Tracker System Specification

Transcription

1 APPROVAL SHEET TITLE : TRACKER SYSTEM SPECIFICATION DOCUMENT NUMBER : 1510AS0001 ISSUE : 1 SYNOPSIS : This document describes the technical requirements of the Tracker subsystem of the Southern African Large Telescope (SALT). KEYWORDS : Tracker, Payload Alignment, Closed Loop Tracking, Open Loop Tracking PREPARED BY : Leon Nel Manager: Tracker, Payload and TCS APPROVED : Gerhard Swart SALT System Engineer : Kobus Meiring SALT Project Manager DATE : December 2000 This issue is only valid when the above signatures are present. Doc No. SALT-1510AS0001 Issue 1 Page 1 of 76

2 ACRONYMS AND ABBREVIATIONS mm arcsec CCAS CCD COTS EE(50) FoV FWHM HET HRS I/O ICD IR ITF 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 Commercial off the shelf Enclosed Energy is 50% of total energy Field-of-View Full Width Half Maximum Hobby-Eberly Telescope High-resolution Spectrograph Input/Output (Device) Interface Control Dossier Infrared Ideal Tracker Frame 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 Doc No. SALT-1510AS0001 Issue 1 Page 2 of 76

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 another object in the same 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. Doc No. SALT-1510AS0001 Issue 1 Page 3 of 76

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(see also overall system diagram in Appendix E) 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 (measured by Payload Alignment Sensors) 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...29 Doc No. SALT-1510AS0001 Issue 1 Page 4 of 76

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 & 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 Measures to achieve efficiency Design and Construction constraints General design guidelines and constraints...51 Doc No. SALT-1510AS0001 Issue 1 Page 5 of 76

6 5.5.2 Materials, Processes and Parts Electromagnetic Radiation Workmanship Interchangeability Safety Safety-critical failures Software safety Safe initialisation Special commissioning requirements Subsystem MMI s Test Points Test Data Spotter Telescope Software Computer Hardware Electrical Design UPS Standby Power generators 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 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 APPENDIX C: System Functional Flow Diagram Doc No. SALT-1510AS0001 Issue 1 Page 6 of 76

7 TABLE OF FIGURES Figure 1. SALT Subsystems...9 Figure 2. SALT Pier, structure, primary mirror and tracker Figure 3. Facility and Dome Figure 4. Tracker on Top Hex above Primary Mirror 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 interfaces29 Figure 9. Schematic showing SALT Tracker External Interfaces Figure 10. Interfaces Figure 11. Plan View of Tracker on upper Hex Figure 12. Schematic of Error Sources Figure 13. Tracker : Layout & Dimensions Figure 14. Detail of beam Figure 15. Conceptual illustration of the HET Carriage Figure 16. Conceptual illustration of the SALT Carriage(h) & Payload Figure 17. HET Linear Dual Drive system Figure 18. Cable and Tube Handlers Doc No. SALT-1510AS0001 Issue 1 Page 7 of 76

8 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 Motion Ranges Table 11 Maximum errors Table 12 Tracker speed Table 13 Tracker accuracy Table 14 Structural dynamics Table 15 Structural deflections: static (Weight & COG Changes) Table 16 Structural deflections: static (Steady State Wind) Table 17 Structural deflections: dynamic Table 18 Orthogonality of Axes : After correction by mount model Table 19 Orthogonality of Axes : Manufacturing Table 20 Accuracy of Payload Alignment Sensors Table 21 Normal Operational Environment Table 22 Marginal Operational Environment Table 23 SALT Survival Operating Environment Table 24 SALT Efficiency Table 25 Typical Steps and 90 th percentile max times to Acquire and Observe an object 50 Table 26 Part identification Table 27 Tracker major components Table 28 Verification cross-reference Matrix (TBD20) Doc No. SALT-1510AS0001 Issue 1 Page 8 of 76

9 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 1520 Payload Figure 1. 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. Doc No. SALT-1510AS0001 Issue 1 Page 9 of 76

10 Tracker & Payload Structure Primary Mirror & Truss Air bearings Azimuth Pier Main Instrument room Figure 2. SALT Pier, structure, primary mirror and tracker Doc No. SALT-1510AS0001 Issue 1 Page 10 of 76

11 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) Doc No. SALT-1510AS0001 Issue 1 Page 11 of 76

12 SALT-1000AS0032 SALT-1000AS0033 SALT-1000AS0040 SALT-1000AS0007 SALT Electrical Requirements (TBC1) SALT Report of Interim Project Team, April 1999 SALT Support Requirements (TBC1) SALT Operational Requirements (TBC1) Applicable South African Building and Construction Standards Applicable South African Legal Requirements (TBC1) Safety, Health and Environment Act SALT System Specification Doc No. SALT-1510AS0001 Issue 1 Page 12 of 76

13 3 Customer Furnished Equipment and Responsibilities There shall be no customer furnished equipment in the tracker system Doc No. SALT-1510AS0001 Issue 1 Page 13 of 76

14 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. These position and attitude requirements 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 4 microns and 1 arc seconds respectively. The following figure illustrates the structural components of the tracker and their relationship to the Telescope Structure. Doc No. SALT-1510AS0001 Issue 1 Page 14 of 76

