THE ENVIRONMENTOF SPACEImage courtesy of NASA.Col. John Keesee1

OUTLINE Overview of effectsSolar CycleGravityNeutral AtmosphereIonosphereGeoMagnetic FieldPlasmaRadiation2

OVERVIEW OF THE EFFECTS OFTHE SPACE ENVIRONMENT Outgassing in near vacuumAtmospheric dragChemical reactionsPlasma-induced chargingRadiation damage of microcircuits, solararrays, and sensors Single event upsets in digital devices Hyper-velocity impacts3

Solar Cycle Solar Cycle affects all space environments. Solar intensity is highly variable Variability caused by distortions in magnetic fieldcaused by differential rotation Indicators are sunspots and flares4

LONG TERMSOLAR CYCLE INDICES Sunspot numberR10 (solar min) d R d 150 (solar max) Solar fluxF10.7Radio emission line of Fe (2800 MHz)Related to variation in EUVMeasures effect of sun on our atmosphereMeasured in solar flux units (10-22 w/m2)50 (solar min) d F10.7 d 240 (solar max)5

SHORT TERMSOLAR CYCLE INDEX Geomagnetic Index Ap– Daily average of maximum variation in the earth’ssurface magnetic field at mid lattitude (units of2 u 10-9 T)Ap 0 quietAp 15 to 30 activeAp 50 major solar storm6

GRAVITYm1m2 force G r2 r 11 3G 6.672u 10 m kg At surface of earthGmefg m 2RE 1Gmem9.8g sec 2R 2E7

MICROGRAVITY Satellites in orbit are in free fall - acceleratingradially toward earth at the rate of free fall. Deviations from zero-gCAD– Atmospheric drag x 0.5 m U a2Z 2– Gravity gradient x xw 2· ¹§ x yw2 z 2zw 2– Spacecraft rotation x xZ 2 z zZ 2(rotation about Y axis)– Coriolis forces x 2zZ y o z zx Z8

ATMOSPHERIC MODELNEUTRAL ATMOSPHERE Turbo sphere (0 120Km) is well mixed (78% N2, 21%O2)– Troposphere (0 10Km) warmed by earth as heatedby sun– Stratosphere (10 50 Km) heated from above byabsorption of UV by 03– Mesosphere (50 90Km) heated by radiation fromstratosphere, cooled by radiation into space– Thermosphere (90 600Km) very sensitive to solarcycle, heated by absorption of EUV. Neutral atmosphere varies with season and time of day9

5,0005,000Pressure2,0002,0001,0001,00010-10mb500 EXOSPHERE500SunlitAuroraTHERMOSPHERE200Spray region-8F1100AirglowMESOSPHERE NoctilucentcloudWarm regionMaximumSound wavesheight forreflected 6DOzone regionMother-of-pearlclouds1mb usTROPOSPHEREcloudsMountBlanccumuluscloudsTemp25 CSTRATOSPHERETropopausekm10mb10-4mb10-2 1cmmbEAurora10010mb 1kmF2IONOSPHERE200100FeetKilometersLayers of theEarth’sAtmosphereMAGNETOSPHEREMolecular mean free pathMiles10,000-500C00CTEMPERATURE500C1000C10

DENSITY ALTITUDE MODELAssume perfect gas and constant temperaturepAp nkTdh§· nkT d dp ¹dhdhp dpn is number density (number/m3) dpA - n m g Ad h· o§d nkT dp¹k is Boltzmann’s constantnMg dhdhMgdnM is average molecular massn KT dhH 8.4km h 120kmn noexp (-h/H)H { kT/mg (scale height)11

Atmospheric Gases At higher altitudes O2 breaks down into O by UVPrimarily O from 80 - 90 km to 500 kmHydrogen and Helium beyond 500 kmKinetic energy of O atom at 7.8 km/s 5eV (enough tobreak molecular bonds 1 - 2eV)O is highly reactive and destructive to spacecraftTemperature at LEO increases with altitudeAtmosphere expands when heated by high UV (solar max)LEO densities 108 particles/cm312

