Payload Specification

Transcription

1 APPROVAL SHEET TITLE : PAYLOAD SPECIFICATION DOCUMENT NUMBER : 1520AS0001 ISSUE : Draft SYNOPSIS : This document describes the technical requirements of the Payload subsystem of the Southern African Large Telescope (SALT). KEYWORDS : Payload, Guidance, Acquisition, Fiber Feed, Payload Alignment, PFIS, 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 : March 2001 This issue is only valid when the above signatures are present. Doc No. SALT-1520AS0001 Draft Page 1 of 86

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 Doc No. SALT-1520AS0001 Draft Page 2 of 86

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. Doc No. SALT-1520AS0001 Draft Page 3 of 86

4 TABLE OF CONTENTS 1 Scope Identification System overview Referenced documents Customer Furnished Equipment and Responsibilities Functional Requirements Main functions 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 Tracker Computer Communication Axes Controllers Communication (ADC, Moving Baffle, Fold Mirrors, Calibration Source) Acquisition Communication Thermal Control Communication Power Switches Communication Time Synchronization Input Payload Algorithms Power Up Shut Down Time Synchronization Payload Mount Model Guidance Corrections Acquisition Axes Command Generator Thermal loop Mode and State Control Diagnostics & Safety Software Set up & Maintenance Payload Man-Machine-Interface (MMI) Axes Control Acquisition Thermal Control Power Switches Guidance Structural and Interface Support Operational Concept Payload Technical Requirements Schematic diagram SALT Payload Interfaces...33 Doc No. SALT-1520AS0001 Draft Page 4 of 86

5 5.2.1 SALT Payload External Interfaces SALT Payload Internal Interfaces SALT Payload Characteristics Performance Characteristics SAC ADC Guidance System Moving Baffle Fold Mirrors Calibration Source Thermal Control Payload Structure Payload Computer Control loop Requirements Safety Structural Frequencies (TBC10) Static Structural Deflections (TBC11) Dynamic Structural Deflections Mounting Points on Payload Structure : (TBC13) Travel limits Payload MMI Physical Characteristics Obscuration Mass Total Power Requirements Total Cooling Requirements Total Dry Pressurised Air Requirements 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 and Subsystem 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...54 Doc No. SALT-1520AS0001 Draft Page 5 of 86

6 Science Efficiency Reliability Payload Maintainability 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 Payload Computer System Computer Hardware: Software Suite Power Switches Structure SAC ADC Moving Baffle...66 Doc No. SALT-1520AS0001 Draft Page 6 of 86

7 6.2.6 Fixed Baffle Fold Mirrors 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-1520AS0001 Draft Page 7 of 86

8 TABLE OF FIGURES Figure 1. SALT Subsystems Figure 2. SALT Pier, structure, primary mirror and tracker Figure 3. Facility and Dome Figure 4. PFIS Position Figure 5. PFIS Responsibilities Figure 6. Fibre Fed Instruments Responsibilities Figure 7. Fibre Fed Instruments Responsibilities Figure 8. Calibration Source Responsibilities Figure 9. Payload & Hexapod Figure 10. System modes Figure 11. Payload Functional Flow Diagram Figure 12. Major Components of Payload Subsystem and Communication interfaces33 Figure 13. Schematic showing SALT Payload External Interfaces Figure 14. Interfaces Figure 15. Tracker and Payload : Layout & Dimension Figure 16. Detail of structure Figure 17. Conceptual illustration of the SALT Payload & SAC Figure 18. Conceptual illustration of the ADC Figure 19. Conceptual illustration of the Moving Baffle Figure 20. Conceptual illustration of the Commissioning Instrument Figure 21. Cable and Tube Handlers Doc No. SALT-1520AS0001 Draft Page 8 of 86

9 LIST OF TABLES Table 1 Description of System Modes Table 2 Description of Mode Transition Events Table 3 Closed loop tracking Table 4 Open Loop Tracking Table 5 Positioning Table 6 Tracker & Payload external interfaces Table 7 Payload external interfaces to Tracker (refer Figure 9) Table 8 Internal Interfaces Table 9 Structural deflections: static Table 10 Structural deflections: dynamic Table 11 Payload Mass Budget Table 12 Payload Power Budget Table 13 Payload Cooling Budget Table 14 Payload Pressurised Air Budget Table 15 Normal Operational Environment Table 16 Marginal Operational Environment Table 17 SALT Survival Operating Environment Table 18 : SALT Efficiency Table 19 Part identification Table 20 Payload major components Table 21 Verification cross-reference Matrix (TBD21) Doc No. SALT-1520AS0001 Draft Page 9 of 86

10 1 Scope 1.1 Identification This document specifies the requirements for the Payload 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 Payload as numbered 1520 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-1520AS0001 Draft Page 10 of 86

