the space environment and its assessment for project · 2012-12-17 · the space environment and...
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The Space Environment and its The Space Environment and its Assessment for Project Assessment for Project
DevelopmentDevelopment
Eamonn DalySpace Environments and Effects Section
ESTEC/[email protected]
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Introduction• The problem
– The environment constituents– Problems from interactions with the environment
• The solution– Knowledge (models, measurements)– Simulation (prediction of effects)– Testing
• Learning lessons (feedback)• The process
– What the engineers do, & when– Standards, “tools”
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The problem
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What is the “Space Environment”
, Damage
, Hazard, Interference
, Drag
envir
onmen
ts effects
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• When we refer to space environment, we do not normally include 2 important “environments”:–Thermal (a major technical issue)–Gravity field (and microgravity conditions)
• But we also consider:–Atmospheres (esp. Earth, Mars)–Magnetic fields (Earth, etc.)–(Electric fields)
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Radiation
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Three main sources of radiation
SunSunSun
Geomagnetic FieldGeomagneticGeomagnetic FieldField
Solar WindSolar WindSolar Wind
Solar Energetic ParticlesSolar Solar EnergeticEnergetic ParticlesParticlesCosmic RaysCosmicCosmic RaysRays
Radiation BeltsRadiationRadiation BeltsBelts
Cosmic RaysCosmic Rays
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Three main sources of radiation
• Radiation Belts– High radiation dose
• Solar Particle Events– Sporadic but
dangerous when they happen
• Galactic Cosmic Rays– Low flux but highly
penetrating
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Three main sources of radiation
• Radiation Belts– High radiation dose
• Solar Particle Events– Sporadic but
dangerous when they happen
• Galactic Cosmic Rays– Low flux but highly
penetrating
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Radiation Belt Regions• Inner belt – dominated by
protons– CRAND
= Cosmic Ray AlbedoNeutron Decay
– ~static– 100’s MeV
• Outer belt – dominated by electrons– Controlled by “storms”– Very dynamic– ~ MeV
• Slot– Usually low intensities of
MeV electrons– Occasional injections of
more particlesOuter Zone
Inner Zone
Slot
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The South Atlantic Anomaly
Earth’s magnetic field is an offset tilted and distorted dipole
→ Brings radiation belt down in the South Atlantic
500km
500km altitude
South Atlanticanomaly
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The Two Source Mechanisms
High Energy Protons (Inner Belt)Cosmic Ray Albedo Neutron Decay• Nuclear interaction in atmosphere• Some products are upward travelling
neutrons• Decay (half life ~10min) into p, e-
• Results in very stable population
High Energy Electrons (Outer Belt)Geomagnetic Storms• Geomagnetic Tail loaded• Reconnection results in earthward
propagation & acceleration• Subsequent acceleration through wave-
particle interactions• Transport through radial diffusion• Loss in storms• Results in very dynamic population
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Characteristics of Particles• Which particles cause the problems?
– Penetrating; damaging => ~MeV electrons; 10’s of MeVprotons
0.001
0.01
0.1
1
10
100
1000
0.1 1 10 100 1000Energy (MeV)
Ran
ge in
Alu
min
ium
(mm
)
Electron Range Proton Range range = 2mm
~20 MeV~1MeV
2mm
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Characteristics of Radiation Belt Particles• electrons 0.5 - 5 MeV; protons up to 100’s MeV
• gyration period tc = 2m/(eB); radius of gyration of Rc = mv2/(eB).Characteristics of typical radiation belt particles
Particle 1MeV
Electron 10MeV Proton
Range in aluminium (mm) 2 0.4 Peak equatorial omni-directional flux (cm-2.s-1)*
4 x 106 3.4 x 105
Radial location (L) of peak flux (Earth radii)*
4.4 1.7
Radius of gyration (km) @ 500km @ 20000km
0.6 10
50 880
Gyration period (s) @ 500km @ 20000km
10-5
2 x 10-4
7 x 10-3
0.13 Bounce period (s)
@ 500km @ 20000km
0.1 0.3
0.65 1.7
Longitudinal drift period (min) @ 500km @ 20000km
10 3.5
3
1.1 * derived from the models discussed later
Pola
r Hor
ns
Slot Region
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Models of Radiation Belts
provide Engineers with Quantitative
Data
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
1.E+08
1 2 3 4 5 6 7 8 9 10 11 12
Geomagnetic L Value (Earth radii)
Om
nidi
rect
iona
l Flu
x >
E (/
cm2/
sec)
0.5 MeV1 MeV2 MeV3 MeV4 MeV5 MeV
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
1.E+07
1.E+08
1 2 3 4 5 6Geomagnetic L value (Earth radii)
Om
nidi
rect
iona
l Flu
x >
E (/
cm2/
sec)
> Energy: 1. MeV> Energy: 10 MeV> Energy: 30 MeV> Energy: 100 MeV
• Based on data from 1960’s-1970’s
• Work on-going to update them
• Long-term averages;but the outer belt is very stormy
GEOISS Nav
electrons
protons
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To be Useful: Convert Flux to Dose• The ionizing dose
environment is normally represented by the dose-depth curve.
