6.2.2 Simplified approaches

6.2.2.1 Planar and spherical geometries

a. For the first-order estimate of the influence of shielding, the analysis shall be performed as follows:

1. Assume that the influence of material type is negligible, and the different materials can be approximated to the equivalent mass of a single material type (such as aluminium) by a proportional change in density.

2. approximate the shielding geometry to one of the geometries shown in Table 6‑2, as follows:

(a) Approximate a configuration with two opposing lightly shielded directions to the summed effects of two finite slab shown in Table 6‑2.

(b) Approximate a configuration with a light shielding in one direction with heavy rear-side shielding to a semi-infinite planar geometry.

(c) Approximate a configuration with uniform shielding in all directions to the solid sphere.

(d) Approximate a configuration with a large cavity and uniform shielding in all directions (thickness < 0,5 cavity diameter) and no significant material local to the dose point to the spherical shell geometry.

3. Obtain the effect-versus-depth information (the so called “dose-depth curve” and/or comparable information for particle fluence or other radiation effects parameters as a function of shielding).

4. Assess the minimum shielding quantity provided by the spacecraft to be used in conjunction with the effect-versus-depth.

5. If the shielding conditions do represent a worst-case analysis, and the component, subsystem or system performs to within the specified RDM for those shielding conditions, consider the result of the analysis as acceptable.

6. In case other than requirement 6.2.2.1a.5, apply the detailed shielding calculation method specified in clause 6.2.2.2 or 6.2.3.

NOTE The first order approximation of the influence of shielding can result in an overestimation of the radiation effects, and a more detailed analysis can indeed show that the component, subsystem or system performs to within the specified RDM. This can be a worst-case estimation and so can indicate a requirement for more detailed analysis.

6.2.2.2 Simple sectoring based on solid angles

a. For the second-order estimate of the influence of shielding, the analysis shall be performed by using the method in clause 6.2.2.1 and accounting for heterogeneous shielding by estimating the percentage of the overall solid angle (4p) subtended by the major elements of the configuration viewed from the shielded point.

NOTE The reason is that the sectoring method based on solid angles takes account of the fact that generally shielding around a point of interest is heterogeneous.