9.2.2                  Solar particle event models

Standard solar particle event models do not include electrons. These electrons can be significant for certain applications and effects like internal charging. Information on typical electron fluxes during solar particle events is given in [RD.15], [RD.16].

9.2.2.1              Directionality

a.              Fluxes and fluences of solar energetic particles shall be assumed to be isotropic.

NOTE              Anisotropic distributions do exist in near-Earth space due to geomagnetic shielding (see clause 9.2.4) and in the early stages of a SPE, where particles arrive along interplanetary field lines. The direction of the interplanetary magnetic field can be variable and not along the Earth-Sun direction. An isotropic distribution is assumed due to a lack of knowledge for specific events.

9.2.2.2              Solar Particle Fluence Models

a.              Proton fluence from Solar Partic Events integrated over mission durations (of 1 year or more) shall be derived using the ESP model [RN.15] described in Annex B.6.

b.              For mission durations shorter than 1 year, the fluences for one year shall be used [RN.15].

NOTE              For mission durations shorter than 1 year, this results in a conservative fluence estimate.

c.               When using the model to calculate fluences for mission durations longer than 1 solar cycle (11 years), the model shall be used with the total number of years of high solar activity during the mission.

d.              For interplanetary missions, the results of the solar particle models shall be scaled by a factor calculated as the mean value over the mission of: r-2 for r<1AU [RN.16] and 1 for r>1AU, where r is in units of AU.

NOTE              Beyond 1 AU using a factor of 1 corresponds to a conservative estimate of the maximum coefficient recommended in [RN.16].

9.2.2.3              Solar ParticlePeak Flux Models

a.              For solar particle fluxes (protons and other ions), either the CREME96 model [RN.18] (only available online) or Table B-9, Table B-10, and Table B-11 shall be used.

b.              In Table B-9, Table B-10, and Table B-11 all ions shall be treated as fully ionised for geomagnetic shielding calculations.

NOTE              In cases where the instantaneous solar proton flux is required or as a function of time during an event, there are several large events that have been measured, their spectral fits are provided in Annex I.2.4.