1

These positions should not be SALT only, i.e. these personnel must be part of the SAAOtechnical staff, who will also work on the other SAAO telescopes. Thus, two Electronictechnicians, each working 50% on SALT, can constitute the one full time ElectronicTechnician listed above.

One mechanical and one of the electrical/electronic technician will also be required to be onstandby during every night of operations. These standby personnel will form part of thenormal SAAO standby team.

In the above requirements, “Technicians” require a N6, T3 or equivalent qualification, and“Engineer” means an S6 or Bachelors degree in Engineering and/or Computer Science.

The SAC system shall be designed such that maintenance requirements shall be compliantwith the mentioned personnel resources, keeping in mind that only part of the humanresources can be allocated to the SAC.

5.4.4 Availability

5.4.4.1 SCIENCE EFFICIENCY

5.4.4.1.1 Reliability

• The SAC shall not cause any downtime except for recoating of the mirrors atintervals of longer than 10 years.

5.4.4.1.2 SAC Maintainability

• Test equipment, jigs and tools for SAC assembly, alignment and testing, shallbe provided.

• The design and construction of the SAC shall include the capability of safelymounting and dismounting it by using the Dome Crane.

5.4.4.2 MEASURES TO ACHIEVE EFFICIENCY

As far as possible local support for all subsystems/components is required

Special tools and equipment required for system operation and maintenance shall be kept toa minimum.

All normal maintenance actions will be able to be completed within one working day, unlessotherwise specified.

Two standard (metric) tool sets will be available, one in the SALT workshop and one in thetelescope chamber. Special tools will be kept to a minimum, and be limited to mirror

SAC Specification


handling.

5.5 Design and Construction constraints

5.5.1 General design guidelines and constraints

The following guidelines and constraints apply to SALT (where these general guidelinescontradict specific requirements in other parts of this document, the other requirements shallhave precedence):

a. Commercial, off the shelf (COTS) equipment will be used unless specifically statedotherwise.

b. The Metric measurement system will be used.c. All surfaces inside the telescope chamber should follow the ambient temperature as closely

as possible, the effect of a positive delta being air turbulence, causing bad seeing, and anegative delta being the risk of condensation, damaging mirrors and equipment.

d. Stray (star/moon) light should be baffled

5.5.2 Materials, Processes and Parts

a. All components will be protected against corrosion by proper surface treatment (e.g.anodising), painting, etc. The use of non-ferrous bolts and nuts is preferred.

b. Wherever a component is mounted in an optically sensitive area, it shall be painted with anon-fluorescing, non-radioactive paint.

c. All components mounted in the optical path or contributing to stray light will be non-reflective, non radiating in the spectrum 320 to 1500nm

d. All custom components will be marked as follows:

Table 8 Part identificationSALT

Supplier nameProduct name

Product numberSerial number (where applicable, e.g. mirror

segments, mirror mounts)Version number (where applicable, e.g.controllers/computers with embedded

software)Hazard/danger/poison warning (where

applicable)

e. No special markings are required on COTS equipment.f. The normal operation of any component/subsystem shall have no negative impact on the

environment, and shall comply with the Montreal Protocol.

5.5.3 Electromagnetic Radiation

The normal operation of any component or system will not affect the normal operation of anyother system or component, or any other equipment at the Observatory at Sutherland., andhas to comply with the FCC standards as per Section 2.

SAC Specification


5.5.4 Workmanship

Workmanship specifications will be specified per type of component, but will not be higherthan required to fulfil the overall SALT performance specification.

5.5.5 Interchangeability

a. Interchangeability will be maximised by using COTS equipment wherever possible, andexceptions will be specified.

5.5.6 Safety

5.5.6.1 SAFETY-CRITICAL FAILURES

All single-point failures that can lead to loss of life, serious injury to personnel or damage toequipment shall be identified and the design modified to prevent such failures.

A preliminary safety analysis to identify such potential failures is contained in the SALTSafety Analysis referred to in section 2.

5.5.6.2 SOFTWARE SAFETY

NA

5.5.6.3 SAFE INITIALISATION

NA

5.5.6.4 LOCAL ELECTRIC OPERATION

NA

5.5.7 Ergonomics

Comfortable working positions and conditions will be provided at all stations where operatorswill spend long times regularly during normal operation.

5.5.8 Special commissioning requirements

5.5.8.1 SAC OPTICAL AXIS

A clear and physical reference of the SAC optical axis position and orientation shall begiven to enable alignment of the optical axis with other subsystems.

5.5.8.2 SAC TEST SYSTEM

A test system shall be delivered to perform image quality tests on an integrated SAC.

5.5.9 Software

SAC Specification


NA

5.5.10 Computer Hardware

NA

5.5.11 Electrical Design

NA

5.5.12 Future growth NA

SAC Specification


6 Subsystem technical requirements

6.1 Major Component List

The major suggested components and subcomponents listed in the following table.

