(LDEF) Archive System
NASA Langley Research Center
Hampton, Virginia
Space Radiation Environment
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Responsible Parties:
Page Content: William H. Kinard Page Construction: Thomas H. See |
LDEF was deployed at an altitude of 479 km (259 nautical mi.) in a circular 28.5 degree inclination orbit. At this orbital altitude and inclination, two sources of energetic particles dominate most of the penetrating charge particle radiation encountered--high energy galactic cosmic rays (>~ 4Gev/nucleon) and the geomagnetically trapped Van Allen protons (E ~100 - 1000 Mev). Where near-surface shielding is less than 1.0 g/cm squared, geomagnetically trapped electrons make a significant contribution. All three sources are strongly modulated by the Earth's magnetic field. Due to this magnetospheric shielding, the absorbed dose induced by galactic cosmic rays and solar fluences are weak. Thus, the trapped proton exposure is primarily responsible for the LDEF absorbed dose measurements which occurs during passes through the South Atlantic Anomaly (SAA), which is produced because the Earth's magnetic field, though approximately dipolar, is not centered on the Earth.
The major activation mechanism in LDEF components is the proton flux in the South Atlantic Anomaly (SAA). This flux is highly anisotropic, and could be sampled by taking advantage of the gravity-gradient stabilization of the spacecraft.
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