15 Figure 4. Tracker on Top Hex above Primary Mirror The coordinate system in which the tracker motions are described is called the Ideal Tracker Frame (ITF) and is defined as: - Origin At vertex of Primary Mirror, XY Plane coincides with bearings on top hex. - X in X drive direction - Y positive uphill direction (completing right handed system) - Z Pointing towards Primary Mirror Vertex and depicted 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. The angular motions will be around a point at a distance 13083mm from the Primary Mirror c) The value of r rotation on the sky will be chosen to orientate Celestial North. d) A computing mount model, in the Tracker, 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 or other commands are available. The Tracker subsystem will be under command from the TCS. The user interface on the Tracker Doc No. SALT-1510AS0001 Issue 1 Page 15 of 76

16 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: a) Closed Loop Tracking: Tracker trajectory 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) Positioning: 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 as a minimum by the Tracker system 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(see section for details): 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 OTHER Make provision for at least 3 other user defined positions 4.3 Major Control Functions Subsystem modes, States and Events Doc No. SALT-1510AS0001 Issue 1 Page 16 of 76

17 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. The details of these modes,states & events will be finalised in the design phase, so the descriptions in figure 6 and table 1 are provisional. Doc No. SALT-1510AS0001 Issue 1 Page 17 of 76

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 Doc No. SALT-1510AS0001 Issue 1 Page 18 of 76

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 starts tracking automatically under local or TCS command with preconditions: Target position received(local axes) Structure position confirmed (origin of coordinate system) Safety green status 2. If under TCS control, receives trajectory commands. 3. Perform closed loop guidance if corrections received, otherwise guides 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 Doc No. SALT-1510AS0001 Issue 1 Page 19 of 76

20 Table 2 Description of Mode Transition Events EVENT From Mode To Mode SENSOR/INPUT 1 STANDBY 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 STANDBY 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 Doc No. SALT-1510AS0001 Issue 1 Page 20 of 76

21 4.3.2 Functional Flow Diagram(see also overall system diagram in Appendix E) PAYLOAD COMPUTER Tracker Computer Comms (Guidance Corrections) TRACKER TRACKER COMPUTER 1.1 Ethernet TCS Comms Payload Computer Comms 1. COMMS 1.2 RS Payload Alignment Comms 1.2.2Thermal Control Comms Time 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(+Focus) 2.8T 2.9M 2.10D 2.11S 3. TRACKER MMI Figure 7. Tracker Functional Flow Diagram Doc No. SALT-1510AS0001 Issue 1 Page 21 of 76

22 4.3.3 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. X Y Z q f r DEPENDENT D.O.F. XL, XU (upper and lower x) drives Y drive H1 to H6 (hexapod legs) H1 to H6 (hexapod legs) H1 to H6 (hexapod legs) Rho stage & H1 to H 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 Trajectory Commands (t,x,y,z,q,f,r) every 1 to 30 seconds with 100ms timesteps. It can be reduced to (t,x,y,r) because of dependencies. (TBC2). These commands are in the IDEAL TRACKER FRAME(ITF) ITF Origin and Attitude Offset Commands (t,x,y,z,q,f,r) every 10 seconds Acquisition Offset Command(to point at user selected objects) (t,dx,dy) at 10Hz Safety Commands (Emergency Stop etc) at 10 Hz (TBC3) Time Synchronisation Signals 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 (via the TCS) as indicated in Figure 7: _ Moving Baffle position commands _ Guidance probe position commands Doc No. SALT-1510AS0001 Issue 1 Page 22 of 76

23 _ ADC rotation command The Payload Computer shall send the following information to the Tracker Computer(via TCS): Guidance Errors (t,dx,dy) in ITF at intervals of 0.1 to 30s (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. Time Synchronisation signals 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 _ 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 thermal control system will be a passive one. All heat generating equipment shall be insulated and the heat removed by chilled glycol. However temperature measurements will be fed back to the TCS, therefore : The Thermal Control Analogue Output shall send the following information to the Tracker Computer: Temperature Measurements (xm) at 1Hz (TBD2) POWER SWITCHES COMMUNICATION The Tracker subsystems shall be powered up in an orderly and selectable fashion. The details shall be agreed upon in the design phase. Typically the Tracker Computer shall send the following information to the Power Switches Doc No. SALT-1510AS0001 Issue 1 Page 23 of 76

24 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 software shall be time synchronized to an accuracy of at least 1ms (TBC8) TRACKER ALGORITHMS Power Up Shut Down The execution of all Tracker Computer functions should be sufficiently fast so as to ensure a cycle time of 100ms or less on control command updates and critical digital functions. The Tracker System shall be powered up and sensors homed in a controlled fashion without operator-initiated movement of the tracker. Safety requirements shall be complied with during power up. 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 Tracker Mount Model This model typically 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) Other relevant conversions to actuator axes 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 conversions shall correct for any non-orthogonality of the various tracker axes, structural deflections and sensor mounting errors. The accuracy of this model shall be sufficient to achieve overall positioning and guidance performance. Doc No. SALT-1510AS0001 Issue 1 Page 24 of 76

