Onboard Data Handling

Gert CaspersenTerma A/S

gec@terma.com

Objectives

Introduction of onboard datahandling concepts andcharacteristics

What Will be Said

S Satellite ElementsS CharacteristicsS PurposeS OperationsS Logical ModelS ArchitectureS FunctionsS Ørsted onboard data handlingS RobustnessS Software DevelopmentS PitfallsS Résumé

Satellite Elements

PurposeLogisticsS Power distributionS CommandingS Time synchronisationS Status reporting

CommunicationS With groundS On satellite

AutonomyS Handle platform & payload without ground contact

Anomaly HandlingS Maintain mission objectivesS Prevent loss of satellite

Characteristics

Limited ResourcesS Processing powerS MemoryS Bandwidth on busses

Embedded Real-Time SoftwareS Hard real-time requirementsS Numerous events & actionsS Boot-strap software & application softwareS No operating system (bare platform)

Hostile EnvironmentS Fault preventionS Fault tolerance

Operations

Satellite

Ground Station

Spacelink

Control Centre

Network

Operators

OperationsProcedures

Command Time Line

MONSDPU

FMCHU

MONSCHU

STRCHU2

DEBUG

CDH

COMANT1

ANT2

RWA1

TEST

STRCHU1

RWA0

RWA3

RWA2

Red

unda

nt D

ata

Bus

PCDU

Subsystems

Rømer Data Handling Context

Exercise: The Black Box

Perceive a computer with a piece of embeddedsoftware.

It is a block box revealing only a limited amount ofstatus information.

What status information shall be available to assess theintegrity of:

1: Hardware

2: Software

OnboardTraffic

Management

ServiceProvider 1

ServiceProvider 2

ServiceProvider n

ServiceUser 1

ServiceUser 2

ServiceUser n

Serv ice Request

Serv ice Reports

Service Requests

Service Reports

...

...

Logical Model: Abstraction

ApplicationProcess N

Space Segment

Data Handling & Control System

OnboardTraffic

Management

ApplicationProcess 1

ApplicationProcess 2

ControlCentre 1

ControlCentre 2

ControlCentre N

Telecommand

Telemetry

Telecommand

Telemetry

...

...

Ground Segment

ProvidedServices

LocalSubsystem Provided

Services

ProvidedServices

RemoteSubsystem

Logical Model: Implementation

ESA Standards

Packet Telecommand StandardS Protocol for uplink: Ground segment ���� Space segmentS Stream of telecommand packets

Packet Telemetry StandardS Protocol for downlink: Space segment ���� Ground segmentS Stream of telemetry packets

Packet Utilisation StandardS Application layer: Ground segment vs. Space segmentS Logical model for satellite operation

Destination ID SequenceCounter Command Type Data Checksum

Head Tail

Telecommand

Originator ID SequenceCounter Telemetry Type Data Checksum

Head Tail

Time StampTelemetry

Telecommand/Telemetry Formats

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

TelecommandPacket ID

Packet SourceControl Code Parameters

TelecommandPacket ID

Packet SourceControl Code ParametersStep Number

Acceptance/Completion

Telemetry

Progress

Telecommand Verification

Telecommand Verification ServiceS Success/failure of telecommand executionS Error codeS Telecommand identification

SID ParametersHousekeeping Report

Telemetry

Housekeeping Data Collection

Housekeeping & Diagnostics Data ReportingS Periodic reading of parameter valuesS Reporting of temporally coherent valuesS Typical period: 60 seconds

RID ParametersEvent Report

Telemetry

Event Reporting

Event ReportingS Nominal eventsS Anomalies/errors

Memory ID N Start Address Data

Memory ID N Start Address Length

Memory ID N Start Address Length Checksum

Load

Dump

Checksum

Telecommand

Memory ID N Start Address Length

Memory ID N Start Address Data

Telemetry

Memory Read/Write

Memory ManagementS Reading/writing/verificationS Software updates (patching)S Debugging/diagnostics

Function ID Parameters

Function ID

Function ID ParametersActivity ID

Activate Funtion

Deactivate Funtion

Perform Activity

Telecommand

Function Activation/Deactivation

Function ManagementS Activation/deactivation of functions, modes etc.S Execution of activitiesS Functions identified by ASCII-string

Time Report

Telemetry

SatelliteTime

Time Synchronisation

Time ReportingS Generate time reports containing time stampS Report related to event on downlinkS Period based on required accuracy

Time Tag 1Range

N Abs/Rel TimeTag

TelecommandPacket

Time Tag 2

N Abs/Rel TimeTag

ApplicationProcess ID

SequenceCount

...Insert Telecommand

Delete Telecommands

Report Schedule

Telecommand Telemetry

Command Time Line

Onboard SchedulingS Time line of telecommandsS Executed when dueS Updated based on operational schedule/time line

N Parameter# ParameterValue Limit Crossed Transition TimeOut-of-Limit report

Telemetry

...

Parameter Monitoring

Onboard MonitoringS Periodic reading of parameter valuesS Comparison against nominal rangeS Report deviationsS Initiate error handling

Telemetry Storage

Onboard Storage & RetrievalS Storage of telemetryS Inserted in downlink during ground contactS Separate stores for different telemetry typesS Prioritised read-out

Exercise: Autonomy

Communication between satellite and control centre ispossible 2 times 10 minutes per day.

The remaining time it must survive on its own.

What anomalies/event/situations should your satellitebe able to handle autonomously?

PowerConditioning &

Distribution

Attitude ControlSystem

Onboard StorageAdministrator

PlatformManager

TelecommandScheduler

Ground Ground I/F PacketRouter Payload Payload

Actuators& Sensors

PCDUSubsystem

PowerConditioning &

Distribution

Attitude ControlSystem

Onboard StorageAdministrator

PlatformManager

TelecommandScheduler

Ground Ground I/F Payload Payload

Actuators& Sensors

PCDUSubsystem

PacketRouter

PowerConditioning &

Distribution

Attitude ControlSystem

Onboard StorageAdministrator

PlatformManager

TelecommandScheduler

Ground Ground I/F PacketRouter Payload Payload

Actuators& Sensors

PCDUSubsystem

Software Architecture

Ørsted

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

Ariane 501

S Error in Inertial Reference SystemS 64-bit float ���� 16-bit integer = OverflowS Chain of errors:S Reuse from Ariane 4; No revalidationS No exception handlingS Post-mortem dump ���� Valid input for data handling software

Fault Prevention Fault Removal Fault Tolerance

Fault Analysis SupportingMethods & Tools

RestrictingMethods & Tools

Static FaultRemoval

Dynamic FaultRemoval

ErrorDetection

ErrorRecovery

Software Robustness Engineering

Fault Prevention Fault Removal Fault Tolerance

Fault Analysis SupportingMethods & Tools

RestrictingMethods & Tools

Static FaultRemoval

Dynamic FaultRemoval

ErrorDetection

ErrorRecovery

Software Robustness Engineering

Fault Prevention Fault Removal Fault Tolerance

Fault Analysis SupportingMethods & Tools

RestrictingMethods & Tools

Static FaultRemoval

Dynamic FaultRemoval

ErrorDetection

ErrorRecovery

Software Robustness Engineering

Fault Prevention Fault Removal Fault Tolerance

Fault Analysis SupportingMethods & Tools

RestrictingMethods & Tools

Static FaultRemoval

Dynamic FaultRemoval

ErrorDetection

ErrorRecovery

Software Robustness Engineering

Robustness

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 ...

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!