Trapped Radiation and the South Atlantic Anomaly
The South Atlantic Anomaly
For low altitude spacecraft (e.g. less than 1,000 km altitude), there
is one region where the a significant population of trapped protons
is encountered - known as the South Atlantic Anomaly (SAA). The reason
for this particular region of high concentrations of particles is complex
- due to the tilt and offset of the magnetic dipole with respect to
the geographic axis. This results in significant populations of particles
located in a relatively close trapped radiation belt being brought down
to low altitudes in an area over the South Atlantic ocean centred just
to the East of Brazil.
The SAA region is relatively stable and gives rise to significant proton
fluxes for low altitude spacecraft. The protons are very penetrating
and give rise to relatively high doses inside the spacecraft. They also
contribute indirectly to single-event effects through proton-induced
nuclear reactions (PINRs).
Surrey satellites have flown a number of experiments to measure and
map the SAA region, including the Cosmic Radiation Environment and Dosimetry
(CREDO) experiment onboard UoSat-3. This experiment was followed by
the more sophisticated Cosmic Ray Experiment (CRE) which was flown on
both KITSAT-1 PoSAT-1.
The images shown on the right illustrate some of the data acquired
from CREDO and CRE, clearly showing the high concentration of particles
located in the SAA region during periods of normal solar activity.
Acknowledgement:
This topic is based on original material written
by Dr Craig Underwood
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