Space Environment and Survivability
Space Vehicles and Missiles
Dr. Julio Gallegos
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The Space Environment
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The problem
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Environment”
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Neutral Atmosphere
Electric and Magnetic Fields
Ultraviolet Radiation
Infrared
Solar Wind Plasma
Ionospheric Plasma
Aurora Plasma
Trapped Radiation
Galactic Cosmic Rays
Solar Proton Events
Meteoroids
Synthetic Debris
Dust
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The Atmosphere
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Neutral Atmosphere
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Effects of the neutral atmosphere
 Atmospheric drag
 Ablation
 High eV energy impacts (Oxygen erosion)
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Electric and Magnetic
Fields
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Electric and magnetic field
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Ultraviolet and Infrared
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Effects of the UV, XUV and IR radiation
 UV and XUV can change the surface chemistry
of materials and causes photoelectron
emission. Mostly dominated by solar
radiation.
 IR environment produced by the Sun, reflected
sunlight, atmospheric glow. IR is a major
source of thermal effects on spacecraft
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Solar Wind Plasma
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Effects of the Solar Wind Plasma
A neutral plasma primarily consisting of
electrons, protons, and alpha particles which flow
radially from the Sun at speed ranging from 400
to 2500 km/s.
Density ranges from 50 particles cm-3 around
Mercury to 0.2 particles cm-3 around Jupiter.
These plasmas induces spacecraft surfaces
potentials of typically 10V
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Ionospheric Plasma
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Effects of the Ionospheric Plasma
 Ionospheric component of a planetary atmosphere, a cold plasma. For Earth is
basically O+ (106 cm-3 in the range from 200 to 500 km and H+ with 105 cm-3 at 500
km to 103 cm-3 at 2000 km.
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Aurora Plasma
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Aurora Plasma
Above the ionosphere at the magnetic field
boundary between high latitude closed and quasiclosed magnetic field lines.
A hot plasma less dense than the ionosphere but
much more energetic. Protons and electrons
precipitating into the atmosphere.
Potential spacecraft charging threat.
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Trapped Radiation
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Trapped Radiation
High energy trapped electron and proton population
(E> 100 keV), the Van Allen belts.
Electrons with energies from 100 keV to a few MeV.
Protons from 100 keV to 100 MeV.
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Van Allen Belts
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Galactic Cosmic Rays
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Galactic Cosmic Rays
Primarily of interplanetary protons and ionized heavy nuclei with energies from
1 MeV/nucleon to higher than 100 GeV/nucleon.
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Solar Proton Events
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Solar Proton Events
Hydrogen and heavy nuclei in the 0.1 to 100 MeV/nucleon energy range are
ejected during a solar proton event (SPE) or a solar energetic particle (SEP
event)
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Meteoroids, Synthetic
Debris and Dust
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Meteoroids, Synthetic Debris and Dust
The mass range of meteoroids goes from 10-12 gr to 1022 g for asteroids. The
density goes from 0.5 g/cm3 to 8.5 g/cm3
Synthetic debris can impact at
10 km/s. Several models and
catalogs are available. MASTER,
PROOF and ORDEM2000.
Dust is an environment of
increasing concern for which
there are few models. Specially
for other planets or the Moon.
Dusty plasmas is an additional
complication.
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Interactions
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Cumulative Radiation Effects
Interactions
 Type of particles, enery and charge.
 Can transmute materials, change its atomic structure or produce free radicals.
 Dose: ammount of energy deposite per unit mass of the absorbing material.
1 rad = 100 erg/gm.
 Rad-hard materials for space >100 Krad(Si), nuclear hardened are >1Mrad(Si)
protons
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electrons
Single Event Upsets
Interactions
 Single Events Upset (SEU) a type
of Single Event Effects (SEE), are
produced in a IC when a single
charged particle passes through
the circuit and causes a change in
the state of a digital logic element.
 Basic measure is the LET (Linear
Energy Transfer) in MeV cm2/mg
 Another type of SEE is the
Latchup, the passage of an
energetic particle through a
sensitive device can cause a
transient short circuit or current
path.
