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Guidance System Specification

Doc No. SALT – 0000AS0000 Issue 1 - 1 -

APPROVAL SHEET

TITLE: GUIDANCE SYSTEM SPECIFICATION

DOCUMENT NUMBER: 1524AS0001 ISSUE: DRAFT

SYNOPSIS:

KEYWORDS:

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

APPROVED: Gerhard Swart SALT System Engineer

: Kobus Meiring SALT Project Manager

DATE:

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



ACRONYMS AND ABBREVIATIONS

mm micronarcsec Seconds of arcCCAS Centre-of-Curvature Alignment SensorCCD Charge-coupled DeviceCOTS Commercial off the shelfEE(50) Enclosed Energy is 50% of total energyFoV Field-of-ViewFWHM Full Width Half MaximumHET Hobby-Eberly TelescopeHRS High-resolution SpectrographI/O Input/Output (Device)ICD Interface Control DossierIR InfraredITF Ideal Tracker FrameLRS 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)XL Lower X-driveXU Upper X-drive



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 acquiredanother object in the same 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.



TABLE OF CONTENTS

1 Scope.................................................................................................... 91.1 Identification..........................................................................................................................91.2 System overview .................................................................................................................91.2.1 Guidance:.........................................................................................................................101.2.2 Focusing: .........................................................................................................................11

2 Referenced documents..................................................................... 123 Customer Furnished Equipment and Responsibilities.................. 124 Functional Requirements ................................................................. 134.1 Operational Concepts........................................................................................................134.2 Functional diagrams ..........................................................................................................134.2.1 Functional Flow Diagram........................................................................................................144.2.2 Functional Definition.........................................................................................................14

4.2.2.1 SALT Operator MMI......................................................................................................144.2.2.2 SALT Astronomer MMI .................................................................................................154.2.2.3 TCS Server...................................................................................................................154.2.2.4 Payload Computer ........................................................................................................154.2.2.5 Guidance Detector Controller.......................................................................................164.2.2.6 Focus Detector Controller ............................................................................................164.2.2.7 Probe Positioning System.............................................................................................164.2.2.8 SALTICAM Computer....................................................................................................16

4.2.3 System Modes .................................................................................................................174.2.4 Time Line Diagram............................................................................................................20

5 System Technical Requirements...................................................... 215.1 Schematic diagram ............................................................................................................215.1.1 Schematic Diagram of Payload ........................................................................................215.1.2 Schematic Diagram of Guidance Layout..........................................................................225.1.3 Schematic Diagram of Guidance System.........................................................................225.2 Interfaces.............................................................................................................................235.2.1 External Interfaces...........................................................................................................235.2.2 Internal Interfaces............................................................................................................255.3 Characteristics ...................................................................................................................255.3.1 Performance ....................................................................................................................26

5.3.1.1 Brightness of Guidance objects...................................................................................265.3.1.2 Guidance Update Rate .................................................................................................265.3.1.3 Focus Update Rate.......................................................................................................265.3.1.4 Guidance and focus error Budget ...............................................................................265.3.1.5 Guidance Probe positioning accuracy .........................................................................265.3.1.6 Guidance field of view (FOV)......................................................................................265.3.1.7 Image Quality................................................................................................................265.3.1.8 Wavelength Performance:............................................................................................275.3.1.9 Motion Ranges of guidance Probes .............................................................................275.3.1.10 Speed of Positioning.................................................................................................275.3.1.11 Thermal Control.........................................................................................................27



5.3.1.12 Safety.......................................................................................................................275.3.1.13 Structural Frequencies.............................................................................................285.3.1.14 Structural deflections ...............................................................................................285.3.1.15 Travel Limits..............................................................................................................285.3.1.16 Guidance System MMI ..............................................................................................28

5.3.2 Physical Characteristics ..................................................................................................285.3.2.1 Mass.............................................................................................................................285.3.2.2 Envelope.......................................................................................................................285.3.2.3 Component/module replacement ..................................................................................29

5.3.3 Environmental Requirements............................................................................................295.3.3.1 Normal Operational Environment ..................................................................................295.3.3.2 Marginal Operational Environment................................................................................295.3.3.3 Survival Environment....................................................................................................30

5.4 Operation and Maintenance Requirements..................................................................305.4.1 Packaging, handling, storage...........................................................................................305.4.2 Product Documentation....................................................................................................305.4.3 Personnel and Training ....................................................................................................31

5.4.3.1 Operation......................................................................................................................315.4.3.2 Maintenance.................................................................................................................31

5.4.4 Availability........................................................................................................................325.4.4.1 Science Efficiency ......................................................Error! Bookmark not defined.

5.4.4.1.1 Reliability ...............................................................................................................325.4.4.1.2 Tracker Maintainability...........................................................................................32

5.4.4.2 Measures to achieve efficiency...................................................................................325.5 Design and Construction constraints............................................................................325.5.1 General design guidelines and constraints......................................................................325.5.2 Materials, Processes and Parts.......................................................................................335.5.3 Electromagnetic Radiation................................................................................................335.5.4 Workmanship ...................................................................................................................335.5.5 Interchangeability.............................................................................................................335.5.6 Safety ..............................................................................................................................34

5.5.6.1 Safety-critical failures..................................................................................................345.5.6.2 Software safety...........................................................................................................345.5.6.3 Safe initialisation...........................................................................................................34

5.5.7 Special commissioning requirements...............................................................................345.5.7.1 Subsystem MMI’s..........................................................................................................345.5.7.2 Test Points....................................................................................................................345.5.7.3 Test Data......................................................................................................................345.5.7.4 Spotter Telescope.......................................................Error! Bookmark not defined.

