Spacecraft Computers:past, present, future;

and gnu/Linux in Space

Patrick H. Stakem

Sheffield, UK

October 2003

As one of my predecessors said,

"I cannot find words to express how deeply I feel the honor of addressing some of the foremost thinkers of the present time, and some many able scientific men, engineers, and electricians, of the country greatest in scientific achievement."

Lecture before IEE, Feb. 1892, Nikola Tesla

FlightLinux Project

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disclaimer

• The opinions expressed are those of the author, and do not necessarily represent NASA or QSS policy.

FlightLinux Project

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What is a flight computer?

• Spacecraft onboard computer– radiation hardened

– low power; wide temperature range

– embedded

– no rotating secondary memory

• Custom versus c.o.t.s.

• Tasks– communications and data handling

– attitude and orbit control

– power and thermal management

– instrument control

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Past

• Earliest computers were much too big and heavy to be placed onboard. (1950’s and 1960’s)

– Mainframes; missile guidance computers

• Simple dedicated hardwired controllers (1960’s-70s)

• general purpose computing power, radiation hardened logic gates (1970’s-1980’s)

• COTS hardware, carefully selected, (1990’s)

• COTS/Open Source software 2000+

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NASA: Using free Softwareon Earth and in Space

• Linux– workstations

– FlightLinux

– Beowulf

• TCP/IP protocols– IP-in-space

– Interplanetary Internet

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Issues in Using Free Software

• Data security and privacy

• Verification, for Mission critical applications

• Policy - management view and understanding– Lack of the cost metric:

– if its free, its not worth anything

• Experience base

FlightLinux

A New Option for Spacecraft

Onboard Computer Operating Systems

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FlightLinux Project

• Selected by NASA Headquarters, Office of Earth Science in May 2000 as a multi-year funded project.

• Government-Industry team

• Principal Investigator: Pat Stakem, QSS Group, Inc.

• Partners:– Surrey Space Technology Labs (UK)

– Omni Project (NASA/Goddard Code 588)

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FlightLinux onboard computer Linux port

AssessmentTarget base architecture assessmentRAD6000 R/6000 - PPC-603e cots

RH32 MIPS, R3000 cots

Mongoose-V MIPS, no MMU cots, modified

RHPPC PPC cots

RAD750 PPC-750 cots

ERC32 SPARC cots

IA-32 Pentium, 80x86 cots

SNAP-1 StrongARM cots

here, cots = a Linux version exists.

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Benefits

• Onboard LAN– FireWire/SpaceWire

– 1553/1773 Master/Slave

– 10Base-T

• Onboard file system, in the bulk memory

• Onboard Java applets, via JVM

• Onboard web page serving

• IP to and on the spacecraft

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FlightLinux Project Web Page

• http://flightlinux.gsfc.nasa.gov/

• The Flight Linux Project officially concluded

on June 30, 2002. We continue to look for partners.

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Related Research

• Posix-compliant application software

• End-to-end IP; IP-to-the-spacecraft– Omni Project - this has been demonstrated.

– CHIPS spacecraft

• Flight Java– algorithm migration demonstrated

• Onboard networked file systems

• Beowulf - distributed processing

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Related research-onboard algorithms

• FlatSat (Omni Project)– 233 MHz Intel-based processor

– embedded system, PC-104 bus, Linux

• Multispectral image classification algorithm– implemented in Java, 7 Megabyte footprint

– 70-90% data downlink reduction (demonstrated 1/2001)

• Onboard LAN connected instrument– TCP/IP over 10Base-T

– simulated scanning instrument, Landsat MSS-class

• Downlink– TCP/IP over 10Base-T

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Other space linux applications

• Space shuttle Experiment on STS-83; plant growth experiment; Debian gnu/linux

• International Space Station; ESA laptop experiments

• Numerous balloon and sounding rocket applications

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Interplanetary Internet

• Extension of Internet off of the Earth’s surface to other planets

– to low Earth Orbit, IP, Mobile-IP works ok.

