Characteristics of cosmic ray cutoffs for a satellite orbiting at 400 km; The effect of the solid earth

Studies of galactic cosmic ray intensity and composition by means of earth orbiting space vehicles often rely on the earth's magnetic field as a momentum analyzer or threshold energy indicator. We have determined, by the trajectory-tracing process, cosmic ray cutoff characteristics for a satellite at 400 km altitude. These calculations indicate that cosmic rays have direct access to the satellite from the magnetic west down to angles of 135° from the zenith. For spacecraft observations it is necessary to employ additional definitions of cutoff beyond the classical Stormer definition because there are regions with allowed orbits where the cutoff, in the classical sense, does not exist.