11 Tracker & Payload Structure Fibre Bundle Primary Mirror & Truss Air bearings Azimuth Pier Main Instrument room Figure 2. SALT Pier, structure, primary mirror and tracker Doc No. SALT-1520AS0001 Draft Page 11 of 86

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) Doc No. SALT-1520AS0001 Draft Page 12 of 86

13 SALT-1000AS0032 SALT-1000AS0033 SALT-1000AS0040 SALT-1523AS0001 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 SAC Specification Doc No. SALT-1520AS0001 Draft Page 13 of 86

14 3 Customer Furnished Equipment and Responsibilities The following equipment shall be customer furnished: a) PFIS Prime Focus Imaging Spectrograph b) Fibre Fed Instrument/s c) Fibre Instrument Feed System d) Calibration Source (for Flat fielding) 3.1 PFIS Figure 4 below shows the position of PFIS on the Payload. Figure 4. PFIS Position Figure 5 shows the division of responsibilities for procuring PFIS between the Customer and the SALT Project Team: TCS Payload Structure Instrument Grade Air Interface PFIS Computer Coolant for Detectors PFIS Power 220V Actuator Air SALT Project Team Figure 5. SALT Project Team PFIS Responsibilities Customer The detailed interfaces are described in document SALT-1520AS0002, PFIS Interface Control Dossier NOTE! The PFIS computer will be located in the computer room. 3.2 Fibre Fed Instruments The fibre fed instruments shall be located in the spectrometer room, under the floor of the telescope chamber, see figure 3. Figure 6 shows the division of responsibilities between the Customer and the SALT Project Team for procuring the fibre fed instruments: TCS Interface HRS & LRS Computer/s Doc No. SALT-1520AS0001 Draft Page 14 of 86 Instrument Grade Air

15 Figure 6. Fibre Fed Instruments Responsibilities The detailed interfaces are described in document SALT-1000AS0027, SALT External Interface Control Dossier NOTES! The HRS & LRS computer/s will be located in the computer room. The fibre bundle forms part of the fibre instrument feed system. 3.3 Fibre Instrument Feed System The fibre instrument feed system shall be located on the payload, the fibre bundle piping the light to the spectrometer room shall be supported by the payload, tracker and telescope structures. Figure 7 shows the division of responsibilities between the Customer and the SALT Project Team for procuring the fibre instrument feed system: TCS Interface FIF Computer Payload Structure Power 220V Fibre Bundle Fibre Instrument Feed SALT Project Team Figure 7. Fibre Bundle SALT Project Team Fibre Fed Instruments Responsibilities HRS & LRS Customer The detailed interfaces are described in document SALT-1000AS0027, SALT External Interface Doc No. SALT-1520AS0001 Draft Page 15 of 86

16 Control Dossier NOTES! The FIF computer will be located in the computer room. The fibre bundle forms part of the fibre instrument feed system. 3.4 Calibration Source The Calibration Source shall be located in the computer room, the fibre bundle piping the light to the calibration screen shall be supported by the payload, tracker and telescope structures. Figure 8 shows the division of responsibilities between the Customer and the SALT Project Team for procuring the Calibration Source: TCS Interface CAL Computer Payload Structure Calibration screen Telescope, Tracker & Payload Structure Fibre Bundle Calibration Source Power 220V SALT Project Team Figure 8. SALT Project Team Calibration Source Responsibilities Customer The detailed interfaces are described in document SALT-1000AS0027, SALT External Interface Control Dossier NOTES! The CAL computer will be located in the computer room. The fibre bundle forms part of the Calibration Source. Doc No. SALT-1520AS0001 Draft Page 16 of 86

17 4 Functional Requirements 4.1 Main functions The main functions of the Payload System in SALT are to: a) Receive light from Primary Mirror and correct its optical aberrations (SAC) b) Distribute the light to the various science instruments or ports: 1) Acquisition System 2) Guidance System 3) Fibre Instrument Feed System 4) Prime Focus Imaging Spectrograph 5) Auxiliary Port c) Provide the telescope with an acquisition capability d) Provide closed loop guidance corrections e) Correct atmospheric dispersion f) Baffle all stray light, especially light emanating from outside the Primary Mirror g) Act as supporting interface for all power, data, cooling and compressed air to all science instruments h) Provide structural support i) Provide communication with the TCS j) Provide the science instruments with a calibration facility (for flat fielding) k) Provide the Guidance and Acquisition MMI (Man Machine Interface) The Payload will be supported and positioned by the Tracker near the paraxial focus of the Primary Mirror. The Tracker will support all the interfaces of the Payload with the rest of the SALT System, except the optical fibres to the Spectrometer Room. Figure 9 illustrates the components of the Payload and their relationship to the Hexapod system of the Tracker. Doc No. SALT-1520AS0001 Draft Page 17 of 86