5.5.8 Software..........................................................................................................................345.5.9 Computer Hardware ........................................................................................................355.5.10 Electrical Design...............................................................................................................35

5.5.10.1 UPS...........................................................................................................................355.5.10.2 Standby Power generators......................................................................................355.5.10.3 Cable sizing ..............................................................................................................355.5.10.4 General Electrical Requirements...............................................................................35

5.5.11 Future growth..................................................................................................................35



5.5.11.1 Remote Observing....................................................................................................36

6 Subsystem Technical Requirements ............................................... 376.1 Major Component List ......................................................................................................376.1.1 Optical Subsystem...........................................................................................................376.1.2 Probe positioner...............................................................................................................376.2 Major Component Characteristics .................................................................................376.2.1 Layout and Positioning of Components............................................................................376.2.2 Beam...............................................................................Error! Bookmark not defined.6.2.3 Carriage ..........................................................................Error! Bookmark not defined.6.2.4 Hexapod System.............................................................Error! Bookmark not defined.6.2.5 Linear Drive Systems......................................................Error! Bookmark not defined.6.2.6 Rho-Drive System...........................................................Error! Bookmark not defined.6.2.7 Payload Alignment System..............................................Error! Bookmark not defined.6.2.8 Thermal Control System..................................................Error! Bookmark not defined.6.2.9 Cable & Tube Handlers and Enclosures .........................Error! Bookmark not defined.

7 Test Requirements ............................................................................ 377.1 Verification cross-reference Matrix...............................................................................377.2 Detailed Test Methods......................................................................................................38

8 Notes................................................................................................... 38APPENDIX A: TIMELINESAPPENDIX B: LIST OF TBC’S AND TBD’SAPPENDIX C: System Functional Flow Diagram



TABLE OF FIGURES

Figure 1. Payload Layout............................................................................................................9Figure 2. Schematic showing Guidance Corrections ....................................................... 10Figure 3. Schematic showing Focus Corrections.............................................................. 11Figure 4. Guidance and Focusing timelines....................................................................... 20Figure 5. Schematic showing Payload Layout.................................................................... 21Figure 6. Schematic showing Guidance layout.................................................................. 22Figure 7. Interfaces .................................................................................................................. 23Figure 8. Interfaces .................................................................Error! Bookmark not defined.Figure 9. Detail of beam.........................................................Error! Bookmark not defined.Figure 10. Conceptual illustration of the HET Carriage..Error! Bookmark not defined.Figure 11. Conceptual illustration of the SALT Carriage(h) & PayloadError! Bookmark

not defined.Figure 12. HET Linear Dual Drive system.........................Error! Bookmark not defined.Figure 13. Cable and Tube Handlers ................................Error! Bookmark not defined.



LIST OF TABLES

Table 1 Description of Modes ................................................................................................. 18Table 2 Description of Mode Transition Events................................................................... 19Table 3 External interfaces ...................................................................................................... 24Table 4 Tracker to Optical Payload interfaces (refer Figure 5)Error! Bookmark not

defined.Table 5 Internal Interfaces ....................................................................................................... 25Table 6 Normal Operational Environment............................................................................ 29Table 7 Marginal Operational Environment.......................................................................... 29Table 8 SALT Survival Operating Environment .................................................................... 30Table 9 SALT Efficiency ...........................................................Error! Bookmark not defined.Table 10 Typical Steps and 90th percentile max times to Acquire and Observe an object

Error! Bookmark not defined.Table 11 Part identification..................................................................................................... 33Table 12 Verification cross-reference Matrix (TBD20)....................................................... 38



1 Scope

1.1 Identification

This document specifies the requirements for the Guidance system of the Southern African LargeTelescope. Where applicable, the possible growth paths for later upgrades have been identified.

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 guidance system shall provide the telescope control system with corrections to keep thetelescope pointing at the designated target and have it in focus within the specified accuracies. Theinstruments on the telescope that are to receive light are:- SALTICAM (Acquisition and Science role)- PFIS- FIF- Auxiliary Port

All these instruments will be located on the payload of which a layout is given in the figure below.

Figure 1. Payload Layout



At each of these stations above a guidance and focusing capability shall be provided. The hardwareto implement this functionality will in principle be two detectors, one for guidance and one forfocusing, and a probe positioning system at each instrument location. The probes will serve as pick-off devices to feed light to the detectors. The probe positioning system shall be closely coupled tothe various instruments to prevent differential flexure due to varying gravitation and temperature.The guidance system has therefore a dual function namely:- Guidance and- Focusing, which will be discussed further in the subsequent sections.

In addition to the guidance described above, which will be default, SALTICAM shall provide pellicleguidance. This shall be implemented by directing part of the light to SALTICAM by means of thepellicle. In this mode the focusing will be as for the default guidance.

