Tracker System Specification

Transcription

1 APPROVAL SHEET TITLE : TRACKER SYSTEM SPECIFICATION DOCUMENT NUMBER : 1510AS0001 ISSUE : Draft SYNOPSIS : This document describes the technical requirements or the Tracker subsystem of the Southern African Large Telescope (SALT). KEYWORDS : Tracker, Payload Alignment, Closed Loop Tracking, Open Loop Tracking PRPEPARED BY : Leon Nel Manager: Tracker, Payload and TCS APPROVED : Gerhard Swart SALT System Engineer : Kobus Meiring SALT Project Manager DATE : August 2000 This issue is only valid when the above signatures are present. SALT-1510AS0001Draft Page 1 of 65

2 ACRONYMS AND ABBREVIATIONS mm arcsec CCAS CCD COTS EE(50) FoV FWHM HET HRS I/O ICD IR LRS MMI MTBF MTTR nm OEM PC PFIS PFP PI RA, DEC RMS SA SAC SALT SO SW TAC TBC TBD TCS UPS UV XL XU micron Seconds of arc Centre-of-Curvature Alignment Sensor Charge-coupled Device (Camera) Commercial off the shelf Enclosed Energy is 50% of total energy Filed-of-View Full Width Half Maximum Hobby-Eberly Telescope High-resolution Spectrograph Input/Output (Device) Interface Control Dossier Infrared Low-resolution Spectrograph Man-Machine Interface Mean Time Between Failures Mean Time to Repair nano-metre Original Equipment Manufacturer Personal Computer Prime Focus Imaging Spectrograph Prime Focus Platform Principal Investigator (Astronomer) Right Ascension and Declination Root Mean Square SALT Astronomer Spherical Aberration Corrector Southern African Large Telescope SALT Operator Software Time Assignment Committee To Be Confirmed To Be Determined Telescope Control System Uninterruptible Power Supply Ultraviolet (light) Lower X-drive Upper X-drive SALT-1510AS0001Draft Page 2 of 65

3 DEFINITIONS Acquisition time Offset accuracy Target Technical Baseline This is the length of time required to put the target at a desired position (a bore-sight), within the offset pointing requirement, from end-of-slew, until start of the integration This is the ability to place a given point in the sky on the bore-sight once the telescope has acquired an object in the FoV. This is a point in the sky. If the target is not visible to the acquisition imager, then the target is defined as an offset from a visible star that is within the focal plane field of view. This is the design baseline that is required to fulfil the requirements of the SALT Observatory Science Requirements, Issue 7.1, and is the topic of this Specification. SALT-1510AS0001Draft Page 3 of 65

4 TABLE OF CONTENTS 1 Scope Identification System overview Referenced documents Customer Furnished Equipment and Responsibilities Functional Requirements Main purpose Functional definition Major Control Functions Subsystem modes, States and Events Functional Flow Diagram Function descriptions TCS Communication Payload Computer Communication Axes Controllers Communication Payload Alignment Communication Thermal Control Communication Power Switches Communication Time Synchronization Input Tracker Algorithms Power Up Shut Down Time Synchronization Tracker Mount Model Guidance Corrections Orthogonality Corrections Axes Command Generator Thermal loop Mode and State Control Diagnostics & Safety Software Set up & Maintenance Tracker Man-Machine-Interface (MMI) Axes Control Payload Alignment Sensors Thermal Control Power Switches Gravity Compensation Structural Support Operational Concept Tracker Technical Requirements Schematic diagram SALT Tracker Interfaces SALT Tracker External Interfaces...28 SALT-1510AS0001Draft Page 4 of 65

5 5.2.2 SALT Tracker Internal Interfaces SALT Tracker Characteristics Performance Characteristics Motion Ranges Motion Symmetry Speed Accuracy (TBC9) Thermal Control Accuracy and Heat Dumping Control loop Requirements Safety Structural Frequencies (TBC10) Static Structural Deflections (TBC11) Dynamic Structural Deflections Orthogonality of Axes : (TBC13) Rotation position of Payload (TBC14) Maximum Acceleration and Jerk Additional search Speeds Forces in Hexapod Struts Travel limits Payload Alignment Tracker MMI Physical Characteristics Obscuration Mass Maximum surface temperatures Objects in the optical path Objects outside the optical path Minimum surface temperatures Objects in the optical path Objects outside the optical path Component/module replacement Payload Clearance and Envelope Environmental Requirements Normal Operational Environment Marginal Operational Environment Survival Environment Operation and Maintenance Requirements Packaging, handling, storage Product Documentation Personnel and Training Operation Maintenance Availability Science Efficiency Reliability Tracker Maintainability...44 SALT-1510AS0001Draft Page 5 of 65

6 Measures to achieve efficiency Design and Construction constraints General design guidelines and constraints Materials, Processes and Parts Electromagnetic Radiation Workmanship Interchangeability Safety Safety-critical failures Software safety Safe initialisation Local electric operation Ergonomics Special commissioning requirements Subsystem MMI s Test Points Test Data Spotter Telescope Software Computer Hardware Electrical Design UPS Installed Capacity Use of UPS power General UPS Requirements Standby Power generators Use of Emergency Power General Emergency Power Requirements Cable sizing General Electrical Requirements Future growth Remote Observing Subsystem technical requirements Major Component List Major Component Characteristics Tracker Computer System Computer Hardware: Software Suite Power Switches Beam Carriage Hexapod System Linear Drive Systems Rho-Drive System Payload Alignment System Thermal Control System...56 SALT-1510AS0001Draft Page 6 of 65

7 6.2.9 Cable & Tube Handlers and Enclosures Test Requirements Verification cross-reference Matrix Detailed Test Methods Notes APPENDIX A: TIMELINES APPENDIX B: LIST OF TBC S AND TBD S SALT-1510AS0001Draft Page 7 of 65

8 TABLE OF FIGURES Figure 1. SALT Subsystems Figure 2. SALT Pier, structure, primary mirror and tracker Figure 3. Facility and Dome Figure 4. Tracker on Top Hex Figure 5. Tracker Coordinate System (ITF) Figure 6. System modes Figure 7. Tracker Functional Flow Diagram Figure 8. Major Components of Tracker Subsystem and Communication interfaces28 Figure 9. Schematic showing SALT Tracker External Interfaces Figure 10. Interfaces Figure 11. View of tracker on upper hex Figure 12. Detail of beam Figure 13. Conceptual illustration of the overall Carriage Figure 14. Linear Dual Drive system Figure 15. Cable and Tube Handlers SALT-1510AS0001Draft Page 8 of 65

9 LIST OF TABLES Table 1 Description of System Modes Table 2 Description of Mode Transition Events Table 3 Degrees of freedom Table 4 Closed loop tracking Table 5 Open Loop Tracking Table 6 Positioning Table 7 Tracker external interfaces Table 8 Tracker to Optical Payload interfaces (refer Figure 10) Table 9 Internal Interfaces Table 10 Coordinate system Table 11 Maximum errors Table 12 Tracker speed Table 13 Tracker accuracy Table 14 Structural dynamics Table 15 Structural deflections: static Table 16 Structural deflections: dynamic Table 17 Orthogonality of Axes : After correction by mount model Table 18 Orthogonality of Axes : Manufacturing Table 19 Normal Operational Environment Table 20 Marginal Operational Environment Table 21 SALT Survival Operating Environment Table 22 : SALT Efficiency Table 23 Part identification Table 24 Tracker major components Table 25 Verification cross-reference Matrix (TBD21) SALT-1510AS0001Draft Page 9 of 65

10 1 Scope 1.1 Identification This document specifies the requirements for the Tracker system of the Southern African Large Telescope. 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 statements are 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 the telescope focal plane from where it will proceed into an optical instrument while tracking the relative movement of the target across the sky to maximise exposure time. The SALT system comprises of the subsystems as depicted in Figure 1 below: 1000 Telescope System 1100 Facility 1300 Dome 1500 Tracker & Payload 1700 TCS 1200 Telescope Structure 1400 Primary Mirror 1600 Commissionin g Instrument 1510 Tracker Figure Payload SALT Subsystems This specification will focus on the Tracker as numbered 1510 in the breakdown of Figure 1. Figure 2 and Figure 3 below are schematic representations of the internal layout of the telescope, the facility and dome SALT-1510AS0001Draft Page 10 of 65

