The most energetic particle populations found in the heliosphere are the constant flux of Galactic Cosmic Rays (GCRs) and the sporadic SEP events. One of the major sources of radiation damages to spacecrafts is attributed to penetrating high energy solar protons. Radiation effects on electrical and electronic space systems and materials are usually considered in terms of cumulative radiation damages and single event effects (SEE) [1].

Cumulative radiation damages can be attributed to both total ionizing (TID) and non-ionizing radiation doses. Radiation dose is the quantity of energy per unit mass transferred by particles at a target material from ionisation and excitation, and it usually refers to the energy absorbed locally per unit mass as a result of radiation exposure. The unit in SI is the gray: 1 Gy = 1 J/kg, but in practice the unit of rad (radiation absorbed dose) is used: 1 rad = 1 cGy.

Materials such as polymers, semiconductors, insulators, and glasses are susceptible to TID effects and can suffer degradation in mechanical, electrical and optical properties. The evaluation of the TID on a component is usually calculated through the "dose profile curve" which indicates the dose received through a shield of varying thickness. The TID that electronic devices can withstand depends on the technology. Typical values for standard CMOS (Complementary Metal-Oxide-Semiconductor) COTS (Commercial-Of-The-Shelf) are in the range of few krad, for CMOS rad hard devices are in the range of 0.1–1 Mrad, for bipolar in the range of 10–100 krad while AsGa can withstand a TID of the order of Mrad [2].

Displacement effects are caused by crystal structure damages due to the energy particle loss induced by elastic or inelastic collisions in a material. The displacement effect is quantitatively measured by the Non Ionising Energy Loss (NIEL) coefficient which expresses the rate of energy loss in a material by a particle due to displacement damage per unit path length. The orders of typical values of displacement effects are 10¹¹ n/cm² for CCD and optolinks, 10¹¹ n/cm² for bipolar, 10¹⁴ n/cm² for MOS and 10¹⁵ n/cm² for AsGa (1 "n" corresponds to 1 MeV) [2].

Solar energetic particles are also responsible for a number of specific effects caused by direct ionization from single particles traversing through the active volume of an electronic device. These can trigger currents within the device leading to non-destructive as well as potentially destructive effects—which are grouped under the heading SEE (Single Event Effect)—such as:

• SEU (Single Event Upset): single bit flip in a digital memory or flip-flop;
• SEL (Single Event Latch-up): triggering of a parasitic PNPN thyristor structure in a device, which can destroy the component, affecting mainly CMOS structure;
• SEB (Single Event Burnout): triggering of a vertical n-channel transistor or power NPN transistor accompanied by regenerative feedback which has destructive impact; affecting mainly power MOSFETs.

The SEPEM application server provides the following utilities for analysis of SEP effects:

• The radiation effect tools GEMAT and MULASSIS
• Calculation tools for flux and fluence spectra for selected SEP events
• Standard and new statistical models for the radiation environment statistical tools.

[1] N.B. Crosby, Universal Heliophysical Processes, Proc. IAU Symposium 257, 47 (2008).
[3] Jean-Claude Boudenot, in R. Velazco et al. (eds.), Radiation Effects on Embedded Systems, Springer. p. 1-9 (2007).