1.2.1 Guidance:Provide the TCS with the movement of the centroides of the designated guidance objects relativeto their initial position at a specified frequency. These measurements will enable the TCS to sendcorrective commands to the Tracker to keep the telescope pointing at the science object within theclosed loop guidance requirement of 0.1”. The guidance corrections as calculated by the guidancesystem can be depicted as follows:

Figure 2. Schematic showing Guidance Corrections X

Y

CCDDetector

Guidance objectscan be single ormultiple asenclosed by thedesignatedwindow

ImageCentroid

Initial ImageCentroid XGE = X component of guidance error

YGE



1.2.2 Focusing:Provide the TCS continuously with a focus error. The selected guidance objects will be imaged asin and out of focus objects on another detector. The difference in size or energy of the two imageswill be proportional to the focus error and can be depicted as follows:

Figure 3. Schematic showing Focus Corrections

Image Plane

BeamSplitter(50%)

Mirror

1 2

Image onDetector

15”15”

6 mm

1 2



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-1000AS0028 Specification for the SALT Fibre-Feed System (Error! Referencesource not found.)

SALT-1000AS0029 Specification for the SALT Prime Focus Instrument (Error! Referencesource not found.)

SALT-1000AS0027 SALT External Interface Control Dossier (Error! Reference sourcenot found.)

SALT-1000AS0013 SALT Electrical Interface Control Dossier (Error! Reference sourcenot found.)

SALT-1000AS0014 SALT Physical Interface Control Dossier (Error! Reference sourcenot found.)

SALT-1000AA0030 SALT Safety Analysis (Error! Reference source not found.)SALT-1000AS0031 SALT Axes and Calibration definition (Error! Reference source not

found.)SALT-1000AA0017 SALT Error Budget (Error! Reference source not found.)SALT-1000BS0021 SALT Requirements for Built-in Testing (Error! Reference source

not found.)SALT-1000BS0010 SALT Software Standard (Error! Reference source not found.)SALT-1000BS0011 SALT Computer Standard (Error! Reference source not found.)SALT-1000AS0032 SALT Electrical Requirements (Error! Reference source not

found.)SALT Report of Interim Project Team, April 1999

SALT-1000AS0033 SALT Support Requirements (Error! Reference source not found.)SALT-1000AS0040 SALT Operational Requirements (Error! Reference source not

found.)Applicable South African Building and Construction StandardsApplicable South African Legal Requirements (Error! Referencesource not found.)Safety, Health and Environment Act

SALT-1000AS0007 SALT System Specification

3 Customer Furnished Equipment and Responsibilities

There shall be no customer furnished equipment in the guidance system



4 Functional Requirements

4.1 Operational ConceptsThe diagram below describes stepwise how the guidance system shall be operated.

4.2 Functional diagrams

1. SA enters or selects the relevant guidestar/s window for a particular observation

2. SA enters or selects the guidance andfocus correction update rates to TCS

3. SO enters or selects the imageparameters of images displayed at SAand SO MMI’s:- Binning- Image resolution, update rate- Update rate

4. Telescope is positioned for targetacquisition, all guide probes are positionedaccording to selected guidance objects andfold mirror/pellicle directs light to SALTICAM

5. Guidance and Acquisition Images aredisplayed at the SO and SA MMI’s

6. Acquisition offsets determined and fed toTCS

7. SO commands incremental positionchanges to telescope and guide probepositions

8. SO Satisfied withtelescope and probepositions?

N Y

9. Select guide objects

10. Verify focus on SALTICAM andguidance system

11.SO Satisfied withfocus?

12. SO commands closed loop guidance13. Guidance and focus corrections are

fed to TCS at required rate

N

Y

----------------------------Initial---------------------------

----------------------------Continuous---------------------------



4.2.1 Functional Flow Diagram

4.2.2 Functional Definition

This section defines the functions of each functional block above in more detail.

4.2.2.1 SALT OPERATOR MMI

• Communication: - Astronomer MMI- TCS

• Receive Guidance Object coordinates from SA• Command Telescope movement & guide probes• Display guidance and acquisition images

SO MMI:Command and Display

SA MMI:Command and Display

SALTICAM COMPUTER:Acquisition Imaging and Pellicle Guidance

PAYLOAD COMPUTER:- Guidance and Focus Algorithms- Command generation- Comms with subsystems & TCS

TCS

TCS SERVER:Process Commands to and

Feedback from PayloadComputer

Time Sinchronization:Provide accurate timingsignals to Payload andSALTICASM Computers

Guidance Detector & Controller:- Imaging- detector control- temperature monitoring- comms with payload computer

Focus Detector & Controller:- Imaging- detector control- temperature monitoring- comms with payload computer

Probe Positioning System:- Position measurement- Closed loop control- temperature monitoring- comms with payload computer

Guidance & Focus ImagesGuide error

Acquisition & Guidance Images

Guidance System



• Receive confirmation of science object from SA• Initiate incremental movements of telescope (TRACKER)• Initiate incremental movements on relevant subsystems (guide probes)• Select guidance objects• Define image parameters (update rate, window, binning, etc)• Initiate closed loop guidance / focusing

4.2.2.2 SALT ASTRONOMER MMI

• Communication: - Operator MMI- TCS

• Object definition / selection (guidance & science objects)• Display acquisition images• Science object identification• Select instruments

4.2.2.3 TCS SERVER

• Communication: - Operator & Astronomer MMI- Payload Computer

• Command generation for Guidance System:- Guidance probe position- Guidance Image parameters

o resolutiono Update rateo Binningo Envelope / Window of guidance objects

• Feedback interpretation- Position of guide probes- Status of guide system

4.2.2.4 PAYLOAD COMPUTER

• Communication:- TCS- Guidance Detector Controller- Focus Detector Controller- Probe Positioning System

