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Electromagnetic CompatibilitySpace System Design, MAE 342, Princeton University

Robert Stengel

Copyright 2016 by Robert Stengel. All rights reserved. For educational use only.http://www.princeton.edu/~stengel/MAE342.html 1

§ Problems, Analysis, and Testing§ Specifications§ Fundamentals§ Systems Approach§ Categories§ Spacecraft Charging§ Electrostatic Discharge§ Grounding Schemes§ Special Problems of Small Satellites

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Electromagnetic Compatibility Goals

• No interference between systems or components

• Systems not susceptible to E/M emissions from any source

• No internal interference within a system• Examples of incompatibility– Static, buzzes, clicks– Electrostatic discharge– Components with different grounding

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EMC Specifications• Enumerated in standards and mission-

specific documents– MIL-STD (US military)– CE (Conformité Européene)

• Various levels of requirements• Details of verification– Inspection– Analysis

• System design guidelines• Limitations imposed by specialized payloads

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Terms and Definitions

• EMC• EMI• RFI• ESD• EMP

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Fundamental Compatibility Issues• Source of emissions• Receiver of emissions• Transfer or coupling that facilitates

interference• Possible fixes– Reduce emissions– Alter the coupling path– Make the receiver less susceptible– Error-correction coding

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Systems Approach to EMC• Top-down (performance-driven) approach• Safety margins and budgets

– Level of emissions– Definition of “worst case” limits

6GWEC, 2001

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Categories of EMC

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Fortescue

RF3KHz-3000GHz

picoTeslas picoTeslas0.05-100KHz

Susceptibility: Emissions picked up by harness or cables

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Categories of EMC

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Fortescue

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External Sources:Magnetosphere and Van Allen Belts

Trapped Energetic Ions and ElectronsLight ions form base population of the magnetosphere

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Earth’s Magnetosphere

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Fortescue, et al, 2011

Earth’s Dipolar Magnetic Field

B Re,λ( ) = 1+ sin2 λ( )1/2B0

Re3

B0 = 0.3 Gauss

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Integral Electron Flux Contours at Earth, Jupiter, and Saturn

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NASA-HDBK-4002A, 2011

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High-Energy Proton Flux in Inner Van Allen Belt

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Spacecraft Charging Hazard Zones

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NASA-HDBK-4002A, 2011

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Spacecraft Charging

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Interaction of sunlight, space plasma, and spacecraft materials and electronics

NASA-HDBK-4002A, 2011

Exterior Interior

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Spacecraft Charging Damage

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Interaction of space plasma and spacecraft materials and electronics

NASA-HDBK-4002A, 2011

SCATHA Satellite, 1979

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Proton and Electron Penetration in Aluminum

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Acceptable Surface

Materials

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Unacceptable Surface

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Differential Solar Charging and Modeling

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Herr, NASA

Holbert, 2006

FEM

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Conducted Emissions/Susceptibility:Differential Mode and Common Mode

Interference Probing

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Fortescue

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0

(to ground)

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Electrostatic Discharge (ESD)

• Always a “spark”• Radiated effect– RF signal due to distant pulse– Testing for radiated emissions from ESD

• Conducted effect– Discharge picked up by conducting element of the

spacecraft– Possibility of high current

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Protection Against ESD• Location of components• Grounding• Bonding (~soldering)• Isolation (“Faraday cage”, “mu metal”)• Power supply to components

– Direct– Regulated– Converted

• High-impedance semiconductors (e.g., MOS)• Less sensitive components (e.g., vacuum

tubes!)• Procedures in preparation of spacecraft

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Spacecraft Grounding• Reference point– 0V, earth, common, ground, chassis

• Current between “grounded” components may not be zero– Small potential between end points– Resistance and inductance of wire

• Minimize signal “cross talk” or power supply voltage differences

• Grounding techniques

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Single-Point Grounding

24Fortescue

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Multi-Point Grounding

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Fortescue

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Hybrid Grounding

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Fortescue

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Major Causes of EMC Problems:Power Supplies

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• Switch mode power converters• Transistor operating speed• Switched voltage and current levels• Stray capacitance• Copper foil shields• Diodes

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Major Causes of EMC Problems:DC Motors and Actuators

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• Inductive nature• PWM• Rise/fall times• Avoidance techniques

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Major Causes of EMC Problems:Harnesses and Cables

• Passive, yet major source of interference• Grounding and bonding• Matched drivers, transmitters, and cables• Slow down rise and fall times• Screened or twisted cables• Filtering at connectors• Impedance matching

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Analysis Methods• Example: PSpice

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• Example: MATLAB: various books and EMPLab

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EMC Testing

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https://en.wikipedia.org/wiki/Electromagnetic_compatibility

• Open-air test sites• Anechoic and reverberation test chambers• Spectrum analysis• High-powered pulse or signal generator

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Small Satellite Design Philosophy

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Fortescue

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Fortescue

Small Satellite System Design

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Use of Commercial-Off-the-Shelf (COTS) Technology

34Fortescue

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Effects of Ionizing Radiationon COTS Components

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• Total dose effects• Single-event

upsets/latchup

• Regular “washing” of memory

• Spot shielding• Radiation hardening

after Fortescue

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Case Study: StangSat Testing• Project at NASA KSC• EM conduction and radiation testing:

MIL-STD-461F, RE102 Limits

36See Lecture 19 Course Materials on

Blackboard

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Next Time:Spacecraft Mechanisms

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