25 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 (measured by Payload Alignment Sensors) A set of of Payload position errors(t,x ort,y ort,z ort,q ort,f ort,r ort ), 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 Extract and display temperature measurements (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/edit Calibration Data Save/retrieve/edit software set up Must be available via TCS (remote operation) TRACKER MAN-MACHINE-INTERFACE (MMI) Implements the MMI (TBD5). The standards as per reference documents shall apply, details shall be approved in design phase AXES CONTROL Implements the mode commands and tracks 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 Doc No. SALT-1510AS0001 Issue 1 Page 25 of 76

26 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 reads and displays the temperature sensor measurements POWER SWITCHES The purpose of this function is to power up all subsystems in an orderly and selectable fashion. This function implements the commands from the Tracker computer. This function shall satisfy the performance requirement in paragraph GRAVITY COMPENSATION The purpose of this function is to alleviate the loading on the Y-Drive motor and minimise safety risks. If through design the motor can be protected sufficiently and safety risks circumvented, this function will become obsolete. Typically this function implements the commands from the Tracker computer. This function shall comply with all the performance requirements 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 (tracker structure) shall satisfy the performance requirements in paragraph Operational Concept The operational concepts for SALT are defined in SALT 1000AS0040, see section 2(details will be determined during design phase), but closed and open loop tracking, and positioning, will typically 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 Acquisition time 3 minutes Once per target positions on TCS terminal minimum Time 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 Acquisition time 3 minutes minimum Acquisition time 2.5 minutes minimum Immediately after 3. Once per target Once per target Star position: RA,DEC,Epoch Time available between Acquisition and Track must be variable by RA Doc No. SALT-1510AS0001 Issue 1 Page 26 of 76

27 to position in Tracker computer reports to TCS when in position Acquisition Time 30 seconds 6. TCS send trajectory Immediately after commands(x,y,z,q,f,r) to 5. Tracker Computer 7. Tracker executes commands in Target and Guide 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. According to time stamp of commands Any time between Acquisition and track start time When locked on guide star/s Start of Track 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) 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 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. Acquisition time 3 minutes minimum 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 Any time Once per target Once per target Once per target Once every 30 sec Continuously (at sampling Star position: RA,DEC,Epoch RA can adjust sidereal rate Time available between Acquisition and Track must be variable by RA Open loop commands Controllers should Doc No. SALT-1510AS0001 Issue 1 Page 27 of 76

28 in 6. time stamp of commands sampling frequency of axes 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 1 Immediately after Tracker computer reports to TCS when in position When position reached Once per target Doc No. SALT-1510AS0001 Issue 1 Page 28 of 76

29 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 (1,2,3,7) 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 Figure 9 and Figure 10 in section SALT Tracker Interfaces SALT Tracker External Interfaces Figure 9 shows the major External interfaces for SALT. Doc No. SALT-1510AS0001 Issue 1 Page 29 of 76

30 Science Instruments 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 D Both Communication cables, Trajectory Commands, Mode Commands, Measurement Feedback, Diagnostics and Safety Feedback, Tracker MMI, see Table 8(e4) below E -> Electrical interlocks, e.g. Tracker Emergency Stop 2 Structure Tracker P Upper and Lower X-Drive physical attachment at top hex ; Doc No. SALT-1510AS0001 Issue 1 Page 30 of 76

31 3 Facility Tracker P -> Tracker E A C attachment at top hex ; Attachment of all cables, cooling lines, fibre optic cables running between Tracker & Payload and other sub systems Provide Access to Tracker Electrical power to various parts of tracker, as per Power Budget (estimated at 17kW). 220VAC Dry Air to Linear Bearings and Roller Screws Liquid cooling capacity, estimated at 9.8 kw 4 Tracker Primary Mirror O Optical alignment signal Table 8 Tracker to Optical Payload interfaces (refer Figure 10) No. Subsystem Subsystem 2 Type Direction Interface Description 1 e4 Tracker Computer D -> Tracker e5 Payload Computer (via TCS) Payload Structure Rho Drive E A Network cable Guidance Corrections Moving Baffle Position Command Guidance Probe Command ADC rotation Command Electrical power to various parts of tracker, as per Power Budget. 220VAC Dry Air to Linear Bearings and Roller Screws C P Both Mounting on rotation stage bolted, adjustable for alignment, kinematic (no moment transfer) Payload Inertial Properties: - Mass : 750 kg - Centre of Gravity (PMF*) X,Y = 0mm Z = -50mm (TBC16) - Inertia about COG(TBC16) Ixx = 800 kgm 2 Iyy = 800 kgm 2 Izz = 350 kgm 2 - Ignore Products of Inertia E A O Electrical Connections for Data, Power, Video Cables Connections Connections Doc No. SALT-1510AS0001 Issue 1 Page 31 of 76