18 Doc No. SALT-1520AS0001 Draft Page 18 of 86

19 Figure 9. Payload & Hexapod The coordinate system, in which the location of the Payload subsystems is described, is called the Payload Mechanical Frame (PMF). A detailed description of all coordinate systems is given in SALT- 1000AS0031: SALT Axes and Calibration definition, listed in Section 2. In operation on SALT, the Payload will perform the following actions when commanded to a particular target in the sky: a) The Payload Computer shall receive its position information, and the relevant instrument configuration from the TCS b) The Payload Computer shall generate the position commands to all relevant subsystems c) The Fold Mirrors shall be positioned such as to direct the light to the Acquisition System d) The following Subsystems shall be slewed to respective X,Y,Z positions corresponding to the instantaneous celestial position of the target : a. ADC b. Moving Baffle e) The payload will be positioned in q,f to align with the normal of the primary mirror at that point, ensuring the correct focus distance at the same time(tracker function) f) The value of r rotation on the sky will be chosen depending on whether the target is an extended or point source (tracker function) g) The Payload Computer shall be notified by the relevant instruments whether the requested target is in the correct position, which in turn shall notify the TCS. The TCS will initiate corrective action if necessary. h) During Acquisition and Closed loop guidance the science and guidance images shall be sent to the TCS, the selection of the target and a guide star on the TCS shall be fed back to the Payload computer, which will calculate offsets and feed it back to the TCS. i) During tracking the TCS shall send the Tracker Trajectory commands(time,x,y) to the Payload Computer, which in turn will then generate the trajectory commands for the ADC and Moving Baffle. The TCS shall update these commands with the feedback from the Tracker regarding its actual position. j) During closed loop tracking the Payload Computer shall compute the guidance corrections and feed it back to the TCS k) When trajectory is complete, the Payload shall stop all motion unless a new preloaded trajectory or other commands are available. The Payload subsystem will be under command from the TCS. The user interface on the Payload 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 Payload subsystem are: a) Configuring of Payload: For each target the SA will specify the configuration of the instruments. The Payload Computer shall ensure that light is directed to the selected instrument, after acquisition. Doc No. SALT-1520AS0001 Draft Page 19 of 86

20 b) Target Acquisition: During the target acquisition phase the light shall be directed to the Acquisition system, the acquisition image shall be sent to the TCS, upon target selection by SA on TCS, the target offsets shall be computed by the Payload computer and fed back to the TCS. During acquisition the Payload Computer shall position the guide probes on the selected guide star. c) Closed loop guidance corrections: The Payload computer will compute these corrections from the guidance images and feed it back to the TCS. d) Calibration: The Payload system shall perform all calibrations which are not instrument specific. e) Positioning: The Payload computer shall position the Moving Baffle and ADC according to TCS commands during open and closed loop tracking, as well as controlling any motion or switching relating to the calibration system. The following major functions have to be performed as a minimum by the Payload system to achieve the main functional objectives as stated above: _ Communication _ with other SALT subsystems (TCS) _ with other Payload subsystems (ADC, Moving Baffle, Acquisition System, Guidance System) _ Algorithm Execution _ Mount Model (Coordinate Transformations) _ Image Processing _ Mode and State Control _ Diagnostics & Safety etc _ Man Machine Interface (MMI) _ Axes Control : Tracking of commands to all axes _ Thermal Control : Ensure that all surface temperatures and heat generation in light path are within specification _ Structural and interface support A detailed functional flow diagram is presented in Figure 11. The following predefined focus positions shall be selectable from Manual and Automatic Modes(see section for details): ACQUISITION - at Acquisition System FIF at Fibre Instrument Feed PFIS at Prime Focus Imaging Spectrograph AUX - at Auxiliary port 4.3 Major Control Functions Subsystem modes, States and Events The operation of the Payload 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 Doc No. SALT-1520AS0001 Draft Page 20 of 86

21 the descriptions in figure 6 and table 1 are typical. Doc No. SALT-1520AS0001 Draft Page 21 of 86

22 10 11 Standby OFF Shut Down 12 8 Error 9 14 Initialise 6 7 Ready 2 3 Automati c 5 4 Manual Figure 10. System modes Table 1 Description of System Modes Mode Description States Off Power to Payload Computer and all other subsystems is switched off Standby Power to all subsystems switched off, except Payload Computer. The Payload computer switches power to all the subsystems except itself. Initialise Payload Computer powers up all Initialisation subsystems of Payload and homes all sensors : Zero all commands to actuators Health Check Check system Health (sensor readings) Do Homing Manual Homing Command all actuators to predefined positions Automatic Homing Ready The Payload is waiting for commands from TCS, whilst performing the Doc No. SALT-1520AS0001 Draft Page 22 of 86