ATMOSPHERIC MODELMost common Mass Spectrometer and IncoherentScatter model - 1986 (MSIS - 1986)– Based on measured data– Requires Ap, F10.7, month as input– Gives average values of n, no, T, atomic mass asfunction of altitude– Instantaneous values can vary by factor of s.html13

AERODYNAMIC DRAGDragDv1 U v xv ( )CDA2vDm'vdvdt1Uv22ª CDA º « » 't« m » ¼ ª º « m » « CDA » ¼ Ballistic coefficient EU density of the atmosphere mono 16x1.67x10-27x1013 2.67x10-13kg/m3V 7.8km/sCD - Drag coefficientA - Cross sectional area14

DRAG COEFFICIENTSDerived from Newtonian Aerodynamics. Dependson what air molecule does at impact– ReflectedCD 4– AbsorbedCD 2Since F d(mv)/dtD - F - d(mv)/dtoA·§CDm V f Vi D¹ 1 UV 2 A 1 UV 2 Adti22m U AvidtCD - 2 (vf - vi)/vi 2 if vf o 4 if vf - viin rarefied atmosphere15

TYPICAL DRAG PARAMETERSE (kg/m2) CDLANDSAT25 - 1233.4 - 4ERS - 112 - 1354Hubble29 - 1923.3 - 490,000KgEcho 10.5152Typically CD 2.2 - 4 for spacecraft. (see SMAD Table 8.3)'V over one year (E 100 kg/m2)h (km)'V /year (m/s)1001072002 - 5 u 103 solar (min - max)30040 - 600164003 - 200

SATELLITE LIFETIMESLarge variation depending on initial altitude andsolar min/max condition (see SMAD Fig. 8 - 4)At LEO, design must compensate for effects ofdrag.17

MAGNETIC FIELD EFFECTS Deflects charged particles/solar wind.– South Atlantic Anomaly Creates the structure of the ionosphere/plasmasphere– Magnetosphere– Van Allen radiation belts Direct effects on Spacecraft systems– Avionics - induced potential effects– Power - induced potential effects– GN&C - magnetic torquer performance, sizing– Structures - induced currents– TT&C - location of SAA18

GEOMAGNETIC FIELD Earth’s Magnetic field comes from three sources– internal field (99%) currents inside the Earth residual magnetism of elements contained in crust– External field 1% Currents in the magnetosphere Bi internal field varies slowlyon the order of 100 years(0.05%/year.) Poles of magnetic field lie inSiberia and South Australia.19



Magnetosphere (continued) Earth’s field extends 10 Earth Radii (RH) toward the sun- terminates at magneto pause Earth’s field slows and deflects solar wind– Compressed, heated, turbulent– Bow shock at about 14 RH Polar field lines are swept back in night-side tail– Does not close– Neutral sheet Surface of discontinuity in magnetic field impliescurrent flow in the surface– Sunward magnetopause - eastward current flow across subsolar point.22– Neutral sheet current flow is westward across the tail

EXTERNAL MAGNETIC FIELD Be generated by ring currents and solar wind. Largevariation with time– Milliseconds to 11-year cycle scales. Variations caused by– Magnetosphere fluctuations (geomagnetic storms)– Solar activity Geomagnetic storms dump large numbers of chargedparticles from magnetosphere into atmosphere– Ionizes and heats the atmosphere– Altitudes from 300 km to over 1000 km– Persist 8-12 hours after storm subsides23

GEOMAGNETICCOORDINATE c Distance (Re)Dipole axis32To northecliptic pole457600.20.1.051B .0Direction ofgeographicnorth poleysmSun direction-90-60.001Dipole axisdirection.02.002zsmysm5x sm nsuToField Strength(Oersteds)yseSolar-magneticx sm3DipoleaxisrseφseL 20zsmφsex sesunToL 81.00Geographicnorth poleSolar-eclipticxmMagnetic longitudeym8yxEast longitude orth ographicB-L-30North Latitude (Degrees)Several coordinate systems used in geomegnetism.24

