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.......