32 e6 e7 Payload Structure Payload Structure C Connections (Liquid Cooling Capacity : 5kW) Payload P Both Mounting of sensors - Bolted Alignment E Electrical Connections for Data, Power Tube & Cable P Both Mounting of Rotation handler - Handler Bolted E Electrical Connections for Data, Power, Video Cables A Connections O Connections C Connections * Definition of PMF (Payload Mechanical Frame): - Origin : Centre of Payload Structure in plane of mounting on Rho Stage - Z: Pointing Downwards - X: Coinciding with ITF X-axis in null position - Y: Completing the right handed system Doc No. SALT-1510AS0001 Issue 1 Page 32 of 76

33 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 STRUCTURE FACILITY PAYLOAD COMPUTER e2 e3 e4 via TCS Tracker Computer XU -Drive System XL -Drive System Y-Drive System Hexapod System (Tip,Tilt,Piston) 8 Rho-Drive System Payload Alignment e5 e6 Tracker Beam 15 Payload STRUCTURE Carriage e7 Tube & Cable Handlers & Enclosures Doc No. SALT-1510AS0001 Issue 1 Page 33 of 76

34 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 No. Subsystem 1 Subsystem 2 Type Direction Interface Description 1,2, See Fig Tracker D Both Electrical Connections for Data, 3,4, 5,6, 7,9 Figure 10 Computer Power Commands Feedback 8 Hexapod Rho Drive D Both Rho drive bolted to Hexapod top plate 9 Thermal All Tracker P Mounting Control Subsystems 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, 16 Cable & Tube Handlers 17 Cable & Tube Handlers Tracker Beam Carriage P E A D O C D E A O C one side via slide bearing Handler Bolted to beam for Y motion; Handlers mounted to XU and XL Drive assemblies for X- motion Connectors Connectors Connectors Connectors 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 Doc No. SALT-1510AS0001 Issue 1 Page 34 of 76

35 below: MOTION RANGES The actuators shall perform motions within the following ranges. The coordinate system used below is the Ideal Tracker Frame(ITF). Table 10 Motion Ranges 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 Additional specifications: i) The rotations about X & Y must ensure that a maximum circular envelope of combined angles of 17 degrees are achieved together with the Z motion ii) A sensor and interlock system apart from normal control logic, software and hardware, shall kill drive power and apply all brakes should skewing exceed a defined limit. Figure 11. Plan View of Tracker on upper Hex Doc No. SALT-1510AS0001 Issue 1 Page 35 of 76

36 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 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 in the Ideal Tracker Frame(ITF). Note that tolerances in Table 12 apply only to the maximum values. 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 asec/ s Doc No. SALT-1510AS0001 Issue 1 Page 36 of 76

37 ACCURACY (TBC9) The following diagram describes the different error sources and their point of entry Payload Computer - Calc Guidance error in local coordinates TCS - Calculate Tracker Commands - Convert Guidance Errors to Tracker space Tracker Commands Guide error Command = 0 + e2 Compensation Correction Command Guide Error Feedback (Dg) Tracker Computer Specifications on: e1 = Local control accuracy - relative to axes sensor measurements e2 = Guidance control loop accuracy (this is tracker contribution to Closed loop guidance error e3 = Outside Control Loop Errors (High frequency tracker structural motion - due to wind, unmo e4 = Local control accuracy - relative to primary mirror (distance & orthogonality) Dg= Max absolute position accuracy when guidance loop not closed = Closed Figure loop accuracy 12. Schematic any position of Error for a Sources distance of 25mm Repeatable absolute positioning should always be within Dg Doc No. SALT-1510AS0001 Issue 1 Page 37 of 76

38 Table 13 Tracker accuracy No Axis(ITF) Units RMS Errorf Max r, about ErrorZ as i POSITION 1 SLEWING Un a X mm 51 GENERAL 1.5PURPOSE b Y mm 1 POINTING*(relative 1.5 to c Z mm 1 Axes 1.5 d q, about Y deg 1 measurements) 1.5 e f, about X deg a1 X 1.5 m f r, about Z deg b1 Y 1.5 m c Z m d q, about Y as e f, about X as f r, about Z as 2 TRACKING(relative to axes measurements (e1) a X mm b Y mm ii SPEED 0.01 c Z mm SLEWING 0.01 d q, about Y asec a1 X 2 mm/s e f, about X asec b1 Y 2 mm/s f r, about Z asec c5 Z 8 mm/s d q, about Y asec/ Precision Pointing e f, about X asec/ f r, about Z asec/ 2 TRACKING(relative to 3 TRACKING(relative to absolute position & Time (Dg): Open Loop guidance) Axes a X mm measurements) 0.3 b Y mm a X 0.3 mm/s c Z mm b Y 0.08 mm/s d q, about Y asec c5 Z 6 mm/s e f, about X asec d5 q, about Y6 asec/ f r, about Z asec e5 f, about X 6 asec/ f r, about Z asec/ 4 TRACKING(relative to absolute position & Time (Dg): Closed Loop guidance and Open Loop Guidance * General Purpose Pointing: Used to over any 25mm position the Tracker in predefined distance) positions or any other position when tracking accuracies can be relaxed. a X mm The purpose of which is to prevent b Y mm unnecessary wear c Z mm d q, about Y asec e f, about X asec Doc No. SALT-1510AS0001 Issue 1 Page 38 of 76