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Single Event Upsets
Interactions
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Surface Charging
Interactions
 Surface immersed in a plasma charge to a potential relative to the plasma. Up
to 1000 V potentials can be generated. Arcing can occur.
 A plasmasheath is often created (characterized by the Debye length L D)
 Small LD compare to the size of the spacecraft tend to balance the potential;
large LD can cause arcing, damaging solar panels.
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Internal Charging
Interactions
 Internal electrostatic charging/discharging (IESD)
 High energy electrons (>100 MeV) can penetrate spacecraft surfaces and
deposit charge on internal surfaces and protons of similar energies are
stopped at the surface this differential can lead to arcing inside the spacecraft.
 At least 2.5 mm of aluminum shielding is needed in the Earth’s environment.
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Other interactions
Interactions
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Power loss
Lorentz effect (
Contamination
Surface Damages
Atmospheric Glow
Particle Impacts
Torques
Thermal
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Other interactions
Interactions
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Power loss
Lorentz effect (
Contamination
Surface Damages
Atmospheric Glow
Particle Impacts
Torques
Thermal
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Radiation
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Three main sources of radiation
Solar Energetic
Particles
Cosmic Rays
Sun
Solar Wind
Radiation Belts
Geomagnetic Field
Cosmic 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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The Magnetosphere System
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The Van Allen Belts
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Relativistic Electron-Proton Telescopes (REPT)
NASA’s Van Allen Probes.
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The Van Allen Belts
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Radiation belts
Gyro Motion
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Bounce Motion
Drift Molion
Radiation Belt Regions
• Inner belt – dominated
by protons
– CRAND
= Cosmic Ray
Albedo Neutron
Decay
– ~static
– 100’s MeV
• Outer belt – dominated
by electrons
– Controlled by “storms”
– Very dynamic
– ~MeV
• Slot
Inner Zone
Slot
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Outer Zone
– Usually low
intensities of MeV
electrons
– Occasional
injections of
more particles
The South Atlantic Anomaly
500km altitude
500k
m
South
Atlantic
anomaly
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Earth’s magnetic field is
an offset tilted and distorted
dipole
→
Brings radiation belt
down in the South
Atlantic
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
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High Energy Electrons
(Outer Belt) Geomagnetic
•
Geomagnetic Tail loaded
Storms
•
•
•
•
•
Reconnection results in
earthward propagation &
acceleration
Subsequent acceleration
through wave- particle
interactions
Transport through radial
diffusion
Loss in storms
Results in very dynamic
Characteristics of Particles
• Which particles cause the problems?
– Penetrating; damaging =>~MeV electrons; 10’s of
Mev protons
1000
Electron
Range Proton
Range in Aluminium (mm)
100
Range range =
10
2mm
1
~1Me
V
0.1
~20
MeV
0.01
0.00
1
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0.1
1
10
Energy (MeV)
100
1000
Characteristics of Radiation Belt Particles
• electrons 0.5 - 5 MeV;protons up to 100’s MeV
• gyration period tc = 2m/(eB); radius of gyration of Rc = mv2/(eB).
Characteristics of typical radiation belt particles
Polar Horns
Particle
Slot
Region
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1MeV
10MeV
Electron
Proton
Range in aluminium (mm)
2
Peak equatorial omni-directional
4 x 106
flux (cm-2.s-1)*
Radial location (L) of peak flux
4.4
(Earth radii)*
Radius of gyration (km)
0.6
@ 500km
@ 20000km
10
Gyration period (s)
10-5
@ 500km
@ 20000km
2 x 10-4
Bounce period (s)
0.1
@ 500km
@ 20000km
* derived
from the models discussed later 0.3
Longitudinal drift period (min)
10
@ 500km
@ 20000km
3.5
0.4
3.4 x 105
1.7
50
880
7 x 10-3
0.13
0.65
1.7
3
1.1
ISS
Nav
GEO
1.E + 07
0.5 M eV
1 M eV
2 M eV
3 M eV
1.E + 06
Omnidirectional Flux > E (/cm2/sec)
Models of
Radiation Belts
provide
Engineers with
Quantitative Data
1.E + 08
4 M eV
5 M eV
1.E + 05
1.E + 04
1.E + 03
1.E + 02
1.E + 01
1.E + 00
2
3
4
5
6
7
9
8
G eom agnetic L V alue (E arth radii)
1.E
+08
Energy 10MeV
Energy 30MeV
Energy 100MeV
1.E
+06
1.E
+05
protons
1.E
+04
1.E
+03
1.E
+02
1.E
+01
1.E
+00 1
2
3
4.