• Algorithms- Command Generation

o Detector Controllerso Probe positions

- Guidance Image Processing (Calculating guidance and focus errors)- Safety- Diagnostics- Power up- Shutdown- Time synchronisation



- Thermal monitoring- Mode & state control

• Payload MMI- MMI to control the guidance system and to display feedback

4.2.2.5 GUIDANCE DETECTOR CONTROLLER

• Controller- Communication with Payload computer (commands, status, feedback, ranges)- Detector control

• Detector- Imaging guidance field

4.2.2.6 FOCUS DETECTOR CONTROLLER

• Controller- Communication with Payload computer (commands, status, feedback, ranges)- Detector control

• Detector- Imaging guidance field (out of focus images of guidance objects)

4.2.2.7 PROBE POSITIONING SYSTEM

• Communication with Payload computer (commands, status and feedback)• Position control of axes

4.2.2.8 SALTICAM COMPUTER

• Communication- Payload computer (guidance errors – pellicle guiding)- SA and SO MMI’s (images)- TCS



4.2.3 System Modes

OFF STANDBY INITIALIZATION

READY

SHUTDOWN

POSITIONING IMAGING

MAINTENANCE

1 2

3

4

MAJORFAULT

56

7

8

9

10

12

13

11



Table 1 Description of ModesMode DescriptionOff Power to Payload Computer and all other subsystems are

switched ofStandby The Payload Computer is running, but power to all

subsystems switched off. The Payload computer switchespower to all the subsystems except itself.

Initialisation Payload Computer powers up all subsystems of theGuidance System and homes all sensors:

• Zero all commands to actuators• Check system Health (sensor/CCD readings)• Do Homing• Go to PARK position

Ready The Guidance probes are parked in previous positions,waiting for new commands.

• Report commanded & feedback values (positions,velocities, motor currents, temperatures)

• Report System HealthCCD controllers maintain previous state, reporting systemhealth.

Positioning Probes are positioned in the guidance field in accordancewith TCS commands. Images from the detectors aredisplayed at a selected rate.

Imaging Guide probes are parked in the required position forguidance. Guidance and focus imaging are executedaccording to specifications and appropriate corrections fedto the TCS.

Maintenance Mode for maintenance and calibration purposesMajor Fault Any errors, which prevent guidance system functions being

executed, will put the guidance system in this mode. Sensorreadings and status reporting will continue in this mode.Depending on the error, commands to actuators might bezero and closed loop position control ceased. In this modeerror reporting must be sufficient to guide the telescopeoperator to the source of the problem.

Shutdown This mode is the opposite of power up and the followingactions will be performed:

• Move system to PARK position• Zero all commands to actuators• Check system Health• Switch power off



Table 2 Description of Mode Transition Events

EVENT From Mode To Mode SENSOR/INPUT1 OFF STANDBY (and

vice versa)Manual power switch

2 STANDBY INITIALISATION Button – Payload Computer3 INITIALISATION READY Software Switch – On

successful power up4 SHUTDOWN STANDBY Button – Payload Computer5 READY POSITIONING (and

vice versa)Button – Payload Computer/ TCSactivated

6 READY IMAGING (andvice versa)

Button – Payload Computer/ TCSactivated

7 READY MAINTENANCE(and vice versa)

Button – Payload Computer

8 INITIALISATION MAJOR FAULT(for reverse)

Software initiated Button – Payload Computer

9 MAINTENANCE MAJOR FAULT(for reverse)


10 IMAGING MAJOR FAULT(for reverse)


11 POSITIONING MAJOR FAULT(for reverse)


12 MAJOR FAULT READY(for reverse)

Button – Payload ComputerSoftware Initiated

13 SHUTDOWN STANDBY Button – Payload Computer



4.2.4 Time Line DiagramThe purpose of this diagram is to allocate time periods for the various operations in the guidanceand focusing process to ensure that updates will occur at the required rates. The figures belowshows time allocations for 2, 1, 0.1Hz update rates.

Accumulated Time since T0[ms] 50 70 80 130 180 280 380 450 500 550 570 580 630Time increments[ms] 50 20 10 50 50 100 100 70 50 50 20 10 50Detector Exposure Read Out Image Processing Send Corrections to TCS Tracker Reads Corrections Publish Images Minimum Update time[ms] 500

Accumulated Time since T0[ms] 50 70 80 130 180 530 880 950 1000 1050 1070 1080 1130Time increments[ms] 50 20 10 50 50 350 350 70 50 50 20 10 50Detector Exposure Time Read Out Image Processing Send Corrections to TCS Tracker Reads Corrections Publish Images Typical Update time [ms] 1000 Accumulated Time since T0[s] 0.05 0.07 0.08 0.13 0.18 3.18 6.18 9.95 10 10 10 10.1 10.1Time increments[ms] 50 20 10 50 50 3000 3000 3770 50 20 10 50 50Detector Exposure Time Read Out Image Processing Send Corrections to TCS Tracker Reads Corrections Publish Images Typical Update time [s] 10

Figure 4. Guidance and Focusing timelines



The exact itemised time allocation in the timelines above is not as important as the overall updaterates, these shall supersede. The following figure shows the requirements in terms of update rateversus guide star brightness.