• dose as a function of shield thickness in as a function of spherical shielding about a point.
Modern electronic components can fail at a few krad (men die at 100’s)
Typical Annual Mission Doses (spherical Al shield)
1.00E+01
1.00E+02
1.00E+03
1.00E+04
1.00E+05
1.00E+06
1.00E+07
1.00E+08
0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00
Depth (mm Al)
Dose
(Rad
s(Si
)
GeoGPSGTOISOPolarMIR (sol min)
SPE
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• Circular equatorial orbits for 1 year
• Doses behind 4mm
1e+0
1e+1
1e+2
1e+3
1e+4
1e+5
1e+6
100 1,000 10,000 100,000
Altitude (km)
Dos
e (R
ads/
yr)
Total doseElectron doseBremsstrahlung doseProton dose
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A Radiation Monitor Crossing the Belts for ~5 Years
Geo-stationaryAltitude
1994 1995 1996 1997 1998
L(~Radial
Distance)(Re)
Colour-coded Dose Rate from REM on STRV in GTO
InnerBelt
“Slot”
OuterBelt
Dos
e
Low
High
5
1
3
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Failure of Equator-S Spacecraft due to “killer electrons”
December 97
Primary CPU FailsApril 98
Back-up CPU Fails
Enhanced Hot Electrons
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“Internal” electrostatic charging
• Meteosat 3 (1988-1992) had many disturbances
• On average, environment was seen to get severe before an anomaly
ThermalBlanket
Cables
Components
InsulatorsDischarge
PrintedCircuitBoards
MeV electrons penetrate material and build up an electrostatic charge
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11-year Solar Cycle Variations
Low altitude protons:• Controlled by the
atmosphere• Atmosphere expands with
increasing solar heating at solar max → soaks up protons
• High at solar min!
1976 1980 1984 1988 1992 1996Date
101
102
103
104
Flux
(pro
tons
/cm
2 -s)
L=1.14
L=1.16
L=1.18
L=1.20
50
75
100
125
150
175
200
225
250
F 10.7
High-altitude electrons:• Controlled by storms• Coronal holes and high speed
streams after solar max have greatest effect
• High between max & min
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Other planets• Jupiter has a very
severe radiation belt• ESA is studying a
possible mission to the Jovian system
• Intensive work on-going to understand and cope with the environment
• Saturn also has a significant RB environment
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Three main sources of radiation
• Radiation Belts– High radiation dose
• Solar Particle Events– Sporadic but
dangerous when they happen
• Galactic Cosmic Rays– Low flux but highly
penetrating
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Solar Particle Events• Associated with energy release
on the Sun• Particles can be accelerated near
to the Sun and all the way to Earth in the plasma “shock” wave
• Often associated with “flares”• First particles can arrive in
minutes• High fluxes can last for days• Geomagnetic field shields some
orbits link
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October 1989: Example of a very large SPEMultiple events, lasting ~10 days
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More Radiation Effects on SOHO
Errors in on-board memory: Single Event Upsets
Caused by solar particle events
And background cosmic rays
Courtesy ESA SOHO Team GSFCFleck, van Overbeek, Olive, …
Bastille Day Event, 2000
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Solar Array degradation
• Steady degradation is normal ageing
• Steps are due to SPEs
More Radiation Effects on SOHO
14 July 2000
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Statistical Models• Give time-integrated
fluence for given mission durations, orbits, “risk” level
• Fluence predictions converted to dose
• Effect of“geomagneticshielding”
Solar Proton Doses (1 yr, 95%)
1.00E+00
1.00E+01
1.00E+02
1.00E+03
1.00E+04
1.00E+05
0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.00
Depth (mm Al)
Dose
(Rad
s(Si
))
Geo (& Interplanetary)
Polar
MIR
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Long Term Record of Solar Particle Events
• More in “maximum” solar activity years• Highly unpredictable• Design for by making statistical assessments
