5.2              Margin approach

a.              The customer shall specify minimum RDMs (MRDMs) for the various radiation effects.

NOTE 1      The customer and supplier can agree to other margins to reflect conducted testing (e.g. supplier-performed lot acceptance tests, published tests on similar components) in specific cases and in accordance with the hardness assurance programme defined according to ECSS-Q-ST-60. These minimum RDMs can be established directly by the customer, or based on a proposal made by the supplier and approved by the customer.

NOTE 2      The margins for SEE are based on the consideration of acceptable risks and rates and are therefore involve system level considerations.

b.              The achieved RDM shall be established by analysis and a justification provided in the applicable radiation hardness assurance programme required by ECSS-Q-ST-60 for Class 1, 2 and 3 components.

NOTE              For RDM, see Clause 5.1.1.

c.               The analysis specified in requirement 5.2b shall include the following elements, and the associated uncertainties and margins, either hidden or explicit:

1.              Space radiation environment, evaluated as specified in clause 5.3.

2.              Deposited dose, calculated as specified in clause 5.4, and including:

(a)            Shielding and

(b)           Calculation of effects parameters

NOTE              For example, ionising dose, displacement dose, SEE rate, instrumental background, and biological effects.

3.              Radiation effect behaviour of entities (including components, payloads, and humans), evaluated as specified in clause 5.5.

NOTE              Hidden margins appear in many aspects of the hardness assurance process (see also the clauses of ECSS-Q-ST-60 relevant to “Radiation hardness”) and they can compensate for uncertainties in other elements of the assessment process. The hardness assurance plan can consider:

•       Part type sensitivity evaluation.

•       Lot-to-lot variation.

•       Worst-case analysis

•       Minimum considered radiation level (since dose-depth curves are often asymptotic to a dose value for thick shielding due to bremsstahlung or high energy protons, a minimum qualification dose can be specified)

d.              For those elements in the design margin analysis, as specified in requirement 5.2c, that assume the following worst case conditions, their contribution to the design margin need not be applied:

1.              For environment, those specified as worst-case in ECSS-E-ST-10-04, Clause 9.

2.              For other than environment, those specified in clauses 5.4 and 5.5.

e.               It shall be ensured that the qualification process demonstrates that the RDMs meet the MRDMs for the design adopted.

NOTE              With this objective, the minimum radiation design margins specified for the equipment are established based on the reliability and availability requirements, and on the methodologies adopted for calculating the radiation environment and effects.