23 Manual from TCS, whilst performing the following tasks: Perform Position Control (low accuracy) on all actuators Report commanded & feedback values (positions, velocities, motor currents, temperatures) Report System Health Manual commands to Payload via Payload computer terminal/keyboard or TCS & Feedback to terminal and TCS Position Subsystems Acquisition Guidance Calibration Automatic 1. Receives Instrument selection commands from TCS 2.Payload subsystems move and start tracking automatically under TCS command with preconditions: Configuration status confirmed Target position received Structure position confirmed (origin of coordinate system) Safety green status 3. Receives Tracker actual position from TCS. 4. Perform Acquisition Task 3. Perform guidance 4. Reports commands, feedback & health to terminal and TCS Position Subsystems Acquisition Guidance Error Shutdown Any errors, which prevent payload functions being executed, will put the payload 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 subsystems to predefined positions Zero all commands to actuators Standby Initialise Ready Manual Automatic Doc No. SALT-1520AS0001 Draft Page 23 of 86

24 Check system Health Switch power off Table 2 Description of Mode Transition Events EVENT From Mode To Mode SENSOR/INPUT 1 OFF INITIALISE Button Payload Computer/TCS 2 INITIALISE READY Software Switch On successful power up 3 READY MANUAL Button Payload Computer 4 MANUAL READY Button Payload Computer/TCS Or Error Condition 5 READY AUTOMATIC Button Payload Computer/TCS 6 AUTOMATIC READY Button Payload Computer/TCS Or Error Condition 7 READY SHUTDOWN Button Payload Computer/TCS 8 READY ERROR Error Conditions 9 ERROR READY Errors Cleared and if state was entered from STANDBY 10 SHUTDOWN OFF Button Payload Computer/TCS 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-1520AS0001 Draft Page 24 of 86

25 4.3.2 Functional Flow Diagram(see also overall system diagram in Appendix E) TRACKER COMPUTER Payload Computer Comms (Payload Actual Position) PAYLOAD PAYLOAD COMPUTER 1.1 Ethernet TCS Comms Acquisition System Comms 1. COMMS 1.2 RS Thermal Control Comms Time Guidance System Comms 1.2.3Power Switches Comms Axes Controllers Comms 2.1Power Up 2.2Shutdown 2.3Time Synchronization 2.PAYLOAD ALGORITHMS 2.5 Guidance 2.6Axes Command Generator 2.8Th 2.9Mo 2.10D 2.4Payload Mount Model 2.7 Acquisition 2.11So Figure PAYLOAD MMI Payload Functional Flow Diagram Doc No. SALT-1520AS0001 Draft Page 25 of 86

26 4.3.3 Function descriptions TCS COMMUNICATION The TCS shall send the following commands to the payload computer: Request Payload Computer MMI and Data (full control at TCS level Operating System Function) Mode & State Commands Tracker trajectory commands and actual positions (t,x,y) every 1 to 30 seconds with 100ms time-steps (TBC2). These commands are in the IDEAL TRACKER FRAME(ITF) Time synchronisation signals Payload configuration commands Target and Guide star selections Safety Commands (Emergency Stop etc) at 10 Hz (TBC3) The Payload Computer shall send the following information back to TCS: MMI Screens (TCS will have access to Payload computer MMI with full functionality of MMI Operating System Function) Current Mode & State at 10Hz Subsystem positions (t,x,y,z) in PMF at 10Hz Temperature measurements at 1Hz Acquisition Image at < 2Hz Acquisition Offset Guidance Image at < 10Hz Guidance Corrections at 0.03 to 10 Hz (TBC4-compensation for structural vibrations) Diagnostics and Safety Status (TBD3) ADC, Moving Baffle, Guide probe and fold mirror 1Hz TRACKER COMPUTER COMMUNICATION The Tracker Computer (TBD4) shall send the payload position to the payload computer via the TCS as indicated in Figure 11, see section The Payload Computer shall send the following information to the Tracker Computer via the TCS: Guidance Errors (t,dx,dy), see section AXES CONTROLLERS COMMUNICATION (ADC, MOVING BAFFLE, FOLD MIRRORS, CALIBRATION SOURCE) The Payload Computer shall send the following information to the Axes Controllers: Axes Commands at frequency of 10Hz TBC5. Doc No. SALT-1520AS0001 Draft Page 26 of 86