GEOMAGNETIC FIELDMagnitude Formula/ModelsTilted dipole (11q from geographic north)§ · 1/ 2§ § · · M2Bi r,Tm,Im ¹ 3 3cos Tm ¹ 1 ¹ at LEOrwhereM 0.311 u 10-4 7.9 u 1015Br M 2cosTmr3BTm M sinTmr3BIm 0T R3eT - m3International Geomagnetic Reference Field1987 (IGRF1987)25

FIELD VALUES Minimum (near equator) 0.25 u 10-4 TMaximum (near polar caps) 0.50 u 10-4 TTwo peaks near north poleTwo minimum near equatorLargest minima is known as South AtlanticAnomaly– Much higher radiation exposure at LEO Geomagnetic storms impose variations of0.01 u 10-4 T26


SOUTH ATLANTIC ANOMALYReduced protection in SAA allows greater effect of high28energy particles - electronic upsets, instrument interference.

PLASMA EFFECTS OVERVIEW Plasma is a gas made up of ions and free electrons inroughly equal numbers. CausesElecromagnetic InterferenceSpacecraft charging & arcingMaterial effects EffectsAvionics - Upsets from EMIPower - floating potential, contaminated solar arrays, currentlossesGN & C - torques from induced potentialMaterials - sputtering, contamination effects on surface29materials

PLASMA EFFECTS (cont.) Effects continuedOptics systems - contamination changes properties ofsurface materials.Propulsion - Thruster firings change/shift the floatingpotential by contacting the plasma.30

PLASMA GENERALIZATION Plasma is caused by UV, EUV, X-ray photoelectriceffect on atmospheric molecules.– Breaks diatomic molecule bonds.– Ejects electrons from outer shells. As UV, EUV, X-ray penetrate the atmosphere, iondensity increases with atmospheric density until mostUV, EUV have been absorbed ( 60 Km altitude).Varies dramatically with altitude, latitude, magneticfield strength, time of day and solar activity. Electrically charged region of atmosphere is called theionosphere. Gas in ionosphere is called ionospheric plasma.31

LEO PLASMA ENVIRONMENT Balance between increasing density and increasing absorptionleads to formation of ionization layers.F - layer150 km - 1000 kmE - layer100 km - 150 kmD - layer60 km - 100 km Transition region from ion-free atmosphere to fully ionizedregion called the plasmasphere. Plasmasphere ion densities peak at 1010/m3 to 1011/m3 at1000 km– Drops to 109/m3 at its boundary Outer boundary called plasmapause– Density drops to 105/m3 to 106/m3– Height is 4 RH between 0000 and 1800 hours– Expands to 7 RH during the local dusk (dusk bulge)32

ELECTRON DENSITY1000Altitude (km)Solar MaxSolar MinNightime ElectronsDaytime Electrons100101103105107Density (cm-3)33

PLASMAPAUSE HEIGHT VSLOCAL TIME4Kp 1102Kp 3Kp 2 -2N(H ) (cm )10Kp 4-510010-21234567LOGO S, Nightside, 1968Kp is Magnetic Activity Index34

ION CONCENTRATIONS– Similar to neutral atmosphereD - layerNO /O E - layerO F - layerO /H -Daytime F layer density peaks at 1012/m3 (300 km)-Nighttime F-layer density drops to 1011/m3 (500 km)– Composition transitions from O to H 35

ION CONCENTRATIONS (cont.)650600H 550Altitude (km)500450400He O2 350300O NO 250200150101103105Ion Concentrations (ions/cm3)36