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Three main sources of radiation
• Radiation Belts– High radiation dose
• Solar Particle Events– Sporadic but
dangerous when they happen
• Galactic Cosmic Rays– Low flux but highly
penetrating
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GalacticCosmic Rays
• Seen as a baseline on particle measurements and SEUs
• Low flux of very high energy heavy ions
• Very penetrating and ionising in matter
• Geomagneticallyshielded
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Summary of Radiation EffectsEffect Assessment
ParameterMain
InteractionComponentDegradation
Ionizing Dose Ionization
Solar CellDegradation
Non-ionizingdose
Displacements
SEU Rate Ionization
RadiationBackground
Rate Ionization
OptoelectronicDegradation
Non-ionizingdose
Displacements
Astronaut Hazards DoseEquivalent
Ionization
Internal Charging Fields Ionization
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Solar arraydegradation
Errors in on-board memory
We saw examples from
SOHO
Image background noise
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“Single-event” effects• A particle crosses (“hits”) a
(small) sensitive target• The energy deposited
causes a noticeable effect:– ionisation charge causes
a bit to “flip” (SEU)e.g. SOHO memory
– pixels of a CCD are “lit up”by creation of free chargee.g. SOHO CCDs
– DNA is damaged
• Component SEU is a growing problem– Intensive work on component
testing at accelerators during a project’s development
Two basic mechanisms
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SEUsSEUs on UoSATon UoSAT--3 3 microsatellitemicrosatellite memory memory
Mapped
Oct ‘89
Time behaviour
SEUs are from:• Cosmic rays and solar ionsat high latitude
• Radiation belt protonnuclear reactions in the South Atlantic anomaly
Note latitude effects
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Manned Missions Away from LEO Risk High Doses (prompt radiation sickness at ~100 REM (1 Sv); death at 400)
Apo
llo 1
6
Apo
llo 1
7
104 REM skin dose
103
CM
LM
suit
August 1972 SPE
April Dec
Fukushima1 year
Workerlimit (5)
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Specify environment
Select component
Select orbit
build
Can it survive?
Don’t know
y
n
Test(dose, p, NIEL, ions)
Select /define shielding
Test data
Can it survive?
Can it survive?
Select payload
Select solar cells
Can it survive?
Basic Radiation Assessment Process- Testing is Crucial
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Modelsand Tools
Space Environment Information System• Models of radiation belts, etc.
– AE8– AP8– Flumic– CRRESELE– …– Have to be used
together with a modelof magnetic field (right one!)and orbit generator
• Calculation of resulting– Doses– NIEL– Solar array damage
fluence– Single event effects
• Shielding tools:– Simple geometrical
shielding– Multi-layer multi-material
shielding (MULASSIS)
www.spenvis.oma.be
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Plasma Environment and Effects
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Spacecraft Surface Charging• 27 February 1982: interruption (ESR)
on Marecs-A Maritime Com. Sat.
• Main anomaly & other small ones coincident with geomagnetic “substorms”
• Anomalies caused by electrostatic charging → discharge– large areas of dielectric thermal blankets – large differential charging
• Marecs-A and ECS-1 satellites had power losses on sections of solar arrays
• Telstar 401 failure on 10th Jan 1997 following storm on 7th
• ANIK-E1 & E2 failures in 1994 and 1996
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Spacecraft Charging Anomalies first seen in the early 1970’s
• ATS-5 (weather technology satellite, launched 1969 into GEO)
• Directly observed high-level charging of its surfaces in hot plasma environments
• Around that time military and early communications satellites in GEO (DSCS, DSP, Intelsat, Skynet, Symphonie) had many anomalies.
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Spacecraft Electrostatic Charging Effects
• Anomalies in ’70’s and ‘80’s found to correlate with locations of “hot plasma”
• Anomalies on solar arrays in ’90’s ’00’s traced to plasma interactions too.
