THE ENVIRONMENT
OF SPACE
Col. John Keesee
1
Image courtesy of NASA.
OUTLINE
? Overview of effects
? Solar Cycle
? Gravity
? Neutral Atmosphere
? Ionosphere
? GeoMagnetic Field
?Plasma
? Radiation
2
OVERVIEW OF THE EFFECTS OF
THE SPACE ENVIRONMENT
? Outgassing in near vacuum
? Atmospheric drag
? Chemical reactions
? Plasma-induced charging
? Radiation damage of microcircuits, solar
arrays, and sensors
? Single event upsets in digital devices
? Hyper-velocity impacts
3
4
? Solar Cycle affects all space environments.
? Solar intensity is highly variable
? Variability caused by distortions in magnetic field
caused by differential rotation
? Indicators are sunspots and flares
Solar Cycle
LONG TERM
SOLAR CYCLE INDICES
5
? Sunspot number R
10 (solar min) d R d 150 (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 atmosphere
Measured in solar flux units (10
-22
w/m
2
)
50 (solar min) d F
10.7
d 240 (solar max)
SHORT TERM
SOLAR CYCLE INDEX
? Geomagnetic Index A
p
– Daily average of maximum variation in the earth’s
surface magnetic field at mid lattitude (units of
2 u 10
-9
T)
A
p
= 0 quiet
A
p
= 15 to 30 active
A
p
> 50 major solar storm
6
GRAVITY
force
At surface of earth
G
m
1
m
2
r
2
r
G 6.672 u 10
11
m
3
kg
1
2
2
E
e
2
E
e
g
sec
m
9.8
R
Gm
g
R
Gm
mf |
7
MICROGRAVITY
8
? Satellites in orbit are in free fall - accelerating
radially toward earth at the rate of free fall.
? Deviations from zero-g
– Atmospheric drag
– Gravity gradient
– Spacecraft rotation
(rotation about Y axis)
– Coriolis forces
22
5.0 Z U a
m
AC
x
D
?
?
?
?
?
1
·
¨
¨
¨
¨
¨
?
§
222
2zwzywxxwx
22
Z Z zzxx
Z Z xzzoyzx
2
ATMOSPHERIC MODEL
NEUTRAL ATMOSPHERE
9
? Turbo sphere (0 ~ 120Km) is well mixed (78% N
2
, 21%
O
2
)
– Troposphere (0 ~ 10Km) warmed by earth as heated
by sun
– Stratosphere (10 ~ 50 Km) heated from above by
absorption of UV by 0
3
– Mesosphere (50 ~ 90Km) heated by radiation from
stratosphere, cooled by radiation into space
– Thermosphere (90 ~ 600Km) very sensitive to solar
cycle, heated by absorption of EUV.
? Neutral atmosphere varies with season and time of day
10
Layers of the
Earth’s
Atmosphere
TEMPERATURE
MAGNETOSPHERE
Pressure
Molecular
m
ean
free
p
ath
EXOSPHERE
Sunlit
Spray region
Warm region
Maximum
height for
balloons
THERMOSPHERE
Aurora
Aurora
Airglow
MESOSPHERE
IONOSPHERE
Noctilucent
cloud
D
E
F
1
F
2
Ozone region
Sound waves
reflected here
Mother-of-pearl
clouds
Cirrus
clouds
Altocumulus
clouds
cumulus
clouds
Stratus
clouds
Tropopause
STRATOSPHERE
Mount
Blanc
Ben
Nevis
Temperature
curve
-100
0
C -50
0
C 0
0
C 50
0
C 100
0
C
1,000
mb
10
-8
mb
10
-6
cm
10
-4
cm
1cm
1km
100
km
100
mb
1
mb
10
-2
mb
10
-4
mb
10
-6
mb
10
-10
mb
Miles
10,000
5,000
5,000
2,000
2,000
1,000
1,000
500
500
200
200
100
100
50
50
20
20
10
50,000
30,000
20,000
10,000
5 ,000
10
5
2
1
Kilometers
Feet
Mount
Everest
TROPOSPHERE
DENSITY ALTITUDE MODEL
Assume perfect gas and constant temperature
n is number density (number/m
3
) dpA - n m g A d h = o
k is Boltzmann’s constant
M is average molecular mass
H ~ 8.4km h ~ 120km n = n
o
exp (-h/H)
H { kT/mg (scale height)
dh
nkTd
dh
dp
Tknp
?
?
1
·
¨
¨
?
§
dh
nkTd
nMg
dh
dp
?
?
1
·
¨
¨
?