39 THERMAL CONTROL ACCURACY AND HEAT DUMPING (a) Measurement accuracy shall be better than 0.5 deg C. (b) All surface temperatures that can rise more than 2 degrees C above ambient shall be passively controlled (by insulation and glycol cooling). Liquid Coolant source /drain points will be supplied at the Top Hex. The coolant supply will be approximately 1.5 degrees C below ambient and the return must be within 1.5 degrees from ambient CONTROL LOOP REQUIREMENTS All Control loops shall not induce excessive vibrations in the Telescope or Tracker Structure, the following stability and small signal bandwidth requirements under all loading conditions, are guidelines: 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 Bandwidth requirements are TBC24, the final values shall be confirmed through structural analysis to ensure that induced structural vibration is not excessive i.e. the total error budget shall be within the closed loop guidance requirements SAFETY The following should be read in conjunction with the SALT Safety Analysis, SALT- 1000AA0030, listed in section 2. a) 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. b) 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. c) Motor overload protection, fusing and sensing shall be implemented and monitored by the control system to ensure that failure mode criteria are met. d) 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. e) The extent to which the beam should make provision for skewing is to be determined by the contractor, the choice of which should not degrade safety or performance in Doc No. SALT-1510AS0001 Issue 1 Page 39 of 76

40 any way. (HET designed for 200mm) f) 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. This shutdown shall be activated at the level of 0.75 mm skewing or beyond. g) A sensor and interlock system apart from normal control logic, software and hardware, shall kill drive power, apply all brakes and initiate an immediate shutdown sequence should skewing exceed a safe limit. h) Where tools must be used on-telescope for servicing and maintenance, they shall be secured by lanyards to the servicer s tool belt or man lift. i) 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. j) No lock washers shall be used for on-telescope accessible fasteners, chemical locking compounds or aircraft-type locking nuts shall be used instead. k) A safety analysis and design shall be presented and implemented to satisfy all safety requirements. l) Shutdown with hardware input from TCS (Emergency stop). m) Software development process to be commensurate with the safety implication of software failure (see SALT1000BS0010) STRUCTURAL FREQUENCIES (TBC10) The Tracker Beam and Carriage shall comply with the following minimum frequencies, with payload integrated and positioned at the centre of the beam. Table 14 Structural dynamics Degree of Freedom (ITF) Mode X 1 10 Y 1 15 Z 1 10 Rotation about X 1 10 Rotation about Y 1 7 Rotation about Z STATIC STRUCTURAL DEFLECTIONS (TBC11) Minimum Frequency [Hz] The following maximum deflections of the Tracker Structure under its own weight, 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. Table 15 Structural deflections: static (Weight & COG Changes) Degree of Freedom (ITF) Units Maximum Displacement Doc No. SALT-1510AS0001 Issue 1 Page 40 of 76

41 X mm 1000 Y mm 500 Z mm 5000 Rotation about X arcsec 100 Rotation about Y arcsec 100 Rotation about Z arcsec 100 The following maximum deflections of the Tracker beam under steady state wind loading, with the payload installed, are guidelines. 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 wind acting on the Payload will contribute less than 15kg to the static load. The centre of pressure position on the payload is (TBC12). The Open Loop guidance requirement (Table 13,i3) shall take precedence. Table 16 Structural deflections: static (Steady State Wind) Degree of Freedom (ITF) Units Maximum Displacement X mm 20 Y mm 20 Z mm 25 Rotation about X arcsec 4 Rotation about Y arcsec 4 Rotation about Z arcsec 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 force component is 3kg, at the same action point as in The frequency of the disturbance force is 2.5 Hz or less. The specs in table 16 are only guidelines, the closed and open loop guidance specifications should be met irrespective. Table 17 Structural deflections: dynamic Degree of Freedom Units (ITF) X mm 3 Y mm 3 Z mm 3.5 Rotation about X arcsec 0.2 Rotation about Y arcsec 1.4 Rotation about Z arcsec ORTHOGONALITY OF AXES : (TBC13) Maximum Displacement The specifications in tables 17 and 18 should be seen as guidelines only since the Doc No. SALT-1510AS0001 Issue 1 Page 41 of 76

42 requirements for tracking accuracy in Table 13 shall have precedence. Table 18 Orthogonality of Axes : After correction by mount model Axes (ITF) Units Value XY arcsec 0.05 XY Plane and Z axis arcsec 0.05 Rotation about Y, non parallelism arcsec 0.05 of rotation axis and Y-Axis Rotation about X, non parallelism arcsec 0.05 of rotation axis and X-Axis Rho rotation, non parallelism to Z arcsec 0.05 Axis Rho Rotation Axis offset from Z Axis mm 3 Table 19 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 mm 20 The purpose of this specification (Table 18) is to ensure that the operating envelope of tracker is not skewed unlimited Provision must be made to adjust the payload on the rho stage so as to ensure alignment with the rotation axis within the value specified in Table ROTATION POSITION OF PAYLOAD (TBC14) (a) The Payload shall be rotated in tip and tilt (q,f) nominally about the paraxial focus of the primary mirror ( mm above vertex op Primary Mirror) (b) The rotation point should be adjustable with mm about the nominal position along the optical axis and 50mm radially MAXIMUM ACCELERATION AND JERK (a) Maximum acceleration under all circumstances shall be less than 0.1ms -2 (b) Maximum jerk under all circumstances shall be less than 1ms ADDITIONAL SEARCH SPEEDS Doc No. SALT-1510AS0001 Issue 1 Page 42 of 76