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13% of failures in space power systems are due to discharges
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Hot Plasma and Spacecraft Charging
• A plasma is a “gas of free electric charges”atoms → ions, electrons
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• Electrons are lighter, more mobile
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Objects usually collect more negative charge
Objects acquire a negative “voltage”sufficient to balance currents(~ electron energy (in electron Volts))
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Ie(Vf) + Ii(Vf) = 0
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Electrons
Backscatteredelectrons
Ions
Secondaryelectrons
Photoemissionelectrons
Solar UV photons
Backscatteredions
Secondaryelectrons
Surface material propertiesplay a major role!
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Equilibrium potential determined by (attempt to achieve) current balance
Currents are affected by geometrical factors:• Shadowing from UV• 3D electric fields features (“barriers”)
Necessitates complex 3D simulations
surface-to-surfacecurrents
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Material Dependence of Charging Levels
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Electron Temperature (keV)
Mat
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l Pot
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l (kV
)Carbon: 0.7 at 0.3keVKapton: 1.7 at 0.3keVTeflon: 2.4 at 0.3keVEpoxy: 1.8 at 0.35keVBlack Paint: 1.8 at 0.35keVOSR: 3.4 at 0.4keVITO: 2.6 at 0.35keVMgF2-glass: 5.6 at 0.8keV
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Mat
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l (kV
)Carbon: 0.7 at 0.3keVKapton: 1.7 at 0.3keVTeflon: 2.4 at 0.3keVEpoxy: 1.8 at 0.35keVBlack Paint: 1.8 at 0.35keVOSR: 3.4 at 0.4keVITO: 2.6 at 0.35keVMgF2-glass: 5.6 at 0.8keV
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Other Issues• Plasma interaction issues also include:
– Electric propulsion interactions– Scientific (plasma) instrument interference
• Analysis techniques:– Current balance assessment
of charging levels(can be simple, or 3D)
– Full plasma simulation codes
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Meteoroids and Space Debris
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Example hole in HST solar cell (Crater size: 4 mm)
Spring of HST solar array cut by impact
HST Solar Arrays Retrieved HST Solar Arrays Retrieved in March 2002in March 2002
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Meteoroids and Debris• Natural meteoroids are
encountered everywhere.
• Space debris mainly below 2000 km altitude and in the geostationary ring.
• Typical impact velocities are 10 km/s for debris and 20 km/s for meteoroids.
• In LEO meteoroids dominate between 10 microns and 1 mm, debris for larger and smaller sizes.
• Rough fluxes (met + deb) at 600 km: – for D > 1 μ : 2000 / m2/year– for D > 10 μ : 200 / m2/year– for D > 100 μ : 4 / m2/year– for D > 1 mm : 0.005 / m2/year
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Chinese anti-satelliteweapon test, 2007
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Hypervelocity particle impact generates a cloud of secondary debris
• Shielding strategy is to use multiple walls= “Whipple shield”
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Analysis of Meteoroids and Debris RisksPopulation models
Damage characteristics (test, simulation)
“Risk of damage”assessment (e.g. ATV)
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Environment Monitoring
Radiation monitors(e.g. Proba, Integral, XMM,Galileo, Herschel, Planck…)
Microparticle monitors(e.g. Proba, Columbus(ISS))
• To improve knowledge of environments• To improve understanding of effects• To support host spacecraft
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What is done in the project “lifecycle”?
• Early phases: – orbit selection, – spacecraft/payload initial design under consideration– environment considered in trade-offs– establish environment specification (can iterate during project)
• Development phase– detailed analysis of problem areas (e.g. 3D radiation shielding);– close interactions with testing activities– assessment of “margins”– reviews
• In-flight:– Assessment of behaviour / anomaly investigation– Feedback; lessons learned
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Space Environment Information System
• Analysis tools for all environments
• Includes many analysis methods
• Links to standards• A lot of help and
background information
• www.spenvis.oma.be
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Available Standards• ECSS-E-10-04
Space Environment (revision)• ECSS-E-10-12
Methods for Calculation of Radiation Effects• ECSS-Q-60-11
Radiation Hardness Assurance• ECSS-E-20-06
Spacecraft-Plasma Interactions