FIGURE (section 5)

5 System Technical Requirements

5.1 Schematic diagram

5.1.1 Schematic Diagram of PayloadThe following figure shows the layout of the PAYLOAD:

Figure 5. Schematic showing Payload Layout

– Guidance System

– Moving Baffle– Calibration Screen– ADC– SAC



5.1.2 Schematic Diagram of Guidance Layout

Figure 6. Schematic showing Guidance layout

5.1.3 Schematic Diagram of Guidance System

(Give dimension of guide volume at each probe position)

Sc

PFIS

AuxiliaryPort

FIF

Light path

SALTICAMSc

Sc

Guidancecamera &Optics

Payload Computer

TCS

Guidance Corrections

Guidance Images

Sc Sc

Guidance Only

Science &/ Guidance

Commands / feedback

Sc

8’1’ 1’

Probe Commands / feedback

Fiber Bundle



5.2 InterfacesThe figure below describes all the interfaces relevant to the Guidance System.

Figure 7. Interfaces5.2.1 External Interfaces

Telescope ControlSystem (TCS)

P

aylo

ad C

om

pu

ter

Not Part of Guidance SystemSystem

Guidance Detecor

Probe positioningSystems (x4)

1

3

Fac

ility

INTERFACES E** : external ** : internal

Focus Detector 2

E1

E6

P

aylo

ad S

tru

ctu

re

E2

P

FIS

Str

uct

ure

E3

Sa

ltic

am

Str

uct

ure

E4

FIF

Str

uct

ure

E5

4

5



The system interfaces shall comply with the Physical, Electrical and External Interface ControlDossiers referred to in Section 2. Table 3 lists the relevant external interfaces as shown in Figure7above.

Table 3 External interfaces

No. Subsystem1

Subsystem 2 Type Direction Interface Description

E1 TCS Payload Computer

D Both Network cableCommands, feedback, ImagesAccurate Time Signal

P Both Mounting of Guidance subsystemsE Electrical Connections for Data,

PowerA ConnectionsO Connections

E2 PayloadStructure

GuidanceSystem

C ConnectionsP Both Mounting of Probe positioning

systemE3 PFIS

StructureGuidanceSystem

EE4 SALTICAM

StructureGuidanceSystem

P Both Mounting of Probe positioningsystem

E5 FIF Structure

GuidanceSystem


E6 Aux PortStructure

GuidanceSystem


E Guidance Power supplyE7 Facility GuidanceSystem C Guidance Coolant supply



5.2.2 Internal Interfaces

Table 4 Internal Interfaces

5.3 Characteristics

No. Subsystem1

Subsystem 2 Type Direction Interface Description

D Both Commands, MeasurementFeedback, Images

1 PayloadComputer

GuidanceDetector

E Both Electrical connectionD Both Commands, Measurement

Feedback, Images2 Payload

ComputerFocusDetector

E Both Electrical connectionD Both Commands, Measurement

Feedback3 Payload

ComputerProbePositioningSystems(x4) E Electrical connection

4 ProbePositioningSystems(x4)

GuidanceDetector

O Optical signal

5 ProbePositioningSystems(x4)

FocusDetector

O Optical signal



5.3.1 Performance

All requirements shall be met under specified environmental conditions and an angle of 28 to 45degrees with respect to the local vertical.

5.3.1.1 BRIGHTNESS OF GUIDANCE OBJECTS

The guidance objects shall be 19th magnitude or brighter.

5.3.1.2 GUIDANCE UPDATE RATE

Update Rate:• 1Hz or faster for 19th magnitude objects in full moonlight conditions• Accuracy of guidance correction faster than 0,05”

5.3.1.3 FOCUS UPDATE RATE

Update Rate:• 0.1Hz or faster for 19th Magnitude objects in full moonlight.• Accuracy: better than 8mm.

5.3.1.4 GUIDANCE AND FOCUS ERROR BUDGETThe table below summarises the error sources contributing to the closed loop guidance error.The last item, Tracker control, does not apply to this specification.

Table 5 Guidance and Focus Error BudgetError

Source Guidance [arcsec] Focus [mm]Image Processing 0.05 7.5Structural Flexure 0.025 3Temperature Effects 0.025 3Tracker Control 0.09 5Total 0.093 9.962

5.3.1.5 GUIDANCE PROBE POSITIONING ACCURACY

The guidance probe shall be positioned to an accuracy of 5mm or better with respect to itsphysical interface with the science instruments (SALTICAM & PFIS FIF), everywhere in itsmotion range. The reason for this is to facilitate the alignment of observation targets with slits.

5.3.1.6 GUIDANCE FIELD OF VIEW (FOV)

The guidance FOV shall be nominally 15 arcsec with a tolerance of +- 1 arcsec.

5.3.1.7 IMAGE QUALITY



The reduction of the guidance image quality by the guidance system shall not be more than5%.

5.3.1.8 WAVELENGTH PERFORMANCE:

All the guidance and focusing functions as expected in this specification shall be met over thewavelength range 400nm to 900nm.

5.3.1.9 MOTION RANGES OF GUIDANCE PROBES

The total FOV of the telescope for the various guidance positions is depicted below:

SALTICAM PFIS FIF Auxiliary Part

The motion ranges shall be such that the guide probe can be positioned anywhere in thescience and guidance fields as shown above. When the probe is positioned anywhere in theguidance annulus, no part of the probe or any other component of the guidance system shallprotrude into the science FOV.

The motion ranges shall be limited in such a way that rotation is effectively limited to only 1800

around the centre of the field.