43 Provision shall be made to adjust the open loop sidereal rate in a band between 11 to 20 arcsec/s( this translates to 0.6 to 1.3mm/s in the XY plane(itf)). Note: The implementation of this functionality will reside in the TCS. The tracker must only be able to perform tracking (at required accuracies) at the maximum and minimum tracking rates to enable this function FORCES IN HEXAPOD STRUTS The struts shall be designed, positioned and actuated such that the force in any strut never changes direction TRAVEL LIMITS The control system hardware and software shall provide for three levels of travel limits for all axes of tracker motion: (a) Software limits Upon reaching these limits, all tracker motions shall be stopped smoothly within 1 second, feeding back to TCS the affected axis, the programmed limit and current position. Additional motion in this direction shall only be possible by issuing a special override command. The full envelope as specified in Table 10 shall be available within the software limits. The initiation of a software limit shutdown shall occur in time to stop the affected axes prior to activating a hardware limit. It shall be possible to command the axis away from the limit (recovery), without special commands. (b) Hardware limits using limit switches Each Tracker motion axis shall be equipped with a fail safe limit switch at either end of its travel range, outside the software limit range defined above. Upon receiving limit switch data all tracker motions shall be stopped smoothly within 0.5 second, feeding back to TCS the affected axis, the tripped limit switch and current position. Only motion in the opposite direction shall be possible. (c) Mechanical hard stops with motor overload protection Cushioned hard stops shall be provided at each end of each tracker motion axis. Each drive motor / actuator shall be equipped with software and limit switch independent overload sensing and shutdown protection, which shall also inform the TCS of its activation and motor current. The Tracker shall initiate shutdown procedure, independent of software, when overload protection activation is sensed. Additional servo commanded motion, in either direction shall not be possible once a hard stop is struck. Provision shall be made in the form of shaft wrench flats, detachable hand crank etc., to manually reverse the motion axis to within normal limits after the drive problem has been found and fixed. Provision shall be made in the software to reinitialise the system after a hard stop event has occurred PAYLOAD ALIGNMENT The Payload Alignment system shall provide measurements regarding the orthogonality and distance of the payload from the Primary Mirror surface in real time. Doc No. SALT-1510AS0001 Issue 1 Page 43 of 76

44 Table 20 Accuracy of Payload Alignment Sensors No Axis(ITF) Units RMS Error Max Error 1 Angular q arcsec f arcsec Range* Distance to Ideal um 4 5 Primary Mirror Surface Note: * It is not required that a single measurement achieves this accuracy, but by mapping the range to the primary mirror through consecutive measurements and a best sphere fit through these points TRACKER MMI Control over all Tracker functions, access to all sensor measurements, adjustment of control loops, software limits and tracker configuration shall be available through the MMI. The MMI shall be accessible through the TCS as well. The requirements of relevant document in Section 2 must be satisfied. Details to be approved in design phase Physical Characteristics OBSCURATION MASS Tracker Shadow on Primary mirror : On - Axis < 3.5m 2 outside a central circle of 3.0m diameter. 8.5 deg Off - Axis < 5m 2 The total tracker (excluding payload) mass shall be less than 3750kg (TBC15) The payload mass shall be less than 750kg (TBC16) MAXIMUM & MINIMUM SURFACE TEMPERATURES All the Tracker related electronics shall as a first option be located in the computer room (70m from Top Hex), as a second option directly underneath the Primary Mirror (25m from Top Hex) in a cooled enclosure. 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 99 th percentile of operation ambient conditions (see ). Section 5.5 provides further guidance in this regard. Doc No. SALT-1510AS0001 Issue 1 Page 44 of 76

45 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. 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. 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 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 1 m of the telescope optical path, 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. 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 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 ). 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. Doc No. SALT-1510AS0001 Issue 1 Page 45 of 76

46 COMPONENT/MODULE REPLACEMENT All major components that might need removal, must provide for interfaces suitable for using the dome crane as lifting device (capacity 1ton). 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 The payload envelope as illustrated on the supplied drawings (see section 6.2) can be used as guideline. This will be finalised in the design phase. Sufficient clearances should exist between potentially interfering subsystems after hard stop limits of actuators have been reached 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 21 below: Table 21 Normal Operational Environment Parameter Value Notes Minimum Temperature 0ºC Maximum Temperature 20ºC Maximum nightly temperature range 8ºC TBC20 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 (outside) 16.8 m/s Gusts up to 22 m/s Maximum wind velocity (at dome 6m/s TBC17 opening) 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 22 below, shall not exceed 10% (TBC18) of the nominal values in paragraph Table 22 Marginal Operational Environment Parameter Value Notes Minimum Temperature -10ºC Maximum Temperature 25ºC Maximum rate environment cooling -2.0ºC/h Maximum rate of environment warming +1ºC/h Estimated value Minimum Humidity 5% Doc No. SALT-1510AS0001 Issue 1 Page 46 of 76