11 Tracker & Payload Structure Primary Mirror & Truss Air bearings Azimuth Pier Main Instrument room Figure 2. SALT Pier, structure, primary mirror and tracker SALT-1510AS0001Draft Page 11 of 65

12 Figure 3. Facility and Dome 2 Referenced documents SALT DB 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 1994 HET Tech Report #44 HET Error Budget, April 94 Keck Visit Report Science with SALT, DAH Buckley, March 1998 SPIE proceedings (various) SALT-1000AS0028 Specification for the SALT Fibre-Feed System (TBC1) SALT-1000AS0029 Specification for the SALT Prime Focus Instrument (TBC1) SALT-1000AS0027 SALT External Interface Control Dossier (TBC1) SALT-1000AS0013 SALT Electrical Interface Control Dossier (TBC1) SALT-1000AS0014 SALT Physical Interface Control Dossier (TBC1) SALT-1000AA0030 SALT Safety Analysis (TBC1) SALT-1000AS0031 SALT Axes and Calibration definition (TBC1) SALT-1000AA0017 SALT Error Budget (TBC1) SALT-1000BS0021 SALT Requirements for Built-in Testing (TBC1) SALT-1000BS0010 SALT Software Standard (TBC1) SALT-1000BS0011 SALT Computer Standard (TBC1) SALT-1510AS0001Draft Page 12 of 65

13 SALT-1000AS0032 SALT-1000AS0033 SALT Electrical Requirements (TBC1) SALT Report of Interim Project Team, April 1999 SALT Support Requirements (TBC1) Applicable South African Building and Construction Standards Applicable South African Legal Requirements (TBC1) Safety, Health and Environment Act SALT-1510AS0001Draft Page 13 of 65

14 3 Customer Furnished Equipment and Responsibilities There shall be no customer furnished equipment in the tracker system SALT-1510AS0001Draft Page 14 of 65

15 4 Functional Requirements 4.1 Main purpose The purpose of the Tracker Subsystem in SALT is to carry and position the Optical Payload in the required position and orientation so that the collected light from the Primary Mirror can enter the SAC and optical instrumentation in such a way that the image quality capability of these subsystems will not be affected more than specified. This position and attitude requirement encompass 6 independent degrees of freedom, which will be implemented by 10 dependent degrees of freedom. The Tracker will be supported by the Telescope Structure at the nominal position of half the radius of curvature of the Primary Mirror. The Telescope Structure will support all the interfaces of the Tracker with the rest of the SALT System. The total mass to be supported by the Tracker, inclusive of its own weight, will nominally be 4500kg. The mass of the Optical Payload will nominally be 750kg. The required nominal linear and angular position accuracies are 6 microns and 0.1 arc seconds respectively. The following figure illustrates the structural components of the tracker and their relationship to the Telescope Structure. SALT-1510AS0001Draft Page 15 of 65

16 Figure 4. Tracker on Top Hex The coordinate system in which the tracker motions are described is called the Ideal Tracker Frame (ITF) and is defined in Figure 5 below. A detailed description of all coordinate systems is given in SALT-1000AS0031: SALT Axes and Calibration definition, listed in Section 2. Figure 5. Tracker Coordinate System (ITF) In operation on SALT, the Tracker will perform the following actions when commanded to a particular target in the sky: a) Slew to an X,Y,Z location corresponding to the instantaneous celestial position of the target in the focal surface b) The payload will be positioned in q,f to align with the normal of the primary mirror at that point c) The value of r rotation on the sky will be chosen depending wether the target is an extended or point source d) A computing mount model will drive all six independent axes along the desired trajectory, correcting for inherent tracker errors(way straightness variations, Beam sag etc) e) When trajectory is complete, the tracker shall stop all motion unless a new preloaded trajectory is available. The Tracker subsystem will be under command from the TCS. The user interface on the Tracker Computer must be duplicated at TCS level. The user interface on both systems must at all times present the same information and system status. 4.2 Functional definition The main functional objectives of the Tracker subsystem are: SALT-1510AS0001Draft Page 16 of 65

17 a) Closed Loop Tracking: Tracker position is corrected based upon the input from an optical guide star. The different axes will be closed loop controlled based upon local sensor measurements. b) Open Loop Tracking: Tracker position is adjusted according to operator selected sidereal rate. The different axes will be closed loop controlled based upon local sensor measurements. c) Pointing: The tracker is positioned at any location and attitude in its travel range, as selected by operator The following major functions have to be performed by the Tracker Subsystem to achieve the main functional objectives as stated above: _ Communication _ with other SALT subsystems (TCS Payload Computer) _ with other Tracker subsystems (Axes Controllers, Sensors) _ Algorithm Execution _ Mount Model (Coordinate Transformations) _ Mode and State Control _ Diagnostics & Safety etc _ Man Machine Interface (MMI) _ Axes Control : Tracking of commands to all axes _ Payload Alignment Sensing (to maintain orthogonality to primary mirror) _ Thermal Control : Ensure that all surface temperatures and heat generation in light path are within specification _ Gravity compensation: To alleviate the effect of gravity on drive systems _ Structural support A detailed functional flow diagram is presented in Figure 7. The following predefined positions shall be selectable from Manual and Automatic Modes: PARK - at Vertex of Primary Mirror MAINTENANCE Most accessible position PM - ALIGN LEFT For Alignment of Left half of Primary Mirror PM - ALIGN RIGHT For Alignment of Right half of Primary Mirror DOME_CRANE Best position to access with Dome Crane 4.3 Major Control Functions Subsystem modes, States and Events The operation of the tracker system has been divided into distinct modes. Each Mode is subdivided into a number of States. Transitions between Modes and States are triggered by Events. SALT-1510AS0001Draft Page 17 of 65

18 10 11 Standby OFF Shut Down 12 8 Error 9 14 Initialise 6 7 Ready 2 3 Automati c 5 4 Manual Figure 6. System modes Table 1 Description of System Modes Mode Description States Off Power to Tracker Computer is switched off subsystems switched of Standby Power to all subsystems switched off. The Tracker computer switches power to all the subsystems except itself. In this state the Tracker Computer is running. Initialise Tracker Computer powers up all subsystems of Tracker and homes all sensors : Zero all commands to actuators Check system Health (sensor readings) Do Homing Go to PARK position(tbd1) Initialisation Health Check Manual Homing Automatic Homing SALT-1510AS0001Draft Page 18 of 65

19 Ready Manual Automatic Error Shutdown The Tracker is actively maintained in PARK position (TBD1): Perform Position Control (low accuracy) Report commanded & feedback values (positions, velocities, motor currents, temperatures) Report System Health Manual commands to Tracker via Tracker computer terminal/keyboard or TCS & Feedback to terminal and TCS 1.Tracker moves and start tracking automatically under local or TCS command with preconditions: Target position received Structure position confirmed Safety green status 2. If under TCS control, receive trajectory commands. 3. Perform closed loop guidance if corrections received, otherwise guide open loop 4. Reports commands, feedback & health to terminal and TCS Any errors, which prevent tracker functions being executed, will put the tracker system in this mode. Sensor readings and status reporting will continue in this mode. Depending on the error commands to actuators might be zero and closed loop position control ceased. In this mode error reporting must be sufficient to guide the telescope operator to the source of the problem. This mode is the opposite of power up and the following actions will be performed: Move system to PARK position Zero all commands to actuators Check system Health Switch power off Axes Commands (Position & Slew) Slew to Position Track - Open Loop Track - Closed Loop Calibration Pre_Def Position Position Input Slew to Position Track Open loop Track Closed loop Pre_Def Position Power Up Stand By Manual Automatic Table 2 Description of Mode Transition Events SALT-1510AS0001Draft Page 19 of 65