5
Geomagnetic L value (Earth radii)
6
10
11
12
electrons
Energy 1MeV
1.E
+07
Omnidirectional Flux > E (/cm2/sec)
• Based on data
from
1960’s-1970’s
• Work ongoing to
update them
• Long-term
averages; but
the outer belt
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is very stormy
1
Dose
• dose as a function of
shield thickness in
as a function of
spherical
shielding about a
point.
Geo
GPS
GTO
1.00E+0
7
ISO
Polar
MIR (sol min)
1.00E+0
6
1.00E+0
5
Dos e (Rads
(Si)
• The ionizing dose
environment is normally
represented by the dosedepth curve.
Typical Annual Mission Doses (spherical Al
1.00E+0shield)
8
SP
E
1.00E+0
4
1.00E+0
3
1.00E+0
2
1.00E+0
1
0.0
0
2.0
0
4.0
0
6.00
8.00
10.00
12.00
14.00
Depth (mm Al)
Modern electronic components can fail
at a few krad (men die at 100’s)
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Doses
1 e+ 6
To tal d o s e
E lec tron d os e
B re m s s tra h lun g
d os e P roto n d o s e
1 e+ 5
1 e+ 4
Dose (Rads/yr)
• Circular
equatorial
orbits for
1 year
• Doses
behind 4mm
1 e+ 3
1 e+ 2
1 e+ 1
1 e+ 0
1 00
1 ,00 0
10 ,00 0
A lt itu de
(k m )
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1 0 0,0 00
A Radiation Monitor Crossing the Belts
for ~5 Years
High
Dose
Colour-coded Dose Rate from REM on STRV in GTO
Geostationary
Altitude
Low
5
L
(
~
R
a
d
i
a
1l
D1994
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s
Outer
Belt
“Slot”
Inner
Belt
1995
1996
1997
1998
Spacecraft due to
“killer electrons”
Back-up CPU Fails
Enhanced Hot Electrons
December 97
Primary CPU Fails
April 98
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charging
MeV electrons penetrate
material and build up an
electrostatic charge
Thermal
Blanket
Components
Printed
Circuit
Boards
Discharge
Insulators
Cables
• Meteosat 3 (1988-1992) had
many disturbances
• On average, environment was seen
to get severe before an anomaly
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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-altitude electrons:
• Controlled by storms
• Coronal holes and high speed
streams after solar max have
greatest effect
• High at solar min!