5.3.1.10 SPEED OF POSITIONING

The guide probes shall be positioned anywhere in the total field of view within 10 seconds orless, to the required accuracy.

5.3.1.11 THERMAL CONTROL

All components producing heat shall be insulated to ensure that surface temperatures do notrise more than 20c above ambient temperature while the heat is conducted away by chilledglycol. A glycol supply and drain connection point will be supplied. Wherever needed, atuneable restrictor valves shall be placed in line. At these components the temperature shallbe measured to an accuracy of 0.50c at a rate of 0.1Hz and fed back to the TCS.

5.3.1.12 SAFETYThe safety requirements as detailed in document 1000AA0030, SALT Safety Analysis shall besatisfied.

77mm

13.5mmm

162mm

27mmm

Science FOV

Guidance annulus



5.3.1.13 STRUCTURAL FREQUENCIES

All mechanical components on the guidance system shall have first mode natural frequenciesof 15Hz or higher. The design of the control system shall be such as not to excite any ofthese modes.

5.3.1.14 STRUCTURAL DEFLECTIONS

The maximum static structural deflection at the pick-off point shall be less than 10mm in anydirection. The variation in static deflection due to tracker motion or temperature changes shallbe less than 5mm.

5.3.1.15 TRAVEL LIMITS

The control system hardware and software shall provide for three levels of travel limits for allaxes of motion of the probe positioning system, software limits, hardware limits (switches)and mechanical hard stops with motor/actuator overload protection.

5.3.1.16 GUIDANCE SYSTEM MMI

Control over all guidance system functions and access to all sensor measurements shall beavailable through the MMI. This MMI shall be accessible to the SALT operator via hisworkstation when the guidance system is integrated with the telescope.

5.3.2 Physical Characteristics

5.3.2.1 MASS

The total mass of the guidance system shall not exceed 25kg. The masses for the maincomponents are provisionally allocated as follows, but will be finalised during the designphase.

Component Mass

Detector, control electronicsand housing

5kg

Mechanical Probe PositioningSystem:at PFISat SALTICAMat FIFat Auxiliary Post

5kg5kg5kg5kg

Total 25kg

5.3.2.2 ENVELOPE

1. The detector, control electronics and housing shall not exceed a 250x250x300mm volume.



2. The mechanical probe positioning system shall fit in an annulus of inner diameter 165mm,outer diameter of 300mm and thickness less than 50mm(TBC).

5.3.2.3 TOTAL POWER REQUIREMENTS

The guidance system shall consume less than 0.4kW of electrical power.

5.3.2.4 COMPONENT/MODULE REPLACEMENT

Any component or assembly that cannot be handled by hand shall provide interfaces suitableto use the dome crane as lifting device. The design of the component or assembly shallfacilitate ease of maintenance and replacement.

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 6 below:

Table 6 Normal Operational EnvironmentParameter Value NotesMinimum Temperature 0ºCMaximum Temperature 20ºCMaximum nightly temperature range 8ºC Error! Reference source not found.Maximum 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 (at domeopening)

6m/s Error! Reference source not found.

Site 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 7 below, shall not exceed 10% (Error! Reference source not found.) of the nominalvalues in paragraph 5.3.1

Table 7 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) 8m/s (Error! Reference source not found.)Solar 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 8 below. Note that the dome and louvers will be closed under these conditions andtherefore the tracker does not have to be designed for this wind loading, but all trackersubsystems must be able to survive the temperature profile.

Table 8 SALT Survival Operating EnvironmentParameter Value NotesMinimum Temperature -20ºC**Maximum Temperature 45ºC**Maximum Humidity 100% Occasional exposure to condensing

conditionsMaximum wind velocity 61 m/s**Rain Note 1Snow Note 1Hail Note 1Icing Present Low temperatures after

condensation or rain are common.Solar Radiation Note 1Other Note 1NOTES:

1. Environmental conditions not specified shall be obtained from the appropriatebuilding/civil standards suitable for Sutherland.

2. **: Use the worst case of these figures and those specified in the appropriatebuilding/civil standards.

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, air-conditioned conditions. Containers shall be sufficient for one return shipping only,unless otherwise specified.

5.4.2 Product Documentation

a) The SALT guidance system shall include operating manuals, training manuals, maintenancemanuals and calibration procedures.

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

c) Calibration certificates for each axis, including measured positions of mechanical stops



d) Acceptance test documentation

e) Build History document.

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: 1Electrical 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 Guidance system shall be designed to be operated and maintained by the mentionedpersonnel, keeping in mind that only a small fraction of the human resources can beallocated to the Guidance system.



5.4.4 Availability

5.4.4.1.1 Reliability

• Unscheduled Guidance System down time during operation shall not exceed2h / year (TBC)

• 20 guidance probe traverses per night over a lifetime of 20 years

5.4.4.1.2 Maintainability

• Scheduled maintenance shall be performed during the day.• Spares shall be provided for components critical to Guidance system

operation of which the failure will lead to a downtime of more than 10% of thespecification in 5.4.4.1.1.

5.4.4.2 MEASURES TO ACHIEVE EFFICIENCY

Subsystems shall be organized into modules for ease of mounting/dismounting andservicing.

COTS equipment will be used as far as possible to reduce spares holding requirements. Afloat level of standard spares (bolts, nuts, wires, oils, grease) will be kept in the SALTStore.

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, and will be provided with each subsystem.

