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

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

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

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 ~80 - 90 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

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

Space Environment Uniform velocity distribution: f(v) Maxwell-Boltzmann velocity distribution f(v) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Normalized velocity H. Kirkici Istanbul Technical University October 3, 2003 Lecture-8 and 9

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

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

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

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

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

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) 0.3 (O) 5.0 (N2) 8.8 400 km 7.7 km/s (H) 0.3 (O) 4.9 (N2) 8.6 H. Kirkici Istanbul Technical University October 3, 2003 Lecture-8 and 9

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

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

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

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