Post on 20-Jul-2020
transcript
MAE 5595: Space Environments and Spacecraft Interactions
Lesson 4: Introduction
Ambient Environment
• Neutral Environment– Low pressure environment (150km ~ 3x10-9 atm)– Ambient neutral gas (LEO atomic oxygen)– Outgassed molecules from spacecraft surfaces– Thruster generated molecules
• Plasma Environment– Ambient plasma (ions/electrons)– Thruster generated ions/electrons– Arc generated plasmas
Ambient Environment
• Radiation Environment– Solar photons (X-Rays)– Electromagnetic interference (EMI)– Cosmic rays
• Particulate Environment– Micro-meteoroids– Orbital debris
Typical Spacecraft Orbits• Low-Earth Orbit (LEO)
– 100 to 1,000 km, i < 65°• Medium-Earth Orbit (MEO)
– 1,000 to 36,000 km, i < 65°• Polar Earth Orbit (PEO)
– > 100 km, i > 65°• Geostationary Earth Orbit (GEO)
– 36,000 km, i ~ 0°• Interplanetary Orbit (IO)
– Outside Earth’s Magnetosphere
Ambient Atmosphere for Typical Spacecraft Orbits
• LEO - Dense neutral gas (AO), ionospheric plasma, solar UV, orbital debris
• MEO - Solar UV, trapped radiation belts, plasmasphere
• PEO - Solar UV, dense ionosphere, orbital debris, auroralenergetic particles, solar flares, cosmic rays, radiation belts
• GEO - High energy plasma sheet, solar UV, solar flares, cosmic rays
• IO - Solar wind plasma, cosmic rays, solar flares
The Sun: Energy Input
The Vacuum Environment
• Low pressure environment• Outgassing• Arcing potential
• Solar UV output• Lack of absorption• Material degradation
The Neutral Environment
The Neutral Environment
• p = nkT (n = no. density)• P(z) = P(zo) exp –((z-zo)/H);
H = kT/mg)
• Troposphere: Adiabatic lapse rate6.5 K/km
• Upper Atmosphere driven by solarconditions
The Plasma Environment
The Plasma Environment
Daytime/Nighttime Differences Solar Input Variations
The Radiation Envirnoment
The Radiation Environment
Trapped Radiation: The Van Allen Belts
The MMOD Environment
Cheyenne Mountain ~ 8000 objects
The MMOD Environment
A Brief Picture of Spacecraft Interactions
Vacuum Environment Effects
• UV Material Degradation– Photon / Surface interactions– Energetic photons can break
molecular bonds– Alters material properties
• Absorptivity, reflectivity, transmissivity
• Conduction• Strength
• Outgassing– Release of adsorbed molecules– Material mass loss due to volatiles
Neutral Environment Effects• Aerodynamic drag• Atomic oxygen
material degradation– Reactive species– Long term exposure
• Spacecraft (“Shuttle”) glow
• Contamination– Material outgassing– Thruster firings– Optical surfaces and
solar panels
Spacecraft Generated Environment
AmbientAtmosphere
MaterialOutgassing
ThrusterFirings
ProcessGenerated
Species
Own AmbientAtmosphere
Neutral Species: POAA > PAmbient
Plasma Environment Effects• Shifting of spacecraft
ground• Arc damage - spacecraft
charging• Electrostatic/Electromagn
etic attraction of contaminates
• High energy plasma sputtering and modification of surfaces
• EMI• Sensor interference
DMSP Aurora
Plasma Environment Effects
An object in a charge neutral plasma will charge slightly negative
Wake charging issues
Plasma Environment Effects
Radiation Environment Effects• Degradation of
materials including solar cells
• High energy particle penetration into materials
• Single event upsets, anomalies
• Electronics damage• Material modification• Arc damage
Radiation Environment Effects
SEU/SEE due to the South Atlantic Anomaly
MMOD Environment Effects
• Destruction• Destruction• Destruction• Destruction• Destruction• Destruction• Destruction
MMOD Environment Effects
LDEF Satellite
Synergistic Effects
• Weak individual effects or interactions couple in such a way as to have a nonlinear effect on the spacecraft
• Example: Some materials experience accelerated degradation when exposed to the the LEO AO and UV environments simultaneously
{D(AO,UV) > D(AO) + D(UV)}
Spacecraft Subsystems• Typical Spacecraft Subsystems
– Propulsion– Attitude Control– Structure– Thermal – Communications– Payload
• Each subsystem can affect the spacecraft environment and be affected by the spacecraft environment
Multidisciplinary Subject• Disciplines Involved in Spacecraft-Environment
Interactions– Solar Physics (Astrophysics)– Rarefied Gas Dynamics– Plasma Physics– Gas-Surface Interactions– Quantum Mechanics– Electronics Engineering– Material Science– Anything Else You Can Think Of.......