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, auroral energetic 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 Troposphere: Adiabatic lapse rate 6.5 K/km Upper Atmosphere driven by solar conditions p = nkt (n = no. density) P(z) = P(z o ) exp ((z-z o )/H); H = kt/mg)
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 Own Ambient Atmosphere Material Outgassing Thruster Firings Process Generated Species Neutral Species: P OAA > P Ambient Ambient Atmosphere
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...