ditUPM

STRAST

UPMSat-2On-board computers

Grupo de Sistemas de Tiempo Real y Arquitectura de Servicios TelemáticosUniversidad Politécnica de Madrid

©2011 grupo STRAST2011-05-12

STRAST

UPMSat-2Computers in spacecraft

• Computers are used on board of spacecraft for a variety of functions, e.g.

‣ computing attitude and orbit control algorithms (AOCS)

‣ performing other platform control functions

‣ processing and storing data for various subsystems

‣ handling communications with the ground segment

• telecommand (TC) / telemetry (TM)

‣ handling payload data and ground communications

• Depending on the size and complexity of the spacecraft these functions may be allocated to one or more on-board computers (OBC)

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UPMSat-2

2011-05-12 ©2011 grupo STRAST

Centralized vs de-centralized architecture

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OBCTMC

actuators

sensors

othersubsystems

OBCTMC

actuators

sensors

othersubsystems

system bus

©2011 grupo STRAST2011-05-12

STRAST

UPMSat-2Computer hardware

• Environment conditions restrict applicable technology

• radiation may cause damage to electronic circuits

• limited power availability

‣ CPU and memory technology slower than state-of-the-art

• ESA has qualified the LEON processor family

‣ based on the SPARC v8 32 bit RISC architecture

‣ open-source VHDL model available under GPL

‣ speed ≈ 100 MHz, power ≈ 1 W

• Computers are connected to other subsystems via high-speed data links

‣ serial buses: SpaceWire, CAN bus, MIL1553B

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©2011 grupo STRAST2011-05-12

STRAST

UPMSat-2Computer software

• Many critical functions depend on software

‣ high-integrity requirements

• Most software functions have real-time requirements

‣ have to be carried out within specific time intervals

• Verification & validation process is crucial

‣ safety management

• Technology choice driven by high-integrity requirements

‣ e.g. Ada, RTOS, static analysis, temporal analysis

• Standards: ECSS-E-ST-40-C / ECSS-Q-ST-80-C

‣ specify software development process depending on criticality level

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©2011 grupo STRAST2011-05-12

STRAST

UPMSat-2Ada

• Programming language for high-integrity, large embedded systems

‣ developed under US DoD contract starting in 1973

‣ the current version is Ada 2005

• Strong support for concurrency and real-time

‣ concurrent tasks, shared data objects

• Support for mixed-language programming

‣ standard interfaces to C and other languages

• Used in critical software domains

‣ aeronautics, railways, nuclear plants, space

‣ Ravenscar profile: tasking subset for high-integrity systems

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©2011 grupo STRAST2011-05-12

STRAST

UPMSat-2Open Ravenscar Kernel (ORK)

• Real-time tasking kernel supporting the Ada Ravenscar profile

‣ running on LEON2-3 bare-board computers

‣ no underlying RTOS needed

• Supports concurrent threads of execution (Ada tasks)

‣ communication by means of shared data objects with mutually exclusive access

• Predictable scheduling and communication

‣ real-time properties can be analysed and proved correct

• Careful, reliable design

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UPMSat-2

2011-05-12 ©2011 grupo STRAST

Cross-compilation chain

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debugger

compilersource

filesobjectfiles

linker

Development platform(Linux workstation)

Target platform(LEON-based computer)

RTSsources

RTSbinaries

simulator executablefile

monitor loadedprogram

• A toolset for generating on-board real-time code from high-level models

• Integrated with timing analysis tools

©2011 grupo STRAST2011-05-12

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UPMSat-2TASTE

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functional view

model transformation

tool

concurrency view

Ocarina

implementation code

AADL

deployment view

AADL

interface view AADL

Ada C

Ada C

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UPMSat-2

2011-05-12 ©2011 grupo STRAST

Example

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Toy example architecture

toy_example

10 ms TMTC

TC

POSBOOST_ORDER

100 ms GNC

TC_POS

20ms PRO

BOOST_ORDER

POSreadupdate

SSWE 5c -14 Master in Space Technologies, 2010 — © 2010 Juan A. de la Puente

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UPMSat-2

2011-05-12 ©2011 grupo STRAST

Software development & validation facilities

1129 DMS-DQS-SUPSC03-PRE-11-E © DEIMOS Space S.L.U., 2010

•  Software Development Environment vs Software Validation Facilities

29 DMS-DQS-SUPSC03-PRE-11-E © DEIMOS Space S.L.U., 2010

•  Software Development Environment vs Software Validation Facilities

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UPMSat-2

2011-05-12 ©2011 grupo STRAST

Testing facilities

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31 DMS-DQS-SUPSC03-PRE-11-E © DEIMOS Space S.L.U., 2010

•  A flatsat schematic

29 DMS-DQS-SUPSC03-PRE-11-E © DEIMOS Space S.L.U., 2010

•  Software Development Environment vs Software Validation Facilities

©2011 grupo STRAST2011-05-12

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UPMSat-2Acronyms

• AOCS Attitude and orbit control system

• GPL GNU public license

• OBC On-board computer

• OBDH On-board data handling

• ORK Open Ravenscar real-time kernel

• RTOS Real-time operating system

• TC Telecommand

• TM Telemetry

• TMC Telemetry and telecommand subsystem

• VHDL Very high speed integrated circuit hardware description language

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