20 EVENT From Mode To Mode SENSOR/INPUT 1 OFF INITIALISE Button Tracker Computer 2 INITIALISE READY Software Switch On successful power up 3 READY MANUAL Button Tracker Computer 4 MANUAL READY Button Tracker Computer Or Error Condition 5 READY AUTOMATIC Button Tracker Computer 6 AUTOMATIC READY Button Tracker Computer Or Error Condition 7 READY SHUTDOWN Button Tracker Computer 8 READY ERROR Error Conditions 9 ERROR READY Errors Cleared and if state was entered from STANDBY 10 SHUTDOWN OFF Button Tracker Computer 11 SHUTDOWN ERROR Error Conditions 12 ERROR SHUTDOWN Errors Cleared and if state was entered from SHUTDOWN or POWER UP 13 INITIALISE ERROR Error Conditions 14 ERROR INITIALISE Errors Cleared and if state was entered from POWER UP 15 OFF/STANDBY STANDBY/OFF Power Switch Functional Flow Diagram PAYLOAD COMPUTER Tracker Computer Comms TRACKER TRACKER COMPUTE 1.1 Ethernet TCS Comms Payload Computer Comms 1. COMMS 1.2 RS Payload Alignment Comms 1.2.2Thermal Control Comms Time SALT-1510AS0001Draft Page 20 of 65

21 1.1.3 Axes Controllers Comms 1.2.3Power Switches Comms 1.2.4Gravity Comp Comms 2.1Power Up 2.2Shutdown 2.3Time Synchronization 2.4Tracker Mount Model 2.TRACKER ALGORITHMS 2.5Guidance Corrections 2.6Axes Command Generator 2.7Orthogonality Corrections 2.8T 2.9M 2.10D 2.11S 3. TRACKER MMI Figure 7. Tracker Functional Flow Diagram Function descriptions All the functions identified in Figure 7 are discussed below. The relationship between the dependent and independent degrees of freedom (D.O.F.) are as follows: Table 3 Degrees of freedom INDEPENDENT D.O.F. DEPENDENT D.O.F. X XL, XU (upper and lower x) drives Y Y drive Z H1 to H6 (hexapod legs),q H1 to H6 (hexapod legs) f H1 to H6 (hexapod legs) r Rho stage TCS COMMUNICATION The TCS shall send the following commands to the tracker computer: Request Tracker Computer MMI and Data (full control at TCS level Operating System Function) Mode & State Commands SALT-1510AS0001Draft Page 21 of 65

22 Trajectory Commands (t,x,y,z,q,f,r) every 30 seconds with 100ms time-steps (TBC2). These commands are in the IDEAL TRACKER FRAME(ITF) Acquisition Offset Command (t,dx,dy) at 10Hz Thermal Control Set points at 0.01Hz Safety Commands (Emergency Stop etc) at 10 Hz (TBC3) The Tracker Computer shall send the following information back to TCS: MMI Screens (TCS will have access to Tracker computer MMI with full functionality of MMI Operating System Function) Current Mode & State at 10Hz Calculated Trajectory position (t,x,y,z,q,f,r) in ITF at 10Hz Temperature measurements for set points at 1Hz Payload Alignment Sensor Measurements (t, q,f,range) in ITF at 10Hz Diagnostics and Safety Status (TBD3) Individual Actuator positions, time stamped (x10) PAYLOAD COMPUTER COMMUNICATION The Tracker Computer/TCS (TBD4) shall send the following commands to the payload computer: _ Moving Baffle position commands _ Guidance probe position commands _ ADC rotation command The Payload Computer shall send the following information to the Tracker Computer: Guidance Errors (t,dx,dy) in ITF at a frequency of 1Hz (TBC4) AXES CONTROLLERS COMMUNICATION The Tracker Computer shall send the following information to the Axes Controllers: Axes Commands(t,XL,XU,Y,h1,h2,h3,h4,h5,h6, r) at frequency of 10Hz TBC5. Mode Commands (Slew / track /emergency stop) at 10 Hz Predefined Positions and Commands whenever required The Axes Controllers shall send the following information to the Tracker Computer: Sensor Measurements (t,xl,xu,y,h1,h2,h3,h4,h5,h6, r,skewing) at 10Hz Current Modes at 10Hz Calculated Position Errors(t,XL,XU,Y,h1,h2,h3,h4,h5,h6, r,skewing) at 10Hz Measured Motor Currents at 10Hz PAYLOAD ALIGNMENT COMMUNICATION The Tracker Computer shall send the following information to the Payload Alignment Sensors SALT-1510AS0001Draft Page 22 of 65

23 _ Commands for set up / calibration (Fixed set of commands as available) The Payload Alignment Sensors shall send the following information to the Tracker Computer: _ Sensor Measurements (t, q,f,range) (TBC6) at 10Hz THERMAL CONTROL COMMUNICATION The Tracker Computer shall send the following information to the Thermal Control Analogue Output Commands for Valves (xn) at 0.01Hz (TBD2) The Thermal Control Analogue Output shall send the following information to the Tracker Computer: Temperature Measurements (xm) at 0.1Hz (TBD2) POWER SWITCHES COMMUNICATION The Tracker Computer shall send the following information to the Power Switches Digital Output _ On/Off Commands for Switches [Axes Controller(x10),Payload Alignment Sensors(x1),Thermal Control(x1), Gravity Compensation(x1)] (TBC7) TIME SYNCHRONIZATION INPUT The TCS and Tracker Computer shall be time synchronized to an accuracy of 10ms (TBC8) TRACKER ALGORITHMS Power Up Shut Down The execution of all Tracker Computer functions should be sufficiently fast as to ensure a cycle time of 100ms or less. The Tracker System shall be powered up and sensors homed in a controlled fashion The Tracker System shall be parked and shut down in a controlled fashion Time Synchronization The Tracker Computer local time shall be synchronised with the TCS computer as specified in SALT-1510AS0001Draft Page 23 of 65

24 Tracker Mount Model This model defines : a conversion to convert from the TCS commands (t,x,y,z,q,f,r) to a Tracker equivalent set (t,x e,y e,z e,q e,f e,r e ), both in ITF. A conversion to convert to Hexapod Frame(HPF) Defines calibration factors and coefficients Rotation point of Payload Correction table for decenters,tip & tilt mounting of payload as a function of rho Guidance Corrections These conversion takes into account the orthogonality of the various tracker axes, structural deflections and sensor mounting errors A set of guidance errors (t,x guid,y guid,z guid,q guid,f guid,r guid ), in ITF, is calculated from the guidance input (t,dx,dy) Orthogonality Corrections A set of of Payload position errors(t,x guid,y guid,z guid,q guid,f guid,r guid ), in ITF, is calculated from the input(t,,q,f,range) Axes Command Generator Using the results from above the commands to XL, XU, Y, H1, H2, H3, H4, H5, H6, r are calculated. The feedback from the axes controllers is used to calculate the measured position in ITF(t,x m,y m,z e,q m,f m,r m ) Thermal loop Close the thermal control loops to ensure temperature errors of less than 1 degree C.(TBD2) Mode and State Control Control the modes and states of the Tracker sub system Diagnostics & Safety Performs all diagnostics and safety functions. (TBD3) Software Set up & Maintenance Performs all set up and maintenance functions: Log real time data to disk for analysis Save/retrieve Calibration Data Save/retrieve software set up SALT-1510AS0001Draft Page 24 of 65

25 TRACKER MAN-MACHINE-INTERFACE (MMI) Implements the MMI (TBD5) AXES CONTROL Implements the mode commands and track the position commands. The X and Y Drives shall be dual drives, one for slewing and one for tracking. Skewing of the X-Drives shall be controlled actively. Axes control shall satisfy the requirements in paragraph PAYLOAD ALIGNMENT SENSORS The attitude and position of the payload relative to the primary mirror shall be measured in real time to satisfy the requirements in paragraph THERMAL CONTROL This function implements the valve commands from the Tracker computer and reads the temperature sensors. The combined thermal control and thermal loop functions shall satisfy the performance requirements in paragraph POWER SWITCHES This function implements the relay commands from the Tracker computer. This function shall satisfy the performance requirement in paragraph GRAVITY COMPENSATION This function implements the relay commands from the Tracker computer. This function shall satisfy the performance requirement in paragraph STRUCTURAL SUPPORT The tracker subsystem shall provide sufficient structural support to carry all the relevant tracker components and Optical Payload at the primary mirror focal surface. This structure will be supported by the top hex of the telescope structure. This support shall satisfy the performance requirements in paragraph Operational Concept Closed and open loop tracking, and pointing, will be executed as follows: Table 4 Closed loop tracking No Action Start Time Frequency Remarks 1. Star position input by SA, SO single position or scheduled positions on TCS terminal Acquisition time 3 minutes minimum Once per target Star position: RA,DEC,Epoch Time SALT-1510AS0001Draft Page 25 of 65

