A review of geomagnetic cutoff rigidities for earth-orbiting spacecraft

Geomagnetic cutoff rigidities are a quantitative measure of the shielding provided by the earth’s magnetic field. More precisely, geomagnetic cutoff rigidities predict the energetic charged particle transmission through the magnetosphere to a specific location as a function of direction. The generally accepted manner for determining cutoff rigidities is by the method of tracing particle trajectories in model magnetospheres. However, the trajectory-tracing process is so computer intensive that in the interest of economy, many approximations are still utilized. The use of modifications of the Störmer equation (with an appropriate magnetic coordinate system) is sufficient for many applications. However, for precise experimental measurements, cutoff rigidities determined by the trajectory-tracing method must be utilized.