– need new approaches at planetary distances» long-haul optical channels between planets

» protocols that are resilient to long delays

– Planetary infrastructure: TDRSS and GPS

• IPN-SIG discussion group– Vint Cerf, Adrian Hooke (JPL), et al

– http://www.ipnsig.org/

GroundApplications

of free software

Low cost workstations

Beowulf clusters

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Low cost workstationsusing gnu/linux

• Commodity pc’s as an alternative to workstations

• Linux as an alternative to proprietary OpSys

• Linux apps as alternatives to commercial packages– with due concern for interoperability of file formats

• When budget is a concern (or, non-existent)

• When application migration is important

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Beowulf clusters

• Concept & code developed at NASA/GSFC by Center of Excellence in Space Data and Information Sciences (Code 930.5). Now commercialized by Scyld Corp.

• Low-cost cluster of workstations working cooperatively to process science data at super-computing speeds.

• Public-domain and open source software (COTS)– Linux Operating System basis

– MPI (Message Passing Interface) or PVM (Parallel Virtual Machine)

• More Information – http://beowulf.gsfc.nasa.gov/

– http://www.scyld.com/

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The QSS Beowulf Cluster

• 16 nodes: single processor Pentium 133 MHz, 32 meg RAM, 1Gbyte hard disk, CD-ROM, no keyboard, mouse or screen.

• 100 Mbps ethernet connection (private network).

• Only the master node has human interface, and a connection to the corporate LAN / internet. Recycled Corporate PCs

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Beowulf cluster performance

• Caveat: There are no general purpose parallel machines; the architecture interacts with the problem space.

• A good parallel machine can transform a compute-bound problem into an I/O bound problem.

• Choosing the right problem is important. We choose “Embarrassingly Parallel” problems to showcase the technique.

• Thus, we can get a 15 x speedup for 16 nodes, in a class of image processing problem.

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Onboard Science Data Processing(OSDP) Testbed

• As part of the task, we studied EOS-era science data processing demands.

• Identified a MODIS product (cloud cover) with potential to migrate onboard the spacecraft (FlatSat).

• Began development of a testbed for analysis of onboard science data processing using the MODIS direct broadcast (OSDP).

• More information:– http://aqua.qssmeds.com/osdp

– Technical report: http://aqua.qssmeds.com/osdp/docs/report.html

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The BIC Architecture

• Uses Java Sockets to Implement a Dedicated Client-Server Application

internet

LAN

Client developed in Java• Platform Independent• Benchmarks Local versus Remote Processing• Serves as Graphical User Interface to the Beowulf• Sends rows of multispectral pixels to server, receives rows of classified pixels and displays results

Server developed in Java and C• Java server connects to client• A Java Native Method (C) creates a parallel application using PVM• Receives rows of pixels from client, distributes rows among processing nodes, collects results and sends to client

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The PNN Image Classifier

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The PNN Image Classifier

S. R. Chettri: “Probabilistic neural network architecturefor high-speed classification of remotely sensed data”,

Telematics and Informatics, vol. 10, No 4, pp. 187-198, 1993

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The Training Data Set

• Ground truth provided by the USGS

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Benchmark Results

10 Mbps 100 Mbps

800 MHz Pentium(local)

333 MHz Pentium(Beowulf master) 14 - Pentiums

(Beowulf nodes)

Row Classification – SecondsProcessor

0.322Remote Beowulf – 15 nodes0.427Local C – P 8000.701Local Java – P 800

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What’s next?

• Flight Beowulf– cluster computing between members of a constellation of spacecraft

– enabled by tcp/ip in space

• NanoSats, with swarm intelligence– social insect behavior model

• Reconfigurable computers– based on rad-hard FPGA’s

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In conclusion…

• The future of Free Software in space looks good.

• It can be accepted in “real-world” applications.

• It requires a new paradigm and new policies.

• It’s a lot more fun.

• It’s use is not limited to the surface of one planet.