26 2. Acquisition and Tracking start times and Observation Duration for each target input by SA on TCS terminal 3. TCS send Acquisition and tracking start times and position to Tracker computer 4. Tracker and Payload slewed to position in 3 5. Tracker computer reports to TCS when in position 6. TCS send trajectory commands(x,y,z,q,f,r) to Tracker Computer 7. Tracker executes commands in Target and Guid Stars selected by SA on TCS terminal 9 Payload Computer sends correction signals to Tracker computer (x,y corrections) 10. Beyond track start time closed loop tracking, if no correction signals from payload open loop tracking Table 5 Open Loop Tracking. Acquisition time 3 minutes minimum Acquisition time 2.5 minutes minimum Immediately after 3. Acquisition Time 30 seconds Immediately after 5. According to time stamp of commands Any time between Acquisition and track start time When locked on guid star/s Start of Track Once per target Once per target Once per target Once every 30 sec Continuously (at sampling frequency of axes controllers) Once per target 1Hz Continuously (at sampling frequency of axes controllers) Time available between Acquisition and Track must be variable by RA Open loop commands Controllers should interpolate commands between trajectory points Controllers should interpolate commands No Action Start Time Frequency Remarks 1. Star position input by SA,SO single position or scheduled positions on TCS terminal Acquisition time 3 minutes minimum Once per target Time 2. Sidereal Rate selected by SA,SO 3. Acquisition and Tracking start times and Observation Duration for each target input by SA on TCS terminal 4. TCS send Acquisition and tracking start times and position to Tracker computer Acquisition time 3 minutes minimum Acquisition time 3 minutes minimum Acquisition time 2.5 minutes minimum Any time Once per target Once per target Star position: RA,DEC,Epoch RA can adjust sidereal rate Time available between Acquisition and Track must be variable by RA SALT-1510AS0001Draft Page 26 of 65

27 position to Tracker computer 5. Tracker and Payload slewed to position in 3 6. Tracker computer reports to TCS when in position 7. TCS send trajectory commands(x,y,z,q,f,r) to Tracker Computer 8. Tracker executes commands in 6. minimum Immediately after 3. Acquisition Time 30 seconds Immediately after 5. According to time stamp of commands Once per target Once every 30 sec Continuously (at sampling frequency of axes controllers) Open loop commands Controllers should interpolate commands between trajectory points Table 6 Positioning. No Action Start Time Frequency Remarks 1. Star position or Tracker Any time Continuously Position in ITF Position input by SA,SO on TCS or Tracker Computer terminal 2. Tracker and Payload slewed to position in 3 Immediately after Tracker computer reports to TCS when in position When position reached Once per target SALT-1510AS0001Draft Page 27 of 65

28 5 Tracker Technical Requirements 5.1 Schematic diagram The figure below shows the major components of the tracker subsystem and the communication interfaces. The numbers inside each block identifies the functions, in Figure 7, implemented by each hardware item Telescope Control System Key : Not Part of TRACKER Payload Computer System Tracker Computer System Telescope Structure X-Drive System(2x) (4) Y-Drive System (4) Cable & Tube Handlers, Enclosures Hexapod System Tip,Tilt,Piston (4) Gravity Comp (8) Beam(9) (9) Carriage (9) Rho-Drive System (4) Thermal Control (6) Payload - Structure Payload Alignment (5) Figure 8. Major Components of Tracker Subsystem and Communication interfaces All the internal interfaces between the Tracker subsystem components and external interfaces between Tracker subsystem and other subsystems of SALT are shown and numbered in the figure below. 5.2 SALT Tracker Interfaces SALT Tracker External Interfaces Figure 9shows the major External interfaces for SALT. SALT-1510AS0001Draft Page 28 of 65

29 External Services 19 1 Structure 2 Facility 3 Tracker & Payload Dome Commissioning Instrument Key to interfaces: 11 Cooling (C) Physical (P) Data (D) Optical (O) Air (A) Electrical (E) Ventilation (V) Primary Mirror 12 Science Instruments TCS Figure 9. Schematic showing SALT Tracker External Interfaces The system interfaces shall comply with the Physical, Electrical and External Interface Control Dossiers referred to in Section 2 Table 7 Tracker external interfaces No. Subsystem Subsystem 2 Type Direction Interface Description 1 8 TCS Tracker r D Both Communication cables, Trajectory Commands, Mode Commands, Measurement Feedback, Diagnostics and Safety Feedback, Tracker MMI 2 Structure Tracker P Upper and Lower X-Drive physical attachment at top hex ; Attachment of all cables, cooling lines, fibre optic cables running between Tracker & Payload and other sub systems SALT-1510AS0001Draft Page 29 of 65

30 3 Facility Tracker P -> Tracker E A other sub systems Provide Access to Tracker Electrical power to various parts of tracker, as per Power Budget. Both 220V and 110V AC Dry Air to Linear Bearings and Roller Screws Liquid cooling capacity : (TBD6) C 4 Tracker Primary Mirror O Optical alignment signal Table 8 Tracker to Optical Payload interfaces (refer Figure 10) e4 Payload Computer Tracker Computer D -> Tracker Network cable Guidance Corrections Moving Baffle Position Command Guidance Probe Command ADC rotation Command E Electrical power to various parts of tracker, as per Power Budget. Both 220V and 110V AC A Dry Air to Linear Bearings and Roller Screws e5 e6 e7 e7 Payload Structure Payload Structure Payload Structure Payload Structure C Liquid cooling capacity : (TBD6) Rho Drive P Both Mounting on rotation stage bolted E Electrical Connections for Data, Power, Video Cables A Connections O Connections C Connections Payload P Both Mounting of sensors - Bolted Alignment E Electrical Connections for Data, Power Tube & Cable P Both Mounting of Rotation handler - Handler Bolted Tube & Cable Handler E Electrical Connections for Data, Power, Video Cables A Connections O Connections C Connections P Both Mounting of Rotation handler - Bolted E Electrical Connections for Data, Power SALT-1510AS0001Draft Page 30 of 65

31 5.2.2 SALT Tracker Internal Interfaces Telescope Control System (TCS) Not Part of TRACKER INTERFACES e** : external ** : internal e1 1 Thermal Control 9 All tracker subsystems e2 e3 e4 Tracker Computer XU -Drive System XL -Drive System Y-Drive System Hexapod System (Tip,Tilt,Piston) Rho-Drive 8 System Payload Alignment e5 e6 Tracker Beam 15 Payload STRUCTURE Carriage e7 Tube & Cable Handlers & Enclosures SALT-1510AS0001Draft Page 31 of 65

32 Figure 10. Interfaces For a complete description of all the interfaces, refer to the interface control dossier, listed in section 2 Table 9 Internal Interfaces 1,2, 3,4, 5,6, 7 See Fig Tracker Computer D Both Electrical Connections for Data, Power Commands Feedback 8 Hexapod Rho Drive D Both Rho drive bolted to Hexapod top plate 9 Thermal All Tracker D TBD2 Control Subsystems E TBD2 A TBD2 C TBD2 10 XU-Drive Tracker Beam P Beam Bolted to bearing slides via slide bearing 11 XL-Drive Tracker Beam P Beam Bolted to bearing slides 12 Y-Drive Tracker Beam P Drive Mount 13 Y-Drive Carriage P Drive Mount 14 Hexapod Carriage P Struts Mount 15 Beam Carriage P Carriage Bolted to bearing slides, one side via slide bearing 16 Cable & Tube Handlers Tracker Beam P Handler Bolted to beam for Y motion; Handlers mounted to XU and XL Drive assemblies for X- motion E Connectors A Connectors D Connectors O Connectors 17 Cable & Tube Handlers Carriage C D E A O C Connectors Connectors Connectors Connectors Connectors Connectors 5.3 SALT Tracker Characteristics Performance Characteristics The tracker system characteristics that are required to perform the functions above are described SALT-1510AS0001Draft Page 32 of 65