104
225
L=1.1
8
200
103
175
L=1.1
6
150
125
102
100
L=1.1
4
75
101
1976
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1980
1984
1988
Date
1992
50
1996
F10.7
Flux (protons/cm2-s)
• High between max & min
250
L=1.2
0
Other planets
• Jupiter has a very severe
radiation belt
• ESA approved a mission
to the
Jovian system (JUICE)
• 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
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some orbits
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Sunspot vs. Magnetic Storm for Solar Cycles 17-13
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October 1989: Example of a very large SPE
Multiple events, lasting ~10 days
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More Radiation Effects on SOHO
Errors in onboard memory:
Single Event
Upsets
Bastille Day Event, 2000
Caused by
solar particle
events
And
background
cosmic rays
Courtesy ESA SOHO Team GSFC Fleck, van Overbeek, Olive, …
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More Radiation Effects on SOHO
Solar Array
degradation
• Steady
degradation
is normal
ageing
• Steps are
due to SPEs
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14 July 2000
Statistical Models
D o s e ( R a d s ( S i) )
• Give time-integrated
fluence for
Solar Proton Doses (1yr, 95%)
GEO (&interplanetary)
given mission
1.00E
Polar
durations,
+05
MR
orbits, “risk”
1.00E
+04
level
1.00E
+03
• Fluence
1.00E
predictions
+02
converted to
1.00E
+01
dose
1.00E
• Effect of
+00 0.0 2.0 4.0 6.00 8.0010.00 12.00 14.00 16.00
0 0 0
18.00 20.00
“geomagneti
c shielding”
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Depth mm Al
Long Term Record of Solar Particle Events
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• More in “maximum” solar activity
years
• Highly unpredictable
• Design for by making statistical
assessments
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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Galactic Cosmic Rays
• Seen as a baseline
on particle
measurements and
SEUs
• Low flux of very
high energy heavy
ions
• Very penetrating
and ionising in
matter
• Geomagnetical
ly shielded
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Effects
E ffect
Ass essm ent
Param eter
M ain
Interaction
C om ponent
D egradation
Ionizing D ose
Ionization
Solar C ell
D egradation
N on-ionizing
dose
D isplacem ents
SEU
R ate
Ionization
R adiation
B ackground
R ate
Ionization
O ptoelectronic
Degradation
N on-ionizing
dose
D isplacem ents
A stronaut H azards
D ose
Equivalent
Ionization
Internal C harging
Fields
Ionization
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SOHO
Errors in
on- board
memory
Solar array
degradation
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Image background
noise
“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 charge
e.g. SOHO CCDs
–
DNA is damaged
• Component SEU is a
growing problem
– Intensive work on component
testing at accelerators during a
project’s development
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Two basic mechanisms
SEUs on UoSAT-3 microsatellite memory
Oct ‘89
Mapped
Time behaviour
SEUs are from:
• Cosmic rays and solar ions
at high latitude
• Radiation belt proton
nuclear reactions in the
South Atlantic anomaly
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Note
latitude
effects
Manned Missions Away from LEO Risk High Doses
(prompt radiation sickness at ~100 REM (1 Sv); death at 400)
sui
t
L
M
Apollo 17
103
Apollo 16
104 REM skin
dose
CM
Worker
limit (5)
Augus
t 1972
SPE
Fukushima 1
year
Apri
l
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De
c
Space Environment Information
System
• Models of radiation belts, etc.
–
–
–
–
–
–
•
AE8
AP8
Flumic
CRRESELE
…
Have to be used
together with a
model
of 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 multimaterial shielding
(MULASSIS)
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www.spenvis.oma.be
Model
s and
Tools
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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+
+
Hot Plasma and Spacecraft Charging
• 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))
Ie(Vf) + Ii(Vf) = 0
Backscattered
electrons
Secondary
electrons
Backscattered
ions
Secondary
electrons
Photoemission
electrons
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Electrons
Ions
Solar UV
photons
Surface material
properties play a major
role!
Equilibrium potential determined by
(attempt to achieve) current balance
surface-tosurface
currents
Currents are affected by geometrical
factors:
•Shadowing from UV
•3D electric fields features
(“barriers”) Necessitates complex 3D
simulations
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Material Dependence of Charging Levels0
16
16
Carbon:
Carbon:0.7
0.7atat0.3keV
Kapton:
at 0.3keV
0.3keV 1.7
Kapton:
Teflon:
2.4 at 0.3keV
1.7 at 0.3keV
Epoxy: 1.8 at 0.35keV
Teflon:
2.41.8
at at 0.35keV
Black
Paint:
0.3keV3.4
Epoxy:
OSR:
at 0.4keV
1.8
at
0.35keV
ITO:
2.6 at 0.35keV
Black Paint: 1.8 at
MgF2-glass: 5.6 at 0.8keV
0.35keV OSR:
3.4
at 0.4keV
ITO:
2.6 at
14
14
(kV)
10
Material Potential (kV)
12
10
12
8
0.35keV
6
5.6 at 0.8keV
MgF2-glass:
4
Potential
8
2
0
Material
4
6
0
2
6
4
8
Electron Temperature
(keV)
2
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0
0
10
2
4
12
14
16
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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HST Solar Arrays
Retrieved in March 2002
Example hole in HST
solar cell (Crater size: 4
mm)
Spring of HST solar
array cut by impact
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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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Space Object Origination
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Chinese anti-satellite
weapon test, 2007
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Top 10 Historical Breakups (As of May 2010)
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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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Debris Risks
Population models
Damage characteristics (test, simulation)
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“Risk of damage”
assessment
(e.g. ATV)
Monitoring
• To improve knowledge of
environments
• To improve understanding of effects
• To support host spacecraft
Radiation monitors
(e.g. Proba, Integral, XMM,
Galileo, Herschel,
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Planck…)
Microparticle monitors
(e.g. Proba,
Columbus(ISS))
(A) Erosion, (B) Penetration, and (C) Catastrophic Effects from Impacts with Debris.
