The effects from the natural space radiation environment may be divided into two categories: long-term and short-term. The long-term effects have two separate concerns: ionizing and non-ionizing damage. Short-term effects are concerned primarily with single particle ionization and/or secondary particle formation. One should note that even short-term effects may be permanent (i.e., destructive single particle events).

Alternatively, one may view ionizing radiation effects in space electronics in two parts: total ionizing dose (TID) and single event effects (SEE). The two effects are distinct, as are their requirements and mitigation techniques. Though these effects are often a prime driver when discussing mission requirements, the non-ionizing radiation effects such as displacement damage dose (DDD) must also be considered.¹²

TID is a long-term degradation of electronics due to the cumulative energy deposited in a material. Typical effects include parametric failures, or variations in device parameters such as leakage current, threshold voltage, etc., or functional failures. Significant sources of TID exposure in the space environment include trapped electrons, trapped protons, and solar protons.

DDD often has similar long-term degradation characteristics to TID, but is a separate physical mechanism. It should be noted that technologies that are tolerant to TID are NOT necessarily tolerant to DDD.

DDD is essentially the cumulative degradation resulting from the displacement of nuclei in a material from their lattice position. Over time, sufficient displacement can occur and may change the device or material performance properties. Prime sources of DDD exposure include trapped protons, solar protons, radioisotope thermoelectric generator (RTG) neutrons, and to a lesser extent for typically electronic systems, trapped electrons.

SEEs occur when a single ion strikes a material, depositing sufficient energy either through its prime strike (e.g., direct ionization via GCR) or by the secondary particles that occur from the strike (e.g., indirect ionization via protons) to cause an effect in the device. The many types of SEE may be divided into two main categories: soft errors and hard errors.

In general, a soft error occurs when a transient pulse or bit-flip in the device causes an error detectable at the device output. Therefore, soft errors are entirely device and design specific, and are best categorized by their impact on the device.

Hard errors may be - but are not necessarily - physically destructive to the device, and may cause permanent functional effects.