1. 20 October 200412004 International Telemetering Conference Flying CFDP MESSENGER Christopher J. Krupiarz and Brian K. Heggestad The Johns Hopkins University Applied Physics Laboratory Richard D. Carper Consultant, Space Data Systems

2. 20 October 200422004 International Telemetering Conference File-Based Data Processing on MESSENGER » MESSENGER Mission Profile » CCSDS File Delivery Protocol (CFDP) » MESSENGER Flight Software » Mission Operations » CFDP Status

3. 20 October 200432004 International Telemetering Conference MESSENGER Mission Profile » MErcury, Surface, Space ENvironment, Geochemistry, and Ranging (MESSENGER) mission » Launched August 3 rd, 2004 » Two flybys each of Venus, Three of Mercury » One year orbit of Mercury beginning in 2011 » Seven instruments –Mercury Dual Imaging System (MDIS) »Narrow-angle and Wide-angle Imagers –Mercury Atmospheric & Surface Composition Spectrometer (MASCS) »Ultraviolet-Visible & Visible-Infrared Spectrometers –Gamma-Ray & Neutron Spectrometers (GRNS) –X-Ray Spectrometer (XRS) –Magnetometer (MAG) –Mercury Laser Altimeter (MLA) –Energetic Particle and Plasma Spectrometer (EPPS)

4. 20 October 200442004 International Telemetering Conference MESSENGER Spacecraft Computer » Each Integrated Electronics Modules (IEM) contains two RAD6000 processors and a solid state data recorder –25-MHz Main Processor (MP) –5-MHz Fault Protection Processor (FPP) –8 Meg RAM for the MP / 4 Meg RAM for FPP –8-Gbit DRAM-based Solid State Recorder (SSR) » MP provides both Command and Data Handling (C&DH) and Guidance and Control (G&C) » CCSDS compliant protocols employed –VxWorks based file system used with CFDP to optimize downlink

5. 20 October 200452004 International Telemetering Conference CFDP Overview » Recommendation of CCSDS, October 2002 » Provides the capability to transfer files to and from a spacecraft mass memory » Interface is conceptually similar to FTP (e.g. get, put, delete…) » Files can be transferred in two types of modes: –Unreliable -- best effort is made –Reliable -- delivery is guaranteed (chosen for MESSENGER) » File transfer can be triggered from a given entity or indirectly through a proxy mode » PDU (Protocol Data Unit) is the common message format between space and ground — Variable length — Used for file requests & file data

6. 20 October 200462004 International Telemetering Conference Example File Transfer Dropped PDUX AcknowledgementACK Finished (receiver to sender)FIN End of file (sender to receiver)EOF Retransmission requestNAK File data segmentFD(n) MetadataM PDU TypeAbbr. » » Acknowledged Mode/Deferred NAKs » » Ground system waits for EOF PDU from flight before issuing NAK PDU » » MIB specified timeout would also cause the generation of a ground system NAK PDU Diagram courtesy of CCSDS Flight Ground

7. 20 October 200472004 International Telemetering Conference CFDP On MESSENGER » CFDP Selections for MESSENGER: –Reliable mode –Deferred NAKs » CFDP Simplifications –One way file transfer--from spacecraft to ground –Commands to downlink files instead of CFDP –File system ops through commanding, not CFDP » Flight Software –JHU/APL implementation –Chose to do in-house due to MESSENGER constraints » Ground Software –Integrated NASA/JPL implementation

8. 20 October 200482004 International Telemetering Conference MESSENGER CFDP Flight Software » Provides the capability to transfer files from spacecraft » Implements a subset of the CFDP Blue Book -- “CFDP Lite” –Deferred NAKs –Sending of files –Reliable transfer –Cancellation of individual transaction » Also performs file system operations » Controlled by the Playback Task » Design consists of two elements –Method calls to CFDP from Playback Task »Get PDU »Processing Control –1 Hz task to perform PDU and timer processing » Limited resource usage part of design

9. 20 October 200492004 International Telemetering Conference File System Data Flow

10. 20 October 2004102004 International Telemetering Conference Non-Image Data » Instruments other than MDIS –Packetized data sent via 1553 Bus » Engineering data » Telemetry data » Directory listings –Individual directories –Cumulative directories

11. 20 October 2004112004 International Telemetering Conference Solid State Recorder File System » /DNL/ Prioritized Sub-directories –/P0 - Critical OpNavs –/P1 - Hskpg Snapshot & Promoted Files –/P2 - High Priority Operational Files –/P3 - High Priority Science, Health & Safety Files –/P4 - Orbit Maintenance/Reconstruction OpNavs –/P5 - Prime Science Files (Medium Priority Science) –/P6 - Bonus Science Files (Low Priority Science) –/P7 - Instrument Burst & Contingency Files –/P8 - Autonomy Spawned Engineering Files –/P9 - Engineering Contingency Files Next Track Some Future Track Data Recovery Not Guaranteed

12. 20 October 2004122004 International Telemetering Conference MESSENGER Orbit » » Periapsis - 200 km » » Apoapsis - 15,193 km » » 8 hr track when spacecraft is furthest away from Mercury

13. 20 October 2004132004 International Telemetering Conference Nominal DSN Track Single Station DSN Track with Ranging Beginning of Allocation (BOA) End of Allocation (EOA) Receiver Re-Configuration & Coherent Downlink Acquisition - Resume Playback - Playback Ancillary Housekeeping as Required - Commence Scheduled Command Activities Station Pre Cal Station Post Cal (15 minutes) Beginning of Track (BOT) End of Track (EOT) Nominal Station Allocation - 8 Hours Nominal Track Duration - 6.75 Hours Nominal Playback Duration - 6.25 Hours Transmitter ON / Uplink Sweep & Non Coherent Downlink Acquisition Real-Time Housekeeping - Initial Spacecraft State & Health Evaluation Begin Housekeeping Telemetry Playback - Evaluate Playback Housekeeping Telemetry via Ground Tools - Suspend Playback RTLT

14. 20 October 2004142004 International Telemetering Conference CFDP Monitoring and Assessment » Mission Operations is responsible for maintaining optimal File System operations » SSR Status –Ops will verify highest priority data is being downlinked –Verify that CFDP properly resumes pre-empted playback transmissions and that ground accounting is correct –Document any Pause/Resume activities to ensure there are no problems –CFDP NAKs, transfer status and complete status will be closely monitored and compared with expected –Ground accounting properly maintained and backed up from one track to the next

15. 20 October 2004152004 International Telemetering Conference File System Management » Mission Operations is responsible for maintaining optimal File System management » SSR Status –Avoiding SSR space saturation »Managing contingency files »Managing /M/TRASH directory –Re-prioritization of files »Determination by Ops team to up the priority of a given file

16. 20 October 2004162004 International Telemetering Conference Mission/CFDP Status » MESSENGER Spacecraft is operating nominally » CFDP has downlinked ~1800 files totaling 1.5 Gigabytes » Initial issues: –Setting of timeouts on both flight and ground software »Handful of transactions improperly failed due to settings of NAK and overall transaction timers »Better communication between developers and mission operations –Large files create difficulties for ground system »Large files were to be avoided, but some were created due to improper or emergency configurations –Rebuild of data from telemetry received on ground »Resending of files can be done during cruise phase, unlikely in orbit »Re-creation of files from archived telemetry necessary

17. 20 October 2004172004 International Telemetering Conference Summary » New architecture for JHU/APL » Driven by MESSENGER constraints » Limited by hardware constraints » Autonomous file selection » CFDP used for delivery files » Mission operations

18. 20 October 2004182004 International Telemetering Conference Flying CFDP on MESSENGER Questions?