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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
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– Feedback; lessons learned
A Stuffed Whipple Shield Used by the International Space Station
This shield design is a multi-layer shield with various distances between the layers.
Non-structural insulation can fill the voids between the layers.
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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-ST-10-04C
Space Environment
• ECSS-E-ST-10-12C
Methods for Calculation of Radiation Effects
• ECSS-Q-60-11
Radiation Hardness Assurance (not revised)
• ECSS-E-ST-20-06C
Spacecraft Charging
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The Atmosphere
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The Atmosphere
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The Atmosphere
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The Atmosphere
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Atomic Oxygen
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Thermal Environment
(more in Thermal Control Subsystem)
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Thermal Environment
Launch Environment and Constraints. Thermal Cycling.
Typical operating temperature ranges:
 Antennas and external equipment: -160 to 120
degree Celsius
 Internal boxes (controlled environment): -10 to
60 degree Celsius
Effects of thermal cycling:
 Thermal fatigue
 Disjointing
 Delamination
 Cracks and distortions.
To counteract this effects we use thermal
coatings and shields.
Thermal cycling and solar simulation in vacuum
allow to verify survival and to evaluate
distortions.
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Space Vacuum
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Space Vacuum
Designing spacecraft to survive in the hazardous space
environment is a challenge.
All it took to punch
this 0.025-cm hole in
a U.S. satellite was a
paint chip moving at
hypervelocity. When
the shuttle brought
back
the
sat,
scientists found six
holes per square foot.
NASA
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What do you know about space vacuum?
What is it?
 Where is it?
 What causes it?
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Vacuum environments
 A pure vacuum, by the strictest
definition of the word, is a volume of
space completely devoid of all
material.
With gas
molecules
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Without
gas
molecules
Space Vacuum
In practice, however a pure vacuum is nearly unattainable.
 Even at an altitude of 960 km (596
mi), we still find about 1,000,000
particles per cubic centimeter.
So when we talk about the vacuum of
space, we’re talking about a “near” or
“hard” vacuum.
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Atmospheric Density decreases with height.
Atmospheric
pressure
represents the
amount of force
per unit area
exerted by the
weight of the
atmosphere
pushing on us.
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Under standard
atmospheric
pressure at sea
level, air exerts
more than 101,325
N/m2 of force on
everything it
touches.
Atmospheric pressure decreases exponentially with altitude.
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So where does space begin?
The atmosphere gradually
thins with increasing
altitude so there is no
tangible boundary between
Earth's upper atmosphere
and Space.
The most widely accepted
altitude where Space
begins is 100 kilometers,
which is about 62 miles.
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11
Oh no what a Drag!
 Although it meets the definition of outer space, the
atmospheric density within the first few hundred kilometers
is still sufficient to produce significant drag on satellites.
 Drag is the force on an object that resists its motion
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13
Atmospheric Drag
The effect of drag on a spacecraft depends on several variables:




Spacecraft speed
Shape
Size
Orientation to the airflow
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How to get through the density of the atmosphere?
GOCE: euro ion-rocket sat
Designed to skim through the
extreme upper atmosphere
using ion drives to compensate
for air drag
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How to get through the density of the atmosphere?