27 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 Payload Computer: Sensor Measurements at 10Hz Current Modes at 10Hz Measured Motor Currents at 10Hz ACQUISITION COMMUNICATION The Payload Computer shall send the following information to the Acquisition system _ Commands for set up / calibration (Fixed set of commands as available) The Acquisition system shall send the following information to the Payload Computer: _ Acquisition Image at 0.2 to 2Hz (TBC6) _ Acquisition system state 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 Payload Computer: Temperature Measurements (xm) at 0.1Hz (TBD2) POWER SWITCHES COMMUNICATION The Payload subsystems shall be powered up in an orderly and selectable fashion. The details shall be agreed upon in the design phase. Typically the Payload Computer shall send the following information to the Power Switches Digital Output _ On/Off Commands for Switches [Axes Controllers, Acquisition System, Guidance System, Fibre Instrument Feed, PFIS, Thermal Control] (TBC7) TIME SYNCHRONIZATION INPUT The TCS and Payload Computer shall be time synchronized to an accuracy of 1ms (TBC8) or better PAYLOAD ALGORITHMS The execution of all Payload Computer functions should be sufficiently fast so as to ensure a cycle time of 100ms or less. Doc No. SALT-1520AS0001 Draft Page 27 of 86

28 Power Up Shut Down The Payload System shall be powered up and sensors homed in a controlled fashion The Payload System shall be parked and shut down in a controlled fashion Time Synchronization The Payload Computer local time shall be synchronised with the TCS computer as specified in Payload Mount Model This model typically defines: a conversion from TCS commands to a Payload equivalent set both in PMF. Conversions to Payload subsystem Frames Calibration factors and coefficients Guidance Corrections Acquisition A set of guidance errors (t,dx,dy), in PMF, is calculated from the guidance image A set of Acquisition offset errors(t,x,y), in PMF, is calculated from the Acquisition image Axes Command Generator Using the Payload position, as reported by TCS, to calculate all subsystem position commands. The feedback from the axes controllers is used to calculate the measured position in PMF Thermal loop Extract and display temperature measurements (TBD2) Mode and State Control Control the modes and states of the Payload system Diagnostics & Safety Performs all diagnostics and safety functions. (TBD3) Software Set up & Maintenance Doc No. SALT-1520AS0001 Draft Page 28 of 86

29 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) PAYLOAD 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 ACQUISITION Implements the mode commands and tracks the position commands. Axes control shall satisfy the requirements in paragraph The observation target shall be identified and pointing offsets be calculated with sufficient accuracy and speed to satisfy the requirements in paragraph THERMAL CONTROL This function reads and displays the temperature sensor measurements POWER SWITCHES GUIDANCE The purpose of this function is to power up all subsystems in an orderly and selectable fashion. This function implements the commands from the Payload computer. This function shall satisfy the performance requirement in paragraph The guide probes shall be positioned with sufficient accuracy to ensure that the selected guide star will be within its field of view at the end of target acquisition. Guidance images shall be collected and sent to the Payload Computer for image processing. The guidance images shall be collected with sufficient accuracy and speed to satisfy the requirements in paragraph STRUCTURAL AND INTERFACE SUPPORT The Payload subsystem shall provide sufficient structural and interface support to accommodate all the relevant payload subsystems. This structure will be supported by the rotation stage of the Tracker. This support (payload structure) shall satisfy the performance requirements in paragraph Operational Concept Doc No. SALT-1520AS0001 Draft Page 29 of 86

30 Is detailed in SALT 1000AS0040, see section 2, but closed and open loop tracking, and positioning, will typically be executed as follows: Table 3 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 2. Exposure start time and Observation Duration for each target input by SA on TCS terminal or predetermined in schedule file 3. TCS sends Acquisition, tracking start times, payload position and configuration to Payload computer 4. Payload subsystems positioned and configured according to 3 5. Payload computer reports to TCS when subsystems in position and configured 6. TCS send tracker trajectory (t,x,y) to Payload Computer 7. Payload position subsystems according to 6, sending Acquisition image to TCS 8. Target and Guide Stars selected by SA on TCS terminal, TCS feed this information to Payload computer 9 Payload Computer sends Acquisition offsets and guidance correction signals to TCS compu ter (t,x,y) Table 4 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 guide star/s Once per target Once per target Once per target Once every 30 sec Continuously (at sampling frequency of axes controllers) Once per target 1Hz Star position: RA,DEC,Epoch Time, ephemeris Time available between Acquisition and Track must be variable by RA Open loop commands Controllers should interpolate commands between trajectory points 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 Doc No. SALT-1520AS0001 Draft Page 30 of 86