33 below: MOTION RANGES The coordinate system used below is the Ideal Tracker Frame(ITF). Table 10 Coordinate system No Axis(ITF) Units Range + Tolerance - Tolerance a X mm b Y mm c Z mm d q, about Y deg e f, about X deg f r, about Z deg Any combination of these motions must be achievable. Figure 11. View of tracker on upper hex MOTION SYMMETRY The Ranges in are symmetrically spaced about the ITF Origin with the following maximum errors: Table 11 Maximum errors No Axis(ITF) Units + Tolerance - Tolerance a X mm SALT-1510AS0001Draft Page 33 of 65

34 b Y mm c Z mm 2-2 d q, about Y deg e f, about X deg f r, about Z deg SPEED The coordinate system used below is the Ideal Tracker Frame(ITF). Table 12 Tracker speed No Axis(ITF) Units Min Speed Max Speed (+ or -) + Toler ance - Tole ranc e i SLEWING a X mm/s b Y mm/s c Z mm/s d q, about Y deg/s e f, about X deg/s f r, about Z deg/s ii TRACKING a X mm/s b Y mm/s c Z mm/s d q, about Y asec/ s e f, about X asec/ s f r, about Z deg/s ACCURACY (TBC9) Table 13 Tracker accuracy No Axis(ITF) Units RMS Error Max Error i POSITION 1 SLEWING a X mm b Y mm c Z mm d q, about Y deg e f, about X deg SALT-1510AS0001Draft Page 34 of 65

35 f r, about Z deg g Skewing mm TRACKING a X mm b Y mm c Z mm d q, about Y asec 1 2 e f, about X asec 1 2 f r, about Z asec 1 2 g Skewing mm STEADY STATE POINTING a X mm b Y mm c Z mm d q, about Y asec e f, about X asec f r, about Z asec g Skewing mm ii SPEED 1 SLEWING a X mm/s b Y mm/s c Z mm/s d q, about Y asec/s e f, about X asec/s f r, about Z asec/s TRACKING a X mm/s b Y mm/s c Z mm/s d q, about Y asec/s e f, about X asec/s f r, about Z asec/s THERMAL CONTROL ACCURACY AND HEAT DUMPING (a) Control accuracy better than 1 deg C from set points (b) All surface temperatures that can rise more than 2 degrees C above ambient shall SALT-1510AS0001Draft Page 35 of 65

36 be actively controlled CONTROL LOOP REQUIREMENTS SAFETY All Control loops shall satisfy the following stability requirements under all loading conditions: Phase margin: > 50 degrees Gain Margin: > 8dB Maximum Overshoot : < 2% Maximum Bandwidth x- Axis < 1Hz Maximum Bandwidth y- Axis < 2Hz Maximum Bandwidth z- Axis < 2Hz Maximum Bandwidth q - Axis < 2Hz Maximum Bandwidth f - Axis < 2Hz Maximum Bandwidth r - Axis < 2Hz Settling time (TBD7) The following should be read in conjunction with the SALT Safety Analysis, SALT- 1000AA0030, listed in section 2 All single point failures that can lead to loss of life, serious injury to personnel or damage to equipment shall be identified and the design modified to prevent such failures. In no case shall it be possible for a component or control system failure to cause the tracker beam to disengage the X ways or for any other component or piece to detach and drop from the Tracker Assembly. Motor overload protection, fusing and sensing shall be implemented and monitored by the control system to ensure that failure mode criteria are met. Beam skew protection shall be independent of encoder measurements which shall initiate system breaking and shutdown for skew in excess of 0.75mm from nominal. Beam skew protection shutdown shall stop both ends of Tracker Beam within a maximum travel of 50mm from full slew speed,not increasing skewing by more than 20mm and within 5mm from maximum tracking speed,not increasing skewing by more than 3mm. Where tools must be used on-telescope for servicing and maintenance, they shall be secured by lanyards to the servicer s tool belt or manlift. All fasteners, cover panels and other components which can be accessed while the tracker is on telescope shall be captivated by the use of _ turn captured fasteners, wire loop, bails, threads or some other like means to prevent accidental injury to personnel below as well as damage to primary mirror. No lock washers shall be used for on-telescope accessible fasteners, chemical locking compounds or aircraft-type locking nuts shall be used instead. A safety analysis and design shall be presented and implemented to satisfy all safety requirements STRUCTURAL FREQUENCIES (TBC10) The following frequencies apply to the tracker beam with payload integrated and positioned at the centre of the beam. Table 14 Structural dynamics SALT-1510AS0001Draft Page 36 of 65

37 Degree of Freedom (ITF) Mode Minimum Frequency [Hz] X 1 10 Y 1 10 Z 1 10 Rotation about X 1 10 Rotation about Y 1 7 Rotation about Z STATIC STRUCTURAL DEFLECTIONS (TBC11) The following maximum deflections of the Tracker beam under its own weight and a steady state wind force of 50kg, with the payload installed, shall be allowed. The payload position shall be at the centre of the beam and the orientation of the payload can be anywhere within the operational envelope. The action point of the wind force is maximally 500mm (TBC12) above the Tracker Beam(ie Z=-500mm in ITF) and can be directed along X and Z. Table 15 Structural deflections: static Degree of Freedom Units (ITF) X um 100 Y um 100 Z um 5000 Rotation about X arcsec 10 Rotation about Y arcsec 10 Rotation about Z arcsec 10 Maximum Displacement DYNAMIC STRUCTURAL DEFLECTIONS The following maximum deflections of the Tracker beam under dynamic forces such as wind and control system induced, shall be allowed. The payload position shall be at the centre of the beam and the orientation of the payload can be anywhere within the operational envelope. The varying component of the wind shall be less than 20kg, at the same action point as in The frequency of the wind force is less than 1 Hz. Table 16 Structural deflections: dynamic Degree of Freedom Units (ITF) X um 10 Y um 10 Z um 10 Rotation about X arcsec 1 Rotation about Y arcsec 1 Rotation about Z arcsec ORTHOGONALITY OF AXES : (TBC13) Maximum Displacement SALT-1510AS0001Draft Page 37 of 65

38 Table 17 Orthogonality of Axes : After correction by mount model Axes (ITF) Units Value XY arcsec 1 XY Plane and Z axis arcsec 1 Rotation about Y, non parallelism arcsec 1 of rotation axis and Y-Axis Rotation about X, non parallelism arcsec 1 of rotation axis and X-Axis Rho rotation, non parallelism to Z arcsec 1 Axis Rho Rotation Axis offset from Z Axis um 2 Table 18 Orthogonality of Axes : Manufacturing Axes (ITF) Units Value XY arcsec 200 XY Plane and Z axis arcsec 200 Rotation about Y, non parallelism arcsec 200 of rotation axis and Y-Axis Rotation about X, non parallelism arcsec 200 of rotation axis and X-Axis Rho rotation, non parallelism to Z arcsec 200 Axis Rho Rotation Axis offset from Z Axis um 20 The purpose of this specification is to ensure that the operating envelope of tracker is not skewed unlimited ROTATION POSITION OF PAYLOAD (TBC14) (a) The Payload shall be rotated (q,f) nominally about the paraxial focus of the primary mirror. This translates to a rotation point in ITF of X=0,Y=0,Z=800mm (b) The rotation point should be variable with mm about the nominal position MAXIMUM ACCELERATION AND JERK (TBD8) ADDITIONAL SEARCH SPEEDS (TBD9) FORCES IN HEXAPOD STRUTS The struts shall be designed, positioned and actuated such that the force in any strut never changes direction. SALT-1510AS0001Draft Page 38 of 65