Maintaining satellite attitude or
orientation in space is a challenge in
space (near vacuum)
Gravity Probe B (GP-B) mission
spacecraft.
For the GP-B experiment, an
unprecedented amount of on-orbit
control was required for the vehicle
to maintain its drag-free flight in
orbit.
This
was
accomplished
by
harnessing the helium gas that
continually evaporates from the
dewar’s porous plug and venting it
as a propellant through eight pairs
of
opposing
or
balanced
proportional micro thrusters.
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Atmospheric Drag in orbit can cause orbital decay.
 Orbital Decay (loss of altitude due to
reduced speed)
 In 1979, the Skylab space station
succumbed to the long-term effects
of drag and plunged back to earth.
http
://www.videojug.com/film/the-skylab-s
pace-station
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Beyond the thin skin of Earth’s atmosphere
is the vacuum of space that challenge space craft engineers.
 Three potential problems for
spacecraft are:
 Out-gassing = (release of
gases from spacecraft
materials)
 Cold-welding = (fusing
together of metal
components)
 Heat transfer = (limited to
radiation)
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Out-gassing
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Out-gassing also known as “off-gassing”
 Out-gassing is the release of a gas
that was dissolved, trapped, frozen,
or absorbed in some material.
 When you get into your car and it has
that “new car smell” is a common
real world example
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Out-gassing
 In a low pressure environment the
problem of out-gassing is increased.
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Out-gassing
In space-based equipment, released gas can condense on such
materials as camera lenses, rendering them inoperative.
 Solutions:
 Laboratory testing to select
materials that have low outgassing properties in a “near”
vacuum environment.
 Moisture sealants, lubricants,
and adhesives are the most
common sources, but even
metals and glasses can
release gases from cracks or
impurities.
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The industry standard
test for measuring
outgassing in adhesives
and other materials is
ASTM E595. Developed
by NASA to screen lowoutgassing materials for
use in space, the test
determines the volatile
content of material
samples placed in a
heated vacuum chamber.
Out-gassing
Before being put into orbit, spacecraft are placed into a thermalvacuum chamber for a process called “bake-out”.
Thermal Vacuum
Chamber at NASA
Goddard
By Corrie
Davidson |
Published October
27, 2010
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Cold Welding
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What is cold-welding?
 Cold welding occurs between
mechanical parts that have very little
separation between them.
 Or cold welding will occur when the
lubricant between moving
mechanical parts outgas or
evaporate.
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Possible solution for cold-welding.
 Ground controllers must try different
strategies to “unstick” the two parts.
 One strategy is to expose one part to
the Sun and the other to shade so
that differential heating causes the
parts to expand and contract.
 Lubricants that don’t evaporate or
outgas must be used. For example
solid molybdenum-disulphide is an
example of lubricant that will not
evaporate or outgas.
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Heat Transfer
(more in Thermal Control Subsystem)
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How is heat managed in a “near vacuum”?
 Heat transfer in and out of a satellite
is a unique problem in a near
vacuum.
 Mechanical systems create heat that
can degrade spacecraft systems.
 In a laptop, fans are used to transfer
heat out of the system. That is not
possible in a vacuum.
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Methods of heat transfer.
Convection takes place when gravity, wind,
or some other force moves a liquid or gas
over a hot surface.
Conduction is heat flow directly
from one point to another
through a medium.
Radiation is the transfer of
heat through space by
electromagnetic waves without
a medium.
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Solutions for heat transfer.
Thermacore loop heat pipes are at work in
aerospace and satellite thermal management
applications, helping designers meet the
strictest specifications and deal with the most
rugged operating environments.
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Staying Cool on the ISS
In a strange new world where hot air doesn't rise and heat
doesn’t conduct, the International Space Station's thermal
control systems maintain a delicate balance between the deepfreeze of space and the Sun's blazing heat.
 Consider the following
questions:
 1. What would it be like
without thermal control on
the ISS.
 2. List and describe the
specific design
considerations for thermal
control.
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Space Environment Hazards by Orbit
The Aerospace Corporation
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