31 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, tracking start times, payload position and configuration to Payload computer 5. Payload subsystems positioned and configured according to 4 6. Payload computer reports to TCS when in position and configured 7. TCS sends tracker trajectory (t,x,y) to Payload Computer 8. Payload position subsystems according to 6, sending Acquisition images to TCS 9 Target or offset Star selected by SA on TCS terminal, TCS feed this information to Payload computer 10 Payload Computer sends Acquisition offsets to TCS computer (t,x,y) 11 Payload Computer positions all relevant subsystems according to Tracker position as received from TCS Acquisition time 3 minutes minimum Acquisition time 3 minutes minimum Acquisition time 2.5 minutes minimum Immediately after 1. Acquisition Time 30 seconds Immediately after 5. According to time stamp of commands Any time between Acquisition and track start time Any time between Acquisition and track start time After Track Start Time Any time Once per target Once per target Once per target Once every 30 sec Continuously (at sampling frequency of axes controllers) Once per target Until Acquisition Completed Until Track completed RA can adjust tracking rate (non sidereal) Time available between Acquisition and Track must be variable by RA Open loop commands Controllers should interpolate commands between trajectory points Table 5 Positioning. No Action Start Time Frequency Remarks 1. Tracker Position and or Payload configuration input by SA,SO on TCS or Payload Computer terminal Any time Continuously Position in ITF Doc No. SALT-1520AS0001 Draft Page 31 of 86

32 Payload Computer terminal 2. Payload Computer positions and configures subsystems according to 3 3. Payload computer reports to TCS when subsystems in position and configured Immediately after 1. When position reached and configured Once per command Doc No. SALT-1520AS0001 Draft Page 32 of 86

33 5 Payload Technical Requirements 5.1 Schematic diagram The figure below shows the major components of the payload subsystem and the communication interfaces. The numbers inside each block identifies the functions, in Figure 11, implemented by each hardware item Telescope Control System Key : Not Part of PAYLOAD Tracker Computer Instrument (HRS) Payload Computer System (1,2,3) Instrument Computer/s Tracker Rotation Stage SAC(9) Acquisition System(5) {Commisi oning Instrument ) Guidance System (8) ADC (4) Fold Mirrors (4) Moving Baffle (4) Thermal Control (6) Calibratio n Source(4) Fiber Feed Visiting Instruments Figure 12. Cable & Tube Handlers, Enclosures (10) Payload Structure (10) PFIS Major Components of Payload Subsystem and Communication interfaces All the internal interfaces between the Payload subsystem components and external interfaces between Payload subsystem and other subsystems of SALT are shown and numbered in the figure below. 5.2 SALT Payload Interfaces SALT Payload External Interfaces Doc No. SALT-1520AS0001 Draft Page 33 of 86

34 Figure 13 shows the major External interfaces for SALT. 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 13. Schematic showing SALT Payload External Interfaces The system interfaces shall comply with the Physical, Electrical and External Interface Control Dossiers referred to in Section 2 Table 6 Tracker & Payload external interfaces (Refer to Figure 13) No. Subsystem Subsystem 2 Type Direction Interface Description 1 8 TCS Payload D Both Communication cables, Trajectory Commands, Mode Commands, Measurement Feedback, Diagnostics and Safety Feedback, Payload MMI, see Table 7(e4) below 2 Structure Payload P Attachment of all cables, cooling lines, fibre optic cables running between Tracker & Payload and other sub systems Doc No. SALT-1520AS0001 Draft Page 34 of 86

35 3 Facility Payload P -> Payload E A lines, fibre optic cables running between Tracker & Payload and other sub systems Provide Access to Payload Electrical power to various parts of payload, as per Power Budget. Both 220V and 110V AC Dry, Instrument Quality Air to Payload subsystems C Liquid cooling capacity : Table 7 Payload external interfaces to Tracker (refer Figure 14) No. Subsystem Subsystem 2 Type Direction Interface Description 1 e3 Payload Computer (via TCS) Tracker Computer D -> Both Network cable Guidance Corrections Payload Position and Attitude E A e4 e5 Visiting Instrument Payload Computer Payload Structure Fibre Feed e6 Fibre Feed Payload Structure e7 e8 Payload Computer Acquisition System Acquisition System Payload Structure C P Both Mountings bolted, adjustable for alignment, volume limitation E Electrical Connections for Data, Power, Video Cables A Connections O Connections C Connections D Both Position and Status commands and feedback E Electrical Connections for Data P Both Mountings Bolted, adjustable for alignment, volume limitation E -> Fibre Electrical Connections for Data, Feed Power, Optical fibres A Connections O Connections C Connections D Both Commands and feedback (Image and Status) E Electrical Connections for Data P Both Mountings Bolted, adjustable for alignment, volume limitation E -> Electrical Connections for Data, Acquisition Power A Connections Doc No. SALT-1520AS0001 Draft Page 35 of 86

