Onboard Data Handling. Gert Caspersen Terma A/S

Transcription

1 Onboard Data Handling Gert Caspersen Terma A/S

2 Objectives Introduction of onboard data handling concepts and characteristics

3 What Will be Said S Satellite Elements S Characteristics S Purpose S Operations S Logical Model S Architecture S Functions S Ørsted onboard data handling S Robustness S Software Development S Pitfalls S Résumé

4 Satellite Elements

5 Purpose Logistics S Power distribution S Commanding S Time synchronisation S Status reporting Communication S With ground S On satellite Autonomy S Handle platform & payload without ground contact Anomaly Handling S Maintain mission objectives S Prevent loss of satellite

6 Characteristics Limited Resources S Processing power S Memory S Bandwidth on busses Embedded Real-Time Software S Hard real-time requirements S Numerous events & actions S Boot-strap software & application software S No operating system (bare platform) Hostile Environment S Fault prevention S Fault tolerance

7 Operations Operations Procedures Command Time Line Satellite Operators Spacelink Control Centre Ground Station Network

8 Rømer Data Handling Context TEST RWA 0 STR CHU1 FM CHU MONS CHU DEBUG MONS DPU Redundant Data Bus RWA 1 RWA 2 RWA 3 STR CHU2 CDH PCDU ANT1 ANT2 COM Subsystems

9 Exercise: The Black Box Perceive a computer with a piece of embedded software. It is a block box revealing only a limited amount of status information. What status information shall be available to assess the integrity of: 1: Hardware 2: Software

10 Logical Model: Abstraction Service Provider 1 Service Provider 2... Service Provider n Service Request Service Reports Onboard Traffic Management Service Requests Service Reports Service User 1 Service User 2... Service User n

11 Logical Model: Implementation Space Segment Rem ote Subsystem Local Subsystem Provided Services Application Process 1 Telecommand Provided Services Application Process 2 Telemetry... Provided Services Application Process N Onboard Traffic Management Data Handling & Control System Telecommand Telemetry Control Centre 1 Control Centre 2... Control Centre N Ground Segment

12 ESA Standards Packet Telecommand Standard S Protocol for uplink: Ground segment Space segment S Stream of telecommand packets Packet Telemetry Standard S Protocol for downlink: Space segment Ground segment S Stream of telemetry packets Packet Utilisation Standard S Application layer: Ground segment vs. Space segment S Logical model for satellite operation

13 Telecommand/Telemetry Formats Head Tail Telecommand Destination ID Sequence Counter Command Type Data Checksum Head Tail Telemetry Originator ID Sequence Counter Telemetry Type Time Stamp Data Checksum

14 Functions S Telecommand verification S Housekeeping data collection S Event reporting S Memory read/write S Function activation/deactivation S Time synchronisation S Command time line S Parameter monitoring S Telemetry storage

15 Telecommand Verification Telecommand Verification Service S Success/failure of telecommand execution S Error code S Telecommand identification Telemetry Acceptance/Completion Telecommand Packet ID Packet Source Control Code Parameters Progress Telecommand Packet ID Packet Source Control Step Number Code Parameters

16 Housekeeping Data Collection Housekeeping & Diagnostics Data Reporting S Periodic reading of parameter values S Reporting of temporally coherent values S Typical period: 60 seconds Telemetry Housekeeping Report SID Parameters

17 Event Reporting Event Reporting S Nominal events S Anomalies/errors Telemetry Event Report RID Parameters

18 Memory Read/Write Memory Management S Reading/writing/verification S Software updates (patching) S Debugging/diagnostics Telecommand Telemetry Load Memory ID N Start Address Data Dump Memory ID N Start Address Length Memory ID N Start Address Data Checksum Memory ID N Start Address Length Memory ID N Start Address Length Checksum

19 Function Activation/Deactivation Function Management S Activation/deactivation of functions, modes etc. S Execution of activities S Functions identified by ASCII-string Telecommand Activate Funtion Function ID Parameters Deactivate Funtion Function ID Perform Activity Function ID Activity ID Parameters

20 Time Synchronisation Time Reporting S Generate time reports containing time stamp S Report related to event on downlink S Period based on required accuracy Telemetry Time Report Satellite Time

21 Command Time Line Onboard Scheduling S Time line of telecommands S Executed when due S Updated based on operational schedule/time line Telecommand Telemetry Insert Telecommand N Abs/Rel Time Tag Telecommand Packet... Delete Telecommands Range Time Tag 1 Time Tag 2 Report Schedule N Abs/Rel Time Tag Application Process ID Sequence Count

22 Parameter Monitoring Onboard Monitoring S Periodic reading of parameter values S Comparison against nominal range S Report deviations S Initiate error handling Telemetry Out-of-Limit report N Parameter# Parameter Value Limit Crossed Transition Time...

23 Telemetry Storage Onboard Storage & Retrieval S Storage of telemetry S Inserted in downlink during ground contact S Separate stores for different telemetry types S Prioritised read-out

24 Exercise: Autonomy Communication between satellite and control centre is possible 2 times 10 minutes per day. The remaining time it must survive on its own. What anomalies/event/situations should your satellite be able to handle autonomously?

25 Software Architecture Onboard Storage Administrator Platform Manager Telecommand Scheduler Packet Ground Ground I/F Payload Payload Router Attitude Control System Power Conditioning & Distribution Actuators & Sensors PCDU Subsystem

26 Ørsted

27 Ørsted onboard data handling Hard Real-Time HOOD Fomral RAISE specifications Automatic code generation + manual programming Ada 83 Scehdulability analysis: Deadline monotonic scheduling In-Circuit emulator for software validation Incremental development: Simulators prototypes final product

28 Ariane 501 S Error in Inertial Reference System S 64-bit float 16-bit integer = Overflow S Chain of errors: S Reuse from Ariane 4; No revalidation S No exception handling S Post-mortem dump Valid input for data handling software

29 Robustness Software Robustness Engineering Fault Prevention Fault Removal Fault Tolerance Fault Analysis Supporting Methods & Tools Restricting Methods & Tools Static Fault Removal Dynamic Fault Removal Error Detection Error Recovery

30 Pitfalls Interfaces: Focus from day one Bidets: Estimate and survey Schedulability: Estimate and survey Fault tolerance: Keep it simple, stupid! (KISS) Verification & validation: Unit test, integration test, system test...

31 Résumé Embedded real-time software Tasking kernel Real-time requirements Schedulability analysis Fault tolerance Fail-stop Numerous interfaces Interface control documents Verification Simulators & prototypes Keep it simple, stupid!