1. Space Environment Neutral Environment Hydrogen
Where space shuttle flies
2,500
Helium
1,000
Ions
Atoms
Diatomic molecules
Oxygen
200km
Ozone (triatomic)
Nitrogen
Triatomic (water, CO2)
0 km
H. Kirkici
Istanbul Technical University
October 3, 2003
Lecture-8 and 9

2. Space Environment Electron Density Mass Density 400km ~10E6 ~10E-14
10 – 100 cm3
0 km
10E-6 kg/m3
Exercise: Convert these mass densities to
number densities, and compare with e-densities
H. Kirkici
Istanbul Technical University
October 3, 2003
Lecture-8 and 9

3. Space Environment
Neutral particle density looks small, but significant
amount of neutrals to cause significant interactions
Example: Shuttle flies with ~8km/s
Aerodynamic drag force
Material sputtering
And others…
Most abundant specie is atomic oxygen (in LEO)
Chemical erosion – cause visible glow, interfere with observations
Neutral environment is a greater concern at altitudes less than 1000 km
Steady effect on long duration space vehicles
H. Kirkici
Istanbul Technical University
October 3, 2003
Lecture-8 and 9

4. Space Environment 2,500 km ~800 – 1000 km
Mainly hydrogen
2,500 km
~1000 K
Mainly helium, some oxygen (lighter atoms move about, less collisions)
~800 – 1000 km
300 K to 800 K rapid increase
Mainly oxygen, some helium
~ km ozone layer (above this level, atomic O is produced)
~78% Nitrogen
~21% Oxygen
others
Room temperature 300 K
0 km
H. Kirkici
Istanbul Technical University
October 3, 2003
Lecture-8 and 9

5. Space Environment Kinetic Theory N molecules ( n number density)
V volume
T temperature
M molecular mass
V constant velocity
Pressure:
Ideal Gas law:
Kinetic energy and Temperature relation:
(temperature is a measure of thermal velocity, it is NOT “heat”)
Very low heat transfer among species/objects
H. Kirkici
Istanbul Technical University
October 3, 2003
Lecture-8 and 9

6. Space Environment Uniform velocity distribution: f(v)
Maxwell-Boltzmann
velocity distribution
f(v)
Normalized velocity
H. Kirkici
Istanbul Technical University
October 3, 2003
Lecture-8 and 9

7. Space Environment Pressure as a function of altitude: Above 100 km,
Exercise:
1. Prove that root-mean-square velocity is:
2. Average velocity is:
Pressure as a function of altitude:
Exponential relationship (good approximation up to 100 km)
Above 100 km,
atmospheric chemistry, temperature,
and relative abundance of species
should be considered
H. Kirkici
Istanbul Technical University
October 3, 2003
Lecture-8 and 9

8. Space Environment 1000 km Ar O2 N2 O He H 800 km 500 km 10E6 10E9
Number Density ( 1/m3)
H. Kirkici
Istanbul Technical University
October 3, 2003
Lecture-8 and 9

9. Space Environment Different models to predict atmospheric parameters
1000 km
MISS
US std Atm
200 km
100 km
200
600
700
900
1000
Temperature (K)
H. Kirkici
Istanbul Technical University
October 3, 2003
Lecture-8 and 9

10. Space Environment Predictions can vary due to: Atmospheric changes:
Not critical
Atmospheric changes:
Energy flow in-and-out of different regions
Atmospheric winds
Tides or waves
Solar output:
solar cycle (solar maximum)
Solar storms
Other solar activities
important
H. Kirkici
Istanbul Technical University
October 3, 2003
Lecture-8 and 9

11. Mechanical Interactions
Space Environment
Mechanical Interactions
Aerodynamic Drag
Collision processes
Elastic scattering and/or adhere to the surface
Momentum exchange
Drag Force is:
Where is the drag coefficient,
and experimentally determined
Is the mass density
is the thermal velocity (~1km/s)
Drag coefficient is shape dependent also
H. Kirkici
Istanbul Technical University
October 3, 2003
Lecture-8 and 9

12. Mechanical Interactions
Space Environment
Mechanical Interactions
Physical Sputtering
Removal of a molecule through a collision
with another free moving molecule
Free molecule energy > binding energy of surface
Example:
Altitude velocity species’ energy (eV/particle)
200 km 7.8 km/s (H) (O) (N2) 8.8
400 km 7.7 km/s (H) (O) (N2) 8.6
H. Kirkici
Istanbul Technical University
October 3, 2003
Lecture-8 and 9

13. Space Environment Sputtering yield versus impact energy yield 1.0 0.1
0.001 1 10
Normalized impact energy
H. Kirkici
Istanbul Technical University
October 3, 2003
Lecture-8 and 9

14. Chemical Interactions
Space Environment
Chemical Interactions
Atomic Oxygen Attack
Atomic Oxygen: Electronegative gas
Reactive
Oxidizer
Causes erosion
Degradation of material properties
Most cases it is damaging
But maybe beneficial in times
Mass loss from a surface area is
Reaction efficiency
H. Kirkici
Istanbul Technical University
October 3, 2003
Lecture-7 and 8

15. Space Environment AO effects are experimentally determined on Earth
LDEF (long duration exposure facility) collected
valuable data in space
Does not depend on line of sight exposure
Solar cell inter connects are most vulnerable
Protective coating may prevent damage
H. Kirkici
Istanbul Technical University
October 3, 2003
Lecture-7 and 8

16. Space Environment questions?.... Lecture-7 and 8 H. Kirkici
Istanbul Technical University
October 3, 2003
Lecture-7 and 8