39 TRAVEL LIMITS (TBD10) PAYLOAD ALIGNMENT (TBD11) TRACKER MMI (TBD5) Physical Characteristics OBSCURATION MASS Tracker Shadow on Primary mirror : On - Axis < 3m deg Off - Axis < 5m 2 The total tracker mass shall be less than 3750kg (TBC15) The payload mass shall be less than 750kg (TBC16) MAXIMUM SURFACE TEMPERATURES Any gradient in the air temperature within the optical path will have a negative influence on the image quality produced by SALT. In order to minimise this effect, the following constraints are imposed. Relaxation of these constraints may be allowed on a case-bycase basis, subject to meeting the overall seeing objectives. {These values are all (TBC20)} Section 5.5 provides further guidance in this regard Objects in the optical path All items of equipment that are within 1m of the telescope optical path or within a vertical cylinder defined as a vertical extension of the pier to the highest point of the top hex, shall comply with the following: a. No item exposed to the ambient air, regardless of its size, shall have a surface temperature of more than 8ºC above ambient. b. No item having forced-air cooling shall blow the exhausted air into the ambient air. c. Items with a surface temperature of more than 2ºC above ambient shall have a Thermal Factor (TF) of less than 0.6 m 2 C, where TF is defined as follows: TF = A T SALT-1510AS0001Draft Page 39 of 65

40 Where A = Exposed surface area of the item in m 2 _T = Temperature difference between the items exposed surface and the ambient air temperature in ºC NOTE: In practice, these constraints mean that many items may require cooling jackets or cooled enclosures. As an example, an item measuring 0.4x0.4x0.4m emitting more than about 4W of heat continuously, will need to be insulated and cooled otherwise its surface temperature will go above the allowed limit Objects outside the optical path All items of equipment that are within the telescope chamber but not included in shall comply with the following: a. No item exposed to the ambient air, regardless of its size, shall have a surface temperature of more than 8ºC above ambient. b. No item having forced-air cooling shall blow the exhausted air into the ambient air. c. Items with a surface temperature of more than 3ºC above ambient shall have a Thermal Factor (TF) of less than 2 m 2 C (with TF defined in ). d. Large areas such and the floor and azimuth pier must not have a heat transfer coefficient of more than 3W/m 2 K. NOTE: In practice, these constraints mean that many items may require cooling jackets or cooled enclosures. As an example, an item measuring 0.4x0.4x0.4m emitting more than about 6.5W of heat continuously, will need to be insulated and cooled otherwise it s surface temperature will go above the allowed limit MINIMUM SURFACE TEMPERATURES Any gradient in the air temperature within the optical path will have a negative influence on the image quality produced by SALT. In order to minimise this effect, the following constraints are imposed. Relaxation of these constraints may be allowed on a case-bycase basis, subject to meeting the overall seeing objectives. These constraints shall be met for the 98 th percentile of operation ambient conditions {these values are all (TBC20)} Section 5.5 provides further guidance in this regard Objects in the optical path All items of equipment that are within 1 meter of the telescope optical path or directly above the primary mirror, shall comply with the following: a. No item exposed to the ambient air, regardless of its size, shall have a surface temperature cooler than 2ºC below ambient to prevent condensation on surfaces. b. No item shall blow exhausted cool air into the ambient air Objects outside the optical path SALT-1510AS0001Draft Page 40 of 65

41 All items of equipment that are within the telescope chamber but not included in shall comply with the following: a. No item exposed to the ambient air, regardless of its size, shall have a surface temperature cooler than 3ºC below ambient. b. No item shall blow exhausted cool air into the ambient air COMPONENT/MODULE REPLACEMENT All major components that might need removal, must provide for interfaces suitable for using the dome crane as lifting device. Any special lifting or handling fixtures for modules by their nature or orientation require such fixtures for safe lifting and positioning PAYLOAD CLEARANCE AND ENVELOPE (TBD12) Environmental Requirements NORMAL OPERATIONAL ENVIRONMENT SALT shall meet all the requirements specified in this document when operated in the nighttime outside ambient condition defined in Table 19 below: Table 19 Normal Operational Environment Parameter Value Notes Minimum Temperature -5ºC Maximum Temperature 20ºC Maximum nightly temperature range 8ºC TBC21 Maximum rate environment cooling -1.5ºC/h Maximum rate of environment warming +0.5ºC/h Estimated value Minimum Humidity 5% Maximum Humidity 97% Non-condensing Maximum wind velocity 16.8 m/s Gusts up to 22 m/s TBC17 Site altitude 1798m Solar radiation 0 W/m 2 Twilight to dawn MARGINAL OPERATIONAL ENVIRONMENT The degradation of system performance as a result of the ambient environment specified in Table 20 below, shall not exceed 10% (TBC18) of the nominal values in paragraph Table 20 Marginal Operational Environment Parameter Value Notes Minimum Temperature -10ºC Maximum Temperature 25ºC SALT-1510AS0001Draft Page 41 of 65

42 Maximum rate environment cooling -2.0ºC/h Maximum rate of environment warming +1ºC/h Estimated value Minimum Humidity 5% Maximum Humidity 97% Non-condensing Maximum wind velocity 21 m/s Gusts up to 25 m/s (TBC17) Solar radiation 0 W/m 2 Twilight to dawn SURVIVAL ENVIRONMENT SALT shall survive when exposed to the day or night ambient environment specified in Table 21 below. Note that the dome and louvers will be closed under these conditions. Table 21 SALT Survival Operating Environment Parameter Value Notes Minimum Temperature -20ºC** Maximum Temperature 45ºC** Maximum Humidity 100% Occasional exposure to condensing conditions Maximum wind velocity 61 m/s** Rain Note 1 Snow Note 1 Hail Note 1 Icing Present Low temperatures after condensation or rain are common. Solar Radiation Note 1 Other Note 1 NOTES: 1. Environmental conditions not specified shall be obtained from the appropriate building/civil standards suitable for Sutherland. 2. **: Use the worst case of these figures and those specified in the appropriate building/civil standards. 5.4 Operation and Maintenance Requirements Packaging, handling, storage Packaging, handling and storage requirements will be determined for each individual type of component, taking into account the specific requirements of the component, the method of shipping and interim storage locations. Storage at SALT will be in the SALT Store Room, in dry, air-conditioned conditions. Containers shall be sufficient for one return shipping only, unless otherwise specified Product Documentation The SALT System shall include a set of SALT specific operating instructions, training manuals, maintenance manuals and calibration procedures at system and subsystem level. Component level documentation will be specified on individual basis, within the following guideline: For COTS equipment, the standard manufacturers documentation will be supplied, and no special SALT-1510AS0001Draft Page 42 of 65

43 documentation will be developed. For custom made equipment, a set of documentation will be specified and will form part of the deliverable. All documentation shall be in English Personnel and Training OPERATION MAINTENANCE Availability SALT will be operated from the control room at the telescope. A SALT operator (SO) and a SALT 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 be called by the SO when required. The SO will have a National Diploma (N6/S3) or equivalent qualification in electronic or mechanical engineering or have adequate experience. The SA will be a PhD astronomer. SALT will be maintained by the SAAO staff at Sutherland and Cape Town. Personnel will be trained in the maintenance of SALT, and be granted a SALT license upon completion of training. All maintenance work carried out on SALT will be supervised/signed off by a SALT licensed person. It is anticipated that the following people will be required to maintain SALT: At Sutherland: Mechanical Technician: 2 Electronic Technician: 1 Electrical Technician: 1 In Cape Town: Mechanical Engineer: 1 Electronic Engineer: 1 Software Engineer: 1 These positions should not be SALT only, i.e. these personnel must be part of the SAAO technical staff, who will also work on the other SAAO telescopes. Thus, two Electronic technicians, each working 50% on SALT, can constitute the one full time Electronic Technician listed above. One mechanical and one of the electrical/electronic technician will also required to be on standby during every night of operations. These standby personnel will form part of the normal 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 SCIENCE EFFICIENCY Table 22 below specifies the required SALT efficiency for various operational aspects. SALT-1510AS0001Draft Page 43 of 65