All normal maintenance actions will be able to be completed within one working day, unlessotherwise specified. Where maintenance actions take more than a day and happenregularly (e.g. primary mirror coating), enough spares will be held to ensure that theoperation of the telescope system is not affected.

Two (Error! Reference source not found.) standard (metric) tool sets will be available, onein the SALT workshop and one in the telescope chamber. Special tools shall be kept to aminimum.

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. Preference will be given to material with low thermal inertia and open section (e.g. I-beamrather than tube) for anything above the telescope chamber floor.

b. The telescope chamber shall have the same temperature as the ambient air during observing,i.e. it shall be cooled during the day, to match ambient temperature at the start of observing

c. No warm air will be exhausted into telescope light path.



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

e. All computer hardware will be COTS equipment, using “mainstream” equipment and vendors.f. Computer operating system and application software will be COTS, using “mainstream”

packages and vendorsg. Optical fibres will be used for any digital communications travelling more than 30mh. The Metric measurement system will be used.i. 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.

5.5.2 Materials, Processes and Parts

a. All components will be protected against corrosion by proper surface treatment (e.g.anodising), painting, etc.

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

c. All components mounted in the optical path will be non-reflective, non radiating in thespectrum 320 to 1500nm

d. All custom components will be marked as follows:

Table 9 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 and hasto comply with the FCC standards as per Section 2.

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.

b. Axes controllers and hexapod legs shall be interchangeable.c. Using of different types of actuators should be limited to an absolute minimum.

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

Where the malfunction of software alone could cause a safety-critical failure, alternatemeans shall be provided to prevent the occurrence of such a failure. This would typicallytake the form of electrical interlocks designed in a fail-safe manner.

5.5.6.3 SAFE INITIALISATION

All systems, when initialising from power-up or when reset, shall be in a safe, non-activestate (e.g. equipment stationary, drives off). It shall take a specific command from the TCS(by exception) or the operator via the TCS, to proceed with potentially unsafe actions(such as rotating the structure or dome, moving the tracker or opening/closing the shutter).

5.5.7 Special commissioning requirements

5.5.7.1 SUBSYSTEM MMI’S

There shall be monitors/keyboards plus good human interface SW at the subsystemcomputers, for use during system commissioning. These controls must include facilities foroverriding automatic functions and monitoring of information communicated to/from the TCS.

5.5.7.2 TEST POINTS

Means shall be provided to measure electrical signals and interpret data transferredbetween subsystems and major electronic items within each subsystem.

5.5.7.3 TEST DATA

Each subsystem shall send to the TCS the values of all internal variables that may need tobe interrogated during commissioning and testing, but would not normally be needed fortelescope control by the TCS. A list of typical variables required is provided below, butdetails will be provided in the SALT Electrical Interface Control Dossier:

5.5.8 Software



Each subsystem shall comply to the requirements defined in SALT Computer SoftwareStandard referred to in Section 2.

This document addresses the following:• Software must separate H/W interfaces with functional software, so that I/O devices can be

replaced later without having to modify all the software• The acceptable languages and operating systems will be specified per computer plus general

interfacing requirements• Specific practices and documentation/design requirements for the software will be defined• Protocols for interfacing between computers will be defined (detail will be in ICD)• Format for PLC software• Each computer shall report the health status of itself and all it’s input/output devices to a

higher level computer, such that the TCS will be notified all major failures.• TCS shall monitor communication health to all systems (ping test?)• Tracker Computer shall use Labview running on Linux on a PC.

5.5.9 Computer Hardware

Each subsystem shall comply to the requirements defined in SALT Computer HardwareStandard referred to in Section 2.

This document addresses the following:• Hardware must be selected such that it is possible to upgrade the PC’s at a later stage• Acceptable types of PLC’s servo drives, axis controllers and amplifiers will also be specified

5.5.10 Electrical Design

5.5.10.1 UPS

UPS power will be available for the guidance system detectors and payload computer.

5.5.10.2 STANDBY POWER GENERATORS

Emergency power will be available for all tracker subsystems.

5.5.10.3 CABLE SIZING

All electrical power cables shall be sized such that their outside surface temperature doesnot rise above ambient by more than 0.5ºC under worst-case operating loads.

5.5.10.4 GENERAL ELECTRICAL REQUIREMENTS

All subsystems shall comply with the SALT Electrical Requirements. This document willaddress the following:• Earthing and bonding of electrical equipment• Measures to minimise electrical interference• General principle to follow for electrical parts of each subsystem

5.5.11 Future growth



The following potential growth areas shall be borne in mind during the design process andaccommodated where this does not have an impact on the achievement of the immediateperformance, schedule and cost requirements.

5.5.11.1 REMOTE OBSERVING

The control room of SALT may be required to be duplicated at the SAAO in Cape Town, toallow remote operating of SALT.



6 Subsystem Technical Requirements

6.1 Major Component List

6.1.1 Optical Subsystem

• Pick off + Relay optics• CCD Detector, controller - Guidance• CCD Detector, controller - Focus• Miscellaneous electronics• Fibre Bundles• All guidance system software

6.1.2 Probe positioner

(X4 at each instrument position – PFIS, SALTICAM, FIF, AUX)• Mechanics• Axes Controllers• Actuators• Sensors• Misc. Electronics

6.2 Major Component Characteristics

6.2.1 Layout and Positioning of Components

TBD

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.

