Big Software for SmallSats: Adapting cFS to CubeSat MissionsAlan Cudmore, Gary Crum, Salman Sheikh, James Marshall

NASA Goddard Space Flight Center

[alan.p.cudmore, gary.a.crum, salman.i.sheikh, james.marshall-1]@nasa.gov

National Aeronautics and Space Administration

www.nasa.gov

cFS for CubeSats 2National Aeronautics and Space Administration

Outline• Motivation

• What is cFS?

• Experience: CSP / CeREs

• Experience: Dellingr

• Performance

• Future Work

• References

• NOTE: All images courtesy of NASA

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Motivation• Expanding requirements

– Science

– Risk tolerance

– This stresses software (and teams!)

• Budgets are not expanding

• “Small” Satellite does not mean “small” software

• Solution: a trusted framework with reusable components

cFS for CubeSats 4National Aeronautics and Space Administration

cFS: core Flight Software• NASA recognized a need to move away

from “Clone and Own”

• Developed to tackle the very issues that

SmallSats now face

• Framework and core services (cFE)

• Common set of applications and libraries

• (McComas, 2012) (Fesq, Dvorak, 2012)

“At Goddard the main driver for changing the development

process is cost, [...] An obvious way to reduce cost and schedule

is to increase the amount of software reuse.”

(Wilmot, 2006)

The cFS follows a product line approach with the goal to support systematic reuse.

(Ganesan, Lindvall, Ackermann, McComas, Bartholomew, 2009)

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Framework and Core Services (cFE)• Layered architecture

• Supports Publish / Subscribe

Applications

• Events

• Tables

• Time

cFS Applications / Libraries

CF

Operating System Abstraction Layer (OSAL)

Operating System (Linux, RTEMS, VxWorks, FreeRTOS)

cFE Services Exec Event TableBus Time

User Applications / Libraries

CS FMDS

HS

MM

HK LC MD

SBN SC SCH

?

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Libraries and Applications• Currently 12 Applications are available (http://cfs.gsfc.nasa.gov/)

• Optional, depends on mission needs.

• Easy to create

– Sample application demonstrates messaging, events, and application loop

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Heritage• cFE:

– Lunar Reconnaissance Orbiter

– Living With a Star / Radiation Belt Storm Probes

• cFS

– Global Precipitation Measurement

– Magnetospheric MultiScale

– Lunar Atmosphere and Dust Environment Explorer

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CHREC Space Processor• Space Test Program, Houston 5 / ISS SpaceCube Experiment Mini

• CHREC Space Processor Experiment

• NSF Center for High-Performance Reconfigurable Computing

• Presented here last year (Rudolph et al, 2014)

• Two CSPv1 in tandem

– Xilinx Zynq 7020

– Arm Dual Core Cortex A9 and Artix-7 FPGA

• Runs cFS!

• Launch 2016

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cFS on the CHREC Space Processor• Work spread over 3 employees

• Created 11 custom applications / libraries

• Code is in well defined applications

• Vary in level of reusability

• This is in addition to existing cFS

functionality

Mission Reusable Specific

CSP HealthCommandInjest

FTDPFTDP

Receive

FTDPSend

CommLibrary

FileTransfer

SelfTimer

ImageProcessing

CameraControl

TelemetryOut

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CeREs• Compact Radiation Belt Explorer

• MERiT: Miniaturized Electron and pRoton Telescope

• Flight computer is a CSP

• cFS used for flight software

• (Kanekal, 2014)

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Dellingr• Hardware:

– ARM7 processor (40 Mhz 2Mb RAM)

– Reaction Wheels

– Magnetorquers

– Sensors (FSS)

• Science

– INMS

– Magnetometer

– Thermal Louvre

cFS for CubeSats 12National Aeronautics and Space Administration

Custom Code for Dellingr Approx. 10k SLOC

ACS

HW Lib

Radio

INMS

GPS

SHK

RW

MAG

Camera

Dellingr and cFS• Work spread over three employees

• Ported OSAL to FreeRTOS

• Integrate with GomSpace software

• Custom

– Hardware Library

– Hardware telemetry

– Radio

– ACS

– Science instruments

• Generated using David A. Wheeler's 'SLOCCount'

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Performance• cFS imposes some performance costs

• Compared build with just FreeRTOS vs cFS

• Code available: https://github.com/jcmarsh/cpek

FreeRTOS CFS

Dhrystone (per second) 11300.7 10576.4

WhetstoneDhrystone (KWIPs) 865.7 852.1

Hardware ping (per second) 757 621

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Application Communication Costs• cFS supports publish /

subscribe message passing

through the software bus.

• Adds functionality to

FreeRTOS queues, increases

overhead.

• Chart shows round trip

messages passed between

two applications.

4 32 64 128 256 512 10240

200

400

600

800

1000

1200

1400

1600

FreeRTOS vs cFS Message Passing

Free RTOS

cFS

Message Size (bytes)

Ap

plic

atio

n R

ou

nd

Tri

ps

(pe

r S

eco

nd

)

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Future Work• 42 Simulator integration: http://fortytwospacecraftsimulation.sourceforge.net/

• cFS SDK

• Man Rated

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Summary• cFS is a mature framework

– Strong heritage

– Reduces personnel requirements

– Available on a variety of platforms

– Well suited to CubeSat missions

• Open Source (http://cfs.gsfc.nasa.gov/)

• Already being used on NASA CubeSats

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References• J. Wilmot, “Implications of responsive space on the flight software architecture,” in Proceedings of Responsive Space Conference.

AIAA, 2006.

• D. Ganesan, M. Lindvall, C. Ackermann, D. McComas, and M. Bartholomew, “Verifying architectural design rules of the flight

software product line,” in Proceedings of the 13th International Software Product Line Conference. Carnegie Mellon University,

2009, pp. 161–170.

• Rudolph, D., Wilson, C., Stewart, J., Gauvin, P., George, A., Lam, H., Crum, G., Wirthlin, M., Wilson, A., Stoddard, A. “CSP: A

Multifaceted Hybrid Architecture for Space Computing” Proceedings of the AIAA/USU Conference on Small Satellites, Advanced

Technologies, SSC14-III-3. http://digitalcommons.usu.edu/smallsat/2014/AdvTechI/3/

• McComas, D. “NASA/GSFC’s Flight Software Core Flight System” Workshop on Spacecraft Flight Software, San Antonio, TX, 2012

• Fesq, L., Dvorak, D., “NASA’s Software Architecture Review Board’s (SARB) Findings from the Review of GSFC’s 'core Flight

Executive/Core Flight Software' (cFE/CFS)” Workshop on Spacecraft Flight Software, San Antonio, TX, 2012

• Kanekal, S., “CeREs: a Compact Radiation bElt Explorer”, Proceedings of the AIAA/USU Conference on Small Satellites, Poster

Session, SSC14. http://digitalcommons.usu.edu/smallsat/2014/Poster/16/

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