44 The values are percentages of the total time allocated to science, and exclude bad weather, engineering time and instrument commissioning. A Problem Reporting and Corrective Action System (PRACAS) shall be implemented from system testing onwards, to monitor the growth in efficiency to achieve these values after ten years of operation. The HET values shown are for information only, and are the measured average for the period October 1999 to June Some of the values are determined by Instrumentation Efficiency and Operator efficiency, which fall outside the scope of this document. Table 22 : SALT Efficiency Activity Reliability SALT spec CCD exposure and readout 66% 34% Move and set* 20% 29% Instrument Calibration 5% 3% Primary Mirror Alignment 5% 24% Down-time 2% 8% Other 2% 1% TOTAL 100% 100% HET at present The above requirement is expanded into specific numbers for Reliability (allowable Mean Time Between Failures, minimum "up" time, maximum data error rates, allowable "false-alarm" rate) and Maintainability (allowable Mean Time To Repair, specific maintenance provisions to be built into items, Built-in Testing, error logging,) in the document SALT Support Requirements, referred to in Section Tracker Maintainability Tracker down time shall not exceed 0.5% (TBC22 of night time hours 70 tracker traverses per night over a lifetime of 20 years Spares shall be provided for components critical to Tracker operation of which the failure will lead to a downtime of more than 10% of the specification in The design and construction of the tracker shall include the capability of safety jacking the Tracker Beam away from the Telescope Structure to provide sufficient clearance for the removal of either or both X-drive units without physically removing the beam from the structure MEASURES TO ACHIEVE EFFICIENCY All parts requiring regular access will be provided with safe access by means of the elevator, stairs, and walkways. The use of a man-lift and dome-crane will be minimised. Specific access must be provided from the catwalk to and on the tracker bridge, and above and below the optical payload. SALT-1510AS0001Draft Page 44 of 65

45 Subsystems shall be organized into modules for ease of mounting/dismounting and servicing. COTS equipment will be used as far as possible to reduce spares holding requirements. A float level of standard spares (bolts, nuts, wires, oils, grease) will be kept in the SALT Store. 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 to a minimum, and will be provided with each subsystem. All normal maintenance actions will be able to be completed within one working day, unless otherwise specified. Where maintenance actions take more than a day and happen regularly (e.g. primary mirror coating), enough spares will be held to ensure that the operation of the telescope system is not affected. Two (TBC23) standard (metric) tool sets will be available, one in the SALT workshop and one in the telescope chamber. Special tools will be kept to a minimum, and be limited to mirror handling and coating. 5.5 Design and Construction constraints General design guidelines and constraints The following guidelines and constraints apply to SALT (where these general guidelines contradict specific requirements in other parts of this document, the other requirements shall have precedence): a. Every part of SALT that is exposed to direct sunlight will be shielded, have a double wall, and/or be made from a material which has a low thermal inertia. b. The area around the circular telescope building will be disturbed as little as possible (e.g. minimum buildings, paving, levelling), and the natural vegetation will be preserved. c. Preference will be given to material with low thermal inertia and open section (e.g. I-beam rather than tube) for anything above the telescope chamber floor. d. The telescope chamber shall not be heated by adjacent rooms, i.e. any rooms underneath or next door which are heated, shall be thermally isolated from the telescope chamber. e. 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 f. No warm air will be exhausted directly from the building. g. Commercial, off the shelf (COTS) equipment will be used unless specifically stated otherwise. h. All computer hardware will be COTS equipment, using mainstream equipment and vendors. i. Computer operating system and application software will be COTS, using mainstream packages and vendors j. Optical fibres will be used for any digital communications travelling more than 30m k. No artificial light will intrude into the telescope chamber, or outside the building during observation. SALT-1510AS0001Draft Page 45 of 65

46 l. The layout of the building and services, (e.g. fire escapes, light switches, toilets) must be logical and intuitive. m. The Metric measurement system will be used. n. 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 a negative delta being the risk of condensation, damaging mirrors and equipment. o. Stray (star/moon) light should be baffled 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 the spectrum 320 to 2500nm d. All custom components will be marked as follows: Table 23 Part identification SALT Supplier name Product name Product number Serial 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 Electromagnetic Radiation The normal operation of any component or system will not affect the normal operation of any other system or component, or any other equipment at the Observatory at Sutherland., and has to comply with the FCC standards as per Section Workmanship Workmanship specifications will be specified per type of component, but will not be higher than required to fulfil the overall SALT performance specification Interchangeability a. Interchangeability will be maximised by using COTS equipment wherever possible, and SALT-1510AS0001Draft Page 46 of 65

47 exceptions will be specified. b. All primary mirror segments and supports will be interchangeable i.t.o. position on the mirror truss, but mirrors and mirror mounts will be matched Safety SAFETY-CRITICAL FAILURES All single-point failures that can lead to loss of life, serious injury to personnel or damage to equipment shall be identified and the design modified to prevent such failures. A preliminary safety analysis to identify such potential failures is contained in the SALT Safety Analysis referred to in section SOFTWARE SAFETY Where the malfunction of software alone could cause a safety-critical failure, alternate means shall be provided to prevent the occurrence of such a failure. This would typically take the form of electrical interlocks designed in a fail-safe manner SAFE INITIALISATION All systems, when initialising from power-up or when reset, shall be in a safe, non-active state (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) LOCAL ELECTRIC OPERATION A means shall be provided at the relevant electrical panel, to control critical equipment manually, even in the event of a Controller failure. A selection switch on the panel shall select either Automatic or Manual control. The status of this switch shall enable/disable the manual control functions on the panel and shall be reported to the TCS. Critical Equipment is equipment identified in the Safety Analysis document as requiring this function to achieve safe operation (e.g. dome shutter) Ergonomics Comfortable working positions and conditions will be provided at all stations where operators will spend long times regularly during normal operation Special commissioning requirements SUBSYSTEM MMI S There shall be monitors/keyboards plus good human interface SW at the subsystem computers, for use during system commissioning. These controls must include facilities for overriding automatic functions and monitoring of information communicated to/from the TCS. SALT-1510AS0001Draft Page 47 of 65

48 TEST POINTS TEST DATA Means shall be provided to measure electrical signals and interpret data transferred between subsystems and major electronic items within each subsystem. Each subsystem shall send to the TCS the values of all internal variables that may need to be interrogated during commissioning and testing, but would not normally be needed for telescope control by the TCS. A list of typical variables required is provided below, but details will be provided in the SALT Electrical Interface Control Dossier: SPOTTER TELESCOPE Software A small telescope pointing at the sky and aligned parallel to the SAC axis, shall be permanently mounted on the tracker. It shall be fitted with a removable video camera at the eyepiece linked to a monitor in the Control Room. The FOV of this telescope shall be determined prior to commissioning, once its role has been fully defined. Each subsystem shall comply to the requirements defined in SALT Computer Software Standard 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?) Computer Hardware Each subsystem shall comply to the requirements defined in SALT Computer Hardware Standard 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 Electrical Design UPS SALT-1510AS0001Draft Page 48 of 65

49 Installed Capacity Use of UPS power The total installed UPS capacity shall be at least the value indicated in the Power Budget (Appendix C) plus 20%. The following items will be placed on UPS power: All computer systems and PLC s Safety monitoring equipment (e.g. dome open-close indication) Sensitive instrumentation General UPS Requirements The UPS shall have the following features: It s battery charge level and overall health shall be monitored by the TCS, with operator warnings as appropriate. A power-fail signal shall be passed to the TCS from the UPS to indicate the loss of normal power so that contingency software can be activated The UPS shall not increase electrical noise on the normal power line but rather provide a filter to protect its load from the Sutherland electrical supply characteristics STANDBY POWER GENERATORS Use of Emergency Power All essential power uses shall be provided with Emergency Power during a normal power failure. The definition of essential is (TBD20), but may mean excluding high power users such as air-conditioning General Emergency Power Requirements CABLE SIZING The emergency power source shall have the following features: It shall become active within 30s of a general power failure and will remain on until manually turned off The quality of power (voltage, frequency drift, harmonics) shall be no worse than the normal electrical supply A signal from the emergency generator to the TCS shall indicate when normal power has failed. At least the following error conditions shall also be reported to the UPS: low fuel, low oil pressure, generator fault, low voltage, over-current, system overheating The system shall have interlocks to prevent damage from the above faults The fuel capacity shall be sufficient to provide at least 15h of continuous operation. All electrical power cables shall be sized such that their outside surface temperature does SALT-1510AS0001Draft Page 49 of 65