PLASMA TEMPERATURESIncreases from 100K at 50 - 60 km to2000 - 3000K above 500 kmElectron temperature Te 4000K - 6000KIon temperatureTi 2000K - 3000KDensity much higher at solar maximum due tohigher UV/EUV fluxes.37

LEO PLASMAENVIRONMENT MODELSInternational Reference Ionosphere (IRI)-Outputs - electron density ne- ion composition ni- Temperature Te, Ti-Inputs (latitude, longitude, altitude, solar activity (R),time).Available at html“Ionospheric models” Carlson, Schunk, Heelis, Basu38

RADIO FREQUENCYTRANSMISSIVITY– Plasma transitions from a perfect conductor toperfect dielectric as a function of frequency.§ n e · – Plasma frequency Z H m ¹ § · § · Z HH 1 – Dielectric constant Z ¹ ¹ – For Z Zpe the plasma appears like free space– For Z Zpe electromagnetic waves cannotpropagate12e2pe2opeo Transmissions from below are reflected Transmissions from within are absorbed– For Z ! Zpe random variations in ne can causerandom delays and phase shifts39

SPACECRAFT CHARGING At LEO spacecraft become negatively charged–––––Plasma is dense but low energyOrbital velocity is higher than ion thermal velocityLower than electron thermal velocityElectrons impact all surfacesIons impact ram surfaces only Geo spacecraft charge during magnetospheric substormsbetween longitudes corresponding to midnight and dawn Biased surfaces (solar arrays) influence the floatingpotential40

CHARGING EFFECTS Instrument reading bias Arcing-induced EMI, electronics upsets Increased current collection Re-attraction of contaminants Ion sputtering, accelerated erosion of materialsSpacecraft must be designed to keep differentialcharging below the breakdown voltages or musttolerate the effects of discharges.41

RADIATION Most radiation effects occur by energy depostion– Function of both energy, type of particle and material intowhich energy is deposited. Definitions1 rad (Si) 100 ergs/gm into Silicon1 Cray (Si) 1 J/kg into Si1 rad (Si) 10-4 Cray42Adapted from SMAD.

RADIATION DAMAGE THRESHOLDSIn many materials the total dose of radiation is the mostcritical issue. In other circumstances the time over whichthe dose is received is equally important.MaterialBiological MatterElectrical MatterLubricants, hydraulic fluidCeramics, glassesPolymeric materialsStructural metalsDamage Threshold (rad)101 - 102102 - 104105 - 107106 - 108107 - 109109 - 101143

SPACECRAFT EFFECTS High energy particles travel through spacecraftmaterial and deposit kinetic energy– Displaces atoms.– Leaves a stream of charged atoms in their wake. Reduces power output of solar arraysCauses sensitive electronics to failIncreases sensor background noiseRadiation exposure to crews44

HIGH ENERGY RADIATION DefinitionFor ElectronsFor protons and heavy ionsE 100 keVE 1 MeV Sources– Van Allen Belt(electrons and protons) (trappedradiation)– Galactic cosmic raysinterplanetary protons and ionizedheavy nuclei– Protons associated with solar proton events45

VAN ALLEN BELTS Torodial belts around the earth made up of electronsand ions (primarily protons) with energies 30 keV. Two big zones– Inner belt 1000 Km 6000 km altitude Protons E 10’s of MeV Electrons E 1 - 10 MeV– Outer belt 10,000 - 60,000 km Electrons E 0.04 - 4.5 MeV46

VAN ALLEN BELTS (cont.) Sources– acceleration of lower-energy particles by magneticstorm activity– trapping of decay products produced by cosmic raycollisions with the atmosphere– solar flares47

CONCENTRATION MECHANISM Earth’s magnetic field concentrates on large fluxes ofelectrons, protons and some heavy ions. Radiation belt particles spiral back and forth alongmagnetic field lines.– Ionizing radiation belts reach lowest altitude of the easterncoast of the eastern coast of South America (SAA).(Image removed due to copyright considerations.)48