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

MethodTestLevel

Test DetailRef.

7.2 Detailed Test Methods

TBD

8 Notes

NA



APPENDIX A: System Functional Flow Diagram



Facility

TCS

StructureDomeSALT Functional Flow Diagram

Doc No. SALT-1000AD0022

Author: GP Swart Issue: 1.1 Date: 21/08/00

ActuatorDrivers

Edge-senseElectronics

ActuatorDrivers

Edge-senseElectronics

AxisController

AxisController

AxisController

AxisController

AxisController

AxisController

AxisController

AxisController

AxisController

CameraElectronics

Soft-startdrive

Soft-startdrive

AxisController

AxisController

FireSystem

PressureController

Temp.Controller

Temp.Controller

Actuators

Z1

Z273

Edge Sensors

E1

E480

T1

T4 Tilt Sensors

OpticalAlignmentSensor

H1

H6 Hexapodservos

Autocollimator

Rangefinder

M

M

M

M

M

M

M

Rho servo

Y-fast servo

Y-slow servo

X1-fast servo

X1-slow servo

X2-fast servo

X2-slow servo

Limit switchesand discretes

Guidance opticsdiscretes

PFIP & calibrationdiscretes

Guidance camera

M

Load balance

Dome Rotation

Az Sensor(s)

M

Soft-startdrive

Shutter open/close

M M

Anti-backlash

Az Sensor(s)

Variable-spd. drive

Variable-spd. drive

Structure rotation

S

Air bearings x 4

S

P

HSLimit switches

ActuatorMirror Model

Edge-sensorMirror Model

PrimaryMirror ControlZ1.....Z273

*E1...*E480

Status

Configure

Error(",$,z)1...91

Error(",$,z)1...91

Reset, Status

Status

AlignmentSensor MirrorModelError(",$,z)1...91

Shutter, Status

PFIP Tip,Tilt, Pistoncontrol

ImmediateGuidance

TrackerMode Control

Tilt(",$)1...4

H1...H6

Configure

H1...H6

",$

Z

Trackerdigital model

Slow/Fast control

Digitalstatus/control

Modeset/reset

Digital I/O signals

X

Y

Rho

Command(!,$,z)

Error(",$,z), H1...H6

Trajectorycalibration &hex axistransform

PFIP andoptics control

Fibre(x,y,z)1...10

Videodigitiser

Guidance &Aquisitionsetup/control

Video data

Selection /status

Spot tracker

Aquisitioncamerafunctions

Convert totracker errors

Selectguidance/scienceobjects

Camera control

Guidanceconfig.

Digitalvideo

(*X,*Y)1..2

Error(x,y,Rho)

P(t)

Error(t)

Trajectorydetermination& adjustment

Digitalvideo

P(t)Error(t)

Dome az.control

Dome digitalcontrol

Structure az.control

Structuredigital control

h1...h4

Systempointingmodel

Displayguidanceobjects

Axesconversion

Image, co- ord’s

Displayscienceobjects

Az angle Az angle

System modecontrol &monitoring

Open/Close

Az Cmd

Actual Az

Az Cmd

Actual Az

Status

Interlocks, mode

Interlocks, mode

Status, mode cmnd

Status, mode cmnd

Status, mode cmnd

Status, mode cmnd

Lock/Adjust

Time Source

t

EventLogging

OperatorReport

SelectScienceObject

Precisiontime synch

System status info

Failure status

RequiredRA, Dec

RA, Dec

t

Object information

AstronomerReport

Interface toScienceInstruments

Observation information

ElectricityMonitor

Fire AlarmSystem

Transformers and switchgear

UPS status, control

Power status, consumption

Emergency power status

Alarm status

M

M

Ventilationcontroller

Open/Close, status

Open/Close, status

CCASshutter

VentilationShutters

UPS

Emergencygenerators

T

T

Air Conditioning

T EnvironmentcontrollerTsetpoint ,T1...TN

T1...TM

Temp monitors

HHumidity

Wind Speed

T

P

P

Aircompressorcontroller

P1...PN

Psetpoint ,Pactual

Pressuremonitors

AirCompressor

TTemp.Controller

Temp.Controller

Temp.Controller

GlycolChillercontroller

GlycolChiller

ControlNode 1

ControlNode N

T

T

TN setpoint ,TN actual

T1 setpoint ,T1 actual

Tsetpoint ,Tactual

PPout ,Pin

Dataconcentrator

Enironmental and facility info, setpoints

OutsideWeathersource

ForcastWeather

VentilationStatus

Display local& forcastweatherLocal

Weather

Setpoint, status

Status

Status

Status

Status

Status

Schedule/filter scienceobjects

Storeobservationdata

PI internetforms,database

ObservationTools

Science data

Configure,status

Short termschedule

What-if info

Long term schedule

Science data

SensorElectronics

What-if info

PI access todata

Science data

Key:

Hardware function and data flow

Discrete function and control/status flow

Analogue function and data flow

Notes:1. Not all control/status data flow is shown.2. TCS and PFIP functions require further definition.

Audio &Telephonesystems

Primary Mirror System

Tracker and Payload

M

Setpoint

Systemcalibration/metrology

Calibration data

RRaindetector

Systemvisualisation

SensorElectronics

Video, & status dataVideo

Status data

CameraElectronics

Aquisition/Science camera

Comm. Instr.

AxisController

Fibre Feedcontrol (XYZ)

Provided byothers

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