36 e9 PFIS Rotation Stage e10 e11 Rotation Stage Payload Alignment System Payload Structure SAC O Connections C Connections P Both Mountings Bolted, adjustable for alignment, volume limitation E -> PFIS Electrical Connections for Data, Power A -> PFIS Connections O -> PFIS Connections C -> PFIS Connections P Both Mountings Bolted, adjustable for alignment, diameter limitation E -> Payload Electrical Connections for Data, Structure Power, Video A Connections O Connections C Connections P Both Mountings Bolted, adjustable for alignment, diameter limitation E -> Electrical Connections for Data, Alignment Power System A Connections O Connections C Connections Doc No. SALT-1520AS0001 Draft Page 36 of 86

37 5.2.2 SALT Payload Internal Interfaces Telescope Control System (TCS) Not Part of PAYLOAD INTERFACES e** : external ** : internal e1 1 Thermal Control 2 All payload subsystems 3 Calibration Source 4 5 Fold Mirrors 6 FACILITY Tracker COMPUTER e2 e3 via TCS Payload Computer PFIS Payload Alignment e5 e7 e9 19 Moving Baffle ADC Guidance System e11 SAC Visit Instr Fibre Feed Acquisition System (Comm Instr) Rho-Drive System e4 e6 e8 e10 Payload STRUCTURE 14 Tube & Cable Handlers & Enclosures Doc No. SALT-1520AS0001 Draft Page 37 of 86

38 Figure 14. Interfaces For a complete description of all the interfaces, refer to the interface control dossier, listed in section 2 Table 8 Internal Interfaces No. Subsystem 1 Subsystem 2 Type Direction Interface Description 1,3, See Fig Payload D Both Electrical Connections for Data, 5,7, 9,11 Figure 14 Computer Power Commands Feedback 2 Thermal All Payload P Mounting, Connectors Control Subsystems D Thermal Temperature Feedback Control C Subsystems Coolant Supply, drain 4,6 8,10 12,13 Payload Structure 14 Cable & Tube Handlers (for r stage, forms part of tracker) E Subsystems Power See Fig Figure P Both Mountings 14 E,A,D, Subsystems Connectors O,C Payload P Handler Bolted to Rotation Stage Structure E Connectors A Connectors D Connectors O Connectors C Connectors 5.3 SALT Payload Characteristics Performance Characteristics The payload consist of the following subsystems: SAC (Spherical Aberration Corrector) ADC (Atmospheric Dispersion Compensator) Guidance System Moving Baffle Fold Mirrors Fixed Baffle Calibration Screen Thermal control system Payload structure Payload computer Cable & Tube Handling Doc No. SALT-1520AS0001 Draft Page 38 of 86

39 The Payload subsystem performance characteristics that are required to perform the functions above are described below: SAC For details of the requirements, refer to Section 2, SAC Specification. a) Image Quality The contribution of the SAC towards image quality shall be less than 0.2 arc seconds (EE50) and less than arc seconds (EE80) in its operational environment. The nominal optical axis of the SAC will be 37 degrees from vertical (when positioned at the Primary Mirror Vertex). Due to tracking this angle can vary with degrees in two directions. The SAC not rotate with the rest of the payload during tracking.(tbc9) b) Field of View(FOV) The FOV shall not be less than 10 arc minutes. c) Entrance Pupil The SAC shall have an entrance pupil within the range 10.5 to 11m. The final selection will be made after cost/performance tradeoffs at the supplier. d) Delivered F-ratio e) Stray Light The final F-ratio shall be A fixed baffle ( not part of SAC) shall be provided at the optical entrance to the SAC to prevent stray light from entering it. Absorbent baffles shall be provided inside the SAC to prevent vignetted stray light from striking the focal plane. The surface finish shall be such that 98% of all impacting light will be absorbed for wavelengths between (TBD5). f) SAC mirror coatings As specified in doc.: SALT-1523AS0002, SAC Optical Specification ADC a) Image Quality The ADC shall not degrade the image at 500nm by more than 5%. b) Wavelength Coverage The ADC shall correct dispersion for wavelengths from 320 to 850nm, with a design goal of 1800nm. At least 95% of the light in these wavelengths shall be transmitted. Doc No. SALT-1520AS0001 Draft Page 39 of 86

40 c) Secondary Dispersion As introduced by the ADC shall not exceed 0.15 arc seconds. d) Insertion The ADC will be installed in a fixed position on the payload structure GUIDANCE SYSTEM a) Guidance Concept Light path Guidance Probe position PFIS Sc Sc Science Field Science & Guidance Field Sc Fibre Bundle Auxiliary Port FIF Acquisition Sc Guidance camera & Optics Guidance Images Guidance Corrections Probe Position commands & feedback Payload Computer Guidance Corrections b) Position of Guide Stars TCS All guide stars will be located in a 1 arc minute annulus, from 4 to 5 arc minutes in radius from the centre of the field. Provision shall be made for guidance using the science field at the Acquisition system by means of a beam splitter where a (TBD6)% of the light will be Doc No. SALT-1520AS0001 Draft Page 40 of 86