50 not rise above ambient by more than 0.5ºC under worst-case operating loads GENERAL ELECTRICAL REQUIREMENTS All subsystems shall comply with the SALT Electrical Requirements. This document will address the following: Earthing and bonding of electrical equipment Measures to minimise electrical interference General principle to follow for electrical parts of each subsystem Future growth The following potential growth areas shall be borne in mind during the design process and accommodated where this does not have an impact on the achievement of the immediate performance, schedule and cost requirements REMOTE OBSERVING The control room of SALT may be required to be duplicated at the SAAO in Cape Town, to allow remote operating of SALT. SALT-1510AS0001Draft Page 50 of 65

51 6 Subsystem technical requirements 6.1 Major Component List The major components and subcomponents with their respective functional allocations are detailed in the following table. Table 24 Tracker major components No Major Component Sub Components Function 1 Tracker Computer System 1.1 Computer Hardware 1.2 Software Suite 1.3 Power Switches 1. Communication 2. Tracker Algorithms 3. Tracker MMI 2 Beam 9. Structural Support 3 Carriage 9. Structural Support 4 Hexapod System 4.1 Drive motors(x6) 4. Axes Control 4.2 Gearboxes(x6) 4.3 Sensors 4.4 Roller Screws(x6) 4.5 Drive Electronics(x6) 4.6 Controllers 4.7 Top Flange 4.8 Thermal enclosures 5 Linear Drive System 5.1 Slew Drive motor 5.2 Tracking Drive motor 5.3 Gearbox (tracking) 5.4 Sensors 5.5 Roller Screw 5.6 Drive Electronics(x2) 5.7 Controllers 5.8 Linear Bearing 5.9 Pneumatic Brakes(x2) 5.10 Sledge Assembly (Top XU and Bottom XL) 5.11 Gravity compensator (Y only) 5.12 Thermal enclosures 6 Rho-Drive System 6.1 Drive motor 6.2 Gearbox 6.3 Sensors 6.4 Bearing 6.5 Drive Mechanism 6.6 Drive Electronics 6.7 Controller 7 Payload Alignment System 8 Thermal Control System 9 Cable & Tube Handlers, Enclosures 6.2 Major Component Characteristics 6.8 Thermal enclosures 7.1 Auto Collimators(x3TBC19) COTS 7.2 Range Finder?( TBC19) 8.1 Analogue output 8.2 Analogue Input 8.3 Valves 8.4 Temperature Sensors 9.1 XL-Cable Tray 9.2 XU-Cable Tray 9.3 Y-Cable Tray 9.4 Rho-Cable Tray 9.5 Electric enclosurestbd13 4. Axes Control 8. Gravity Compensation 4.Axes Control 5. Payload Alignment 6. Thermal Control 2.8 Thermal Loop 9.Structural Support SALT-1510AS0001Draft Page 51 of 65

52 6.2.1 Tracker Computer System The computer system shall be located in the computer room in the Facility. The maximum wire length between the Computer Room and the top of the Telescope Structure will be less than 80m. This room will be maintained at temperatures between 5 to 25 degrees C and relative humidity 5% to 95%. The Tracker Computer System shall perform all functions reliably in this environment COMPUTER HARDWARE: Rack mounted(19 ) industrial type PC. At least a Pentium III class machine running at 450 MHz or higher, with at least 32MB RAM and a 6.2GB Hard Drive, 40x CD Drive and 1.44MB Stiffy Drive, Super VGA Card, Keyboard Ethernet Communications Card, TBASE100 RS485 Communication Ports (x2) RS232 Communication Ports (x2) Time Synchronisation Card (TBD14) 4 Empty Slots shall remain SOFTWARE SUITE Operating system : Real Time Linux (TBD14) Communication Software shall include TCP/IP Protocol Tracker software development environment : (TBD14) Tracker Software : Specified in Reference Tracker should be fully commanded from either the TCS or Tracker Computer with the Tracker MMI fully available at TCS level POWER SWITCHES Motor & Drive Electronic Relays : Hexapod System: X-Drives : Y-Drives : Rho Drive: Axes Controllers & Sensors Relays Hexapod System: X-Drives : Y-Drives : Rho Drive: Payload Alignment Sensors Relay Thermal Control Relay: Gravity Compensation Relay RS485 Digital Output Unit to command relays SALT-1510AS0001Draft Page 52 of 65

53 6.2.2 Beam (a) The Beam shall consist of a tubular structural framework. A conceptual illustration of the overall beam dimensions and concept is given below: Figure 12. Detail of beam (b) The Beam shall be designed to comply with all the performance requirements in (c)the Beam Shall be supported at either end by the X-drive assemblies. (d) The Beam shall be carried by two zero play non circulating crossed roller linear bearings running in the Y direction at the upper (XU) Drive Assembly support points. This feature shall decouple the Beam from any Y direction forces that would otherwise be generated by misalignment of the XL and XU bearing ways. (e) All Y direction force due to self weight of the Beam and wind loads shall be reacted by the lower X Drive Assembly Carriage (a) The Carriage shall consist of a structural steel framework. A conceptual illustration of the overall Carriage dimensions and concept is given below: SALT-1510AS0001Draft Page 53 of 65

54 6.2.4 Hexapod System (TBD15) Linear Drive Systems Figure 13. Conceptual illustration of the overall Carriage (b) The Carriage shall be supported on the beam semi-kinematically by three bearing units, two on the drive side of the Beam at either end of the Carriage support frame and one on the narrow side in the middle of the Carriage support frame. (c) The Carriage shall be driven on the wide Beam side by a powered roller nut and screw as detailed in the Y-Drive Assembly. (d) The Carriage shall be designed to comply with all the performance requirements in paragraph (a) The Hexapod System shall be configured as shown in the figure below. (b) The hexapod system shall basically consist of the Components as listed in section 6.1, but not limited thereto. (c) The hexapod system shall fulfil all the applicable requirements in paragraph (d) The hexapod system shall implement the q,f and Z motions and accommodate r adjustments of +-5 degrees (TBD16) (e) Duty Cycle of Motors (TBD17) (f) Pressurised dust cover bellows to be supplied on all bearing ways and Roller screws All the linear drive systems, i.e. the upper and lower X drives (XU and XL) and the Y-drive will be as follows: (a) The Sledge Assembly shall mount as a unit on the top Hex as per Interface dossier referred to in section 2. (b) The linear Drive systems shall consist of the Components as listed in paragraph SALT-1510AS0001Draft Page 54 of 65

55 6.1, but not limited thereto. (c) The-Drive system shall fulfil all the applicable requirements in section (d) The Drive system shall implement the Y motion and the X motion subject to skewing requirements (e) All Y direction force due to self weight of the Beam and wind loads shall be reacted by this Drive Assembly. (f) Any joints in bearing or roller screw sections shall be matched to such an extend that satisfies all performance requirements. (g) The linear Drives shall consist of a dual drive arrangement unless a single drive can be found which will meet all performance requirements. The drive assembly is driven in slew by the powered roller screw nut unit(roller screw locked) and by a harmonic drive rotating the roller screw (nut locked) during tracking. (h) Brakes shall be used on all drives to provide a fail safe stopping mode and as a mechanism to switch between Tracking and Slewing. (i) Duty Cycle of Motors (TBD17) (j) Pressurised dust cover bellows to be supplied on all bearing ways and Roller screws Figure 14. Linear Dual Drive system Rho-Drive System (a) The Rho Drive System shall be configured as shown in the figure below. (TBD19) (b) The Rho Drive system shall consist of the Components as listed in section 6.1, but not limited thereto. (c) The Rho Drive system shall fulfil all the applicable requirements in section (d) The Rho Drive system shall implement the r motion (e) Duty Cycle of Motor (TBD) SALT-1510AS0001Draft Page 55 of 65