Table 9 SAC systemNo Major Component Sub Components

1 Integrated SAC 1.1 Optical elements1.2 Baffles (stray light)1.3 SAC Structure

2 SAC Test bench Inclusive of all optics, sensors, jigs and toolsto perform SAC optical test (of integratedSAC)

3 Handling equipment

SAC Specification


6.2 Major Component CharacteristicsAll systems & subsystems shall comply with the requirements of Section 2 documents.The figure below shows the major dimensions of the SAC and Payload

Figure 8. SAC : Layout & Dimension

SAC Specification


6.2.1 Integrated SAC

6.2.1.1 OPTICAL ELEMENTS

Details as specified in “SAC Optical Specification”, doc no SALT-1523AS0002.

6.2.1.2 LIGHT BAFFLES

Details as specified in “SAC Optical Specification”, doc no SALT-1523AS0002.

6.2.1.3 SAC STRUCTURE

The interface details shall be finalised during the design phase.

6.2.2 SAC Test Bench

The test bench and set-up with specialised tools and or sensors shall be delivered as part ofthe SAC system. Details to be defined in design phase.

6.2.3 Handling Equipment

All specialised handling equipment, for the integrated SAC, assembly and disassembly, shallbe delivered as part of the SAC system. Details to be defined in design phase.

7 Test Requirements

7.1 Verification cross-reference Matrix

Per paragraph in sections 3,4,5 and 6, identification of how the product’s compliance of therequirement will be measured to test compliance is indicated in the table below.

Note that compliance to a requirement may be proven at the “system” (S), “subsystem” (SS) orcomponent (C) level, depending on the particular requirement (e.g. the mass of the total product canbe proven by weighing all the components, it needn't be in the assembled state).

The "Test Method" may be any one of the following:_ Review (R) - the design is reviewed and it is obvious to all whether or not the item complies

(e.g. whether or not the system has a particular mode)._ Inspection (I) - the completed item is inspected and compliance can be easily observed. This

is normally used for physical characteristics such as colour, dimensions and mass._ Testing (T) - this entails a technical effort whereby the system is stimulated in a certain

fashion and its response compared to the required response._ Analysis (A) – compliance of the design to the requirement is proved by mathematical

analysis.Where it is considered important, reference to the detail of the test method should be provided in the"Details" column of the table.

SAC Specification


Table 10 Verification cross-reference Matrix (TBD2)Para. Requirement Test

MethodTestLevel

Test DetailRef.

“SAC Optical Specification”, doc noSALT-1523AS0002

1.2.1 Entrance pupil A,T S1.2.2 Field of view A,T S1.2.3 F-ratio A,T S1.2.4 Image Quality A,T S1.2.5 SAC Design Form I S1.2.6 SAC Mirror Coating T C,S1.2.7 SAC Vignetting T S1.2.8 SAC Envelope I S1.2.9 SAC Mirror Finish A,T C1.2.10 SAC Mounting I,T S1.2.11 SAC Design A,R C,S1.2.12 Guide Star Field of View T S1.2.13 Stray Light A S1.2.14 Acceptance testing R C,S

“SAC Specification”, doc no SALT-1523AS0001

4 Functional Requirements R C,S5.2 SAC Interfaces R,I C,S5.3.1.1 SAC Error Budget A,T C,S5.3.1.2 SAC Optics Section

above)5.3.1.3 SAC Structure I,A,T SS,S5.3.2.1 Obscuration A S5.3.2.2 Mass T S5.3.2.3 Envelope I S5.3.2.4 Maximum Surface Temperatures R C,SS,S5.3.2.5 Minimum Surface Temperatures R C,SS,S5.3.2.6above

Component/Module Replacement I,R C,SS,S

5.3.3 Environmental Requirements A,T SS,S5.4 Operation and maintenance Requirements R,I SS,S5.5above

Design and construction Constraints R,I SS,S

6.1 Major Component list R,I C,SS,S6.2 Major Component Characteristics R,I,T C,SS,S

7.2 Detailed Test Methods

(TBD3)

8 NotesNA

SAC Specification


SAC Specification


APPENDIX B : LIST OF TBD’S AND TBC’S

TBC PARA DESCRIPTION/DATETBC1 4 SAC Rotating / non-rotatingTBC2 5.3.1.3 Payload Alignment SystemTBC3 5.3.1.3 Stability of Payload alignment mountsTBC4 5.3.1.3 Stability of ADC mountsTBC5 5.3.2.2 SAC total MassTBC6 5.3.3.2 Degrading of performance under marginal conditions

SAC Specification


TBD PARA DESCRIPTION/DATETBD1 5.3.1.3 Mounting Position of ADC and Moving BaffleTBD2 7.1 Verification Cross matrix testsTBD3 7.2 Detailed test methods

SAC Specification - University of Wisconsin–Madison · SAC Specification Doc No. SALT-1523AS0001...

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