5.3 Space radiation environment

a. When using the AE-8 model for electrons at the worst-case longitude on geostationary orbit for long-term exposure (greater than 11 years), no additional margin shall be applied.

b. When using the AE-8 model under conditions other than specified in requirement 5.3a, or using standard models of the particle environment other than AE-8, it shall be demonstrated that the achieved RDM includes the model uncertainties.

NOTE The model uncertainties are reported in the radiation environment specification as specified in ECSS-E-ST-10-04, clause 9.3.

c. Where the radiation environment models are worst-case in the radiation environment specification, as specified in ECSS-E-ST-10-09 clause 9, no additional margin shall be applied.

d. Where models are of a probabilistic nature, the level of risk to be used shall be agreed between customer and supplier and reported alongside the achieved RDM.

NOTE Examples of models of a probabilistic nature are statistical solar proton models. Examples of an acceptable level of risk are worst case and specific percentiles.

e. Where models are of a probabilistic nature further margin need not be applied if it is demonstrated that the intrinsic uncertainties in the instrument data underlying the model are included in the model’s probabilistic formulation.

NOTE Any margin associated with the environment prediction is strongly dependent on the available knowledge and is used to mitigate against the uncertainties in the environment. Experience with certain types of Earth orbit is extensive, giving rise to smaller margins, but uncertainties for others, and for example other planets, necessitate careful consideration of uncertainties.