20 October 200412004 International Telemetering Conference Flying CFDP MESSENGER Christopher J....
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Transcript of 20 October 200412004 International Telemetering Conference Flying CFDP MESSENGER Christopher J....
20 October 2004 12004 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
20 October 2004 22004 International Telemetering Conference
File-Based Data Processing on MESSENGER
» MESSENGER Mission Profile
» CCSDS File Delivery Protocol (CFDP)
» MESSENGER Flight Software
» Mission Operations
» CFDP Status
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MESSENGER Mission Profile
» MErcury, Surface, Space ENvironment, Geochemistry, and Ranging (MESSENGER) mission
» Launched August 3rd, 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)
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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
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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
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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
M
FD(1)
FD(2)
FD(i)
FD(last)
EOF
(close)
FIN
Sender Receiver
M
FD(i)
X
X
ACK(FIN)
NAK(M,FD(i))
ACK(EOF)
(close)
Flight GroundFlight Ground
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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
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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
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File System Data Flow
GRNS MLA MASCS
EPPS XRS MAG
MDIS Compression
1553 Bus
TelemetryPackets
RawImages
Ground CFDP
Main Processor Ground Software
FlightFile
System
UnixFile
System
Compressed
Images
Instruments
Flight CFDP
CFDPPDUs
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Non-Image Data
» Instruments other than MDIS– Packetized data sent via 1553 Bus
» Engineering data
» Telemetry data
» Directory listings– Individual directories– Cumulative directories
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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
NextTrack
Some Future Track
DataRecovery
NotGuaranteed
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MESSENGER Orbit
» Periapsis - 200 km» Apoapsis - 15,193
km» 8 hr track when
spacecraft is furthest away from Mercury
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Nominal DSN Track
Single Station DSN Track with Ranging
Beginning of Allocation Beginning of Allocation (BOA)(BOA)
End of Allocation End of Allocation (EOA)(EOA)
Receiver Re-Configuration & Coherent Downlink Acquisition Receiver Re-Configuration & Coherent Downlink Acquisition - Resume Playback - Resume Playback - Playback Ancillary - Playback Ancillary Housekeeping as Required - Commence Housekeeping as Required - Commence Scheduled Command ActivitiesScheduled Command Activities
Station Station Pre CalPre Cal
StationStationPost CalPost Cal
(15 minutes)(15 minutes)
Beginning of Track Beginning of Track (BOT)(BOT)
End of Track End of Track (EOT)(EOT)
Nominal Station Allocation - 8 HoursNominal Station Allocation - 8 Hours
Nominal Track Duration - 6.75 HoursNominal Track Duration - 6.75 Hours
Nominal Playback Duration - 6.25 HoursNominal Playback Duration - 6.25 Hours
Transmitter ON / Uplink Sweep &Transmitter ON / Uplink Sweep &Non Coherent Downlink AcquisitionNon Coherent Downlink Acquisition
Real-Time Housekeeping Real-Time Housekeeping - Initial Spacecraft State & Health Evaluation - Initial Spacecraft State & Health Evaluation Begin Housekeeping Telemetry Playback Begin Housekeeping Telemetry Playback - Evaluate Playback Housekeeping Telemetry via Ground Tools - Evaluate Playback Housekeeping Telemetry via Ground Tools - Suspend Playback- Suspend Playback
RTLTRTLT
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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
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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
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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
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Summary
» New architecture for JHU/APL
» Driven by MESSENGER constraints
» Limited by hardware constraints
» Autonomous file selection
» CFDP used for delivery files
» Mission operations