47 Maximum Humidity 97% Non-condensing Maximum wind velocity (outside) 21 m/s Gusts up to 25 m/s Maximum wind velocity (inside) 8m/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 23 below. Note that the dome and louvers will be closed under these conditions and therefore the tracker does not have to be designed for this wind loading, but all tracker subsystems must be able to survive the temperature profile. Table 23 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 a) The SALT Tracker shall include operating manuals, training manuals, maintenance manuals and calibration procedures at Tracker 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 Doc No. SALT-1510AS0001 Issue 1 Page 47 of 76

48 special documentation will be developed. For custom made equipment, a set of documentation will be specified and will form part of the deliverable. b) An operations log shall be maintained beginning when the Tracker first starts off-telescope trail operation (integration & Testing at vendor). The Log shall record the dates the tracker was operated, by whom, and with what purpose (routine test, troubleshooting etc.), duration (hours), error conditions & Failures. c) Full size copies of as built component specifications, drawings and CAD files. d) Calibration certificates for each axis, including measured positions of mechanical stops e) Acceptance test documentation f) Build History document. All documentation shall be in English Personnel and Training OPERATION MAINTENANCE 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 Doc No. SALT-1510AS0001 Issue 1 Page 48 of 76

49 5.4.4 Availability Technician listed above. One mechanical and one of the electrical/electronic technician will also be 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. The Tracker system shall be designed to be operated and maintained by the mentioned personnel, keeping in mind that only part of the human resources can be allocated to the Tracker SCIENCE EFFICIENCY Table 24 below specifies the required SALT efficiency for various operational aspects. The values are percentages of the total time allocated to science, and exclude bad weather, engineering time and instrument commissioning. Only items 2,5 and 6 have relevance to the Tracker. 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. How the Tracker effects will be incorporated, forms part of this specification. 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 24 SALT Efficiency Activity 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 2. Table 25 shows how the Tracker impacts on the SALT operation: Doc No. SALT-1510AS0001 Issue 1 Page 49 of 76

50 Table 25 Typical Steps and 90 th percentile max times to Acquire and Observe an object Tracker Structur e Dome SO or SA actions Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Step 7 Slew to destination (120s) Select Object from list (120s) Lift up (15s) Rotate (150s) Rotate (180s) Lower (15s) Open-loop tracking of object and implementation of tracking offsets Setting to guidance object (60s) Closedloop tracking of guide object Integrate science object Select next object from list Reliability Tracker Maintainability Unscheduled Tracker down time during operation shall not exceed 2h / year (TBC21) 50 tracker traverses per night over a lifetime of 20 years Scheduled maintenance shall be performed during the day. 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 Tracker Down-time shall not be more than 20% of the total allocated for SALT in Table 24 The design and construction of the tracker shall include the capability of safely 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. 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 Doc No. SALT-1510AS0001 Issue 1 Page 50 of 76

51 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 (TBC22) standard (metric) tool sets will be available, one in the SALT workshop and one in the telescope chamber. Special tools shall be kept to a minimum. 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. 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. 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 stated otherwise. 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 vendors g. Optical fibres will be used for any digital communications travelling more than 30m h. 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 a negative delta being the risk of condensation, damaging mirrors and equipment 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: Doc No. SALT-1510AS0001 Issue 1 Page 51 of 76

52 Table 26 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 exceptions 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 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 Doc No. SALT-1510AS0001 Issue 1 Page 52 of 76

53 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) Special commissioning requirements SUBSYSTEM MMI S TEST POINTS TEST DATA 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. 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 Doc No. SALT-1510AS0001 Issue 1 Page 53 of 76

54 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 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 UPS power will be available for the tracker computer STANDBY POWER GENERATORS Emergency power will be available for all tracker subsystems CABLE SIZING All electrical power cables shall be sized such that their outside surface temperature does 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 Doc No. SALT-1510AS0001 Issue 1 Page 54 of 76

55 allow remote operating of SALT. Doc No. SALT-1510AS0001 Issue 1 Page 55 of 76

56 6 Subsystem technical requirements 6.1 Major Component List The major suggested components and subcomponents with their respective functional allocations are detailed in the following table. The selection and design of these components will be finalised in the design phase. The contractor is encouraged to motivate any cost/risk/performance enhancing changes which are to be accepted by the subcontractor. The table below reflects the HET breakdown to a large extent. Table 27 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 2 Tracker Structure 2.1 Beam 2.2 Carriage 3 Hexapod System 3.1 Drive motors(x6) 3.2 Gearboxes(x6) 3.3 Sensors 3.4 Roller Screws(x6) 3.5 Drive Electronics(x6) 3.6 Controllers 3.7 Top Flange 3.8 Thermal enclosures 4 X-Drive System (XU Drive, XL-Drive ) 4.1 Slew Drive motor 4.2 Tracking Drive motor 4.3 Gearbox (tracking) 4.4 Sensors 4.5 Roller Screw 4.6 Drive Electronics(x2) 4.7 Controllers 4.8 Linear Bearing 4.9 Pneumatic Brakes(x2) 4.10 Sledge Assembly (Top XU and Bottom XL) 4.11 Thermal enclosures 5 Y- 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 Gravity compensator 5.11 Thermal enclosures 6 Rho-Drive System Drive motor Gearbox Sensors Bearing Drive Mechanism Drive Electronics Controller 7 Payload Alignment System Thermal enclosures Auto Collimators(x2TBC19) COTS 1. Communication 2. Tracker Algorithms 3. Tracker MMI 9. Structural Support 4. Axes Control 4. Axes Control 4. Axes Control 8. Gravity Compensation 4.Axes Control 5. Payload Alignment Doc No. SALT-1510AS0001 Issue 1 Page 56 of 76

