Flying CFDP MESSENGER

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


File-Based Data Processing on MESSENGER

» MESSENGER Mission Profile

» CCSDS File Delivery Protocol (CFDP)

» MESSENGER Flight Software

» Mission Operations

» CFDP Status


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)


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


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


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


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


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


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


Non-Image Data

» Instruments other than MDIS– Packetized data sent via 1553 Bus

» Engineering data

» Telemetry data

» Directory listings– Individual directories– Cumulative directories


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


MESSENGER Orbit

» Periapsis - 200 km» Apoapsis - 15,193

km» 8 hr track when

spacecraft is furthest away from Mercury


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


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


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


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


Summary

» New architecture for JHU/APL

» Driven by MESSENGER constraints

» Limited by hardware constraints

» Autonomous file selection

» CFDP used for delivery files

» Mission operations


Flying CFDP on MESSENGER

Questions?

Documents

Flying CFDP MESSENGER