41 used for guidance and the rest for science at any of the science instruments. c) Number of Guidance Positions Provision shall be made for guidance pickups at the following positions: - Acquisition System (in 4-5 field and in science field using beam splitter) - Fibre Feed - PFIS NOTE: The instrument at the auxiliary port shall provide guidance corrections to the TCS. d) Brightness of Guidance Objects Shall be brighter than 21st magnitude. e) Guidance correction and image update rates The guidance errors and image shall be fed back to the TCS at rates between 10 Hz to 1/30 Hz (TBC4). f) Guidance Field of view The pointing accuracy of the telescope will be 15 arc seconds. It shall be ensured that once the telescope is pointed towards a target, the guide star will be on the guidance pickup. g) Guidance Error The guidance system shall introduce a guidance error of less than 0.05 arc seconds for all guidance positions and object brightness. Doc No. SALT-1520AS0001 Draft Page 41 of 86

42 MOVING BAFFLE The moving Baffle shall ensure that no light from outside the Primary Mirror enters the focal plane. a) Degrees of Freedom The Moving Baffle shall have 4 degrees of freedom (TBC10), x, y, z and rotation. b) Range of Motion The Moving Baffle shall have a sufficient range in each degree of freedom to compensate for the payload motions and the curvature of the exit pupil, which are: - 17 degrees rotation in tip and tilt degrees in rotation (TBC9) - 210mm radius of curvature in exit pupil c) Accuracy of Motion The Moving Baffle Aperture shall be aligned within 0.5 arc minutes from the edge of the Primary Mirror. d) Speed of Motion The Moving Baffle Aperture shall maintain accuracy at tracking speeds, 0 to 20 arc seconds per second and at flat fielding speeds, 5 degrees per second. e) Aperture Stop An aperture stop shall be mounted on the fixed part of the moving baffle to ensure no light outside the entrance pupil propagate to the focal plane FIXED BAFFLE a) Stray light b) Structure The surface finish shall be such that 98% of all impacting light will be absorbed for wavelengths between (TBD6). The drivers for the design has still to be determined (TBD7) The structure shall not interfere in any way with the SAC structure. The deflections under wind loading and or varying gravity components shall not cause it to touch the SAC structure at any point FOLD MIRRORS Doc No. SALT-1520AS0001 Draft Page 42 of 86

43 The Fold Mirrors shall ensure that light is channelled to the selected instrument/s. a) Reflectivity The same as SACmirrors b) Degrees of Freedom Each Fold Mirrors shall have 1 linear degree of freedom for insertion. c) Range of Motion The Fold mirrors shall have sufficient range in each degree of freedom for insertion - Insertion Range (TBD8) and depend on design d) Accuracy of Motion The Fold Mirrors shall be positioned with such accuracy that the image position in the focal plane is repeatable to within 0.05 arc seconds. e) Speed of Motion The insertion time of any mirror should be less than 5 seconds. f) Number of Mirrors Light shall be directed to the following instruments, which will be at different locations: - Acquisition System (x2 make provision for beam splitter) - PFIS - Fibre Feed - Auxiliary Port g) Optical Quality The mirrors shall be flat to 1/20l rms CALIBRATION SOURCE AND SCREEN The Calibration Source shall illuminate the selected instrument with equal intensity anywhere in the telescope pupil. Note that the Calibration Source is CFE equipment as described under section 3. a) Intensity variations in the FOV TBD9. Doc No. SALT-1520AS0001 Draft Page 43 of 86

44 b) Light Sources Flat Field lamp (Halogen) Blue diode Lamp Arc lamps: Cu-Ar, Cu-Ne,He,Fe-Ar,Th-Ar,Th-Ne c) Degrees of freedom Shall have a linear degree of freedom for sliding in and out of the light path. d) Other functions TBD THERMAL CONTROL PAYLOAD STRUCTURE (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). Glycol source /drain points will be supplied at the Tracker rotation stage. The Payload structure shall support all the Payload subsystems and relevant Client Furnished Equipment (PFIS, Fibre Feed, Commissioning Instrument), under the operating conditions, operational envelope, ensuring that structural deflections due to external forces and mass distribution of the various subsystems as well as temperature effects shall not affect the image quality by more than: arc seconds (EE50) arc seconds (EE80) PAYLOAD COMPUTER The Payload Computer shall execute all software reliably within a cycle time sufficiently short not to compromise the performance of the various payload subsystems and other telescope subsystems CONTROL LOOP REQUIREMENTS All Control loops shall satisfy the following stability and bandwidth requirements under all loading conditions: Phase margin: > 50 degrees Gain Margin: > 8dB Maximum Overshoot: < 2% SAFETY Doc No. SALT-1520AS0001 Draft Page 44 of 86