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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

GEOMAGNETIC FIELD20

MAGNETOSPHERE21

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

TOTAL FIELD INTENSITY27

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