§
dh
KT
Mg
n
dn
p
A
dh
p+dp
11
Atmospheric Gases
? At higher altitudes O
2
breaks down into O by UV
? Primarily O from 80 - 90 km to 500 km
? Hydrogen and Helium beyond 500 km
? Kinetic energy of O atom at 7.8 km/s ~ 5eV (enough to
break molecular bonds ~1 - 2eV)
? O is highly reactive and destructive to spacecraft
? Temperature at LEO increases with altitude
? Atmosphere expands when heated by high UV (solar max)
? LEO densities ~ 10
8
particles/cm
3
12
ATMOSPHERIC MODEL
13
Most common Mass Spectrometer and Incoherent
Scatter model - 1986 (MSIS - 1986)
– Based on measured data
– Requires A
p
, F
10.7
, month as input
– Gives average values of n, n
o
, T, atomic mass as
function of altitude
– Instantaneous values can vary by factor of 10
http://nssdc.gsfc.nasa.gov/space/model/atmos/msis.html
AERODYNAMIC DRAG
Drag
Ballistic coefficient
U=density of the atmosphere=m
o
n
o
=16x1.67x10
-27
x10
13
=2.67x10
-13
kg/m
3
V=7.8km/s
C
D
- Drag coefficient
A - Cross sectional area
D
1
2
Uv xv (
v
v
)CDA
D m
dv
dt
'v
1
2
Uv
2
CDA
m
a
?
?
?
o
?
?
?
't
E
m
CDA
a
?
?
?
o
?
?
?
14
DRAG COEFFICIENTS
Derived from Newtonian Aerodynamics. Depends
on what air molecule does at impact
– Reflected C
D
= 4
– Absorbed C
D
= 2
Since F = d(mv)/dt
D = - F = - d(mv)/dt o
m = U Av
i
dt
C
D
= - 2 (v
f
-v
i
)/v
i
= 2 if v
f
= o in rarefied atmosphere
= 4 if v
f
= - v
i
AdtV
VVm
AV
D
C
i
if
D
2
2
2
1
2
1
U
U
?
?
1
·
¨
¨
?
§
A
15
TYPICAL DRAG PARAMETERS
16
E (kg/m
2
) C
D
LANDSAT 25 - 123 3.4 - 4
ERS - 1 12 - 135 4
Hubble 29 - 192 3.3 - 4 90,000Kg
Echo 1 0.515 2
Typically C
D
~ 2.2 - 4 for spacecraft. (see SMAD Table 8.3)
'V over one year ( E = 100 kg/m
2
)
h (km) 'V /year (m/s)
100 10
7
200 2 - 5 u 10
3
solar (min - max)
300 40 - 600
400 3 - 200
17
SATELLITE LIFETIMES
Large variation depending on initial altitude and
solar min/max condition (see SMAD Fig. 8 - 4)
At LEO, design must compensate for effects of
drag.
MAGNETIC FIELD EFFECTS
18
? 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 SAA
GEOMAGNETIC FIELD
19
? 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
?B
i
internal field varies slowly
on the order of 100 years
(0.05%/year.)
? Poles of magnetic field lie in
Siberia and South Australia.
20
GEOMAGNETIC FIELD
MAGNETOSPHERE
21
Magnetosphere (continued)
22
? Earth’s field extends 10 Earth Radii (R
H
) toward the sun
- terminates at magneto pause
? Earth’s field slows and deflects solar wind
– Compressed, heated, turbulent
– Bow shock at about 14 R
H
? Polar field lines are swept back in night-side tail
– Does not close
– Neutral sheet
? Surface of discontinuity in magnetic field implies
current flow in the surface
– Sunward magnetopause - eastward current flow across sub-
solar point.
– Neutral sheet current flow is westward across the tail
EXTERNAL MAGNETIC FIELD
23
?B
e
generated by ring currents and solar wind. Large
variation with time
– Milliseconds to 11-year cycle scales.
? Variations caused by
– Magnetosphere fluctuations (geomagnetic storms)
– Solar activity
? Geomagnetic storms dump large numbers of charged
particles from magnetosphere into atmosphere
– Ionizes and heats the atmosphere
– Altitudes from 300 km to over 1000 km
– Persist 8-12 hours after storm subsides
GEOMAGNETIC
COORDINATE SYSTEMS
24
Geomagnetic B - L
B
L=8
Greenwich
meridian
Geog
r
aphic
nor
th
pole
Geographic
north pole
Geographic Geomagnetic
Solar-ecliptic Solar-magnetospheric
Solar-magnetic
Colatitude
z
z
se
x se x sm
x sm
y
sm
z
sm
z
sm
y
sm
T
o
sun
T
os
u
n
y
se
y
r
r
m
z
m
r se
x mx
y
m
Magnetic
colatitude
East longitude
T
o
nor
th
ecliptic
pole
Sun direction
Several coordinate systems used in geomegnetism.
Direction of
geographic
north pole
Dipole axis
direction
Dipole
axis
Dipole
axis
Magnetic longitude
φ
φ
se
θ
φ
m
φ
se
θ
m
B=.01
.02
.05
0.1
30
20 15
10
9
8
L=2 3 4 5 6 7
0
0
-90 -60 -30
1
2
3
4
0.2
.005
.002
.001
Field
Strength
(Oersteds)
North Latitude (Degrees)
Geocentric
Distance
(Re)
GEOMAGNETIC FIELD
Magnitude Formula/Models
Tilted dipole (11 q from geographic north)
at LEO
where
M = 0.311 u 10
-4
=7.9 u 10
15
T - m
3
International Geomagnetic Reference Field
1987 (IGRF1987)
B
i
r, T
m
, I
m
§