57 Range Finder?( TBC19) (7.1 & 2 can be combined) 8 Thermal Control System 9 Cable & Tube Handlers, Enclosures 8.1 Analogue Input 8.2 Temperature Sensors 8.3 Insulation 9.1 XL-Cable Tray 9.2 XU-Cable Tray 9.3 Y-Cable Tray 9.4 Rho-Cable Tray 9.5 Electric enclosurestbd13 6. Thermal Control 2.8 Thermal Loop 9.Structural Support Doc No. SALT-1510AS0001 Issue 1 Page 57 of 76

58 6.2 Major Component Characteristics All systems & subsystems shall comply with the requirements of Section 2 documents. Figure 13 shows the major dimensions of the Tracker and interfaces with the Top Hex(TBC). Figure 13. Tracker : Layout & Dimensions Doc No. SALT-1510AS0001 Issue 1 Page 58 of 76

59 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: At least a Pentium III class machine, shall comply with SALT Computer hardware Standard (Section 2). The selection of hardware should not limit future upgrading with advances in technology SOFTWARE SUITE Operating system : Real Time Linux (TBD14) Communication Software shall include TCP/IP Protocol Tracker software development environment : Labview Preferable(TBD14) Tracker Software : Comply with standard as in section 2 (SALT Software Standard ) Tracker should be fully commanded from either the TCS or Tracker Computer with the Tracker MMI fully available at TCS level POWER SWITCHES Functionality must be provided to power up the Tracker subsystems in an orderly fashion either fully or selectively. The details will be finalised in the design phase. A typical grouping of these switches may be as follows: a) Motor & Drive Electronic Relays for : - Hexapod System: - X-Drives : - Y-Drives : - Rho Drive: b) Axes Controllers & Sensors Relays: - Hexapod System: - X-Drives : - Y-Drives : - Rho Drive: c) Payload Alignment Sensors Relay d) Thermal Control Relay: e) Gravity Compensation Relay f) RS485 Digital Output Unit to command relays Doc No. SALT-1510AS0001 Issue 1 Page 59 of 76

60 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 14. 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 forces due to self weight of the Beam and wind loads shall be reacted by the lower X Drive Assembly. f) Provision shall be made for walking platforms and Handrails to access any part on the top of the beam g) The Beam shall be able to carry an additional load of 300kg anywhere on the span (2 persons with tools) Carriage (a) The Carriage shall consist of a structural steel framework. A conceptual illustration of the HET carriage dimensions and concept is given below: Doc No. SALT-1510AS0001 Issue 1 Page 60 of 76

61 Figure 15. Conceptual illustration of the HET Carriage (b) The Carriage shall be supported on the beam 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 SALT carriage will differ in layout and design as a result of the differences in payloads. The SALT carriage and payload are depicted in the figures below (dimensions TBC). Doc No. SALT-1510AS0001 Issue 1 Page 61 of 76

62 Figure 16. Conceptual illustration of the SALT Carriage(h) & Payload (d) The Carriage shall preferably be driven on the wide Beam side by a powered roller nut and screw as detailed in the Y-Drive Assembly. (e) The Carriage shall be designed to comply with all the performance requirements in paragraph (f) Carriage shall make provision for a working platform and handrails Hexapod System (a) The Hexapod System shall be configured as shown in Figure 16 above. Details to be finalised in design phase. (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) Doc No. SALT-1510AS0001 Issue 1 Page 62 of 76

63 6.2.5 Linear Drive Systems (f) Pressurised dust cover bellows to be supplied on all bearing ways and Roller screws (g) Hexapod motions shall in no event cause any damage to itself or any other subsystem. 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 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 (k) The viability of single drives for slewing and tracking in X and Y shall be investigated. Any changes have to be approved by client. Doc No. SALT-1510AS0001 Issue 1 Page 63 of 76

64 Figure 17. HET 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 (TBD17) (f) Pressurised dust cover bellows to be supplied on all bearing ways and Roller screws (g) Loss of power shall not result in uncontrolled rotation even with asymmetric payload loads Payload Alignment System This assumed to be a COTS item (e.g. autocollimators reflecting off Primary mirror). The position and mechanical interface with the payload will be finalised in the design phase Thermal Control System The thermal control system will be a passive system as far as the tracker is concerned, heat generating equipment will be insulated and heat removed by chilled glycol. A glycol source and drain will be supplied at the Top Hex. Temperature measurements at these subsystems will be fed back to the TCS via the Tracker computer. Doc No. SALT-1510AS0001 Issue 1 Page 64 of 76