ELECTRON AND PROTONFLUXES2.5105104 1031022x106AP8Min Proton Fluxes (cm-2 s-1)02x106z (Re)3x106106-2.5105104103 102AE8Max Electron Fluxes (cm-2 s-1)02.55.0x (Re)7.510.049

5 YEAR DOSE106Natural environment5 YEAR DOSE, Rad (Si)1050063.40104900 InclinationFree space(Flare only)1035 Timessynchronous altDMSPAltitude(960)102102GPSAltitudeSynchronous altitudeo(550-630) (DSP, DSCS, Fltsatcom - 0 )No operationalsatellites103104ALTITUDE, nml10510650

TRAPPED RADIATION BELTSN310621071Distance from centerof earth (Earth Radii)104 1031021091011085x108Protons 100 MevElectrons 40 Kev51

VAN ALLEN BELTRADIATION STABILITY Inner belt– Fairly stable with changes in solar cycle– May change by a factor of three as a result of geomagneticstorms loading in high energy electrons. Outer belt– Electron concentrations may change by a factor of 1000 duringgeomagnetic storms. Standard Models (AP8 protons) and (AE8 electrons)– Require B, L and whether solar min/solar max– Provide omni-directional fluxes of protons 50 keV E 500MeV and electrons 50 keV 7 Mev52

SOLAR CELL DEGRADATIONNORMALIZED EFFICIENCIES1. MeV ELECTRON FLUENCE (cm-2)InPGaAs/GeS1 (2.6-3.1 mils thick)S1 (8 mils thick)Degradation caused by the radiation of InP, GaAs,conventional (8mil) Si, and thin (3 mil) Si solar cells.53

GALACTIC COSMIC RAYS Primarily interplanetary protons and ionized heavynuclei– 1 MeV E 1 GeV per nucleonCause Single Event Upsets (SEU) Sources are outside the solar system– other solar flares– nova and supernova explosions– quasars54

PARTICLE RANGERANGE (cm)1010.10.010.1110100PARTICLE ENERGY (MeV)ElectronsProtonsRanges of Protons and Electrons in Aluminum55

MAGNETIC SHIELDING48 MeV87 MeVβ173 MeV384 MeV907 MeV2900 MeV/nMagnetic Equator12345671147 MeV/n313 MeV/n109 MeV/n46 MeV/n23 MeV/n12 MeV/nAnyIon56

SOLAR PROTON EFFECTS Solar flares often eject high energy hydrogenand other nuclei– 1 MeV E 10 GeV/nucleon– At low energies the number can be much greaterthan galactic comic radiation level Solar events are sporadic but correlatesomewhat with the solar cycle These events make a Mass Mission hazardous57

PARTICLE ENERGY1x108Particles/ m2 sec (MeV) ster1x106Worst CaseSolar Flare Event1x1041x1021Galactic ergy (MeV)58


FEYNMAN MODELPROBABILITY10.11 Year2 Year3 Year0.015 Year7Year0.00110910101011FLUENCE (cm-2)Based on data from 1963 to 199160

ELECTROMAGNETIC RADIATION Radio– 1 - 10 MHz galactic electromagnetic radiation– terminal noise– not significant for single event environment Visible/IR– solar flux– heating UV/EUV/X-ray– EUV @ 100 to 1000 Å is significant for surface chemistry61

References Wertz, James R. and Wiley JH. Larson, Space MissionAnalysis and Design, Third edition, Microcosm Press, ElSegundo CA 1999 Pisacane, Vincenti and Robert C. Moore, Fundamentals ofSpace Systems, Oxford University Press, NY, 1994. home.html rf.html62

SOLAR CYCLE INDICES 5 Sunspot number R 10 (solar min) dR d150 (solar max) Solar flux F 10.7 Radio emission line of Fe (2800 MHz) Related to variation in EUV Measures effect of sun on our atmosphe